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21 Mar 2011

Volume 98, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 123101 (2011); http://dx.doi.org/10.1063/1.3567492 (3 pages)

Linus C. Chuang, Michael Moewe, Kar Wei Ng, Thai-Truong D. Tran, Shanna Crankshaw, Roger Chen, Wai Son Ko, and Connie Chang-Hasnain
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GaAs nanoneedles grown on sapphire

Linus C. Chuang, Michael Moewe, Kar Wei Ng, Thai-Truong D. Tran, Shanna Crankshaw, Roger Chen, Wai Son Ko, and Connie Chang-Hasnain

Appl. Phys. Lett. 98, 123101 (2011); http://dx.doi.org/10.1063/1.3567492 (3 pages) | Cited 8 times

Online Publication Date: 21 March 2011

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Heterogeneous integration of dissimilar single crystals is of intense research interests. Lattice mismatch has been the most challenging bottleneck which limits the growth of sufficient active volume for functional devices. Here, we report self-assembled, catalyst-free, single crystalline GaAs nanoneedles grown on sapphire substrates with 46% lattice mismatch. The GaAs nanoneedles have a 2–3 nm tip, single wurtzite phase, excellent optical quality, and dimensions scalable with growth time. The needles have the same sharp, hexagonal pyramid shape from ∼ 100 nm (1.5 min growth) to ∼ 9 μm length (3 h growth).
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81.16.Dn Self-assembly
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
81.07.Bc Nanocrystalline materials
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors

Structural stability and electronic properties of SiC nanocones: First-principles calculations and symmetry considerations

G. Alfieri and T. Kimoto

Appl. Phys. Lett. 98, 123102 (2011); http://dx.doi.org/10.1063/1.3567535 (3 pages) | Cited 2 times

Online Publication Date: 21 March 2011

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The structural and electronic properties of SiC nanocones (SiCNCs), as a function of the disclination angle and electric field intensity and orientation, are investigated by means of ab initio calculations. Phonon analysis revealed that SiCNCs with only three disclination angles are allowed and, among these, the band gap of only one SiCNC is affected by a transverse electric field. An interpretation of these findings, from a group theoretical point of view, is also given.
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71.20.Nr Semiconductor compounds
73.22.-f Electronic structure of nanoscale materials and related systems
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
63.22.Gh Nanotubes and nanowires

Few graphene layers/carbon nanotube composites grown at complementary-metal-oxide-semiconductor compatible temperature

V. Jousseaume, J. Cuzzocrea, N. Bernier, and V. T. Renard

Appl. Phys. Lett. 98, 123103 (2011); http://dx.doi.org/10.1063/1.3569142 (3 pages) | Cited 8 times

Online Publication Date: 21 March 2011

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We investigate the growth of the recently demonstrated composite material composed of vertically aligned carbon nanotubes capped by few graphene layers. We show that the carbon nanotubes grow epitaxially under the few graphene layers. By using a catalyst and gaseous carbon precursor different from those used originally we establish that such unconventional growth mode is not specific to a precise choice of catalyst–precursor couple. Furthermore, the composite can be grown using catalyst and temperatures compatible with complementary-metal-oxide-semiconductor processing (T<450 °C).
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.Hc Catalytic methods
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Nanostructured carbon films with oriented graphitic planes

E. H. T. Teo, J. Kulik, Y. Kauffmann, R. Kalish, and Y. Lifshitz

Appl. Phys. Lett. 98, 123104 (2011); http://dx.doi.org/10.1063/1.3570625 (3 pages) | Cited 4 times

Online Publication Date: 22 March 2011

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Nanostructured carbon films with oriented graphitic planes can be deposited by applying energetic carbon bombardment. The present work shows the possibility of structuring graphitic planes perpendicular to the substrate in following two distinct ways: (i) applying sufficiently large carbon energies for deposition at room temperature (E>10 keV), (ii) utilizing much lower energies for deposition at elevated substrate temperatures (T>200 °C). High resolution transmission electron microscopy is used to probe the graphitic planes. The alignment achieved at elevated temperatures does not depend on the deposition angle. The data provides insight into the mechanisms leading to the growth of oriented graphitic planes under different conditions.
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68.55.A- Nucleation and growth
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.05.uf Graphite

