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12 Mar 2012

Volume 100, Issue 11, Articles (11xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 111101 (2012); http://dx.doi.org/10.1063/1.3691957 (3 pages)

Christina Alpmann, Michael Esseling, Patrick Rose, and Cornelia Denz
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Enhanced surface-enhanced Raman scattering performance by folding silver nanorods

Qin Zhou, Xian Zhang, Yu Huang, Zhengcao Li, Yiping Zhao, and Zhengjun Zhang

Appl. Phys. Lett. 100, 113101 (2012); http://dx.doi.org/10.1063/1.3694056 (3 pages) | Cited 3 times

Online Publication Date: 12 March 2012

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Folding straight Ag nanorods into zig-zag structures could generate corners or bends that become potential hot spots for surface-enhanced Raman scattering (SERS). Using a dynamic shadowing growth method, zig-zag silver nanorod arrays of different bending number N with a fixed total rod length are fabricated, and their SERS performance are measured and compared using the Raman probe Rhodamine 6G. The SERS intensity increases with N when N < 4 and decreases when N > 4. The results suggest that folding silver nanorods into three-dimensional structures is a promising way to design highly sensitive SERS substrates.
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78.30.Er Solid metals and alloys
78.68.+m Optical properties of surfaces
78.67.Qa Nanorods
81.16.-c Methods of micro- and nanofabrication and processing

A dual-silicon-nanowires based U-shape nanoelectromechanical switch with low pull-in voltage

You Qian, Liang Lou, Minglin Julius Tsai, and Chengkuo Lee

Appl. Phys. Lett. 100, 113102 (2012); http://dx.doi.org/10.1063/1.3693382 (3 pages) | Cited 1 time

Online Publication Date: 12 March 2012

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A dual-silicon-nanowires based U-shape nanoelectromechanical switch with low pull-in voltage is fabricated using standard complementary metal-oxide-semiconductor compatible process on silicon-on-insulator wafer. The switch consists of a capacitive paddle with dimension of 2 μm by 4 μm supported by two silicon nanowires, suspended on top of the substrate with a gap of 145 nm. The nanowires are 5 μm long with cross-section of 90 nm by 90 nm. The average pull-in voltage is about 1.12 V and the ratio of the ON/OFF current is measured to be over 10 000. According to the preliminary results, this U-shape structure demonstrates great potential in lowering down the pull-in voltage.
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84.32.Dd Connectors, relays, and switches
85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices

Single-valued estimation of the interface profile from intersubband absorption linewidth data

Doan Nhat Quang, Nguyen Nhu Dat, Nguyen Thanh Tien, and Dinh Nhu Thao

Appl. Phys. Lett. 100, 113103 (2012); http://dx.doi.org/10.1063/1.3693398 (3 pages)

Online Publication Date: 12 March 2012

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We study the ratio between different linewidths of the intersubband absorption in a quantum well. For roughness-related absorption, this ratio turns out to be independent of the roughness amplitude, so being a function of the correlation length only. Therefore, in contrast to the earlier belief, we may propose an efficient method for individual single-valued estimation of the two sizes of an interface profile from optical data. Instead of the simultaneous fitting of both sizes to the functional dependence of the linewidth at many experimental points, we perform a two-step fitting of (i) correlation length to the linewidth ratio at one point and then (ii) roughness amplitude to a linewidth at one point. This method is useful for experimental study of the interface morphology.
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78.67.De Quantum wells
68.35.Ct Interface structure and roughness
78.40.Fy Semiconductors
78.30.Fs III-V and II-VI semiconductors

A nanomachined optical logic gate driven by gradient optical force

J. F. Tao, J. Wu, H. Cai, Q. X. Zhang, J. M. Tsai, J. T. Lin, and A. Q. Liu

Appl. Phys. Lett. 100, 113104 (2012); http://dx.doi.org/10.1063/1.3693610 (3 pages) | Cited 3 times

