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30 Aug 2004

Volume 85, Issue 9, pp. 1451-1650

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 1592 (2004); http://dx.doi.org/10.1063/1.1787938 (3 pages)

Mehdi M. Yazdanpanah, Steven A. Harfenist, and Robert W. Cohn
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Tunable transmission and bistability in left-handed band-gap structures

Michael W. Feise, Ilya V. Shadrivov, and Yuri S. Kivshar

Appl. Phys. Lett. 85, 1451 (2004); http://dx.doi.org/10.1063/1.1787612 (3 pages) | Cited 30 times

Online Publication Date: 27 August 2004

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We study the defect-induced nonlinear transmission of a periodic structure created by alternating slabs of two materials with positive and negative refractive index. We demonstrate bistable switching and tunable nonlinear transmission in an unconventional band gap that corresponds to the vanishing average refractive index, and compare the observed effects for two different types of band gaps.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)

Transmission of convoluted periodic loop element with selective reflection

P. T. Teo, X-F Luo, and C. K. Lee

Appl. Phys. Lett. 85, 1454 (2004); http://dx.doi.org/10.1063/1.1769076 (3 pages)

Online Publication Date: 27 August 2004

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The transmission and reflectivity of electromagnetic energy across a planar layer consisting of periodic arrays of convoluted loop elements (with interelement spacing of 6.08 cm) is investigated in the lower microwave spectrum at 1.575 GHz (λ=19 cm). This relatively close spacing is achieved by convoluting the conventional 1λ square loop element at its four corners. The close interelement spacing provides a stable passband frequency response over wide angles of wave incidence, while the convoluted segment provides a short circuit response when the segment length is λ∕4 long. The short circuit will provide a reflection to the electromagnetic energy at the selected band-stop frequency range. Various design considerations have been adopted to meet the challenge of ensuring a common passband bandwidth of 22.47% (1.5–1.95 GHz), with a transmission loss of less than 0.5 dB for scan angles up to 45° in both TE and TM polarization.
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84.40.Ba Antennas: theory, components and accessories
41.20.Jb Electromagnetic wave propagation; radiowave propagation

Planar optical waveguides in β-BaB2O4 produced by oxygen ion implantation at low doses

Xue-Lin Wang, Feng Chen, Ke-Ming Wang, Qing-Ming Lu, Ding-Yu Shen, and Rui Nie

Appl. Phys. Lett. 85, 1457 (2004); http://dx.doi.org/10.1063/1.1787940 (3 pages) | Cited 14 times

Online Publication Date: 27 August 2004

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The planar waveguides have been fabricated in z-cut β-BaB2O4 crystal by 2.2 MeV O+ ion implantation at doses ranging from 5×1012 to 5×1014 ions∕cm2 at room temperature. The waveguides were characterized by the prism-coupling method. Monomode, nonleaky planar waveguides at λ=633 nm in β-BBO single crystals were fabricated at doses from 5×1012 to 2×1013 ions∕cm2, and two mode and three mode waveguides were fabricated at doses from 4×1013 to 5×1014 ions∕cm2, respectively. The refractive index profiles of the waveguides are reconstructed using reflectivity calculation method. The propagation loss of the measured ion implanted waveguide was about 1.6 dB∕cm. It was found that positive changes of extraordinary refractive indices happened in the guiding regions, and such changes increased with the doses, which were different from most of the observed ion-implanted waveguides.
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42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer
61.72.uf Ge and Si
61.72.S- Impurities in crystals
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

A microfabricated atomic clock

Svenja Knappe, Vishal Shah, Peter D. D. Schwindt, Leo Hollberg, John Kitching, Li-Anne Liew, and John Moreland

Appl. Phys. Lett. 85, 1460 (2004); http://dx.doi.org/10.1063/1.1787942 (3 pages) | Cited 103 times

