CA2247868C - Method and apparatus for performing chemical analysis using imaging by scanning thermal microscopy - Google Patents
Method and apparatus for performing chemical analysis using imaging by scanning thermal microscopy Download PDFInfo
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- CA2247868C CA2247868C CA002247868A CA2247868A CA2247868C CA 2247868 C CA2247868 C CA 2247868C CA 002247868 A CA002247868 A CA 002247868A CA 2247868 A CA2247868 A CA 2247868A CA 2247868 C CA2247868 C CA 2247868C
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/72—Investigating presence of flaws
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/20—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity
- G01N25/48—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity on solution, sorption, or a chemical reaction not involving combustion or catalytic oxidation
- G01N25/4806—Details not adapted to a particular type of sample
- G01N25/4826—Details not adapted to a particular type of sample concerning the heating or cooling arrangements
- G01N25/4833—Details not adapted to a particular type of sample concerning the heating or cooling arrangements specially adapted for temperature scanning
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/02—Devices for withdrawing samples
- G01N1/22—Devices for withdrawing samples in the gaseous state
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/02—Devices for withdrawing samples
- G01N1/04—Devices for withdrawing samples in the solid state, e.g. by cutting
- G01N2001/045—Laser ablation; Microwave vaporisation
Abstract
Sub-micron chemical analysis of the surface and sub-surface of a sample material is performed at, above or under atmospheric pressure, or on for a sample material submerged in a substance. A thermal and/or topographic image of the surface of the sample material is obtained. A location for study is selected using the image. The activation device is positioned over the selected location and surface and/or sub-surface products are ablated, desorbed or decomposed from the sample material to a chemical analyzer for analysis.
Description
MEIHOD AND APPARATUS pOR PERFORAENG CI3 EMICAL ANALYSIS USMG
IMAGING BY SCANNINGUER1VlAL MICROSCOPY
BACKGRQUND
Field of the Invention The present invention relates to analyzing the chemical nature of materials. More particularly, the present invention relates to sub-micron analysis of chemical properties of a sample material at a particular location of interest by decomposing, desorbing or ablating a smaIl portion of the sample nnaterial and transfercuig the small portion to a chemical analyzer.
Background of the Invention.
A conventional method for imaging the chemical nature of polymeric systems is amaging Secondary Ion Mass Spectroscopy (SIMS). In imaging S1MS, the surface of a sample is bombarded by a beam of ions (usually argon) that is rastered over the surface. The ions cause material on the surface of the sample to be ejected and ionized. These secondary ions are swept into a mass spectrometer for analysis.
SIMS is a very expensive technique that is not easily applicable to insulating samples such as polymers. This is because a charge that builds on the surface of insulaiting polymer samples deflects the incident ion beam Although this can be overcome in some cases by bathing the insulating polymer sample with electrons, a great deal of expertise is required to obtain satisfactory results. A further Iimitation of SIMS is that the sample must be analyzed under high vacuum. It would be desirable in manv cases to analyze _~_ samples at or above atmospheric pressure or submerged in a substance, for example water.
Another problem with SIMS is that is a continuously destructive imaging technique. As described above, the bombardment of the material by the ion beam causes the surface material to be ejected, thereby destroying the surface. It would be advantageous to have an imaging system which can image the topology and thermal properties of the material without destroying the surface. It is also desirable to be able to study the material after any damage is done as a result of desorption or pyrolysis.
Neither kind of study can be performed using conventional SI VlS techniques.
SCfNIl61tLR.Y OF THE INVh'N7I0N
The present invention allows chemical studies to be performed on the surface and sub-surface of a material- An image of a sample material is created using any conventional sample imaging fiecbuiaque. Using the image, an area of the sample on which to perform analysis is determined. An activation device i.s positioned at the selected area of interest. The activation device is activated to cause a portion of the sample to be emitted. The emitted portion of the sample is coIlected and analyzed to determine its chemicaI properties. The present invention can be used below, at or above atmospheric pressure or submerged in a substance, for example, water.
In a preferred embodiment of the present invention, the activation device is a highty miniaturized resistive probe as described below. In the preferred embodiment, an image of the sample is created using the probe. Using the resulting image, the probe is positioned at a desired location on the surface. Using a selected _7_ SUBSTITUTE SHEET (RULE 26) heating mode, the probe is heated to cause a portion of the sample to decompose or desorb into a gaseous form- The evolved gas is swept into a heated capillary tube, which is positioned close to the probe. The heated capillary tube is connected to a chemical analyzer, which analyzes the evolved gases. The area from which the material was decomposed or desorbed can further be rescanned to assess the volume ablated.
The process is then repeated for another selected area.
The process can be placed under computer control. Using a computer the selected area can be scanned- Further, either an operator or the computer can select areas for analysis.
Obkcls of the Irventiun A first object of the present invention is to provide sub-micron imaging and chemical analysis over a wide-variety of atmospheric pressures, including at or above atmospheric pressure, under a vacuu.m, and submerged under a substance, for example, water.
Another object of the present invention is to image a sample topology and thermal properties in a non-destructive martner, in addition to obtriining information using pyrolysis and desorption.
Another object of the present invention is to reduce the problems associated with imaging insulators such as polymers.
Another object of the present invention is to provide precise temperature control to increase the resolution of chemical species analysis.
SUBSTITUTE SHEET (RULE 26) Another object of the present invention is to reduce the cost of conventional sub-micron imaging.
-These and other objects of the present invention are described in greater detail in the detailed description of the invention, the appended drawings and the attached claims.
DESCRIMON OF TBE DItAV1TINGS
Figure 1 is a schematic diagram of a sub-micron chemical analysis system according to a preferred embodirnent of the present invention.
Figure 2 is a flow chart for analyzing a sample according to a preferred embodiment of the present invention.
