TEMPERATURE CONTROL FOR MICROSCOPY

Abstract: A temperature control unit provides means for observing samples under microscopy at greatly elevated and greatly reduced temperatures. The temperature control unit is constructed to insulate a sample from ambient temperatures while providing a highly heat conductive substrate for the sample that provides for rapid heat transfer to/from the sample. A dry gas provides a positive pressure around the sample, as compared to atmospheric pressure to help prevent atmospheric contract with the sample.

Description: TEMPERATURE CONTROL FOR MICROSCOPY This invention relates to temperature control for microscopy. Background of the Invention Those skilled in the materials art recognize that most materials exhibit different properties at different temperatures. A comparison of observable properties of materials at different temperatures may provide valuable information about how materials perform in a product at different temperatures. The present invention is directed to an apparatus and a method whereby such materials may be observed at different temperatures using microscopy, such as atomic force microscopy (afm), as well as light microscopy. Summary of the Invention An apparatus for controlling the temperature of a microscopy sample comprises an external housing made of a highly heat insulating material, an internal housing made of a highly heat conducting material within said external housing for holding a sample to be subjected to microscopy, and conduit means for the flow of a temperature controlling gas through said external and internal housings, and means for directing the flow of the temperature controlling gas around the sample. A thermocouple is associated with the sample for measuring the temperature of the sample. Also, a heater may be associated with the sample for heating the sample, and heaters may be located in the internal and external housings for heating the temperature controlling gas. Also, cooling means are provided for reducing the temperature of the temperature controlling gas. The internal and external housings are made of materials that have specific heat conducting properties designed to optimize temperature control and mύiimize temperature fluctuation of the sample. The external housing is made of a material and construction having heat conductivity in the range of 0.00001 to 0.25 W/m-K (watt per meter Kelvin), and the internal housing is made of a material having a heat conductivity in the range of 20 to 2000 W/m-K. In an illustrated embodiment the exterior housing is made of polyvinyl chloride (PVC) and the internal housing is made of aluminum. The temperature of the sample can be maintained at -270° C to 200° C. The sample is mounted on a sample holder made of highly thermally conductive material and a thermocouple is mounted in the proximity of the sample and the sample holder. A computer can be used for monitoring the temperature of the sample, and controlling the flow of the temperature controlling gas, as well as any heaters that may be used in the apparatus, to maintain the temperature at a constant level. Brief Description of Drawings Fig. 1 illustrates one possible embodiment of the temperature control apparatus of the invention. Fig. 2 illustrates a side view of a housing of a temperature control apparatus of the invention. Fig. 3 illustrates a top view of the housing illustrated in Fig. 2. Fig. 4 illustrates a preferred embodiment of a housing for temperature control of a sample. Fig. 5 illustrates a top view of a sample holder of the housing of Fig. 4. Detailed Description of the Invention With reference now to Fig. 1 , an illustrated variable temperature control device 10 of the invention includes a sample holding portion 12, temperature control center 14, and fluid source 16. With reference as well to Figs. 2 and 3, sample holding portion 12 comprises an exterior housing 20 made of a highly heat insulating material and construction having a heat conductivity of 0.00001 to 0.25, preferably 0.02 to 0.15 W/m-K (watt per meter Kelvin), and an interior housing 22 made of a low heat insulating material having a heat conductivity of 20 to 2000, preferably 50 to 400 W/m-K, and sample holder 24. Examples of highly heat insulating materials used to make exterior housing 20 are polyvinyl chloride (PVC), celluloid, particle board, cork, and foamed polyurethane. Examples of low heat insulating material used to make the interior housing 22 are aluminum, copper, carbon steel, pyrolytic graphite, gold and brass. A highly heat insulating material is used to make outer housing 20 to help prevent heat transfer to or from external housing 20 to the surroundings, which saves energy and helps maintain a constant temperature within external housing 20 with little or no fluctuation. The low heat insulating material (i.e. highly heat conductive material) used to make internal housing 22 aids in quickly drawing heat from or transferring heat to the sample so that a substantially constant sample temperature can be quickly achieved and maintained using the temperature control devices associated with temperature control center 14. The construction of external housing 20 may enhance the insulating effect of the material used to make the housing. For example, if a material having a heat conductivity outside the range described above is used, and the material is used to make a double walled exterior housing, the effective insulating properties of the exterior housing may be in the range described, even though the material used has properties outside the range. The temperature at which a sample is maintained during microscopy may also have some bearing on the materials chosen for fabricating the temperature control device of the invention. For example, if samples are maintained at 200° C, PVC may soften and break down, and coated cork or particle board may be preferred for making exterior housing 20. Other material substitutions will be apparent to those skilled in the art. In the illustrated embodiment, temperature control is achieved using counter balancing temperature raising and lowering devices. When low temperatures are desired, fluid 16a, such as nitrogen (N 2 ) gas, is passed through cooling means 26a in refrigeration means 26. Cooling means 26a can conveniently be a liquefied or solidified gas, such as N 2 , CO 2 , He, or Ar. Those skilled in the art will recognize that mechanical refrigeration can be used for cooling means 26a, especially if only mild cooling is needed. When higher temperatures are desired, heaters 30,34,36 may be employed to raise the temperature of temperature controlling fluid 16a. When pressurized gas is used as the temperature controlling fluid 16a, the flow of the gas is controlled by pressure control valve 