Online Publication Date: 12 March 2012

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In this letter, a nanomachined optical logic gate using optical gradient force is demonstrated. The device consists of a partially free-hanging silicon double-ring resonator developed by the nano-electro-mechanical system technology. The logic NOR gate function is demonstrated at 20 Mb/s with a high extinction ratio of about 21.3 dB. This proposed NOR gate has the advantages of low power consumption (∼0.5 mW), highly compacted size (40 μm × 45 μm), and easy batch fabrication which has potential applications in silicon-photonic integration for digital signal processing.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
84.30.Sk Pulse and digital circuits
84.40.Az Waveguides, transmission lines, striplines

Extremely long carrier lifetime over 200 ns in GaAs wall-inserted type II InAs quantum dots

Kazutaka Nishikawa, Yasuhiko Takeda, Tomoyoshi Motohiro, Daisuke Sato, Junya Ota, Naoya Miyashita, and Yoshitaka Okada

Appl. Phys. Lett. 100, 113105 (2012); http://dx.doi.org/10.1063/1.3694284 (3 pages) | Cited 3 times

Online Publication Date: 13 March 2012

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To realize highly efficient intermediate-band (IB) solar cells, long lifetime of photo-generated carriers in the IB is essential. For this purpose, we propose a concept for IB absorbers using GaAs wall-inserted type II InAs quantum-dots (QDs), in which electrons at the IB of the InAs QDs and holes in the valence band of the GaAsSb layers are farther separated compared to those in conventional type II QDs. We fabricated InAs/GaAs/GaAs0.82Sb0.18 type II QDs and performed time-resolved photoluminescence spectroscopy. The obtained lifetime was as long as 220 ns for electrons at the IB.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
73.21.La Quantum dots
71.20.Nr Semiconductor compounds
73.20.At Surface states, band structure, electron density of states

Enhancing gas induced charge doping in graphene field effect transistors by non-covalent functionalization with polyethyleneimine

Shadi S. Sabri, Jonathan Guillemette, Abdelaadim Guermoune, Mohamed Siaj, and Thomas Szkopek

Appl. Phys. Lett. 100, 113106 (2012); http://dx.doi.org/10.1063/1.3694741 (4 pages)

Online Publication Date: 13 March 2012

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We demonstrate that large-area, graphene field effect transistors with a passive parylene substrate and a polyethyleneimine functional layer have enhanced sensitivity to CO2 gas exposure. The electron doping of graphene, caused by protonated amine groups within the polyethyleneimine, is modulated by the formation of negatively charged species generated by CO2 adsorption. The charge doping mechanism is general, and quantitative doping density changes can be determined from the graphene field effect transistor characteristics.
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85.30.Tv Field effect devices

Optical properties of Ag conic helical nanostructures

N. Sobhkhiz and A. Moshaii

Appl. Phys. Lett. 100, 113107 (2012); http://dx.doi.org/10.1063/1.3694021 (4 pages)

Online Publication Date: 14 March 2012

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The optical properties of an Ag conic helical nanostructure have been studied and compared with a similar corresponding normal helix by calculating the extinction spectra and the near electric field distributions. For most polarizations of the incident light, a number of resonance peaks appear in the extinction spectra of the conic helix, making the spectra more broadband. The peaks are originated from different radii of the conic helix pitches. The smaller side of the conic is more related to the optical properties at low wavelengths and the larger side to the high wavelength.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.Er Solid metals and alloys
78.40.Kc Metals, semimetals, and alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

High ON/OFF ratio and multimode transport in silicon nanochains field effect transistors

M. A. Rafiq, K. Masubuchi, Z. A. K. Durrani, A. Colli, H. Mizuta, W. I. Milne, and S. Oda

Appl. Phys. Lett. 100, 113108 (2012); http://dx.doi.org/10.1063/1.3694046 (4 pages) | Cited 3 times

Online Publication Date: 14 March 2012

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We have observed multimode transport and high ON/OFF ratio in silicon nanochain devices. Silicon nanochains grown by thermal evaporation of SiO solid sources consisted of chains of silicon nanocrystals ∼10 nm in diameter, separated by SiO2 regions. The devices were fabricated using electron beam lithography on SiO2 thermally grown on silicon substrate. These devices exhibited high ON/OFF current ratio up to 104. The inverse subthreshold slope as small as ∼500 mV/decade was observed in these devices. Therefore, we believe silicon nanochains hold great potential to be used in field effect transistors.
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85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices

