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25 Dec 2006

Volume 89, Issue 26, Articles (26xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 263110 (2006); http://dx.doi.org/10.1063/1.2424541 (3 pages)

Ch. Deneke, U. Zschieschang, H. Klauk, and O. G. Schmidt
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Enhanced plasticity in Mg-based bulk metallic glass composite reinforced with ductile Nb particles

D. G. Pan, H. F. Zhang, A. M. Wang, and Z. Q. Hu

Appl. Phys. Lett. 89, 261904 (2006); http://dx.doi.org/10.1063/1.2423234 (3 pages) | Cited 30 times

Online Publication Date: 26 December 2006

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The authors report the synthesis of Mg-based metallic glass composite reinforced with Nb particles which are simply added during melting process. The ductile Nb particles effectively impede shear band propagation and upon yielding, deformed Nb particles distribute the load uniformly to the surrounding glassy matrix to promote the initiation and branching of abundant secondary shear bands. In contrast to the previous Mg-based metallic glass composites which fracture with very little plasticity, the composite shows great resistance to crack growth. The high strength of 900 MPa and large plasticity of 12.1±2% have made it comparable to excellent Zr- or Ti-based metallic glass composite.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.35.Gy Mechanical properties; surface strains
81.05.Kf Glasses (including metallic glasses)
81.05.Bx Metals, semimetals, and alloys

Direct observation of the epitaxial growth of molecular layers on molecular single crystals

A. Sassella, A. Borghesi, M. Campione, S. Tavazzi, C. Goletti, G. Bussetti, and P. Chiaradia

Appl. Phys. Lett. 89, 261905 (2006); http://dx.doi.org/10.1063/1.2423322 (3 pages) | Cited 8 times

Online Publication Date: 26 December 2006

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In this letter the authors use the evolution of reflectance anisotropy spectra with film thickness during the growth of organic molecular films of a prototype molecular system (α-quarterthiophene grown onto a single crystal of the same material) to demonstrate homoepitaxy. The real time monitoring of the optical anisotropy of a thin film during deposition by organic molecular beam epitaxy is assessed as a powerful tool to achieve an effective in situ control of the growth starting from the very early deposition stages.
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68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Qn Polymers; organic compounds

Raman scattering and electroluminescence of ZnS:Cu,Cl phosphor powder

Yung-Tang Nien and In-Gann Chen

Appl. Phys. Lett. 89, 261906 (2006); http://dx.doi.org/10.1063/1.2423326 (3 pages) | Cited 18 times

Online Publication Date: 26 December 2006

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Raman spectra of ZnS:Cu,Cl powders show a structural transition from hexagonal to cubic and a crystal growth with increasing Cu addition (>400 ppm), which is supposed to result from Cu incorporation or CuxS precipitation. The redshift of longitudinal optical mode in ZnS:Cu,Cl with increased amounts of Cu suggests that the excess Cu ions were located interstitially in the lattice and created a tensile strain. Under an electric field (3.75×106 V/m), a broad emission spectrum superposing of green, self-activated blue, and blue bands can be observed in the powders (Cu ≥ 400 ppm), which agrees with the luminescence centers of CuZn+, vacancies, and Cui+, respectively.
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78.30.Fs III-V and II-VI semiconductors
78.60.Fi Electroluminescence
64.70.K- Solid-solid transitions
81.30.Mh Solid-phase precipitation
61.72.J- Point defects and defect clusters

Insight into the periodicity of Schallamach waves in soft material friction

Charles J. Rand and Alfred J. Crosby

Appl. Phys. Lett. 89, 261907 (2006); http://dx.doi.org/10.1063/1.2408640 (3 pages) | Cited 15 times

