Scanning Thermal Microscopy Probe Research Articles

Two omega method for active thermocouple microscopy

We present a contribution to a new mode of scanning thermal microscopy (SThM) based on the use of thermoelectric junction operating in ac active mode. This is the first alternative to 3omega operating mode of a resistive SThM probe for measuring thermophysical parameters of materials at micro- and nanoscale. Whereas a current at omega frequency generates by Joule effect a 2omega thermal oscillation along the wires, the junction thermoelectric voltage can be measured by means of a differential bridge scheme associated to a lock-in amplifier. A thermal model is presented that confirms measurements performed in different situations with different wire probes. Values of thermal contact conductance of different materials have been extracted and a comparison has been performed between this technique and the resistive 3omega mode.

AFM/FTIR: A New Technique for Materials Characterization

A new type of infrared spectroscopy for obtaining the molecular composition of the surfaces of materials at ultra-high spatial resolution has been developed by combining atomic force microscopy (AFM) with Fourier-transform infrared spectroscopy (FTIR). This new analytical technique involves the use of an AFM to detect the response of a material to the absorption of modulated infrared radiation from an FTIR spectrometer and is referred to as AFM/FTIR spectroscopy. When the technique of AFM/FTIR spectroscopy is completely developed, we plan to use it to probe the molecular structure of interphases in polymer composites and adhesive bonds. Two approaches have been used to measure the response of polymer systems to infrared absorption. The first involves the use of a contact mode AFM probe to measure the thermal expansion of the polymer; the second involves using a scanning thermal microscopy (SThM) probe to measure the polymer's temperature increase. In either case, the output of the probe resembles an interferogram to which a Fourier-transform can be applied to obtain the infrared absorption spectrum. The first approach was used to obtain excellent quality AFM/FTIR spectra from various neat polymer films, including polystyrene, polycarbonate, and a model adhesive system consisting of an epoxy resin cross-linked with dicyandiamide. Excellent spectra were also obtained from polystyrene beads having a diameter of about 2 µm. The second approach, using an SThM probe to determine the temperature increase that accompanies infrared absorption, was also used to obtain interferograms of polymer samples such as polystyrene. However, the interferograms were noisy and the AFM/FTIR spectra obtained from them had a low signal-to-noise ratio. The present results, thus, show that AFM/FTIR spectroscopy is feasible but the spatial resolution of the technique remains to be shown.

Scanning thermal microscopy probe capable of simultaneous electrical imaging and the addition of diamond tip

Scanning Thermal Microscopy (SThM) is a scanning probe technique that allows the mapping of the thermal properties and/or temperature of a substrate. Developments in this scanning probe technique are of great importance to further the study of thermal transport at the micron and at the nano scale, for instance to better the understanding of heat transport in nano-electronic devices or energy transfer in biological systems. Here we describe: 1) the scanning technique developed to acquire simultaneous images of the topography, the thermal and electrical properties of the substrate using a commercially available Veeco SThM probe; 2) how the SThM probe was modified by mounting a micron-sized diamond pyramid on its tip in order to improve the probe's lateral resolution and the topography resolution tests on the performance of the modified probe.

A temperature-dithering closed-loop interface circuit for a scanning thermal microscopy system

This work presents an interface circuit for low-frequency dithering measurements of resistor-based transducers. It is demonstrated in the context of a polyimide-shank scanning thermal microscopy probe which provides high thermal sensitivity and spatial resolution, but has a low bandwidth from both mechanical and thermal perspectives. These pose challenges in temperature dithering and control, as well as noise immunity. The circuit includes a proportional-integral controller and a demodulator, along with appropriate amplifier and filter blocks. It keeps the average temperature of the probe tip constant while synchronously detecting variations in the second harmonic of the modulated signal as the tip is scanned across the sample surface. Strategic choices in the circuit architecture and topology are evaluated, and the overall system including the sensor and the circuit is simulated. Measurements of the implemented system show that a signal-to-noise ratio (SNR) of 15.7 is achieved while scanning a photoresist sample of 218 nm thickness on a silicon substrate, and that the detection limit for variations in thermal conductance is <3 pW/K.