Online Publication Date: 27 August 2004

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Fabrication techniques usually applied to microelectromechanical systems (MEMS) are used to reduce the size and operating power of the core physics assembly of an atomic clock. With a volume of 9.5 mm3, a fractional frequency instability of 2.5×10−10 at 1 s of integration, and dissipating less than 75 mW of power, the device has the potential to bring atomically precise timing to hand-held, battery-operated devices. In addition, the design and fabrication process allows for wafer-level assembly of the structures, enabling low-cost mass-production of thousands of identical units with the same process sequence, and easy integration with other electronics.
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06.30.Ft Time and frequency
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
06.20.F- Units and standards
42.79.-e Optical elements, devices, and systems

Tuning of emission color for blue dendrimer blend light-emitting diodes

Jonathan P. J. Markham, Ebinazar B. Namdas, Thomas D. Anthopoulos, Ifor D. W. Samuel, Gary J. Richards, and Paul L. Burn

Appl. Phys. Lett. 85, 1463 (2004); http://dx.doi.org/10.1063/1.1784521 (3 pages) | Cited 23 times

Online Publication Date: 27 August 2004

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We demonstrate efficient tunable blue electroluminescence from blends of two solution-processible light-emitting dendrimers. These materials can be blended to form optical quality thin films with no phase-separation effects, irrespective of the blend ratio. External quantum efficiencies of 1% have been measured for the blend systems and the emission color can be tuned from deep blue (emission peak 401 nm) to blue green (477 nm) by blend composition. A power efficiency of 1.5 lm∕W (at 200 Cd∕m2 and 5.4 V) is measured for a single layer, first-generation blue-green fluorene-thiophene dendrimer. These results show that by choice of a dendrimer structure with common branching units and surface groups, dissimilar cores can be blended with excellent miscibility. This provides a simple way of tuning the color of organic light-emitting diodes.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
61.41.+e Polymers, elastomers, and plastics
61.25.H- Macromolecular and polymers solutions; polymer melts
64.75.-g Phase equilibria
78.66.Qn Polymers; organic compounds
78.55.Qr Amorphous materials; glasses and other disordered solids

Slow-light enhancement of radiation pressure in an omnidirectional-reflector waveguide

M. L. Povinelli, Mihai Ibanescu, Steven G. Johnson, and J. D. Joannopoulos

Appl. Phys. Lett. 85, 1466 (2004); http://dx.doi.org/10.1063/1.1786660 (3 pages) | Cited 35 times

Online Publication Date: 27 August 2004

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We study the radiation pressure on the surface of a waveguide formed by omnidirectionally reflecting mirrors. In the absence of losses, the pressure goes to infinity as the distance between the mirrors is reduced to the cutoff separation of the waveguide mode. This divergence at constant power input is due to the reduction of the modal group velocity to zero, which results in the magnification of the electromagnetic field. Our structure suggests a promising alternative, microscale system for observing the variety of classical and quantum-optical effects associated with radiation pressure in Fabry–Perot cavities.
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42.79.Gn Optical waveguides and couplers
42.79.Bh Lenses, prisms and mirrors
37.10.Vz Mechanical effects of light on atoms, molecules, and ions

Room-temperature continuous-wave operation of GaInNAs∕GaAs quantum dot laser with GaAsN barrier grown by solid source molecular beam epitaxy

Z. Z. Sun, S. F. Yoon, K. C. Yew, B. X. Bo, Du An Yan, and Tung Chih-Hang

Appl. Phys. Lett. 85, 1469 (2004); http://dx.doi.org/10.1063/1.1789236 (3 pages) | Cited 12 times

Online Publication Date: 27 August 2004

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We present the results of GaInNAs∕GaAs quantum dot structures with GaAsN barrier layers grown by solid source molecular beam epitaxy. Extension of the emission wavelength of GaInNAs quantum dots by ∼170 nm was observed in samples with GaAsN barriers in place of GaAs. However, optimization of the GaAsN barrier layer thickness is necessary to avoid degradation in luminescence intensity and structural property of the GaInNAs dots. Lasers with GaInNAs quantum dots as active layer were fabricated and room-temperature continuous-wave lasing was observed. Lasing occurs via the ground state at ∼1.2 μm, with threshold current density of 2.1 kA∕cm2 and maximum output power of 16 mW.
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42.55.Px Semiconductor lasers; laser diodes
68.47.Fg Semiconductor surfaces
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.67.Hc Quantum dots

