Field of Invention

The present specification relates to transmission electron microscopy (TEM) systems and to sample substrates for use in such systems.

Background of Invention

Transmission electron microscopy (TEM) is an imaging technique in which a beam of electrons is transmitted through a sample to form an image. The sample to be imaged is usually a thin film (e.g. less than 100 nm thick) or a suspension supported on a sample substrate. An image is formed from the interaction of electrons with the sample as an electron beam is transmitted through the sample. The image is then magnified and focused onto an imaging device, such as a fluorescent screen, a layer of photographic film, or a sensor such as a charge-coupled device.

Samples may be self-supporting but are more often supported on a sample substrate which is conventionally in the form of a grid having through holes for transmission of an electron beam. Standard TEM grid sizes are of the order of 3 mm in diameter, with a thickness and mesh size ranging from 1 to 100 pm. The sample is placed onto the meshed area for imaging. TEM grid materials are conventionally metals such as copper, molybdenum, gold or platinum. This grid is placed into a sample holder, which is mounted on a specimen stage. A wide variety of designs of holders and stages exist, depending upon the type of experiment being performed.

TEM grids can also be metal based grids with a thin electron transparent support disposed over the grid. Thin electron transport support films can be, for example, a film of carbon. It has also recently been proposed to use diamond material for a TEM grid (see https://www.2spi.com/category/grids-diamond- grids/ and http://www.agarscientific.com/diamond-grids.html). A diamond film could be provided as a thin film on a support substrate or otherwise be in free-standing diamond wafer form.

It is also known in the art to combine electrochemical and TEM imaging techniques. For example, Hodnik et al. (Acc. Chem. Res. 2016, 49, 2015 - 2022) discuss the importance and challenges of electrochemical in situ liquid cell transmission electron microscopy for energy conversion research. In such combined techniques, a liquid cell transmission electron microscope is provided with electrodes which are integrated into the cell, enabling electrochemistry to be performed in the TEM cell (see, for example, http://hummingbirdscientific.com/products/liquid/liquid-syst em-electrochemistry/ and http://www.protochips.com/products/poseidon-select/). These arrangements tend to use very thin Si ₃ N (50 nm) windows attached to Si supports with metal electrodes e.g. Pt / Au lithographically defined on the thin Si ₃ N windows. Glassy carbon electrodes may also be used as an alternative to metal electrodes.

In the energy field this type of dynamic electrochemical TEM imaging is of increasing importance. For example, the technique is being used to understand the mechanisms of why batteries fail and the mechanisms of fuel cell catalysts in order to provide improved batteries and fuel cells. Liquid cell TEM is pushing the boundaries of our understanding of such systems.

US 2010/0038557 discloses an addressable transmission electron microscope grid. It is described that a planar substrate for electrochemical experimentation provides multiple isolated electrical conductors sandwiched between insulating layers of ultrananocrystalline diamond. The ultrananocrystaline diamond is un-doped and is thus electrically insulating. It is described that the isolated electrical conductors may be formed by a layer of N-doped (nitrogen doped) ultrananocrystaline diamond which is indicated to be electrically conductive. In use, electrons are passed through holes in the substrate rather than through the substrate material itself. As such, the configuration images material in the holes rather than material disposed over the substrate.

US 5821544 also discloses the use of diamond in a transmission electron microscope specimen support. An electron microscope having a holder for examining a specimen by transmission electron microscopy is described. A specimen support for engaging the holder and for supporting the specimen during examination is disclosed, the specimen support consisting essentially of a free-standing, rigid film of a diamond material (undoped), the diamond material extending throughout the film.

US 8852408 discloses an electrochemical liquid cell that can be used with a transmission electron microscope (TEM) to examine, evaluate, study, improve, and use electrochemical reactions, for example in the design and manufacture of integrated circuits. An electrochemical cell is described, the cell having a chamber for containing an electrolyte. The chamber is situated between a bottom and a top substrate. One or more bottom windows are in the bottom substrate and one or more top windows are in the top substrate. The top window and bottom window each have a portion in alignment so that an electron beam passes through both respective portions. Two or more electrodes are located on the chamber side of the bottom substrate. The electrodes are formed of metals such as gold, copper, nickel, or silver. Despite the above, there is still a need to provide improved transmission electron microscopy (TEM) systems and to better sample substrates for use in such systems. It is an aim of the present invention to provide such improved TEM systems and sample substrates.

Summary of Invention

According to one configuration as described herein, there is provided a transmission electron microscopy system comprising: a transmission electron microscope; and a sample substrate for supporting a sample within the transmission electron microscope, wherein the sample substrate comprises a film of diamond material, wherein the film of diamond material comprises an electrochemical electrode disposed on an outer surface of the diamond material for driving electrochemical reactions, and wherein the film of diamond material comprises at least one region having a thickness of less than 300 nm forming a window for transmission of electrons therethrough, the transmission electron microscope and sample substrate being configured such that in use when the sample substrate is located within the transmission electron microscope with a sample disposed over the sample substrate, an electron beam is transmitted through the window of the sample substrate and the sample disposed over the sample substrate to generate a transmission electron microscopy image of the sample.

This configuration combines the provision of a thin diamond window and electrochemical electrodes in a TEM system. The film of diamond material has one or more non-diamond electrodes disposed on an outer surface of the diamond for driving electrochemical reactions. Alternatively, or additionally, the film of diamond material comprises at least a portion of boron doped diamond material forming the electrochemical electrode for driving electrochemical reactions. In this regard, the present inventors have found that boron doped diamond can be used to provide an improved sample substrate for transmission electron microscopy (TEM) systems. Boron doped diamond (BDD) has been found to have a number of advantages. Despite being optically opaque (black), it has been found to have good electron transmittance characteristics in thin film form for TEM imaging of samples. The opaque boron doped diamond material actually exhibits lower electron scatter than optically transparent diamond material (undoped or N-doped) due to the boron atoms having fewer electrons than carbon or nitrogen. Furthermore, boron doped diamond has increased electrically conductance compared to other forms of diamond material and has a high thermal stability. It is also robust and reusable. For example, using a boron doped diamond TEM sample substrate it is possible to image electrodeposited metal nanoparticles and study their nucleation and growth characteristics. Metal nanoparticles on the surface of boron doped diamond material have been found to remain stable during the TEM imaging process due to the electrical and thermal properties of the boron doped diamond material. The electrical and thermal properties of the BDD alleviate problems associated with the electron beam adversely affecting particles disposed thereon (location and/or morphology). In addition, the electrodeposition of particles on a BDD substrate has been found to provide very stable surface particles when compared with other electrode materials and/or when compared with other deposition processes such as evaporation.

As such, it possible to repeatedly image the same nanoparticles on the same area of a boron doped diamond substrate without the electron beam causing adverse local thermal (e.g. melting or moving) and electrical (e.g. charging) effects interfering with the surface nanoparticles. That is, electrodeposited particles on a BDD substrate are more stable with the BDD substrate enabling particles to be TEM imaged and re-imaged without the electron beam moving the particles or adversely affecting their morphology. As such, using a boron doped diamond TEM sample substrate it has been found to be possible to grow metal nanoparticles and study their dynamics when undergoing important electrochemical processes. One technique, known as identical location TEM (or IL-TEM) involves electrodeposition of metal nanoparticles onto a boron doped diamond substrate, TEM imaging at a defined position, putting the boron doped diamond substrate back into solution to undergo further electrochemistry, taking out from solution, and TEM imaging again in the same position, etc.

Another technique is to provide an electrochemical cell in-situ within a transmission electron microscope system. A liquid sample is provided between two electron transparent windows, one or both of which can be provided by a film of diamond material. At least one of these windows can be formed of boron doped diamond material or have boron doped diamond electrodes patterned in undoped diamond material. The boron doped diamond material forms one or more electrodes of the electrochemical cell for driving electrochemical reactions which can be imaged by TEM through the electrochemical cell.