Structure and magnetic properties of three-dimensional (La,Sr)MnO3 nanofilms on ZnO nanorod arrays

Haiyong Gao, M. Staruch, Menka Jain, Pu-Xian Gao, Paresh Shimpi, Yanbing Guo, Wenjie Cai, and Hui-jan Lin

Appl. Phys. Lett. 98, 123105 (2011); http://dx.doi.org/10.1063/1.3567544 (3 pages) | Cited 3 times

Online Publication Date: 22 March 2011

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Three-dimensional (3D) cubic perovskite (La,Sr)MnO3 (LSMO) nanofilms have been deposited on ZnO nanorod arrays with controlled dimensionality and crystallinity by radio frequency (rf) magnetron sputtering and post thermal annealing. Compared to the two-dimensional (2D) LSMO nanofilm on flat Si, the structure and magnetic properties of 3D LSMO nanofilms on ZnO nanorod arrays have a strong anisotropic morphology and thickness dependence. Ferromagnetic property has been observed in both 2D and 3D LSMO nanofilms while a ferromagnetic–superparamagnetic transition was revaled in 3D LSMO nanofilms on ZnO nanorod array with decreasing nanofilm thickness, due to a large surface dispersion effect. The LSMO/ZnO nanofilm/nanorod structures could open up new avenues for intriguing magnetic properties studies and applications of nanoscale perovskites.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.40.Gh Other heat and thermomechanical treatments
68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering

Enhanced spin contrast of epitaxial Mn films on Fe(100) by spin-polarized scanning tunneling microscopy

Puneet Mishra, Takashi Uchihashi, and Tomonobu Nakayama

Appl. Phys. Lett. 98, 123106 (2011); http://dx.doi.org/10.1063/1.3567939 (3 pages)

Online Publication Date: 22 March 2011

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The magnetic ordering in ultrathin Mn films grown on Fe(100) substrates is studied using spin-polarized scanning tunneling microscopy/scanning tunneling spectroscopy. Enhancement of spin contrast is observed due to a tip modification. Detailed analysis carried out using normalized dI/dV spectra indicates the appearance of resonant tunneling behavior. This is attributed to the attachment of a magnetic cluster at the apex of the magnetic thin film tip. Our results compare well with a recent theoretical prediction of a high vacuum spin-polarization of an Fe tip with an antiferromagnetically coupled Mn adatom [ Ferriani et al., Phys. Rev. B 82, 054411 (2010)] .
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.at Other materials
73.40.Gk Tunneling

Electron field emission enhancement of carbon nanowalls by plasma surface nitridation

Wakana Takeuchi, Hiroki Kondo, Tomomi Obayashi, Mineo Hiramatsu, and Masaru Hori

Appl. Phys. Lett. 98, 123107 (2011); http://dx.doi.org/10.1063/1.3532114 (3 pages) | Cited 6 times

Online Publication Date: 22 March 2011

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Carbon nanowalls (CNWs) are two-dimensional carbon nanostructures consisting of stacked graphene sheets standing vertically on the substrate. The sharp edges of CNWs provide us with opportunities for applications as electron field emitter arrays. The effects of nitrogen plasma (NP) treatment on the surface of CNWs have been investigated in order to improve the electron field emission properties. The electron emission current from the edges of CNWs was drastically increased by the NP treatment. Morphological and chemical changes in the CNWs after the NP treatment were characterized using scanning electron microscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy.
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85.45.Db Field emitters and arrays, cold electron emitters
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
78.30.Na Fullerenes and related materials
78.67.Ch Nanotubes
79.60.-i Photoemission and photoelectron spectra

Exponential tuning of the coupling constant of coupled microcantilevers by modifying their separation

