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3 Dec 2012

Volume 101, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 101, 233101 (2012); http://dx.doi.org/10.1063/1.4749281 (3 pages)

S. A. Studenikin, J. Thorgrimson, G. C. Aers, A. Kam, P. Zawadzki, Z. R. Wasilewski, A. Bogan, and A. S. Sachrajda
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Enhanced charge detection of spin qubit readout via an intermediate state

S. A. Studenikin, J. Thorgrimson, G. C. Aers, A. Kam, P. Zawadzki, Z. R. Wasilewski, A. Bogan, and A. S. Sachrajda

Appl. Phys. Lett. 101, 233101 (2012); http://dx.doi.org/10.1063/1.4749281 (3 pages)

Online Publication Date: 3 December 2012

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We employ an intermediate excited charge state of a lateral quantum dot device to increase the charge detection contrast during the qubit state readout procedure, allowing us to increase the visibility of coherent qubit oscillations. This approach amplifies the coherent oscillation magnitude but has no effect on the detector noise resulting in an increase in the signal to noise ratio. In this letter, we apply this scheme to demonstrate a significant enhancement of the fringe contrast of coherent Landau-Zener-Stückelberg oscillations between singlet S and triplet T+ two-spin states.
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68.65.Hb Quantum dots (patterned in quantum wells)
87.19.ln Oscillations and resonance

Size, composition, and doping effects on In(Ga)As nanowire/Si tunnel diodes probed by conductive atomic force microscopy

Tao Yang, Simon Hertenberger, Stefanie Morkötter, Gerhard Abstreiter, and Gregor Koblmüller

Appl. Phys. Lett. 101, 233102 (2012); http://dx.doi.org/10.1063/1.4768001 (5 pages)

Online Publication Date: 3 December 2012

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We investigate the effect of various parameters on the room–temperature interband tunneling characteristics of molecular beam epitaxy grown, intrinsically n-type In(Ga)As nanowires (NWs) on p-type silicon (Si) substrate using conductive atomic force microscopy. Large interband tunnel currents (>40 kA/cm2) and reduced breakdown voltages are obtained by increasing the p-type substrate doping level to >1 × 1019 cm−3. Current mapping under forward bias reveals a bimodal distribution of NW/Si hetero-junction tunnel diodes exhibiting either negative differential resistance (NDR, Esaki diode) or high excess currents (without NDR). By downscaling the NW diameter from ∼90 nm to ∼25 nm, peak-to-valley current ratios in NDR-type diodes increase and saturate with maximum values of ∼3. Increasing Ga content (xGa up to ∼0.1) in In–rich ternary InGaAs NWs preserves the NDR behavior, while the peak current shifts to lower voltages due to reduced Fermi energy in InGaAs. Band profile calculations were performed to further support these findings.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Thermodynamic mechanism of nickel silicide nanowire growth

Joondong Kim

Appl. Phys. Lett. 101, 233103 (2012); http://dx.doi.org/10.1063/1.4768231 (4 pages)

Online Publication Date: 3 December 2012

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A unique growth mechanism of nickel silicide (NiSi) nanowires (NWs) was thermodynamically investigated. The reaction between Ni and Si primarily determines NiSi phases according to the deposition condition. Optimum growth conditions were found at 375 °C leading long and high-density NiSi NWs. The ignition of NiSi NWs is determined by the grain size due to the nucleation limited silicide reaction. A successive Ni diffusion through a silicide layer was traced from a NW grown sample. Otherwise Ni-rich or Si-rich phase induces a film type growth. This work demonstrates specific existence of NiSi NW growth.
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81.07.Gf Nanowires
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
66.30.Pa Diffusion in nanoscale solids
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
66.30.Fq Self-diffusion in metals, semimetals, and alloys
68.55.-a Thin film structure and morphology

Efficiency and droop improvement in green InGaN/GaN light-emitting diodes on GaN nanorods template with SiO2 nanomasks

Da-Wei Lin, Chia-Yu Lee, Che-Yu Liu, Hau-Vei Han, Yu-Pin Lan, Chien-Chung Lin, Gou-Chung Chi, and Hao-Chung Kuo

Appl. Phys. Lett. 101, 233104 (2012); http://dx.doi.org/10.1063/1.4768950 (4 pages)

