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Limited nonrenewable resources on earth motivate people to use natural polymer materials in the development of environment-friendly devices for flexible electronics. In this work, a biocompatible and biodegradable organic memristor based on regenerated cellulose is prepared by a facile and green route. Here, cellulose, the key functional layer material, is used as not only the resistive switching layer but also a substrate to construct a flexible self-supporting memristor. Both volatile and nonvolatile resistive switching can be achieved by controlling the compliance current in the SET process. Moreover, this cellulose-based memristor performs competitive environmental and temperature stability compared with other organic memristors. This research provides a facile strategy for constructing an environment-friendly memristor based on natural polymer-based materials. [ABSTRACT FROM AUTHOR]

The electronic states of a hydrogenic donor impurity in GaAs/GaAlAs quantum wells are investigated theoretically in the framework of effective-mass envelope function theory, including the effect of Rashba spin-orbit coupling. The splits of electron energy levels are calculated. The results show that (1) the split energy of the excited state is larger than that of the ground state; (2) the split energy peak appears as the GaAs well width increases from zero; and (3) the maximum split energy reaches about 1.6 meV. Our results are useful for the application of Rashba spin-orbit coupling to photoelectric devices. [ABSTRACT FROM AUTHOR]

The electronic structures of N quantum dot molecules (QDMs) are investigated theoretically in the framework of effective-mass envelope function theory. The electron and hole energy levels are calculated. In the calculations, the effects of finite offset and valence-band mixing are taken into account. The theoretical method can be used to calculate the electronic structures of any QDM. The results show that (1) electronic energy levels decrease monotonically and the energy difference between the N QDMs decreases as the quantum dot (QD) radius increases; (2) the electron energy level is lower and quantum confinement is smaller for the larger N QDM; (3) the hole ground state energy level is lower for the one dot QDM than N (greater 1) QDMs if the QD radius is larger than about 5 nm due to the valence-band mixing. The results are useful for the application of the N QDM to photoelectric devices. [ABSTRACT FROM AUTHOR]

Acoustic asymmetric focusing (AAF) has a great potential application in medical ultrasound imaging, focused ultrasound therapy, and nondestructive testing. The advancement of acoustic metamaterials and metasurfaces has provided various mechanisms to design AAF lenses. However, due to the existence of a certain difficulty in realizing sound focusing and asymmetric transmission simultaneously, the realization of the AAF lens with a broad bandwidth and an integrative planar structure still remains a challenge. Here, we theoretically propose and experimentally demonstrate an integrative planar AAF lens based on a type of mode-conversion meta-atom composed of two types of phased unit cells with a phase difference of π and a step waveguide. The meta-atom can realize the conversion between the zero-order and first-order waves and asymmetric sound transmission, which arises from the phase modulation and the cutoff frequency of the first-order wave, respectively. Based on the proposed mode-conversion meta-atoms, we design a broadband AAF lens with high performance, in which its fractional bandwidth can reach about 0.19 and the focus size is only about 0.38λ. The proposed mode-conversion meta-atom and its associated AAF lens provide diverse routes for designing asymmetric multi-functional sound devices with promising applications. [ABSTRACT FROM AUTHOR]

Using the first-principles band-structure method and the special quasirandom structures approach, the authors have investigated the band structure of random AlxInyGa1-x-yN quaternary alloys. They show that the wave functions of the band edge states are more localized on the InN sites. Consequently, the photoluminescence transition intensity in the alloy is higher than that in GaN. The valence band maximum state of the quaternary alloy is also higher than GaN with the same band gap, indicating that the alloy can be doped more easily as p-type. [ABSTRACT FROM AUTHOR]

The atomistic pseudopotential quantum mechanical calculations for million atom nanosized metal-oxide-semiconductor field-effect transistors (MOSFETs) are presented. When compared with semiclassical Thomas-Fermi simulation results, there are significant differences in I-V curve, electron threshold voltage, and gate capacitance. In many aspects, the quantum mechanical effects exacerbate the problems encountered during device minimization, and it also presents different mechanisms in controlling the behaviors of a nanometer device than the classical one. [ABSTRACT FROM AUTHOR]

