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21 Nov 2011

Volume 99, Issue 21, Articles (21xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 212501 (2011); http://dx.doi.org/10.1063/1.3662032 (3 pages)

Ken-ichi Uchida, Toshu An, Yosuke Kajiwara, Masaya Toda, and Eiji Saitoh
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A threshold for laser-driven linear particle acceleration in unbounded vacuum

Liang Jie Wong and Franz X. Kärtner

Appl. Phys. Lett. 99, 211101 (2011); http://dx.doi.org/10.1063/1.3664226 (3 pages) | Cited 2 times

Online Publication Date: 21 November 2011

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We hypothesize that a charged particle in unbounded vacuum can be substantially accelerated by a force linear in the electric field of a propagating electromagnetic wave only if the accelerating field is capable of bringing the particle to a relativistic energy in its initial rest frame during the interaction. We consequently derive a general formula for the acceleration threshold of such schemes and support our conclusion with the results of numerical simulations over a broad range of parameters for different kinds of pulsed laser beams.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Temperature dependent optical properties of pentacene films on zinc oxide

J. Helzel, S. Jankowski, M. El Helou, G. Witte, and W. Heimbrodt

Appl. Phys. Lett. 99, 211102 (2011); http://dx.doi.org/10.1063/1.3663863 (3 pages) | Cited 4 times

Online Publication Date: 22 November 2011

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The optical transitions of pentacene films deposited on ZnO have been studied by absorption spectroscopy as a function of temperature in the range of room temperature down to 10 K. The pentacene films were prepared with thicknesses of 10 nm, 20 nm, and 100 nm on the ZnO-O(000-1) surface by molecular beam deposition. A unique temperature dependence has been observed for the two Davydov components of the excitons for different film thicknesses. At room temperature, the energetic positions of the respective absorption bands are the same for all films, whereas the positions differ more than 20 meV at 10 K caused by the very different expansion coefficients of pentacene and ZnO. Although the pentacene is just bonded via van der Waals interaction to the ZnO substrate, the very first pentacene monolayer (adlayer) is forced to keep the initial position on the ZnO surface and suffering, therefore, a substantial tensile strain. For all the subsequent pentacene monolayers, the strain is reduced step by step resulting electronically in a strong potential gradient at the interface.
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78.66.Qn Polymers; organic compounds
68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.40.Me Organic compounds and polymers

Low density carbon nanotube forest as an index-matched and near perfect absorption coating

Haofei Shi, Jong G. Ok, Hyoung Won Baac, and L. Jay Guo

Appl. Phys. Lett. 99, 211103 (2011); http://dx.doi.org/10.1063/1.3663873 (3 pages) | Cited 7 times

Online Publication Date: 22 November 2011

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We demonstrate broadband, near perfect absorption with a conformal coating of a multi-walled carbon nanotube (CNT) forest on an arbitrarily shaped surface. The complex refractive index of such a CNT forest is retrieved from the measured transmission and reflection spectra using Kramers-Kronig constrained variational analysis, which gives a typical value of neff = 1.04 + 0.01i at visible wavelengths. Therefore, when used as a conformal coating on an object, a thick layer of the CNT forest can provide an excellent impedance match to air and near perfect absorption, preventing any detectable light reflection and scattering from the object.
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78.67.Ch Nanotubes
78.40.Ri Fullerenes and related materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Optical resonances in tubular microcavities with subwavelength wall thicknesses

Tianrong Zhan, Chun Xu, Fangyuan Zhao, Zhiqiang Xiong, Xinhua Hu, Gaoshan Huang, Yongfeng Mei, and Jian Zi

Appl. Phys. Lett. 99, 211104 (2011); http://dx.doi.org/10.1063/1.3664110 (3 pages) | Cited 6 times

