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24 Jan 2011

Volume 98, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 043101 (2011); http://dx.doi.org/10.1063/1.3536475 (3 pages)

Zhichao Ruan and Shanhui Fan
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Unpolarized H1 photonic crystal nanocavities fabricated by stretched lattice design

I. J. Luxmoore, E. D. Ahmadi, A. M. Fox, M. Hugues, and M. S. Skolnick

Appl. Phys. Lett. 98, 041101 (2011); http://dx.doi.org/10.1063/1.3544932 (3 pages) | Cited 4 times

Online Publication Date: 24 January 2011

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We investigate the factors that affect the mode splitting in H1 planar photonic crystal cavities and hence demonstrate unpolarized emission with a high quality factor. Finite difference time domain simulations show that systematic errors in the fabrication process such as hole shape and period lift the degeneracy of the orthogonally polarized fundamental modes. By intentionally stretching the photonic crystal lattice in one direction, we show that the wavelength and mode splitting can be tuned to compensate for such fabrication errors. By using this technique, we demonstrate unpolarized emission at 951 nm with a quality factor of ∼ 4500.
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42.70.Qs Photonic bandgap materials
42.82.Cr Fabrication techniques; lithography, pattern transfer
02.70.Bf Finite-difference methods

Thermo-optic tuning of erbium-doped amorphous silicon nitride microdisk resonators

Aaron C. Hryciw, Rohan D. Kekatpure, Selçuk Yerci, Luca Dal Negro, and Mark L. Brongersma

Appl. Phys. Lett. 98, 041102 (2011); http://dx.doi.org/10.1063/1.3545845 (3 pages) | Cited 3 times

Online Publication Date: 24 January 2011

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We demonstrate a technique to yield a direct and sensitive measurement of the thermo-optic coefficient (TOC) for light-emitting materials in optical microdisk resonators. Using photoluminescence from erbium-doped amorphous silicon nitride (a-SiNx:Er) as an example, we show how the TOC can be extracted from thermally induced shifts in the resonant microdisk modes. For the highest-performance a-SiNx:Er material composition, we find a TOC at 1.54 μm of ∼ 3×10−5 K−1 in the 300–500 K range. Additionally, our work demonstrates a convenient all-optical spectroscopic technique for sensitive temperature measurements, with a resolution of ∼ 30 mK in this temperature range.
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78.20.N- Thermo-optic effects
85.60.Jb Light-emitting devices
42.82.Et Waveguides, couplers, and arrays

Limiting performance analysis of cascaded interband/intersubband thermophotovoltaic devices

Jian Yin and Roberto Paiella

Appl. Phys. Lett. 98, 041103 (2011); http://dx.doi.org/10.1063/1.3548672 (3 pages) | Cited 1 time

Online Publication Date: 24 January 2011

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This work addresses the question of how much electrical power can in principle be extracted from heat radiation via the combined use of interband and intersubband photodetection as a way to overcome the fundamental limitations of existing thermophotovoltaic devices using mature InP-based technology. Very efficient coverage of the incident radiation spectrum and optimal current matching can be achieved using multiple quantum-cascade structures monolithically integrated with a p-n junction by taking advantage of their intrinsic cascading scheme, spectral agility, and design flexibility. Numerical simulations indicate that this approach can effectively double the present state-of-the-art in thermophotovoltaic output electrical power.
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84.60.Jt Photoelectric conversion
02.60.-x Numerical approximation and analysis

Optofluidic Fabry–Pérot cavity biosensor with integrated flow-through micro-/nanochannels

Yunbo Guo, Hao Li, Karthik Reddy, Hrishikesh S. Shelar, Vasuki R. Nittoor, and Xudong Fan

Appl. Phys. Lett. 98, 041104 (2011); http://dx.doi.org/10.1063/1.3548673 (3 pages) | Cited 10 times