Online Publication Date: 27 December 2006

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A dominant mechanism in friction of soft material interfaces is the onset and propagation of Schallamach waves. Schallamach waves are “tunnels” of air that provide relative displacement between the slider and the substrate rather than the instantaneous interfacial failure involved with stick-slip. Here, through model experiments and analysis, the authors present a fundamental relationship between the periodicity of Schallamach waves (λ) and the ratio of interfacial adhesion (Gc) over complex elastic modulus (E*). This deconvolution of bulk and interfacial contributions to the friction of soft materials leads to interesting predictions that will impact material design for a wide range of applications.
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81.40.Pq Friction, lubrication, and wear
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.Qp Friction, tribology, and hardness
62.20.D- Elasticity
68.35.Af Atomic scale friction
68.35.Np Adhesion
62.30.+d Mechanical and elastic waves; vibrations

Influence of stoichiometry on phase transition pressure of LiNbO3

A. Suchocki, W. Paszkowicz, A. Kamińska, A. Durygin, S. K. Saxena, L. Arizmendi, and V. Bermudez

Appl. Phys. Lett. 89, 261908 (2006); http://dx.doi.org/10.1063/1.2424662 (3 pages) | Cited 2 times

Online Publication Date: 27 December 2006

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Results of Raman and x-ray diffraction studies under high pressures generated in diamond anvil cell of pure lithium niobate with different stoichiometries are reported. It is shown that the pressure at which the phase transition occurs depends on crystal stoichiometry and is strongly reduced as compared with those for LiNbO3 with congruent composition.
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62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions
61.66.Bi Elemental solids
61.66.Dk Alloys
78.30.Hv Other nonmetallic inorganics

Temperature dependence of serrated flows in compression in a bulk-metallic glass

W. H. Jiang, F. Jiang, F. X. Liu, H. Choo, P. K. Liaw, and K. Q. Qiu

Appl. Phys. Lett. 89, 261909 (2006); http://dx.doi.org/10.1063/1.2424275 (3 pages) | Cited 14 times

Online Publication Date: 27 December 2006

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The authors investigated the effect of temperature on the plastic-flow and shear-banding behaviors of a Zr-based bulk-metallic glass in compression. The results indicate that at a subambient temperature (194.5 K) the plastic deformation of the bulk-metallic glass is still inhomogeneous and is characterized by the serrated flow and shear banding. But, compared to the ambient-temperature results, the subambient temperature moderates serrations in the plastic flow and leads to the formation of fewer shear bands. In view of the spatiotemporality of shear banding, the authors correlate the plastic-flow behaviors to shear-band patterns.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Influence of the substrate orientation on the electronic and optical properties of InAs/GaAs quantum dots

V. Mlinar and F. M. Peeters

Appl. Phys. Lett. 89, 261910 (2006); http://dx.doi.org/10.1063/1.2424435 (3 pages) | Cited 8 times

Online Publication Date: 27 December 2006

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Using three-dimensional k∙p calculation including strain and piezoelectricity the authors predict the variation of electronic and optical properties of InAs/GaAs quantum dots (QDs) with the substrate orientation. The QD transition energies are obtained for high index substrates, [11k] where k = 1,2,3, and are compared with [001]. They find that the QD size in the growth direction determines the degree of influence of the substrate orientation: the flatter the dots, the larger the difference from the reference [001] case.
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73.21.La Quantum dots
78.67.Hc Quantum dots
71.15.-m Methods of electronic structure calculations
77.65.-j Piezoelectricity and electromechanical effects

Biologically inspired polymer microfibers with spatulate tips as repeatable fibrillar adhesives

Seok Kim and Metin Sitti

Appl. Phys. Lett. 89, 261911 (2006); http://dx.doi.org/10.1063/1.2424442 (3 pages) | Cited 65 times

