Apparatus for microscopic imaging of electrical and magnetic properties of room-temperature objects

• US 5,894,220 A
• Filed: 02/12/1996
• Issued: 04/13/1999
• Est. Priority Date: 02/12/1996
• Status: Expired due to Term

• Current Assignee: PNC Bank National Association (The PNC Financial Services Group, Inc.), University of Maryland
• Original Assignee: University of Maryland
• Inventors: Gim, Yonggyu, Green, Steven M., Wellstood, Frederick Charles, Black, Randall Christopher
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US08/600,168
• Time in Patent Office: 1,156 Days
• Field of Search: 324/201, 324/226, 324/235, 324/240-242, 324/248, 324/249, 324/251, 324/252, 324/260-262, 324/95, 324/96, 324/451, 324/452, 324/457, 324/750, 250/330, 250/336.2, 250/338.1, 250/352, 250/372, 382/145, 382/147, 505/842, 505/843, 505/845-847, 505/160-162, 235/449
• US Class Current: 324/248
• CPC Class Codes: G01N 27/82 for investigating the presence of flaws
• CPC Class Codes: G01R 27/2623 Measuring-systems or electronic circuits G01R27/2635, G01R27/2682 take precedence
• CPC Class Codes: G01R 33/10 Plotting field distribution ; Measuring field distribution
• CPC Class Codes: Y10S 505/842 Measuring and testing
• CPC Class Codes: Y10S 505/846 using superconductive quantum interference device, i.e. squid
• CPC Class Codes: Y10S 505/849 Infrared responsive electric signaling

Abstract

A cryogenic apparatus for microscopy of physical properties of an object including a thin, stiff, transparent substrate or window within the outer wall of the vacuum space of a dewar and a cryogenic sensor within the vacuum space and spaced very close distances to the window. This construction allows for positioning a sample for measurement outside of the vacuum space, at room temperature or higher and for microscopy of physical properties of the sample by monitoring the output from the cryogenic sensor as it is scanned along the surface of the sample.

Claims

1. An apparatus for enabling a cryogenic measuring device to generate microscopic spatially resolved images of physical properties of a sample, comprising

a housing comprised of a first section for holding a cryogen or a cryogenic cooling apparatus and a second section enclosing a vacuum space, at least a portion of the second section is a thin transparent window separating the vacuum space from ambient atmosphere;

a cryogenic measuring device for measuring the physical properties of a sample to obtain resolved images thereof, said cryogenic device is located within the housing having a measuring end disposed adjacent the thin transparent window of the housing for scanning said sample, said sample being located outside of the housing;

alignment of said sample measuring device and thin transparent window of the housing facilitated by the transparency of the window;

means for adjusting the distance between the cryogenic measuring device and the window and means for adjusting the distance between the sample and the cryogenic measuring device to allow the cryogenic sensor to be within microns of the sample; and

means for converting an output from the cryogenic measuring device measuring the sample to images from physical properties of said sample.

2. The apparatus of claim 1 including means for recording the output from the cryogenic measuring device.

3. The apparatus of claim 1 wherein the window is microscopically thin and has a stiffness such that at 1 atmosphere it will flex less than its thickness.

4. The apparatus of claim 1 wherein the cryogenic measuring device comprises a thermally conducting substrate and at least a portion of the thermally conducting substrate is in heat exchange contact with the cryogen or cryogenic cooling apparatus and at least a second portion of the thermally conducting substrate has affixed thereto a cryogenic sensor defining the measuring end of the cryogenic measuring device.

5. The apparatus of claim 1 wherein the thin, transparent window is selected from plastic, sapphire, diamond, metallized films, MgO, SiN, and LaAlO₃.

6. The apparatus of claim 4 wherein the thermally conducting substrate is rod shaped, wherein a first end thereof has a blunt-point shape and mounted to the blunt-point shape is the cryogenic sensor.