Online Publication Date: 24 January 2011

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An optofluidic Fabry–Pérot cavity label-free biosensor with integrated flow-through micro-/nanochannels is proposed and demonstrated, which takes advantages of the large surface-to-volume ratio for analyte concentration and high detection sensitivity and built-in fluidic channels for rapid analyte delivery. The operating principle is first discussed, followed by assembly of a robust sensing system. Real-time measurements are performed to test its sensing feasibility and capability including bulk solvent change and removal/binding of molecules from/onto the internal surface of fluidic channels. The results show that this sensor provides a very promising platform for rapid, sensitive, and high-throughput biological and chemical sensing.
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87.80.Ek Mechanical and micromechanical techniques
87.85.Rs Nanotechnologies-applications
87.85.gf Fluid mechanics and rheology
87.15.hj Transport dynamics

Influence of pulse duration, energy, and focusing on laser-assisted water condensation

Y. Petit, S. Henin, J. Kasparian, J. P. Wolf, P. Rohwetter, K. Stelmaszczyk, Z. Q. Hao, W. M. Nakaema, L. Wöste, A. Vogel, T. Pohl, and K. Weber

Appl. Phys. Lett. 98, 041105 (2011); http://dx.doi.org/10.1063/1.3546172 (3 pages) | Cited 6 times

Online Publication Date: 26 January 2011

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We investigate the influence of laser parameters on laser-assisted water condensation in the atmosphere. Pulse energy is the most critical parameter. Nanoparticle generation depends linearly on energy beyond the filamentation threshold. Shorter pulses are more efficient than longer ones with saturation at ∼ 1.5 ps. Multifilamenting beams appear more efficient than strongly focused ones in triggering the condensation and growth of submicronic particles, while polarization has a negligible influence on the process. The data suggest that the initiation of laser-assisted condensation relies on the photodissociation of the air molecules rather than on their photoionization.
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42.62.-b Laser applications
68.03.Fg Evaporation and condensation of liquids
82.50.Hp Processes caused by visible and UV light

Observation of anisotropically reflected colors in chiral monomer-doped cholesteric liquid crystals

Cheng-Kai Liu, Ko-Ting Cheng, and Andy Ying-Guey Fuh

Appl. Phys. Lett. 98, 041106 (2011); http://dx.doi.org/10.1063/1.3545848 (3 pages) | Cited 1 time

Online Publication Date: 27 January 2011

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Observations of the anisotropically reflected colors from a film that is based on chiral monomer-doped cholesteric liquid crystals (CM-CLCs) are made. The key to obtaining such anisotropically reflected colors is the produced multidomain planar-CLCs structures, which can simultaneously reflect and scatter the incident light. UV polymerization of the CMs from one side of the cell results in an inhomogeneous distribution of pitch lengths across the cell, which is responsible for the anisotropically reflected colors from the two surfaces of the sample. Furthermore, the reflectivity and the bandwidth of the reflection spectrum depend on the cell gap.
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78.66.Qn Polymers; organic compounds
78.30.C- Liquids
68.15.+e Liquid thin films
61.30.-v Liquid crystals
78.40.Dw Liquids

ZnO homojunction photodiodes based on Sb-doped p-type nanowire array and n-type film for ultraviolet detection

Guoping Wang, Sheng Chu, Ning Zhan, Yuqing Lin, Leonid Chernyak, and Jianlin Liu

Appl. Phys. Lett. 98, 041107 (2011); http://dx.doi.org/10.1063/1.3551628 (3 pages) | Cited 12 times

Online Publication Date: 28 January 2011

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ZnO p-n homojunctions based on Sb-doped p-type nanowire array and n-type film were grown by combining chemical vapor deposition (for nanowires) with molecular-beam epitaxy (for film). Indium tin oxide and Ti/Au were used as contacts to the ZnO nanowires and film, respectively. Characteristics of field-effect transistors using ZnO nanowires as channels indicate p-type conductivity of the nanowires. Electron beam induced current profiling confirmed the existence of ZnO p-n homojunction. Rectifying I-V characteristic showed a turn-on voltage of around 3 V. Very good response to ultraviolet light illumination was observed from photocurrent measurements.
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81.05.Dz II-VI semiconductors
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.07.Gf Nanowires
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Radial elasticity of single-walled carbon nanotube measured by atomic force microscopy