It has been found that very thin regions of highly electron transparent diamond material can be achieved using reactive ion etching. It has further been found that using boron doped diamond material it is possible to image individual particles growing at an atomistic level. Also described herein is a transmission electron microscope sample substrate for use in the transmission electron microscopy system. The transmission electron microscope sample substrate comprises: a film of diamond material; and one or more electrochemical electrodes for driving electrochemical reactions, wherein the film of diamond material comprises at least one region having a thickness of less than 300 nm forming a window for transmission of electrons therethrough.

While the aforementioned configurations are for providing a combination of electrochemical and TEM imaging techniques, in other non-electrochemical applications it has still been found to be advantageous to provide a TEM sample substrate formed of boron doped diamond material. An electrically conductive boron doped form of diamond is preferred forTEM applications to prevent sample charging. Such a boron doped diamond sample substrate been found to be advantageous in TEM applications as it combines features of good electrical conductance, chemical inertness, and physical robustness. Thus, according to another configuration as described herein, there is provided a transmission electron microscopy system comprising: a transmission electron microscope; and a sample substrate for supporting a sample within the transmission electron microscope, wherein the sample substrate comprises a film of boron doped diamond material. The boron doped diamond sample substrate may be configured according to the previously described configuration including a thinned window for electron transmission. Alternatively, one or more holes can be provided in the boron doped diamond sample substrate for transmission of electrons therethrough. In applications which do not require electrochemistry, no electrochemical electrode is required. Rather, the boron doped diamond sample holder can be merely supported by a holder. The boron doped diamond sample holder is configured to be grounded in use to prevent sample charging. In this regard, the boron doped diamond sample holder can be ground via the TEM holder by virtue of being in electrical / physical contact with the TEM holder which itself is grounded.

Brief Description of the Drawings

Embodiments of the present invention are described by way of example only with reference to the accompanying drawings in which:

Figures 1(a) to 1(e) illustrate an ion milling procedure employed to produce a boron doped diamond sample substrate for a transmission electron microscope, the boron doped diamond sample substrate having a thinned, electron transparent, region for transmission of an electron beam to perform transmission electron microscopy; Figures 2(a) and 2(b) show images of the boron doped diamond sample substrate, the thinned region being formed around the periphery of a central hole;

Figure 2(c) shows a schematic of an alternative diamond sample substrate comprising a central region which is thinned from a rear side of the diamond substrate and electrodes disposed on a front surface side of the diamond substrate;

Figure 2(d) shows a schematic of a transmission electron microscope system comprising an electron beam source, a diamond substrate on which a sample is electro-deposited; and a detector for detecting electrons after passing through the sample.

Figure 2(e) shows a schematic of a transmission electron microscope system comprising an electrochemical cell, the system comprising an electron beam source, an electrochemical cell comprising lower and upper windows with a thin liquid sample therebetween, at least one of the windows being formed of a diamond substrate, and a detector for detecting electrons after passing through the sample;

Figures 3(ai) and (aii) show images of the BDD before ion milling using AFM and SEM, respectively;

Figures 3(bi) and (bii) show images of the BDD after ion milling using AFM and SEM, respectively;

Figure 4 illustrates the electrochemical setup used to run electrochemical deposition experiments utilizing the boron doped diamond sample substrate with the inset image showing an optical microscope image of the boron doped diamond sample substrate with an Au band that functions as an ohmic contact;

Figure 5(a) shows an optical microscope image of the boron doped diamond sample substrate illustrating regions where C Is XPS spectra were collected;

Figure 5(b) is a corresponding XPS image;

Figure 5(c) shows C Is XPS spectra of the boron doped diamond sample substrate before ion milling (control) and the thinnest part next to the hole divided into five regions to ease XPS spectra collection;

Figures 6(a) to 6(f) show deconvoluted C Is spectra collected for a control and five regions next to the hole of the boron doped diamond sample substrate;

Figure 7(a) shows an SEM image of a boron doped diamond sample substrate after ion milling using a STEM detector; Figures 7(b) and 7(c) show TEM images of a boron doped diamond sample substrate after ion milling where (b) represent low magnification, (c) high magnification, and the corresponding SAED as inset showing a single crystal of boron doped diamond;

Figures 8(a) to 8(c) show derivatives of C KLL spectra for BDD (control) and BDD after ion milling represented as five regions (as shown in Figures 5 and 6);

Figure 9 shows energy electron loss spectra from the BDD support film at two different thickness: (a) 40 nm; and (b) 4 nm;

Figure 10 shows a cyclic voltammogram performed using a boron doped diamond sample substrate in 1 mM Ru(N H3)b ³⁺ + 0.1 M KNO3 at a scan rate of 0.1 V s ¹ ;

Figure 11 shows the response of the boron doped diamond sample substrate towards Au deposition and stripping, in a solution containing 1 mM [TWCU] in 0.1 M HCI0 ₄ ;

Figures 12(a) to 12(d) show a comparative study examining the response of the same solution using gold, glassy carbon (GC) and boron doped diamond electrodes;

Figure 13 shows FIR-STEM images of Au nanoparticles deposited on a BDD TEM plate electrode: (a) bright field-low magnification of Au NPs; and (b-d) dark field-high magnification images of Au atoms, cluster of atoms and nanoparticles;

Figure 14 shows ADF-STEM images: (a) of Au on BDD (sp ³ ); (b) their standard deviation of an image stack; and (c) a montage of the Au NPs movements under the electron beam;

Figure 15 shows current-time transients for Au electrodeposition at E _dep = -0.5 V for different deposition times;

Figure 16 shows representative IL-ADF-STEM images of a BDD TEM electrode after electrodeposition of Au from solution containing 1 mM [AuCI ₄ ] and 0.1 M HCIO4. Electrodeposition was carried by applying E _app = -0.5 V for t _dep = 5 ms (a), 10 ms (b) and 30 ms (c);

Figure 17 shows sequential high magnification IL-ADF-STEM images of the electrodeposited Au nucleation from two regions on the BDD TEM surface observed by applying a potential of E _app = -0.5 V for t _dep = (ai and aii) 5 ms, (bi and bii) 10 ms, (ci and cii) 30 ms; Figure 18 shows high magnification IL-ADF-STEM images of early stage phase formation of Au atoms and nanostructures and the effect of short time electrodeposition (E _app = -0.5 V and t _dep = 5 ms and 10 ms) on structure evolution of Au obtained from the deposition;

Figure 19 shows high magnification IL-ADF-STEM images of Au atoms and nanostructures of Au and their evolution;

Figure 20 shows high magnification IL-ADF-STEM images of a single crystal NP, a cluster of electrodeposited atoms, and their coalescence after applying an electrodeposition potential;

Figure 21 shows high magnification IL-ADF-STEM images of Au NP surface restructure and growth evolution during the transition from (a) a second deposition (E _app = -0.5 V and t _dep = 5 ms, total deposition time is 10 ms) to (b) a third deposition (E _app = -0.5 V and t _dep = 20 ms, total deposition time is 30 ms); and

Figure 22 shows Au NPs made by electrodeposition on BDD TEM plate after applying E _app = -0.5 V for t _dep = 100 ms: (a) low magnification SEM (BF-STEM mode); (b) high magnification SEM (BF-STEM mode); and (c-h) ADF-STEM images of polycrystalline, single crystal, multiple twinned, aggregates of NPs, respectively.

Detailed Description

As described in the summary of invention section, a transmission electron microscopy system is provided which comprises a transmission electron microscope and a sample substrate for supporting a sample within the transmission electron microscope. The sample substrate comprises a film of diamond material which comprises one or more electrochemical electrodes for driving electrochemical reactions. Furthermore, the film of diamond material comprises at least one region having a thickness of less than 300 nm, 200 nm, 100 nm, 50 nm, 30 nm, 20 nm, 10 nm, 5 nm, 1 nm, 0.1 nm or down to atomic levels of thickness forming a window for transmission of electrons therethrough. As such, the transmission electron microscope and sample substrate are configured such that in use when the sample substrate is located within the transmission electron microscope with a sample disposed over the sample substrate, an electron beam is transmitted through the thin diamond material forming the window in the sample substrate and the sample disposed over the sample substrate to generate a transmission electron microscopy image of the sample.