Online Publication Date: 27 December 2006

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Being inspired by gecko foot hairs, microfibers with flat spatulate tips are proposed as repeatable adhesives. They are fabricated by molding a master template fabricated using deep reactive ion etching and the notching effect. Fabricated polyurethane fiber arrays with 4.5 μm fiber and 9 μm tip diameter demonstrated macroscale adhesion pressures up to 18 N/cm2 and overall work of adhesion up to 11 J/m2 on a 6 mm diameter glass hemisphere for a preload pressure of 12 N/cm2. These results show around four times higher adhesion and five times higher overall work of adhesion as compared to the flat polyurethane surface.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.10.Fq Growth from melts; zone melting and refining
81.65.Cf Surface cleaning, etching, patterning
68.35.Np Adhesion

Method to analyze dislocation injection from sharp features in strained silicon structures

Zhen Zhang, Juil Yoon, and Zhigang Suo

Appl. Phys. Lett. 89, 261912 (2006); http://dx.doi.org/10.1063/1.2424665 (3 pages) | Cited 9 times

Online Publication Date: 27 December 2006

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A microelectronic device usually contains sharp features (e.g., edges and corners) that may intensify stresses, inject dislocations into silicon, and fail the device. The authors describe a method to analyze dislocation injection on the basis of singular stress fields near the sharp features, and apply the method to interpret available experiments of nitride pads on silicon substrates.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.35.Gy Mechanical properties; surface strains

Infrared emission from Ge metal-insulator-semiconductor tunneling diodes

M. H. Liao, T.-H. Cheng, and C. W. Liu

Appl. Phys. Lett. 89, 261913 (2006); http://dx.doi.org/10.1063/1.2420783 (3 pages) | Cited 13 times

Online Publication Date: 28 December 2006

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The Ge light-emitting diode with ∼ 1.8 μm strong infrared emission is demonstrated using a metal-insulator-semiconductor tunneling structure. The intensity of a Ge device is one order of magnitude stronger than a similar Si device. At the positive gate bias, the holes in the Al gate electrode tunnel to the n-type Ge through the ultrathin oxide and recombine radiatively with electrons. An electron-hole-plasma model can be used to fit all the emission spectra from room temperature down to 65 K. From the measurement temperature range, the extracted band gap is ∼ 40 meV lower than the reported band gap data, and the linewidth drops from 70 to 25 meV. The longitudinal acoustic phonon ( ∼ 28 meV) and/or the band gap renormalization at high carrier density are proposed to be responsible for the reduction of photon energy. The band gap reduction on the mechanically strained n-type Ge and Si is also investigated experimentally and theoretically.
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85.60.Jb Light-emitting devices
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Configurations and diffusion of point defects in two-dimensional colloidal crystals

Tian Hui Zhang and Xiang Yang Liu

Appl. Phys. Lett. 89, 261914 (2006); http://dx.doi.org/10.1063/1.2424672 (3 pages) | Cited 4 times

Online Publication Date: 28 December 2006

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Configurations and diffusion of crystal defects are studied in a two-dimensional colloidal model system in the presence of an attraction. Monomer vacancies are immobile and have identical symmetry with the underlying triangular lattice. Both dimer vacancies and trimer vacancies have two different configurations and the configurations with higher symmetry are more stable. Dimer vacancies in the authors’ our experiments exhibit the highest diffusivity, whereas the global diffusion of vacancies of larger clusters, such as trimer vacancies, is inhibited. Compared with previous studies, it is found that defect dynamics is strongly dependent on the nature of the interaction potential.
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82.70.Dd Colloids
66.30.Lw Diffusion of other defects
61.72.J- Point defects and defect clusters

Red photoluminescence in praseodymium-doped titanate perovskite films epitaxially grown by pulsed laser deposition

Hiroshi Takashima, Kazushige Ueda, and Mitsuru Itoh

Appl. Phys. Lett. 89, 261915 (2006); http://dx.doi.org/10.1063/1.2424438 (3 pages) | Cited 10 times