Y. H. Yang and W. Z. Li

Appl. Phys. Lett. 98, 041901 (2011); http://dx.doi.org/10.1063/1.3546170 (3 pages) | Cited 6 times

Online Publication Date: 24 January 2011

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Effective radial modulus (Eradial) of straight single-walled carbon nanotubes (SWCNTs) grown directly on quartz substrate have been measured by using well-calibrated tapping mode and contact mode atomic force microscopies. It is found that the measured Eradial decreases from 57 to 9 GPa as the diameter of the SWCNTs increases from 0.92 to 1.91 nm. The current experimental results are consistent with the recently reported simulation data in both the data pattern and values. The method used in this research can also be applied to measure the mechanical properties of other low-dimension nanostructures, such as nanowires and nanodots.
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81.07.De Nanotubes
81.16.-c Methods of micro- and nanofabrication and processing
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dj Poisson's ratio

Influence of ultrathin amorphous silicon layers on the nucleation of microcrystalline silicon films under hydrogen plasma treatment

Z. W. Zuo, W. T. Guan, Y. Wang, J. Lu, J. Z. Wang, L. Pu, Y. Shi, Y. D. Zheng, X. Y. Luo, and H. H. Wang

Appl. Phys. Lett. 98, 041902 (2011); http://dx.doi.org/10.1063/1.3548674 (3 pages) | Cited 1 time

Online Publication Date: 24 January 2011

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Microstructures of phosphorus-doped hydrogenated microcrystalline silicon (μc-Si:H) thin films deposited by plasma-enhanced chemical vapor deposition are certainly dependent on the thickness of the H2 plasma-treated amorphous silicon (a-Si:H) layers. An ultrathin H-treated a-Si:H layer is beneficial in obtaining a very thin μc-Si:H film with high conductivity. Experimental results indicate that H2 plasma treatment induces the occurrence of high-pressure H2 in microvoids and causes compressive stress inside the ultrathin a-Si:H layers, thereby enhancing the generation of strained Si–Si bonds and nucleation sites and consequently accelerating the nucleation of μc-Si:H films.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Misfit relaxation of La0.7Sr0.3MnO3 thin films by a nanodot segregation mechanism

P. Abellán, C. Moreno, F. Sandiumenge, X. Obradors, and M.-J. Casanove

Appl. Phys. Lett. 98, 041903 (2011); http://dx.doi.org/10.1063/1.3549182 (3 pages) | Cited 3 times

Online Publication Date: 25 January 2011

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Partially segregated La0.7Sr0.3MnO3 (LSMO) nanocomposite films are shown to exhibit a thickness dependent self-assembled structure. The morphological evolution of the nanocomposite and the misfit strain of the LSMO phase are linked through the topological distribution of La–Sr oxide nanodots within the film. Misfit relaxation occurs above a critical thickness, hc, coinciding with the nucleation of La–Sr oxide nanodots at the film-substrate interface. Below hc, the same dots outcrop the film surface, forming islands. As a consequence of this misfit relaxation mechanism, an enhancement in the magnetoresistance with increasing thickness is measured.
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81.16.Dn Self-assembly
75.47.Pq Other materials
68.35.Dv Composition, segregation; defects and impurities
68.37.Og High-resolution transmission electron microscopy (HRTEM)

Defect dynamics and spectral observation of twinning in single crystalline LaAlO3 under subbandgap excitation

J. Q. Chen, X. Wang, Y. H. Lu, A. Roy Barman, G. J. You, G. C. Xing, T. C. Sum, S. Dhar, Y. P. Feng, Ariando, Q.-H. Xu, and T. Venkatesan

Appl. Phys. Lett. 98, 041904 (2011); http://dx.doi.org/10.1063/1.3543840 (3 pages) | Cited 2 times

