Sub-nanometer thickness accuracy and excellent conformity make atomic layer deposited films prevalent in modern electronics, continuously shrinking in size. The thermal resistance of these films plays a major role in the overall energy efficiency of miniaturized devices. We report very sensitive thermal conductivity measurements of amorphous Al2O3 thin films grown using atomic layer deposition in the temperature range of 100–300 K. The 3ω method is used to characterize these films ranging from 17.0 to 119.4 nm in thickness, using a series-resistor model to deconvolve the intrinsic thermal conductivity of the film from thermal boundary resistances inherently present in the multilayer system. The thermal conductivity of amorphous alumina films with a density of 2.77±0.14 g cm−3 is measured to be 1.73±0.08 W m−1 K−1 at 300 K. Measurements were carried out on germanium and sapphire substrates, leading to no substrate dependence of the films’ thermal conductivity, within experimental accuracy. On the other hand, thermal boundary resistances of the systems Pt/Al2O3/substrate are observed to be strongly substrate-dependent, with values ranging from 2.1×10−8 m2 K W−1 to 3.7×10−8 m2 K W−1 at 300 K for films deposited on sapphire and germanium, respectively. These results provide further insights into the significance of interfaces in thermal transport across layered materials, in particular, for potential germanium-based devices.
The 3 method is a dynamic measurement technique developed for determining the thermal conductivity of thin films or semi-infinite bulk materials. A simplified model is often applied to deduce the thermal conductivity from the slope of the real part of the ac temperature amplitude as a function of the logarithm of frequency, which in-turn brings a limitation on the kind of samples under observation. In this work, we have measured the thermal conductivity of a forest of nanowires embedded in nanoporous alumina membranes using the 3 method. An analytical solution of 2D heat conduction is then used to model the multilayer system, considering the anisotropic thermal properties of the different layers, substrate thermal conductivity, and their thicknesses. Data treatment is performed by fitting the experimental results with the 2D model on two different sets of nanowires (silicon and BiSbTe) embedded in the matrix of nanoporous alumina templates, having thermal conductivities that differ by at least one order of magnitude. These experimental results show that this method extends the applicability of the 3 technique to more complex systems having anisotropic thermal properties.
Electron beam lithography (EBL) on non-planar, suspended, curved or bent surfaces is still one of the most frequently stated problems for fabricating novel and innovative nano-devices and sensors for future technologies. Although spin coating is the most widespread technique for electron resist (e-resist) deposition on 2D or flat surfaces, it is inadequate for suspended and 3D architectures because of its lack of uniformity. In this work, we use a thermally evaporated electron sensitive resist the QSR-5 and study its sensitivity and contrast behaviour using EBL. We show the feasibility of utilizing the resist for patterning objects on non-planar, suspended structures via EBL and dry etching processes. We demonstrate the integration of metal or any kind of thin films at the apex of an atomic force microscopy (AFM) tip. This is showing the great potential of this technology in various fields, such as magnetism, electronic, photonics, phononics and other fields related to near field microscopy using AFM probe like for instance scanning thermal microscopy.
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