In-situ real-space imaging of single crystal surface reconstructions via electron microscopy
Here, we report a high temperaturein-situ atomic resolution scanning transmission electron microscopy (STEM) study ofsingle crystalsurface structuredynamics. With the approach, we gain direct insight into adouble layerreconstruction that occurs on the polar SrTiO3 (110)surface. We find thatstructural details of thisreconstruction can be directly attributed to charge redistribution and the thermal mismatch between thesurface and the bulk material. Periodicsurface defects, similar todislocations, are found, which act to relieve stress as the temperature is lowered. Combining STEM observations,electron energy loss spectroscop...
Source: Applied Physics Letters - November 15, 2016 Category: Physics Authors: Weizong Xu, Preston C. Bowes, Everett D. Grimley, Douglas L. Irving and James M. LeBeau Source Type: research
Sub-milliwatt AlGaN nanowire tunnel junction deep ultraviolet light emitting diodes on silicon operating at 242 nm
We reportAlGaNnanowirelight emitting diodes(LEDs) operating in the ultraviolet-C band. TheLED structures are grown by molecular beam epitaxy on Si substrate. It is found that with the use of then+-GaN/Al/p+-AlGaN tunnel junction (TJ), the device resistance is reduced by one order of magnitude, and the light output power is increased by two orders of magnitude, compared toAlGaNnanowireLEDs without TJ. For unpackaged TJultravioletLEDs emitting at 242 nm, a maximum output power of 0.37 mW ismeasured, with a peak external quantum efficiency up to 0.012%. (Source: Applied Physics Letters)
Source: Applied Physics Letters - November 15, 2016 Category: Physics Authors: S. Zhao, S. M. Sadaf, S. Vanka, Y. Wang, R. Rashid and Z. Mi Source Type: research
Performance of a large-scale barrier discharge plume improved by an upstream auxiliary barrier discharge
Enhanced by an upstream auxiliarydielectric barrier discharge (ADBD), a transverse barrierdischarge plume with a fairly large scale is generated downstream of a narrow slit. Electrical and optical characteristics are compared for the twodischarges with and without the ADBD. Results indicate that the plume with the ADBD is longer, more uniform, and dissipates a higher power. Moreover, its inception voltage is much lower. High-speedimaging presents that the uniformplasma plume with the ADBD comprises a series of moving micro-discharge filaments in aglow regime, which are much smoother than those without the ADBD. (Source: Ap...
Source: Applied Physics Letters - November 14, 2016 Category: Physics Authors: Xuechen Li, Jingdi Chu, Qi Zhang, Panpan Zhang, Pengying Jia and Jinling Geng Source Type: research
Surface smoothing during plasma etching of Si in Cl2
Effects of initial roughness on the evolution of plasma-inducedsurface roughness have been investigated during Sietching in inductively coupled Cl2plasmas, as a function of rf bias power or ion incident energy in the rangeEi ≈ 20–500 eV. Experiments showed that smoothing of initiallyrough surfaces as well as non-roughening of initially planarsurfaces can be achieved byplasma etching in the smoothing mode (at highEi) with some threshold for the initial roughness, above which laterally extended crater-like features were observed to evolve during smoothing. Monte Carlo simulations of thesurface feature evolution indic...
Source: Applied Physics Letters - November 14, 2016 Category: Physics Authors: Nobuya Nakazaki, Haruka Matsumoto, Hirotaka Tsuda, Yoshinori Takao, Koji Eriguchi and Kouichi Ono Source Type: research
Vibration energy harvester with low resonant frequency based on flexible coil and liquid spring
This paper reports an electromagnetic vibration-energy harvester with lowresonant frequency based onliquid spring composed offerrofluid. Cylindermagnet array formed by four disc NdFeBmagnets is suspended byferrofluid in a laser-machined acrylic tube which is wrapped by flexible planarcoil fabricated with microfabrication process. Themagnet array andcoil are aligned automatically by theferrofluid. Restoring force when themagnet array is deviated from the balance position is proportional to the deviated distance, which makes theferrofluid work as aliquid spring obeying Hook's law. Experimental results show that the electroma...