Extraordinary infrared transmission of Cu-coated arrays with subwavelength apertures: Hole size and the transition from surface plasmon to waveguide transmission

Shaun M. Williams, Amanda D. Stafford, Trisha M. Rogers, Sarah R. Bishop, and James V. Coe

Appl. Phys. Lett. 85, 1472 (2004); http://dx.doi.org/10.1063/1.1786664 (3 pages) | Cited 24 times

Online Publication Date: 27 August 2004

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The zero-order, infrared transmission spectra were recorded and studied at varying angles of incidence to study the dispersion of the resonances in both the Γ−X and Γ−M reciprocal lattice directions. Reduction of hole size shows dramatic effects on the intensity of transmission, the width of the resonances, the identity of the most prominent resonances, and the dispersion behavior of resonances.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.30.Er Solid metals and alloys
78.68.+m Optical properties of surfaces

Excitonic signature in gain and carrier induced change of refractive index spectra of (In,Al)GaN quantum well lasers

Ulrich T. Schwarz, E. Sturm, W. Wegscheider, V. Kümmler, A. Lell, and V. Härle

Appl. Phys. Lett. 85, 1475 (2004); http://dx.doi.org/10.1063/1.1789243 (3 pages) | Cited 10 times

Online Publication Date: 27 August 2004

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The exciton is observed in (In,Al)GaN laser diodes as resonance in the optical gain spectra and in the spectra of the carrier induced change of the refractive index. The observed instability of the exciton with respect to the free electron-hole plasma with increasing carrier densities is accompanied by a blueshift of the exciton resonance due to the quantum confined Stark shift. The experiments confirm central points of many-body simulations of InGaN∕GaN quantum wells. The exciton becomes unstable near threshold and so lasing occurs from the electron–hole plasma.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
71.35.Ee Electron-hole drops and electron-hole plasma
72.30.+q High-frequency effects; plasma effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.67.De Quantum wells
78.60.Fi Electroluminescence

Above room temperature operation of short wavelength (λ=3.8 μm) strain-compensated In0.73Ga0.27As–AlAs quantum-cascade lasers

M. P. Semtsiv, M. Ziegler, S. Dressler, W. T. Masselink, N. Georgiev, T. Dekorsy, and M. Helm

Appl. Phys. Lett. 85, 1478 (2004); http://dx.doi.org/10.1063/1.1789246 (3 pages) | Cited 35 times

Online Publication Date: 27 August 2004

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We demonstrate the design and implementation of a broad-gain and low-threshold (Jth=860 A∕cm2 at 8 K) quantum-cascade laser emitting between 3.7 and 4.2 μm. The active region design is based on strain-compensated In0.73Ga0.27As–AlAs on InP. Laser operation in pulsed mode is achieved up to a temperature of 330 K with maximum single-facet output peak powers of 6 W at 8 K and 240 mW at 296 K. The temperature coefficient T0 is 119 K.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Efficient large-area polymer solar cells on flexible substrates

Maher Al-Ibrahim, H. Klaus Roth, and Steffi Sensfuss

Appl. Phys. Lett. 85, 1481 (2004); http://dx.doi.org/10.1063/1.1787158 (3 pages) | Cited 33 times

Online Publication Date: 27 August 2004

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Polymer solar cells based on poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene]:[6,6]-phenyl-C61-butyric acid methyl ester (1:3 wt %) were fabricated using flexible 5×5 cm2 polyester foils. These cells show a white-light power conversion efficiency of 3% comparable to smaller cells on glass published by other authors. Ten cells were arranged on one substrate with an active area of 25 and 175 mm2 demonstrating a remarkably high reproducibility. It was found that the open-circuit voltage does not depend on the device area. An increase of the cell area caused a slightly lower short-circuit current, lower fill factor, and lower white-light power conversion efficiency.
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84.60.Jt Photoelectric conversion
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Ferroinductor coupled discharge

