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11 Jan 2010

Volume 96, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 96, 021101 (2010); http://dx.doi.org/10.1063/1.3290633 (3 pages)

Ahmet Ali Yanik, Min Huang, Alp Artar, Tsung-Yao Chang, and Hatice Altug
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Integrated nanoplasmonic-nanofluidic biosensors with targeted delivery of analytes

Ahmet Ali Yanik, Min Huang, Alp Artar, Tsung-Yao Chang, and Hatice Altug

Appl. Phys. Lett. 96, 021101 (2010); http://dx.doi.org/10.1063/1.3290633 (3 pages) | Cited 35 times

Online Publication Date: 11 January 2010

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Performances of the biosensors are often limited by the depletion zones created around the sensing area which impede the effective analyte transport. To overcome this limitation, we propose and demonstrate a nanoplasmonic-nanofluidic sensor enabling targeted delivery of analytes to the sensor surface with dramatic improvements in mass transport efficiency. Our sensing platform is based on extraordinary light transmission effect in suspended plasmonic nanoholes. This scheme allows three-dimensional control of the fluidic flow by connecting separate layers of microfluidic channels through plasmonic/nanofluidic holes. To implement the proposed sensor platform, we also introduce a lift-off free nanofabrication method.
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87.80.-y Biophysical techniques (research methods)
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)

Ultrafast insulator-to-metal phase transition as a switch to measure the spectrogram of a supercontinuum light pulse

Federico Cilento, Claudio Giannetti, Gabriele Ferrini, Stefano Dal Conte, Tommaso Sala, Giacomo Coslovich, Matteo Rini, Andrea Cavalleri, and Fulvio Parmigiani

Appl. Phys. Lett. 96, 021102 (2010); http://dx.doi.org/10.1063/1.3291105 (3 pages) | Cited 9 times

Online Publication Date: 11 January 2010

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In this letter we demonstrate the possibility to determine the temporal and spectral structure (spectrogram) of a complex light pulse exploiting the ultrafast switching character of a nonthermal photoinduced phase transition. As a proof, we use a VO2 multifilm, undergoing an ultrafast insulator-to-metal phase transition when excited by femtosecond near-infrared laser pulses. The abrupt variation in the multifilm optical properties, over a broad infrared/visible frequency range, is exploited to determine, in situ and in a simple way, the spectrogram of a supercontinuum pulse produced by a photonic crystal fiber. The determination of the structure of the pulse is mandatory to develop pump-probe experiments with frequency resolution over a broad spectral range (700–1100 nm).
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71.30.+h Metal-insulator transitions and other electronic transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
78.66.-w Optical properties of specific thin films
78.47.J- Ultrafast spectroscopy (<1 psec)
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Development of a nonlinear nanoprobe for interferometric autocorrelation based characterization of ultrashort optical pulses

Haifeng Li, Yaoshun Jia, Qian Xu, Kebin Shi, Jian Wu, Peter C. Eklund, Yong Xu, and Zhiwen Liu

Appl. Phys. Lett. 96, 021103 (2010); http://dx.doi.org/10.1063/1.3276081 (3 pages) | Cited 3 times

Online Publication Date: 11 January 2010

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Near-field scanning can achieve nanoscale resolution while ultrashort pulse diagnostic tools can characterize femtosecond pulses. Yet currently it is still challenging to nonperturbatively characterize the near field of an ultrashort optical pulse with nanofemtoscale spatiotemporal resolution. To address this challenge, we propose to develop a nonlinear nanoprobe composed of a silica fiber taper, a nanowire, and nonlinear fluorescent spheres. Using such a nanoprobe, we also report proof-of-principle characterization of femtosecond optical pulse through interferometric autocorrelation measurement.
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07.79.-v Scanning probe microscopes and components
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
07.60.Ly Interferometers
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
81.07.Gf Nanowires
81.07.Oj Nanoelectromechanical systems (NEMS)

