REFRIGERATOR

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application Serial No 61/529,711, filed on August 31, 2011 and U.S. Provisional Patent

Application Serial No. 61/534,172, filed on September 13, 2011, the disclosure of each of which is incorporated by reference herein in its entirety.

BACKGROUND

For certain devices performing reduced temperature measurements, reference samples can be utilized for calibration before an experiment is performed. Such reference samples can also be utilized to prepare a measurement probe, for example to have a geometrically and energetically suitable probe tip, and to verify certain properties of the probe tip.

Certain reduced-temperature measuring devices have shielding, which can block radiation, as well as thermally insulate the measuring device to maintain a suitable internal temperature. Storing the reference samples at room temperature, transporting the reference samples from an external storage refrigerator to the measuring device or otherwise exposing the reference samples to room temperature can render the reference samples unsuitably warm for measurements. Further, cooling the reference sample to a suitable temperate within the measuring device can require significant time, and necessitate the use of expensive cooling liquids, such as liquid Helium. Accordingly, there is a need for an alternative mechanism for providing a reference sample in a reduced-temperature measuring device.

SUMMARY

Systems and methods for exchanging samples at a reduced temperature in a measuring device are disclosed herein.

The disclosed subject mater provides systems for exchanging samples at a reduced temperature in a measuring device. In an exemplary embodiment, a measuring device includes shielding, a measurement stage, a cooling source, a sample container, and a transfer mechanism. The sample container can be thermally coupled to the cooling source and configured to be disposed within the shielding of the measuring device. The sample container can also include one or more slots, with each slot configured to hold a sample at the reduced temperature. The transfer mechanism can be configured to transfer each sample between the measurement stage and the slots.

In some embodiments, the sample container can be fabricated from copper, gold and/or silver. The sample container can include a mesh material or a wire. The sample container can have a wedge shape.

In some embodiments, two or more slots are provided, with each slot configured to hold one of multiple samples at the reduced temperature. The sample can include a reference sample.

In some embodiments, the transfer mechanism can include one or more of a ceramic, plastic, rubber or fiber material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary measuring device with an exemplary system for exchanging samples according to the disclosed subject matter.

FIGS. 2A-2C illustrate an exemplary method for exchanging samples according to the disclosed subject matter.

FIG. 3 illustrates an alternative embodiment of a sample container according to the disclosed subject matter.

FIG. 4 is a diagram illustrating further features of the exemplary system for exchanging samples of FIG. 1.

DETAILED DESCRIPTION

The disclosed subject matter provides systems and methods for exchanging samples at a reduced temperature in a device for taking measurements at the reduced temperature. The disclosed subject matter can be used, for example and without limitation, in connection with a scanning probe microscope, a scanning tunneling microscope, an atomic force microscope, a Kelvin probe force microscope, or an optical microscope (e.g., near-field scanning optical microscope). The systems and methods of the disclosed subject matter can also be used for other measurement techniques that require so-called ultra high vacuum (UHV), which are not necessarily at reduced temperatures. For example, surface science measurements (e.g., X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and the like) can require ultra-clean samples at high vacuum, which can be challenging when samples are exchanged from outside the shielding of the measuring device. The systems and methods of disclosed subject matter can also be configured for exchanging samples for a measurement device taking measurements at an increased temperature.

FIG. 1 illustrates an exemplary measuring device 100 with an exemplary sample-exchange system 102 according to the disclosed subject matter. The sample-exchange system 102 is configured to exchange samples at a reduced temperature in measuring device 100, embodied herein, for purpose of illustration and not limitation, as a scanning tunneling microscope. However, the sample-exchange system 102 described herein can be configured to exchange samples in, for example and not limited to a scanning probe microscope, scanning tunneling microscope, atomic force microscope, Kelvin probe force microscope, optical microscope, or other suitable measuring device.

Measuring device 100 can include one or more coolant reservoirs 104, 106, each adapted for containing a coolant. Measuring device 100 can also be cooled using a closed-cycle refrigerant system. In the exemplary measuring device, two coolant reservoirs 104, 106 are provided, although more or less can be utilized depending on the desired performance of the device 100. In the exemplary measuring device, the reservoirs 104, 106 have a capacity of 17 liters of liquid nitrogen and 8 liters of liquid helium. However, any suitable capacity of reservoirs can be used depending on the performance of the device 100 and the desired measurements to be performed.

