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Register a new userQuantitative Measurements of Nanoscale Permittivity and Conductivity Using Tuning-fork-based Microwave Impedance Microscopy
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We report quantitative measurements of nanoscale permittivity and conductivity using tuning-fork (TF) based microwave impedance microscopy (MIM). The system is operated under the driving amplitude modulation mode, which ensures satisfactory feedback stability on samples with rough surfaces. The demodulated MIM signals on a series of bulk dielectrics are in good agreement with results simulated by finite-element analysis. Using the TF-MIM, we have visualized the evolution of nanoscale conductance on back-gated $MoS_2$ field effect transistors and the results are consistent with the transport data. Our work suggests that quantitative analysis of mesoscopic electrical properties can be achieved by near-field microwave imaging with small distance modulation.
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Characterization of electronic properties of novel materials is of great importance for exploratory materials development and also for the discovery of new correlated phases. As several novel compounds are available in powder form only, contactless methods, which also work on air sensitive samples, are higly desired. We present that the microwave cavity perturbation technique is a versatile tool to study conductivity in such systems. The examples include studies on semiconducting-metallic crossover in carbon nanotubes upon alkali doping, study of vortex motion in the K$_3$C$_{60}$ superconductor, and the characterization of various alkali atom doped phases of black phosphorus.
Polymer composite electrolytes of Nafion and phosphotungstic acid (PWA) are fabricated and analyzed using electrochemical strain microscopy (ESM) and conductive atomic force microscopy (C-AFM) to visualize hydrophilic ion channels near the surface, which are composed of water and sulfonic acid groups. The results indicate that the fibrillar objects in ESM image, without significant changes in topography, are hydrophilic ion channels and additional ion channels formed by interaction between PWA and sulfonic groups in Nafion. In this study, the buried ion channels lying under the surface are probed as well as the inlet and outlet of the channels on the surface through combined use of ESM and C-AFM. The results further enhance the understanding of ionic conduction in composite polymer electrolytes in various fields.
Powered by the mutual developments in instrumentation, materials andtheoretical descriptions, sensing and imaging capabilities of quantum emitters insolids have significantly increased in the past two decades. Quantum emitters insolids, whose properties resemble those of atoms and ions, provide alternative waysto probing natural and artificial nanoscopic systems with minimum disturbance andultimate spatial resolution. Among those emerging quantum emitters, the nitrogen-vacancy (NV) color center in diamond is an outstanding example due to its intrinsicproperties at room temperature (highly-luminescent, photo-stable, biocompatible,highly-coherent spin states). This review article summarizes recent advances andachievements in using NV centers within nano- and single crystal diamonds in sensingand imaging. We also highlight prevalent challenges and material aspects for differenttypes of diamond and outline the main parameters to consider when using color centersas sensors. As a novel sensing resource, we highlight the properties of NV centersas light emitting electrical dipoles and their coupling to other nanoscale dipoles e.g.graphene.
Strain engineering has arisen as a powerful technique to tune the electronic and optical properties of two-dimensional semiconductors like molybdenum disulfide (MoS2). Although several theoretical works predicted that biaxial strain would be more effective than uniaxial strain to tune the band structure of MoS2, a direct experimental verification is still missing in the literature. Here we implemented a simple experimental setup that allows to apply biaxial strain through the bending of a cruciform polymer substrate. We used the setup to study the effect of biaxial strain on the differential reflectance spectra of 12 single-layer MoS2 flakes finding a redshift of the excitonic features at a rate between -40 meV/% and -110 meV/% of biaxial tension. We also directly compare the effect of biaxial and uniaxial strain on the same single-layer MoS2 finding that the biaxial strain gauge factor is 2.3 times larger than the uniaxial strain one.
The control of optically driven high-frequency strain waves in nanostructured systems is an essential ingredient for the further development of nanophononics. However, broadly applicable experimental means to quantitatively map such structural distortion on their intrinsic ultrafast time and nanometer length scales are still lacking. Here, we introduce ultrafast convergent beam electron diffraction (U-CBED) with a nanoscale probe beam for the quantitative retrieval of the time-dependent local distortion tensor. We demonstrate its capabilities by investigating the ultrafast acoustic deformations close to the edge of a single-crystalline graphite membrane. Tracking the structural distortion with a 28-nm/700-fs spatio-temporal resolution, we observe an acoustic membrane breathing mode with spatially modulated amplitude, governed by the optical near field structure at the membrane edge. Furthermore, an in-plane polarized acoustic shock wave is launched at the membrane edge, which triggers secondary acoustic shear waves with a pronounced spatio-temporal dependency. The experimental findings are compared to numerical acoustic wave simulations in the continuous medium limit, highlighting the importance of microscopic dissipation mechanisms and ballistic transport channels.
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