Eduardo Gil-Santos, Daniel Ramos, Valerio Pini, Montserrat Calleja, and Javier Tamayo

Appl. Phys. Lett. 98, 123108 (2011); http://dx.doi.org/10.1063/1.3569588 (3 pages) | Cited 1 time

Online Publication Date: 22 March 2011

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Vibration localization in coupled nanomechanical resonators has emerged as a promising concept for ultrasensitive mass sensing. It possesses intrinsic common mode rejection and the mass sensitivity can be enhanced with no need of extreme miniaturization of the devices. In this work, we have experimentally studied the role of the separation between cantilevers that are elastically coupled by an overhang. The results show that the coupling constant exponentially decays with the separation. In consistency with the theoretical expectations, the mass sensitivity is inversely proportional to the coupling constant. Finite element simulations show that the coupling constant can be exponentially reduced by increasing the ratio of the cantilever separation to the overhang length.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Cm Micromechanical devices and systems
06.30.Dr Mass and density

Fast growth of graphene patterns by laser direct writing

J. B. Park, W. Xiong, Y. Gao, M. Qian, Z. Q. Xie, M. Mitchell, Y. S. Zhou, G. H. Han, L. Jiang, and Y. F. Lu

Appl. Phys. Lett. 98, 123109 (2011); http://dx.doi.org/10.1063/1.3569720 (3 pages) | Cited 12 times

Online Publication Date: 22 March 2011

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Rapid single-step fabrication of graphene patterns was developed using laser-induced chemical vapor deposition (LCVD). A laser beam irradiates a thin nickel foil in a CH4 and H2 environment to induce a local temperature rise, thereby allowing the direct writing of graphene patterns in precisely controlled positions at room temperature. Line patterns can be achieved with a single scan without pre- or postprocesses. Surprisingly, the growth rate is several thousand times faster than that of general CVD methods. The discovery and development of the LCVD growth process provide a route for the rapid fabrication of graphene patterns for various applications.
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81.16.Mk Laser-assisted deposition
81.05.ue Graphene
81.15.Fg Pulsed laser ablation deposition
81.16.Rf Micro- and nanoscale pattern formation
61.82.Fk Semiconductors

Carbon nanotube field-effect transistors with molecular interface

Kan-Sheng Chen, Stephen A. McGill, and Peng Xiong

Appl. Phys. Lett. 98, 123110 (2011); http://dx.doi.org/10.1063/1.3571281 (3 pages) | Cited 2 times

Online Publication Date: 23 March 2011

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We report on a study of molecular modifications of the electronic characteristics of single-walled carbon nanotube (SWNT) field-effect transistors (FETs) through insertion of different organic self-assembled monolayers (SAMs) between the SWNT and an electrode. The changes induced by the molecular interface were elucidated using a device structure created by directed assembly of a single SWNT over three prepatterned electrodes, one of which had a SAM deposited via dip-pen nanolithography. The resulting direct comparison of two FETs sharing the same SWNT revealed pronounced modification of the transfer characteristics, on/off ratio, and threshold voltages due to the SWNT/molecule/metal junction. The effects are attributed primarily to the alteration of the electronic bands in the Au electrode and the SWNT, and the resulting changes in the effective Schottky barrier height/thickness, by the ordered and well-aligned molecular SAM.
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85.30.Tv Field effect devices
85.35.Kt Nanotube devices

Growth study of Co thin film on nanorippled Si(100) substrate

Sarathlal K. V., Dileep Kumar, and Ajay Gupta

Appl. Phys. Lett. 98, 123111 (2011); http://dx.doi.org/10.1063/1.3567731 (3 pages) | Cited 3 times

Online Publication Date: 23 March 2011

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The growth behavior of Co thin film on nanorippled Si(100) substrate has been studied. A clear anisotropy in the growth behavior along and normal to the ripples has been observed, resulting in preferential coalescence of islands normal to the ripple wave vector. A preferential orientation of c-axis along the ripple wave vector is observed, which may be a result of minimization of magnetoelastic and anisotropic energies in the presence of internal stresses.
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75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
68.55.-a Thin film structure and morphology