Online Publication Date: 22 November 2011

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Based on the Mie scattering theory, we study optical resonances with whispering gallery modes (WGMs) in tubular microcavities. Rigorous formulas are present to obtain resonant wavelengths and Q factors for the WGM resonances. It is found that the Q factors of microtubes can be dramatically increased by increasing the dielectric constants in tube walls. For common SiO/SiO2 based microtubes, Q factors can be improved by one order when the microtubes are coated with thin high-index HfO2 layers (n = 1.95, thickness = 10 nm). The results could be useful for designing better optical devices based on tubular microcavities.
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42.25.Fx Diffraction and scattering
42.79.-e Optical elements, devices, and systems

Diagnostics of fs pulses by noncollinear random quasi-phase-matched frequency doubling

A. S. Aleksandrovsky, A. M. Vyunishev, A. I. Zaitsev, G. I. Pospelov, and V. V. Slabko

Appl. Phys. Lett. 99, 211105 (2011); http://dx.doi.org/10.1063/1.3664094 (3 pages) | Cited 3 times

Online Publication Date: 23 November 2011

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Noncollinear random quasi-phase-matched frequency doubling in nonlinear photonic crystal (NPC) of strontium tetraborate (SBO) can be used for background-free autocorrelation measurements of ultrashort pulses in wide spectral range without any angular tuning of nonlinear photonic crystal. Nonuniformity of reciprocal superlattice vectors spectrum of random structure does not affect the accuracy of measurement. Nonlinear photonic crystals of strontium tetraborate are attractive medium for cross-correlation measurements in deep and vacuum ultraviolet.
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42.70.Qs Photonic bandgap materials
78.40.Ha Other nonmetallic inorganics
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.47.N- High resolution nonlinear optical spectroscopy

Scaling of losses with size and wavelength in nanoplasmonics and metamaterials

Jacob B. Khurgin and Greg Sun

Appl. Phys. Lett. 99, 211106 (2011); http://dx.doi.org/10.1063/1.3664105 (3 pages) | Cited 11 times

Online Publication Date: 23 November 2011

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We show that, for the resonant metal-dielectric structures with sub-wavelength confinement of light in all three dimensions, the loss cannot be reduced considerably below the loss of the metal itself unless one operates in the far IR and THz regions of the spectrum or below. Such high losses cannot be compensated by introducing gain due to Purcell-induced shortening of recombination times. The only way low loss optical meta-materials can be engineered is with, as yet unknown, low loss materials with negative permittivity.
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42.79.-e Optical elements, devices, and systems
73.22.Lp Collective excitations
42.70.-a Optical materials

Beam steering in GaInAs/GaAs slow-light Bragg reflector waveguide amplifier

Xiaodong Gu, Toshikazu Shimada, Ayumi Fuchida, Akihiro Matsutani, Akihiro Imamura, and Fumio Koyama

Appl. Phys. Lett. 99, 211107 (2011); http://dx.doi.org/10.1063/1.3664118 (3 pages) | Cited 5 times

Online Publication Date: 23 November 2011

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A high-resolution beam steering technique was proposed with a slow-light Bragg reflector waveguide amplifier. By tuning the wavelength of the propagating slow-light mode, a giant change in a deflection angle is predicted and high-resolution beam steering is prospective. In this paper, the first experimental demonstration of the beam steering technique is presented. We demonstrated a continuous beam steering of over 30°. The deflection angles are in good agreement with simulation results. By injecting larger current, the effective radiation window length is increased and sharp divergence angle is obtained, exhibiting a potential in getting a large number of resolution points.
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42.60.-v Laser optical systems: design and operation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Dj Gratings
42.79.Gn Optical waveguides and couplers
42.55.Wd Fiber lasers
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Third harmonic generation by a low intensity laser pulse in a corrugated discharge capillary

Y. Katzir, Y. Ferber, E. Megidish, A. Zigler, and H. M. Milchberg

Appl. Phys. Lett. 99, 211501 (2011); http://dx.doi.org/10.1063/1.3664221 (3 pages)

