61,136 research outputs found
Thermal spin injection and interface insensitivity in permalloy/aluminum metallic non-local spin valves
We present measurements of thermal and electrical spin injection in nanoscale
metallic non-local spin valve (NLSV) structures. Informed by measurements of
the Seebeck coefficient and thermal conductivity of representative films made
using a micromachined Si-N thermal isolation platform, we use simple analytical
and finite element thermal models to determine limits on the thermal gradient
driving thermal spin injection and calculate the spin dependent Seebeck
coefficient to be $-0.5\ \mu\mathrm{V}/\mathrm{K}< S_{s}<-1.3\
\mu\mathrm{V}/\mathrm{K}$. This is comparable in terms of the fraction of the
absolute Seebeck coefficient to previous results, despite dramatically smaller
electrical spin injection signals. Since the small electrical spin signals are
likely caused by interfacial effects, we conclude that thermal spin injection
is less sensitive to the FM/NM interface, and possibly benefits from a layer of
oxidized ferromagnet, which further stimulates interest in thermal spin
injection for applications in sensors and pure spin current sources
Modelling Heat Transfer of Carbon Nanotubes
Modelling heat transfer of carbon nanotubes is important for the thermal
management of nanotube-based composites and nanoelectronic device. By using a
finite element method for three-dimensional anisotropic heat transfer, we have
simulated the heat conduction and temperature variations of a single nanotube,
a nanotube array and a part of nanotube-based composite surface with heat
generation. The thermal conductivity used is obtained from the upscaled value
from the molecular simulations or experiments. Simulations show that nanotube
arrays have unique cooling characteristics due to its anisotropic thermal
conductivity.Comment: 10 pages, 4 figure
Large thermal biasing of individual gated nanostructures
We demonstrate a novel nanoheating scheme that yields very large and uniform
temperature gradients up to about 1K every 100nm, in an architecture which is
compatible with the field-effect control of the nanostructure under test. The
temperature gradients demonstrated largely exceed those typically obtainable
with standard resistive heaters fabricated on top of the oxide layer. The
nanoheating platform is demonstrated in the specific case of a short-nanowire
device.Comment: 6 pages, 6 figure
Dimension- and shape-dependent thermal transport in nano-patterned thin films investigated by scanning thermal microscopy
Scanning thermal microscopy (SThM) is a technique which is often used for the measurement of the thermal conductivity of materials at the nanometre scale. The impact of nano-scale feature size and shape on apparent thermal conductivity, as measured using SThM, has been investigated. To achieve this, our recently developed topography-free samples with 200 and 400 nm wide gold wires (50 nm thick) of length of 400–2500 nm were fabricated and their thermal resistance measured and analysed. This data was used in the development and validation of a rigorous but simple heat transfer model that describes a nanoscopic contact to an object with finite shape and size. This model, in combination with a recently proposed thermal resistance network, was then used to calculate the SThM probe signal obtained by measuring these features. These calculated values closely matched the experimental results obtained from the topography-free sample. By using the model to analyse the dimensional dependence of thermal resistance, we demonstrate that feature size and shape has a significant impact on measured thermal properties that can result in a misinterpretation of material thermal conductivity. In the case of a gold nanowire embedded within a silicon nitride matrix it is found that the apparent thermal conductivity of the wire appears to be depressed by a factor of twenty from the true value. These results clearly demonstrate the importance of knowing both probe-sample thermal interactions and feature dimensions as well as shape when using SThM to quantify material thermal properties. Finally, the new model is used to identify the heat flux sensitivity, as well as the effective contact size of the conventional SThM system used in this study
Broadband nanodielectric spectroscopy by means of amplitude modulation electrostatic force microscopy (AM-EFM)
In this work we present a new AFM based approach to measure the local dielectric response of polymer films at the nanoscale by means of Amplitude Modulation Electrostatic Force Microscopy (AM-EFM). The proposed experimental method is based on the measurement of the tip–sample force via the detection of the second harmonic component of the photosensor signal by means of a lock-in amplifier. This approach allows reaching unprecedented broad frequency range (2–3×104 Hz) without restrictions on the sample environment. The method was tested on different poly(vinyl acetate) (PVAc) films at several temperatures. Simple analytical models for describing the electric tip–sample interaction semi-quantitatively account for the dependence of the measured local dielectric response on samples with different thicknesses and at several tip–sample distances
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