High throughput technique for characterizing liquid crystal alignment in complex geometries

E. G. Edwards, T. S. Taphouse, S. L. Cornford, and S. C. Kitson

Appl. Phys. Lett. 96, 021104 (2010); http://dx.doi.org/10.1063/1.3279145 (3 pages)

Online Publication Date: 12 January 2010

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We present a high throughput technique for characterizing liquid crystal electro-optic devices. We show that the optical transmission as a function of incident light polarization for an untwisted nematic device doped with dichroic dye can be simulated as a birefringent slab with uniform tilt and azimuthal alignment angles. Although the actual liquid crystal alignment may be more complex, these slab angles provide the basis of a rapid assessment technique. Implementation of the experiment using machine vision allows many measurements to be made in parallel and so very high throughput characterization of devices is possible.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
42.79.Kr Display devices, liquid-crystal devices
42.70.Df Liquid crystals
42.25.Ja Polarization
42.25.Bs Wave propagation, transmission and absorption

A general few-projection method for tomographic reconstruction of samples consisting of several distinct materials

Glenn R. Myers, C. David L. Thomas, David M. Paganin, Timur E. Gureyev, and John G. Clement

Appl. Phys. Lett. 96, 021105 (2010); http://dx.doi.org/10.1063/1.3279150 (3 pages) | Cited 3 times

Online Publication Date: 12 January 2010

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We present a method for tomographic reconstruction of objects containing several distinct materials, which is capable of accurately reconstructing a sample from vastly fewer angular projections than required by conventional algorithms. The algorithm is more general than many previous discrete tomography methods, as: (i) a priori knowledge of the exact number of materials is not required; (ii) the linear attenuation coefficient of each constituent material may assume a small range of a priori unknown values. We present reconstructions from an experimental x-ray computed tomography scan of cortical bone acquired at the SPring-8 synchrotron.
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87.57.Q- Computed tomography
87.59.bd Computed radiography
87.57.nf Reconstruction

Effect of dielectric thin films on reflection properties of metal hole arrays

Fumiaki Miyamaru, Yuki Sasagawa, and Mitsuo Wada Takeda

Appl. Phys. Lett. 96, 021106 (2010); http://dx.doi.org/10.1063/1.3292024 (3 pages) | Cited 4 times

Online Publication Date: 12 January 2010

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We study the effect of a dielectric film attached to the surface of a metal hole array (MHA) on the reflection spectrum in the terahertz (THz) region. The frequency of the reflection dip, attributed to the excitation of surface waves in the vicinity of the MHA surface, shifts to lower frequencies with increasing dielectric film thickness. This resonant characteristic of MHAs can be applied to highly sensitive THz sensing for samples attached to the MHA surface. We also investigate the dependence of the reflection spectrum on the MHA’s thickness and the side to which the dielectric film is attached.
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77.55.-g Dielectric thin films
78.70.Gq Microwave and radio-frequency interactions
78.40.-q Absorption and reflection spectra: visible and ultraviolet
78.68.+m Optical properties of surfaces
78.66.Bz Metals and metallic alloys

Laser spectroscopy of gas confined in nanoporous materials

Tomas Svensson and Zhijian Shen

Appl. Phys. Lett. 96, 021107 (2010); http://dx.doi.org/10.1063/1.3292210 (3 pages) | Cited 9 times

Online Publication Date: 13 January 2010

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We show that high-resolution laser spectroscopy can probe surface interactions of gas confined in nanocavities of porous materials. We report on strong line broadening and unfamiliar line shapes due to tight confinement, as well as signal enhancement due to multiple photon scattering. This new domain of laser spectroscopy constitute a challenge for the theory of collisions and spectroscopic line shapes, and open for new ways of analyzing porous materials and processes taking place therein.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.62.-b Laser applications

Microwave modulation of terahertz quantum cascade lasers: a transmission-line approach