The film of diamond material may comprises at least a portion of boron doped diamond material forming the electrochemical electrode(s) for driving electrochemical reactions. As described in the summary of invention section, the use of boron doped diamond in a TEM sample substrate has been found to have a number of advantages over non-diamond materials and other forms of diamond material. It has been found that the mechanical, electrical, and thermal properties of boron doped diamond are such that it can be used to electrochemically deposit and image individual particles growing at an atomistic level.

However, it is also envisaged that one or more non-diamond electrodes can be disposed on an outer surface of the diamond material for driving electrochemical reactions. For example, the one or more non diamond electrodes may be metallic or formed of sp2 hybridized carbon.

A transmission electron microscope sample substrate is also provided for use in the transmission electron microscopy system as described herein. The transmission electron microscope sample substrate comprises a film of diamond material and one or more electrochemical electrodes for driving electrochemical reactions. The film of diamond material comprises at least one region having a thickness of less than 300 nm forming a window for transmission of electrons therethrough. As previously stated, one or more of the electrochemical electrodes can be formed of boron doped diamond material and/or a metal or sp2 hybridized carbon. The electrode material is exposed on an outer surface of the sample substrate and in use an electron beam passes through a thin region of the diamond material.

A method of analysing the growth of nanoparticles using the transmission electron microscopy system as described herein is also provided. The method comprises electrodepositing nanoparticle material on the window of the film of diamond material and imaging the nanoparticle material by transmitting electrons through a region of the window of the film of diamond material and the nanoparticle material disposed thereon. Further electrodeposition is then performed to grow the nanoparticles and imaging is repeated by transmitting electrons through the same region of the window of the film of diamond material and the nanoparticles disposed thereon. Additional electrodeposition and imaging steps can be performed to monitor the dynamics of nanoparticle growth.

The film of diamond material can be provided in the form of a free-standing wafer of diamond material and may be single crystal or polycrystalline. To provide mechanical support, the film of diamond material can be formed to include one or more regions which are thicker than the thinned electron transmission window. For example, the diamond film can be processed by polishing and reactive ion etching to form thinned window regions within thicker regions being retained for mechanical support. In one methodology, very thin diamond windows are produced by ion implantation into a single crystal of diamond material, graphitising the implanted layer, etching away the graphitized layer, and lifting off the thin overlying layer of diamond. The resultant diamond layer can then be further processed such as by reactive ion etching to produce very thin regions within the thin diamond plate. Such a diamond plate can be formed of boron doped diamond material or formed of electrically insulating diamond with one or more boron doped diamond electrodes grown thereon.

In one configuration, the electron transmission window region of the sample substrate is formed of boron doped diamond material and in certain configurations the film of diamond material is formed entirely of boron doped diamond material. Alternatively, the sample substrate comprises at least one region of boron doped diamond material and at least one region of diamond material which is not boron doped. For example, an undoped film of diamond material can be etched and overgrown with boron doped diamond material to form boron doped diamond electrodes in a matrix of electrically insulating diamond material. Alternatively, one or more electrodes can be disposed on the top surface of the diamond material without the etching process in order to simplify the fabrication procedure. The boron doped diamond material may be located in the same region as the electron transmission window of the substrate or in a different region. An ohmic contact can be provided to the boron doped diamond material for electrically addressing the boron doped diamond material.

The window region of the sample substrate can have a thickness: no more than 300 nm, 200 nm, 100 nm, 50 nm, 30 nm, 20 nm, 10 nm, 1 nm, 0.1 nm or down to atomic levels of thickness; no less than an atomic layer thickness, 0.01 nm, 0.1 nm, 1 nm, 2 nm, 4 nm, 8 nm, 10 nm, or 20 nm; or in a range defined by any of the aforementioned upper and lower limits. Furthermore, at least the window region and/or a portion of the boron doped diamond material has a surface roughness R _a of no more than 50 nm, 30 nm, 15 nm, 10 nm, 5 nm, 3 nm, 2 nm, 1 nm, 0.5 nm, 0.2 nm, or 0.1 nm. Low surface roughness fulfils three functions: (i) a low surface roughness boron doped diamond electrode has better electrochemical functionality when compared to a rougher surface of the same material; (ii) a lower surface roughness enables a very thin electron transmission window to be processed into the diamond material for improved TEM imaging; and (iii) a low surface roughness reduces electron scatter.

The boron doped diamond material may have a boron concentration in a range 1 x 10 ²⁰ boron atoms cm ³ to 7 x 10 ²¹ boron atoms cm ³ . Such a material has improved electrochemical electrode properties, e.g. in terms of solvent window, capacitance, and reversibility. That said, for certain applications a lower boron content diamond material may be utilized. For example, a lower boron content semi-conductive BDD material can be provided and is useful, for example, as a heater element which heats up when current is passed therethrough. For example, boron doped diamond material may be provided having a boron concentration in a range 1 x 10 ¹⁷ boron atoms cm ³ to 1 x 10 ²⁰ boron atoms cm ³ . In certain configurations both lower boron content and higher boron content BDD electrodes can be provided in combination.

In one (in situ) configuration, the transmission electron microscope comprises an electrochemical cell integrated therein for performing in situ electrochemistry and transmission electron microscopy, the sample substrate being integrated into the electrochemical cell with the boron doped diamond material forming an electrochemical electrode of the electrochemical cell. For example, a liquid sample can be provided between two electron transparent windows, one or both of which can be provided by a film of diamond material. At least one of these windows can be formed of boron doped diamond material or have boron doped diamond electrodes patterned in electrically insulating diamond material. The boron doped diamond material forms one or more electrodes of the electrochemical cell for driving electrochemical reactions which can be imaged by TEM through the electrochemical cell.

Alternatively, the sample substrate is removably insertable into the transmission electron microscope such that a sample can be deposited onto the sample substrate (ex situ) and then inserted into the transmission electron microscope for transmission electron microscopy imaging.

To illustrate the functionality of the transmission electron microscopy technology as described herein, the present inventors have performed an atomic scale investigation of the initial stages of metal nanoparticle nucleation and growth using identical location scanning transmission electron microscopy and boron doped diamond electrodes.

Metal nanoparticles, clusters or aggregates of atoms and nanocrystals, show enhanced physical and chemical properties compared to their bulk counterparts and are thus of extreme interest for fundamental and applications studies. When supported on a conducting substrate, in order to become electrochemically accessible, significant applications in the areas of electrocatalysis and electroanalysis ensue. Although there are a variety of methods to produce metal nanoparticles, electrodeposition is attractive due to the fact that the particles can be synthesised directly attached to the conducting support structure. Furthermore, electrodeposition results in bare nanoparticles, unlike many solution phase approaches where ligands are used to prevent the particles agglomerating, and can thus impede subsequent electron transfer between the analyte and support electrode.

Although electrodeposition has been used extensively it is only in recent years, with the advent of advanced microscopic techniques, that the conventional view of metal nucleation and growth, has been challenged. Historically, models such as those proposed by Scharifker and Hills, proved popular, which treated growth as either instantaneous (fixed number of growth sites) or progressive (time dependant variable number). These allowed microscopic parameters such as nucleation rate (i.e. nuclei per second) or nuclei density (i.e. active sites) to be extracted by fitting experimental current-time transients to mathematical models. However, ex-situ microscopy of the surface, post growth, often showed a discrepancy between the numbers extracted from the electrochemical data and what the microscopy images revealed.

Whilst techniques such as scanning tunnelling microscopy (STM), atomic force microscopy (AFM) and field emission scanning electron microscopy (FE-SEM) proved useful in this regard, they are limited in their ability to resolve atomic structure and hence elucidate the initial stages of metal nucleation and growth, in particular investigating heterogeneous nanostructures. In contrast transmission electron microscopy (TEM) and related higher resolution, aberration corrected techniques, do have the necessary resolving power, howeverthe challenge has been to apply these methods to solving such electrochemical problems.