Source: Applied Physics Letters - November 14, 2016 Category: Physics Authors: Y. Wang, Q. Zhang, L. Zhao, Y. Tang, A. Shkel and E. S. Kim Source Type: research
Enhanced visible photoelectrochemical properties of ZnO/CdS core/shell nanorods and their correlation with improved optical properties
ZnO/CdS core/shellnanorods (NRs) constructed ofZnO NR cores andCdS coating shells were fabricated by hydrothermally growingZnO NRs and pulsed laser depositingCdS coatings on the grownZnO NRs. The fabricated ZnO/CdS NRs were characterized by field-emission scanning electron microscopy,transmission electron microscopy, selected-area electron diffraction,X-ray diffraction, and Raman backsattering spectroscopy. The optical and photoelectrochemicalproperties were evaluated and their correlation was studied. TheZnO cores andCdS shells are both in a hexagonal wurtzite structure withc-axis orientation. Compared with the bareZnO NR...
Source: Applied Physics Letters - November 14, 2016 Category: Physics Authors: Xu Yang, Hui Li, Wu Zhang, Mingxuan Sun, Lequn Li, Ning Xu, Jiada Wu and Jian Sun Source Type: research
Realization of low power-laser induced thermionic emission from Ag nanoparticle-decorated CNT forest: A consequence of surface plasmon resonance
Enhancement ofelectron emission fromAgnanoparticle-decoratedcarbon nanotube(CNT) forest, using low power-lasers, is reported in this work. Realization ofthermionic emission fromCNTs using the low power laser can be achievable when theCNT forest is illuminated by a narrowlaser beam which leads to localized heating of theCNT forest surface. For this purpose,CNT forest was decorated withAgnanoparticles.Surface plasmon resonance ofAgnano-particles led to intense local electric field which is responsible for localized heating andthermionic emission fromCNTs. Enhancement of emission current fromCNTs depends on the wavelength of ...
Source: Applied Physics Letters - November 14, 2016 Category: Physics Authors: Mahta Monshipouri, Yaser Abdi and Sara Darbari Source Type: research
Field-effect transistors of high-mobility few-layer SnSe2
We report the transport properties of mechanically exfoliated few-layer SnSe2 flakes, whosemobility is found to be ∼85 cm2 V−1 s−1 at 300 K, higher than those of the majority of few-layer transitional metal dichalcogenides. Themobility increases strongly with decreasedtemperature, indicating aphonon limited transport. The conductivity of the semiconducting SnSe2 shows a metallic behavior, which is explained by two competing factors involving the differenttemperature dependence ofmobility andcarrier density. TheFermi level is found to be 87 meV below the conduction band minima (CBM) at 300 K and 12 meV...
Source: Applied Physics Letters - November 14, 2016 Category: Physics Authors: Chenglei Guo, Zhen Tian, Yanjun Xiao, Qixi Mi and Jiamin Xue Source Type: research
Defect formation in GaAs/GaNxAs1-x core/shell nanowires
Photoluminescence andoptically detected magnetic resonance(ODMR) spectroscopies are used to investigate the formation and role of defects in GaAs/GaNxAs1-x core/shell nanowires (NWs) grown by molecular beam epitaxy on Si substrates.Galliumvacancies, which act as non-radiative recombination (NRR) centers, are identified byODMR. It is shown that the defects are formed in bulk regions, i.e., not on the surface, of the GaNAs shell and that their concentration increases with increasing nitrogen content. Temperature dependentphotoluminescence experiments reveal, on the other hand, suppressed thermal quenching of the near-band-ed...
Source: Applied Physics Letters - November 14, 2016 Category: Physics Authors: J. E. Stehr, S. L. Chen, M. Jansson, F. Ishikawa, W. M. Chen and I. A. Buyanova Source Type: research
Decoupling and ordering of multilayer graphene on C-face 3C-SiC(111)
We show experimentally that few layergraphene (FLG) grown on the carbon terminated surface (C-face) of 3C-SiC(111) is composed of decoupledgraphene sheets.Landau levelspectroscopy on FLGgraphene is performed using the infrared optical Hall effect. We find thatLandau level transitions in the FLG exhibitpolarization preserving selection rules and the transition energies obey a square-root dependence on themagnetic field strength. These results show that FLG on C-face 3C-SiC(111) behave effectively as a single layergraphene with linearly dispersing bands (Dirac cones) at thegraphene K point. We estimate from theLandau levelsp...