A combined imaging, microthermal and spectroscopic study of a multilayer packaging system

AbstractThe effectiveness of a packaging solution for the pharmaceutical and food industry is dependent on the integrity of the constituent layers and the interfaces formed between them. The deconvolution and analysis of the many intimate layers found in packaging is analytically challenging, requiring techniques capable of identifying sub‐micron regions. Here we have characterized the chemical and physical nature of the layers in a multilayer packaging system along with the interfaces, using a combination of high‐resolution atomic force microscopy (AFM), microthermal analysis using scanning thermal microscopy (SThM), and Fourier transform infrared (FT‐IR) spectroscopy. In particular, localized thermal analysis is shown to reveal the thermal transitions of the individual layers, but it was found that care must be exercised when melting through one layer to the next, as this can result in overestimates of melting temperatures of the underlying layer due to excess power loss from the SThM probe to the already molten top layer surrounding the probe. Copyright © 2004 John Wiley &amp; Sons, Ltd.

SCANNING THERMAL MICROSCOPY

▪ Abstract This chapter presents a review of the technology of scanning thermal microscopy (SThM) and its applications in thermally probing micro- and nanostructured materials and devices. We begin by identifying the parameters that control the temporal and temperature resolution in thermometry. The discussion of SThM research is divided into three main categories: those that use (a) thermovoltage-based measurements, (b) electrical resistance techniques, and (c) thermal expansion measurements. Within each category we describe numerous techniques developed for (a) the method of probe fabrication, (b) the experimental setup used for SThM, (c) the applications of that technique, and (d) the measurement characteristics such as tip-sample heat transfer mechanism, spatiotemporal resolution, and interpretation of data for property measurements. Because most of the SThM techniques require fundamental knowledge of tip-sample heat transfer, all possible heat transfer mechanisms are discussed in depth, and relations for estimating the tip-sample conductance for each mechanism are provided. This is critical because tip-sample heat transfer controls spatial resolution, temperature accuracy and resolution, and imaging artifacts. Based on this discussion, a simple model is given for future design of SThM probes. The review concludes by describing some new developments on the applications of near-field optical microscopy for temperature measurements.

Scanning thermal microscopy using batch fabricated thermocouple probes

We have developed scanning thermal microscopy probes for high resolution analysis of thermal properties in an atomic force microscope (AFM). Electron beam lithography and silicon micromachining have been used to batch fabricate Au/Pd thermocouples situated at the end of Si3N4 cantilevers. The cantilevers are patterned on the side of traditional style pyramidal AFM tips, giving a new shape of probe which is favorable for access to specimens containing significant topographic variation. Tip radius is approximately 50 nm and the probe has a macroscopic opening angle of 70°. The probes were scanned in the repulsive mode using a conventional AFM. Force feedback was optically employed to give topographic and thermal maps simultaneously by maintaining a constant force of approximately 5 nN. During initial scans using a photothermal test specimen, 80 nm period metal gratings were thermally resolved.

Anomalous Resolutions in Scanning Thermal Microscopy of Graphite

The local thermal conductivity of various kinds of graphite surfaces has been investigated by scanning thermal microscopy (SThM) on a scale comparable to the size of a SThM probe. SThM operates under a constant force feedback and scans a sample surface with a resistive wire which makes direct contact with the surface. The probe consists of a bent platinum wire of 5 μm in diameter. The surface topography of the same sample is also studied by atomic force microscopy (AFM) using silicon cantilevers. Highly oriented pyrolytic graphite shows large flat terraces by AFM and large areas of uniform conductivity by SThM. Various graphite films made by chemical vapor deposition exhibit different AFM images unique to each sample but contain a stack of flat graphite plates as a common element. The overall features of SThM images agree with those of the AFM images of the corresponding sample. In addition to this similarity on the micrometer scale, SThM shows complex fine structures as small as 50 nm wide, which are not detected by AFM. We propose that a complex SThM feature results from a depth-probing characteristic of SThM and that the anomalous high resolution is due to contamination-assisted sharpening of the probe.