DETAILED DESCREMON OF THE INVIEI~OhT
A preferred embodiment of the present invention is illustrated schematically in Figuxe 1. In the preferred embodirnenf, a computer 102 is operatively coupled to a scanning thermal microscope (STM) systea1104. STM 104 includes a probe 106, which is used to analyze local thermal properties at a location 107 of a sample 108, placed on a stage 110 of STM 104. According to the preferred embodiment, a heated capillary tube 112 is placed in close proximity to location 107 to collect evolved gases 114 that result from heating location 107 according to the present invention.
In the preferred embodiment, evolved gases 114 are analyzed for their chemical composition by a gas chromatograph 115 and/or a mass spectrometer 116.
SUBSTITUTE SHEET (RULE 26) STM 104 is preferably the Explorer scanning probe microscope (SPM) manufactured by the Topometrix Corporation, located in Santa Clara, California. Probe 106 is preferably a thermal resistive element that functions as both a heater and a sensor- Alternately, probe 106 is heated by a Iaser and the temperature sen.sed by a thermocouple. When operating as a heater a current proportional to the desired temperatiire is passed through probe 106. When operating as a sensor, the resistance of probe 106 varies in response to changes in temperature. A more detailed description of STM 104 and probe 106 is presented in tI . s. Patent No. 6,095,679 issued August 1, 2000 to TA Instruments.
Probe 106 can be used as a highly localized heat source as well as a detector. When heated by the passage of an electric current through the resistive portion of probe 106, its contact with the sample acts as a point like heat source.
Therefore, no other means of sample heating, such as a laser, is required The probe 106 is attached to a scanning mechanisin, and is controlled to obtain thermal image contrast that corresponds to variations in either thermal conductivity (using DC
i,ntaging) or thermal diffusivity (using AC imaging).
In the preferred embodiment, computer 102 controls the position and the temperature of probe 106, by executing a probe control process 118. Thus, the scanning mechanism in the preferred embodiment is computer 102 Computer 102 executes a probe position process 120. Probe position process 120 sends commands to STM
104 to control the position of probe 106. This position control can simply be a command to probe 106 to move to a particula.T locatdon, for example location 107. In addition, the position control can be complex so as to effectuate a scan or raster of a particular area of interest. Progranuning computer 102 to perform the functions described herein for probe position process 120 is well-know to those skiIIed in the art.
Computer 102 also executes a heating program process 122, which sends probe control cominands to probe 106 to cause it to heat according to a selected or calculated temperature program- The temperature program can be selected or chosen in a number of well-known ways. For example, the temperature program can be selected by choosing the exact parameters that describe the temperature program-Alternately, the temperature program can be entered by parameters that are then used to calculate the desired temperature program. Programming computer 102 to perform the functions described herein performed by heating control process 122 is well-known to those skilled in the arr.
Several methods for causing probe 106 to generate the desired temperature program can be used with the present invention. In the preferred embodiment, computer 102 sends probe control commands to STM 104 in a well-known manner over an interface 118. STM 104 receives the probe control cornmands and causes a current to flow through probe 106 to generate the requested temperature program According to the preferred embodiment of the present invention, a particular location, for example location 107, on sample 108 at which to perform a localized thermal analysis is selected by first obtaining a thermal and/or topographic image of the sainple- The thermal and/or topographic image can be obtained by any of SUBSTITUTE SHEET (RULE 26) the tecfuiiques disctosed in the Parent Application, or any other technique.
Using the therm-al and/or topographic image, the particular iocation is selected.
In the preferred embodiment, selection is performed using a pointing device 126. For example, pointing device 126 can be a conventional mouse device conttroiled by mouse control software 128 executing on computer 102.
Preferably, the thermal and/or topographic image is generated on a display device 130.
Referring to Figure 1, a thermal image 132 of sample 108 is illustrated on display device 130.
Display device 130 can be any of a number of well-known cathode ray tube (CRT) devices that can be coupled to computer 102. Once the area is selected, probe position process 120, executing on computer 102, converts the selected location to probe position control commands. Probe position process 120 sends the probe position control commands to STM 104 to cause probe 106 to be positioned at location 107. Probe 106 is preferably placed approxisnately a micron above the surface of sample 108 at location 107.
Once probe 106 is located at the position 107, probe position process 120 places probe 106 on the surface of sample 108. Preferably, this is accomplished by placing the probe in contact with the surface of sample 108 at location 107 and applying a known force to probe 106 to mainfain contact with the surface of sample 108.
Sample 108 is then heated by heating probe 106. Preferably, sample 108 is heated by applying one of the heating modes described below to probe 106. Alternately, probe 106 can be placed at a known distance above the surface of sample 108. Sample 108 would then be heated, preferably by applying one of the heating modes described below to probe 106.
SUBSTITUTE SHEET (RULE 26) When probe 106 is properly positioned at location 107, a heating mode is selected to cause probe 106 to heat sample 108 at location 107. The heating modes are selectable or can be pre-selected, as by choosing one mode to be a default mode. There are several heating modes available in the preferred embodiment:
a) Temperature Ram-p Mode: Probe 106 is placed on the area of interest and its temperature ramped. Adsorbed material is driven off at low temperatures. Then decomposition products are generated at higher temperatures.
b) Heat PuLse rn.ode: Probe 106 is heated to some temperature above the normal decomposition or desorption temperature for sample 108. Probe 106 is then briefly placed on the surface of sample 108. Desorption and decomposition products are generated. The amount of time that probe 106 remains in contact with the surface of sample 108 can be used to regulate the size of the region over which decomposition jdesorption occurs. The heat pulse mode is afternately referred to as a tapping mode.
That is the hot probe 106 is tapped on the surface of sample 108 to heat it.
c) Transfer Mode: Probe 106 is deaned by heating to a high temperature.
Then probe 106 is allowed to cool. Probe 106 is then placed on the surface of sample 108 and raised. Material from the surface of sample 108 is adsorbed onto the probe. The adsorbed material can then be desorbed by flash heating. The process can be repeated as required to obtain sufficient material for analysis. Because repetition may be required, this process is SUBSTITUTE SHEET (RULE 26) preferably automated. That is computer 102 controls the process of cleaning, cooling, lowering, raising and flash heating of probe 106.