Online Publication Date: 23 November 2011

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Quasi phase matching and increase of laser interaction length were promoted by periodically modulated plasma guide formed by a discharge current ablating the inner capillary walls. The phenomenon was demonstrated through the use of third harmonics. For Ti:Sapphire laser pulses propagating through 1 cm long corrugated discharge capillaries, with an axial corrugation period of 200 μm, the third harmonic was generated at intensities as low as ∼109 W/cm2.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.60.Fc Modulation, tuning, and mode locking
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Threading-dislocation blocking by stacking faults formed in an undoped GaN layer on a patterned sapphire substrate

Sung Bo Lee, Tae-Wan Kwon, Sung-Hak Lee, Jungwon Park, and Won-Jin Choi

Appl. Phys. Lett. 99, 211901 (2011); http://dx.doi.org/10.1063/1.3658451 (3 pages)

Online Publication Date: 21 November 2011

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The microstructure of an undoped GaN grown on a hemisphere-patterned sapphire substrate is characterized by transmission electron microscopy. Interestingly, basal-plane stacking faults are formed in GaN at the height of hemispheres, leading to a substantial reduction in threading-dislocation density. It is believed that the formation of the stacking faults is characteristic of the lateral growth mode. This study looks at an unexplored feature of the lateral growth behavior that both so-called epitaxial lateral overgrowth mechanism and stacking faults function to reduce the dislocation density for the GaN growth on hemisphere-patterned sapphire substrates.
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68.55.A- Nucleation and growth
61.72.Bb Theories and models of crystal defects
61.72.Nn Stacking faults and other planar or extended defects
81.05.Ea III-V semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.16.Rf Micro- and nanoscale pattern formation

Pressure-induced magnetoresistivity reversal in magnetite

Ningning Su, Yonghao Han, Yanzhang Ma, Hongwu Liu, Boheng Ma, and Chunxiao Gao

Appl. Phys. Lett. 99, 211902 (2011); http://dx.doi.org/10.1063/1.3663217 (3 pages) | Cited 1 time

Online Publication Date: 21 November 2011

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The magnetoresistivity (MR) of nano-powdered magnetite has been measured under pressures up to 19.0 GPa and magnetic fields up to 15 kG. An unexpected quasi-linear positive MR below 6.0 GPa and an MR transition from positive to negative around 6.0 GPa have been found. The abnormal positive MR below 6.0 GPa originates from the confinement effect caused by nano-scale heterogeneity at the contact surface between Mo and Fe3O4 sample and the high negative spin polarization of magnetite. The MR transition at about 6.0 GPa comes from a phase transition from half-metal to metal induced by pressure.
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81.07.Wx Nanopowders
72.20.My Galvanomagnetic and other magnetotransport effects
72.25.-b Spin polarized transport
72.60.+g Mixed conductivity and conductivity transitions
73.63.Bd Nanocrystalline materials

Polarity-driven nickel oxide precipitation in LaNiO3-LaAlO3 superlattices

E. Detemple, Q. M. Ramasse, W. Sigle, G. Cristiani, H.-U. Habermeier, E. Benckiser, A. V. Boris, A. Frano, P. Wochner, M. Wu, B. Keimer, and P. A. van Aken

Appl. Phys. Lett. 99, 211903 (2011); http://dx.doi.org/10.1063/1.3663568 (3 pages) | Cited 7 times

Online Publication Date: 22 November 2011

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We have studied the microstructure of LaNiO3-LaAlO3 superlattices using transmission electron microscopy in combination with electron energy loss spectroscopy. In superlattices grown on non-polar SrTiO3 substrates, nanometer-sized NiO precipitates form directly at the interface between the substrate and the initial LaNiO3 layer, while control measurements on polar substrates show no NiO. Because of the drastically different electronic properties of NiO and LaNiO3, such precipitates can strongly affect measurements on atomically thin LaNiO3-based films and multilayers on SrTiO3. In general, polarity-driven secondary phase formation should be carefully evaluated as a possible consequence of the polarity mismatch at metal-oxide interfaces.
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81.30.Mh Solid-phase precipitation
73.21.Cd Superlattices
79.20.Uv Electron energy loss spectroscopy

