Temperature mapping of operating nanoscale devices by scanning probe thermometry.

Imaging temperature fields at the nanoscale is a central challenge in various areas of science and technology. Nanoscopic hotspots, such as those observed in integrated circuits or plasmonic nanostructures, can be used to modify the local properties of matter, govern physical processes, activate chemical reactions and trigger biological mechanisms in living organisms. The development of high-resolution thermometry techniques is essential for understanding local thermal non-equilibrium processes during the operation of numerous nanoscale devices. Here we present a technique to map temperature fields using a scanning thermal microscope. Our method permits the elimination of tip-sample contact-related artefacts, a major hurdle that so far has limited the use of scanning probe microscopy for nanoscale thermometry. We map local Peltier effects at the metal-semiconductor contacts to an indium arsenide nanowire and self-heating of a metal interconnect with 7 mK and sub-10 nm spatial temperature resolution.

Kelvin probe force microscopy for local characterisation of active nanoelectronic devices.

Frequency modulated Kelvin probe force microscopy (FM-KFM) is the method of choice for high resolution measurements of local surface potentials, yet on coarse topographic structures most researchers revert to amplitude modulated lift-mode techniques for better stability. This approach inevitably translates into lower lateral resolution and pronounced capacitive averaging of the locally measured contact potential difference. Furthermore, local changes in the strength of the electrostatic interaction between tip and surface easily lead to topography crosstalk seen in the surface potential. To take full advantage of the superior resolution of FM-KFM while maintaining robust topography feedback and minimal crosstalk, we introduce a novel FM-KFM controller based on a Kalman filter and direct demodulation of sidebands. We discuss the origin of sidebands in FM-KFM irrespective of the cantilever quality factor and how direct sideband demodulation enables robust amplitude modulated topography feedback. Finally, we demonstrate our single-scan FM-KFM technique on an active nanoelectronic device consisting of a 70 nm diameter InAs nanowire contacted by a pair of 120 nm thick electrodes.

In situ doping of catalyst-free InAs nanowires.

We report on in situ doping of InAs nanowires grown by metal-organic vapor-phase epitaxy without any catalyst particles. The effects of various dopant precursors (Si(2)H(6), H(2)S, DETe, CBr(4)) on the nanowire morphology and the axial and radial growth rates are investigated to select dopants that enable control of the conductivity in a broad range and that concomitantly lead to favorable nanowire growth. In addition, the resistivity of individual wires was measured for different gas-phase concentrations of the dopants selected, and the doping density and mobility were extracted. We find that by using Si(2)H(6) axially and radially uniform doping densities up to 7 × 10(19) cm(-3) can be obtained without affecting the morphology or growth rates. For sulfur-doped InAs nanowires, we find that the distribution coefficient depends on the growth conditions, making S doping more difficult to control than Si doping. Moreover, above a critical sulfur gas-phase concentration, compensation takes place, limiting the maximum doping level to 2 × 10(19) cm(-3). Finally, we extract the specific contact resistivity as a function of doping concentration for Ti and Ni contacts.