Online Publication Date: 28 December 2006

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Intense red photoluminescence (PL) under ultraviolet (UV) excitation was observed in epitaxially grown Pr-doped Ca0.6Sr0.4TiO3 perovskite films. The films were grown on SrTiO3 (100) substrates by pulsed laser deposition, and their epitaxial growth was confirmed by x-ray diffraction and reflected high-energy electron diffraction. The observed sharp PL peak centered at 610 nm was assigned to the transition of Pr3+ ions from the math state to the math state. The PL intensity was markedly enhanced by postannealing treatments at 1000 °C, above the film-growth temperature of 600 or 800 °C. Because the excitation and absorption spectra are similar to each other, it was suggested that the UV energy absorbed by the host lattice was transferred to the Pr ions, resulting in the red luminescence.
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78.66.-w Optical properties of specific thin films
78.55.Hx Other solid inorganic materials
78.40.Ha Other nonmetallic inorganics

Optical measurements of the thermal properties of nanofluids

Roberto Rusconi, Erica Rodari, and Roberto Piazza

Appl. Phys. Lett. 89, 261916 (2006); http://dx.doi.org/10.1063/1.2425015 (3 pages) | Cited 21 times

Online Publication Date: 28 December 2006

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The authors show that the thermal conductivity and diffusivity of colloidal particle dispersions can be rapidly obtained with high accuracy and reproducibility by exploiting a noninvasive, all-optical thermal lensing method. Applications of this technique to model suspensions of spherical monodisperse particles suggest that classical models for the effective properties of composite media hold up to rather high volume fractions, while no “anomalous” thermal conductivity effects are found.
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66.25.+g Thermal conduction in nonmetallic liquids
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
82.70.Dd Colloids
82.70.Kj Emulsions and suspensions

Structural short-range order of the β-Ti phase in bulk Ti–Fe–(Sn) nanoeutectic composites

J. Das, J. Eckert, and R. Theissmann

Appl. Phys. Lett. 89, 261917 (2006); http://dx.doi.org/10.1063/1.2424274 (3 pages) | Cited 16 times

Online Publication Date: 28 December 2006

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The authors report lattice distortion and “ω-like” structural short-range order (SRO) of the β-Ti phase in a Ti–Fe–(Sn) bulk nanoeutectic composite prepared by slow cooling from the melt. The nanoeuetctic phases are chemically homogeneous, but the addition of Sn releases the local lattice strain, modifies the structural SRO, and prevents the formation of stacking faults in the body centered cubic (bcc) β-Ti phase resulting in improved plastic deformability. The elastic properties and the structural SRO of the β-Ti phase are proposed to be important parameters for developing advanced high strength, ductile Ti-base nanocomposite alloys.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.66.Dk Alloys
62.20.D- Elasticity
68.35.Gy Mechanical properties; surface strains

Twisted phase gratings induced by photoregulated mesogenic molecules on the surface of photoreactive polymer liquid crystal film

Hiroshi Ono, Tomoyuki Sasaki, Akira Emoto, Emi Uchida, and Nobuhiro Kawatsuki

Appl. Phys. Lett. 89, 261918 (2006); http://dx.doi.org/10.1063/1.2425031 (3 pages) | Cited 1 time

Online Publication Date: 29 December 2006

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Three-dimensional phase gratings with twisted structures were self-organized by photoregulated mesogenic molecules on the surface of photocrosslinkable polymer liquid crystal film. The molecules are selectively photoreacted only at the surface of the film under the polarization holographic illumination, and the resultant photocrosslinked mesogenic molecules induce the three-dimensional twisted gratings in the film during annealing process. The diffraction properties were well explained by means of Jones calculus and diffraction theory.
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42.79.Dj Gratings
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Df Liquid crystals
42.70.Gi Light-sensitive materials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
61.30.Vx Polymer liquid crystals

Influence of cohesive energy on unit cell volume of perovskite manganites La1−xMxMnO3

G. D. Tang, D. L. Hou, Z. Z. Li, X. Zhao, W. H. Qi, S. P. Liu, and F. W. Zhao

Appl. Phys. Lett. 89, 261919 (2006); http://dx.doi.org/10.1063/1.2425046 (3 pages) | Cited 8 times

