Title of Invention

A MINIATURE HEATED STAGE FOR SURFACE FORCE APPARATUS

Abstract A miniature heated stage for surface force apparatus". This invention relates to a miniature heated stage for surface force apparatus comprising a low thermal conducting glass plate (107), Resistance Temperature Detector (Thermistor) sensors (106) adapted to monitor and control the temperature of said heating element (103) and said sample plates (101), two copper leads (108,109) fIXed to the opposite sides of the said heating element (103) by high temperature silver pastes which is cured in high temperature for over 24 hours, characterized in that a heating element (103) comprising a borone doped silicon semiconductor supported on low thermal conducting glass plate (104), a sample plate (101) electrically insulated from said heating element by mica sheets (102), an alumina casing (105) housing said heating element (103) and said low thermal conducting glass plate (104) and the said sample plate (101) being fIXed to the said alumina casing (105) by screw means (110, 111) and bottom of the said alumina casing (105), said low thermal conducting glass plate (107) being fIXed to force sensor with screw means (112 to 115), the temperature of sample plate and heating element is controlled by Proportional Integral Derivative Control (PID / General Purpose Interface Bus (GPIB) for computer interface with LAB VIEW 61 program. «A miniature heated stage for surface force apparatus". This invention relates to a miniature heated stage for surface force apparatus comprising a low thermal conducting glass plate (107), Resistance Temperature Detector (Thermistor) sensors (106) adapted to monitor and control the temperature of said heating element (103) and said sample plates (101), two copper leads (108,109) fIXed to the opposite sides of the said heating element (103) by high temperature silver pastes which is cured in high temperature for over 24 hours, characterized in that a heating element (103) comprising a borone doped silicon semiconductor supported on low thermal conducting glass plate (104), a sample plate (101) electrically insulated from said heating element by mica sheets (102), an alumina casing (105) housing said heating element (103) and said low thermal conducting glass plate (104) and the said sample plate (101) being fIXed to the said alumina casing (105) by screw means (110, 111) and bottom of the said alumina casing (105), said low thermal conducting glass plate (107) being fIXed to force sensor with screw means (112 to 115), the temperature of sample plate and heating element is controlled by Proportional Integral Derivative Control (PID/General Purpose Interface Bus (GPIB) for computer interface with LAB VIEW 61 program.
Full Text

FIELD OF INVENTION
This invention relates to a miniature heated stage for surface force
apparatus.
PRIOR ART
A heater built by M. DiBattista et. al., and described in "a micro fabricated hot stage for scanning force microscopes" (1996) using integrated-circuit manufacturing technology is illustrated in fig 1 of the accompanying drawings. In fig. 1 the sample stage is a silicon wafer high resistivity, onto which is patterned pair of electrical contacts 12a and 12b. a small region 14 located between contacts 12a, 12b is born doped so as to make it electrically conductive; electrical current passed from contacts 12a to 12b (or vice versa) will cause resistive heating in region 14 depending upon the level of born doping in region 14 and the magnitude of the electrical current applied. The system is too small for SFA, which require large size sample. Furthermore, expensive micro fabrication procedures are required for fabrication of this heating system.
Another approach, described by W. J. Kulnis, Jr. et al. In "a thermal stage for nanoscale structure studies with the scanning force microscope". Mat. Res. Soc. Symp. Proc. Vol. 332, pp. 105-108 (1994), uses a small peltier thermoelectric device to heat the sample and illustrated in fig. 2. A peltier thermoelectric device uses electric currents to carry heat from one side of device to another, and usually find application as small coolers. However, because heat is actively transported across the device, the device itself serves as excellent insulator. In FIG.2, a Peltier device 16 is glued on to an X-Y scanner 18 pf a scanning probe microscope. A sample to be studied 20 is glued onto the hot side 22 of Peltier device 16, so that the whole assembly of Peltier device 16 and sample 20 is scanned under probe tip 24 of the scanning probe microscope. This arrangement is simple, however the heat applied to sample 20 is removed from the cold side 26 of the

