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Resistive-switching memory with ultralow-power consumption is very promising technology for next-generation data storage and high-energy-efficiency neurosynaptic chips. Herein, Ta2O5-xbased multilevel memories with ultralow-power consumption and good data retention were achieved by simple Gd-doping. The introduction of a Gd ion, as an oxygen trapper, not only suppresses the generation of oxygen vacancy defects and greatly increases the Ta2O5-x resistance but also increases the oxygen-ion migration barrier. As a result, the memory cells can operate at an ultralow current of 1 μA with the extrapolated retention time of >10 years at 85 °C and the high switching speeds of 10 ns/40 ns for SET/RESET processes. The energy consumption of the device is as low as 60 fJ/bit, which is comparable to emerging ultralow-energy consumption (<100 fJ/bit) memory devices. [ABSTRACT FROM AUTHOR]

We demonstrated transferable and flexible resistive switching (RS) memory devices using a nondestructive water-dissolution method. To satisfy future demands, the free-standing Al/Fe3O4-PMMA/Al devices were transferred onto various nonconventional substrates to demonstrate various features, such as flexibility, 3-D conformality, and biocompatibility. Thanks to the strong van der Waals interaction, the devices can easily conform to these substrates and normally display RS behavior even after undergoing bending tests. In particular, the memory devices with the PET substrate present excellent memory performance as well as high flexibility, including fast switching speed (<50 ns), large ROFF/RON ratio (~4 x 105), and long retention time (>104 s). No performance degradation occurs after bending the device to different angles and up to 104 times. The RS mechanism can be attributed to the trapping/de-trapping of electrons at the sites of Fe3O4 nanoparticles. This result provides a feasible approach to achieve transferable RS memory device for future conformal and flexible electronics. [ABSTRACT FROM AUTHOR]

In this work, flexible and energy-efficient transparent heaters based on graphene and aligned silver nanowire (G-ASNW) hybrid structures are fabricated by thermal evaporation of silver on the aligned electrospun nanofiber templates and subsequent transfer of monolayer graphene onto the ASNWs. The G-ASNW films exhibit few wire-wire junctions and low resistance along the aligned direction, which are favorable for low-voltage transparent heater applications. Coating the ASNW network with monolayer graphene increases the saturated temperature of the hybrid heater due to the high thermal conductivity and low convective heat-transfer coefficient of graphene. Meanwhile, G-ASNW films show excellent electromechanical stability under cyclic bending because the graphene anchoring on the top surface of ASNWs could share tensile stress and serve as local conducting pathways at break-points even if small cracks were generated. The G-ASNW hybrid structures present a perspective on wearable transparent heaters. [ABSTRACT FROM AUTHOR]

Single crystal ferromagnetic Fe3Si(111) films were grown epitaxially on GaAs(111)A by molecular beam epitaxy. These hetero-structures possess extremely low surface roughness of 1.3 Å and interfacial roughness of 1.9 Å, measured by in-situ scanning tunneling microscope and X-ray reflectivity analyses, respectively, showing superior film quality, comparing to those attained on GaAs(001) in previous publications. The atomically smooth interface was revealed by the atomic-resolution Z (atomic number)-contrast scanning transmission electron microscopy (STEM) images using the correction of spherical aberration (Cs)-corrected electron probe. Excellent crystallinity and perfect lattice match were both confirmed by high resolution x-ray diffraction. Measurements of magnetic property for the Fe3Si/GaAs(111) yielded a saturation moment of 990 emu/cm³ with a small coercive field ≤1 Oe at room temperature. [ABSTRACT FROM AUTHOR]

A high-quality high-σ/Ge interface has been achieved by combining molecule beam epitaxy grown Ge epitaxial layer and in-situ deposited high j dielectric. The employment of Ge epitaxial layer has sucessfully buried and/or removed the residue of unfavorable carbon and native oxides on the chemically cleaned and ultra-high vacuum annealed Ge(100) wafer surface, as studied using angleresolved x-ray photoelectron spectroscopy. Moreover, the scanning tunneling microscopy analyses showed the significant improvements in Ge surface roughness from 3.5Å to 1Å with the epi-layer growth. Thus, chemically cleaner, atomically more ordered, and morphologically smoother Ge surfaces were obtained for the subsquent deposition of high j dielectrics, comparing with those substrates without Ge epi-layer. The capacitance-voltage (C-V) characteristics and low extracted interfacial trap density (Dit) reveal the improved high-σ/Ge interface using the Ge epi-layer approach. [ABSTRACT FROM AUTHOR]