An alternative technique for using the transfer mode is to coat the tip of probe 106 with a material that assists the adhesion of the surface material to probe 106. For example, probe 106 can be dipped in the requisite fluid. Any adhesion promoting or reactive fluid can be used. A
reactive fluid chemically reacts with the surface of sample 108 to promote adhesion products. To assist drying, probe 106 is preferably warmed.
Probe 106 is then placed on the surface of sample 108. Surface znaterial can adhere to the coating. Alternately, probe 106 can be wanned to assist the adhesion process. Probe 106 can then be cooled and raised. Then the adhesion products can be desorbed through flash heating. I3uring chemical analysis, the decomposition products of the coating would be known, and therefore can be eliaunated from the analysis. Alternately, the raised probe 106 can be moved to a different location where it is dipped into a transfer medium. The transfer medium dissolves the sample into a small dot of the new ma.terial. This product is then analyzed by any analytical technique, including conventional I-IPLC and electrophoresis. Using a coating that is not water-soluble, the transfer mode can be applied to a sample that is under water- Materials = submerged in substance other than water can be studied by using a solvent-insoluble coating, or any coating not soluble by the substance in SUBSTlTUTE SHEET (RULE 26) which the material is submerged. The particular coating that is used in the transfer mode can contain reactive species to obtain specific products.
d) Ballistic Mode: Probe 106 is heated to a commanded temperature very =
rapidly. The heating is uncontxoIled, mearwlg that the temperature of the probe reaches the commanded temperature as rapidly as it can.
e) Scanning Mode: An area of the surface of sample 108 is selected for analysis, rather than a single point. Probe 106 is heated. The heated probe 106 is then rastered over the selected area of the surface of sample 108.
Material that is ablated from sample 108 is trapped and armlyzed. The temperature of probe 106 and the speed of the raster are both controllable using computer 102 and probe control process 118. The temperature of probe 106 and the speed of the raster deternmine the depth of the material that is ablated. For example, an area of 10 by 10 microns can be scanned with ablation occurring to 100 nanometezs. This results in 10 cubic microns of ablated material. Preferably, the scann;ng mode is automatically controlled by computer 102. The scanmng mode can aLso be combined with any heating mode (a) -(d) to heat probe 106.
The present invention is not Iimited to the above heating modes. Other modes of heating to obtain the benefits of the present invention would be known to those skilled in the art- Further, in the preferred embodiment, it is the tip of probe 106 that is heated.
In each of the heating modes, material is decomposed, desorbed or ablated for subsequent chemical analysis. Two methods of chemical analysis are used SUBSTITUTE SHEET (RULE 26) in the preferred embodiment: mass spectroscopy and gas chromatography. Both methods are well-known to those skiited in the art. There is a problem, however, associated with transferring the nztaterial to the analyzer, whether it is mass spectrometer 116 andJor gas chroinatograph 115. In the preferred embodiment, this problem is solved by using a heated capiIlary 112. The heated capillary 112 is positioned in clQse proximity to probe 116, so that desorbed, decomposed or ablated species are "sucked" into capillary tube as a result of a low pressure maintained on the other side. For example, the low pressure can be generated by connecting the other end of the capiTlary to the vacuum ctuamber 134 of the mass spectrometer 116. Once the evolved material 114 has entered mass spectrometer 116, its chemical properties are analyzed in a conventional n>anõer. In this manner, the present invention allows sub-miicron study of the chemical properties of materials. Using the scanning method of heating described above, the present irnvention allows sub-micron chemical imaging of a sample.
The heating modes described above provide a high degree of control of the surface selectivity. The transfer mode provides information very near the surface, including the top monolayer in many cases. The temperature scanning and heat pulse modes can sample tens, and even hundreds, of microns below the surface. If an isolated partude is the object of interest, whether lying on, or buried below within a matrix with one side exposed, then the entire particle can be volatilized to ensure a = good analysis with high signal to noise ratio.
SUBSTITUTE SHEET (RULE 26) As described above, the scanning mode can be combined with any of the other modes as probe I06 is rastered along the selected analysis area in two dimensions.
For exainple, by combining the heat pulse mode and the scanning mode, probe 106 is effectively tapped on the surface of material 108 as it is rastered in two dimensions. The resulting series of gases can be analyzed by mass spectrometer 116, thus building up a cllemical map of the surface of sample 108. That is, acquisition of gases is coordinated with the position in the image that is being generated.
To provide additional information a gas chromatograph 115 is added to the sub-micron chemical analysis system of the present invention. In the preferred embodiment, gas chromatograph 115 is interposed between heated capiltary 112 and mass spectrometer 116, as illustrated schematically in Figure 1. In this manner, the evolved material can be chemically anaiyzed by gas chromatography using gas chroznatograph 115.
Using computer 102, the foregoing analyses can be auroaiated.
Preferably, areas of interest for analysis are pre-selected. This can be done by pre-selecting multiple areas on using a thermal isnage, such as thermal image 132.
Alternately, computer 102 can select the areas of interest, for example, by using a random number generator. In addition, the heating mode is selected. This can be done by selecting the heating prograzn. AlternateIy, computer 102 can select the heating mode. For example, heating control process 122, executing on computer 102, can select a default heating mode. After the selection is made, probe position process 120 causes the probe to automatically go to the first selected area. Heating mode process 122 sends SUBSTITUTE SHEET (RULE 26) appropriate probe control commands to STM 104 to cause probe 106 to heat the selected area according to the selected heating mode. The evolved gases are transferred into the analyzer through capiUary 112, where their chemical nature is analyzed. After the analysis, probe position process 120 automatically causes probe 106 to move to the second pre-selected area, and the process repeats. This is done for all selected areas designated in the autornatic analysis. In the autornatic mode of operation different heating programs can be selected for different areas of the sample 108. For example, the first selected area can be heated according to the temperature ramp mde, while a second azea can be analyzed using a scanning mode.