In operation, each reservoir 104, 106 can receive a certain volume of the same or a different coolant. For example, the first coolant reservoir 104 can contain 8 liters of liquid helium~4 (1He-4), which can have a loss rate of about 30 mL/hour, and the second coolant reservoir 106 can contain 17 liters of liquid nitrogen (IN), which can have a loss rate of about 220 mL/hour. In this example, the first coolant reservoir 104 is at approximately 4.2 K, the boiling point of liquid helium-4, and the second coolant reservoir 106 at approximately 77.2 K, the boiling point of liquid nitrogen. However, coolant reservoirs 104, 106 can contain any suitable coolant having cooling properties to achieve a desired temperature for performing measurements, which can depend on, among other factors, the type of measuring device 100 being used, the type of sample being measured and/or the type of measurement being performed.

Coolant reservoirs 104, 106 can each be connected to one or more layers of shielding 108, 1 10. The shielding 108, 1 10 can serve to conduct coolant into and thermally isolate a region inside the shielding from a region outside the shielding and/or from outside air. The shielding can also prevent radiation or other undesired contaminants that could affect a measurement taken by the measuring device from entering the shielded region. As embodied herein, shielding 108, 110 is configured as one or more layers of aluminum having 2 mm thickness. However, any suitable material can be utilized having thermal properties suitable for achieving a desired temperature within the region. For example and without limitation, shielding 108, 1 10 can utilize silver, copper, including oxygen- free copper, gold, tungsten, zirconium, or any other suitable material. Further, depending on the space available and the desired cooling properties, the shielding can have a thickness from 10 μηι up to 100 cm. In addition the material of the shields can have one or more coatings, for example and without limitation of gold, copper, nickel and/or any alloy.

Measuring device 100 can include a body 112 housed within one or more of the layers of shielding 108, 110. The body 112 can include a measurement stage to hold a sample and a sensor to take a physical measurement of the sample. As embodied herein, the sensor in body 112 of measuring device 100 includes one or more probes, which, when placed proximate to a sample, sends an output signal to an output port to provide information about measured properties of the sample. The measurement stage of body 112 can be directly, thermally coupled to one or more of coolant reservoirs 104, 106 or via shielding 108, 110. Alternatively, the measurement stage of body 112 can be spaced apart from and not thermally coupled to coolant reservoirs 104, 106.

The sample-exchange system 102 of measuring device 100 includes a sample container 114. Sample container 114 is disposed within one or more layers of shielding 108, 110, and can be thermally-coupled to the one or more coolant reservoirs 104, 106, for example via shielding 108, 1 10. As embodied herein, sample container 114 can be disposed within the inner-most layer of shielding 108. However, sample container 114 can be disposed within any layer of shielding 108, 110 of measuring device 100, and sample-exchange system 102 can include two or more sample containers 1 14, each disposed within a corresponding layer of shielding, and thus a different temperature zone, to hold different samples at different temperatures.

Sample container 114 includes one or more slots 118 in which each sample can be stored. As embodied herein, sample container 114 includes two slots 118. In some applications, and as described further herein, a first slot can hold a reference sample and a second slot can hold a sample to be measured. However, sample container 114 can be configured to have only one slot, for example where space inside the shielding 108, 110 is limited, and sample container can be configured to have three or more slots, for example where access to many samples is desired in a reduced period of time, as described further below.