Yu. P. Bliokh, J. Felsteiner, Ya. Z. Slutsker, and P. M. Vaisberg

Appl. Phys. Lett. 85, 1484 (2004); http://dx.doi.org/10.1063/1.1785282 (3 pages) | Cited 9 times

Online Publication Date: 27 August 2004

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An inductively coupled discharge was obtained at low gas pressure. Unlike an ordinary inductively coupled discharge with an inductorlike rf antenna, we used a magnetic core with a primary winding (“ferroinductor”). In this way, we increased the electric field and eliminated the magnetic field of the winding. Gas breakdown was obtained at a pressure as low as 10−4 Torr, the discharge plasma ionization rate reached almost 100%, and the maximum plasma density was about 1013 cm−3. The high inductance of the ferroinductor allowed us to work even with single pulses. The efficiency of such a discharge as a plasma source could reach 90%, which makes this kind of discharge attractive for many applications.
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52.50.Dg Plasma sources
52.80.Pi High-frequency and RF discharges
52.25.Jm Ionization of plasmas

Measurements of helium metastable density in an atmospheric pressure glow discharge

G. Nersisyan, T. Morrow, and W. G. Graham

Appl. Phys. Lett. 85, 1487 (2004); http://dx.doi.org/10.1063/1.1784514 (3 pages) | Cited 21 times

Online Publication Date: 27 August 2004

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The density of metastable helium atoms in a dielectric barrier discharge operating in helium with some impurities present has been measured using laser-collisional-induced fluorescence and absorption techniques. Time-resolved measurements indicate that helium metastables contribute to the production of impurity ions, in this case N2+, in the postdischarge current phase of a glow discharge. In our particular discharge environment, the helium metastable density is (1.5±1.4)×1010 cm−3, a result consistent with failure to observe absorption by metastables in a multipass absorption measurement.
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52.25.Tx Emission, absorption, and scattering of particles
52.25.Mq Dielectric properties
52.80.Hc Glow; corona
52.25.Vy Impurities in plasmas
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
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Thermoelectric properties–texture relationship in highly oriented Ca3Co4O9 composites

E. Guilmeau, R. Funahashi, M. Mikami, K. Chong, and D. Chateigner

Appl. Phys. Lett. 85, 1490 (2004); http://dx.doi.org/10.1063/1.1785286 (3 pages) | Cited 19 times

Online Publication Date: 27 August 2004

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The correlation between thermoelectric properties and texture strength is discussed within the framework of Ca3Co4O9 textured ceramics. Based on an innovative method of x-ray diffraction analysis, the distribution density (i.e., the degree of orientation) of composite material composed of Ca3Co4O9 powder and single crystals was determined. Electrical resistivity of the prepared composites was shown to be reduced with increasing single crystals weight ratios and, in parallel, was directly correlated to an improvement of grain alignment. The incorporated single crystals help the texture development of the powder via an enhanced stacking of grains and fulfill a role as bypasses of the grain boundaries. This letter highlights the value of quantitative texture analysis to explain the evolution of anisotropic physical properties, as demonstrated here concerning textured thermoelectric materials.
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81.05.Mh Cermets, ceramic and refractory composites
72.20.Pa Thermoelectric and thermomagnetic effects
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
61.72.Mm Grain and twin boundaries
72.80.Tm Composite materials

Near-infrared laser ablation of poly tetrafluoroethylene (Teflon) sensitized by nanoenergetic materials

Yanqiang Yang, Shufeng Wang, Zhaoyong Sun, and Dana D. Dlott

Appl. Phys. Lett. 85, 1493 (2004); http://dx.doi.org/10.1063/1.1785291 (3 pages) | Cited 15 times

