We have batch-fabricated a microdevice consisting of two adjacent symmetric silicon nitride membranes suspended by long silicon nitride beams for measuring thermophysical properties of one-dimensional nanostructures (nanotubes, nanowires, and nanobelts) bridging the two membranes. A platinum resistance heater/thermometer is fabricated on each membrane. One membrane can be Joule heated to cause heat conduction through the sample to the other membrane. Thermal conductance, electrical conductance, and Seebeck coefficient can be measured using this microdevice in the temperature range of 4-400 K of an evacuated Helium cryostat. Measurement sensitivity, errors, and uncertainty are discussed. Measurement results of a 148 nm and a 10 nm-diameter single wall carbon nanotube bundle are presented.

Roughness measurements by optical interferometry and scanning tunneling microscopy on a magnetic thin-film rigid disk surface have shown that its surface is fractal in nature. This leads to a scale-dependence of statistical parameters such as r.m.s height, slope and curvature, which are extensively used in classical models of contact between rough surfaces. Based on the scale-independent fractal roughness parameters, a new model of contact between isotropic rough surfaces is developed. The model predicts that all contact spots of area smaller than a critical area are in plastic contact. When the load is increased, these plastically deformed spots join to form elastic spots. Using a power-law relation for the fractal size-distribution of contact spots, the model shows that for elastic deformation, the load P and the real area of contact Ar are related as P~Ar(3−D)/2, where D is the fractal dimension of a surface profile which lies between 1 and 2. This result explains the origins of the area exponent which has been the focus of a number of experimental and theoretical studies. For plastic loading, the load and area are linearly related. The size-distribution of spots also suggests that the number of contact spots contributing to a certain fraction of the real area of contact remains independent of load although the spot sizes increase with load. The model shows that the load-area relation and the fraction of the real area of contact in elastic and plastic deformation are quite sensitive to the fractal roughness parameters.

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.

The Boltzmann Transport Equation (BTE) for phonons best describes the heat flow in solid nonmetallic thin films. The BTE, in its most general form, however, is difficult to solve analytically or even numerically using deterministic approaches. Past research has enabled its solution by neglecting important effects such as dispersion and interactions between the longitudinal and transverse polarizations of phonon propagation. In this article, a comprehensive Monte Carlo solution technique of the BTE is presented. The method accounts for dual polarizations of phonon propagation, and non-linear dispersion relationships. Scattering by various mechanisms is treated individually. Transition between the two polarization branches, and creation and destruction of phonons due to scattering is taken into account. The code has been verified and evaluated by close examination of its ability or failure to capture various regimes of phonon transport ranging from diffusive to the ballistic limit. Validation results show close agreement with experimental data for silicon thin films with and without doping. Simulation results show that above 100 K, transverse acoustic phonons are the primary carriers of energy in silicon.

Generation of nanomechanical cantilever motion from biomolecular interactions can have wide applications, ranging from highthroughput biomolecular detection to bioactuation. Although it has been suggested that such motion is caused by changes in surface stress of a cantilever beam, the origin of the surface-stress change has so far not been elucidated. By using DNA hybridization experiments, we show that the origin of motion lies in the interplay between changes in configurational entropy and intermolecular energetics induced by specific biomolecular interactions. By controlling entropy change during DNA hybridization, the direction of cantilever motion can be manipulated. These thermodynamic principles were also used to explain the origin of motion generated from protein-ligand binding. U nderstanding the mechanisms of how biological reactions produce motion is fundamental to several physiological processes (1-3). Although most past effort (4-6) has focused on studying single molecular motors (7-9), recent experiments (10, 11) by using microcantilever beams have led to observations that multiple DNA hybridization and antigen-antibody reactions can collectively produce nanomechanical motion. The promising prospects of interfacing molecular biology with micro-and nanomechanical systems can best be exploited if we learn how to control and manipulate nanomechanical motion generated by biomolecular interactions. Although an understanding of the origins of this motion would allow such control, it has so far remained elusive. It has been suggested (11) that the motion is induced by changes in surface stress of the cantilever caused by biomolecular binding. Although this may be true, the origin of surface-stress change is not understood. In this paper, we show that cantilever motion is created because of the interplay between changes in configurational entropy and intermolecular energetics induced by specific biomolecular reactions. The entropy contribution can be critical in determining the direction of motion. By using thermodynamic principles in conjunction with DNA hybridization experiments, we demonstrate that both the direction and magnitude of cantilever motion can be controlled. These thermodynamic principles are also used to explain the nanomechanical motion created by protein-ligand binding. Materials and MethodsExperimental Setup and Approach. Fig. 1 illustrates the experiment we used for studying nanomechanical motion created by multiple specific biomolecular reactions. The experimental setup consisted of a transparent fluid cell, within which a gold-coated silicon nitride (Au͞SiN x ) cantilever was mounted. The fluid cell and the V-shaped micromechanical silicon nitride cantilevers were purchased from Digital Instruments (Santa Barbara, CA). The cantilevers used were 200 m long and 0.5 m thick, and each leg was 20 m wide. The gold films originally coated on cantilevers were etched away, and a fresh 25-nm-thick gold coating was deposited. For good adhesion between gold and silicon nitride, a 5-nm-thick chro...

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Characterization of single-nucleotide polymorphisms is a major focus of current genomics research. We demonstrate the discrimination of DNA mismatches using an elegantly simple microcantilever-based optical deflection assay, without the need for external labeling. Gold-coated silicon AFM cantilevers were functionalized with thiolated 20- or 25-mer probe DNA oligonucleotides and exposed to target oligonucleotides of varying sequence in static and flow conditions. Hybridization of 10-mer complementary target oligonucleotides resulted in net positive deflection, while hybridization with targets containing one or two internal mismatches resulted in net negative deflection. Mismatched targets produced a stable and measurable signal when only a four-base pair stretch was complementary to the probe sequence. This technique is readily adaptable to a high-throughput array format and provides a distinct positive/negative signal for easy interpretation of oligonucleotide hybridization.

We have experimentally investigated the heat transfer mechanisms at a 90±10 nm diameter point contact between a sample and a probe tip of a scanning thermal microscope (SThM). For large heated regions on the sample, air conduction is the dominant tip-sample heat transfer mechanism. For micro/nano devices with a submicron localized heated region, the air conduction contribution decreases, whereas conduction through the solid-solid contact and a liquid meniscus bridging the tip-sample junction become important, resulting in the sub-100 nm spatial resolution found in the SThM images. Using a one dimensional heat transfer model, we extracted from experimental data a liquid film thermal conductance of 6.7±1.5 nW/K. Solid-solid conduction increased linearly as contact force increased, with a contact conductance of 0.76±0.38W/m2-K-Pa, and saturated for contact forces larger than 38±11 nN. This is most likely due to the elastic-plastic contact between the sample and an asperity at the tip end.