Tuneable electromechanical comb generation

I. Mahboob, Q. Wilmart, K. Nishiguchi, A. Fujiwara, and H. Yamaguchi

Appl. Phys. Lett. 100, 113109 (2012); http://dx.doi.org/10.1063/1.3694041 (4 pages)

Online Publication Date: 15 March 2012

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An array of equally spaced oscillations or a comb is created within the bandwidth of the fundamental mode of an electromechanical resonator. This phenomenon utilises 2 continuous-wave (CW) pump excitations that piezoelectrically modulate the tension in the mechanical element and is seeded by a CW harmonic excitation of the first mode i.e., the signal. The resultant comb can be dynamically manipulated via the pumps and signal where the teeth separation can be tuned over 3 orders of magnitude and the comb density can be increased from just 2 teeth to nearly 102.
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77.65.Fs Electromechanical resonance; quartz resonators
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Phonon transport in Si nanowires with elastically dissimilar barriers

Jung Hyun Oh, Moon-Gyu Jang, Mincheol Shin, and Seok-Hee Lee

Appl. Phys. Lett. 100, 113110 (2012); http://dx.doi.org/10.1063/1.3694043 (3 pages)

Online Publication Date: 15 March 2012

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As one of the efforts to enhance the thermoelectric conversion efficiency, phonon transport through elastically dissimilar barriers embedded in Si nanowires is investigated. Using a Green’s function method based on an elastic wave equation, the transmission function is calculated for various barrier materials with different acoustic impedance. It is found that the insertion of silicide (especially PtSi) layers into the Si nanowire substantially suppresses the phonon transmission function and, thus, is promising alternative to enhance the efficiency of thermoelectric devices.
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63.22.Gh Nanotubes and nanowires
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)

Field emission from single-crystalline HfC nanowires

Jinshi Yuan, Han Zhang, Jie Tang, Norio Shinya, Kiyomi Nakajima, and Lu-Chang Qin

Appl. Phys. Lett. 100, 113111 (2012); http://dx.doi.org/10.1063/1.3694047 (3 pages)

Online Publication Date: 16 March 2012

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Single HfC nanowire field emitter/electrode structures have been fabricated using nano-assembling and electron beam induced deposition. Field ion microscopy has been applied to study the atomic arrangement of facets formed on a field evaporation-modified HfC nanowire tip. Field evaporation and crystal form studies suggest that the {111} and {110} crystal planes have lower work functions, while the {100}, {210}, and {311} planes have higher work functions. Field emission measurement permits us to obtain that the work function of the {111} crystal plane is about 3.4 eV.
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81.16.Dn Self-assembly
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.30.+y Surface double layers, Schottky barriers, and work functions
81.15.Jj Ion and electron beam-assisted deposition; ion plating
82.45.-h Electrochemistry and electrophoresis

Tuning of mid-infrared emission of ternary PbSrTe/CdTe quantum dots

A. Hochreiner, S. Kriechbaumer, T. Schwarzl, H. Groiss, M. Hassan, and G. Springholz

Appl. Phys. Lett. 100, 113112 (2012); http://dx.doi.org/10.1063/1.3694286 (4 pages)

Online Publication Date: 16 March 2012

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Tunable room-temperature mid-infrared photoluminescence emission from epitaxial PbSrTe quantum dots embedded in CdTe is demonstrated. By variation of the Sr content, the emission wavelength can be tuned over the whole 3 to 1.6 μm range. Comparing the emission of PbSrTe quantum dots, quantum wells and bulk material, a one order of magnitude increase in the emission efficiency is found for the quantum dots, contrary to the bulk behavior. Theoretical modelling of the transition energies shows that at higher Sr content, segregation of Sr into CdTe occurs. This conclusion is supported by annealing experiments.
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73.21.La Quantum dots
78.55.Et II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
73.21.Fg Quantum wells
81.05.Dz II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
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