Online Publication Date: 25 January 2011

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We have investigated the photoluminescence and ultrafast dynamics of LaAlO3 crystal. The photoluminescence consists of a broad spectrum and two sharp peaks, which arise from various defect levels within the bandgap. A doublet splitting of roughly 6 nm is seen in these two sharp peaks. An Al displacement of 0.09 Å in a sublattice, which is possible because of twinning, is adequate to explain the spectral splitting. Femtosecond pump probe experiments reveal further that many of these defect levels have a few picosecond decay times while the lowest defect states have decay times longer than nanosecond to the valence band.
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78.55.Hx Other solid inorganic materials
71.20.Ps Other inorganic compounds
71.55.Ht Other nonmetals
61.72.Mm Grain and twin boundaries
78.47.J- Ultrafast spectroscopy (<1 psec)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Second harmonic generation probing of dopant type and density at the Si/SiO2 interface

Julie L. Fiore, Vasiliy V. Fomenko, Dora Bodlaki, and Eric Borguet

Appl. Phys. Lett. 98, 041905 (2011); http://dx.doi.org/10.1063/1.3505356 (3 pages) | Cited 3 times

Online Publication Date: 25 January 2011

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Time-dependent second-harmonic generation (TD-SHG) is shown to be a sensitive, noncontact probe of dopant type and concentration at Si/SiO2 interfaces. TD-SHG signal magnitude increases for n-Si(111)/SiO2, while for p-Si(111)/SiO2 TD-SHG is nonmonotonic. This behavior is interpreted as a consequence of SHG sensitivity to electric fields induced by interfacial charge transfer and trapping.
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78.20.Jq Electro-optical effects
61.72.up Other materials

Hole-channel conductivity in epitaxial graphene determined by terahertz optical-Hall effect and midinfrared ellipsometry

T. Hofmann, A. Boosalis, P. Kühne, C. M. Herzinger, J. A. Woollam, D. K. Gaskill, J. L. Tedesco, and M. Schubert

Appl. Phys. Lett. 98, 041906 (2011); http://dx.doi.org/10.1063/1.3548543 (3 pages) | Cited 12 times

Online Publication Date: 25 January 2011

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We report noncontact, optical determination of free-charge carrier mobility, sheet density, and resistivity parameters in epitaxial graphene at room temperature using terahertz and midinfrared ellipsometry and optical-Hall effect measurements. The graphene layers are grown on Si- and C-terminated semi-insulating 6H silicon carbide polar surfaces. Data analysis using classical Drude functions and multilayer modeling render the existence of a p-type channel with different sheet densities and effective mass parameters for the two polar surfaces. The optically obtained parameters are in excellent agreement with results from electrical Hall effect measurements.
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72.80.Vp Electronic transport in graphene
73.61.Wp Fullerenes and related materials
72.20.My Galvanomagnetic and other magnetotransport effects

Continuously voltage-tunable electroluminescence from a monolayer of ZnS quantum dots

Rong-Wei Xuan (宣荣卫), Jian-Ping Xu (徐建萍), Xiao-Song Zhang (张晓松), Ping Li (李萍), Cheng-Yuan Luo (罗程远), Yan-Yu Wu (吴燕宇), and Lan Li (李岚)

Appl. Phys. Lett. 98, 041907 (2011); http://dx.doi.org/10.1063/1.3544570 (3 pages) | Cited 4 times

Online Publication Date: 26 January 2011

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A monolayer electroluminescence (EL) device with ZnS quantum dots (QDs) as emitting layer was fabricated by spin-coating technique. Continuously tunable EL spectra from ZnS QDs are observed at room temperature. By increasing excitation voltage, the EL spectra can be tuned from yellow green (560 nm) to blue (470 nm), corresponding to chromaticity coordinates from (0.45, 0.52) to (0.22, 0.26). In order to understand the mechanism of the device, the dependences of the photoluminescence of the ZnS QDs on temperature, excitation energy, and particle size have been studied, respectively, which indicates that the possible mechanisms of tunable EL spectra are related to selective excitation of QDs with different particle sizes.
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78.60.Fi Electroluminescence
78.55.Et II-VI semiconductors
78.67.Hc Quantum dots
64.75.Jk Phase separation and segregation in nanoscale systems
81.05.Dz II-VI semiconductors