56, flow regulating solenoid valve 50, and flow buffer 48. Flow buffer 48 provides a reservoir for compression and expansion of the gas to help smooth out the gas flow since solenoid valve 50 operates only to turn on and turn off the flow of the gas. A pressure of 5 to 30 psi (pounds per square inch) for the temperature controlling gas in the system is desirable, and pressures in the lower end of the range are preferred. The controlled flow of fluid then passes through refrigerator means 26. If cooling is desired, the gas flows through cooling means 26a and exits refrigeration means 26 through tubing 28a. Optionally heater 34 may be placed adjacent tubing 28a downstream of refrigeration means 26, and optional thermocouple 32b may be placed in tubing 28a in the proximity of heater 34. Additional thermocouples may be provided, for example thermocouple 32a in exterior housing 20, in the path of temperature controlling fluid 16a as desired. The temperature of the fluid 16a can be controlled somewhat by the choice of cooling means 26a and by the amount of time fluid 16a spends in cooling means 26a, such time being dependant on the flow rate of fluid 16a and the amount of tubing 28a passing through cooling means 26a. Heaters 30,34,36, in temperature control center 14, external housing 20, and internal housing 22 may be used in conjunction with cooling means 26a to precisely control the temperature of fluid 16a. The temperature of fluid 16a may be monitored by thermocouples 32,32a,32b. The heaters 30,34,36, and fluid flow regulator 50, may be controlled by computer 42, and optionally other computers, in response to input received from thermocouples 32,32a,32b and flow meter 46. If different thermocouples are used in different portions of the apparatus, separate computers may be required to handle the information gathered from each thermocouple. In the illustrated embodiment, ANSI type T sub miniature thermocouples, available from Omega Engineering, Inc, Stamford, Conn, were used. In the illustrated embodiment, nitrogen is used as temperature controlling fluid 16a, and the nitrogen is passed from tank 16 through tubing 28 into tubing 28a which passes through refrigeration means 26. Tubing 28 can be a polymer such as rubber or polypropylene or the like, or a metal such as copper. Tubing 28a is a material which can withstand very low temperatures that may potentially be encountered in refrigeration means 26, and is preferably a metal such as copper. Refrigeration means 26 may be mechanical refrigeration means known in the art, or it may simply be an insulating double walled container, known as a Dewar flask, used to contain liquefied gases, or solidified gases or liquids. In the illustrated embodiment, liquid nitrogen is used in a Dewar flask as the refrigeration means 26 for controlling the temperature of fluid 16a. From temperature control unit 14, temperature controlling fluid 16a is directed into exterior housing 20, in the illustrated embodiment through conduit 38, over second optional heater 36, and into chamber 44. Chamber 44 serves to stabilize the temperature around the sample by collecting a quantity of the temperature controlling fluid at the desired temperature. A third optional heater 30 may be located directly adjacent sample holder 24. When microscopy at very low temperatures is desired, atmospheric air must be kept away from the sample to prevent icing or frosting of the sample from atmospheric moisture. To help maintain an envelope of dry fluid around the sample, means for creating a chamber above the sample may be provided, or an optional flow tube 40 may be provided above the sample to direct additional dry fluid over the top of the sample. In the illustrated embodiment, vent holes 26 in sample holder 24 (a portion of internal housing 22) permit temperature controlling fluid 16a to flow out of chamber 44 around the sample, controlling the temperature of the sample and enveloping the sample in dry fluid which forces atmospheric moisture away from the sample. With reference now to Figs. 4 and 5, in a preferred embodiment of the invention, housing 12a comprises exterior housing 20a similar to that described in Fig. 2, with an interior housing 22 which is substantially the same as that described in Fig. 2. Housing 12a also comprises, however, deflector 52 contained within insulated ring 53. Deflector 52 rests over sample holder 24 and creates a protective area around the sample that reduces the exposure of the sample to the atmosphere. In the illustrated embodiment of Fig. 4, vents 26 were found to be sufficient to keep moisture away from the sample when baffles 54 were placed over deflector 52 to help control the flow of fluid away from sample 55. In the illustrated embodiment, baffles 54 comprise flat, semi circular pieces of plastic, for example polycarbonate, which are designed to fit on the top of insulated ring 53 to enclose a circle. The sample is accessible by the head of an atomic force microscope, or other microscope, through the center of the circle formed by the semi circular pieces, and the temperature controlling fluid escapes through the center of the circle, creating a positive pressure over the sample, as compared to atmospheric pressure, that prevents atmospheric moisture from entering the deflector and reaching the sample. Those skilled in the art will recognize other means that may be used to keep moisture away from the sample. Thermocouple 32 is provided adjacent to the sample to help monitor the temperature of the sample. Computer 42, and optionally other computers, may be provided to accept input from the various thermocouples used in the apparatus, and use the data collected to control the various heaters, the flow rate of temperature controlling fluid 16a, and the refrigeration means 26 to control the temperature automatically. In the illustrated embodiment, the liquid nitrogen used for the cooling means 26a in refrigeration means 26 has a boiling point of -196° C, and a temperature of -100° C +0.4° C was achieved when a PVC external housing 20 and an aluminum inner housing 22 were used. It is believed that lower temperatures can be achieved, but this was left to further experimentation since the durability of the head of the afm microscope (used in this experiment) at low temperatures is not known at this time. It was found that temperatures could be maintained without using heaters 30,34,36 for this test, but it is believed that heaters 30,34,36 will have utility in other applications. While the invention has been specifically illustrated and described, those skilled in the art will recognize that the invention may be variously modified and practiced without departing from the spirit of the invention. The invention is limited only by the following claims.