Transport and optical properties of the gapless Heusler compound PtYSb

Siham Ouardi, Gerhard H. Fecher, Claudia Felser, Jaroslav Hamrle, Kamil Postava, and Jaromír Pištora

Appl. Phys. Lett. 99, 211904 (2011); http://dx.doi.org/10.1063/1.3663569 (3 pages) | Cited 9 times

Online Publication Date: 22 November 2011

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This work presents a systematic study on the optical and transport properties of the Heusler compound PtYSb. The optical properties were investigated in a wide spectral range from 10 meV to 6.5 eV and compared to ab-initio calculations. For photon energies below 2.5 eV, the optical absorption increases linearly with photon energy. This is related with the conical shape of the electronic structure in the vicinity of the Fermi energy. The optical spectra reveal a maximum band gap of about 60 meV. Furthermore, the temperature dependence of thermal conductivity, electrical resistivity, Seebeck coefficient and Hall mobility were investigated. PtYSb exhibits very good thermoelectric properties with a high figure of merit ZT of 0.2 and a Hall mobility μh of 300 cm2/Vs at 350 K, which is the highest value obtained for Heusler compounds up to now. The carrier concentration ranges from 5 × 1018 at low temperature to 1019 cm−3 at 400 K.
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72.80.Ga Transition-metal compounds
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Pa Thermoelectric and thermomagnetic effects

Sn diffusion during Ni germanide growth on Ge1–xSnx

J. Demeulemeester, A. Schrauwen, O. Nakatsuka, S. Zaima, M. Adachi, Y. Shimura, C. M. Comrie, C. Fleischmann, C. Detavernier, K. Temst, and A. Vantomme

Appl. Phys. Lett. 99, 211905 (2011); http://dx.doi.org/10.1063/1.3662925 (3 pages) | Cited 2 times

Online Publication Date: 22 November 2011

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We report on the redistribution of Sn during Ni germanide formation on Ge1–xSnx/〈Ge(100)〉 and its influence on the thin film growth and properties. These results show that the reaction involves the formation of Ni5Ge3 and NiGe. Sn redistributes homogenously in both phases, in which the Sn/Ge ratio retains the ratio of the as-deposited Ge1–xSnx film. Sn continues to diffuse after full NiGe formation and segregates in two regions: (1) at the interface between the germanide and Ge1–xSnx and (2) at the surface, which has major implications for the thin film and contact properties.
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68.35.Fx Diffusion; interface formation
68.55.aj Insulators
66.30.-h Diffusion in solids
68.35.Dv Composition, segregation; defects and impurities

Two-dimensional electron gas related emissions in ZnMgO/ZnO heterostructures

Hui Chen, Shulin Gu, Jiagao Liu, Jiandong Ye, Kun Tang, Shunming Zhu, and Youdou Zheng

Appl. Phys. Lett. 99, 211906 (2011); http://dx.doi.org/10.1063/1.3662964 (3 pages) | Cited 3 times

Online Publication Date: 22 November 2011

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Radiative recombination of two-dimensional electron gas (2DEG), induced by polarization and validated by Hall effect measurements, is investigated in ZnMgO/ZnO heterostructures grown by metal-organic chemical vapor deposition. The Mg composition, the depth profile distribution of Mg, the residual strain in ZnMgO caplayer, and the thickness of caplayer all significantly influence the 2DEG-related transitions in ZnMgO/ZnO heterostructures. Below or above ZnO donor bound exciton, three additional broad emissions persisting up to 100 K are assigned to the spatially indirect transitions from 2DEG electrons to the photoexcited holes towards the ZnO flat-band region or remaining at the heterointerface.
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81.05.Dz II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
71.35.-y Excitons and related phenomena
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.20.My Galvanomagnetic and other magnetotransport effects
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

A high-reflectivity, ambient-stable graphene mirror for neutral atomic and molecular beams