Commonly, after electrodeposition, metal particles are removed from the conducting substrate and transferred to a TEM grid, using removal procedures such as mechanical force, sonication, focused ion beam sectioning. Whilst atomic resolution is achievable, there is the possibility of damage/change to the particles during transfer. Furthermore, this approach offers no solution to monitoring the growth of individual particles and assessing their interaction in an ensemble. To reduce the transfer step, researchers have used a TEM grid as both the electrode and imaging plate. For example, carbon coated TEM grids, as well as thin metal films (Au or Pt), have been employed.

To follow a dynamic electrochemical process, identical location (IL-TEM) and related techniques have emerged, often in combination with dual purpose TEM-electrode plates. To avoid removing the TEM- electrode from solution, a necessity in IL-TEM, liquid cell TEM enables in-situ electrochemistry to be performed simultaneously with TEM imaging. However, the resolution is typically lower than the ex-situ approach due to the thickness of the cell and the effect of the solution through which the electron beam must pass. Moreover, electron beam effects on the solvent, such as analyte decomposition, radiolysis, bubble formation, and dissolution of the thin film metal electrodes, can be problematic. To the best of our knowledge, no-one has used IL-TEM to resolve individually isolated atoms or the initial stages of metal nanoparticle nucleation and growth on electron transparent boron doped diamond.

In this specification we introduce a new substrate for IL-TEM, electron transparent boron doped diamond (BDD) and apply it to look at the initial stages of metal nanoparticle nucleation and growth, with atomic resolution. BDD is used in the polycrystalline form, containing boron at a suitable density for the material to be useful as an electrode material. It complements the use of carbon coatings in TEM grids due to its low atomic number, but brings additional attributes such as robustness (for repeated use without damage), extremely high thermal conductivity (to aid in quickly dissipating the heat from the electron beam and minimising electron beam damage), and very low Bremsstrahlung background radiation; comparable to toxic beryllium but without the concern of toxicity. The BDD electrode is used in conjunction with IL-STEM to monitor the initial stages (0 - 30 ms) of the nucleation and growth of metal (gold) particles on the BDD surface, providing fundamental mechanistic information.

EXPERIMENTAL

Solutions and chemicals

Au electrodeposition solutions were prepared from potassium tetrachloroaurate (KAuCU, 99.99 %, Sigma- Aldrich) with perchloric acid (HCI0 ₄ , 99.99%, Sigma Aldrich) as a supporting electrolyte in ultra-pure Milli- Q. water (18.2 MW cm, Millipore Corp., U.S.) at 20 °C. All chemicals were used as received without further purification. Au deposition solutions contained 1 x 10 ³ M [AuCI ₄ ] in 0.1 M HCI0 (pH = 1.09) which was deaerated with Argon (Ar) gas for 20 minutes before experiments to exclude oxygen. Ar flow was maintained over the solution during the experiment.

Materials and electrode fabrication

Experiments were performed using a freestanding polycrystalline BDD plate, suitably doped for electrochemical studies (boron dopant level of ~3 ^c ΐq ²⁰ B atoms cm ³ ) and grown using microwave chemical vapor deposition. The plate was mechanically polished to ~ 50 pm thickness, both sides showing a surface roughness finish of ca. 0.2 nm on the surface of a grain. The plate was cut into disks of diameter 3 mm (suitable for insertion into a TEM holder) using laser micromachining and acid cleaned to remove machining debris. The plates were Ar ⁺ ion milled to electron transparency at an accelerating voltage of 6 kV and an angle of incidence of ~4°. The sample was mounted on a post support using glycolphthalate bonding wax (agar scientific), allowing continuous milling as the sample rotated. Each side was milled in turn (approx. 2 hours each side) until a small hole (ca. 50-500 pm in diameter) was formed in the centre of the BDD disk. The disk was mounted in a clamp support for a final low energy ion mill of both sides of the disk at an accelerating voltage of 2 kV with a modulated ion beam to achieve a smooth finish. The BDD was finally acid cleaned (in 0.1 M HN0 ₃ and 0.1 M H ₂ S0 ) before electrochemical measurements. Figures 1(a) to 1(e) illustrate the ion milling procedure employed to produce thin electron transparent BDD. 3D and side view schematics of the ion beam milling system are shown in Figure 1(a) and 1(b). A 3 mm BDD substrate is shown in Figures 1(c) to 1(e) before ion milling (c), during the ion milling (d), and after generating a thin electron transparent area around the hole (e).

Figure 2(a) shows a top-view optical microscope image of the black disc of BDD after the thinning procedure to produce an electron transparent region around the hole. Figure 2(b) shows a schematic sectional side view of the BDD. In use, imaging is performed through the thin region of diamond material around the central hole (not through the hole itself).

Figure 2(c) shows a schematic of an alternative diamond sample substrate 2 comprising a central region 4 which is thinned from a rear side 6 of the diamond substrate 2 for transmission of electrons therethrough. Electrodes 8 are disposed on a front surface side 10 of the diamond substrate 2. While this configuration shows the electrodes either side of the central window, one or more electrodes can be disposed in the thinned central window region or the whole diamond component can be formed of boron doped diamond material. If electrodes are disposed in the window region then they should be suitable transparent to electrons passing therethrough as part of the TEM imaging process. Boron doped diamond has been found to be particularly useful in this regard although it is also possible to graphitize a surface layer of diamond material to form a thin sp2 carbon electrode on the diamond surface.

Figure 2(d) shows a schematic of a transmission electron microscope system 12 comprising an electron beam source 14, a diamond substrate 2 on which a sample 16 is electro-deposited; and a detector 18 for detecting electrons after passing through the sample 16.

Figure 2(e) shows a schematic of a transmission electron microscope system 20 comprising an electrochemical cell 22. The system comprises an electron beam source 24 and the electrochemical cell 22 comprises lower and upper windows 26, 28 with a thin liquid sample 30 therebetween. The spacing between the windows forming the electrochemical cell can be controlled by a suitable spacer element. At least one of the windows can be formed of a diamond substrate. A detector 32 is provided for detecting electrons after passing through the sample.

The roughness of the surface before and after ion milling was measured by AFM as shown in Figure 3 which illustrates an experimental analysis of the surface roughness of BDD before and after ion milling. Figures 3(ai) and (aii) show images of the BDD before ion milling using AFM and SEM, respectively. Figures 3(bi) and (bii) show images of the BDD after ion milling using AFM and SEM, respectively, and the inset is an amplitude image of the thin surface. The analysis indicates that the surface roughness on a grain has increased to 14.4 nm. To make an ohmic contact to the electrode the upper quarter of one of the edges was sputtered (Moorfield MiniLab 060 Platform) with Ti (20 nm)/Au (400 nm) and annealed in a tube furnace for 5 hr at 450 °C.

Electrochemical Set-Up

All electrochemical experiments were carried out using a three electrode set-up controlled by a potentiostat (CHI730A, CH Instruments, Inc. Austin, TX). A commercial saturated calomel electrode was used as the reference electrode and a helical Pt wire served as the counter electrode. The BDD electrode was electrically connected using fine metal tweezers to clamp the disk by the Au contact only. The disk was then dipped into the electrolyte solution using a manual x,y,z micropositioner (Newport, Oxford) such that the central hole was in the solution but the Au contact outside. Figure 4 illustrates the electrochemical setup that has been used to run the electrochemical deposition experiments. The inset image is an optical microscope image of the BDD TEM plate with a Ti/Au band that functions as an ohmic contact. Immediately after depositing the Au particles onto the BDD TEM plate, the grid was rinsed with deoxygenated ultra-pure water and left to dry in a desiccator under an Ar atmosphere, to minimize oxidation of the Au particles.

