Showing papers by "Philip Kim published in 2003"

Thermal conductivity of individual silicon nanowires

Abstract: 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.

Measuring Thermal and Thermoelectric Properties of One-Dimensional Nanostructures Using a Microfabricated Device

Abstract: 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 manostructures (nanotubes, nanowires, and mmobelts) 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.

Alcohol Vapor Sensors Based on Single-Walled Carbon Nanotube Field Effect Transistors

Abstract: We have measured conductance of single-walled semiconducting carbon nanotubes in field-effect transistor (FET) geometry and investigated the device response to alcoholic vapors. We observe significant changes in FET drain current when the device is exposed to various kinds of alcoholic vapors. These responses are reversible and reproducible over many cycles of vapor exposure. Our experiments demonstrate that carbon nanotube FETs are sensitive to a wide range of alcoholic vapors.

Modulation of Thermoelectric Power of Individual Carbon Nanotubes

Abstract: Thermoelectric power (TEP) of individual single walled carbon nanotubes (SWNTs) has been measured at mesoscopic scales using a microfabricated heater and thermometers. Gate electric field dependent TEP modulation has been observed. The measured TEP of SWNTs is well correlated to the electrical conductance across the SWNT according to the Mott formula. Strong modulations of TEP were observed in the single-electron conduction limit. In addition, semiconducting SWNTs exhibit large values of TEP due to the Schottky barriers at SWNT-metal junctions.

Conductance measurement of single-walled carbon nanotubes in aqueous environment

Abstract: We report measurement of conductance of single-walled carbon nanotubes in aqueous media using a field effect geometry in which source and drain electrodes are protected with a photopolymerized epoxy. Without this protection, exposure to aqueous media degrades the device instantly. The 2.6 μm width open slits are prepared by photolithography at the central region between source and drain electrodes, whose spacing, or channel length, is 5 μm, so that only the nanotube channel can be directly exposed to an aqueous environment, while the metal–nanotube junctions are protected. For protected devices, the response to water as characterized primarily by changes in threshold voltage is reversible and reproducible.

Nanoscale Thermal and Thermoelectric Mapping of Semiconductor Devices and Interconnects

Abstract: Three scanning probe microscopy techniques have been developed and applied for thermal and thermoelectric characterization of semiconductor devices and interconnects. These methods are Scanning Thermal Microscopy (SThM), Electrostatic Force Microscopy (EFM), and Scanning Thermoelectric Microscopy (SThEM). The SThM uses a temperature sensor microfabricated at the tip end of an Atomic Force Microscope (AFM) probe to map out temperature distribution on a surface with a spatial resolution approaching 50 nm. This nanoscale thermal imaging method has been applied to obtain surface temperature distribution of nanotransistors, interconnect structures, and molecular electronic devices. Combined with the nanoscale electric field distribution obtained using the EFM, the thermal imaging results can shed light on electron‐phonon transport mechanisms in nanoelectronics and can locate defects in the devices. The SThEM employs an ultra‐high‐vacuum (UHV) Scanning Tunneling Microscope (STM) tip to measure the Seebeck coefficient of nanostructures with a spatial resolution of about 6 nm. This method has been applied to obtain the Seebeck coefficient profile of a p‐n junction. An abrupt change of Seebeck coefficient across the junction is observed. This abrupt change allows for accurate junction delineation. The obtained Seebeck coefficient profile further reveals detailed bandstructure and carrier concentration profile.