Interdiffusion and barrier layer formation in thermally evaporated Mn/Cu heterostructures on SiO2 substrates

J. G. Lozano, S. Lozano-Perez, J. Bogan, Y. C. Wang, B. Brennan, P. D. Nellist, and G. Hughes

Appl. Phys. Lett. 98, 123112 (2011); http://dx.doi.org/10.1063/1.3569146 (3 pages) | Cited 7 times

Online Publication Date: 23 March 2011

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Mn/Cu heterostructures thermally evaporated onto SiO2 and, subsequently, annealed were investigated by transmission electron microscopy related techniques in order to study the diffusion interactions which lead to barrier layer formation. Energy dispersive x-ray spectroscopy and electron energy loss spectroscopy provide evidence for the interdiffusion between the Mn and Cu layers following a 450 °C anneal, where the Mn diffuses toward the surface of the structure, while Cu diffuses toward the Mn/SiO2 but does not propagate into the dielectric. The chemical composition of the 2–3 nm interfacial layer is primarily a mixture of +2 and +3 Mn valences, in good agreement with previously reported results.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
81.40.Gh Other heat and thermomechanical treatments
68.37.Lp Transmission electron microscopy (TEM)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
79.20.Uv Electron energy loss spectroscopy

Stability and evolution of low-surface-tension metal catalyzed growth of silicon nanowires

Linwei Yu, Franck Fortuna, Benedict O’Donnell, Gilles Patriache, and Pere Roca i Cabarrocas

Appl. Phys. Lett. 98, 123113 (2011); http://dx.doi.org/10.1063/1.3569817 (3 pages) | Cited 4 times

Online Publication Date: 23 March 2011

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Low-surface-tension metals were predicted to be insufficient to catalyze the growth of silicon nanowires (SiNWs) in vapor-liquid-solid (VLS) mode while counter examples do exist, for example, in the tin- or indium-catalyzed SiNWs. This puzzle remains largely unresolved. We first examine the local tension-force-balance in a tin-catalyzed SiNW by using a cross-section analysis. We found that the existence of an ultrathin sidewall-spreading catalyst layer helps to stabilize the catalyst drop during growth. The predicted contact-angle evolution, by an energetic balance model, is also supported by the experimental data. These results bring critical understanding on the low-surface-tension catalyzed VLS process.
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81.16.Hc Catalytic methods
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.07.Gf Nanowires
68.65.La Quantum wires (patterned in quantum wells)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.03.Cd Surface tension and related phenomena

Absence of vapor-liquid-solid growth during molecular beam epitaxy of self-induced InAs nanowires on Si

S. Hertenberger, D. Rudolph, S. Bolte, M. Döblinger, M. Bichler, D. Spirkoska, J. J. Finley, G. Abstreiter, and G. Koblmüller

Appl. Phys. Lett. 98, 123114 (2011); http://dx.doi.org/10.1063/1.3567496 (3 pages) | Cited 14 times

Online Publication Date: 24 March 2011

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The growth mechanism of self-induced InAs nanowires (NWs) grown on Si (111) by molecular beam epitaxy was investigated by in situ reflection high energy electron diffraction and ex situ scanning and transmission electron microscopy. Abrupt morphology transition and in-plane strain relaxation revealed that InAs NWs nucleate without any significant delay and under the absence of indium (In) droplets. These findings are independent of the As/In-flux ratio, revealing entirely linear vertical growth rate and nontapered NWs. No evidence of In droplets nor associated change in the NW apex morphology was observed for various growth termination procedures. These results highlight the absence of vapor-liquid-solid growth, providing substantial benefits for realization of atomically abrupt doping and composition profiles in future axial InAs-based NW heterostructures on Si.
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81.07.Gf Nanowires
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.46.Np Structure of nanotubes (hollow nanowires)

