Archival Journals Publications

2003
L. Shi, Li, D., Yu, C. H., Jang, W., Yao, Z., Kim, P., and Majumdar, A., “Measuring Thermal and Thermoelectric Properties of One-Dimensional Nanostructures Using a Microfabricated Device,” J. Heat Transfer, vol. 125, pp. 881–888, 2003. LinkAbstract
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. @DOI: 10.1115/1.1597619#
J. P. Small, Shi, L., and Kim, P., “Mesoscopic Thermal and Thermoelectric Measurements of Individual Carbon Nanotubes,” Solid State Comm., vol. 127, no. 2, pp. 181–186, 2003. LinkAbstract
We discuss the mesoscopic experimental measurements of electron energy dissipation, phonon thermal transport, and thermoelectric phenomena in individual carbon nanotubes. The temperature distributions in electrically heated individual multiwalled carbon nanotubes have been measured with a scanning thermal microscope. The temperature profiles along the tube axis in nanotubes indicate the bulk dissipation of electronic energy to phonons. In addition, thermal conductivity of an individual multiwalled nanotube has been measured using a microfabricated suspended device. The observed thermal conductivity is two orders of magnitude higher than the estimation from previous experiments that used macroscopic mat samples. Finally, we present thermoelectric power (TEP) of individual single walled carbon nanotubes using a novel mesoscopic device. A strong modulation of TEP as a function of the gate electrode was observed.
O. Kwon, Shi, L., and Majumdar, A., “Scanning Thermal Wave Microscopy,” J. Heat Transfer, vol. 125, pp. 156–163, 2003. LinkAbstract
This paper presents a technique, scanning thermal wave microscopy (STWM), which can image the phase lag and amplitude of thermal waves with sub-micrometer resolution by scanning a temperature-sensing nanoscale tip across a sample surface. Phase lag measurements during tip-sample contact showed enhancement of tip-sample heat transfer due to the presence of a liquid film. The measurement accuracy of STWM is proved by a benchmark experiment and comparison to theoretical prediction. The application of STWM for sub-surface imaging of buried structures is demonstrated by measuring the phase lag and amplitude distributions of an interconnect via sample. The measurement showed excellent agreement with a finite element analysis offering the promising prospects of three-dimensional thermal probing of micro and nanostructures. Finally, it was shown that the resolving power of thermal waves for subsurface structures improves as the wavelengths of the thermal waves become shorter at higher modulation frequencies.
D. Li, Wu, Y., Kim, P., Shi, L., Yang, P., and Majumdar, A., “Thermal Conductivity of Individual Silicon Nanowires,” Appl. Phys. Lett., vol. 83, pp. 2934–2936, 2003. LinkAbstract
The thermal conductivities of individual single crystalline intrinsic Si nanowires with diameters of 22, 37, 56, and 115 nm were measured using a microfabricated suspended device over a temperature range of 20–320 K. Although the nanowires had well-defined crystalline order, the thermal conductivity observed was more than two orders of magnitude lower than the bulk value. The strong diameter dependence of thermal conductivity in nanowires was ascribed to the increased phonon-boundary scattering and possible phonon spectrum modification.
2002
U. Ghoshal, Ghoshal, S., McDowell, C., Shi, L., Cordes, S., and Farinelli, M., “Enhanced Thermoelectric Cooling at Cold Junction Interfaces,” Appl. Phys. Lett., vol. 80, pp. 3006–3008, 2002. LinkAbstract
We describe a thermoelectric devicestructure that confines the thermal gradients and electric fields at the boundaries of the cold end, and exploits the reduction of thermal conductivity at the interfaces and the poor electron-phonon coupling at the junctions. The measuredtemperature–current and voltage–current characteristics of a prototype cold point-contactthermoelectric cooler based on a p-type Bi0.5Sb1.5Te3 and n-type Bi2Te2.9Se0.1material system indicate an enhanced thermoelectric figure-of-merit ZT in the range of 1.4–1.7 at room temperature.
