• Willoughby Futtrup posted an update 1 year, 7 months ago

    Understanding the interplay between the structure, composition and opto-electronic properties of semiconductor nano-objects requires combining transmission electron microscopy (TEM) based techniques with electrical and optical measurements on the very same specimen. Recent developments in TEM technologies allow not only the identification and in-situ electrical characterization of a particular object, but also the direct visualization of its modification in-situ by techniques such as Joule heating. Over the past years, we have carried out a number of studies in these fields that are reviewed in this contribution. In particular, we discuss here i) correlated studies where the same unique object is characterized electro-optically and by TEM, ii) in-situ Joule heating studies where a solid-state metal-semiconductor reaction is monitored in the TEM, and iii) in-situ biasing studies to better understand the electrical properties of contacted single nanowires. In addition, we provide detailed fabrication steps for the silicon nitride membrane-chips crucial to these correlated and in-situ measurements.The DyPdBi(DPB) is a topological semi-metal which belongs to rare earth based half Heusler alloy family. In this work, we studied the thickness dependent structural and magneto-transport properties of DPB thin films (20 to 60nm) grown using pulsed laser deposition. The DPB thin films show (110) oriented growth on MgO(100) single crystal substrates. Longitudinal resistance data indicate metallic surface states dominated carrier transport and suppression of semiconducting bulk state carriers for films ≤40nm. We observe the Weak anti localization (WAL) effect and Shubnikov de Hass (SdH) oscillations in the magneto-transport data. Presence of single coherent transport channel (α~-0.50) is observed in Hikami-Larkin-Nagaoka(HLN) fitting of WAL data. Power law temperature dependence of phase coherence length (L~T-0.50 indicates the observation of 2D WAL effect and the presence of topological nontrivial surface states for films≤40nm. The 60nm sample show semiconducting resistivity behavior at higher temperature (>180K) and HLN fitting results (α~-0.72, L~T-0.68) indicate the presence of partial decoupled top and bottom surface states. The Berry’s phase~ π is extracted for thin films ≤40nm, which further demonstrate the presence of Dirac fermions and non-trivial surface states. Band structure parameters are extracted by fitting SdH data to standard Lifshitz-Kosevich formula. The sheet carrier concentration and cyclotron mass of carriers decrease with increase in thickness (20nm to 60nm) from ~1.35×1012cm-2 to 0.68×1012cm-2 and ~0.26me to 0.12me, respectively. find more Our observations suggest that samples with thickness ≤40nm have surface states dominated transport properties and ≥ 60nm sample samples have contributions from both bulk and surface states.In this paper, we study theoretically the doping evolution behaviors of the magnetic excitations(MEs) in the monolayer CuO2 grown on Bi2Sr2CaCu2O8+δ substrate. For the undoped system, the MEs exhibit the low energy commensurate behavior around (π, π). They turn to be incommensurate when the system is slightly hole-doped. In the intermediate doping regime, the low energy MEs diminish gradually. They turn to be dominated by the high energy modes. With further doping, an exotic structure transition of the MEs occurs in the heavily hole-doped regime which is directly related to the Lifshitz transition. Distinct MEs are separated by the transition point around which the low energy MEs exhibit the ring-like structure around (0, 0). Before the transition, the MEs are dominated by the broad particle-hole continuum at very high energies. In contrast, across the transition point, two new low energy modes develop around (0, 0) and (π, π) attributing to the intrapocket and interpocket particle-hole scatterings, respectively.Inspired by the fastest observed live fishes, we have designed, built and tested a robotic fish that emulates the fast-start maneuver of these fishes and generates acceleration and velocity magnitudes comparable to those of the live fishes within the same time scale. We have designed the robotic fish such that it uses the snap-through bucking of its spine to generate the fast-start response. We have used a dynamic snap-through buckling model and a series of experiments on a beam under snap-through buckling to describe the robotic fish’s motion. Our under-actuated robot relies on passive dynamics of a continuous beam to generate organic waveforms. In its transient fast-start maneuver, our robotic fish produces mode shapes very similar to those observed in live fishes, by going through a snap-though bifurcation. We have also used a nonlinear structural model subjected to a non-conservative eccentric compressive force, which is constrained to act tangential to the structure at all times, coupled with a simple fluid dynamic model to approximate the transient behavior of the robot. We relate the numerical results from our nonlinear model to the dynamics observed in the live system proposing an updated kinematic model to understand the mode shapes observed in the fast-start maneuver of the live fishes. We also report on deploying the robotic fish in a river.Voltage-controlled magnetic anisotropy (VCMA), observed at the interfaces of ultrathin ferromagnetic metallic films and oxide layer, has proven to be a useful tool for the development of all-electric field controlled spintronics devices. Here, we have studied the symmetric and asymmetric behavior of VCMA in CoFeB/MgO heterostructures, grown on different underlayer materials, by measuring ferromagnetic resonance using spin pumping and inverse spin Hall effect technique. We observed symmetric behavior of VCMA in CoFeB films with Ta underlayer, whereas a systematic transformation from symmetric to asymmetric behavior of VCMA with decreasing CoFeB thickness is observed for Pt underlayer. We speculate that the increased interfacial roughness, defects and strain of ultrathin CoFeB films with Pt buffer layer probably leads to the complicated band structure at CoFeB/MgO interface resulting in asymmetric behavior of VCMA. The observed symmetric behavior of VCMA in control samples justifies the role of interfacial roughness, defects and discards the role of oxide overlayer on the observed asymmetric behavior of VCMA in ultrathin CoFeB films.

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