Source: Applied Physics Letters - November 14, 2016 Category: Physics Authors: C. Bouhafs, V. Stanishev, A. A. Zakharov, T. Hofmann, P. K ühne, T. Iakimov, R. Yakimova, M. Schubert and V. Darakchieva Source Type: research
Quantum point contacts and resistive switching in Ni/NiO nanowire junctions
Metal oxide devices that exhibitresistive switching are leading candidates for non-volatile memory applications due to their potential for fast switching, low-power operation, and high device density. It is widely accepted in many systems that two-stateresistive behavior arises from the formation and rupture of conductive filaments spanning the oxide layer. However, means for controlling the filament geometry, which critically influences conduction, have largely been unexamined. Here, we explore the connection between filament geometry and conductance in amodelresistive switching system based on thejunction of two nickel/n...
Source: Applied Physics Letters - November 14, 2016 Category: Physics Authors: Sean M. Oliver, Jessamyn A. Fairfield, Allen T. Bellew, Sunghun Lee, James G. Champlain, Laura B. Ruppalt, John J. Boland and Patrick M. Vora Source Type: research
Effect of cooling rate on phase transitions and ferroelectric properties in 0.75BiFeO3-0.25BaTiO3 ceramics
The effect of the cooling rate on the electrical properties was investigated in the 0.75BiFeO3-0.25BaTiO3ceramics. The air-quenched samples had superiorferroelectric andpiezoelectric properties to the slowly cooled samples. Thequenching effect weakened when thequenching temperature was less than 700 °C and eventually disappeared at 500 °C and below. TheX-ray diffraction and transmission electron microscopy showed that the cooling rate had a significant effect on thecrystal structure and domainstructure. The slowly cooled sample showed a very small rhombohedral distortion and a poorly developed domainstructure, which...
Source: Applied Physics Letters - November 14, 2016 Category: Physics Authors: Dae Su Kim, Chae Il Cheon, Seong Su Lee and Jeong Seog Kim Source Type: research
Electrical characteristics and conduction mechanisms of amorphous subnanometric Al2O3 –TiO2 laminate dielectrics deposited by atomic layer deposition
Electric conduction mechanisms ofamorphous Al2O3/TiO2 (ATO)-laminates deposited by atomic layer deposition with sub-nanometer individual layer thicknesses were studied in a large temperature range. Two characteristic field regions are identified. In the low field region (E ≤ 0.31 MV/cm), theleakage current is dominated by the trap-assistedtunneling through oxygenvacancies occurring in the TiO2, while in the highelectric field region (E > 0.31 MV/cm) the Poole Frenkel (PF) hopping is the appropriate conduction process with energy levels depending on the temperature and theelectric field. It is shown that the PF po...
Source: Applied Physics Letters - November 14, 2016 Category: Physics Authors: Abdelkader Kahouli, Oleg Lebedev, Vu Hung Dao, Marwa Ben Elbahri, Wilfrid Prellier and Ulrike L üders Source Type: research
Intrinsic spin dynamics in optically excited nanoscale magnetic tunnel junction arrays restored by dielectric coating
We report the all-optical observation of intrinsic spindynamics and extraction of magnetic material parameters from arrays of sub-100 nm spin-transfer torque magnetic random access memory (STT-MRAM) devices with a CoFeB/MgO interface. To this end, the interference ofsurface acoustic waves with time-resolved magneto-optic signals via magneto-elastic coupling was suppressed using adielectric coating. The efficacy of this method is demonstrated experimentally and via modeling on anickelnanomagnet array. Themagnetization dynamics for both coatednickel and STT-MRAM arrays shows a restored field-dependent Kittel mode from whi...
Source: Applied Physics Letters - November 14, 2016 Category: Physics Authors: M. Jaris, Y. Yahagi, B. K. Mahato, S. Dhuey, S. Cabrini, V. Nikitin, J. Stout, A. R. Hawkins and H. Schmidt Source Type: research
Scalable synchronization of spin-Hall oscillators in out-of-plane field
A strategy for a scalablesynchronization of an array of spin-Halloscillators (SHOs) is illustrated. In detail, we present themicromagnetic simulations of two and five SHOs realized by means of couples of triangular golden contacts on the top of a Pt/CoFeB/Ta trilayer. The results highlight that thesynchronization occurs for the whole current region that gives rise to the excitation of self-oscillations. This is linked to the role of the magnetodipolar coupling, which is the phenomenon driving thesynchronization when the distance betweenoscillators is not too large.Synchronization also turns out to be robust against geometr...
Source: Applied Physics Letters - November 14, 2016 Category: Physics Authors: V. Puliafito, A. Giordano, A. Laudani, F. Garesc ì, M. Carpentieri, B. Azzerboni and G. Finocchio Source Type: research