Online Publication Date: 27 August 2004

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Laser ablation of Teflon doped with size-selected (30–250 nm) Al nanoparticles is studied. Unlike pure Teflon, which requires a vacuum-ultraviolet or femtosecond excimer laser for ablation, this sensitized Teflon can be ablated with a near-infrared laser. Using 100 ps duration pulses, near-infrared ablation thresholds are lower by about a factor of 10 from excimer ablation of pure Teflon. A mechanism is discussed that involves Teflon decomposition by spherical shock fronts originating at each irradiated nanoparticle. Studies of the distance dependence of this process as a function of particle diameter and oxide layer thickness suggest ways of optimizing the ablation process.
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82.35.Np Nanoparticles in polymers
61.46.-w Structure of nanoscale materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
78.30.Jw Organic compounds, polymers
61.82.Pv Polymers, organic compounds

Ostwald ripening and flattening of epitaxial ZnO layers during in situ annealing in metalorganic vapor phase epitaxy

A. Krost, J. Christen, N. Oleynik, A. Dadgar, S. Deiter, J. Bläsing, A. Krtschil, D. Forster, F. Bertram, and A. Diez

Appl. Phys. Lett. 85, 1496 (2004); http://dx.doi.org/10.1063/1.1785871 (3 pages) | Cited 12 times

Online Publication Date: 27 August 2004

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ZnO films were grown at 450°C by metalorganic vapor phase epitaxy on GaN∕Si(111) substrate and subsequently annealed in situ at 900°C for times ranging from 0 to 8 min. The epitaxial layers were characterized by atomic force microscopy, x-ray diffraction, and cathodoluminescence measurements. The as-grown ZnO layers consist of three-dimensional nanoscale-sized clusters of [0001]-oriented monocrystallites. During the first 1 min of annealing, a surface smoothening due to a redistribution of material is observed leading to a decrease of both the island numbers and their heights. After 2 min of annealing, the surface morphology has completely changed and is transformed into a nearly two-dimensional cluster-free surface. This phase transition is accompanied by a strong improvement of the crystalline and optical properties. The effect is attributed to Ostwald ripening with a subsequent flattening of the crystal surface.
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81.05.Dz II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
78.66.Hf II-VI semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.60.Hk Cathodoluminescence, ionoluminescence
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)

Surface morphology of AlN buffer layer and its effect on GaN growth by metalorganic chemical vapor deposition

D. G. Zhao, J. J. Zhu, Z. S. Liu, S. M. Zhang, Hui Yang, and D. S. Jiang

Appl. Phys. Lett. 85, 1499 (2004); http://dx.doi.org/10.1063/1.1784034 (3 pages) | Cited 19 times

Online Publication Date: 27 August 2004

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The in situ optical reflectivity measurements are employed to monitor the GaN epilayer growth process above low-temperature AlN buffer layer on c-plane sapphire substrate by metalorganic chemical vapor deposition. It is found that the lateral growth of GaN islands and their coalescence is promoted in the initial growth stage if the AlN buffer layer is treated with a long annealing time and has an optimal thickness: As confirmed by atomic force microscopy observations, the quality of GaN epilayers is closely dependent on the surface morphology of AlN buffer layer, especially the grain size and nuclei density after the annealing treatment.
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81.05.Ea III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Fd III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.40.Gh Other heat and thermomechanical treatments
61.72.Cc Kinetics of defect formation and annealing
68.37.Ps Atomic force microscopy (AFM)

Reduction of dislocations in GaN epilayers grown on Si(111) substrate using SixNy inserting layer

Kang Jea Lee, Eun Ho Shin, and Kee Young Lim

Appl. Phys. Lett. 85, 1502 (2004); http://dx.doi.org/10.1063/1.1784046 (3 pages) | Cited 23 times