W. Maineult, L. Ding, P. Gellie, P. Filloux, C. Sirtori, S. Barbieri, T. Akalin, J.-F. Lampin, I. Sagnes, H. E. Beere, and D. A. Ritchie

Appl. Phys. Lett. 96, 021108 (2010); http://dx.doi.org/10.1063/1.3284518 (3 pages) | Cited 8 times

Online Publication Date: 14 January 2010

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We report on microwave impedance measurements of metal-metal ridge-waveguide terahertz quantum cascade lasers. Experimental data, recorded at 4 K in the 100 MHz–55 GHz range, are well reproduced by distributed-parameter transmission-line simulations, showing that the modulation cutoff is limited by the propagation losses that increase for higher microwave frequencies, yielding a 3 dB modulation bandwidth of ∼ 70 GHz for a 1 mm-long ridge. By using a shunt-stub matching we demonstrate amplitude modulation of a 2.3 THz QCL up to 24 GHz.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
84.40.-x Radiowave and microwave (including millimeter wave) technology

Mechanism of effective three-photon induced lasing

H. H. Fan, Y. J. He, J. W. Dong, B. C. Chen, H. Z. Wang, Y. P. Tian, and M. F. Reid

Appl. Phys. Lett. 96, 021109 (2010); http://dx.doi.org/10.1063/1.3291671 (3 pages) | Cited 1 time

Online Publication Date: 14 January 2010

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The experimental and theoretical results in this letter reveal that three-photon absorption effect can help light wave to form solitonlike filament; and a stable solitonlike filament is observed in solution with high quintic nonlinearity. This stable solitonlike filament makes pumping infrared laser be localized within the filament and reach high pumping density for a long distance. This high density pumping laser in the filament generates high efficiency lasing induced by three-photon absorption. This work is an approach to make practical application of high order nonlinear optical processes possible.
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42.65.Tg Optical solitons; nonlinear guided waves
42.55.-f Lasers

Paraboloid electronic eye cameras using deformable arrays of photodetectors in hexagonal mesh layouts

Inhwa Jung, Gunchul Shin, Viktor Malyarchuk, Jeong Sook Ha, and John A. Rogers

Appl. Phys. Lett. 96, 021110 (2010); http://dx.doi.org/10.1063/1.3290244 (3 pages) | Cited 6 times

Online Publication Date: 15 January 2010

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We report on a type of digital camera that uses a hexagonal array of silicon photodetectors on a substrate whose surface has parabolic curvature. This elliptical paraboloid shape closely matches the image surface formed by a simple, planoconvex lens. The hexagonal arrangement provides high area coverage with an approximately circular peripheral view. Details of the design strategies and underlying features of the mechanics and optics are described. Full imaging with these parabolic cameras and comparison to planar layouts reveals improved uniformity of illumination and focus across a wide field of view.
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07.68.+m Photography, photographic instruments; xerography
42.79.Pw Imaging detectors and sensors
85.60.Gz Photodetectors (including infrared and CCD detectors)
42.79.Bh Lenses, prisms and mirrors

Dynamic response of metamaterials in the terahertz regime: Blueshift tunability and broadband phase modulation

J.-M. Manceau, N.-H. Shen, M. Kafesaki, C. M. Soukoulis, and S. Tzortzakis

Appl. Phys. Lett. 96, 021111 (2010); http://dx.doi.org/10.1063/1.3292208 (3 pages) | Cited 12 times

Online Publication Date: 15 January 2010

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Terahertz time-domain spectroscopy is used to probe the electromagnetic properties of metamaterials, which are dynamically photoexcited, using synchronized femtosecond near-infrared laser pulses. Blueshift tunability of the electric dipole metamaterial’s resonance, as well as a broadband phase tunability reaching ∼ π/4, are demonstrated. Numerical simulations show the observations are due to changes in the complex index of the photoexcited semiconductor substrate.
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78.70.Gq Microwave and radio-frequency interactions
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.70.-a Optical materials
78.47.J- Ultrafast spectroscopy (<1 psec)
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Self-injection of electrons in a laser-wakefield accelerator by using longitudinal density ripple