Sample-exchange system 102 of measuring device 100 can include a transfer mechanism 116 to transfer samples from sample container 114 to the measurement stage in the body 112 of the measuring device 100. As embodied herein, transfer mechanism 116 is configured as a wobblestick (for example, VG Scienta, Mechanical Hand, MH series), which includes a gripping mechanism attached to the end of a movable arm. As described further below, transfer mechanism 116 can be moved through a corresponding door in each of the layers of shielding 108, 110 to physically grasp a sample from the sample container 1 14 and transport it from the corresponding slot 1 18 to the measurement stage of the body 112, and vice versa. The transfer mechanism 116 can be operated manually, or can be configured as an automated sample transfer mechanism. Further, the transfer mechanism, as embodied herein, is thermally decoupled from the one or more coolant reservoirs 104, 106. As such, the transfer mechanism 116 can include or be coated with a relatively low thermally-conducting material, such a ceramic, plastic, rubber or fiber material to reduce the amount of heat transferred to the sample during transfer. Alternatively, the transfer mechanism 116 can be thermally coupled to the coolant reservoir 104, 106, either directly or via shielding 108, 110.

Sample container 114 can include the same or similar materials as one or more of the layers of shielding 108, 110, which as described above can have thermal properties sufficient to conduct heat from and achieve the desired temperature in the corresponding temperature zone. Additionally or alternatively, sample container 1 14 can include a mesh material or wire material, for example to increase the heat flow away from the sample container 114 to cool the samples. Sample container 114 can be shaped to provide the transfer mechanism 1 16 access to the slots 118. As shown in FIG. 1 , transfer mechanism 116 can be configured to enter the shielding 108, 110, for example and without limitation at an angle of 20° relative to horizontal, and thus sample container 114 can be configured with a wedge-shaped base to angle slots 118 at a corresponding angle to be in-line with the path of transfer mechanism 116. The sample container 114 can be positioned at any suitable to correspond to any transfer mechanism 116 of a measuring device 100.

FIGS. 2A-2C illustrate the operation of sample-exchange system 102 in an exemplary exchange of samples. In FIG. 2A, a reference sample 120 is shown on the measurement stage of body 112. Reference sample 120 in this configuration can be utilized to calibrate measuring device 100. For example, reference sample 120 can be measured by measuring device 100 to take a reference measurement, which can be used to determine an output value from measuring device 100 corresponding to the known reference sample 120. Additionally or alternatively, reference sample 120 can be utilized to train a probe and/or probe tip of measuring device 100.

Certain measuring devices utilize probes and/or probe tips, which can be replaced. Replacing the probe and/or probe tip can include training the new, untrained probe and/or probe tip. Training the probe and/or probe tip can include moving the probe proximate to or across the surface of reference sample 120, at least once or in some cases more than once to train the probe and/or probe tip for taking measurements. Once reference sample 120 has been utilized, transfer mechanism 116 can enter the region within shielding 108 through a door proximate to reference sample 120 and grasp the reference sample. Transfer mechanism 1 16 can move out of shielding 108 and back into shielding 108 through a door proximate to the sample container 114 to insert reference sample 120 into the empty slot 118 in the sample container 114.

FIG. 2B shows sample container 1 14 with reference sample 120 reinserted. Sample container 114 also includes sample to be measured 122, which as embodied herein is a sample of which the user desires to measure one or more properties, which can be unknown to the user or desired to be investigated by the user. As sample container 114 is disposed within shielding 108 and thermally coupled to coolant reservoir 104, sample 122 can be at a desired temperature for performing the measurement, which can be determined, for example, from the measuring device 100, the type of sample or the measurement to be performed. Transfer mechanism 116 can enter the slot 118 holding sample 122 through the door proximate to the sample container 114 and grasp sample 122. Transfer mechanism 116 can move out of shielding 108 and back into shielding 108 through a door proximate to body 112 to insert sample 122 into the measurement stage of body 112. FIG. 2C shows sample 122 attached to the measurement stage of the body 112, where measurement by measuring device 100 can be performed.

FIG. 3 is a diagram showing the change of temperature over time of an exemplary reference sample during an exemplary sample exchange using sample- exchange system 102 according to the disclosed subject matter. As shown in FIG. 3, at 0 mins, a sample, here a reference sample 120 located in a slot 118 of sample container 114 is at a desired temperature for measurement of 77 K. Between about 30 to 45 mins, reference sample 120 is moved as described above from sample container 1 14 to the measurement stage of body 1 12, which is thermally coupled to coolant reservoir 104.