Online Publication Date: 27 August 2004

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High-quality GaN films have been grown on Si(111) substrate by metalorganic chemical vapor deposition using a SixNy inserting layer. Due to the large difference of lattice constant and thermal expansion coefficient between GaN and Si,GaN growth on Si(111) substrate usually leads to an initially high dislocation density and cracks. It is found that the SixNy inserting layer plays a very important role in the enhancement of crystal quality and surface morphology of GaN films. The crystalline quality of overlying GaN layer grown on SixNy inserting layer depends on the deposition time of SixNy inserting layer. The high-resolution x-ray diffraction results show that the dislocation density in GaN epilayer decreases with increasing SixNy growth time. It was confirmed that the misfit dislocations in the GaN films with 5 min deposition time for SixNy inserting layer almost stop at the SixNy inserting layer by transmission electron microscope measurements.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
65.40.De Thermal expansion; thermomechanical effects
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
68.60.Bs Mechanical and acoustical properties

Distribution of α and β phases in the coexistence regime in MnAs(0001) layers grown on GaAs(111)B

Y. Takagaki, E. Wiebicke, L. Däweritz, and K. H. Ploog

Appl. Phys. Lett. 85, 1505 (2004); http://dx.doi.org/10.1063/1.1786359 (3 pages) | Cited 11 times

Online Publication Date: 27 August 2004

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The discontinuous change in the lattice constant that occurs at the first-order phase transition between α- and β-MnAs gives rise to a coexistence of the two phases in MnAs layers grown on GaAs substrates. When the GaAs substrates are oriented in the (111)B direction, the c axis of MnAs is aligned normal to the growth plane. We identify the domain structure of α- and β-MnAs for this crystal orientation by utilizing the different reactivities of the two phases against wet chemical etching. Submicrometer-size islands of α-MnAs are found to be interwoven in a honeycomblike network of β-MnAs. We also show that this domain structure combined with strain effects results in a formation of MnAs lumps by etching.
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75.50.Cc Other ferromagnetic metals and alloys
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Synthesis of bulk superhard semiconducting B–C material

Vladimir L. Solozhenko, Natalia A. Dubrovinskaia, and Leonid S. Dubrovinsky

Appl. Phys. Lett. 85, 1508 (2004); http://dx.doi.org/10.1063/1.1786363 (3 pages) | Cited 33 times

Online Publication Date: 27 August 2004

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A bulk composite superhard material was synthesized from graphitelike BC3 at 20 GPa and 2300 K using a multianvil press. The material consists of intergrown boron carbide B4C and B-doped diamond with 1.8 at.%B. The material exhibits semiconducting behavior and extreme hardness comparable with that of single-crystal diamond.
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81.05.Hd Other semiconductors
81.05.Mh Cermets, ceramic and refractory composites
61.72.up Other materials
61.72.S- Impurities in crystals

Systematic correlation between Raman spectra, photoluminescence intensity, and absorption coefficient of silica layers containing Si nanocrystals

Leonid Khriachtchev, Markku Räsänen, Sergei Novikov, and Lorenzo Pavesi

Appl. Phys. Lett. 85, 1511 (2004); http://dx.doi.org/10.1063/1.1781733 (3 pages) | Cited 31 times

Online Publication Date: 27 August 2004

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The correlation between optical, structural, and light-emitting properties of annealed Si-rich silica samples containing different amounts of Si nanocrystals is studied. The intensity of the 1.6 eV emission band weakens when the Raman signal coming from the Si nanocrystals gets stronger. On the contrary, the absorption coefficient follows the increase of the Raman intensity with the Si nanocrystal density. The decrease of the photoluminescence is accompanied with the increase of tensile stress, which is suggested by the Raman spectra. Possible explanations of the observed dependencies are discussed.
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78.66.Db Elemental semiconductors and insulators
78.30.Am Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
61.46.-w Structure of nanoscale materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.Cc Kinetics of defect formation and annealing

Compression of Zr2InC to 52 GPa

Bouchaib Manoun, S. K. Saxena, H. P. Liermann, R. P. Gulve, E. Hoffman, M. W. Barsoum, G. Hug, and C. S. Zha

Appl. Phys. Lett. 85, 1514 (2004); http://dx.doi.org/10.1063/1.1784516 (3 pages) | Cited 35 times