P. Kim, Shi, L., Majumdar, A., and McEuen, P. L., Mesoscopic Thermal Transport and Energy Dissipation In Carbon Nanotubes, vol. 323. Physica B, 2002, pp. 67–70. LinkAbstract
We have measured the thermal conductivity of an individual multiwalled carbon nanotube (MWNT) using a microfabricated suspended device. The observed thermal conductivity is more than 3000 W/K-m at room temperature, which is two orders of magnitude higher than the estimation from previous experiments that used macroscopic mat samples. In addition, the temperature distributions in electrically heated MWNTs have been measured with a scanning thermal microscope. The temperature profiles along the tube axis in MWNTs indicate the bulk dissipation of electronic energy to phonons, which suggests diffusive electronic transport.
L. Shi and Majumdar, A., “Thermal Transport Mechanisms at Nanoscale Point Contacts,” J. Heat Transfer, vol. 124, pp. 329–337, 2002. LinkAbstract
We have experimentally investigated the heat transfer mechanisms at a 90610 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 tipsample 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 6.761.5 nW/K. Solid-solid conduction increased linearly as contact force increased, with a contact conductance of 0.7660.38 W/m2-K-Pa, and saturated for contact forces larger than 38611 nN. This is most likely due to the elasticplastic contact between the sample and an asperity at the tip end. @DOI: 10.1115/1.1447939# Keywords: Contact Resistance,
2001
L. Shi, Kwon, O., Miner, C. C., and Majumdar, A., “Design and batch fabrication of probes for sub-100 nm scanning thermal microscopy,” Journal of Microelectromechanical Systems, vol. 10, pp. 370-378, 2001. Publisher's Version
P. Kim, Shi, L., Majumdar, A., and McEuen, P. L., “Thermal Transport Measurements of Individual Multiwalled Carbon Nanotubes,” Phy. Rev. Lett., vol. 87, pp. 215502:1-4, 2001. Publisher's VersionAbstract
The thermal conductivity and thermoelectric power of a single carbon nanotube were measured using a microfabricated suspended device. The observed thermal conductivity is more than 3000 W/K m at room temperature, which is 2 orders of magnitude higher than the estimation from previous experiments that used macroscopic mat samples. The temperature dependence of the thermal conductivity of nanotubes exhibits a peak at 320 K due to the onset of umklapp phonon scattering. The measured thermoelectric power shows linear temperature dependence with a value of 80μV/K at room temperature.
L. Shi and Majumdar, A., “Recent Developments in Micro and Nanoscale Thermometry,” Microscale Thermophyscial Eng., vol. 5, pp. 251-265, 2001. LinkAbstract
One of the key issues related to studies in microscale heat transfer is the ability to measure temperature at small scales. In the recent past, rapid and significant progress has enabled temperature measurements to be made with unprecedented high spatial and temporal resolutions. This has allowed heat transfer research to enter a new regime which was previously inaccessible. This article reviews recent developments and discusses future directions, indicating the variety of opportunities for research that are of scientific and technological importance.
2000
L. Shi, Plyasunov, S., Bachtold, A., McEuen, P. L., and Majumdar, A., “Scanning Thermal Microscopy of Carbon Nanotubes using Batch-Fabricated Probes,” Appl. Phys. Lett., vol. 77, pp. 4295–4298, 2000. LinkAbstract
We have designed and batch-fabricated thin-film thermocouple cantilever probes for scanning thermal microscopy (SThM). Here, we report the use of these probes for imaging the phonon temperature distribution of electrically heated carbon-nanotube (CN) circuits. The SThM images reveal possible heat dissipation mechanisms in CN circuits. The experiments also demonstrate that heat flow through the tip-sample nanoscale junction under ambient conditions is dominated by conduction through a liquid film bridging the two surfaces. With the spatial resolution limited by tip radius to about 50 nm, SThM now offers the promising prospects of studying electron-phonon interactions and phonon transport in low dimensional nanostructures.

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