7. The apparatus of claim 1 measuring device wherein the cryogenic comprises a member selected from the group consisting of single SQUIDS, multiple SQUIDS, Hall probes, single junction superconducting devices, multiple junction superconducting devices, Giant Magneto-Resistance (GMR) Effect devices, Collosal Magneto-Resistance (CMR) Effect devices, single electron transistors, coulomb blockade devices, bolometers, photocathodes, photoresistive devices, cryogenic field effect devices, and 2-D electron gas devices.

8. The apparatus of claim 5 where the cryogenic measuring device is a SQUID sensor.

9. The apparatus of claim 8 wherein the SQUID sensor is made from YBA₂ CU₃ O₂.

10. The apparatus of claim 1 further comprising a holder for holding the sample in a position in the front of the window and outside of the housing, a means for moving the holder, and means for controlling movement of the means for moving the holder.

11. The apparatus of claim 10 wherein said holder is a stage and said means for moving the holder includes at least one motor.

12. The apparatus according to claim 11 wherein said stage has a composition such that the operation of the stage does not adversely affect said sensor or sensitivity to said sample.

13. The apparatus of claim 11 wherein the stage is an x-y-z stage.

14. The apparatus according to claim 1 further comprising a computer for controlling the sample position, and for monitoring the sensor output.

15. The apparatus according to claim 12 where the apparatus is composed of non-magnetic and non-conducting materials.

16. An apparatus according to claim 1 where the window is thinner than 0.1 mm and consists essentially of sapphire.

17. A method for imaging microwave, optical, UV or infrared radiation of a sample, comprising:

scanning the sample with a cryogenic measuring device positioned within microns of the sample and capable of detecting microwave, optical, UV and infrared radiation of the sample, the cryogenic measuring device located in a housing comprised of a first section for holding a cryogen or a cryogenic cooling apparatus and a second section enclosing a vacuum space, at least a portion of the second section is a thin transparent window separating the vacuum space from ambient atmosphere;

the cryogenic measuring device having a detecting end disposed adjacent the thin transparent window of the housing for scanning the sample located outside of the housing;

detecting the microwave, optical, UV or infrared radiation of the sample with the detecting end of the cryogenic measuring device, said cryogenic measuring device generating an output; and

converting the output to obtain images from the microwave, optical, UV or infrared radiation properties of said sample.

18. A method according to claim 17 wherein the cryogenic measuring device comprises a bolometer.

19. A method for obtaining images of magnetic fields from a sample, comprising scanning the sample with a cryogenic measuring device, the cryogenic measuring device located in an apparatus comprising a housing comprised of a first section for holding a cryogen or a cryogenic cooling apparatus and a second section enclosing a vacuum space, at least a portion of the second section is a thin transparent window separating the vacuum space from ambient atmosphere;

the cryogenic measuring device within the housing having a measuring end disposed adjacent the thin transparent window of the housing for scanning the sample through the thin transparent window, said sample located outside of the housing;

detecting the magnetic field of the sample to spatial resolutions of 50 μ

m with the measuring end of the cryogenic measuring device, said cryogenic measuring device generating an output; and

converting the output to obtain images from the magnetic field of said sample.

20. The method of claim 19 wherein the cryogenic measuring device comprises a SQUID, Hall probe, GMR or CMR device.

21. A method for measuring electric fields from a sample, comprising scanning the sample with a cryogenic measuring device, the cryogenic measuring device located in an apparatus comprising a housing comprised of a first section for holding a cryogen or a cryogenic cooling apparatus and a second section enclosing a vacuum space, at least a portion of the second section is a thin transparent window separating the vacuum space from ambient atmosphere;

the cryogenic measuring device within the housing having a measuring end disposed adjacent the thin transparent widow of the housing for scanning through the thin transparent window, a sample located outside of the housing; and

detecting the electrical field of the sample to spatial resolutions of 50 μ

m with the measuring end of the cryogenic measuring device, said cryogenic measuring device generating an output; and

converting the output to obtain images of the sample from the electrical field.

