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Register a new userModeling of a Cantilever-Based Near-Field Scanning Microwave Microscope
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We present a detailed modeling and characterization of our scalable microwave nanoprobe, which is a micro-fabricated cantilever-based scanning microwave probe with separated excitation and sensing electrodes. Using finite-element analysis, the tip-sample interaction is modeled as small impedance changes between the tip electrode and the ground at our working frequencies near 1GHz. The equivalent lumped elements of the cantilever can be determined by transmission line simulation of the matching network, which routes the cantilever signals to 50 Ohm feed lines. In the microwave electronics, the background common-mode signal is cancelled before the amplifier stage so that high sensitivity (below 1 atto-Farad capacitance changes) is obtained. Experimental characterization of the microwave probes was performed on ion-implanted Si wafers and patterned semiconductor samples. Pure electrical or topographical signals can be realized using different reflection modes of the probe.
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We present the design and experimental results of a near-field scanning microwave microscope (NSMM) working at a frequency of 1GHz. Our microscope is unique in that the sensing probe is separated from the excitation electrode to significantly suppress the common-mode signal. Coplanar waveguides were patterned onto a silicon nitride cantilever interchangeable with atomic force microscope (AFM) tips, which are robust for high speed scanning. In the contact mode that we are currently using, the numerical analysis shows that contrast comes from both the variation in local dielectric properties and the sample topography. Our microscope demonstrates the ability to achieve high resolution microwave images on buried structures, as well as nano-particles, nano-wires, and biological samples.
We present the main features of a home-built scanning tunneling microscope that has been attached to the mixing chamber of a dilution refrigerator. It allows scanning tunneling microscopy and spectroscopy measurements down to the base temperature of the cryostat, T approx. 30mK, and in applied magnetic fields up to 13T. The topography of both highly-ordered pyrolytic graphite (HOPG) and the dichalcogenide superconductor NbSe2 have been imaged with atomic resolution down to T approx. 50mK as determined from a resistance thermometer adjacent to the sample. As a test for a successful operation in magnetic fields, the flux-line lattice of superconducting NbSe2 in low magnetic fields has been studied. The lattice constant of the Abrikosov lattice shows the expected field dependence B^{-0.5} and measurements in the STS mode clearly show the superconductive density of states with Andreev bound states in the vortex core.
Microscopic imaging of local magnetic fields provides a window into the organizing principles of complex and technologically relevant condensed matter materials. However, a wide variety of intriguing strongly correlated and topologically nontrivial materials exhibit poorly understood phenomena outside the detection capability of state-of-the-art high-sensitivity, high-resolution scanning probe magnetometers. We introduce a quantum-noise-limited scanning probe magnetometer that can operate from room to cryogenic temperatures with unprecedented DC-field sensitivity and micron-scale resolution. The Scanning Quantum Cryogenic Atom Microscope (SQCRAMscope) employs a magnetically levitated atomic Bose-Einstein condensate (BEC), thereby providing immunity to conductive and blackbody radiative heating. It has a field sensitivity of 1.4 nT per resolution-limited point ($sim$2 $mu$m), or 6 nT/$sqrt{text{Hz}}$ per point at its duty cycle. Compared to point-by-point sensors, the long length of the BEC provides a naturally parallel measurement, allowing one to measure nearly one-hundred points with an effective field sensitivity of 600 pT$/sqrt{text{Hz}}$ for each point during the same time as a point-by-point scanner would measure these points sequentially. Moreover, it has a noise floor of 300 pT and provides nearly two orders of magnitude improvement in magnetic flux sensitivity (down to $10^{-6}$ $Phi_0/sqrt{text{Hz}}$) over previous atomic probe magnetometers capable of scanning near samples. These capabilities are, for the first time, carefully benchmarked by imaging magnetic fields arising from microfabricated wire patterns, in a system where samples may be scanned, cryogenically cooled, and easily exchanged. The SQCRAMscope will provide charge transport images at temperatures from room to 4 K in unconventional superconductors and topologically nontrivial materials.
We constructed a dilution-refrigerator (DR) based ultra-low temperature scanning tunneling microscope (ULT-STM) which works at temperatures down to 30 mK, in magnetic fields up to 6 T and in ultrahigh vacuum (UHV). Besides these extreme operation conditions, this STM has several unique features not available in other DR based ULT-STMs. One can load STM tips as well as samples with clean surfaces prepared in a UHV environment to an STM head keeping low temperature and UHV conditions. After then, the system can be cooled back to near the base temperature within 3 hours. Due to these capabilities, it has a variety of applications not only for cleavable materials but also for almost all conducting materials. The present ULT-STM has also an exceptionally high stability in the presence of magnetic field and even during field sweep. We describe details of its design, performance and applications for low temperature physics.
We present a Scanning Hall Probe Microscope operating in ambient conditions. One of the unique features of this microscope is the use of the same stepper motors for both sample positioning as well as scanning, which makes it possible to have a large scan range (few mm) in x and y directions, with a scan resolution of 0.1 $mu$m. Protocols have been implemented to enable scanning at different heights from the sample surface. The z range is 35 mm. Microstructured Hall probes of size 1-5 $mu$m have been developed. A minimum probe-sample distance textless{} 2 $mu$m has been obtained by the combination of new Hall probes and probe-sample distance regulation using a tuning fork based force detection technique. The system is also capable of recording local B(z) profiles. We discuss the application of the microscope for the study of micro-magnet arrays being developed for applications in micro-systems. * [email protected].; Present address:
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