Resistive-switching (RS) memories with good performance and flexibility are demonstrated in p-type amorphous CuAlOx. The nature of conducting filaments (CFs) is studied via the dependence of RS behaviors on the oxygen concentration of CuAlOx. It is observed that with increasing oxygen concentration, (1) both resistance-states and switching-voltages reduce, showing an opposite trend to popular n-type oxide devices; and (2) a transition from non-degenerate to degenerate states occurs in CFs. These observations indicate that the CFs are composed of Cu-vacancy shallow acceptors. The oxygen-concentration dependence of CFs' resistance results from the change of Cu-vacancy content, rather than CFs' size or number. [ABSTRACT FROM AUTHOR]

Quantum transport properties of two-dimensional electron gas (2DEG) in undoped MgxZn1-xO/ZnO heterostructures grown by metal organic vapor phase epitaxy have been investigated. A large zero-field spin-splitting energy more than 15 meV in the 2DEG is determined at 1.6 K. Meanwhile, ferromagnetism is observed in the heterostructures. The findings reveal that the 2DEG is spin polarized at zero magnetic fields. It is believed that the exchange interaction between the itinerant electrons in the two-dimensional channel and the magnetic polarons in the MgxZn1-xO barrier around the interface results in the spin polarization of the 2DEG. [ABSTRACT FROM AUTHOR]

Photoluminescence study of ZnO/Mg0.1Zn0.9O quantum wells with graded well width (Lw) was carried out at 4.2 K. The emission evolution from quantum confinement regime to quantum-confined Stark regime was observed clearly. For large Lw, the emission splits into two peaks which are attributed to the emissions of ZnO band edge and separately localized carriers, respectively. The internal electric field in the well layer was estimated to be ∼0.3 MV/cm, being similar to previous reports. The results are useful in designing ZnO QW based optoelectronic devices. [ABSTRACT FROM AUTHOR]

A densely stacked silicon nanocrystal layer embedded in a SiO2 thin film is synthesized with Si ion implantation. The dielectric functions of the nanocrystal layer are determined with spectroscopic ellipsometry. The dielectric functions show a significant suppression as compared to that of bulk crystalline Si. Thermal annealing leads to an evolution of the dielectric functions from the amorphous towards crystalline state. For an insufficient annealing, the dielectric functions present a single broad peak, being similar to that of amorphous Si. However, a sufficient annealing leads to the emergence of the two-peak structure which is similar to that of bulk crystalline Si. In addition, the dielectric functions increase with annealing with a trend towards bulk Si. [ABSTRACT FROM AUTHOR]

∼1 micron thick Cu2-xMnxO films were grown both on Au-coated and uncoated (001) Si from sulphate solutions at 60 °C, several hundred degrees lower than normally used for growth of dilute magnetic semiconductors. The Mn concentration in the films was controlled very sensitively by controlling both the ratio of Mn:Cu in solution and the deposition potential. An optimum Mn concentration of 0.3% in the films produced saturation magnetization values of 0.6 μB/Mn at room temperature. The Cu2-xMnxO films were semiconducting with resistivitity value lower than the undoped film. Photoluminscence measurements showed that Mn substitutes on the Cu lattice sites. [ABSTRACT FROM AUTHOR]

The thermal annealing effect on band gap and dielectric functions of silicon nanocrystals (nc-Si) embedded in a SiO2 matrix synthesized by Si ion implantation is investigated by spectroscopic ellipsometry. A large band-gap expansion of nc-Si relative to bulk crystalline silicon has been observed. The band gap of the nc-Si for the nonannealing condition (i.e., as implanted) is 1.78 eV while it is 1.72 eV for the annealing at 1000 °C for 100 min. The slight decrease in the band gap is attributed to the slight increase in the nc-Si size with annealing. The dielectric functions of nc-Si show a significant suppression, as compared to bulk crystalline silicon, due to the quantum size effect. Annealing results in a small change in the static dielectric constant, which can be explained in terms of the size effect also. [ABSTRACT FROM AUTHOR]

High-quality ZnO nanocrystals have been fabricated by zinc ion implantation (160 keV, 1×10[sup 17] ions/cm[sup 2]) into a CaF[sub 2](111) single-crystal substrate followed by thermal annealing from 300 to 700 °C. X-ray diffraction results show that ZnO nanocrystals in CaF[sub 2](111) substrate have a (002) preferred orientation. The average grain size is ranging from 14 to 19 nm corresponding to the annealing temperatures from 500 to 700 °C. A very strong ultraviolet near-band edge emission is observed from 372 to 379 nm. The emission intensity is enhanced and linewidth is narrowed as the annealing temperature increases. The commonly observed visible green emission associated with deep-level defects in ZnO is suppressed. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]