Thermal nanoprobes spatial resolution

The silicon nanoprobes, as used in micro/nano-TA, are a far more recent development, and consequently the spatial resolution that can be achieved with these probes is not yet well established but must be of the same order for topographic imaging as conventional AFM tips because the sharpness of the tip is the same. The capabilities for thermal property imaging remain, at the time of writing, unexplored. 

At the time of writing, there are two major types of probe, both of which are described above the Wollaston and the nanoprobes. The Wollaston probe is very robust, can be used at temperatures of 00 °C, and can provide the calorimetric measurement required for the thermal force-distance curves described above as well as AC and DC thermal imaging. Its disadvantages are that the spatial resolution is of the order of a micro-meter and can be used only in contact mode. 

The nanoprobes are less robust, but as robust as most conventional silicon AFM probes, and can be used in aU of the conventional AFM imaging modes, including contact, tapping, and pulsed-force mode. When used in this way, the spatial resolution is similar to that in conventional AFM microscopy, (i.e., of the order of 1 nm). For L-TA the spatial resolution is of the order of 100 nm or better. Their disadvantages are that they cannot, at the time of writing, be used for calorimetric measurements or thermal imaging. This is because the heater is located at the top of the pyramid that forms the tip rather than immediately adjacent to the surface. However, they perform well for local TMA. The maximum temperature is -250 °C undoubtedly more versions of these probes will become available in the future with a wider range of capabilities. 

At the time of writing there is only one manufacturer of micro/nano-TA equipment Anasys Instruments, (www.anasysinstruments.com). They supply the hardware and software for local thermal analysis and thermal imaging that can be interfaced with the most popular types of atomic force microscope. More recently they have launched an instrument based on an optical microscope, the Vesta system, which is simpler to use than an atomic force microscope but the spatial resolution is limited to approximately 1.5 micrometers, see Fig. 7.22. The Wollaston probes are supplied by Veeco (www.veeco.com) and are, therefore, compatible only with Veeco AFMs. The nanoprobes are supplied by Anasys Instruments and can be used with most popular makes of AFM. In addition, Anasys Instruments supply calibration kits containing temperature standards. More recently they have launched an instrument based on an optical microscope, the Vesta system, which is simpler to use than an atomic force microscope, but the spatial resolution is limited to approximately 1.5 pm. 

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