Realization of freestanding wrinkled thin films with flexible deformability

Tomohiro Maruyama, Hiroyuki Hirakata, Akio Yonezu, and Kohji Minoshima

Appl. Phys. Lett. 98, 041908 (2011); http://dx.doi.org/10.1063/1.3549203 (3 pages) | Cited 1 time

Online Publication Date: 26 January 2011

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We propose a technique for producing freestanding films having a wrinkled structure. In an experiment, we discovered that a wrinkle pattern can be made on the surface of a sacrificial resin layer by applying compressive strain under the appropriate conditions. Using this phenomenon, we made a freestanding wrinkled film by depositing a film on the wrinkled resin surface and then removing the resin layer with an organic solvent. Uniaxial tensile tests for 300 nm thick freestanding copper wrinkled films revealed that the films have superior deformability: the fracture elongation is more than ten times larger than that of its straight film counterpart.
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81.40.Lm Deformation, plasticity, and creep
62.20.mm Fracture
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.60.Bs Mechanical and acoustical properties
81.70.Bt Mechanical testing, impact tests, static and dynamic loads
62.20.F- Deformation and plasticity

Strain dependence of thermal conductivity of [0001]-oriented GaN nanowires

Kwangsub Jung, Maenghyo Cho, and Min Zhou

Appl. Phys. Lett. 98, 041909 (2011); http://dx.doi.org/10.1063/1.3549691 (3 pages) | Cited 4 times

Online Publication Date: 28 January 2011

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The thermomechanical behavior of [0001]-oriented GaN nanowires with 2.26 and 3.55 nm in diameter under tensile loading is analyzed using molecular dynamics simulations with the Green–Kubo method and quantum correction. A phase transformation from wurtzite to a tetragonal structure is observed. The thermal conductivity is found to decrease as the wires undergo tensile deformation and phase transformation, except for the smallest diameter and temperatures above 1495 K at which it remains largely constant as the axial strain increases. The different trends appear to result from phonon behavior changes primarily associated with the surface structures of the nanowires at the different conditions.
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66.70.Df Metals, alloys, and semiconductors
81.40.Lm Deformation, plasticity, and creep
64.70.Nd Structural transitions in nanoscale materials
64.70.kg Semiconductors
68.65.La Quantum wires (patterned in quantum wells)
63.22.Gh Nanotubes and nanowires

Thickness dependence of the integrated Bragg intensity for statistically disturbed silicon crystals

J. Will, A. Gröschel, M. Weißer, and A. Magerl

Appl. Phys. Lett. 98, 041910 (2011); http://dx.doi.org/10.1063/1.3531761 (3 pages) | Cited 1 time

Online Publication Date: 28 January 2011

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The thickness dependence of the integrated Bragg intensities for Czochralski-grown silicon was measured with the characteristic tungsten Kα1-line at 59.3 keV. In contrast to previous experiments the sample is wedge shaped, which allows to take data over a wide range of Pendellösung fringes in one exposure only and without any mechanical movement of the sample. The period length, the oscillation amplitude, and the mean value of the Bragg intensity can be explored to identify the presence of point defects, and the temperature dependence of the period length allows to quantify the thermal Debye-coefficient with high precision.
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61.72.J- Point defects and defect clusters
61.66.Bi Elemental solids
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
81.10.Fq Growth from melts; zone melting and refining
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Single-crystalline (100) Ge networks on insulators by rapid-melting growth along hexagonal mesh-pattern

Kaoru Toko, Yasuharu Ohta, Takashi Sakane, Taizoh Sadoh, Ichiro Mizushima, and Masanobu Miyao

Appl. Phys. Lett. 98, 042101 (2011); http://dx.doi.org/10.1063/1.3544057 (3 pages) | Cited 5 times