Deepak Dahiya, Vivek Sajal, and A. K. Sharma

Appl. Phys. Lett. 96, 021501 (2010); http://dx.doi.org/10.1063/1.3291674 (3 pages) | Cited 1 time

Online Publication Date: 13 January 2010

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By introducing a longitudinal density ripple (periodic modulation in background plasma density), we demonstrate self-injection of electrons in a laser-wakefield accelerator. The wakefield driven plasma wave, in presence of density ripple excites two side band waves of same frequency but different wave numbers. One of these side bands, having smaller phase velocity compared to wakefield driven plasma wave, preaccelerates the background plasma electrons. Significant number of these preaccelerated electrons get trapped in the laser-wakefield and further accelerated to higher energies.
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52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
52.38.Kd Laser-plasma acceleration of electrons and ions
52.25.-b Plasma properties
52.59.-f Intense particle beams and radiation sources

DNA damage and mitochondria dysfunction in cell apoptosis induced by nonthermal air plasma

G. J. Kim, W. Kim, K. T. Kim, and J. K. Lee

Appl. Phys. Lett. 96, 021502 (2010); http://dx.doi.org/10.1063/1.3292206 (3 pages) | Cited 22 times

Online Publication Date: 15 January 2010

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Nonthermal plasma is known to induce animal cell death but the mechanism is not yet clear. Here, cellular and biochemical regulation of cell apoptosis is demonstrated for plasma treated cells. Surface type nonthermal air plasma triggered apoptosis of B16F10 mouse melanoma cancer cells causing DNA damage and mitochondria dysfunction. Plasma treatment activated caspase-3, apoptosis executioner. The plasma treated cells also accumulated gamma-H2A.X, marker for DNA double strand breaks, and p53 tumor suppressor gene as a response to DNA damage. Interestingly, cytochrome C was released from mitochondria and its membrane potential was changed significantly.
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87.53.Jw Therapeutic applications, including brachytherapy
87.55.-x Treatment strategy
87.53.-j Effects of ionizing radiation on biological systems
87.14.gk DNA
87.17.-d Cell processes
87.19.xj Cancer
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Effect of local structures and atomic packing on glass forming ability in CuxZr100−x metallic glasses

H. L. Peng, M. Z. Li, W. H. Wang, C.-Z. Wang, and K. M. Ho

Appl. Phys. Lett. 96, 021901 (2010); http://dx.doi.org/10.1063/1.3282800 (3 pages) | Cited 17 times

Online Publication Date: 11 January 2010

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Molecular dynamics simulations are performed for CuZr metallic alloys to study the structural and dynamical features for glass forming ability (GFA). Our analysis shows that in CuZr metallic system, although 〈0,0,12,0〉 icosahedral clusters are important, some Zr-centered clusters such as 〈0,1,10,4〉 and 〈0,1,10,5〉 play a key role in slowing down the dynamics. It is found that these Zr-centered clusters are intrinsically slow and fundamentally determine the stability and slow dynamics. Due to the strong spatial correlation between 〈0,0,12,0〉 and Zr-centered clusters, their relative population influences the dense packing and dynamics in metallic glasses, and further the GFA.
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61.43.Fs Glasses
81.05.Kf Glasses (including metallic glasses)
61.43.Bn Structural modeling: serial-addition models, computer simulation
64.70.pe Metallic glasses

Defect physics of the kesterite thin-film solar cell absorber Cu2ZnSnS4

Shiyou Chen, X. G. Gong, Aron Walsh, and Su-Huai Wei

Appl. Phys. Lett. 96, 021902 (2010); http://dx.doi.org/10.1063/1.3275796 (3 pages) | Cited 51 times