22. An apparatus for enabling a cryogenic measuring device to generate microscopic spatially resolved images of physical properties of a sample, comprising

a housing comprised of a first section for holding a cryogen or a cryogenic cooling apparatus and a second section enclosing a vacuum space, at least a portion of the second section is a thin transparent window separating the vacuum space from ambient atmosphere;

a cryogenic measuring device for measuring the physical properties of a sample to obtain resolved images thereof, said cryogenic measuring device is located within the housing having a measuring end disposed adjacent the transparent window for scanning a sample, said sample is located outside of the housing;

means for moving the transparent window and the cryogenic measuring device relative to one another so that the sample and the cryogenic measuring device are positioned within microns of one another;

means for delivering a cryogen from the first section of the housing to a thermally conducting substrate in heat exchange with the cryogenic measuring device; and

means for converting an output from the cryogenic measuring device measuring the sample to obtain images of physical properties of said sample.

23. The apparatus of claim 22 wherein means for delivering a cryogen from the first section of said housing to the substrate in heat exchange with the cryogenic measuring device comprises a bellowed conduit having a first end in open communication with the cryogen and a second end for delivering cryogen to the substrate.

24. The apparatus of claim 23 wherein said substrate comprises sapphire.

25. An apparatus for enabling a cryogenic measuring device to generate microscopic spatially resolved images of physical properties of a sample, the apparatus comprising:

a housing comprising a first section for holding a cryogen or a cryogenic cooling apparatus and a second section enclosing a vacuum space, at least a portion of the second section being a thin transparent window separating the vacuum space from ambient atmosphere;

a cryogenic measuring device for measuring the physical properties of the sample and for producing an output representative of the physical properties to obtain resolved images of the sample, the cryogenic device being located in the housing and having a measuring end disposed adjacent the thin transparent window of the housing for scanning the sample, the sample being located outside of the housing, alignment of the cryogenic measuring device and the thin transparent window of the housing being facilitated by a transparency of the window;

sample holding means for holding the sample outside of the housing;

moving means for causing relative movement between the cryogenic measuring device and the sample holding means which allow the cryogenic sensor to be within microns of the sample and so that the cryogenic measuring device and the sample holding means successively attain a plurality of relative positions;

position detecting means for detecting the plurality of relative positions and for outputting a position signal representing the plurality of relative positions; and

imaging means, receiving the position signal and the output from the cryogenic measuring device at each of the plurality of relative positions, for deriving the resolved images of the sample from the position signal and the output.

26. The apparatus of claim 25, wherein:

the sample holding means is movable in at least x and y directions relative to the cryogenic measuring device; and

the moving means comprises means for moving the sample holding means in at least the x and y directions relative to the cryogenic measuring device to achieve a raster scan of the sample.

27. The apparatus of claim 26 wherein, the sample holding means comprises a sample stage movable in at least the x and y directions;

and

the moving means comprises stepper motors for moving the sample stage in at least the x and y directions.

28. An apparatus for enabling a cryogenic measuring device to generate microscopic spatially resolved images of physical properties of a sample, comprising

a housing comprised of a first section for holding a cryogen or a cryogenic cooling apparatus and a second section enclosing a vacuum space, the second section comprises a plate defining an opening, a window support spaced apart from said plate, means for connecting the plate to the window support enabling movement of the window support relative to the plate and a thin transparent window positioned on the window support, said window, window support, means for connecting, and plate defining structure enclosing the vacuum space;

a cryogenic measuring device for measuring the physical properties of a sample to obtain resolved images thereof, said cryogenic device is located within the second section of the housing having a measuring end disposed adjacent the thin transparent window for scanning said sample, said sample being located outside of the housing;

alignment of said sample measuring device and thin transparent window of the housing facilitated by the transparency of the window;

threaded means for adjusting the distance between the cryogenic measuring device and the window, and stage means supporting the sample for adjusting the distance between the sample and the window, said threaded means and said stage means allowing the cryogenic sensor to be within microns of the sample; and

means for converting an output from the cryogenic measuring device measuring the sample to images from physical properties of said sample.

29. The device of claim 28 wherein said means for connecting comprises a bellows which also defines a thermal cooling path.

30. The device of claim 28 wherein the window is thinner than 0.1 mm and comprises sapphire.

31. The device of claim 30 wherein the cryogenic measuring device is a SQUID.