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Register a new userElectrostatically tunable adhesion in a high speed sliding interface
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Added by
Sukumar Rajauria dr
Publication date
2017
fields
Physics
and research's language is
English
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Contact hysteresis between sliding interfaces is a widely observed phenomenon from macro- to nano- scale sliding interfaces. Most of such studies are done using an atomic force microscope (AFM) where the sliding speed is a few {mu}m/s. Here, we present a unique study on stiction between the head-disk interface of commercially available hard disk drives, wherein vertical clearance between the head and the disk is of the same order as in various AFM based fundamental studies, but with a sliding speed that is nearly six orders of magnitude higher. We demonstrate that although the electrostatic force (DC or AC voltage) is an attractive force, the AC voltage induced out-of-plane oscillation of the head with respect to disk is able to suppress completely the contact hysteresis.
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Development of memory devices with ultimate performance has played a key role in innovation of modern electronics. As a mainstream technology nonvolatile memory devices have manifested high capacity and mechanical reliability, however current major bottlenecks include low extinction ratio and slow operational speed. Although substantial effort has been employed to improve their performance, a typical hundreds of micro- or even milli- second write time remains a few orders of magnitude longer than their volatile counterparts. We have demonstrated nonvolatile, floating-gate memory devices based on van der Waals heterostructures with atomically sharp interfaces between different functional elements, and achieved ultrahigh-speed programming/erasing operations verging on an ultimate theoretical limit of nanoseconds with extinction ratio up to 10^10. This extraordinary performance has allowed new device capabilities such as multi-bit storage, thus opening up unforeseen applications in the realm of modern nanoelectronics and offering future fabrication guidelines for device scale-up.
Uncooled Terahertz (THz) photodetectors (PDs) showing fast (ps) response and high sensitivity (noise equivalent power (NEP) < $nWHz^{-1/2}$) over a broad (0.5THz-10THz) frequency range are needed for applications in high-resolution spectroscopy (relative accuracy ~ $10^{-11}$), metrology, quantum information, security, imaging, optical communications. However, present THz receivers cannot provide the required balance between sensitivity, speed, operation temperature and frequency range. Here, we demonstrate an uncooled THz PD combining the low (~2000 $k_{B}{mu}m^{-2}$) electronic specific heat of high mobility (> 50000 $cm^{2}V^{-1}s^{-1}$) hBN-encapsulated graphene with the asymmetric field-enhancement produced by a bow-tie antenna resonating at 3 THz. This produces a strong photo-thermoelectric conversion, which simultaneously leads to a combination of high sensitivity (NEP $leq$ 160 $pWHz^{-1/2}$), fast response time ($leq 3.3 ns$) and a four orders of magnitude dynamic range, making our devices the fastest, broadband, low noise, room temperature THz PD to date.
As spin-orbit-torque magnetic random-access memory (SOT-MRAM) is gathering great interest as the next-generation low-power and high-speed on-chip cache memory applications, it is critical to analyze the magnetic tunnel junction (MTJ) properties needed to achieve sub-ns, and ~fJ write operation when integrated with CMOS access transistors. In this paper, a 2T-1MTJ cell-level modeling framework for in-plane type Y SOT-MRAM suggests that high spin Hall conductivity and moderate SOT material sheet resistance are preferred. We benchmark write energy and speed performances of type Y SOT cells based on various SOT materials experimentally reported in the literature, including heavy metals, topological insulators and semimetals. We then carry out detailed benchmarking of SOT material Pt, beta-W, and BixSe(1-x) with different thickness and resistivity. We further discuss how our 2T-1MTJ model can be expanded to analyze other variations of SOT-MRAM, including perpendicular (type Z) and type X SOT-MRAM, two-terminal SOT-MRAM, as well as spin-transfer-torque (STT) and voltage-controlled magnetic anisotropy (VCMA)-assisted SOT-MRAM. This work will provide essential guidelines for SOT-MRAM materials, devices, and circuits research in the future.
The ability to manipulate individual atoms and molecules using a scanning tunnelling microscope (STM) has been crucial for the development of a vast array of atomic scale devices and structures ranging from nanoscale motors and switches to quantum corrals. Molecular motors in particular have attracted considerable attention in view of their potential for assembly into complex nanoscale machines. Whereas the manipulated atoms or molecules are usually on top of a substrate, motors embedded in a lattice can be very beneficial for bottom-up construction, and may additionally be used to probe the in uence of the lattice on the electronic properties of the host material. Here, we present the discovery of controlled manipulation of a rotor in Fe doped Bi$_{2}$Se$_{3}$. We find that the current into the rotor, which can be finely tuned with the voltage, drives omni-directional switching between three equivalent orientations, each of which can be frozen in at small bias voltage. Using current fluctuation measurements at 1MHz and model simulations, we estimate that switching rates of hundreds of kHz for sub-nA currents are achieved.
We report on the engineering of broadband quantum cascade lasers (QCLs) emitting at Terahertz (THz) frequencies, which exploit a heterogeneous active region scheme and have a current density dynamic range (Jdr) of 3.2, significantly larger than the state of the art, over a 1.3 THz bandwidth. We demonstrate that the devised broadband lasers operate as THz optical frequency comb synthesizers in continuous wave, with a maximum optical output power of 4 mW (0.73 mW in the comb regime). Measurement of the intermode beatnote map reveals a clear dispersion-compensated frequency comb regime extending over a continuous 106 mA current range (current density dynamic range of 1.24), significantly larger than the state of the art reported under similar geometries, with a corresponding emission bandwidth of 1.05 THz ans a stable and narrow (4.15 KHz) beatnote detected with a signal-to-noise ratio of 34 dB. Analysis of the electrical and thermal beatnote tuning reveals a current-tuning coefficient ranging between 5 MHz/mA and 2.1 MHz/mA and a temperature-tuning coefficient of -4 MHz/K. The ability to tune the THz QCL combs over their full dynamic range by temperature and current paves the way for their use as powerful spectroscopy tool that can provide broad frequency coverage combined with high precision spectral accuracy.
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