In some cases, it is desirable to trap the evolved gases 114 into a cryo-trap or an adsorbate (not shown). Subsequently, the material is flash desorbed and forwarded to the gas chromatograph and/or mass spectrometer for anal.ysis.
Capillary tube 112 can be placed close to the sample by "eyeballing" the appropriate IocatiorL However, other techniques can place capiUary tube 112 more accurately. In the preferred embodiment, a hunt-seek type proximity determination method is used to locate heated capiUary tube 112 next to the tip of probe 106. One hunt-seek metiiod, for example, is to use an automated micro-positioner, such as is conventionaIly used in optical microscopy. In this method, probe 106 and heated capiUary tube 112 are made to form two halves of a capacitor. Heated capillary tube 112 is initially located by eye. Then a capacitance signal generated by the two halves is = used to bring capillary tube 112 closer to probe 106, but not to close.
SUBSTITUTE SHEET (RULE 26) To prevent, capillary tube 106 from being moved too close to probe 106, a threshold for the capacitance signal can be used. If the capacitance signal exceeds the threshold, capillary tube 112 is too close to probe 106. A second threshold can be used =
to determine whether capillary tube 112 is close enough to probe 106. That is, if the capacitance signal is below the second threshold, then capillary tube 112 must be moved closer to probe 106. Thus, in effect a range is determined for the capacitance sigrnal. When the capacitance signal faIls within that range, capillary tube 112 is properly positioned relative to probe 106.
An atterriative hunt-seek method for properly positioning capillary tube 112 relative to probe 106 is to embed a temperature sensor 136 in capillary tube 112. As before a threshold range is determined. In this case the thresholds correspond to temperatures. If the temperature sensed by temperature sensor 136 is too great, capillary tube 112 is too close to probe 106. If the te.mperature sensed by temperatvre sensor 136 is too small, capillary tube 112 is too far from probe 106.
Another alterative for properly positioning ca.pillary tube 112 relative to probe 1Q6 is to caiibrate the micro-manipulator of S'lm 104 and probe 106 in the x, y and z planes. By so doing, probe 106 can be precisely positioned without the need for a feedback loop based on some form of prozimity determination By calibrating the micro-inanipulator and probe 106 in this m.anner, probe 106 can be precisely positioned.
As a result, capillary tube 112 can be precisely positioned relative to probe 106's known position. =
SUBSTITUTE SHEET (RULE 26) A preferred method for performing a process according to the present invention using the apparatus discussed above and illustrated in Figure 1 is shown by a flow chart in Figure 2 In step 202 an image of a sample is obtained_ As described above, this image can be obtained using any imaging technique, including thermal and photothermal imaging techniques. In step 204 an area of the image is selected for analysis. This selection can be by a user or performed automatically, for example, by computer 102. In step 206,probe 106 is positioned over the selected area. In the preferred esnbodim.erct, this is done by probe position process 120, and can use the proximity determiriation hunt-seek or calibration methods described above. A
heating mode is then selected in step 208- Once again, the selection can be by a user or autoniatic, for example, by computer 102 using a default. In step 210 heated capillary tube 112 is positioned in proximity to probe 106 to collect nnaterial that evolves from sample 108 upon heating. The heating made is initiated in step 212. In the preferred embodiment, the heating mode is controlled by heating control process 172 executing on computer 102. The material that evolves is collected in step 214. The collected material is ar.ialyyzed in a chemical analyzer in step 216. In the preferred embodiment, the chemical analysis is performed by gas chromatograph 115 andJor mass spectrometer 116. In step 218, any desired post-processing is performed. For example, the sample 108 from which material evolved can be analyzed to assess the volume ablated, or to iniage the resulting crater. Steps 202-218 can be repeated at another location if desired.
SUBSTITUTE SHEET (RULE 26) The foregoing disclosure of examples and embodiments of the present inve.ntion has been presented for purposes of iIlustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disciosed_ Many variations and modifications of the embodiments described herein wi1l be obvious to one of ordinary skill in the art in light of the above disclosure. The scope of the invention is to be defined only by the daims appended hereto, and by their equivalents.
_16_ SUBSTiTUTE SHEET (RULE 26)
IMAGING BY SCANNINGUER1VlAL MICROSCOPY
BACKGRQUND
Field of the Invention The present invention relates to analyzing the chemical nature of materials. More particularly, the present invention relates to sub-micron analysis of chemical properties of a sample material at a particular location of interest by decomposing, desorbing or ablating a smaIl portion of the sample nnaterial and transfercuig the small portion to a chemical analyzer.
Background of the Invention.
A conventional method for imaging the chemical nature of polymeric systems is amaging Secondary Ion Mass Spectroscopy (SIMS). In imaging S1MS, the surface of a sample is bombarded by a beam of ions (usually argon) that is rastered over the surface. The ions cause material on the surface of the sample to be ejected and ionized. These secondary ions are swept into a mass spectrometer for analysis.
SIMS is a very expensive technique that is not easily applicable to insulating samples such as polymers. This is because a charge that builds on the surface of insulaiting polymer samples deflects the incident ion beam Although this can be overcome in some cases by bathing the insulating polymer sample with electrons, a great deal of expertise is required to obtain satisfactory results. A further Iimitation of SIMS is that the sample must be analyzed under high vacuum. It would be desirable in manv cases to analyze _~_ samples at or above atmospheric pressure or submerged in a substance, for example water.
Another problem with SIMS is that is a continuously destructive imaging technique. As described above, the bombardment of the material by the ion beam causes the surface material to be ejected, thereby destroying the surface. It would be advantageous to have an imaging system which can image the topology and thermal properties of the material without destroying the surface. It is also desirable to be able to study the material after any damage is done as a result of desorption or pyrolysis.
Neither kind of study can be performed using conventional SI VlS techniques.
SCfNIl61tLR.Y OF THE INVh'N7I0N
The present invention allows chemical studies to be performed on the surface and sub-surface of a material- An image of a sample material is created using any conventional sample imaging fiecbuiaque. Using the image, an area of the sample on which to perform analysis is determined. An activation device i.s positioned at the selected area of interest. The activation device is activated to cause a portion of the sample to be emitted. The emitted portion of the sample is coIlected and analyzed to determine its chemicaI properties. The present invention can be used below, at or above atmospheric pressure or submerged in a substance, for example, water.
