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25 Oct 2004

Volume 85, Issue 17, pp. 3657-3939

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 3851 (2004); http://dx.doi.org/10.1063/1.1808886 (3 pages)

P. Guha, S. Kar, and S. Chaudhuri
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Theoretical optimization of the self-organized growth of nanoscale arrays through a figure of merit

E. Vasco

Appl. Phys. Lett. 85, 3714 (2004); http://dx.doi.org/10.1063/1.1807032 (3 pages) | Cited 2 times

Online Publication Date: 29 October 2004

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A figure of merit is proposed in order to optimize the self-organized growth of nanoscale elements into one-/two-dimensional arrays via a fine selection of the deposition/annealing conditions. This figure of merit has been designed to account for the most significant defects inherent in such arrays. Its versatility has been studied by kinetic Monte Carlo simulations of self-organized growth of metal clusters on the 7×7 reconstructed Si(111) surface. The optimization relationships between deposition/annealing conditions and characteristics of the metal-on-Si(111)7×7 systems are obtained and analyzed within the framework of competition between thermodynamical tendencies and kinetic limitations.
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81.07.Bc Nanocrystalline materials
81.16.Dn Self-assembly
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.J- Point defects and defect clusters
61.46.-w Structure of nanoscale materials

Composition profiling of InAs∕GaAs quantum dots

A. Lemaître, G. Patriarche, and F. Glas

Appl. Phys. Lett. 85, 3717 (2004); http://dx.doi.org/10.1063/1.1811796 (3 pages) | Cited 35 times

Online Publication Date: 29 October 2004

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We propose a simple and straightforward technique to measure the composition distribution of In(Ga)As∕GaAs quantum dots (QDs). This method is based on the quantitative analysis of 002 dark field image contrast in cross-sectional transmission electron microscopy. InAs∕GaAs QDs show strong InGaAs alloying resulting in the formation, prior to capping, of an inverted indium composition gradient, with higher In concentration at the top. Such a mechanism implies a large Ga mass transport from the substrate. The capping process is also investigated. It strongly affects the QD shape by dissolving the apex via surface migration of indium atoms away from the dot.
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81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
68.35.Fx Diffusion; interface formation
68.37.Lp Transmission electron microscopy (TEM)

Abnormal reduction of Eu ions and luminescence in CaB2O4: Eu thin films

J. H. Hao and J. Gao

Appl. Phys. Lett. 85, 3720 (2004); http://dx.doi.org/10.1063/1.1808876 (3 pages) | Cited 17 times

Online Publication Date: 29 October 2004

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Thin films of CaB2O4: Eu were deposited on glass substrates by spray pyrolysis. The abnormal reduction of Eu3+ to Eu2+ in as-grown thin films was found at the growth temperatures from 300 to 500 °C. Blue cathodoluminescence was observed by annealing films in air, correlating with further abnormal reduction of Eu ions and crystallization of compounds. These phenomena were explained by an electron transfer mechanism. The chromaticity coordinates were x=0.193 and y=0.089 with a dominant wavelength of 455 nm. Our results indicate calcium borate doped with Eu is a blue phosphor at temperatures suitable for the use of glass substrates in flat panel applications.
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68.55.A- Nucleation and growth
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
78.66.Nk Insulators
81.15.Rs Spray coating techniques
81.40.Gh Other heat and thermomechanical treatments
78.60.Hk Cathodoluminescence, ionoluminescence
64.70.K- Solid-solid transitions

Observation of negative thermo-optical coefficient in cubic MgZnO thin films

H. P. Zhou, W. Z. Shen, N. B. Chen, and H. Z. Wu

Appl. Phys. Lett. 85, 3723 (2004); http://dx.doi.org/10.1063/1.1808882 (3 pages) | Cited 5 times

Online Publication Date: 29 October 2004

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We report on the investigation of thermo-optical coefficient (dn∕dT) in cubic MgZnO thin films through temperature-dependent (10–295 K) optical transmission measurements. As a result of potential fluctuation, we observe an anomalous thermal behavior of the band gap in the ternary MgZnO alloy, which limits the observation of negative dn∕dT up to 200 K. The negative dn∕dT is evidenced by the phase shift from the prominent Fabry-Pérot interference fringes and modeled by taking into account the thermal and electronic background contribution, as well as the Wannier exciton effect. It is found that the large thermal expansion in cubic MgZnO plays a key role in the observed negative dn∕dT.
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81.05.Dz II-VI semiconductors
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Hf II-VI semiconductors
65.40.De Thermal expansion; thermomechanical effects
71.35.-y Excitons and related phenomena

The generation of highly monodisperse droplets through the breakup of hydrodynamically focused microthread in a microfluidic device

