Broadband dielectric microwave microscopy on μ\mum 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 CaCu3_{3}Ti4_{4}O12_{12}

We investigated the dielectric response of CaCu$_3$Ti$_4$O$_{12}$ (CCTO) thin films grown epitaxially on LaAlO$_3$ (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 $\epsilon'\sim10^2$. The film conductance and dielectric response decrease upon decrease of the temperature with dielectric response being dominated by the power law frequency dependence. Below $\sim$80 K, the dielectric response of the films is frequency independent with $\epsilon'$ close to $10^2$. 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