In a preferred embodiment of the present invention, the activation device is a highty miniaturized resistive probe as described below. In the preferred embodiment, an image of the sample is created using the probe. Using the resulting image, the probe is positioned at a desired location on the surface. Using a selected _7_ SUBSTITUTE SHEET (RULE 26) heating mode, the probe is heated to cause a portion of the sample to decompose or desorb into a gaseous form- The evolved gas is swept into a heated capillary tube, which is positioned close to the probe. The heated capillary tube is connected to a chemical analyzer, which analyzes the evolved gases. The area from which the material was decomposed or desorbed can further be rescanned to assess the volume ablated.
The process is then repeated for another selected area.
The process can be placed under computer control. Using a computer the selected area can be scanned- Further, either an operator or the computer can select areas for analysis.
Obkcls of the Irventiun A first object of the present invention is to provide sub-micron imaging and chemical analysis over a wide-variety of atmospheric pressures, including at or above atmospheric pressure, under a vacuu.m, and submerged under a substance, for example, water.
Another object of the present invention is to image a sample topology and thermal properties in a non-destructive martner, in addition to obtriining information using pyrolysis and desorption.
Another object of the present invention is to reduce the problems associated with imaging insulators such as polymers.
Another object of the present invention is to provide precise temperature control to increase the resolution of chemical species analysis.
SUBSTITUTE SHEET (RULE 26) Another object of the present invention is to reduce the cost of conventional sub-micron imaging.
-These and other objects of the present invention are described in greater detail in the detailed description of the invention, the appended drawings and the attached claims.
DESCRIMON OF TBE DItAV1TINGS
Figure 1 is a schematic diagram of a sub-micron chemical analysis system according to a preferred embodirnent of the present invention.
Figure 2 is a flow chart for analyzing a sample according to a preferred embodiment of the present invention.
DETAILED DESCREMON OF THE INVIEI~OhT
A preferred embodiment of the present invention is illustrated schematically in Figuxe 1. In the preferred embodirnenf, a computer 102 is operatively coupled to a scanning thermal microscope (STM) systea1104. STM 104 includes a probe 106, which is used to analyze local thermal properties at a location 107 of a sample 108, placed on a stage 110 of STM 104. According to the preferred embodiment, a heated capillary tube 112 is placed in close proximity to location 107 to collect evolved gases 114 that result from heating location 107 according to the present invention.
In the preferred embodiment, evolved gases 114 are analyzed for their chemical composition by a gas chromatograph 115 and/or a mass spectrometer 116.
SUBSTITUTE SHEET (RULE 26) STM 104 is preferably the Explorer scanning probe microscope (SPM) manufactured by the Topometrix Corporation, located in Santa Clara, California. Probe 106 is preferably a thermal resistive element that functions as both a heater and a sensor- Alternately, probe 106 is heated by a Iaser and the temperature sen.sed by a thermocouple. When operating as a heater a current proportional to the desired temperatiire is passed through probe 106. When operating as a sensor, the resistance of probe 106 varies in response to changes in temperature. A more detailed description of STM 104 and probe 106 is presented in tI . s. Patent No. 6,095,679 issued August 1, 2000 to TA Instruments.
Probe 106 can be used as a highly localized heat source as well as a detector. When heated by the passage of an electric current through the resistive portion of probe 106, its contact with the sample acts as a point like heat source.
Therefore, no other means of sample heating, such as a laser, is required The probe 106 is attached to a scanning mechanisin, and is controlled to obtain thermal image contrast that corresponds to variations in either thermal conductivity (using DC
i,ntaging) or thermal diffusivity (using AC imaging).
In the preferred embodiment, computer 102 controls the position and the temperature of probe 106, by executing a probe control process 118. Thus, the scanning mechanism in the preferred embodiment is computer 102 Computer 102 executes a probe position process 120. Probe position process 120 sends commands to STM
104 to control the position of probe 106. This position control can simply be a command to probe 106 to move to a particula.T locatdon, for example location 107. In addition, the position control can be complex so as to effectuate a scan or raster of a particular area of interest. Progranuning computer 102 to perform the functions described herein for probe position process 120 is well-know to those skiIIed in the art.
Computer 102 also executes a heating program process 122, which sends probe control cominands to probe 106 to cause it to heat according to a selected or calculated temperature program- The temperature program can be selected or chosen in a number of well-known ways. For example, the temperature program can be selected by choosing the exact parameters that describe the temperature program-Alternately, the temperature program can be entered by parameters that are then used to calculate the desired temperature program. Programming computer 102 to perform the functions described herein performed by heating control process 122 is well-known to those skilled in the arr.
Several methods for causing probe 106 to generate the desired temperature program can be used with the present invention. In the preferred embodiment, computer 102 sends probe control commands to STM 104 in a well-known manner over an interface 118. STM 104 receives the probe control cornmands and causes a current to flow through probe 106 to generate the requested temperature program According to the preferred embodiment of the present invention, a particular location, for example location 107, on sample 108 at which to perform a localized thermal analysis is selected by first obtaining a thermal and/or topographic image of the sainple- The thermal and/or topographic image can be obtained by any of SUBSTITUTE SHEET (RULE 26) the tecfuiiques disctosed in the Parent Application, or any other technique.
Using the therm-al and/or topographic image, the particular iocation is selected.
In the preferred embodiment, selection is performed using a pointing device 126. For example, pointing device 126 can be a conventional mouse device conttroiled by mouse control software 128 executing on computer 102.
Preferably, the thermal and/or topographic image is generated on a display device 130.
Referring to Figure 1, a thermal image 132 of sample 108 is illustrated on display device 130.