Qingyi Xu and Mitsutoshi Nakajima

Appl. Phys. Lett. 85, 3726 (2004); http://dx.doi.org/10.1063/1.1812380 (3 pages) | Cited 76 times

Online Publication Date: 29 October 2004

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We used a controllable three-stream laminar flow system to hydrodynamically focus a viscous stream, flowing between two inviscid streams, to cause instability and eventual breakup. The characteristics of the focusing and breakup of the viscous stream are presented here. Breakup occurred as the viscous stream was focused to a characteristic width of several micrometers. Highly monodisperse droplets with diameters smaller than the width of the junction of the three inlet channels were formed through the rapid periodic breakup of the focused microthread. Size, production rate, and patterning can be precisely controlled with this approach.
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47.15.Fe Stability of laminar flows
47.55.D- Drops and bubbles
47.85.Dh Hydrodynamics, hydraulics, hydrostatics
47.20.Cq Inviscid instability
47.85.Np Fluidics

Blue emission from CaS:Cu,F thin-film electroluminescent device fabricated on Si substrate

Shintaro Hakamata, Mami Ehara, Haruki Fukada, Hiroko Kominami, Yoichiro Nakanishi, and Yoshinori Hatanaka

Appl. Phys. Lett. 85, 3729 (2004); http://dx.doi.org/10.1063/1.1812381 (2 pages)

Online Publication Date: 29 October 2004

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Thin-film electroluminescent (TFEL) devices were fabricated on Si substrates by using SiO2 and Y2O3 films as insulator layers, and ZnS films as buffer layers. The device annealed at 850 °C for 10 min in Ar showed a purple EL with a peak at 425 nm. Commission Internationale de l’Eclairage (CIE) color coordinates of x=0.217, y=0.223 under driving at 220 V0−p of 1 kHz trapezoidal wave. The purple EL from CaS:Cu TFEL device could be achieved, although luminance was weak, and a little longer wavelength component was included.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
68.55.A- Nucleation and growth
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.40.Gh Other heat and thermomechanical treatments
61.72.Cc Kinetics of defect formation and annealing

Fluorine-enhanced low-temperature wafer bonding of native-oxide covered Si wafers

Q.-Y. Tong, Q. Gan, G. Fountain, P. Enquist, R. Scholz, and U. Gösele

Appl. Phys. Lett. 85, 3731 (2004); http://dx.doi.org/10.1063/1.1809279 (3 pages) | Cited 7 times

Online Publication Date: 29 October 2004

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The bonding energy of bonded native-oxide-covered silicon wafers treated in the HNO3∕H2O∕HF or the HNO3∕HF solution prior to room-temperature contact is significantly higher than bonded standard RCA1 cleaned wafer pairs after low-temperature annealing. The bonding energy reaches over 2000 mJ∕m2 after annealing at 100 °C. The very slight etching and fluorine in the chemically grown oxide are believed to be the main contributors to the enhanced bonding energy. Transmission-electron-microscopic images have shown that the chemically formed native oxide at bonding interface is embedded with many flake-like cavities. The cavities can absorb the by-products of the interfacial reactions that result in covalent bond formation at low temperatures allowing the strong bond to be retained.
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81.65.Cf Surface cleaning, etching, patterning
61.72.Cc Kinetics of defect formation and annealing

Periodic precipitation of crystalline Ge nanoparticles in Ge–B–SiO2 thin glass films

Hiroaki Nishiyama, Isamu Miyamoto, Shin-ichi Matsumoto, Mitsunori Saito, Kohei Fukumi, Kenji Kintaka, and Junji Nishii

Appl. Phys. Lett. 85, 3734 (2004); http://dx.doi.org/10.1063/1.1812369 (3 pages) | Cited 5 times

Online Publication Date: 29 October 2004

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Crystalline 20- to 40-nm-diam Ge nanoparticles were precipitated periodically in Ge–B–SiO2 thin glass films fabricated by the plasma-enhanced chemical vapor deposition method. Such a periodic structure was created by exposure to an interference pattern with a KrF excimer laser (248 nm wavelength) and successive annealing at 600°C. Nanoparticles were precipitated predominantly in the unirradiated region after photoinduced refractive index change was erased completely after annealing up to 500°C.
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81.05.Kf Glasses (including metallic glasses)
61.43.Fs Glasses
61.46.-w Structure of nanoscale materials
68.55.A- Nucleation and growth
81.30.Mh Solid-phase precipitation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.40.Gh Other heat and thermomechanical treatments
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Jg Amorphous semiconductors; glasses
81.65.Cf Surface cleaning, etching, patterning