Peltier device 16 causing thermal gradient at the scanner 18. The effect is small because much of the surrent appliced a second limitation lies with the materials used to fabricate the Peltier device itself: the manufacture below 60C to avoid damage to internal solder contacts and semiconductor elements, thus the available heating range is necessarily limited by this constraint to be about 60C or less.
Musevic et al. have constructed another arrangement in "Temperature controlled micro stage for an atomic force microscope." Rev, Sci. Instrumm, 67(7), pp 2554-2556, 1996. The Musevic et al. Arrangement is shown in FIG.3. A heater assembly 28, consisting of thin film 30 of indium-tin-oxide ("ITO") is coated onto underside 32 of glass slide 34, the under side 40 of which also serves as a support for a sample to be studied by a scanning probe microscope. Heat is developed in the heater assembly 28 by applying an electric current to a multi core, flexible copper wire solered to the ITO surface at mounted onto drops 36 of an epoxy adhesive which act as thermal insulating stand-off supports for the heater assembly 28 and hold onto an X-Y scanner 38 of scanning probe microscope. This arrangement is capable heating the sample higher temperatures than Peltier based heater FIG.2. but the entire thermal gradient must be sustained across the epoxy drops 36 and their air space between the ITO layer 30 and the scanner 38. The thermal gradient across the drops 36 (typically 2mm in diameter) provides only very limited thermal isolation of the sample stage 40 from the rest of the microscope and thus the rest of the microscope is substantially radiatively heated when the stage is hot.
Stuart M. Lindsay et al. Developed a heated stage for a scanning probe microscope. In this design (U.S. Patent Number: 5,821,545) thermal insulation and thermal stability of system is improved by increasing the thermal path between system and the heating stage. This heating stage is illustrated in FIG.4; a thin film-hating element 40 is bonded to the underside 42 of a sample stage 44, which is made of metal of high thermal conductivity.

The stage/heater assembly 46 is mounted onto a thermally insulating support element 48 is attached directly to the sample stage 44 at the outer periphery 50 of underside 42 of assembly 46. This is preferably arranged so as to leave an air gap 52 between heater 40 and ring-shaped support portion 54 of element 48 and an air gap 56 in conjuction with ring shaped support portion 54 of element 48 provide a means for supporting stage/heater assembly 46 without permitting heater 40 to contact support portion 54. The elements 60, 62 are fabricated from a single ceramic insulating element 48, by making similar concentric element alternatively thermal path is increased. The sample platen or support sheet 73, is suspended below the scanning tip 74 by means of magnetic mounts 76 which extend downwardly from a suspension mechanism and attract platen 73 which is made up of a material attracted by magnets such as steel or other well known magnetically attractive materials. Sample stage 44 attached at its outer periphery to supports 54 of the elements 48 by means of screws, support sheet 73 is attached to element 48 by means of screws.
In the existing SFA system S, of fig. 5, the sample is heated by the principle of heating the environment E, (liquid or gaseous medium) of the sample. In such a heating arrangement H, force sensor (double cantilever) is subjected thermal distortion; thermal current fluctuation (localized) of chamber is causing thermal drift. Maximum temperature is achieved in such an arrangement is limited by operating temperature of actuators which is directly affected by temperature sample chamber or enclosure.
The heating system of Fig. 1 is too small for SFA, which requires large size sample. Furthermore, expensive micro fabrication procedures are required for fabrication of this heating system, for study of SAM/LB monolayer detachable sample stage is required, no provision is given in this system. In SFA for the measurement of "immobile layer thickness" sample/probe surfaces should be made up of conducting material. The heating system mentioned in prior art is not suitable for SGA.

Thermal gradient between tip and sample exists, solution for this problem is not provided and suggested by the apparatus of fig.2. Maximum temperature is around 60C, In SFA, for the study SAM/LB monolayer require higher temperature range up to 200C. Detachable sample stage is not provided, SAM/LB coating procedure require detachable stage.
A heating system proposed by I. Musevic et al. of fig.3 to some extent could be used for SFA after redesign, the excessive use of epoxy is not desirable, since the magnitude of force and stiffnesses involved in SFA is three order magnitude higher than the SPM type instrument. The maximum temperature attained is just over lOOC. Even at this temperature the problem of thermal insulation and thermal gradient are not handled very well.
The heating system of the prior art are specifically made for AFM/SPM/STM, where the scan area is very small typically lOnm- l|xm diameter size, but in the case of SFA the interacting surface is large 1 mm-1 cm-diameter size. The maximum operating temperature of the heater is 60C to lOOC.
In Stuart M, Lindsay et al of fig.4, the sample stage is permanently fixed to heater, coating of SAM.LB monolayer on substrate/sample stage require removing and replacing of the sample. It is specifically made for particular kind of SPM, where the heating system is not mounted on its base, but it is attached to a structure in suspension by magnetic balls. But in the case of SFA, measurements of force and immobile layer necessitates heater should be fixed rigidly to force sensor spring. In SFA, the force sensor stiflfness is very large so the magnitude forces also, many portions of heater mentioned in prior art 4. acts as compliant flexures, it is undesirable in the case of SFA.