Surface characterisation

SEM was used to image the BDD plate before and after ion milling and also to obtain low magnification images of the Au particles after electrochemical deposition. FE-SEM images were recorded using the In lens and STEM detector on a Zeiss Gemini operating at 15 kV and 25 kV, respectively. AFM was employed to measure the roughness of the surface before and after ion milling, AFM images were acquired at a low scan rate (0.25 Hz) in intermittent contact (tapping mode) using a Bruker Innova AFM. For examining the suitability of the BDD TEM plate for imaging and diffraction, TEM characterization was carried out using a JEOL-JEM 2100FX (LaB ₆ filament) microscope operated at 200 kV, bright field (BF) mode. Energy dispersive X-ray spectroscopy (EDXS) spectra were recorded using an Oxford instrument Si-Li detector unit, using a beam current of 10 ~pA and an acquisition dwell time of 15 ps per pixel. IL-STEM was employed for the time dependent study of particle shape, structure, size, composition and evolution, during electrochemical growth. IL-STEM utilized a JEOL JEM-ARM200F with probe and image aberration CEOS correctors, performed at 200 kV to obtain high resolution images. Annular dark field (ADF) STEM images were obtained using a JEOL annular field detector with a fine-imaging probe, a probe current of approximately 23 pA, a convergence semi-angle of ~25 mrad and an inner angle of 50 mrad, a camera length of 8 cm, a coefficient of spherical aberration Cs of about +800 nm, and a scan angle of 97.8°. Images were recorded on a Gatan SC1000 Orius CCD camera.

X-ray photoelectron spectroscopy (XPS)

XPS was conducted using a Kratos Analytical Axis Ultra DLD photoelectron spectrometer with a monochromated Al Ka X-ray source (1486.69 eV) operated at 10 mA (150 W) in a 2 x 10 ¹⁰ mbar chamber. Survey spectra were collected using an analyzer pass energy of 160 eV, and binding energies were collected from -5 to 1200 eV scanned at 1 eV increments. Each step was integrated for 500 ms and the entire spectrum was averaged across 5 sweeps. Regional C Is spectra (276.9-300.0 eV) were collected using the same conditions as the survey spectra, except a pass energy of 20 eV (resolution of 0.4 eV) was used with a 55 miti spot size. In order to investigate the different carbon chemical environments at the electrode surface, all data collected were fitted using Lorentzian-Gaussian peaks after a Shirley background subtraction. The C Is peak was calibrated to 285 eV for charge correction.

Figures 5 and 6 show results from the XPS analysis of the BDD surface before and after ion milling. Figure 5(a) shows an optical microscope image of the BDD and the regions where C Is XPS spectra were collected (indicated by color codes). Figure 5(b) is the corresponding XPS image. Figure 5(c) shows C Is XPS spectra of the BDD before ion milling (control) and the thinnest part next to the hole divided into five regions to ease XPS spectra collection. Figure 6 shows deconvoluted C Is spectra collected for five region next to the hole (XPS spot size was 55 miti). Figure 6(a) represents the deconvoluted C Is spectra of a control BDD and Figures 6(b) to (f) represent the deconvoluted C Is spectra of the BDD TEM plate.

Electrochemical deposition method and IL-STEM monitoring ofAu nucleation and growth

Early stage nucleation and growth of Au particles was achieved by applying an external potential of E _dep = -0.5 V (corresponding to an overpotential h = -0.28 V), from a starting potential of +1.3 V (where no faradaic reaction occurs) for a deposition time of t _dep = 5 ms. ADF-STEM images of the first Au electrochemical deposition were collected, in defined regions of the surface, after which the substrate was again immersed in the electrodeposition solution and a second electrodeposition performed using the conditions above (corresponding to a total time of 10 ms growth). The regions that were imaged after the first Au growth process were re-imaged using IL-STEM. Finally using the same conditions as above, a longer t _dep was applied = 20 ms, in total corresponding to 30 ms of electrodeposition and the surface re imaged for a final time. Note, utmost care was taken to minimize salt contamination and surface oxidation in between electrochemical measurements by storing the BDD TEM substrate in an air free desiccator and carrying out electrochemical deposition under deaerated conditions (Ar atmosphere). Finally, to complement the study, an independent Au deposition was carried out but using a longer t _dep = 100 ms.

RESULTS AND DISCUSSION

Suitability of BDD for atomic resolution imaging by TEM

The suitability of the BDD electrode as an electron transparent substrate after ion beam milling was investigated using SEM and TEM.

Figure 7(a) shows an SEM image of a BDD electrode after ion milling using a STEM detector. Figure 7(b) and 7(c) show TEM images of a BDD electrode after ion milling where (b) represent low magnification, (c) high magnification, and the corresponding SAED as inset showing a single crystal of BDD. A dominant [110] texture is revealed using SAED (inset Figure 7(c)), with the image appearing brighter in the thinner region.

To investigate any possible changes to the surface of the BDD after ion beam milling, XPS and EELS analysis were carried out.

As previously indicated, Figures 5 and 6 show results from the XPS analysis of the BDD surface before and after ion milling. XPS spectra were recorded on both the unmilled BDD surface (the control) and the ion milled surface at the edge of the hole and then four distances from the hole edge (XPS spot size ~ 55 pm). Prior to XPS the BDD surfaces had been cleaned. Results indicate the presence of various carbon-oxygen groups across the surface of the BDD. Figures 8(a) to 8(c) show derivatives of C KLL spectra for BDD (control) and BDD after ion milling represented as five regions (shown in Figures 5 and 6).

Figure 9 shows energy electron loss spectra from the BDD support film at two different thickness: (a) 40 nm; and (b) 4 nm. Only in the thinnest region is there any evidence of non-diamond carbon. As the sample gets thicker the response is dominated by bulk diamond and this surface effect is lost.

The BDD TEM plate as an Electrode

The electrochemical response of the BDD TEM plate was first investigated using the simple one electron outer sphere fast electron transfer couple Ru(NH ₃ ) ₆ ³⁺ , whose formal potential £° is -0.16 V vs. SCE. Figure 10 shows a cyclic voltammogram performed using a 3 mm BDD TEM plate in 1 mM Ru(NH ₃ ) ₆ ³⁺ + 0.1 M KN0 ₃ at a scan rate of 0.1 V s ¹ . The peak to peak separation, DE _R = 0.061 V, indicates electrochemical reversibility and shows that ohmic limitations, arising from material resistance affects, are negligible under these conditions. The response of the BDD TEM plate towards Au deposition and stripping, in a solution containing 1 mM [Au ^m CI ] in 0.1 M HCI0 , is illustrated in Figure 11 which shows CV for Au electrodeposition recorded in a solution containing 1 mM [AuCI ] in 0.1 M HCI0 at 0.1 V s ¹ .

The CV had a starting potential of +1.3 V, where no faradaic process takes place, scanning negatively to - 0.5 V and then anodically to +1.5 V, at 0.1 V s ¹ . In the first scan, in the negative direction, Au ³⁺ is reduced, characterised by a cathodic peak at + 0.15 V, scanning positively a single oxidation peak at + 1.15 V is revealed. Scanning a further three cycles, sees the Au ³⁺ reduction peaks occur at less negative potentials due to Au deposition now becoming more kinetically facile, due to deposition on Au rather than BDD. The predominant species is Au ³⁺ and the overall reduction process is assumed to proceed as shown in equation 1:

[AuCl ₄ ] ^~ + 3e ^~ Au° + 4 Cl ^~ (1)

It has also been found that there is no evidence of spontaneous Au electrodeposition on boron doped diamond (i.e. spontaneous electrodeposition without a controlled current being applied). This contrasts with other sp2 carbon materials such as glassy carbon and single walled carbon nanotubes which do exhibit spontaneous Au electrodeposition. Spontaneous electrodeposition is undesirable for controlled TEM / electrochemical experiments and thus BDD is additionally advantageous over other substrate materials in this respect.

As the potential is made negative the CV reaches a diffusion limited process, after which at more negative potentials (> -0.6 V) solvent electrolysis may commence. On the anodic sweep, the oxidation peak is likely associated with Au dissolution in such acidic media, nonetheless, Au oxidation can't be ignored.