P. Sutter, M. Minniti, P. Albrecht, D. Farías, R. Miranda, and E. Sutter

Appl. Phys. Lett. 99, 211907 (2011); http://dx.doi.org/10.1063/1.3663866 (3 pages) | Cited 3 times

Online Publication Date: 22 November 2011

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We report a He and H2 diffraction study of graphene-terminated Ru(0001) thin films grown epitaxially on c-axis sapphire. Even for samples exposed for several weeks to ambient conditions, brief annealing in ultrahigh vacuum restored extraordinarily high specular reflectivities for He and H2 beams (23% and 7% of the incident beam, respectively). The quality of the angular distributions recorded with both probes exceeds the one obtained from in-situ prepared graphene on Ru(0001) single crystals. Our results for graphene-terminated Ru thin films represent a significant step toward ambient tolerant, high-reflectivity curved surface mirrors for He-atom microscopy.
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42.79.Bh Lenses, prisms and mirrors
07.60.Pb Conventional optical microscopes

Temperature dependence of ultrafast phonon dynamics in graphite

M. Scheuch, T. Kampfrath, M. Wolf, K. von Volkmann, C. Frischkorn, and L. Perfetti

Appl. Phys. Lett. 99, 211908 (2011); http://dx.doi.org/10.1063/1.3663867 (3 pages) | Cited 3 times

Online Publication Date: 22 November 2011

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Nonequilibrium optical phonons are generated in graphite following the excitation of electron-hole pairs with a femtosecond laser pulse. Their energy relaxation is probed by means of terahertz pulses. We find that the hot-phonon lifetime increases by a factor of 2 when the sample temperature decreases from 300 to 5 K. These results suggest that the energy relaxation in graphite at room temperature and above is dominated by the anharmonic decay of hot A1′ phonons at the K point into acoustic phonons with energies of about 10 meV.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.47.D- Time resolved spectroscopy (>1 psec)
78.70.Gq Microwave and radio-frequency interactions

Quantifying pulsed laser induced damage to graphene

Marc Currie, Joshua D. Caldwell, Francisco J. Bezares, Jeremy Robinson, Travis Anderson, Hayden Chun, and Marko Tadjer

Appl. Phys. Lett. 99, 211909 (2011); http://dx.doi.org/10.1063/1.3663875 (3 pages) | Cited 12 times

Online Publication Date: 22 November 2011

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As an emerging optical material, graphene’s ultrafast dynamics are often probed using pulsed lasers yet the region in which optical damage takes place is largely uncharted. Here, femtosecond laser pulses induced localized damage in single-layer graphene on sapphire. Raman spatial mapping, SEM, and AFM microscopy quantified the damage. The resulting size of the damaged area has a linear correlation with the optical fluence. These results demonstrate local modification of sp2-carbon bonding structures with optical pulse fluences as low as 14 mJ/cm2, an order-of-magnitude lower than measured and theoretical ablation thresholds.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.30.Na Fullerenes and related materials
61.48.Gh Structure of graphene
78.67.Wj Optical properties of graphene

Domain matching epitaxy of ferrimagnetic CoFe2O4 thin films on Sc2O3/Si(111)

F. Sánchez, R. Bachelet, P. de Coux, B. Warot-Fonrose, V. Skumryev, L. Tarnawska, P. Zaumseil, T. Schroeder, and J. Fontcuberta

Appl. Phys. Lett. 99, 211910 (2011); http://dx.doi.org/10.1063/1.3663216 (3 pages) | Cited 5 times

Online Publication Date: 22 November 2011

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Ferrimagnetic spinel CoFe2O4 (CFO) films are integrated with Si(111) using Sc2O3 buffer layers. The huge lattice mismatch (17%) between CFO and Sc2O3 is accommodated by domain matching, and CFO grows epitaxially with (111) out-of-plane orientation and coexistence of A- and B-type in-plane crystal variants. CFO films have low roughness of 4 Å and saturation magnetization of about 300 emu/cm3. These properties make CFO films on Sc2O3-buffered Si(111) comparable to those grown on oxide single crystals and thus extend the possibilities of using spinel oxides in electronic devices.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Gg Ferrimagnetics
68.55.-a Thin film structure and morphology