Online Publication Date: 3 December 2012

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This study presents the green InGaN/GaN multiple quantum wells light-emitting diodes (LEDs) grown on a GaN nanorods template with SiO2 nanomasks by metal–organic chemical vapor deposition. By nanoscale epitaxial lateral overgrowth, microscale air voids were formed between nanorods and the threading dislocations were efficiently suppressed. The electroluminescence measurement reveals that the LEDs on nanorods template with SiO2 nanomasks suffer less quantum-confined Stark effect and exhibit higher light output power and lower efficiency droop at a high injection current as compared with conventional LEDs.
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85.60.Jb Light-emitting devices
85.30.Kk Junction diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Ultra-thin planar fully relaxed Ge pseudo-substrate on compliant porous silicon template layer

M. Aouassa, S. Escoubas, A. Ronda, L. Favre, S. Gouder, R. Mahamdi, E. Arbaoui, A. Halimaoui, and I. Berbezier

Appl. Phys. Lett. 101, 233105 (2012); http://dx.doi.org/10.1063/1.4769040 (5 pages)

Online Publication Date: 3 December 2012

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Porous silicon (PSi) layers are used as templates to grow epitaxial planar and fully relaxed Ge pseudo-substrates. An annealing at 600 °C, dramatically changes the PSi morphology and produces compliant template layers which serve in a second step, as substrate for the epitaxy of fully relaxed SiGe layers with a Ge content between 50% and 94%. The SiGe pseudo-substrates produced by such process exhibit a remarkable planar surface resulting from the penetration of Ge inside the pores. They could be integrated into conventional microelectronic technology for the subsequent deposition of active layers such as tensily strained Si or relaxed Ge.
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81.05.Cy Elemental semiconductors
81.15.Np Solid phase epitaxy; growth from solid phases
68.55.ag Semiconductors
71.55.Cn Elemental semiconductors
81.05.Rm Porous materials; granular materials
61.43.Gt Powders, porous materials
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Electron-state engineering of bilayer graphene by ionic molecules

Nguyen Thanh Cuong, Minoru Otani, and Susumu Okada

Appl. Phys. Lett. 101, 233106 (2012); http://dx.doi.org/10.1063/1.4769098 (4 pages) | Cited 1 time

Online Publication Date: 4 December 2012

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Based on the first-principles total-energy calculations, we demonstrate the possibility of controlling the band-gap and carrier type of bilayer graphene using ionic molecules. Our calculations suggest that bilayer graphene sandwiched by a pair of cation-anion molecules is a semiconductor with a moderate energy gap of 0.26 eV that is attributable to the strong local dipole field induced by the cation-anion pair. Furthermore, we can control the semiconducting carrier type—intrinsic, p-type, or n-type—of bilayer graphene sandwiched by ionic molecules by changing the cation-anion pair.
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73.22.Pr Electronic structure of graphene
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Nc Total energy and cohesive energy calculations
71.20.Tx Fullerenes and related materials; intercalation compounds

Reverse mass transport during capping of In0.5Ga0.5As/GaAs quantum dots

H. Eisele, Ph. Ebert, N. Liu, A. L. Holmes, Jr., and C.-K. Shih

Appl. Phys. Lett. 101, 233107 (2012); http://dx.doi.org/10.1063/1.4769100 (4 pages) | Cited 2 times

Online Publication Date: 4 December 2012

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The rates of indium mass transport between the wetting layer, the quantum dots, and the capping layer are derived from the indium distributions probed by cross-sectional scanning tunneling microscopy of the In0.5Ga0.5As/GaAs quantum dot system. During capping, a lateral back-segregation from the quantum dots toward the wetting layer is found, reversing the Stranski-Krastanov growth mode during quantum dot formation. This lateral back-segregation critically affects the resulting indium distribution in the wetting layer, the apparent segregation coefficients as well as the quantum dot shape. Furthermore, the strain effect on the segregation coefficient is quantified.
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68.35.Ct Interface structure and roughness
68.08.Bc Wetting
81.30.Mh Solid-phase precipitation
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
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The c-axis thermal conductivity of graphite film of nanometer thickness measured by time resolved X-ray diffraction

M. Harb, C. von Korff Schmising, H. Enquist, A. Jurgilaitis, I. Maximov, P. V. Shvets, A. N. Obraztsov, D. Khakhulin, M. Wulff, and J. Larsson