Display device 130 can be any of a number of well-known cathode ray tube (CRT) devices that can be coupled to computer 102. Once the area is selected, probe position process 120, executing on computer 102, converts the selected location to probe position control commands. Probe position process 120 sends the probe position control commands to STM 104 to cause probe 106 to be positioned at location 107. Probe 106 is preferably placed approxisnately a micron above the surface of sample 108 at location 107.
Once probe 106 is located at the position 107, probe position process 120 places probe 106 on the surface of sample 108. Preferably, this is accomplished by placing the probe in contact with the surface of sample 108 at location 107 and applying a known force to probe 106 to mainfain contact with the surface of sample 108.
Sample 108 is then heated by heating probe 106. Preferably, sample 108 is heated by applying one of the heating modes described below to probe 106. Alternately, probe 106 can be placed at a known distance above the surface of sample 108. Sample 108 would then be heated, preferably by applying one of the heating modes described below to probe 106.
SUBSTITUTE SHEET (RULE 26) When probe 106 is properly positioned at location 107, a heating mode is selected to cause probe 106 to heat sample 108 at location 107. The heating modes are selectable or can be pre-selected, as by choosing one mode to be a default mode. There are several heating modes available in the preferred embodiment:
a) Temperature Ram-p Mode: Probe 106 is placed on the area of interest and its temperature ramped. Adsorbed material is driven off at low temperatures. Then decomposition products are generated at higher temperatures.
b) Heat PuLse rn.ode: Probe 106 is heated to some temperature above the normal decomposition or desorption temperature for sample 108. Probe 106 is then briefly placed on the surface of sample 108. Desorption and decomposition products are generated. The amount of time that probe 106 remains in contact with the surface of sample 108 can be used to regulate the size of the region over which decomposition jdesorption occurs. The heat pulse mode is afternately referred to as a tapping mode.
That is the hot probe 106 is tapped on the surface of sample 108 to heat it.
c) Transfer Mode: Probe 106 is deaned by heating to a high temperature.
Then probe 106 is allowed to cool. Probe 106 is then placed on the surface of sample 108 and raised. Material from the surface of sample 108 is adsorbed onto the probe. The adsorbed material can then be desorbed by flash heating. The process can be repeated as required to obtain sufficient material for analysis. Because repetition may be required, this process is SUBSTITUTE SHEET (RULE 26) preferably automated. That is computer 102 controls the process of cleaning, cooling, lowering, raising and flash heating of probe 106.
An alternative technique for using the transfer mode is to coat the tip of probe 106 with a material that assists the adhesion of the surface material to probe 106. For example, probe 106 can be dipped in the requisite fluid. Any adhesion promoting or reactive fluid can be used. A
reactive fluid chemically reacts with the surface of sample 108 to promote adhesion products. To assist drying, probe 106 is preferably warmed.
Probe 106 is then placed on the surface of sample 108. Surface znaterial can adhere to the coating. Alternately, probe 106 can be wanned to assist the adhesion process. Probe 106 can then be cooled and raised. Then the adhesion products can be desorbed through flash heating. I3uring chemical analysis, the decomposition products of the coating would be known, and therefore can be eliaunated from the analysis. Alternately, the raised probe 106 can be moved to a different location where it is dipped into a transfer medium. The transfer medium dissolves the sample into a small dot of the new ma.terial. This product is then analyzed by any analytical technique, including conventional I-IPLC and electrophoresis. Using a coating that is not water-soluble, the transfer mode can be applied to a sample that is under water- Materials = submerged in substance other than water can be studied by using a solvent-insoluble coating, or any coating not soluble by the substance in SUBSTlTUTE SHEET (RULE 26) which the material is submerged. The particular coating that is used in the transfer mode can contain reactive species to obtain specific products.
d) Ballistic Mode: Probe 106 is heated to a commanded temperature very =
rapidly. The heating is uncontxoIled, mearwlg that the temperature of the probe reaches the commanded temperature as rapidly as it can.
e) Scanning Mode: An area of the surface of sample 108 is selected for analysis, rather than a single point. Probe 106 is heated. The heated probe 106 is then rastered over the selected area of the surface of sample 108.
Material that is ablated from sample 108 is trapped and armlyzed. The temperature of probe 106 and the speed of the raster are both controllable using computer 102 and probe control process 118. The temperature of probe 106 and the speed of the raster deternmine the depth of the material that is ablated. For example, an area of 10 by 10 microns can be scanned with ablation occurring to 100 nanometezs. This results in 10 cubic microns of ablated material. Preferably, the scann;ng mode is automatically controlled by computer 102. The scanmng mode can aLso be combined with any heating mode (a) -(d) to heat probe 106.
The present invention is not Iimited to the above heating modes. Other modes of heating to obtain the benefits of the present invention would be known to those skilled in the art- Further, in the preferred embodiment, it is the tip of probe 106 that is heated.
In each of the heating modes, material is decomposed, desorbed or ablated for subsequent chemical analysis. Two methods of chemical analysis are used SUBSTITUTE SHEET (RULE 26) in the preferred embodiment: mass spectroscopy and gas chromatography. Both methods are well-known to those skiited in the art. There is a problem, however, associated with transferring the nztaterial to the analyzer, whether it is mass spectrometer 116 andJor gas chroinatograph 115. In the preferred embodiment, this problem is solved by using a heated capiIlary 112. The heated capillary 112 is positioned in clQse proximity to probe 116, so that desorbed, decomposed or ablated species are "sucked" into capillary tube as a result of a low pressure maintained on the other side. For example, the low pressure can be generated by connecting the other end of the capiTlary to the vacuum ctuamber 134 of the mass spectrometer 116. Once the evolved material 114 has entered mass spectrometer 116, its chemical properties are analyzed in a conventional n>anõer. In this manner, the present invention allows sub-miicron study of the chemical properties of materials. Using the scanning method of heating described above, the present irnvention allows sub-micron chemical imaging of a sample.
The heating modes described above provide a high degree of control of the surface selectivity. The transfer mode provides information very near the surface, including the top monolayer in many cases. The temperature scanning and heat pulse modes can sample tens, and even hundreds, of microns below the surface. If an isolated partude is the object of interest, whether lying on, or buried below within a matrix with one side exposed, then the entire particle can be volatilized to ensure a = good analysis with high signal to noise ratio.