Claims: CLAIMS What is claimed is: I . An apparatus for controlling the temperature of a microscopy sample comprising an external housing made of a highly heat insulating material, an internal housing made of a highly heat conducting material within said external housing for holding a sample to be subjected to microscopy, conduit means for the flow of a temperature controlling gas through said external and internal housings, and means for directing the flow of said temperature controlling gas around said sample. 2. The apparatus of claim 1 further comprising a thermocouple associated with said sample for measuring the temperature of said sample. 3. The apparatus of claim 2 further comprising a heater associated with said sample for heating said sample. 4. The apparatus of claim 3 further comprising heaters contained in said external and interior housings for heating said temperature controlling gas. 5. The apparatus of claim 1 further comprising cooling means for reducing the temperature of said temperature controlling gas. 6. The apparatus of claim 1 wherein said exterior housing is made of polyvinyl chloride (PVC). 7. The apparatus of claim 1 wherein said internal housing is made of aluminum. 8. The apparatus of claim 1 wherein the temperature of said sample can be maintained at -270° C to 200° C. 9. The apparatus of claim 2 wherein said sample is mounted on a sample holder made of highly thermally conductive material and said thermocouple is mounted between said sample and said sample holder. 10. The apparatus of claim 1 further comprising a computer for monitoring the temperature of the sample and controlling the flow of the temperature controlling gas to maintain the temperature at a constant level. I I . The apparatus of claim 4 further comprising a computer for monitoring the temperature of the sample and αmtrolling the flow of the temperature jntrolling gas and the output of the heaters to maintain the temperature at a constant level. 12. The apparatus of claim 1 wherein said exterior housing has a heat conductivity of 0.00001 to 0.25 W/m-K. 13. The apparatus of claim 1 wherein said exterior housing comprises a material selected from the group comprising polyvinychloride, cellulite, cork, particle board, and foamed polyurethane. 14. The apparatus of claim 1 wherein said interior housing has a heat conductivity of 20 to 2000 W/m-K. 15. The apparatus of claim 1 wherein said interior housing comprises a material selected from the group comprising aluminum, carbon steel , pyrloytic graphite, gold and brass. 16. The apparatus of claim 1 wherein said refrigeration means comprises liquefied or solidified N 2 , CO 2 , He, or Ar. 17. The apparatus of claim 1 wherein said sample holder includes means for partially enclosing said sample. 18. The apparatus of claim 1 which includes means for mamtai iing a greater than atmospheric pressure around said sample. 19. A method for microscopy at controlled temperatures comprising the steps of (a) providing a gas mtaπiing little or no moisture (b) modifying the temperature of said gas to that required for microscopy (c) providing means for flowing said gas at the temperature required over said sample, and (d) providing means for mamtaining a greater than atmospheric pressure over said sample using said gas.

Inventors: ARNOLD WILLIAM ALLEN, MARCELLI ANGELA MARIE, MARTENY PERRY, ARNOLD, WILLIAM, ALLEN, MARCELLI, ANGELA, MARIE, MARTENY, PERRY
Applicants: ARNOLD WILLIAM ALLEN, GOODYEAR TIRE & RUBBER, MARCELLI ANGELA MARIE, MARTENY PERRY, ARNOLD, WILLIAM, ALLEN, MARCELLI, ANGELA, MARIE, MARTENY, PERRY, THE GOODYEAR TIRE & RUBBER COMPANY
Application year: 1997
Main classification: G02B21
IPC codes: G01B7, G01N13, G02B21, G05D23