Online Publication Date: 24 January 2011

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Single-crystalline-Ge (c-Ge) networks on insulator films formed on Si substrates are essential for integrating high-speed and multifunctional devices onto the Si-platform. Rapid-melting-growth of mesh-patterned amorphous-Ge is examined over large areas (500×250 μm2). For squared-mesh-pattern, polycrystalline-Ge forms throughout most of the mesh, though c-Ge is obtained near (<100 μm) Si-seed. Based on the consideration of geometric-effects, mesh-patterns are changed to hexagonal. This realizes c-Ge networks over the entire insulator area. These results indicate that Ge growth initiated from Si-seed propagates laterally over the hexagonal-mesh-pattern though bending and branching. These unique c-Ge-networks on insulators facilitate Ge-based advanced-devices on the Si-platform.
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81.10.Fq Growth from melts; zone melting and refining
81.05.Cy Elemental semiconductors
64.70.dj Melting of specific substances
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Effect of vacancy-type oxygen deficiency on electronic structure in amorphous alumina

Hiroyoshi Momida, Seisuke Nigo, Giyuu Kido, and Takahisa Ohno

Appl. Phys. Lett. 98, 042102 (2011); http://dx.doi.org/10.1063/1.3548549 (3 pages) | Cited 1 time

Online Publication Date: 24 January 2011

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Electronic and atomic structures associated with a vacancy-type oxygen deficiency in an amorphous alumina model are studied by first-principles calculations. The energy levels of the oxygen defects significantly shift depending on their charge states because of remarkable changes of local atomic structures. That is different in character from the α crystal case. We discuss a possibility of the oxygen defects as a conductive path and present an atomistic mechanism of the resistive switching effects in the memory devices.
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71.23.Cq Amorphous semiconductors, metallic glasses, glasses
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.jd Vacancies

Top-down fabrication of AlGaN/GaN nanoribbons

M. Azize and T. Palacios

Appl. Phys. Lett. 98, 042103 (2011); http://dx.doi.org/10.1063/1.3544048 (3 pages) | Cited 2 times

Online Publication Date: 25 January 2011

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Lateral AlGaN/GaN nanoribbons (NRs) have been fabricated through a top-down technology on planar AlGaN/GaN samples grown on a silicon substrate. Electron-beam lithography and Cl2-based dry etching were used to define the NRs with widths in the 70–145 nm range. The electrical and structural properties of the AlGaN/GaN NRs have been measured and compared to standard planar structures fabricated on the same chip. External mechanical stress and adequate surface passivation have an important effect on the NR’s performance. A 50% improvement in the current density of SixNy passivated AlGaN/GaN NRs was obtained with respect to planar samples.
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81.16.Nd Micro- and nanolithography
61.46.-w Structure of nanoscale materials
81.65.Rv Passivation
85.30.Tv Field effect devices
72.80.Ey III-V and II-VI semiconductors
73.61.Ey III-V semiconductors

Mg doped InN and confirmation of free holes in InN

K. Wang, N. Miller, R. Iwamoto, T. Yamaguchi, M. A. Mayer, T. Araki, Y. Nanishi, K. M. Yu, E. E. Haller, W. Walukiewicz, and J. W. Ager, III

Appl. Phys. Lett. 98, 042104 (2011); http://dx.doi.org/10.1063/1.3543625 (3 pages) | Cited 16 times

Online Publication Date: 25 January 2011

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We report a systematic investigation on Mg doped InN epilayers grown by radio-frequency plasma-assisted molecular beam epitaxy. Electrolyte capacitance voltage (ECV) combined with thermopower measurements find p-type conduction over an Mg concentration range. For InN:Mg in this p-type “window” the Seebeck coefficients dramatically change their signs from negative to positive when the thickness of undoped InN interlayer decreases to zero. This notable sign change of Seebeck coefficient explains the previous inconsistency between ECV and thermopower results and confirms the existence of mobile holes in the InN:Mg. Taking into account the undoped InN interlayer, the hole density and mobility are extracted.
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73.61.Ey III-V semiconductors
73.50.Lw Thermoelectric effects
72.20.Pa Thermoelectric and thermomagnetic effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.50.Dn Low-field transport and mobility; piezoresistance
72.20.Fr Low-field transport and mobility; piezoresistance

Gd-doping effect on performance of HfO2 based resistive switching memory devices using implantation approach

Haowei Zhang, Lifeng Liu, Bin Gao, Yuanjun Qiu, Xiaoyan Liu, Jing Lu, Ruqi Han, Jinfeng Kang, and Bin Yu

