223 research outputs found
Broadband dielectric microwave microscopy on m length scales
We demonstrate that a near-field microwave microscope based on a transmission
line resonator allows imaging in a substantially wide range of frequencies, so
that the microscope properties approach those of a spatially-resolved impedance
analyzer. In the case of an electric probe, the broadband imaging can be used
in a direct fashion to separate contributions from capacitive and resistive
properties of a sample at length scales on the order of one micron. Using a
microwave near-field microscope based on a transmission line resonator we
imaged the local dielectric properties of a Focused Ion Beam (FIB) milled
structure on a high-dielectric-constant Ba_{0.6}Sr_{0.4}TiO_3 (BSTO) thin film
in the frequency range from 1.3 GHz to 17.4 GHz. The electrostatic
approximation breaks down already at frequencies above ~10 GHz for the probe
geometry used, and a full-wave analysis is necessary to obtain qualitative
information from the images.Comment: 19 pages (preprint format), 5 figures; to be published in Review of
Scientific Instrument
Evidence for power-law frequency dependence of intrinsic dielectric response in the CaCuTiO
We investigated the dielectric response of CaCuTiO (CCTO) thin
films grown epitaxially on LaAlO (001) substrates by Pulsed Laser
Deposition (PLD). The dielectric response of the films was found to be strongly
dominated by a power-law in frequency, typical of materials with localized
hopping charge carriers, in contrast to the Debye-like response of the bulk
material. The film conductivity decreases with annealing in oxygen, and it
suggests that oxygen deficit is a cause of the relatively high film
conductivity. With increase of the oxygen content, the room temperature
frequency response of the CCTO thin films changes from the response indicating
the presence of some relatively low conducting capacitive layers to purely
power law, and then towards frequency independent response with a relative
dielectric constant . The film conductance and dielectric
response decrease upon decrease of the temperature with dielectric response
being dominated by the power law frequency dependence. Below 80 K, the
dielectric response of the films is frequency independent with
close to . The results provide another piece of evidence for an
extrinsic, Maxwell-Wagner type, origin of the colossal dielectric response of
the bulk CCTO material, connected with electrical inhomogeneity of the bulk
material.Comment: v4: RevTeX, two-column, 9 pages, 7 figures; title modified, minor
content change in p.7, reference adde
Controlled Growth, Patterning and Placement of Carbon Nanotube Thin Films
Controlled growth, patterning and placement of carbon nanotube (CNT) thin
films for electronic applications are demonstrated. The density of CNT films is
controlled by optimizing the feed gas composition as well as the concentration
of growth catalyst in a chemical vapor deposition process. Densities of CNTs
ranging from 0.02 CNTs/{\mu}m^2 to 1.29 CNTs/{\mu}m^2 are obtained. The
resulting pristine CNT thin films are then successfully patterned using either
pre-growth or post-growth techniques. By developing a layered photoresist
process that is compatible with ferric nitrate catalyst, significant
improvements over popular pre-growth patterning methods are obtained.
Limitations of traditional post-growth patterning methods are circumvented by
selective transfer printing of CNTs with either thermoplastic or metallic
stamps. Resulting as-grown patterns of CNT thin films have edge roughness (< 1
{\mu}m) and resolution (< 5 {\mu}m) comparable to standard photolithography.
Bottom gate CNT thin film devices are fabricated with field-effect mobilities
up to 20 cm^2/Vs and on/off ratios of the order of 10^3. The patterning and
transfer printing methods discussed here have a potential to be generalized to
include other nanomaterials in new device configurations
Correlative confocal Raman and scanning probe microscopy in the ionically active particles of LiMn 2 O 4 cathodes
In this contribution, a correlative confocal Raman and scanning probe microscopy approach was implemented to find a relation between the composition, lithiation state, and functional electrochemical response in individual micro-scale particles of a LiMn 2 O 4 spinel in a commercial Li battery cathode. Electrochemical strain microscopy (ESM) was implemented both at a low-frequency (3.5 kHz) and in a high-frequency range of excitation (above 400 kHz). It was shown that the high-frequency ESM has a significant cross-talk with topography due to a tip-sample electrostatic interaction, while the low-frequency ESM yields a response correlated with distributions of Li ions and electrochemically inactive phases revealed by the confocal Raman microscopy. Parasitic contributions into the electromechanical response from the local Joule heating and flexoelectric effect were considered as well and found to be negligible. It was concluded that the low-frequency ESM response directly corresponds to the confocal Raman microscopy data. The analysis implemented in this work is an important step towards the quantitative measurement of diffusion coefficients and ion concentration via strain-based scanning probe microscopy methods in a wide range of ionically active materials. © 2019 by the authors
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