Online Publication Date: 29 December 2006

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Ionic size is considered to be an important factor influencing the unit cell volume of manganites with an ABO3 structure. For La1−xSrxMnO3, however, although the average effective ion radius of all cations taken together increases with increasing x, the unit cell volume decreases for x<0.5. In the case of La1−xNaxMnO3, the unit cell volume reaches a minimum when x = 0.3. Up to now, no satisfactory explanation of these phenomena has been found. In this letter, an explanation based on the ionic cohesive energy with a small additional metallic cohesive energy is described.
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61.50.Lt Crystal binding; cohesive energy
71.15.Nc Total energy and cohesive energy calculations
61.66.Bi Elemental solids
61.66.Dk Alloys
61.66.Fn Inorganic compounds
82.80.-d Chemical analysis and related physical methods of analysis
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Subpicosecond time-resolved Raman studies of field-induced transient transport in an InxGa1−xAs-based p-i-n semiconductor nanostructure

K. T. Tsen, Juliann G. Kiang, D. K. Ferry, and H. Morkoç

Appl. Phys. Lett. 89, 262101 (2006); http://dx.doi.org/10.1063/1.2420782 (3 pages) | Cited 1 time

Online Publication Date: 26 December 2006

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Electron transient transport in an InxGa1−xAs-based (x = 0.53) p-i-n nanostructure under the application of an electric field has been studied by time-resolved Raman spectroscopy on a subpicosecond time scale and at T = 300 K. The experimental results reveal the time evolution of the electron distribution function and electron drift velocity with subpicosecond time resolution. These experimental results are compared with those of both InP-based and GaAs-based p-i-n nanostructures and provide a consistent understanding and better insight of electron transient transport phenomena in semiconductors.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.63.-b Electronic transport in nanoscale materials and structures
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.30.Fs III-V and II-VI semiconductors
78.47.-p Spectroscopy of solid state dynamics

Electron transport in naphthylamine-based organic compounds

S. C. Tse, K. C. Kwok, and S. K. So

Appl. Phys. Lett. 89, 262102 (2006); http://dx.doi.org/10.1063/1.2420785 (3 pages) | Cited 50 times

Online Publication Date: 26 December 2006

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Two naphthylamine-based hole transporters, namely, N,N′-diphenyl-N,N′-bis(1-naphthyl)(1,1′-biphenyl)-4,4′diamine (NPB) and 4,4′,4″-tris(n-(2-naphthyl)-n-phenyl-amino)-triphenylamine (2TNATA), were found to possess electron transporting (ET) abilities. From time-of-flight measurements, values of electron mobilities for NPB and 2TNATA are (6–9)×10−4 and (1–3)×10−4 cm2/V s, respectively, under an applied electric field range of 0.04–0.8 MV/cm at 290 K. An organic light-emitting diode that employed NPB as the ET material was demonstrated. The electron conducting mechanism of NPB and 2TNATA in relation to the Marcus theory [ Rev. Mod. Phys. 65, 599 (1993) ] from quantum chemistry will be discussed.
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72.20.Ee Mobility edges; hopping transport
72.80.Le Polymers; organic compounds (including organic semiconductors)
85.60.Jb Light-emitting devices

Selective epitaxial growth of 4H-SiC at reduced temperatures using halo-carbon precursor

Bharat Krishnan, Hrishikesh Das, Huang-De Lin, and Yaroslav Koshka

Appl. Phys. Lett. 89, 262103 (2006); http://dx.doi.org/10.1063/1.2423323 (3 pages) | Cited 2 times