Online Publication Date: 27 August 2004

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Using a synchrotron-radiation source and a diamond-anvil cell, we measured the pressure dependence of the lattice parameters of a polycrystalline Zr2InC sample. Up to a pressure of 52 GPa, no phase transformations were observed. As observed in Ti3SiC2 and Ti3Si0.5Ge0.5C2, the compressibility of Zr2InC along the c axis was greater than along the a axis. The bulk modulus is 127±5 GPa, with a pressure derivative of 4.25±0.3; the former is in excellent agreement with our ab initio calculations (130.9 GPa). The a (3.367 math) and c (15.100 math) parameters from the ab initio calculations are also slightly larger than those measured here, viz., 3.35 and 14.91 math. Surprisingly, a hysteresis was observed in the a-lattice parameters; they were higher upon unloading than loading. The reason for this hysteresis is not clear at this time.
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81.40.Lm Deformation, plasticity, and creep
61.66.Fn Inorganic compounds
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
62.50.-p High-pressure effects in solids and liquids

Calculation of phonon spectra to predict the high-pressure metastable phase in an equilibrium immiscible Cu–Ta system

Y. Kong, H. R. Gong, and B. X. Liu

Appl. Phys. Lett. 85, 1517 (2004); http://dx.doi.org/10.1063/1.1786659 (3 pages) | Cited 7 times

Online Publication Date: 27 August 2004

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Under the framework of lattice dynamics, the phonon spectra of the possible metastable Cu3Ta compounds at zero pressure are computed based on an n-body potential by fitting to some physical properties acquired from ab initio calculations. For the three ideal lattices, i.e., L12, D03, and D019, imaginary phonons appear along all high symmetry directions in the Brillouin zone and disappear while subjected to high pressure at about 2.7, 11.8, and 14.7 GPa, respectively. Interestingly, one of the predicted compounds in an L12 structure has indeed been obtained by ion-beam mixing under an appropriate condition.
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61.66.Dk Alloys
62.50.-p High-pressure effects in solids and liquids
63.20.-e Phonons in crystal lattices
61.80.Jh Ion radiation effects

Photonic crystals with silver nanowires as a near-infrared superlens

Xinhua Hu and C. T. Chan

Appl. Phys. Lett. 85, 1520 (2004); http://dx.doi.org/10.1063/1.1784883 (3 pages) | Cited 31 times

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Lensing effect can be achieved in photonic crystal (PC) slabs, but in many situations, the mechanism can be traced to the self-collimation effect of a square-like constant frequency surface. We show that using a metal-in-dielectric configuration, circular constant frequency surface can be obtained, and the lensing effect then obeys fairly well the image–distance relationship characteristic of an n=−1 material. As a two-dimensional example, far-field imaging is realized in square arrays of silver nanowires in air for transverse-electric waves at 400 nm. A high resolution of resolution of about 100 nm obtained with a three layer slab of such PCs. By varying the matrix, the results are extended to optic and near-infrared regime.
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42.79.Bh Lenses, prisms and mirrors
42.70.Qs Photonic bandgap materials
42.30.Va Image forming and processing
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
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Effective mass of InN epilayers

S. P. Fu and Y. F. Chen

Appl. Phys. Lett. 85, 1523 (2004); http://dx.doi.org/10.1063/1.1787615 (3 pages) | Cited 61 times

Online Publication Date: 27 August 2004

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We report on the study of plasma edge absorption of InN epilayers with free electron concentration ranging from 3.5×1017 to 5×1019 cm−3. Together with the previously reported data, the wide range variation of effective mass cannot be explained by Kane’s two band k⋅p model alone. We show that the combination of Kane’s two band k⋅p model, band renormalized effect due to electron–electron interaction, and electron–ionized impurity interaction can provide an excellent description. The effective mass of the free electron at the bottom of the conduction band was found to be m*=0.05 m0, which is in good agreement with the very recent theoretical calculation.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.20.Nr Semiconductor compounds
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