Online Publication Date: 11 January 2010

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Cu2ZnSnS4 is one of the most promising quaternary absorber materials for thin-film solar cells. Examination of the thermodynamic stability of this quaternary compound reveals that the stable chemical potential region for the formation of stoichiometric compound is small. Under these conditions, the dominant defect will be p-type CuZn antisite, which has an acceptor level deeper than the Cu vacancy. The dominant self-compensated defect pair in this quaternary compound is [CuZn−+ZnCu+]0, which leads to the formation of various polytype structures of Cu2ZnSnS4. We propose that to maximize the solar cell performance, growth of Cu2ZnSnS4 under Cu-poor/Zn-rich conditions will be optimal, if the precipitation of ZnS can be avoided by kinetic barriers.
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88.40.jn Thin film Cu-based I-III-VI2 solar cells
61.66.Bi Elemental solids
61.66.Dk Alloys
65.40.G- Other thermodynamical quantities
71.55.Ht Other nonmetals
61.72.jd Vacancies

Natural frequencies of C60, C70, and C80 fullerenes

A. Sakhaee-Pour and A. Vafai

Appl. Phys. Lett. 96, 021903 (2010); http://dx.doi.org/10.1063/1.3276562 (2 pages) | Cited 1 time

Online Publication Date: 12 January 2010

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This letter adopts an atomistic modeling approach to study free vibrational characteristics of C60, C70, and C80 fullerenes. In this regard, we use the molecular structural mechanics consisting of equivalent structural beams to calculate the nonzero natural frequencies. The simulation results indicate that the first natural frequency of the fullerene is in the order terahertz and decreases nonlinearly with respect to the number of the carbon atoms.
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78.66.Tr Fullerenes and related materials
78.30.Na Fullerenes and related materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Interfacial intermixing in InAs/GaSb short-period-superlattices grown by molecular beam epitaxy

E. Luna, B. Satpati, J. B. Rodriguez, A. N. Baranov, E. Tournié, and A. Trampert

Appl. Phys. Lett. 96, 021904 (2010); http://dx.doi.org/10.1063/1.3291666 (3 pages) | Cited 8 times

Online Publication Date: 12 January 2010

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The unique properties of the noncommon-atom InAs/GaSb short-period-superlattices (SPSL) strongly depend on the interface structure. These interfaces are characterized using transmission electron microscopy (TEM). The compositional sharpness is obtained from the comparison of the experimental contrast in g002 two-beam dark-field TEM images with simulated intensity profiles, which are calculated assuming that the element distribution profiles are described by sigmoidal functions. The interfacial intermixing, defined by the chemical width, is obtained for SPSL with different periods and layer thicknesses, even in the extreme case of nominally less than 3 ML thick InAs layers. Nominal 1 ML InSb layers intentionally inserted are also identified.
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68.65.Cd Superlattices
68.35.Ct Interface structure and roughness
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Phase stabilization of δ-Bi2O3 nanostructures by epitaxial growth onto single crystal SrTiO3 or DyScO3 substrates

D. L. Proffit, G.-R. Bai, D. D. Fong, T. T. Fister, S. O. Hruszkewycz, M. J. Highland, P. M. Baldo, P. H. Fuoss, T. O. Mason, and J. A. Eastman

Appl. Phys. Lett. 96, 021905 (2010); http://dx.doi.org/10.1063/1.3291068 (3 pages) | Cited 3 times

Online Publication Date: 13 January 2010

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We observe that the high-temperature δ-phase of Bi2O3 is stabilized to room temperature by the epitaxial growth of nanostructures onto either (001)-oriented SrTiO3 or (001)p-oriented DyScO3 single crystal substrates. In addition, the morphology can be controlled by the miscut of the substrate. Synchrotron x-ray scattering observations at controlled temperatures and oxygen partial pressures reveal that the δ-Bi2O3 nanostructures are coherently strained to the substrates at room temperature. Annealing the nanostructures at 600 °C causes gradual conversion of the (001)-oriented δ-phase to an unidentified strain-relaxed phase.
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68.55.A- Nucleation and growth
61.72.Cc Kinetics of defect formation and annealing
68.55.J- Morphology of films
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials

