Towards building a prototype spin-logic device

Since the late 1980s, several key discoveries, such as Giant and Tunneling Magne- toresistance, and advances in magnetic materials have paved the way for exponentially higher bit-densities in magnetic storage. In particular, the discovery of Spin-Transfer Torque (STT) has allowed information to be written to individual magnets using spin-currents. This has replaced the more traditional Oersted-field control used in field-MRAMs and allowed further scaling of magnetic-memories. A less obvious con- sequence of STT is that it has made possible a logic-technology based on magnets controlled by spin-polarized currents. Charge-coupled Spin Logic (CSL) is one such device proposal that couples a giant spin Hall effect(GSHE) write-unit with a Mag- netic Tunnel Junction read-unit. Several theoretical reports have demonstrated that a CSL-style device can function as a fundamental building block for neuromorphic computing by harnessing the intrinsic properties of magnets. This thesis describes the working of a CSL device. Experimental progress towards building the individual components of CSL and also our efforts to integrate these components into a CSL prototype will be presented. In addition to the integration effort, this work also explores spin-injection from a GSHE metal to a nanoscale magnet through an intermediate non-magnetic metal. Our results indicate that with the right choice of intermediate layers, the spin-angular mo- mentum absorbed by the magnet can be increased without engineering the intrinsic spin Hall angle of the GSHE metal. Finally, this work also proposes a Schottky-barrier model to describe the current flow through low-dimensional semiconductors and uses it to extract the band gap of black-phosphorus thin-films in an attempt to characterize novel 2D-materials

Synthesis of an isotopically labelled analog of the antimicrobial peptide ll-37

LL-37 is a cationic cathelin-associated broad spectrum antibiotic peptide of human neutrophils. Its mechanism of action is by disruption of the bacterial cell membrane structure. LL-21 is a simplified form of the peptide that contains only the core portion of LL-37, which retains antimicrobial activity and is easier to synthesize. We synthesized an 15N –Val-labeled LL-21 peptide which allows us to perform antimicrobial assays to know the antimicrobial activity of the new peptide LL-21 on various gram positive and gram negative bacteria. We found that our new peptide LL-21 shows good minimum inhibitory concentrations on various gram positive and gram negative bacteria except in the case of Bacillus subtilis and when compared with the parent analog, the new peptide requires slightly higher concentrations to kill the bacteria. Solid state NMR studies on LL-21 help to measure helix tilt in the bacterial cell membranes. This will provide information on its precise mode of action, either detergentlike activity or pore formation. In the future, the replacement of some of the amino acids in LL-21 with 19F and deuterium labels in specified positions will give more information on the orientation, dynamics, and rotation of the peptide in bacterial cell bilayers

Limitations of the High-Low C-V Technique for MOS Interfaces With Large Time Constant Dispersion

We discuss the limitations of the high-low CV technique in evaluating the interface trap density (D-TT) in MOS samples with a large time constant dispersion, as occurs in silicon carbide (SiC). We show that the high-low technique can seriously underestimate D-IT for samples with large time constant dispersion, even if elevated temperatures are used to extend the range of validity

Market Equilibrium for CES Exchange Economies: Existence, Multiplicity, and Computation

We consider exchange economies where the traders’ preferences are expressed in terms of the extensively used constant elasticity of substitution (CES) utility functions. We show that for any such economy it is possible to say in polynomial time whether an equilibrium exists. We then describe a convex formulation of the equilibrium conditions, which leads to polynomial time algorithms for a wide range of the parameter defining the CES utility functions. This range includes instances that do not satisfy weak gross substitutability. As a byproduct of our work, we prove the uniqueness of equilibrium in an interesting setting where such a result was not known. The range for which we do not obtain polynomial-time algorithms coincides with the range for which the economies admit multiple disconnected equilibria

Keratocystic odontogenic tumor of the right mandibular condyle: A rare case

Odontogenic keratocyst (OKC) was first described by Hans Philipsen in 1956. The World Health Organization (WHO) has designated OKC as a Keratocystic Odontogenic Tumor (KCOT). KCOT is defined as ′a benign uni- or multicystic, intraosseous tumor of odontogenic origin, with a characteristic lining of parakeratinized stratified squamous epithelium, with a potential for aggressive, infiltrative behavior′. Radiographically, most OKCs are unilocular, presenting a well-defined peripheral rim and a central cavity having satellite cysts. It is characterized by a thin fibrous capsule and a lining of keratinized stratified squamous epithelium, which is typically corrugated, usually about 6 to 10 cells in thickness, and generally without rete pegs. The present case report describes an unusual case of KCOT with minimal clinical presentation indicative of a tumor highlighting the potential difficulties in determining the diagnosis

Spin-torque switching of a nano-magnet using giant spin hall effect

The Giant Spin Hall Effect(GSHE) in metals with high spin-orbit coupling is an efficient way to convert charge currents to spin currents, making it well-suited for writing information into magnets in non-volatile magnetic memory as well as spin-logic devices. We demonstrate the switching of an in-plane CoFeB magnet using a combination of GSHE and an external magnetic field. The magnetic field dependence of the critical current is used to estimate the spin hall angle with the help of a thermal activation model for spin-transfer torque switching of a nanomagnet

High Performance Multilayer MoS₂ Transistors with Scandium Contacts

While there has been growing interest in two-dimensional (2-D) crystals other than graphene, evaluating their potential usefulness for electronic applications is still in its infancy due to the lack of a complete picture of their performance potential. The focus of this article is on contacts. We demonstrate that through a proper understanding and design of source/drain contacts and the right choice of number of MoS₂ layers the excellent intrinsic properties of this 2-D material can be harvested. Using scandium contacts on 10-nm-thick exfoliated MoS₂ flakes that are covered by a 15 nm Al₂O₃ film, high effective mobilities of 700 cm²/(V s) are achieved at room temperature. This breakthrough is largely attributed to the fact that we succeeded in eliminating contact resistance effects that limited the device performance in the past unrecognized. In fact, the apparent linear dependence of current on drain voltage had mislead researchers to believe that a truly Ohmic contact had already been achieved, a misconception that we also elucidate in the present article

Improvement of Spin Transfer Torque in Asymmetric Graphene Devices

A graphene lateral spin valve structure with asymmetric contacts is presented for the first time, with enhancement of spin angular momentum absorption in its receiving magnet. The asymmetric device with tunneling barrier only at the injector magnet shows a comparable spin valve signal but lower electrical noises compared to the device with two tunneling barriers. We also report experimental measurements of spin transfer torque. Assisted by an external magnetic field of 2.5 mT, spin diffusion current-induced magnetization reversal occurs at a nonlocal charge current density of 33 mA/mu m(2), smaller than that needed in devices with two tunneling barriers