A local defect resonance to enhance acoustic wave-defect interaction in ultrasonic nondestructive evaluation

Igor Solodov, Juxing Bai, Sumbat Bekgulyan, and Gerd Busse

Appl. Phys. Lett. 99, 211911 (2011); http://dx.doi.org/10.1063/1.3663872 (3 pages) | Cited 2 times

Online Publication Date: 23 November 2011

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It is experimentally shown that, to provide maximum acoustic wave-defect interaction, the concept of a local defect resonance should be applied. The model of a resonant defect is used for the selection of the wave frequency to enhance the excitation of the defect in nonlinear acoustics and ultrasonic thermography. An increase in nonlinear response of the defect at its local resonance exceeds substantially the one at natural frequencies of the specimen. The strong wave-defect interaction is confirmed by resonance induced rise of local temperature of the defect in the frequency band of its local resonance.
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81.70.Cv Nondestructive testing: ultrasonic testing, photoacoustic testing
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
43.25.Gf Standing waves; resonance

Kinetic and relativistic effects on the surface alloy formation of submonolayer Au adsorbed on Si(111)-math×math-Pb surface

Chong Li, Fengmin Wu, and Jingbo Li

Appl. Phys. Lett. 99, 211912 (2011); http://dx.doi.org/10.1063/1.3663967 (3 pages)

Online Publication Date: 23 November 2011

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Experiment reveals that the two-dimensional ordered phase of 3 × 3-Au/Pb alloy formed on Si(111)-math×math-Pb surface is dominated by Au parallelogram tetramers (4P). However, theoretical results indicate that three-dimensional tetrahedral tetramers (4T) grown on such surface is more energetically favorable. Using first-principles methods, we show that the discrepancy originates from a lower potential energy barrier of formation of the metastable 4P phase than that of the formation of stable 4T phase in nucleation and subsequent growth processes from triangular trimers (3T) islands and from stronger competition between Au s and d states caused by spin-orbit coupling effects.
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68.43.Mn Adsorption kinetics
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Characterization of amorphous In2O3: An ab initio molecular dynamics study

Antonio Aliano, Alessandra Catellani, and Giancarlo Cicero

Appl. Phys. Lett. 99, 211913 (2011); http://dx.doi.org/10.1063/1.3664224 (3 pages)

Online Publication Date: 23 November 2011

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In this work, we report on the structural and electronic properties of amorphous In2O3 obtained with ab initio molecular dynamics. Our results show crystal-like short range InO6 polyhedra having average In-O distance consistent with x-ray spectroscopy data. Structural disorder yields band tailing and localized states, which are responsible of a strong reduction of the electronic gap. Most importantly, the appearance of a peculiar O–O bond imparts n-type character to the amorphous compound and provides contribution for interpreting spectroscopic measurements on indium based oxidized systems. Our findings portray characteristic features to attribute transparent semiconductive properties to amorphous In2O3.
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71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.70.Dm X-ray absorption spectra
71.23.An Theories and models; localized states
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Atomic-scale determination of band offsets at the Gd2O3/GaAs (100) hetero-interface using scanning tunneling spectroscopy

Y. P. Chiu, B. C. Huang, M. C. Shih, J. Y. Shen, P. Chang, C. S. Chang, M. L. Huang, M.-H. Tsai, M. Hong, and J. Kwo

Appl. Phys. Lett. 99, 212101 (2011); http://dx.doi.org/10.1063/1.3663628 (3 pages) | Cited 3 times