Effect of strain rate on the yielding mechanism of amorphous metal foam

Joseph P. Schramm, Marios D. Demetriou, William L. Johnson, Benny Poon, Guruswami Ravichandran, and Daniel Rittel

Appl. Phys. Lett. 96, 021906 (2010); http://dx.doi.org/10.1063/1.3279132 (3 pages)

Online Publication Date: 14 January 2010

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Stochastic amorphous Pd43Ni10Cu27P20 foams were tested in quasistatic and dynamic loading. The strength/porosity relations show distinct slopes for the two loading conditions, suggesting a strain-rate-induced change in the foam yielding mechanism. The strength/porosity correlation of the dynamic test data along with microscopy assessments support that dynamic foam yielding is dominated by plasticity rather than elastic buckling, the mechanism previously identified to control quasistatic yielding. The strain-rate-induced shift in the foam yielding mechanism is attributed to the rate of loading approaching the rate of sound wave propagation across intracellular membranes, thereby suppressing elastic buckling and promoting plastic yielding.
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82.70.Rr Aerosols and foams
62.65.+k Acoustical properties of solids
62.20.fq Plasticity and superplasticity
81.40.Lm Deformation, plasticity, and creep
62.20.mq Buckling

Interplay between magnetic impurities and photoinduced carriers in surface depletion layer of anatase Ti1−xCoxO2−δ thin film probed by x-ray photoemission spectroscopy

N. Yamashita, T. Sudayama, T. Mizokawa, Y. Yamada, T. Fukumura, and M. Kawasaki

Appl. Phys. Lett. 96, 021907 (2010); http://dx.doi.org/10.1063/1.3291680 (3 pages) | Cited 5 times

Online Publication Date: 14 January 2010

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X-ray photoemission spectroscopy measurements with ultraviolet laser illumination have been performed for anatase Ti1−xCoxO2−δ thin films with x = 0.05 and 0.10 in order to investigate the interplay between the Co spins and the photoinduced carriers in the surface region. We have found that the surface band bending is removed by the ultraviolet illumination, indicating that photoinduced carriers are injected into the surface depletion layer. After the carrier injection, the position of the chemical potential is governed by the exchange splitting of the Ti 3d conduction band due to the magnetic interaction between the photoinduced carriers and the Co spins.
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75.30.Hx Magnetic impurity interactions
75.50.Pp Magnetic semiconductors
72.20.-i Conductivity phenomena in semiconductors and insulators
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.60.-s Chemical thermodynamics
71.20.-b Electron density of states and band structure of crystalline solids

Band bowing and band alignment in InGaN alloys

Poul Georg Moses and Chris G. Van de Walle

Appl. Phys. Lett. 96, 021908 (2010); http://dx.doi.org/10.1063/1.3291055 (3 pages) | Cited 47 times

Online Publication Date: 15 January 2010

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We use density functional theory calculations with the HSE06 hybrid exchange-correlation functional to investigate InGaN alloys and accurately determine band gaps and band alignments. We find a strong band-gap bowing at low In content. Band positions on an absolute energy scale are determined from surface calculations. The resulting GaN/InN valence-band offset is 0.62 eV. The dependence of InGaN valence-band alignment on In content is found to be almost linear. Based on the values of band gaps and band alignments, we conclude that InGaN fulfills the requirements for a photoelectrochemical electrode for In contents up to 50%.
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71.20.Gj Other metals and alloys
73.20.At Surface states, band structure, electron density of states
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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On the possibility of a shunt-stabilized superlattice terahertz emitter

Huidong Xu and Stephen W. Teitsworth

Appl. Phys. Lett. 96, 022101 (2010); http://dx.doi.org/10.1063/1.3291614 (3 pages)