As FIG. 3 shows, the exchange of reference sample 120 increased the temperature of sample 120 by about 2 K. The increased temperature of reference sample 120 can be due at least in part to heat transferred to the reference sample 120 from the transfer mechanism or exposure of the reference sample 120 to external temperatures. However, having reference sample 120 stored at the desired temperature within the shielding 108 of the measuring device 100, the increase in temperature of reference sample 120 can be much less than that of other sample- exchange systems, in which the sample is stored at room temperature and/or transported from a larger distance and for a longer period of time. As such, as shown in FIG. 3, reference sample 120 on the measurement stage of body 112 can be cooled to the desired temperature of 77 K in about 2-3 hours (i.e., as shown from t = 45 mins to t = 210 mins in FIG. 3), which can be less than other sample-exchange systems for other, similar measuring devices that can take from overnight to 24 hours to cool a new sample to the desired temperature for measurement.

FIG. 4 shows an alternative configuration for a sample-exchange system 102 according to the disclosed subject matter. As shown in FIG, 4, sample- exchange system 102 can have a plurality of temperature zones. As embodied herein, sample-exchange system 102 has 4 zones 202, 204, 206, 208; however, other numbers of zones can be included depending on the application. Each zone can be thermally coupled to a different coolant reservoir 104, 106 or other coolant source, or the same coolant source configured at different flow rates to provide a different temperature level in each zone. Each zone 202, 204, 206, 208 can have one or more layers of shielding between each zone, or between the zones and outside of the measuring device 100. The inner-most zone 202 can represent a final, lowest temperature zone of the measuring device (for example, 20 mK), zone 204 can represent a next higher temperature zone (for example, 1 K), zone 206 can represent a yet higher temperature zone (for example, 4 K) and zone 208 can represent a highest temperature zone (for example, 77 K).

In the configuration of FIG. 4, a sample container 114 can be placed in each of the zones 202, 204, 206, 208. Alternatively, a single sample container 114 can be movable, manually or automatically, between each zone to allow samples in the sample container 114 to be selectively cooled to a desired temperature. As such, less coolant resources can be utilized to keep the samples in the sample container 114 at a reduced temperature in one of the relatively higher temperature zones, while still reducing the amount of time necessary to cool the sample to the desired temperature if a user desires to measure the sample in a relatively lower temperature zone.

Additionally or alternatively, one or more zones or regions described herein can be coupled to one or more vacuum sources, which can provide one or more vacuum levels for measuring a sample in measurement device 100. For example, zone 202 can represent a so-called deep Ultra High Vacuum (deep UHV) at a pressure of less than 10 ⁹ torr, zone 204 can represent an Ultra High Vacuum (UHV) at a pressure of about 10 ⁹ torr, zone 206 can represent a High Vacuum (HV) at a pressure of about 10 ⁶ to 10 ⁸ torr, and zone 208 can represent a Rough Vacuum at a pressure of about 10 ³ to 10 ⁶ torr. Each zone 202, 204, 206, 208 can have the same temperature with a different pressure, or each zone 202, 204, 206, 208 can have a combination of temperature and pressure difference relative to other zones.

As a further alternative, sample- exchange system 102 can be coupled to a heat source for measuring samples in a device at an increased temperature. In this configuration, samples can be stored in sample container 114 at a desired increased temperature relative to outside of measuring device 100, and thus less time would be required to heat the sample before measurement.

While the disclosed subject matter is described herein in terms of certain exemplary embodiments, those skilled in the art will recognize that various modifications and improvements can be made to the disclosed subject matter without departing from the scope thereof. For example, sample-exchange system 102 can be configured to adapt to additional features of a measuring device 100 depending on the application. In a particular example, sample-exchange system 102 can include an exhaust or venting system, or the like, which can remove, reduce or prevent contaminants, for example from outside the measuring device 100 or from in-situ evaporation and/or deposition of materials on a sample in the measurement stage of measuring device 100.

The foregoing merely illustrates the principles of the disclosed subject matter. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will be appreciated that those skilled in the art will be able to devise numerous modifications which, although not explicitly described herein, embody its principles and are thus within its spirit and scope.