A comparative study was carried out by examining the response of the same solution using gold, glassy carbon (GC) and BDD electrodes, which is shown in Figures 12(a) to 12(d) for 1 mM [AuCI ₄ ] in 0.1 M HCI0 ₄ at 0.1 V s ¹ using (a) Au disk, (b) GC disk, (c) BDD disk and (d) BDD TEM plate.

Au atoms, clusters and nanoparticles imaging on a BDD TEM plate electrode

Initial studies were carried out to examine the suitability of a BDD TEM plate electrode for high resolution imaging of Au NP deposited structures. Au NPs were deposited onto the BDD under conditions based on the CV shown in Figure 11). Figure 13 shows HR-STEM images of Au nanoparticles deposited on a BDD TEM plate electrode: (a) bright field-low magnification of Au NPs; and (b-d) dark field-high magnification images of Au atoms, cluster of atoms and nanoparticles.

For the proposed identity location experiments, vide supra, it is also important to examine the effect the electron beam has on the particles and atoms under investigation, in order to assign changes in particle size / position to growth and not electron beam induced affects. This is especially important as Au is a volatile metal and under certain operating conditions the Au atoms / nanoparticles on carbon (sp ² ) films have been shown to move around significantly on the surface of the carbon (sp ² ) films. It has been found that using a BDD TEM plate electrode the Au particles are stable. Figure 14 shows ADF-STEM images: (a) of Au on BDD (sp ³ ); and (b) their standard deviation of an image stack. Figure 14(c) is a montage of the Au NPs movements under the electron beam.

Identity location TEM characterisation (IL-STEM)

The early stages of Au nucleation and growth was studied using electrochemical chronoamperometry and IL-ADF-STEM on the same electrode. The electrochemical deposition was achieved by applying a single potential pulse from +1.0 V to -0.5 V vs SCE (h = -0.28 V) for t _dep = 5 ms (first), 5 ms (second, total deposition time is 10 ms) and 20 ms (third, total deposition time is 30 ms). Under these potential conditions Au deposition should be diffusion controlled, with no other faradaic reactions such as hydrogen evolution or solvent electrolysis contributing to the current.

Figure 15 shows i-t curves for the three different deposition times, referred to as 5 ms (black line), 10 ms (red line) and 30 ms (blue line) deposition (total time). These results represent a chronoamperometric study of Au electrochemical deposition. In general, an initial increase in current with time is observed, characteristic of Au nucleation and growth. The current continues its serge due to an increase in the number of the nuclei of the new phase on the electrode surface. The current reaches a maximum and starts to decay with time ascribed to diffusional field overlap and coalescence at the growing 3D phase (i.e. planar diffusion limited growth). Flowever, from these i-t curves extracting the complex heterogeneous dynamics of nucleation and growth at the atomistic level is impossible.

Figures 16 and 17 show representative low magnification IL-ADF-STEM images from two different regions of a BDD TEM electrode after electrodeposition of Au from solution containing 1 mM [AuCI ₄ ] and 0.1 M HCIO4. Electrodeposition was carried by applying E _app = -0.5 V for t _dep = 5 ms (a), 10 ms (b) and 30 ms (c). Figure 18 shows high magnification IL-ADF-STEM images of early stage phase formation of Au atoms and nanostructures and the effect of short time electrodeposition (E _app = -0.5 V and t _dep = 5ms and 10 ms) on structure evolution of Au obtained from the deposition. An advantage of using ADF-STEM is the ability to resolve particle dynamics at the single atom level. After 5 ms deposition atoms, clusters of atoms (with no clear crystalline structure defined) and small crystalline Au particles (not larger than 3 nm diameter) form close to each other and are surrounded by other atoms and clusters of atoms. With further growth different modes of growth are depicted, the small clusters of atoms transform to monocrystalline NPs of d = 1-3 nm but coalescence and reconstruction is also seen, along with aggregation and coagulation.

Figure 19 shows high magnification IL-ADF-STEM images of Au atoms and nanostructures of Au obtained by a second deposition for t _dep = 5 ms (E _app = -0.5 V and total t _dep =10ms), and their evolution by applying a potential of E _app = -0.5 V for t _dep = 20 ms (total t _dep = 30 ms). FFT of Au NP highlighted as 2. FFT of Au NP highlighted by a circle. FFT of Au N P highlighted as 2. FFT of Au NP highlighted by a circle.

Figure 20 shows high magnification IL-ADF-STEM images of a single crystal NP and a cluster of atoms electrodeposited by applying E _app =-0.5 V for t _dep =5ms (second deposition and total deposition time is 10 ms) and their coalescence after applying the same electrodeposition potential for t _dep = 20 ms (third deposition and total deposition time is 30 ms).

The modes of growth in Figures 19 and 20 follow coalescence and reconstruction to a monocrystalline defect free NP. The diameter of larger NPs increases only slightly. However, their surface has changed by reconstruction and surface atom diffusion, which is obvious from the changes in the corresponding FFT. This behaviour is expected because the surface atoms have less coordination number (i.e. less neighbours) hence are susceptible for such phenomena.

Figure 21 shows high magnification IL-ADF-STEM images of Au NP surface restructure and growth evolution during the transition from (a) the second deposition (E _app = -0.5 V and t _dep = 5 ms, total deposition time is 10 ms) to (b) the third deposition (E _app = -0.5 V and t _dep = 20 ms, total deposition time is 30 ms). Change of the surface and atoms diffusion is apparent, a plot profile shows how one side of the surface has gained height, which indicates surface volume reconstruction.

Figure 22 shows Au NPs made by electrodeposition on the BDD TEM plate after applying E _app = -0.5 V for t _deP = 100 ms: (a) low magnification SEM (BF-STEM mode); (b) high magnification SEM (BF-STEM mode); and (c-h) ADF-STEM images of polycrystalline, single crystal, multiple twinned, aggregates of NPs, respectively. The variation in size is clear as we obtain NPs in the range 3 - 10 nm. Both polycrystalline and monocrystalline with and without defect NPs have been formed. Also two or more NPs have fused together. If we link this to what was obtained from the early stage deposition, we find that the different modes of nucleation and growth (i.e. direct attachment, crystalline formation, coalescence and aggregation, and fusion by aggregation and coagulation) lead to a variety of structures, with different sizes.

In addition to using the BDD-TEM plate to monitor the dynamics of electrodeposition, the plates can be used for any dynamic imaging application where a deposited material on the substrate (be that by electrochemical or non-electrochemical methods) is modified in response to an electrochemical potential. Examples include e.g. (but not limited to) dissolution, reconstruction and rearrangement.

TEM Configurations without electrochemistry

While the aforementioned configurations are for providing a combination of electrochemical and TEM imaging techniques, in other non-electrochemical applications it has still been found to be advantageous to provide a TEM sample substrate formed of boron doped diamond material. Such a boron doped diamond sample substrate been found to be advantageous in TEM applications as it combines features of good electrical conductance, chemical inertness, and physical robustness. Such properties are desirable in TEM applications for the high resolution imaging of batteries, light emitting and energy storage devices, semiconductor materials, biological molecules, as examples. Thus, according to another configuration as described herein, there is provided a transmission electron microscopy system comprising: a transmission electron microscope; and a sample substrate for supporting a sample within the transmission electron microscope, wherein the sample substrate comprises a film of boron doped diamond material. The boron doped diamond sample substrate may be configured according to the previously described configuration including a thinned window for electron transmission. Alternatively, one or more holes can be provided in the boron doped diamond sample substrate for transmission of electrons therethrough. Holes in diamond, or thinning of the diamond, can be produced/achieved using techniques such as dry etching, laser micromachining and water assisted electron beam induced etching. In applications which do not require electrochemistry, no electrochemical electrode is required. Rather, the boron doped diamond sample holder can be merely supported by a holder and is configured to be grounded in use to prevent sample charging. Features of the boron doped diamond sample substrate may be as previously described in terms of physical and chemical parameters. While this invention has been described in relation to certain embodiments it will be appreciated that various alternative embodiments can be provided without departing from the scope of the invention which is defined by the appending claims.

