As semiconductor devices scale to new dimensions, the materials and designs become more dependent on atomic details. NEMO5 is a nanoelectronics modeling package designed for comprehending the critical multi-scale, multi-physics phenomena through efficient computational approaches and quantitatively modeling new generations of nanoelectronic devices as well as predicting novel device architectures and phenomena. This article seeks to provide updates on the current status of the tool and new functionality, including advances in quantum transport simulations and with materials such as metals, topological insulators, and piezoelectrics.

We report on the fabrication and characterization of synthesized multiwall MoS 2 nanotube (NT) and nanoribbon (NR) field-effect transistors (FETs). The MoS 2 NTs and NRs were grown by chemical transport, using iodine as a transport agent. Raman spectroscopy confirms the material as unambiguously MoS 2 in NT, NR, and flake forms. Transmission electron microscopy was used to observe cross sections of the devices after electrical measurements and these were used in the interpretation of the electrical measurements allowing estimation of the current density. The NT and NR FETs demonstrate n-type behavior, with ON/OFF current ratios exceeding 10 3 , and with current densities of 1.02 µA/µm, and 0.79 µA/µm at V DS = 0.3 V and V BG = 1 V, respectively. Photocurrent measurements conducted on a MoS 2 NT FET, revealed short-circuit photocurrent of tens of nanoamps under an excitation optical power of 78 W and 488 nm wavelength, which corresponds to a responsivity of 460 A/W. A long channel transistor model was used to model the common-source characteristics of MoS 2 NT and NR FETs and was shown to be consistent with the measured data. , sensors 7,8 , field-effect transistors 9,10,11,12 , and logic circuits 13,14 . The absence of surface dangling bonds, the excellent gate electrostatics of the few-layer transistor, and the potential for large area planar processing are all motivating this research. While planar processing is desirable for manufacturing, at the limits of scaling, the properties of these materials may be compromised by unpassivated dangling bonds at the sheet edges. Edges introduce traps, which can degrade subthreshold swing and increase tunneling leakage, 1/f noise, and variability in the device characteristics. Edges can be substantially eliminated by using nanotubes (NTs), and nanoribbons (NRs) formed from collapsed NTs. . The silica ampoule containing MoS 2 powder and iodine in amount of 1.5 mg/cm 3 was evacuated and sealed at a pressure of 7 x 10 -4 Pa. The transport reaction using iodine as a transport agent ran from 1133 K to 1010 K with a temperature gradient of 6.2 K/cm in a two-zone furnace. After three weeks of growth, the silica ampoules were cooled to room temperature with a controlled cooling rate of 60º C/hour. Approximately a few percent of the starting material was transported by the reaction to form nanotubes, while the rest of the transported material grows as strongly undulated thin plate-like crystals. The nearly equilibrium growth conditions enable the synthesis of nanotubes of different diameters, length, and wall thickness, but with extremely low density of structural defects. They grow up to several millimeters in length. The Raman measurements, shown in Fig. 3(a), were performed on the NR, the NT, and a flake that was exfoliated from the same material source. Measurements were done in the backscattering configuration using a WITec Alpha 300 system at room . The conduction of heat out of the NT may be expected to be less than the NR because of smaller contact area to the substrate...

Thermal properties are of great interest in modern electronic devices and nanostructures. Calculating these properties is straightforward when the device is made from a pure material, but problems arise when alloys are used. Specifically, only approximate bandstructures can be computed for random alloys and most often the Virtual Crystal Approximation (VCA) is used. Unfolding methods [T. B. Boykin, N. Kharche, G. Klimeck, and M. Korkusinski, J. Phys.: Condens. Matt. 19, 036203 (2007).] have proven very useful for tight-binding calculations of alloy electronic structure without the problems in the VCA, and the mathematical analogy between tight-binding and valence-force-field approaches to the phonon problem suggest they be employed here as well. However, there are some differences in the physics of the two problems requiring modifications to the electronic structure approach. We therefore derive a phonon alloy bandstructure (vibrational mode) approach based on our tight-binding electronic structure method, modifying the band-determination method to accommodate the different physical situation. Using the method, we study In$_x$Ga$_{1-x}$As alloys and find very good agreement with available experiments.Comment: Main paper with attached supplemental materia

Complex bands k(⊥)(E) in a semiconductor crystal, along a general direction n, can be computed by casting Schrödinger's equation as a generalized polynomial eigenvalue problem. When working with primitive lattice vectors, the order of this eigenvalue problem can grow large for arbitrary n. It is, however, possible to always choose a set of non-primitive lattice vectors such that the eigenvalue problem is restricted to be quadratic. The complex bands so obtained need to be unfolded onto the primitive Brillouin zone. In this paper, we present a unified method to unfold real and complex bands. Our method ensures that the measure associated with the projections of the non-primary wavefunction onto all candidate primary wavefunctions is invariant with respect to the energy E.