Online Publication Date: 21 November 2011

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Direct measurements of band profile and band offsets across the Gd2O3/GaAs(100) hetero-interface have been performed using cross-sectional scanning tunneling microscopy and spectroscopy. The spatial variation of the local density of states with atomic precision revealed the interfacial band alignment in this model high-κ/III-V system. In conjunction with the theoretical modeling, the band offsets for both conduction and valence states are identified, revealing critical information about the electrostatic potential landscape of the GaAs semiconductor transistor with a Gd2O3 gate dielectric.
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85.30.Tv Field effect devices
89.20.Kk Engineering

Graphene arch gate SiO2 shell silicon nanowire core field effect transistors

J. E. Jin, J. H. Lee, D. H. Hwang, D. W. Kim, M. J. Kim, K. S. Son, D. Whang, and S. W. Hwang

Appl. Phys. Lett. 99, 212102 (2011); http://dx.doi.org/10.1063/1.3663629 (3 pages)

Online Publication Date: 21 November 2011

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We report the realization of graphene arch gate silicon nanowire field effect transistors with SiO2 shell serving as a gate insulator. The arch coverage of the SiO2 shell was achieved by the flexible graphene layers complying the top of the shell. The wrapping angle was defined by the relative strength of the van der Waals forces on the shell and the substrate. The leakage current of the graphene gate was only 55 fA, while the maximum on-off ratio of 16.7 was obtained. The effective mobility and quantum capacitance of the graphene layers were also obtained from the electronic transport data.
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85.30.Tv Field effect devices
72.80.Vp Electronic transport in graphene
73.61.Wp Fullerenes and related materials

First-principles study of Ge dangling bonds in GeO2 and correlation with electron spin resonance at Ge/GeO2 interfaces

M. Houssa, G. Pourtois, V. V. Afanas’ev, and A. Stesmans

Appl. Phys. Lett. 99, 212103 (2011); http://dx.doi.org/10.1063/1.3662860 (3 pages) | Cited 1 time

Online Publication Date: 21 November 2011

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The g-tensors of dangling bonds at defective Ge atoms in GeO2 are computed using density functional theory. The isotropic g-values of these defects are found to increase with the number of Ge backbonds. By comparing these calculations with the isotropic g-value of a Ge-related defect at Ge/GeO2 interfaces, recently observed by electron spin resonance (ESR) experiments, we tentatively identify this defect as a Ge2O≡Ge• center, i.e., a dangling bond on a Ge atom backbonded to two Ge atoms and one O atom, likely present near the Ge/GeO2 interface. The interaction of this defect with molecular hydrogen is investigated using first-principles molecular dynamics simulations. Our simulations predict that the Ge dangling bond can be hardly passivated by H2 molecules, in agreement with the electron spin resonance study.
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71.55.Ht Other nonmetals
76.30.Lh Other ions and impurities
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations

Colossal tuning of an energy gap in Sn2P2S6 under pressure

Vladimir V. Shchennikov, Natalia V. Morozova, Iryna Tyagur, Yuriy Tyagur, and Sergey V. Ovsyannikov

Appl. Phys. Lett. 99, 212104 (2011); http://dx.doi.org/10.1063/1.3662926 (3 pages) | Cited 3 times

Online Publication Date: 23 November 2011

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We report results of investigation of electrical and thermoelectric properties of Sn2P2S6 under strong compression up to 20 GPa. An “insulator-metal”(I-M)-type transition was discovered by a monotonic and reversible lowering of electrical resistivity by 9–10 orders. The energy gap (Eg = 2.3 eV) was estimated to decrease to ∼0.25–0.3 eV at 20 GPa. X-ray diffraction and Raman studies on samples recovered from the high pressure experiments confirm a conservation of the original monoclinic lattice. Thus, a colossal “band-gap engineering” potential is revealed in this optical material. Sn2P2S6 is a potential candidate for emergent multi-functional switches, between transparent “insulator” state and conducting state with magneto-dependent properties.
Show PACS
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Sk Insulators
62.50.-p High-pressure effects in solids and liquids
71.20.Ps Other inorganic compounds
71.30.+h Metal-insulator transitions and other electronic transitions
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