Thermal boundary conductance between refractory metal carbides and diamond

The thermal boundary conductance (TBC) between thin films of Cr, Mo, Nb and W and diamond substrates has been measured using time domain thermoreflectance before and after a high-vacuum heat treatment at 800 degrees C for 2 h. While no signs of carbide formation could be detected in as-deposited layers by scanning transmission electron microscopy energy dispersive X-ray spectroscopy elemental analysis, the heat treatment led to partial (W,Mo) or full conversion (Cr,Nb) of the film into carbide. The measured TBC values on as-deposited samples of 315, 220, 220 and 205 MW m (-2) K (-1) measured for, respectively, the Cr, Mo, Nb and W samples, were found to not be significantly altered by the heat treatment. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Influence of a Nanometric Al2O3 Interlayer on the Thermal Conductance of an Al/(Si, Diamond) Interface

The effect of an Al2O3 interlayer on the thermal conductance of metal (Al)/non-metal (diamond and silicon) interfaces is investigated using Time Domain ThermoReflectance (TDTR). Interlayers between 1.7 and 20nm are deposited on oxygen-terminated diamond and hydrogen-terminated silicon substrates using atomic layer deposition (ALD). Their overall conductance is then measured at temperatures ranging from 78 to 290K. The contributions of the interlayer bulk and its interfaces with both substrate and metallic overlayer are then separated. Values thus obtained for the bulk interlayer conductivity are comparable with existing data, reaching 1.25Wm(-1)K(-1) at 290K. Interface contributions are shown to be very similar to the values obtained when a single Al/substrate interface is investigated, suggesting that interfacial oxides may govern TBC independently of the interlayer's thickness

Influence of diamond surface termination on thermal boundary conductance between Al and diamond

The effect of diamond surface treatment on the Thermal Boundary Conductance (TBC) between Al and diamond is investigated. The treatments consist in either of the following: exposition to a plasma of pure Ar, Ar:H and Ar:O, and HNO3:H2SO4 acid dip for various times. The surface of diamond after treatment is analyzed by X-ray Photoelectron Spectroscopy, revealing hydrogen termination for the as-received and Ar: H plasma treated samples, pure sp(2) termination for Ar treated ones and oxygen (keton-like) termination for the other treatments. At ambient, all the specific treatments improve the TBC between Al and diamond from 23 +/- 2 MW m(-2) K-1 for the as-received to 65 +/- 5, 125 +/- 20, 150 +/- 20, 180 +/- 20 MW m(-2) K-1 for the ones treated by Ar:H plasma, acid, pure Ar plasma, and Ar:O plasma with an evaporated Al layer on top, respectively. The effect of these treatments on temperature dependence are also observed and compared with the most common models available in the literature as well as experimental values in the same system. The results obtained show that the values measured for an Ar:O plasma treated diamond with Al sputtered on top stay consistently higher than the values existing in the literature over a temperature range from 78 to 290 K, probably due a lower sample surface roughness. Around ambient, the TBC values measured lay close to or even somewhat above the radiation limit, suggesting that inelastic or electronic processes may influence the transfer of heat at this metal/dielectric interface. (C) 2013 AIP Publishing LLC

Thermal boundary conductance of transition metals on diamond

An experimental process that was used to obtain a direct measurement of Thermal Boundary Conductance (TBC) between a diamond substrate and several transition metals, deposited by sputtering, is described. Using Time-Domain ThermoReflectance (TDTR), the critical parameters, for a proper interpretation of the results, are evaluated to be the laser spot size and the thickness of the metallic thin films. Values of TBC between Cu, Cr, Nb, Mo, W and diamond are presented and vary between 30 and 280 MWm-2K-1. The adhesion of the layer to the substrate is seen to be critical to obtain a high TBC. Annealing in vacuum at temperatures up to 600°C does not significantly seem to change the results obtained. When diamond surface is oxygen plasma-treated for better adhesion, the TBC between Cr and diamond is measured to be 325 MWm-2K-1.This represents an 11-fold increase compared to untreated diamond

Effect of diamond surface orientation on the thermal boundary conductance between diamond and aluminum