Appl. Phys. Lett. 101, 233108 (2012); http://dx.doi.org/10.1063/1.4769214 (4 pages)

Online Publication Date: 5 December 2012

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We report on the use of time resolved X-ray diffraction to measure the dynamics of strain in laser-excited graphite film of nanometer thickness, obtained by chemical vapour deposition (CVD). Heat transport in the CVD film is simulated with a 1-dimensional heat diffusion model. We find the experimental data to be consistent with a c-axis thermal conductivity of ∼0.7 W m−1 K−1. This value is four orders of magnitude lower than the thermal conductivity in-plane, confirming recent theoretical calculations of the thermal conductivity of multilayer graphene.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
68.55.jd Thickness
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Piezoresistance behaviors of ultra-strained SiC nanowires

Ruiwen Shao, Kun Zheng, Yuefei Zhang, Yujie Li, Ze Zhang, and Xiaodong Han

Appl. Phys. Lett. 101, 233109 (2012); http://dx.doi.org/10.1063/1.4769217 (4 pages)

Online Publication Date: 5 December 2012

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In situ electrical measurement experiments were carried out in individual SiC nanowires (NWs) subjected to tensile strain using a transmission electron microscope. Fracture strain approaching 10% was achieved for a diamond-structure SiC NW with a 〈111〉 direction. With an increase in the tensile strain, the conductance increased monotonously. The current rate of increase remained constant prior to fracture. The calculated piezoresistance coefficient of this SiC NW was −1.15 × 10−11 Pa−1, which is similar to the coefficient of the bulk material. Our results indicate that these SiC NWs can be used as pressure sensors even in very high-pressure environments.
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81.05.Hd Other semiconductors
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mm Fracture
81.07.Gf Nanowires
72.20.Fr Low-field transport and mobility; piezoresistance
73.63.-b Electronic transport in nanoscale materials and structures

A bright cadmium-free, hybrid organic/quantum dot white light-emitting diode

Xuyong Yang, Yoga Divayana, Dewei Zhao, Kheng Swee Leck, Fen Lu, Swee Tiam Tan, Agus Putu Abiyasa, Yongbiao Zhao, Hilmi Volkan Demir, and Xiao Wei Sun

Appl. Phys. Lett. 101, 233110 (2012); http://dx.doi.org/10.1063/1.4769347 (4 pages)

Online Publication Date: 6 December 2012

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We report a bright cadmium-free, InP-based quantum dot light-emitting diode (QD-LED) with efficient green emission. A maximum brightness close to 700 cd/m2 together with a relatively low turn-on voltage of 4.5 V has been achieved. With the design of a loosely packed QD layer resulting in the direct contact of poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (poly-TPD) and 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) in the device, a ternary complementary white QD-LED consisting of blue component (poly-TPD), green component (QDs), and red component (exciplex formed at the interface between poly-TPD and TPBi) has been demonstrated. The resulting white QD-LED shows an excellent color rendering index of 95.
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85.60.Jb Light-emitting devices

Optical response in subnanometer gaps due to nonlocal response and quantum tunneling

Tianyu Dong, Xikui Ma, and Raj Mittra

Appl. Phys. Lett. 101, 233111 (2012); http://dx.doi.org/10.1063/1.4769348 (5 pages)

Online Publication Date: 6 December 2012

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In this paper, we derive the optical response of nanowire dimers with subnanometer gap sizes using different models, viz., the classical, quantum-corrected, nonlocal, and quantum-corrected nonlocal models. Our results indicate that both the quantum tunneling and the nonlocal response should be considered for the gap sizes less than 0.5 nm. We find that, when the quantum tunneling cannot be neglected, the nonlocal response is crucial in explaining the field enhancement at higher frequencies instead of the field collapse phenomenon if the nonlocal effect is ignored.
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73.22.Lp Collective excitations
78.66.Bz Metals and metallic alloys

Energy transfer from a single nitrogen-vacancy center in nanodiamond to a graphene monolayer

Xiaodi Liu, Guanzhong Wang, Xuerui Song, Fupan Feng, Wei Zhu, Liren Lou, Junfeng Wang, Hong Wang, and Pengfei Bao

Appl. Phys. Lett. 101, 233112 (2012); http://dx.doi.org/10.1063/1.4769367 (4 pages) | Cited 1 time