References

1. Corma, A.; Concepcion, P.; Boronat, M.; Sabater, M. J.; Navas, J.; Yacaman, M. J.; Larios, E.; Posadas, A.; Lopez-Quintela, M. A.; Buceta, D.; Mendoza, E.; Guilera, G.; Mayoral, A., Exceptional oxidation activity with size-controlled supported gold clusters of low atomicity. Nat Chem 2013, 5 (9), 775-781.

2. Jain, P. K.; Huang, X.; El-Sayed, I. H.; El-Sayed, M. A., Noble Metals on the Nanoscale: Optical and Photothermal Properties and Some Applications in Imaging, Sensing, Biology, and Medicine. Acc. Chem. Res.2008, 41 (12), 1578-1586.

3. Quan, Z.; Wang, Y.; Fang, J., High-Index Faceted Noble Metal Nanocrystals. Acc. Chem. Res.2013, 46 (2), 191-202.

4. Campbell, C. T., The Active Site in Nanoparticle Gold Catalysis. Science 2004, 306 (5694), 234-235.

5. Eustis, S.; El-Sayed, M. A., Why gold nanoparticles are more precious than pretty gold: Noble metal surface plasmon resonance and its enhancement of the radiative and nonradiative properties of nanocrystals of different shapes. Chem. Soc. Rev.2006, 35 (3), 209-217.

6. Stark, W. J.; Stoessel, P. R.; Wohlleben, W.; Hafner, A., Industrial applications of nanoparticles. Chem. Soc. Rev.2015, 44 (16), 5793-5805.

7. Hayden, B. E., Particle Size and Support Effects in Electrocatalysis. Acc. Chem. Res.2013, 46 (8), 1858-1866.

8. Arico, A. S.; Bruce, P.; Scrosati, B.; Tarascon, J.-M.; van Schalkwijk, W., Nanostructured materials for advanced energy conversion and storage devices. Nat Mater 2005, 4 (5), 366-377.

9. Stamenkovic, V. R.; Mun, B. S.; Arenz, M.; Mayrhofer, K. J. J.; Lucas, C. A.; Wang, G.; Ross, P. N.; Markovic, N. M., Trends in electrocatalysis on extended and nanoscale Pt-bimetallic alloy surfaces. Nat Mater 2007, 6 (3), 241-247.

10. Stamenkovic, V. R.; Strmcnik, D.; Lopes, P. P.; Markovic, N. M., Energy and fuels from electrochemical interfaces. Nat Mater 2017, 16 (1), 57-69.

11. Kim, J.; Dick, J. E.; Bard, A. J., Advanced Electrochemistry of Individual Metal Clusters Electrodeposited Atom by Atom to Nanometer by Nanometer. Acc. Chem. Res.2016, 49 (11), 2587-2595. 12. Kim, J.; Bard, A. J., Electrodeposition of Single Nanometer-Size Pt Nanoparticles at a Tunneling Ultramicroelectrode and Determination of Fast Heterogeneous Kinetics for Ru(NH3)63+ Reduction.7. Am. Chem. Soc.2016, 138 (3), 975-979.

13. Qian, H.; Zhu, M.; Wu, Z.; Jin, R., Quantum Sized Gold Nanoclusters with Atomic Precision. Acc. Chem. Res. 2012, 45 (9), 1470-1479.

14. Yuk, J. M.; Park, J.; Ercius, P.; Kim, K.; Hellebusch, D. J.; Crommie, M. F.; Lee, J. Y.; Zettl, A.; Alivisatos, A. P., High-Resolution EM of Colloidal Nanocrystal Growth Using Graphene Liquid Cells. Science 2012, 336 (6077), 61-64.

15. Tiruvalam, R. C.; Pritchard, J. C.; Dimitratos, N.; Lopez-Sanchez, J. A.; Edwards, J. K.; Carley, A. F.; Hutchings, G. J.; Kiely, C. J., Aberration corrected analytical electron microscopy studies of sol-immobilized Au + Pd, Au{Pd} and Pd{Au} catalysts used for benzyl alcohol oxidation and hydrogen peroxide production. Faraday Discuss.2011, 152 (0), 63-86.

16. Budevski, E. B.; Staikov, G. T.; Lorenz, W. J., Electrochemical phase formation and growth: an introduction to the initial stages of metal deposition. John Wiley & Sons: 2008.

17. Zhang, Z.; Lagally, M. G., Atomistic Processes in the Early Stages of Thin-Film Growth. Science 1997, 276 (5311), 377-383.

18. Budevski, E.; Staikov, G.; Lorenz, W. J., Electrocrystallization: Nucleation and growth phenomena. Electrochim. Acta 2000, 45 (15-16), 2559-2574.

19. Zalineeva, A.; Baranton, S.; Coutanceau, C.; Jerkiewicz, G., Octahedral palladium nanoparticles as excellent hosts for electrochemically adsorbed and absorbed hydrogen. Science Advances 2017, 3 (2).

20. Niihori, Y.; Matsuzaki, M.; Pradeep, T.; Negishi, Y., Separation of precise compositions of noble metal clusters protected with mixed ligands.7. Am. Chem. Soc.2013, 135 (13), 4946-9.

21. Axet, M. R.; Philippot, K.; Chaudret, B.; Cabie, M.; Giorgio, S.; Henry, C. R., TEM and H RTEM Evidence for the Role of Ligands in the Formation of Shape-Controlled Platinum Nanoparticles. Small 2011, 7 (2), 235-241.

22. Brust, M.; Kiely, C. J., Some recent advances in nanostructure preparation from gold and silver particles: a short topical review. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2002, 202 (2), 175-186. 23. Reynal, A.; Lakadamyali, F.; Gross, M. A.; Reisner, E.; Durrant, J. R., Parameters affecting electron transfer dynamics from semiconductors to molecular catalysts for the photochemical reduction of protons. Energy & Environmental Science 2013, 6 (11), 3291-3300.

24. Aubin-Tam, M.-E.; Hwang, W.; Hamad-Schifferli, K., Site-directed nanoparticle labeling of cytochrome c. Proceedings of the National Academy of Sciences 2009, 106 (11), 4095-4100.

25. Honma, H.; Oyamada, K.; Koiwa, I., Advanced plating technology for electronic devices. Electrochemistry 2006, 74 (1), 2-11.

26. Yan, Y.; Li, B.; Guo, W.; Pang, H.; Xue, H., Vanadium based materials as electrode materials for high performance supercapacitors. J. Power Sources 2016, 329 (Supplement C), 148-169.

27. Zhu, C.; Liu, T.; Qian, F.; Chen, W.; Chandrasekaran, S.; Yao, B.; Song, Y.; Duoss, E. B.; Kuntz, J. D.; Spadaccini, C. M.; Worsley, M. A.; Li, Y., 3D printed functional nanomaterials for electrochemical energy storage. Nano Today 2017, 15 (Supplement C), 107-120.

28. Lai, S. C. S.; Lazenby, R. A.; Kirkman, P. M.; Unwin, P. R., Nucleation, aggregative growth and detachment of metal nanoparticles during electrodeposition at electrode surfaces. Chem. Sci.2015, 6 (2), 1126-1138.

29. Ustarroz, J.; Hammons, J. A.; Altantzis, T.; Hubin, A.; Bals, S.; Terryn, H., A generalized electrochemical aggregative growth mechanism.7. Am. Chem. Soc.2013, 135 (31), 11550-11561.

30. Velmurugan, J.; Noel, J.-M.; Mirkin, M. V., Nucleation and growth of mercury on Pt nanoelectrodes at different overpotentials. Chemical Science 2014, 5 (1), 189-194.

31. Harniman, R. L.; Plana, D.; Carter, G. H.; Bradley, K. A.; Miles, M. J.; Fermin, D. J., Real-time tracking of metal nucleation via local perturbation of hydration layers. Nature Communications 2017, 8 (1), 971.