Online Publication Date: 26 December 2006

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Selective homoepitaxial growth of 4H-SiC polytype at temperatures down to 1300 °C was investigated using novel halo-carbon epitaxial growth technique. More than three times higher growth rate than in blanket epitaxy without morphology degradation was due to the local loading effect, which demonstrated that the growth rate of SiC homoepitaxy at low temperatures is limited by the gas-phase reaction mechanisms rather than surface mechanisms. It was established that the step-flow growth without undesirable nucleation may be maintained at growth rates in excess of 6 μm/h. Strong dependence of the growth rate on the ratio of the seed area to the masked area indicated that the growth rate is predominantly mass transport limited. Facet formation and conditions for suppressing defect generation at the mesa walls were investigated.
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68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Strong magnetic scattering from TiOx adhesion layers

A. Trionfi, S. Lee, and D. Natelson

Appl. Phys. Lett. 89, 262104 (2006); http://dx.doi.org/10.1063/1.2423327 (3 pages) | Cited 2 times

Online Publication Date: 26 December 2006

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Electronic phase coherence in normal metals is incredibly sensitive to magnetic scattering. As a result, the weak localization magnetoresistance and time-dependent universal conductance fluctuations are powerful probes of magnetic impurities. The authors report measurements of these effects in Au and Ag nanowires with a 1.5 nm thick Ti adhesion layer underneath the deposited metal. The results indicate an anomalously large magnetic impurity concentration due to the Ti layer. The results also suggest that this magnetic scattering and its evolution are related to the oxidation state of the Ti.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.30.Hx Magnetic impurity interactions

Defect reduction in (11math0) a-plane GaN by two-stage epitaxial lateral overgrowth

X. Ni, Ü. Özgür, Y. Fu, N. Biyikli, J. Xie, A. A. Baski, H. Morkoç, and Z. Liliental-Weber

Appl. Phys. Lett. 89, 262105 (2006); http://dx.doi.org/10.1063/1.2423328 (3 pages) | Cited 23 times

Online Publication Date: 26 December 2006

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The authors report a two-stage epitaxial lateral overgrowth (ELO) method to get uniformly coalesced (11math0) a-plane GaN using metal organic chemical vapor deposition by employing a relatively lower growth temperature in the first stage followed by conditions leading to enhanced lateral growth in the second. Using a two-stage ELO method the average Ga-polar to N-polar wing growth rate ratio has been reduced from 4–6 to 1.5–2, which consequently reduced the height difference between the two approaching wings at the coalescence front that resulted from the wing tilt (0.44° for Ga and 0.37° for N wings, measured by x-ray diffraction), thereby making their coalescence much easier. Transmission electron microscopy showed that the threading dislocation density in the wing areas was 1.0×108 cm−2, more than two orders of magnitude lower than that in the window areas (4.2×1010 cm−2). However, high density of basal stacking faults of 1.2×104 cm−1 was still present in the wing areas as compared to c-plane GaN where they are rarely observed away from the substrate. Atomic force microscopy and photoluminescence measurements on the coalesced ELO a-plane GaN sample also indicated improved material quality.
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68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Investigation of void nucleation and propagation during electromigration of flip-chip solder joints using x-ray microscopy

S. H. Chiu and Chih Chen

Appl. Phys. Lett. 89, 262106 (2006); http://dx.doi.org/10.1063/1.2425040 (3 pages) | Cited 5 times

Online Publication Date: 27 December 2006

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X-ray microscopy was employed to investigate void nucleation and propagation during electromigration in solder joints. The shape of the voids at various stages can be clearly observed. The voids became irregular when they propagated to deplete the contact opening. Growth velocity at the early stage was found to be 1.3 μm/h under 6.5×103 A/cm2 at 150 °C, and it decreased to 0.3 μm/h at later stages. Formation of intermetallic compound (IMC) and compositional changes at the interface of solder/IMC on the chip side were attributed to the retarded growth rate at later stages.
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85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Qa Electromigration

