Schematic and SEM images of a conventional SThM tip based on an Au–Cr thermocouple.[1]SThM using the N-V center in diamond. (a) Schematics of experimental setup. An electric current is applied to the arms of an AFMcantilever (phosphorus-doped Si, P:Si) and heats up the end section above the tip (intrinsic Si, i-Si). The bottom lens excites a diamond nanocrystal with a green laser light and collects photoluminescence (PL). The crystal hosts an N-V center and is attached to the AFM tip. A wire on the sample surface serves as the microwave source (mw). The temperature of the cantilever Th is determined from the applied current and voltage. (b) Optically detected magnetic resonance spectra of the N-V center at three temperatures. (c) Thermal conductivity image of a gold letter E on sapphire. White circles indicate features that do not correlate with the AFM topography. (d) PL image of the AFM cantilever end and tip where the diamond nanocrystal appears as the bright spot. (e) Zoomed PL image of the N-V center in d.[2]
Scanning thermal microscopy (SThM) is a type of scanning probe microscopy that maps the local temperature and thermal conductivity of an interface. The probe in a scanning thermal microscope is sensitive to local temperatures – providing a nano-scale thermometer. Thermal measurements at the nanometer scale are of both scientific and industrial interest. The technique was invented by Clayton C. Williams and H. Kumar Wickramasinghe in 1986.[3]
SThM requires the use of specialized probes. There are two types of thermal probes: Thermocouple probes where the probe temperature is monitored by a thermocouple junction at the probe tip and resistive or bolometer probes where the probe temperature is monitored by a thin-film resistor at probe tip. These probes are generally made from thin dielectric films on a silicon substrate and use a metal or semiconductor film bolometer to sense the tip temperature. Other approaches, using more involved micro machining methods, have also been reported.[20] In a bolometer probe the resistor is used as a local heater and the fractional change in probe resistance is used to detect the temperature and/or the thermal conductance of the sample.[15] When the tip is placed in contact with the sample, heat flows from the tip to sample. As the probe is scanned, the amount of heat flow changes. By monitoring the heat flow, one can create a thermal map of the sample, revealing spatial variations in thermal conductivity in a sample. Through a calibration process, the SThM can reveal the quantitative values of thermal conductivity.[21] Alternately the sample may be actively heated, for example a powered circuit, to visualize the distribution of temperatures on the sample.
Tip-sample heat transfer can include
Solid-solid conduction. Probe tip to sample. This is the transfer mechanism which yields the thermal scan.
Liquid-liquid conduction. When scanning in non-zero humidity, a liquid meniscus forms between the tip and sample. Conduction can occur through this liquid drop.
Gas conduction. Heat can be transferred through the edges of the probe tip to the sample.
^ abLi, M-H., Gianchandani, Y. B. (2003). "Applications of a low contact force polyimide shank bolometer probe for chemical and biological diagnostics". Sensors and Actuators A: Physical. 104 (3): 236–245. doi:10.1016/S0924-4247(03)00026-8.((cite journal)): CS1 maint: multiple names: authors list (link)
^ abLi, M-H.; et al. (2001). "Surface micromachined polyimide scanning thermocouple probes". Journal of Microelectromechanical Systems. 10: 3–9. doi:10.1109/84.911085.
^Ocola, L. E.; et al. (1996). "Latent image formation: Nanoscale topography and calorimetric measurements in chemically amplified resists". Journal of Vacuum Science and Technology B. 14 (6): 3974–3979. Bibcode:1996JVSTB..14.3974O. doi:10.1116/1.588626.
^Basu, A. S.; et al. (2004). "Scanning thermal lithography: Maskless, submicron thermochemical patterning of photoresist by ultracompliant probes". Journal of Vacuum Science and Technology B. 22 (6): 3217–3220. Bibcode:2004JVSTB..22.3217B. doi:10.1116/1.1808732. S2CID15455318.
^Luo, K.; et al. (1996). "Nanofabrication of sensors on cantilever probe tips for scanning multiprobe microscopy". Appl. Phys. Lett. 68 (3): 325–327. Bibcode:1996ApPhL..68..325L. doi:10.1063/1.116074.
^Vettiger, P.; et al. (2000). "The "Millipede"—More than thousand tips for future AFM storage". IBM J. Res. Dev. 44 (3): 323–340. doi:10.1147/rd.443.0323.
^Lerchner, J.; et al. (2000). "Calorimetric detection of volatile organic compounds". Sensors and Actuators B: Chemical. 70 (1–3): 57–66. doi:10.1016/S0925-4005(00)00554-2.
^ abLee, J-H. et al. International Workshop on Thermal Investigations of ICs and Systems (THERMINIC 2002), Madrid, Spain, October 2002, pp. 111–116.
^Hendarto, E.; et al. (2005). Proceedings 43rd Annual IEEE International Reliability Physics Symposium: 294–299
^J.Wu, M.Reading, D. Q. M. Craig (2008). "Application of Calorimetry, Sub-Ambient Atomic Force Microscopy and Dynamic Mechanical Analysis to the Study of Frozen Aqueous Trehalose Solutions". Pharmaceutical Research. 25 (6): 1396–1404. doi:10.1007/s11095-007-9530-y. PMID18256792. S2CID9471815.((cite journal)): CS1 maint: multiple names: authors list (link)
^R. Meckenstock; I. Barsukov; C. Bircan; A. Remhoff; D. Dietzel; D. Spoddig (2006). "Imaging of ferromagnetic resonance excitations in Permalloy nano structures on Si using scanning near-field thermal microscopy". J. Appl. Phys. 99 (8): 08C706. Bibcode:2006JAP....99hC706M. doi:10.1063/1.2171929.
^Gianchandani Y., Najafi, K. (1997). "A silicon micromachined scanning thermal profiler with integrated elements for sensing and actuation". IEEE Transactions on Electron Devices. 44 (11): 1857–1868. Bibcode:1997ITED...44.1857G. doi:10.1109/16.641353.((cite journal)): CS1 maint: multiple names: authors list (link)
^Nasr Esfahani, Ehsan; Ma, Feiyue; Wang, Shanyu; Ou, Yun; Yang, Jihui; Li, Jiangyu (2017). "Quantitative nanoscale mapping of three-phase thermal conductivities in filled skutterudites via scanning thermal microscopy". National Science Review. 5: 59–69. arXiv:1702.01895. Bibcode:2017arXiv170201895N. doi:10.1093/nsr/nwx074.