32. Gunawardena, G.; Hills, G.; Montenegro, L; Scharifker, B., Electrochemical nucleation: Part I. General considerations.7. Electroanal. Chem. Interfacial Electrochem.1982, 138 (2), 225-239.

33. Scharifker, B.; Hills, G., Theoretical and experimental studies of multiple nucleation. Electrochim. Acta 1983, 28 (7), 879-889.

34. Scharifker, B. R.; Mostany, J., Three-dimensional nucleation with diffusion controlled growth: Part I. Number density of active sites and nucleation rates per site. 7. Electroanal. Chem. Interfacial Electrochem. 1984, 777 (1), 13-23. 35. Scharifker, B. R.; Mostany, J., Electrochemical Nucleation and Growth. In Encyclopedia of Electrochemistry, Bard, A. J.; Stratmann, M., Eds. Wiley-VCH: Germany, 2007; Vol. 1, pp 512-534.

36. Ustarroz, J.; Ke, X.; Hubin, A.; Bals, S.; Terryn, H., New insights into the early stages of nanoparticle electrodeposition.7. Phys. Chem. C2012, 116 (3), 2322-2329.

37. Radisic, A.; Vereecken, P. M.; Hannon, J. B.; Searson, P. C.; Ross, F. M., Quantifying Electrochemical Nucleation and Growth of Nanoscale Clusters Using Real-Time Kinetic Data. Nano Lett.2006, 6 (2), 238- 242.

38. Radisic, A.; Long, J. G.; Hoffmann, P. M.; Searson, P. C., Nucleation and Growth of Copper on TiN from Pyrophosphate Solution. 7. Electrochem. Soc.2001, 148 (1), C41-C46.

39. Holze, R., SPECTROSCOPIC METHODS IN ELECTROCHEMISTRY - NEW TOOLS FOR OLD PROBLEMS. Bull. Electrochem.1994, 10 (1), 45-55.

40. Simm, A. O.; Ji, X.; Banks, C. E.; Hyde, M. E.; Compton, R. G., AFM studies of metal deposition: instantaneous nucleation and the growth of cobalt nanoparticles on boron-doped diamond electrodes. ChemPhysChem 2006, 7 (3), 704-709.

41. Dudin, P. V.; Unwin, P. R.; Macpherson, J. V., Electrochemical Nucleation and Growth of Gold Nanoparticles on Single-Walled Carbon Nanotubes: New Mechanistic Insights.7. Phys. Chem. C2010, 114 (31), 13241-13248.

42. Pei, A.; Zheng, G.; Shi, F.; Li, Y.; Cui, Y., Nanoscale Nucleation and Growth of Electrodeposited Lithium Metal. Nano Lett.2017, 77 (2), 1132-1139.

43. Voigtlander, B., Introduction. In Scanning Probe Microscopy: Atomic Force Microscopy and Scanning Tunneling Microscopy, Springer Berlin Heidelberg: Berlin, Heidelberg, 2015; pp 1-11.

44. Voigtlander, B., Noise in Atomic Force Microscopy. In Scanning Probe Microscopy: Atomic Force Microscopy and Scanning Tunneling Microscopy, Springer Berlin Heidelberg: Berlin, Heidelberg, 2015; pp 255-267.

45. Tao, F.; Crazier, P. A., Atomic-Scale Observations of Catalyst Structures under Reaction Conditions and during Catalysis. Chem. Rev.2016, 116 (6), 3487-3539.

46. Williams, D. B.; Carter, C. B., High-Resolution TEM. In Transmission Electron Microscopy: A Textbook for Materials Science, Springer US: Boston, MA, 2009; pp 483-509. 47. Ayache, J.; Beaunier, L; Boumendil, J.; Ehret, G.; Laub, D., Sample Preparation Handbook for Transmission Electron Microscopy: Techniques. Springer New York: New York, NY, 2010; p 1-4.

48. Ustarroz, J.; Gupta, U.; Hubin, A.; Bals, S.; Terryn, H., Electrodeposition of ag nanoparticles onto carbon coated tem grids: A direct approach to study early stages of nucleation. Electrochem. Commun. 2010, 12 (12), 1706-1709.

49. Mayrhofer, K. J. J.; Ashton, S. J.; Meier, J. C.; Wiberg, G. K. H.; Hanzlik, M.; Arenz, M., Non destructive transmission electron microscopy study of catalyst degradation under electrochemical treatment.7. Power Sources 2008, 185 (2), 734-739.

50. Ustarroz, J.; Hammons, J. A.; Van Ingelgem, Y.; Tzedaki, M.; Hubin, A.; Terryn, H., Multipulse electrodeposition of Ag nanoparticles on HOPG monitored by in-situ by Small-Angle X-Ray Scattering. Electrochem. Commun.2011, 13 (12), 1320-1323.

51. Williamson, M. J.; Tromp, R. M.; Vereecken, P. M.; Hull, R.; Ross, F. M., Dynamic microscopy of nanoscale cluster growth at the solid-liquid interface. Nat Mater 2003, 2 (8), 532-536.

52. Hartl, K.; Hanzlik, M.; Arenz, M., IL-TEM investigations on the degradation mechanism of Pt/C electrocatalysts with different carbon supports. Energy & Environmental Science 2011, 4 (1), 234-238.

53. Park, J. H.; Steingart, D. A.; Kodambaka, S.; Ross, F. M., Electrochemical electron beam lithography: Write, read, and erase metallic nanocrystals on demand. Science Advances 2017, 3 (7).

54. de Jonge, N.; Ross, F. M., Electron microscopy of specimens in liquid. Nature Nanotechnology 2011, 6, 695.

55. Ross, F. M., Opportunities and challenges in liquid cell electron microscopy. Science 2015, 350 (6267).

56. Hodnik, N.; Dehm, G.; Mayrhofer, K. J. J., Importance and Challenges of Electrochemical in Situ Liquid Cell Electron Microscopy for Energy Conversion Research. Acc. Chem. Res.2016, 49 (9), 2015-2022.

57. Macpherson, J. V., A practical guide to using boron doped diamond in electrochemical research. PCCP 2015, 17 (5), 2935-49.

58. Klein, R. K.; Kephart, J. O.; Pantell, R. H.; Park, H.; Berman, B. L.; Swent, R. L.; Datz, S.; Fearick, R. W., Electron channeling radiation from diamond. Physical Review B 1985, 31 (1), 68-92. 59. Masood, A.; Aslam, M.; Tamor, M. A.; Potter, T. J., Synthesis and electrical characterization of boron-doped thin diamond films. Appl. Phys. Lett.1992, 61 (15), 1832-1834.

60. Hutton, L. A.; lacobini, J. G.; Bitziou, E.; Channon, R. B.; Newton, M. E.; Macpherson, J. V., Examination of the Factors Affecting the Electrochemical Performance of Oxygen-Terminated Polycrystalline Boron-Doped Diamond Electrodes. Anal. Chem.2013,85 (15), 7230-7240.

61. Boxley, C. J.; White, H. S.; Lister, T. E.; Pinhero, P. J., Electrochemical Deposition and Reoxidation of Au at Highly Oriented Pyrolytic Graphite. Stabilization of Au Nanoparticles on the Upper Plane of Step Edges. J. Phys. Chem. B 2003, 107 (2), 451-458.

62. Komsiyska, L.; Staikov, G., Electrocrystallization of Au nanoparticles on glassy carbon from HCI04 solution containing [AuCI4]-. Electrochim. Acta 2008, 54 (2), 168-172.

63. Lomax, D. J.; Dryfe, R. A. W., Electrodeposition of Au on basal plane graphite and graphene. J. Electroanal. Chem.2017.

64. Webb, J. R.; Martin, A. A.; Johnson, R. P.; Joseph, .M. B.; Newton, M. E.; Aharonovich, L; Toth, M.; Macpherson, J. V. Carbon, 2017, 122, 319-328.