Carrier concentration induced band-gap shift in Al-doped Zn1−xMgxO thin films

J. G. Lu, S. Fujita, T. Kawaharamura, H. Nishinaka, Y. Kamada, and T. Ohshima

Appl. Phys. Lett. 89, 262107 (2006); http://dx.doi.org/10.1063/1.2424308 (3 pages) | Cited 17 times

Online Publication Date: 27 December 2006

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Transparent conducting Al-doped Zn1−xMgxO thin films were grown on glass substrates by chemical vapor deposition. The resistivity could be lowered to 10−3 Ω cm with optical transmittance above 85% in visible regions. The influence of carrier concentration on band-gap shift in Zn1−xMgxO alloys was systematically studied. The shift of energy gap could be fully explained by the Fermi-level band filling and band-gap renormalization effects. As the Mg content increased, the electron effective masses in Zn1−xMgxO (x = 0–0.21) alloys increased from 0.30m0 to 0.49m0. The Al-doping efficiency was reduced with the increase in alloy composition.
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73.61.Le Other inorganic semiconductors
78.66.Li Other semiconductors
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.20.Ps Other inorganic compounds
61.72.up Other materials

Control of structure, conduction behavior, and band gap of Zn1−xMgxO films by nitrogen partial pressure ratio of sputtering gases

C. X. Cong, B. Yao, G. Z. Xing, Y. P. Xie, L. X. Guan, B. H. Li, X. H. Wang, Z. P. Wei, Z. Z. Zhang, Y. M. Lv, D. Z. Shen, and X. W. Fan

Appl. Phys. Lett. 89, 262108 (2006); http://dx.doi.org/10.1063/1.2424449 (3 pages) | Cited 12 times

Online Publication Date: 27 December 2006

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Zn1−xMgxO films were grown by radio-frequency reactive magnetron sputtering using mixture of nitrogen and argon as sputtering gases. It was found that Mg concentration, structures, electrical properties, and band gaps of the films can be tuned by changing nitrogen partial pressure ratio of the sputtering gases. The Zn1−xMgxO film consists of wurtzite phase at the ratios from 0% to 50%, mixture of wurtzite and cubic phases at the ratios of 78% to 83%, and cubic phase at 100%. The Mg concentration increased linearly with increasing the ratio. The band gap increases from 3.64 eV at x = 0.172 to 4.02 eV at x = 0.44 for the wurtzite Zn1−xMgxO and reaches 6.30 eV for cubic Zn1−xMgxO with x = 0.84. All the as-grown Zn1−xMgxO films show high resistivity at room temperature, but transform into p-type conduction after annealing at 600 °C for 30 min under 10−4 Pa, except for the film grown at the ratio of zero.
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68.55.-a Thin film structure and morphology
73.61.Ga II-VI semiconductors
71.20.Nr Semiconductor compounds
81.15.Cd Deposition by sputtering
61.66.Bi Elemental solids
61.66.Dk Alloys
61.72.Cc Kinetics of defect formation and annealing

Experimental study of the subwavelength imaging by a wire medium slab

Pavel A. Belov, Yan Zhao, Sunil Sudhakaran, Akram Alomainy, and Yang Hao

Appl. Phys. Lett. 89, 262109 (2006); http://dx.doi.org/10.1063/1.2424557 (3 pages) | Cited 17 times

Online Publication Date: 27 December 2006

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An experimental investigation of subwavelength imaging by a wire medium slab is performed. A complex-shaped near field source is used in order to test imaging performance of the device. It is demonstrated that the ultimate bandwidth of operation of the constructed imaging device is 4.5% that coincides with theoretical predictions [ P. A. Belov and M. G. Silveirinha, Phys. Rev. E 73, 056607 (2006) ]. Within this band the wire medium slab is capable of transmitting images with λ/15 resolution irrespective of the shape and complexity of the source. Actual bandwidth of operation for particular near-field sources can be larger than the ultimate value, but it strongly depends on the configuration of the source.
Show PACS
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.-a Optical materials
07.60.-j Optical instruments and equipment
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