SUBSTITUTE SHEET (RULE 26) As described above, the scanning mode can be combined with any of the other modes as probe I06 is rastered along the selected analysis area in two dimensions.
For exainple, by combining the heat pulse mode and the scanning mode, probe 106 is effectively tapped on the surface of material 108 as it is rastered in two dimensions. The resulting series of gases can be analyzed by mass spectrometer 116, thus building up a cllemical map of the surface of sample 108. That is, acquisition of gases is coordinated with the position in the image that is being generated.
To provide additional information a gas chromatograph 115 is added to the sub-micron chemical analysis system of the present invention. In the preferred embodiment, gas chromatograph 115 is interposed between heated capiltary 112 and mass spectrometer 116, as illustrated schematically in Figure 1. In this manner, the evolved material can be chemically anaiyzed by gas chromatography using gas chroznatograph 115.
Using computer 102, the foregoing analyses can be auroaiated.
Preferably, areas of interest for analysis are pre-selected. This can be done by pre-selecting multiple areas on using a thermal isnage, such as thermal image 132.
Alternately, computer 102 can select the areas of interest, for example, by using a random number generator. In addition, the heating mode is selected. This can be done by selecting the heating prograzn. AlternateIy, computer 102 can select the heating mode. For example, heating control process 122, executing on computer 102, can select a default heating mode. After the selection is made, probe position process 120 causes the probe to automatically go to the first selected area. Heating mode process 122 sends SUBSTITUTE SHEET (RULE 26) appropriate probe control commands to STM 104 to cause probe 106 to heat the selected area according to the selected heating mode. The evolved gases are transferred into the analyzer through capiUary 112, where their chemical nature is analyzed. After the analysis, probe position process 120 automatically causes probe 106 to move to the second pre-selected area, and the process repeats. This is done for all selected areas designated in the autornatic analysis. In the autornatic mode of operation different heating programs can be selected for different areas of the sample 108. For example, the first selected area can be heated according to the temperature ramp mde, while a second azea can be analyzed using a scanning mode.
In some cases, it is desirable to trap the evolved gases 114 into a cryo-trap or an adsorbate (not shown). Subsequently, the material is flash desorbed and forwarded to the gas chromatograph and/or mass spectrometer for anal.ysis.
Capillary tube 112 can be placed close to the sample by "eyeballing" the appropriate IocatiorL However, other techniques can place capiUary tube 112 more accurately. In the preferred embodiment, a hunt-seek type proximity determination method is used to locate heated capiUary tube 112 next to the tip of probe 106. One hunt-seek metiiod, for example, is to use an automated micro-positioner, such as is conventionaIly used in optical microscopy. In this method, probe 106 and heated capiUary tube 112 are made to form two halves of a capacitor. Heated capillary tube 112 is initially located by eye. Then a capacitance signal generated by the two halves is = used to bring capillary tube 112 closer to probe 106, but not to close.
SUBSTITUTE SHEET (RULE 26) To prevent, capillary tube 106 from being moved too close to probe 106, a threshold for the capacitance signal can be used. If the capacitance signal exceeds the threshold, capillary tube 112 is too close to probe 106. A second threshold can be used =
to determine whether capillary tube 112 is close enough to probe 106. That is, if the capacitance signal is below the second threshold, then capillary tube 112 must be moved closer to probe 106. Thus, in effect a range is determined for the capacitance sigrnal. When the capacitance signal faIls within that range, capillary tube 112 is properly positioned relative to probe 106.
An atterriative hunt-seek method for properly positioning capillary tube 112 relative to probe 106 is to embed a temperature sensor 136 in capillary tube 112. As before a threshold range is determined. In this case the thresholds correspond to temperatures. If the temperature sensed by temperature sensor 136 is too great, capillary tube 112 is too close to probe 106. If the te.mperature sensed by temperatvre sensor 136 is too small, capillary tube 112 is too far from probe 106.
Another alterative for properly positioning ca.pillary tube 112 relative to probe 1Q6 is to caiibrate the micro-manipulator of S'lm 104 and probe 106 in the x, y and z planes. By so doing, probe 106 can be precisely positioned without the need for a feedback loop based on some form of prozimity determination By calibrating the micro-inanipulator and probe 106 in this m.anner, probe 106 can be precisely positioned.
As a result, capillary tube 112 can be precisely positioned relative to probe 106's known position. =
SUBSTITUTE SHEET (RULE 26) A preferred method for performing a process according to the present invention using the apparatus discussed above and illustrated in Figure 1 is shown by a flow chart in Figure 2 In step 202 an image of a sample is obtained_ As described above, this image can be obtained using any imaging technique, including thermal and photothermal imaging techniques. In step 204 an area of the image is selected for analysis. This selection can be by a user or performed automatically, for example, by computer 102. In step 206,probe 106 is positioned over the selected area. In the preferred esnbodim.erct, this is done by probe position process 120, and can use the proximity determiriation hunt-seek or calibration methods described above. A
heating mode is then selected in step 208- Once again, the selection can be by a user or autoniatic, for example, by computer 102 using a default. In step 210 heated capillary tube 112 is positioned in proximity to probe 106 to collect nnaterial that evolves from sample 108 upon heating. The heating made is initiated in step 212. In the preferred embodiment, the heating mode is controlled by heating control process 172 executing on computer 102. The material that evolves is collected in step 214. The collected material is ar.ialyyzed in a chemical analyzer in step 216. In the preferred embodiment, the chemical analysis is performed by gas chromatograph 115 andJor mass spectrometer 116. In step 218, any desired post-processing is performed. For example, the sample 108 from which material evolved can be analyzed to assess the volume ablated, or to iniage the resulting crater. Steps 202-218 can be repeated at another location if desired.