Here, we demonstrate self-powered ultraviolet photodetectors that are capable of generating opposite current flow when illuminated at different wavelengths. The photodetectors are composed of n-ZnO/Polyaniline (PANI) p-n and PANI/ZnGa2O4 type-II heterojunctions and operate without any need for external power source. Devices display superior stability in ambient conditions within months. Results provide opportunities for developing devices for optical recognition. [ABSTRACT FROM AUTHOR]

First principles calculations and special quasirandom structure approach have been used to study the origin of the unintentional high and constant background electron density observed in InxGa1-xN alloys. Our results show that the formation energy of nitrogen vacancy (VN) surprisingly becomes nearly constant for alloys with relatively high In concentration. In strong contrast, the formation energy of hydrogenated nitrogen vacancy (HN) or interstitial hydrogen (Hi) monotonically decreases as x increases, indicating that neither HN nor Hi, but VN is the main sources of the experiment observed high and constant electron density in the alloys. The underlying mechanism is discussed. [ABSTRACT FROM AUTHOR]

Using first-principles calculations and analysis, we show that to create shallow n-type dopants in oxides, anion site doping is preferred for more covalent oxides such as SnO2 and cation site doping is preferred for more ionic oxides such as ZnO. This is because for more ionic oxides, the conduction band minimum (CBM) state actually contains a considerable amount of O 3s orbitals, thus anion site doping can cause large perturbation on the CBM and consequently produces deeper donor levels. We also show that whether it is cation site doping or anion site doping, the oxygen-poor condition should always be used. [ABSTRACT FROM AUTHOR]

Our Raman measurement indicates that the intensity of the peaks (510 and 645 cm-1) related to nitrogen concentration is enhanced in MgZnO compared with that in ZnO. Using first-principles band structure methods, we calculated the formation energy and transition energy level for nitrogen acceptor in ZnO and random MgxZn1-xO (with x=0.25) alloy. Our calculations show that the incorporation of nitrogen can be enhanced as Mg is alloyed into ZnO, which agrees with our experiments. The acceptor energy level deeper in the alloy ascribes to the downward shift of the valence-band maximum edge in the presence of magnesium. [ABSTRACT FROM AUTHOR]

The hole-mediated Curie temperature in Mn-doped wurtzite ZnO nanowires is investigated using the k·p method and mean field model. The Curie temperature TC as a function of the hole density has many peaks for small Mn concentration (xeff) due to the density of states of one-dimensional quantum wires. The peaks of TC are merged by the carriers’ thermal distribution when xeff is large. High Curie temperature TC>400 K is found in (Zn,Mn)O nanowires. A transverse electric field changes the Curie temperature a lot. (Zn,Mn)O nanowires can be tuned from ferromagnetic to paramagnetic by a transverse electric field at room temperature. [ABSTRACT FROM AUTHOR]

The electronic structure and Zeeman splittings of wurtzite Cd1-xMnxSe quantum spheres are studied using the k·p method and mean-field model. It is interesting to find that the Zeeman splittings of some hole states in quantum spheres are highly anisotropic due to the spin-orbit coupling and wurtzite crystal structure. The anisotropy of the Zeeman splittings of hole ground states in large dots is large, while that in small dot is small because the hole ground states vary with radius. An external electrical field can change the Zeeman splitting significantly, and tune the g factor from nearly 0 to about 100. [ABSTRACT FROM AUTHOR]

The Curie temperature of diluted magnetic semiconductor (DMS) nanowires and nanoslabs is investigated using the mean-field model. The Curie temperature in DMS nanowires can be much larger than that in corresponding bulk material due to the density of states of one-dimensional quantum wires, and when only one conduction subband is filled, the Curie temperature is inversely proportional to the carrier density. The TC in DMS nanoslabs is dependent on the carrier density through the number of the occupied subbands. A transverse electric field can change the DMS nanowires from the paramagnet to ferromagnet, or vice versae. [ABSTRACT FROM AUTHOR]

The magnetic and spin transport properties of asymmetrically hydrogenated zigzag graphene nanoribbon homojunction are studied from first-principles calculations. Due to the energy gain obtained from super-exchange interaction, antiferromagnetic coupling is preferred in the homojunction, which makes it a natural not gate in logic operations. Moreover, the homojunction exhibits intrinsic spin filtering effect without the need of doping. It can serve as a spin filter for spin-unpolarized current and as a rectifier for fully spin-polarized current. These characters are related to the overlaps between the electronic states of the electrodes under different bias voltages. [ABSTRACT FROM AUTHOR]