Appl. Phys. Lett. 98, 042105 (2011); http://dx.doi.org/10.1063/1.3543837 (3 pages) | Cited 16 times

Online Publication Date: 25 January 2011

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An implantation doping approach is implemented to fabricate Gd-doped HfO2 resistive random access memory (RRAM) devices. The significantly enhanced performances are achieved in the Gd-doped HfO2 RRAM devices including improved uniformity of switching parameters, enlarged ON/OFF ratio, and increased switching speed without obvious reliability degradation. This performance improvement in the Gd-doped HfO2 RRAM devices is clarified to the suppressed randomicity of oxygen vacancy filaments’ formation and the reduced oxygen ion migration barrier induced by trivalent Gd-doping effect. The achieved results also demonstrate the validity of implantation doping approach for the fabrication of RRAM devices.
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84.30.Sk Pulse and digital circuits

Niobium substitution in Zr0.5Hf0.5NiSn based Heusler compounds for high power factors

Michael Schwall and Benjamin Balke

Appl. Phys. Lett. 98, 042106 (2011); http://dx.doi.org/10.1063/1.3548867 (3 pages) | Cited 6 times

Online Publication Date: 26 January 2011

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This work reports on the structural and physical properties of the Heusler alloy (Zr0.5Hf0.5)1−xNbxNiSn with varying Nb concentrations. The structure of the (Zr0.5Hf0.5)1−xNbxNiSn solid solution was investigated by means of X-ray diffraction. It is found that the alloys exhibit the C1b structure for all Nb concentrations. The physical properties were studied using the physical properties measurement system from low temperature to room temperature. It was shown that the thermoelectric properties like the dimensionless Figure of Merit are increased five times by substituting (Zr0.5Hf0.5) with Nb to 0.09 at 300 K and the Powerfactor is increased 10 times to 1.8 mW/K2 m at 300 K.
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72.15.Jf Thermoelectric and thermomagnetic effects
61.50.-f Structure of bulk crystals

Subgap optical conductivity in semihydrogenated graphene

Yee Sin Ang and C. Zhang

Appl. Phys. Lett. 98, 042107 (2011); http://dx.doi.org/10.1063/1.3549201 (3 pages) | Cited 2 times

Online Publication Date: 27 January 2011

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We report that for graphene with a finite band gap (such as semihydrogenated graphene or graphene with spin-orbit coupling), there exists a strong nonlinear optical response for energies lower than the band gap where the linear response is forbidden. At low temperatures, the nonlinear current in graphene with a gap is much stronger than that in gapless graphene. Our result suggests that semihydrogenated graphene can have a unique potential as a two-color nonlinear material in the terahertz frequency region. The relative intensity of the two colors can be tuned with the electric field.
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81.05.ue Graphene
78.67.Wj Optical properties of graphene
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.22.Pr Electronic structure of graphene

Ohmic contact properties of magnetron sputtered Ti3SiC2 on n- and p-type 4H-silicon carbide

K. Buchholt, R. Ghandi, M. Domeij, C.-M. Zetterling, J. Lu, P. Eklund, L. Hultman, and A. Lloyd Spetz

Appl. Phys. Lett. 98, 042108 (2011); http://dx.doi.org/10.1063/1.3549198 (3 pages) | Cited 7 times

Online Publication Date: 28 January 2011

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Epitaxial Ti3SiC2 (0001) thin film contacts were grown on doped 4H-SiC (0001) using magnetron sputtering in an ultra high vacuum system. The specific contact resistance was investigated using linear transmission line measurements. Rapid thermal annealing at 950 °C for 1 min of as-deposited films yielded ohmic contacts to n-type SiC with contact resistances in the order of 10−4 Ω cm2. Transmission electron microscopy shows that the interface between Ti3SiC2 and n-type SiC is atomically sharp with evidence of interfacial ordering after annealing.
Show PACS
68.55.ag Semiconductors
68.55.-a Thin film structure and morphology
81.15.Aa Theory and models of film growth
61.72.Cc Kinetics of defect formation and annealing
68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering
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