Visualization of graphite atomic arrangement by stereo atomscope

Fumihiko Matsui, Hiroshi Daimon, Fang Zhun Guo, and Tomohiro Matsushita

Appl. Phys. Lett. 85, 3737 (2004); http://dx.doi.org/10.1063/1.1810214 (3 pages) | Cited 19 times

Online Publication Date: 29 October 2004

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The direct visualization of an atomic arrangement is essential for understanding the nature of materials. The rotation of forward focusing peaks in photoelectron angular distribution (PEAD) patterns excited by circularly polarized light with the opposite helicities are found to be the same as the parallax in stereo view. Taking advantage of this phenomenon of PEAD circular dichroism, the three-dimensional atomic arrangement image of graphite crystal was realized. Taking a stereo picture around carbon atom, which has been thought difficult due to a small angular momentum of photoelectron, proved that this method is applicable to all materials including biomolecules.
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78.20.Fm Birefringence
79.60.-i Photoemission and photoelectron spectra
61.66.Bi Elemental solids

Characterization of light-induced modification of the nonlinear refractive index using a one-laser-shot nonlinear imaging technique

G. Boudebs and Cid B. de Araújo

Appl. Phys. Lett. 85, 3740 (2004); http://dx.doi.org/10.1063/1.1810624 (3 pages) | Cited 11 times

Online Publication Date: 29 October 2004

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We report the exploitation of a one-laser-shot measurement technique to study photo-induced effects in semiconductor-doped glasses. The technique, based on the use of a phase object in a 4f coherent imaging system, allows one to characterize the kinetics of the nonlinear refractive index of samples versus the light exposure time.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
61.82.Rx Nanocrystalline materials
61.46.-w Structure of nanoscale materials
42.65.-k Nonlinear optics
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Determination of the nitrogen distribution in InGaNAs∕GaAs quantum wells by transmission electron microscopy

D. Litvinov, D. Gerthsen, A. Rosenauer, M. Hetterich, A. Grau, Ph. Gilet, and L. Grenouillet

Appl. Phys. Lett. 85, 3743 (2004); http://dx.doi.org/10.1063/1.1810643 (3 pages) | Cited 10 times

Online Publication Date: 29 October 2004

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We report on measurements of the nitrogen-concentration profile in an InGaNAs heterostructure by high-resolution transmission electron microscopy. Two samples grown by gas-source molecular-beam epitaxy on GaAs(001) substrates were investigated which contain InGaAs and InGaNAs wells with the same thickness and In concentration. The indium concentration was determined by high-resolution x-ray diffractometry. Indium-concentration profiles were obtained with the composition evaluation by lattice fringe analysis (CELFA) technique from the sample with the InGaAs wells exploiting the chemical sensitivity of the diffracted (002) beam. Nitrogen-concentration profiles were measured in the InGaNAs wells by comparison of the CELFA results observed in the samples with and without nitrogen.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
68.65.Fg Quantum wells
61.72.S- Impurities in crystals
68.35.Ct Interface structure and roughness
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.67.De Quantum wells
78.55.Cr III-V semiconductors
68.37.Lp Transmission electron microscopy (TEM)

Study on the growth mechanism of pentacene thin films by the analysis of island density and island size distribution

M. Tejima, K. Kita, K. Kyuno, and A. Toriumi

Appl. Phys. Lett. 85, 3746 (2004); http://dx.doi.org/10.1063/1.1812591 (3 pages) | Cited 13 times

Online Publication Date: 29 October 2004

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The growth mechanism of pentacene thin films on a thermally grown SiO2 on Si(100) substrate is examined in detail for a wide substrate temperature range (223–342 K) by analyzing the saturated island density and island size distribution. It is found that the log plot of the saturated island density as a function of inverse substrate temperature can be well represented by two straight lines and that these two regions have different critical cluster sizes for nucleation which is independently confirmed by island size distribution analysis. It is concluded that the nucleation behavior of pentacene thin films can be explained by the diffusion-mediated growth model well known in inorganic thin-film growth.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Aa Theory and models of film growth
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)

Effect of stacking fault energy on plastic deformation of nanocrystalline face-centered cubic metals

F. Ebrahimi, Z. Ahmed, and H. Li

Appl. Phys. Lett. 85, 3749 (2004); http://dx.doi.org/10.1063/1.1810629 (3 pages) | Cited 21 times