Online Publication Date: 11 January 2010

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High field electronic transport through a strongly coupled superlattice (SL) with a shunting side layer is numerically studied using a drift-diffusion model that includes both vertical and lateral dynamics. The bias voltage corresponds to an average electric field in the negative differential conductivity region of the intrinsic current-field curve of the SL, a condition that generally implies space charge instability. Key structural parameters associated with both the shunt layer and SL are identified for which the shunt layer stabilizes a uniform electric field profile. These results support the possibility to realize a SL-based terahertz oscillator with a carefully designed structure.
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73.21.Cd Superlattices
72.20.-i Conductivity phenomena in semiconductors and insulators
72.25.-b Spin polarized transport

Metal-insulator transition in epitaxial V1−xWxO2(0 ≤ x ≤ 0.33) thin films

Keisuke Shibuya, Masashi Kawasaki, and Yoshinori Tokura

Appl. Phys. Lett. 96, 022102 (2010); http://dx.doi.org/10.1063/1.3291053 (3 pages) | Cited 11 times

Online Publication Date: 12 January 2010

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We have fabricated epitaxial V1−xWxO2(0 ≤ x ≤ 0.33) thin films on TiO2 (001) substrates. The metal-insulator transition temperature of VO2 is systematically reduced by W doping, and eventually a metallic ground state is realized at 0.08 ≤ x ≤ 0.09. Tiny resistivity upturn around 50 K observed for these films suggests an electronic phase separation between a majority metallic matrix and minority insulating puddles. With further increasing x above 0.095, another insulating phase appears while increasing the metal-insulator transition temperature. The elucidated phase diagram gives basic knowledge for devices based on Mott transition.
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71.30.+h Metal-insulator transitions and other electronic transitions
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.30.Bx Phase diagrams of metals, alloys, and oxides
61.72.up Other materials
73.61.Ng Insulators
72.60.+g Mixed conductivity and conductivity transitions

Strong localization effect in magnetic two-dimensional hole systems

U. Wurstbauer, S. Knott, A. Zolotaryov, D. Schuh, W. Hansen, and W. Wegscheider

Appl. Phys. Lett. 96, 022103 (2010); http://dx.doi.org/10.1063/1.3291673 (3 pages) | Cited 2 times

Online Publication Date: 12 January 2010

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We report an extensive study of the magnetotransport properties of magnetically doped two-dimensional hole systems. Inverted manganese modulation doped InAs quantum wells with localized manganese ions providing a magnetic moment of S = 5/2 were grown by molecular beam epitaxy. Strong localization effect found in low-field magnetotransport measurements on these structures can either be modified by the manganese doping density or by tuning the two-dimensional hole density p via field effect. The data reveal that the ratio between p and manganese ions inside or in close vicinity to the channel enlarges the strong localization effect. Moreover, asymmetric broadening of the doping layer due to manganese segregation is significantly influenced by strain in the heterostructure.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.30.Cr Saturation moments and magnetic susceptibilities
61.72.U- Doping and impurity implantation
81.07.St Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Determination of the minority carrier diffusion length in compositionally graded Cu(In,Ga)Se2 solar cells using electron beam induced current

Gregory Brown, Vladimir Faifer, Alex Pudov, Sergey Anikeev, Eugene Bykov, Miguel Contreras, and Junqiao Wu

Appl. Phys. Lett. 96, 022104 (2010); http://dx.doi.org/10.1063/1.3291046 (3 pages) | Cited 9 times

Online Publication Date: 14 January 2010

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A method is proposed and tested which allows for the accurate determination of the carrier collection efficiency and minority carrier diffusion length in Cu(In,Ga)Se2 solar cells using energy dependent electron beam induced current. Gallium composition gradients across the film thickness introduce quasielectric fields that are found to improve collection efficiency when they are located toward the rear of the sample. The quasielectric fields are also shown to reduce the influence of back surface recombination. The strengths and limitations of this technique are discussed and compared with external quantum efficiency measurements.
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88.40.jn Thin film Cu-based I-III-VI2 solar cells
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