Online Publication Date: 6 December 2012

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In this work, we experimentally demonstrate energy transfer from a single negatively charged nitrogen-vacancy (NV) center in nanodiamond to a graphene monolayer. The mode values of lifetime and intensity of the fluorescence from the single NV center in nanodiamond on monolayer graphene are shorter and weaker than that on bare quartz substrate. The energy transfer efficiency is measured about 40%, consistent with our theoretical estimation.
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61.72.jd Vacancies
78.67.Wj Optical properties of graphene
78.55.Hx Other solid inorganic materials

Crystallization of Ge2Sb2Te5 nanometric phase change material clusters made by gas-phase condensation

G. E. Ghezzi, R. Morel, A. Brenac, N. Boudet, M. Audier, F. Fillot, S. Maitrejean, and F. Hippert

Appl. Phys. Lett. 101, 233113 (2012); http://dx.doi.org/10.1063/1.4769435 (4 pages)

Online Publication Date: 6 December 2012

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The crystallization behavior of Ge2Sb2Te5 nanometric clusters was studied using X-ray diffraction with in situ annealing. Clusters were made using a sputtering gas-phase condensation source, which allowed for the growth of well-defined, contaminant-free, and isolated clusters. The average size for the clusters is 5.7 ± 1 nm. As-deposited amorphous clusters crystallize in the fcc cubic phase at 180 °C, while for thin films, the phase change temperature is 155 °C. This observation illustrates the scalability of the Ge2Sb2Te5 phase change from the amorphous to the cubic state in three-dimensionally confined systems in this size range.
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81.16.-c Methods of micro- and nanofabrication and processing
81.40.Gh Other heat and thermomechanical treatments
64.70.fm Thermodynamics studies of evaporation and condensation
78.66.Nk Insulators

High thermoelectric figure of merit in silicon-germanium superlattice structured nanowires

Lihong Shi, Jinwu Jiang, Gang Zhang, and Baowen Li

Appl. Phys. Lett. 101, 233114 (2012); http://dx.doi.org/10.1063/1.4769443 (4 pages)

Online Publication Date: 7 December 2012

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By using a combination of the first-principles density functional theory and nonequilibrium Green's function for electron and phonon transport, we investigate the thermoelectric properties of silicon-germanium superlattice nanowires (NWs). Our results show that introducing superlattice structures always increases thermoelectric figure of merit, ZT, which depends on the periodic length of the superlattice NWs. For n-type superlattice NWs, the achievable maximum ZT is 4.7, which is 5-fold increase as compared to the equivalent pristine silicon NWs. For p-type wires, the achieved maximum ZT is 2.74, which is 4.6-fold increase as compared to the pristine silicon NWs.
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72.20.Pa Thermoelectric and thermomagnetic effects
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
02.30.-f Function theory, analysis
05.60.-k Transport processes
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Low-frequency noise in gallium nitride nanowire mechanical resonators

Jason M. Gray, Kris A. Bertness, Norman A. Sanford, and Charles T. Rogers

Appl. Phys. Lett. 101, 233115 (2012); http://dx.doi.org/10.1063/1.4769445 (5 pages)

Online Publication Date: 7 December 2012

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We report on the low-frequency 1/f (flicker) parameter noise displayed by the resonance frequency of doubly clamped c-axis gallium nitride nanowire (NW) mechanical resonators. The resonators are electrostatically driven and their mechanical response is electronically detected via NW piezoresistance. With an applied dc voltage bias, a NW driven near its mechanical resonance generates a dc and Lorentzian rf current that both display 1/f noise. The rf current noise is proportional to the square of the derivative of the Lorentzian lineshape with a magnitude highly dependent on NW dc bias voltage conditions, consistent with a model wherein noise in the NW's electrical impedance leads to temperature noise from local Joule heating, which in turn generates resonance frequency noise via thermal expansion and the temperature-dependent Young's modulus. An example device with a 27.8 MHz resonance frequency experiences an approximate resonance frequency shift of −1.4 Hz/nW. The resonance frequency noise increases as the square of the bias voltage, indicating specific operating conditions that optimize the signal-to-noise ratio in proposed NW sensors.
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07.10.Cm Micromechanical devices and systems
68.65.La Quantum wires (patterned in quantum wells)
72.20.Fr Low-field transport and mobility; piezoresistance
72.70.+m Noise processes and phenomena
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.07.Gf Nanowires
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