Online Publication Date: 29 October 2004

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The effect of stacking fault energy (SFE) on the tensile stress–strain behavior of nanocrystalline face-centered cubic (fcc) metals was investigated. The stacking fault energy of nickel was decreased by alloying with copper or iron. It was found that, as predicted by a recent simulation study, decreasing the SFE increases the strain hardening rate of the nanocrystalline fcc metals. The effect was more pronounced in the nickel–copper alloy, which had a smaller average grain size.
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81.07.Bc Nanocrystalline materials
61.72.Nn Stacking faults and other planar or extended defects
62.25.-g Mechanical properties of nanoscale systems
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
61.46.-w Structure of nanoscale materials

Axial strain redistribution resulting from off-axis ply cracking in polymer composites

Dionisis G. Katerelos and Costas Galiotis

Appl. Phys. Lett. 85, 3752 (2004); http://dx.doi.org/10.1063/1.1811395 (3 pages) | Cited 10 times

Online Publication Date: 29 October 2004

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The initial mode of damage in multidirectional composites is the accumulation of matrix cracks in the off-axis plies. Remote laser Raman spectroscopy, using aramid (Kevlar 49®) fibers as Raman strain sensors, has been employed to monitor the local strains in cracked crossply composites. The strain magnification in the 0° ply caused by 90° matrix cracking are measured at different levels of loading. A relationship between the values of strain magnification and the distance between the position of the fibers sensors vis-à-vis the crack front has been established. The effect of damage progression within the 0° plies on the remaining∕surviving glass fibers is modeled satisfactorily and verified against predictions on the basis of a generalized plane strain model by assuming that the 90° ply “expands” in relative size against the 0° ply thickness.
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81.05.Qk Reinforced polymers and polymer-based composites
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials

Electronic structure of secondary phases in Cu-rich CuGaSe2 solar cell devices

D. Fuertes Marrón, Th. Glatzel, A. Meeder, Th. Schedel-Niedrig, S. Sadewasser, and M. Ch. Lux-Steiner

Appl. Phys. Lett. 85, 3755 (2004); http://dx.doi.org/10.1063/1.1812582 (3 pages) | Cited 10 times

Online Publication Date: 29 October 2004

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Kelvin probe force microscopy in ultrahigh vacuum was used to image the electronic structure of thin-film solar cell cross sections based on as-grown Cu-rich CuGaSe2 absorbers. We observe different secondary phases in the absorber film. A p-type degenerate Cu2−xSe phase is identified by a higher work function (Φ∼5.35 eV) than CuGaSe2 (Φ∼5.1 eV), allowing good contrast mappings of both phases within the absorber film. Besides entire Cu2−xSe crystallites we also observed this secondary phase segregated as an interfacial layer along CuGaSe2 grain boundaries. An additional high-work function phase at the CuGaSe2∕window junction is attributed to the formation of an improper CuS buffer layer during chemical bath processing. The detrimental effect of these secondary phases on the solar cell performance is discussed.
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84.60.Jt Photoelectric conversion
71.20.Nr Semiconductor compounds
61.72.Mm Grain and twin boundaries
73.30.+y Surface double layers, Schottky barriers, and work functions

The influence of scandium in effecting fragile to strong glass transition in aluminium-based alloys

Dmitri V. Louzguine, Shintaro Sobu, and Akihisa Inoue

Appl. Phys. Lett. 85, 3758 (2004); http://dx.doi.org/10.1063/1.1808502 (2 pages) | Cited 15 times

Online Publication Date: 29 October 2004

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The “fragile”–“strong glass” transition in Al-based alloys is observed as a function of Sc content. The Sc-bearing alloys suffer glass transition as well as Sc-free Al0.84Y0.09Ni0.05Co0.02 alloy, however, the value of ΔCp decreases drastically and comes within the variation of the baseline at higher than 2 at. % of Sc. The studied glasses are free from pre-existing nuclei.
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81.05.Kf Glasses (including metallic glasses)
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.43.Fs Glasses

Photon-directed colloidal crystallization

Tieying Gong and David W. M. Marr

Appl. Phys. Lett. 85, 3760 (2004); http://dx.doi.org/10.1063/1.1808471 (3 pages) | Cited 11 times

Online Publication Date: 29 October 2004

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We have recently shown that electric fields can be used to induce rapid three-dimensional colloidal crystallization from isotropic colloidal dispersions through a combination of dielectrophoretic and electro-osmotic mechanisms. In this letter we demonstrate that light itself can be used to drive colloidal crystallization in a local and directed fashion under applied electric fields, allowing one to effectively write colloidal crystals in arbitrary and reversible patterns. This ability will provide great flexibility in the construction of colloid-based devices and allow their reversible operation as a function of an applied optical or electric field.
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82.70.Dd Colloids
64.70.D- Solid-liquid transitions
82.45.-h Electrochemistry and electrophoresis
78.35.+c Brillouin and Rayleigh scattering; other light scattering
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