[100] and [111] oriented diamond substrates were treated using Ar:H and Ar:O plasma treatments, and 1:1 HNO3:H2SO4 heated at 200 ̊C. Subsequent to these treatments, an aluminum layer was either evaporated or sputte- red on the substrates. The Thermal Boundary Conductance (TBC) as well as the interfacial acoustical reflection coefficient between this layer and the diamond substrate was then measured using a Time Domain ThermoReflec- tance (TDTR) experiment. For the Ar:H plasma treated surfaces the [111] oriented faces exhibited conductances 40 % lower than the [100] oriented ones, with the lowest measured TBC at 32±5 MWm−2K−1. The treatments that led to oxygen-terminated diamond surfaces (i.e. acid or Ar:O plasma treatments) showed no TBC anisotropy and the highest measured value was 230±25 MWm−2K−1 for samples treated with Ar:O plasma with a sputtered Al layer on top. Sputtered layers on oxygen-terminated surfaces showed sys- tematically higher TBC than their evaporated counterparts. The interfacial acoustic reflection coefficient correlated qualitatively with TBC when com- paring samples with the same type of surface terminations (O or H), but this correlation failed when comparing H and O terminated interfaces with each other

Influence of sample processing parameters on thermal boundary conductance value in an Al/AlN system

The influence of sample processing parameters on the thermal boundary conductance (TBC) between aluminum and aluminum nitride has been investigated by transient thermoreflectance. An evaporated Al layer on the polished substrate yielded a TBC at ambient of roughly 47 MW m(-2) K-1. The largest improvement (by a factor of 5) was obtained by plasma-etching of the substrate and subsequent evaporation of the metal layer. Electron microscopy suggests that the differences in TBC were mainly due to the (partial) elimination of the native oxide layer on the substrate. The importance of an adequate model for data extraction on measured TBC is highlighted. (C) 2011 American Institute of Physics. [doi:10.1063/1.3560469

Thermal Boundary Conductance: A Materials Science Perspective

The thermal boundary conductance (TBC) of materials pairs in atomically intimate contact is reviewed as a practical guide for materials scientists. First, analytical and computational models of TBC are reviewed. Five measurement methods are then compared in terms of their sensitivity to TBC: the 3 omega method, frequency- and time-domain thermoreflectance, the cut-bar method, and a composite effective thermal conductivity method. The heart of the review surveys 30 years of TBC measurements around room temperature, highlighting the materials science factors experimentally proven to influence TBC. These factors include the bulk dispersion relations, acoustic contrast, and interfacial chemistry and bonding. The measured TBCs are compared across a wide range of materials systems by using the maximum transmission limit, which with an attenuated transmission coefficient proves to be a good guideline for most clean, strongly bonded interfaces. Finally, opportunities for future research are discussed

Cathodoluminescence-based nanoscopic thermometry in a lanthanide-doped phosphor

Crucial to analyze phenomena as varied as plasmonic hot spots and the spread of cancer in living tissue, nanoscale thermometry is challenging: probes are usually larger than the sample under study, and contact techniques may alter the sample temperature itself. Many photostable nanomaterials whose luminescence is temperature-dependent, such as lanthanide-doped phosphors, have been shown to be good non-contact thermometric sensors when optically excited. Using such nanomaterials, in this work we accomplished the key milestone of enabling far-field thermometry with a spatial resolution that is not diffraction-limited at readout. We explore thermal effects on the cathodoluminescence of lanthanide-doped NaYF$_4$ nanoparticles. Whereas cathodoluminescence from such lanthanide-doped nanomaterials has been previously observed, here we use quantitative features of such emission for the first time towards an application beyond localization. We demonstrate a thermometry scheme that is based on cathodoluminescence lifetime changes as a function of temperature that achieves $\sim$ 30 mK sensitivity in sub-$\mu$m nanoparticle patches. The scheme is robust against spurious effects related to electron beam radiation damage and optical alignment fluctuations. We foresee the potential of single nanoparticles, of sheets of nanoparticles, and also of thin films of lanthanide-doped NaYF$_4$ to yield temperature information via cathodoluminescence changes when in the vicinity of a sample of interest; the phosphor may even protect the sample from direct contact to damaging electron beam radiation. Cathodoluminescence-based thermometry is thus a valuable novel tool towards temperature monitoring at the nanoscale, with broad applications including heat dissipation in miniaturized electronics and biological diagnostics.Comment: Main text: 30 pages + 4 figures; supplementary information: 22 pages + 8 figure