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Register a new userWide bandwidth nanowire electromechanics on insulating substrates at room temperature
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Added by
Abhilash Thanniyil Sebastian Dr
Publication date
2016
fields
Physics
and research's language is
English
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We study InAs nanowire resonators fabricated on sapphire substrate with a local gate configuration. The key advantage of using an insulating sapphire substrate is that it results in a reduced parasitic capacitance thus allowing both wide bandwidth actuation and detection using a network analyzer as well as signal detection at room temperature. Both in-plane and out-of-plane vibrational modes of the nanowire can be driven and the non-linear response of the resonators studied. In addition this technique enables the study of variation of thermal strains due to heating in nanostructures
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Topological insulators are new states of quantum matter with surface states protected by the time-reversal symmetry. In this work, we perform first-principle electronic structure calculations for $Sb_2Te_3$, $Sb_2Se_3$, $Bi_2Te_3$ and $Bi_2Se_3$ crystals. Our calculations predict that $Sb_2Te_3$, $Bi_2Te_3$ and $Bi_2Se_3$ are topological insulators, while $Sb_2Se_3$ is not. In particular, $Bi_2Se_3$ has a topologically non-trivial energy gap of $0.3 eV$, suitable for room temperature applications. We present a simple and unified continuum model which captures the salient topological features of this class of materials. These topological insulators have robust surface states consisting of a single Dirac cone at the $Gamma$ point.
In this study, InSb nanowires have been formed by electrodeposition and integrated into NW-FETs. NWs were formed in porous anodic alumina (PAA) templates, with the PAA pore diameter of approximately 100 nm defining the NW diameter. Following annealing at 125C and 420C respectively, the nanowires exhibited the zinc blende crystalline structure of InSb, as confirmed from x-ray diffraction and high resolution transmission electron microscopy. The annealed nanowires were used to fabricate nanowire field effect transistors (NW-FET) each containing a single NW with 500 nm channel length and gating through a 20nm SiO2 layer on a doped Si wafer. Following annealing of the NW-FETs at 300C for 10 minutes in argon ambient, transistor characteristics were observed with an ION ~ 40 uA (at VDS = 1V in a back-gate configuration), ION/IOFF ~ 16 - 20 in the linear regime of transistor operation and gd ~ 71uS. The field effect electron mobility extracted from the transconductance was ~1200 cm2 V-1 s-1 at room temperature. We report high on-current per nanowire compared with other reported NW-FETs with back-gate geometry and current saturation at low source-drain voltages. The device characteristics are not well described by long-channel MOSFET models, but can qualitatively be understood in terms of velocity saturation effects accounting for enhanced scattering
We show that it is possible to prepare and identify ultra--thin sheets of graphene on crystalline substrates such as SrTiO$_3$, TiO$_2$, Al$_2$O$_3$ and CaF$_2$ by standard techniques (mechanical exfoliation, optical and atomic force microscopy). On the substrates under consideration we find a similar distribution of single, bi- and few layer graphene and graphite flakes as with conventional SiO$_2$ substrates. The optical contrast $C$ of a single graphene layer on any of those substrates is determined by calculating the optical properties of a two-dimensional metallic sheet on the surface of a dielectric, which yields values between $C=$ ~- 1.5% (G/TiO$_2$) and $C=$ ~- 8.8% (G/CaF$_2$). This contrast is in reasonable agreement with experimental data and is sufficient to make identification by an optical microscope possible. The graphene layers cover the crystalline substrate in a carpet-like mode and the height of single layer graphene on any of the crystalline substrates as determined by atomic force microscopy is $d_{SLG}=0.34$ nm and thus much smaller than on SiO$_2$.
A new platform for fabricating polariton lasers operating at room temperature is introduced: nitride-based distributed Bragg reflectors epitaxially grown on patterned silicon substrates. The patterning allows for an enhanced strain relaxation thereby enabling to stack a large number of crack-free AlN/AlGaN pairs and achieve cavity quality factors of several thousands with a large spatial homogeneity. GaN and ZnO active regions are epitaxially grown thereon and the cavities are completed with top dielectric Bragg reflectors. The two structures display strong-coupling and polariton lasing at room temperature and constitute an intermediate step in the way towards integrated polariton devices.
We report room temperature long-distance spin transport of magnons in antiferromagnetic thin film hematite doped with Zn. The additional dopants significantly alter the magnetic anisotropies, resulting in a complex equilibrium spin structure that is capable of efficiently transporting spin angular momentum at room temperature without the need for a well-defined, pure easy-axis or easy-plane anisotropy. We find intrinsic magnon spin-diffusion lengths of up to 1.5 {mu}m, and magnetic domain governed decay lengths of 175 nm for the low frequency magnons, through electrical transport measurements demonstrating that the introduction of non-magnetic dopants does not strongly reduce the transport length scale showing that the magnetic damping of hematite is not significantly increased. We observe a complex field dependence of the non-local signal independent of the magnetic state visible in the local magnetoresistance and direct magnetic imaging of the antiferromagnetic domain structure. We explain our results in terms of a varying and applied-field-dependent ellipticity of the magnon modes reaching the detector electrode allowing us to tune the spin transport.
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