The approach adopted in fig. 5. by J.N. Israelachvili et al. is very simple. That is the principle of environmental heating, but excessive design care should be taken for thermal insulation, thermal drifts and thermal distortion. Maximum temperature is reported so far 60C to 80C, for higher temperature lot of design complications is involved. So the principle of on spot heating is the best approach in such a situation.
In the heating system of fig.l to 4, thermal gradient between tip and sample exists, solution for this problem is not provided and suggested.
Further, they are specifically made for AFM/SPM/STM, where the scan area is very small but in the case of SFA the interacting surface are large 1 mm-1 cm-diameter size.
OBJECTS
An object of this invention is to propose a heater for heating sample in another surface force apparatus.
Another object of this invention is to propose a heater for heating sample in another surface force apparatus having high temperature range 30C to 200C.
Still another object of this invention is to propose a heater for heating sample in another surface force apparatus having high thermal insulation.
Yet another object of this invention is to propose a heater for heating sample in another surface force apparatus having high thermal efficiency, low radiative loss.

A further object of this invention is to propose a heater for heating sample in another surface force apparatus having no or minimal use of high temperature and high stiffness adhesive.
A still further object of this invention is to propose a heater for heating sample in another surface force apparatus having provision for different fixing procedures and design variants depend on application.
Set a further object of this invention is to propose a heater for heating sample in another surface force apparatus requiring no temperature gradient between probe surface and sample (plate).
STATEMENT OF INVENTION
1. According to this invention there is provided a miniature heated stage for
surface force apparatus comprising:-
(a) a low thermal conducting glass plate (107);
(b) Resistance Temperature Detector (Thermistor) sensors (106) adapted to monitor and control the temperature of said heating element (103) and said sample plates (101);
(c) two copper leads (108,109) fixed to the opposite sides fo the said heating element (103) by high temperature silver pastes which is cured in high temperature for over 24 hours;
characterized in that:
(d) a heating element (103) comprising a boron doped silicon semiconductor supported on low thermal conducting glass plate (104);
(e) a sample plate (101) electrically insulated from said heating element by mica sheets (102)

(f) an alumina casing (105) housing said heating element (103) and said low thermal conducting glass plate (104) and the said sample plate (101) being fixed to the said alumina casing (105) by screw means (110,111) and bottom of the said alumina casing (105), said low thermal conducting glass plate (107) being fixed to force sensor with screw means (112 to 115);
(g) the temperature of sample plate and heating element is controlled by Proportional Integral Derivatie Control (PID)/General Purpose Interface Bus (GPIB) for computer interface with LAB VIEW 6i program;
DESCRIPTION OF FIGURES
In the accompanying drawings:-
Fig 1:- shows a heater of known-art built by M.Di Battista et al;
Fig 2> shows a heater of known-art built by W. J.Kulnis Jr. et al;
Fig 3:- shows a heater arrangement constructed by Musevic et al;
Fig 4:- shows a heated stage for a scanning probe microscope;
Fig 5:- shows a heating arrangement in existing Surface Force Apparatus (SFA);
Fig 6(a) to (c)>show the miniature heated stage of present invention for Surface Force
Apparatus;
Fig 7:- shows further details of heated stage of present invention of SFA.
DESCRIPTION OF INVENTION W.RTJRAWINGS
The miniature heater of the present invention and its parts are shown in figure 6. It consists of sample plate (101) electrically insulated fi"om heating element (103). by mica sheets (102). Heating element (103) is based doped silicon semiconductor, supported or low thermal conducting glass plate (104) for minimizing heat flux transfer. An alumina encasing HOS"^ houses 101 102 103 104 RTD sensor 106 is feed hack svstem to monitor

and control the temperature of heater 103-sample plates 101 by Proportional Integral Derivative Control (PID)/ General Purpose Interface Bus (GPIB) computer interface with LAB VIEW 6i program. A low thermal conducting glass plate 107 minimize the heat flux transfer to force sensor. Two copper leads 108, 109 as shown in Fig.6(a) are fixed to the opposite sides of heating element 103 by high temperature silver pastes, then cured in high temperature over for 24 hrs, which ensure the contact intact. The screws 110, 111 as shown in Fig.6(b) are used to fix sample plate 101 rigidly with top of alumina encasing 105, glass and screws 112-115 Fig.6(c) are used to fix bottom of alumina encasing 105, glass plate 107 rigidly with force sensor. An electrical connection 124 is taken auLfi:om the sample plate 101 by copper wire. Though the heater made for SFA, it could be used in instruments like IR, RAMAN-SPEC for sample heating. The SFA probe is shown in Fig. 7. It consists of metal (aluminum) pin 116 of hemi spherical fi'ont surface; rear side of pin 116 is cylindrical which is pressed by alumina cylindrical shank 117. Both 116 and 117 are encased in alumina cylinder 118, the outer surface of 118 is covered by a tight-fit steel jacket 119 which is threaded on its surface, another steel jacket 120, which is threaded inside, is pressing the alumina cylindrical shank 117, tightened against steel jacket 119. Through the side hole 121 of alumina 118, an electrical contact 122 fi^om metal pin 116 is made, which is wired by copper lead 123 through the hole 121. The capacitance measurement between 101 and 116 (by copper leads 123 and 124) gives 'immobile layer' thickness.
Fixing procedure of heater with instrument varies depends on the application, so accordingly different design of this heater could be used. Here we have explained two design variant of the heater and their fixing procedures.
Embodiment I-fixing aluminium sample plate with alumina encasing. Embodiment Il-fixing aluminium encasing with SFA (Force sensor).
There are many ways these could be done. But considering many aspects and sensitiveness nano scale measurements, following methods are chosen and optimized;