Nonlinear microwave response of aluminum weak-link Josephson oscillators

E. M. Levenson-Falk, R. Vijay, and I. Siddiqi

Appl. Phys. Lett. 98, 123115 (2011); http://dx.doi.org/10.1063/1.3570693 (3 pages) | Cited 4 times

Online Publication Date: 24 March 2011

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We present the driven response at T = 30 mK of 6 GHz superconducting resonators constructed from capacitively-shunted three-dimensional (3D) aluminum nanobridge superconducting quantum interference devices (nanoSQUIDs). We observe flux modulation of the resonant frequency in quantitative agreement with numerical calculation and characteristic of near-ideal short weak-link junctions. Under strong microwave excitation, we observe stable bifurcation in devices with coupled quality factor (Q) ranging from 30–3500. Near this bias point, parametric amplification with >20 dB gain, 40 MHz bandwidth, and near quantum-limited noise performance is observed. Our results indicate that 3D nanobridge junctions are attractive circuit elements to realize quantum bits.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)

Tailoring the electrostatic screening effect during field emission from hollow multiwalled carbon nanotube pillars

Kiran Shankar Hazra, Tanuj Gigras, and D. S. Misra

Appl. Phys. Lett. 98, 123116 (2011); http://dx.doi.org/10.1063/1.3565243 (3 pages) | Cited 1 time

Online Publication Date: 25 March 2011

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Field emission from hollow pillars of multi wall carbon nanotubes show lower screening effect and their turn on field can be tailored by tuning the annular width of the pillars. Simulations show that the energy variation in the extracted electrons can be decreased by lowering the annular width of the hollow pillars; for the hollow pillars of 10 μm annular width the energy width is ∼ 0.5 eV, fourfold lower than the solid pillars. This can reduce further by reducing the annular width of the pillars paving the way forward for the monochromatic electron emission.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems

Nano-Schottky barrier diodes based on Sb-doped ZnS nanoribbons with controlled p-type conductivity

Qiang Peng, Jiansheng Jie, Chao Xie, Li Wang, Xiwei Zhang, Di Wu, Yongqiang Yu, Chunyan Wu, Zhi Wang, and Peng Jiang

Appl. Phys. Lett. 98, 123117 (2011); http://dx.doi.org/10.1063/1.3569590 (3 pages) | Cited 5 times

Online Publication Date: 25 March 2011

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ZnS nanoribbons (NRs) with controlled p-type doping were synthesized by using Sb as dopant. The p-type conductivity of the ZnS:Sb NRs could be tuned in a wide range of seven orders of magnitude by adjusting the Sb doping level. Nano-Schottky barrier diodes based on Al/p-ZnS NRs junctions exhibited excellent device performances with a high rectification ratio >107 and a small ideality factor of ∼ 1.22. The diodes also showed the potential as high-sensitive UV detectors. The p-ZnS NRs are expected to act as key building blocks in nano-optoelectronics.
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85.30.Kk Junction diodes
85.35.-p Nanoelectronic devices

Measurement of valley splitting in high-symmetry Si/SiGe quantum dots

M. G. Borselli, R. S. Ross, A. A. Kiselev, E. T. Croke, K. S. Holabird, P. W. Deelman, L. D. Warren, I. Alvarado-Rodriguez, I. Milosavljevic, F. C. Ku, W. S. Wong, A. E. Schmitz, M. Sokolich, M. F. Gyure, and A. T. Hunter

Appl. Phys. Lett. 98, 123118 (2011); http://dx.doi.org/10.1063/1.3569717 (3 pages) | Cited 9 times

Online Publication Date: 25 March 2011

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We have demonstrated few-electron quantum dots in Si/SiGe and InGaAs, with occupation number controllable from N = 0. These display a high degree of spatial symmetry and identifiable shell structure. Magnetospectroscopy measurements show that two Si-based devices possess a singlet N = 2 ground state at low magnetic field, and therefore, the twofold valley degeneracy is lifted. The valley splittings in these two devices were 270 and 120 μeV, suggesting the presence of atomically sharp interfaces in our heterostructures.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
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