SUBSTITUTE SHEET (RULE 26) The foregoing disclosure of examples and embodiments of the present inve.ntion has been presented for purposes of iIlustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disciosed_ Many variations and modifications of the embodiments described herein wi1l be obvious to one of ordinary skill in the art in light of the above disclosure. The scope of the invention is to be defined only by the daims appended hereto, and by their equivalents.
_16_ SUBSTiTUTE SHEET (RULE 26)
Claims (11)
1. A system for sub-micron chemical imaging of a sample, comprising:
a computer;
a scanning thermal microscope coupled to said computer, having a sample stage having a sample disposed thereon;
a probe to heat said sample;
a probe control process executing on said computer to cause said probe to heat an area of said sample according to a heating mode;
a chemical analyzer; and a capillary tube positioned in proximity to a tip of said probe to collect gases that evolve as a result of said probe heating said sample.
a computer;
a scanning thermal microscope coupled to said computer, having a sample stage having a sample disposed thereon;
a probe to heat said sample;
a probe control process executing on said computer to cause said probe to heat an area of said sample according to a heating mode;
a chemical analyzer; and a capillary tube positioned in proximity to a tip of said probe to collect gases that evolve as a result of said probe heating said sample.
2. The system of claim 1, wherein said probe control process comprises:
a probe position process to position said probe in proximity to said capillary tube; and a heating control process to control heating of said probe tip.
a probe position process to position said probe in proximity to said capillary tube; and a heating control process to control heating of said probe tip.
3. The system of claim 2, wherein said probe position process comprises a first threshold for determining when said probe is too far from said capillary tube; and a second threshold for determining when said probe is too dose to said capillary tube.
4. The system of claim 3, wherein said first and second thresholds comprise capacitance values.
5. The system of claim 3, wherein said first and second thresholds comprise temperature values.
6. The system of claim 2, wherein said probe position process comprises a calibration process for calibrating said probe in the x, y and z planes so that said probe can be placed at an accurately determined location.
7. The system of claim 1, further comprising a gas chromatograph disposed between said capillary tube and a mass spectrometer.
8. The system of claim 1, wherein said capillary tube is heated.
9. The system of claim 1, wherein said probe is a thermal resistive probe.
10. A method for chemically imaging a sample, comprising the steps of:
(a) obtaining an image of a sample;
(b) selecting an area of said image for analysis;
(c) positioning a probe over said area selected in step (b);
(d) selecting a heating mode;
(e) positioning a capillary tube in proximity to a tip of said probe;
(f) initiating said heating mode;
(g) collecting material that evolves from said sample in response to said heating mode initiated in step (f); and (h) analyzing the chemical nature of said material that evolved in step (g).
(a) obtaining an image of a sample;
(b) selecting an area of said image for analysis;
(c) positioning a probe over said area selected in step (b);
(d) selecting a heating mode;
(e) positioning a capillary tube in proximity to a tip of said probe;
(f) initiating said heating mode;
(g) collecting material that evolves from said sample in response to said heating mode initiated in step (f); and (h) analyzing the chemical nature of said material that evolved in step (g).
11. The method of claim 10, further comprising the step of (i) performing post processing on said area selected in step (b).
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US3395996P | 1996-12-31 | 1996-12-31 | |
| US60/033,959 | 1996-12-31 | ||
| PCT/GB1997/003456 WO1998029737A1 (en) | 1996-12-31 | 1997-12-30 | Method and apparatus for performing chemical analysis using imaging by scanning thermal microscopy |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2247868A1 CA2247868A1 (en) | 1998-07-09 |
| CA2247868C true CA2247868C (en) | 2007-05-22 |
Family
ID=21873461
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002247868A Expired - Lifetime CA2247868C (en) | 1996-12-31 | 1997-12-30 | Method and apparatus for performing chemical analysis using imaging by scanning thermal microscopy |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0895591B1 (en) |
| JP (1) | JP4436935B2 (en) |
| CA (1) | CA2247868C (en) |
| DE (1) | DE69734153T2 (en) |
| WO (1) | WO1998029737A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111024750A (en) * | 2019-12-04 | 2020-04-17 | 南京航空航天大学 | Device and method for testing ablation of ceramic matrix composite material with controllable gas atmosphere |
| JP7312694B2 (en) * | 2019-12-26 | 2023-07-21 | 日本電子株式会社 | Analysis system and analysis method |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB8322709D0 (en) * | 1983-08-24 | 1983-09-28 | British Steel Corp | Analysis of materials |
| US5037611A (en) * | 1988-11-29 | 1991-08-06 | Icr Research Associates, Inc. | Sample handling technique |
| US5248199A (en) * | 1992-03-02 | 1993-09-28 | Ta Instruments, Inc. | Method and apparatus for spatially resolved modulated differential analysis |
| US5441343A (en) * | 1993-09-27 | 1995-08-15 | Topometrix Corporation | Thermal sensing scanning probe microscope and method for measurement of thermal parameters of a specimen |
| US6095679A (en) * | 1996-04-22 | 2000-08-01 | Ta Instruments | Method and apparatus for performing localized thermal analysis and sub-surface imaging by scanning thermal microscopy |
-
1997
- 1997-12-30 DE DE69734153T patent/DE69734153T2/en not_active Expired - Lifetime
- 1997-12-30 CA CA002247868A patent/CA2247868C/en not_active Expired - Lifetime
- 1997-12-30 EP EP97950255A patent/EP0895591B1/en not_active Expired - Lifetime
- 1997-12-30 WO PCT/GB1997/003456 patent/WO1998029737A1/en active IP Right Grant
- 1997-12-30 JP JP52973598A patent/JP4436935B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0895591B1 (en) | 2005-09-07 |
| DE69734153T2 (en) | 2006-06-22 |
| JP4436935B2 (en) | 2010-03-24 |
| JP2001517302A (en) | 2001-10-02 |
| CA2247868A1 (en) | 1998-07-09 |
| EP0895591A1 (en) | 1999-02-10 |
| WO1998029737A1 (en) | 1998-07-09 |
| DE69734153D1 (en) | 2005-10-13 |
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