1. High temperature glue (pyroputty) fixing: In embodiment I, top annular surface 105 of the alumina encasing and corresponding bottom surface 101 of the aluminium plate are roughened mechanically. The pyroputty glue applied on the roughened portion of the surface, then the two surfaces pressed together and allowed for curing. Similarly in embodiment II, bottom surface 105 of the alumina or glass plate 107 and counter surface instrument (surface of the SFA force sensor) are roughened mechanically, the pyroputty glue applied on the roughened surfaces, then the surfaces are pressed and allowed for curing. It is important that amount of pyroputty glue used in embodiments I and 11 should be minimal to avoid errors, which could be introduced in the measurements due to behavior of the glue itself. It is essential to calibrate heater for this purpose.
2. Mechanical fixing: for the mechanical fixing, the heater is modified as shown in the figure.6. Collars 110,111,112,113,114,115 are provided in the alumina casing top and bottom portions as well as in the aluminium sample plate. Using fine screws, collars 110, 111 of the alumina and aluminium plate fastened, and collars 112,113,114,115 of the alumina fastened to counter surface.
Thermal insulation and efficiency: In this design, in the heater part thermal insulation enhanced by low thermal conducting glass plate (104,107) in addition with alumina encasing (105). This minimizes any heat flux transfer to the instrument. High temperature black paint coating (125) over the surface of alumina encasing (105) minimizes the radiation loss and heat flux to instrument. The overall design innovation improved the efficiency of the heater. In the SFA probe part, the thermal insulation enhanced by low thermal conducting alumina cylinder 117 and alumina encasing 118.



WE CLAIM;
1. A miniature heated stage for surface force apparatus comprising:-
(a) a low thermal conducting glass plate (107);
(b) Resistance Ten^rature Detector (Thermistor) sensors (106) adapted to monitor and control the temperature of said heating element (103) and said sample plates (101);
(c) two copper leads (108,109) fixed to the opposite sides of the said heating element (103) by high temperature silver pastes which is cured in high temperature for over 24 hours;
characterized in that:
(d) a heating element (103) comprising a boron doped silicon semiconductor supported on low thermal conducting glass plate (104);
(e) a san^le plate (101) electrically insulated from said heating element by mica sheets (102)
(f) an aliraiina casing (105) housing said heating elen^nt (103) and said low thermal conducting glass plate (104) and the said sample plate (101) being fixed to the said alumina casing (105) by screw means (110,111) and bottom of the said alumina casing (105), said low thermal conducting glass plate (107) being fixed to force sensor with screw means(112to 115);
(g) the ten:q)erature of sample plate and heating element is controlled by Proportional Integral Derivative Control (PID)/General Purpose Interface Bus (GPIB) for computer interface with LAB VIEW 6i program;

2. A miniature heated stage for surface force apparatus as substantially herein
described and illustrated with accompnying drawings.


Documents:

243-che-2003-claims.pdf

243-che-2003-correspondnece-others.pdf

243-che-2003-correspondnece-po.pdf

243-che-2003-description(complete).pdf

243-che-2003-description(provisional).pdf

243-che-2003-drawings.pdf

243-che-2003-form 1.pdf

243-che-2003-form 18.pdf

243-che-2003-form 3.pdf


Patent Number 248198
Indian Patent Application Number 243/CHE/2003
PG Journal Number 26/2011
Publication Date 01-Jul-2011
Grant Date 27-Jun-2011
Date of Filing 24-Mar-2003
Name of Patentee INDIAN INSTITUTE OF SCIENCE
Applicant Address BANGALORE, KARNATAKA, PIN 560 012
Inventors:
# Inventor's Name Inventor's Address
1 BISWAS KUMAR SANJAY INDIAN INSTITUTE OF SCIENCE, BANGALORE
2 D. DEVAPRAKASAM INDIAN INSTITUTE OF SCIENCE BANGALORE
PCT International Classification Number G12B 21/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA