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9 Apr 2001

Volume 78, Issue 15, pp. 2095-2255

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Temperature profile of GaInAs/AlInAs/InP quantum cascade-laser facets measured by microprobe photoluminescence

Vincenzo Spagnolo, Mariano Troccoli, Gaetano Scamarcio, Claire Gmachl, Federico Capasso, Alessandro Tredicucci, A. Michael Sergent, Albert L. Hutchinson, Deborah L. Sivco, and Alfred Y. Cho

Appl. Phys. Lett. 78, 2095 (2001); http://dx.doi.org/10.1063/1.1359146 (3 pages) | Cited 36 times

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The local temperature of quantum-cascade lasers operating in continuous wave mode is reported. This information is extracted from the thermal shift of the band-to-band photoluminescence peaks in the AlInAs and InP cladding layers of quantum-cascade laser facets using a high-resolution microprobe setup. Interpolation by means of a two-dimensional heat diffusion model allows to obtain the temperature profile and the thermal conductivity in the waveguide core. Comparison between substrate and epilayer-side mounted lasers shows the superior thermal dissipation capability of the latter, and explains their better performance with respect to threshold current and maximum operating temperature. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.55.Cr III-V semiconductors
78.67.De Quantum wells
68.65.Fg Quantum wells
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Dispersion of the ordinary refractive-index change in a proton-exchanged LiNbO3 waveguide

R. Ramponi, M. Marangoni, and R. Osellame

Appl. Phys. Lett. 78, 2098 (2001); http://dx.doi.org/10.1063/1.1359136 (3 pages) | Cited 9 times

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The wavelength dependence of the ordinary refractive-index change of a proton exchanged LiNbO3 waveguide is determined by applying a recently proposed method based on radiation modes. A peculiar behavior is observed since the absolute value of the ordinary index change increases with the wavelength, while the extraordinary one decreases. The Sellmeier curves for the dispersion of both the index changes are provided in the wavelength range from λ = 0.514 μm to λ = 1.554 μm. © 2001 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.65.Wi Nonlinear waveguides
42.86.+b Optical workshop techniques

Leveraging deep photonic band gaps in photonic crystal impurity bands

Sheng Lan, Satoshi Nishikawa, and Osamu Wada

Appl. Phys. Lett. 78, 2101 (2001); http://dx.doi.org/10.1063/1.1362328 (3 pages) | Cited 34 times

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Photonic band gaps can be generated in the impurity bands of photonic crystals formed by periodically placed defects. Even slight periodic modulation of the properties of these defects can open up very deep band gaps in the impurity bands. This phenomenon originates from the concentration of electromagnetic field at the defect regions, making electromagnetic wave extremely sensitive to the small changes of the defects. A dynamical photonic band gap in the impurity band created by a control light, provides a mechanism for constructing high-efficiency optical switches. © 2001 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Origin of abnormal temperature dependence of electroluminescence from Er/O-doped Si diodes

G. V. Hansson, W.-X. Ni, C.-X. Du, A. Elfving, and F. Duteil

Appl. Phys. Lett. 78, 2104 (2001); http://dx.doi.org/10.1063/1.1359781 (3 pages) | Cited 12 times

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The temperature dependencies of the current–voltage characteristics and the electroluminescence (EL) intensity of molecular beam epitaxy grown Er/O-doped Si light emitting diodes at reverse bias have been studied. To minimize the scattering of electrons injected from the p-doped Si1−xGex electron emitters, an intrinsic Si layer was used in the depletion region. For many diodes, there is a temperature range where the EL intensity increases with temperature. Data are reported for a structure that shows increasing intensity up to 100 °C. This is attributed to an increasing fraction of the pumping current being due to phonon-assisted tunneling, which gives a higher saturation intensity, compared to ionization-dominated breakdown at lower temperatures. © 2001 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices

High-performance InAs/GaSb superlattice photodiodes for the very long wavelength infrared range

H. Mohseni, M. Razeghi, G. J. Brown, and Y. S. Park

Appl. Phys. Lett. 78, 2107 (2001); http://dx.doi.org/10.1063/1.1362179 (3 pages) | Cited 30 times

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We report on the demonstration of high-performance p-i-n photodiodes based on type-II InAs/GaSb superlattices with 50% cut-off wavelength λc = 16 μm operating at 80 K. Material is grown by molecular beam epitaxy on GaSb substrates with excellent crystal quality as evidenced by x-ray diffraction and atomic force microscopy. The processed devices show a current responsivity of 3.5 A/W at 80 K leading to a detectivity of ∼ 1.51×1010 cmHz1/2/W. The quantum efficiency of these devices is about 35% which is comparable to HgCdTe detectors with a similar active layer thickness. © 2001 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
68.65.Cd Superlattices
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Low-loss polymeric optical waveguides using electron-beam direct writing

W. H. Wong, J. Zhou, and E. Y. B. Pun

Appl. Phys. Lett. 78, 2110 (2001); http://dx.doi.org/10.1063/1.1361287 (3 pages) | Cited 27 times

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Low-loss optical waveguides based on a negative tone epoxy Novolak resin polymer have been fabricated using electron-beam direct writing. This polymer has a high refractive index, high sensitivity, large hardness, and Tg>200 °C. For single-mode channel waveguides with upper claddings, the propagation losses measured were 0.22 and 0.48 dB/cm at 1330 and 1550 nm, respectively. For waveguides without upper claddings, the losses were 0.5 dB/cm at both wavelengths. The stability of these waveguides was also investigated, and no significant change was observed after 200 h at 90 °C and 95% relative humidity. © 2001 American Institute of Physics.
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42.70.Jk Polymers and organics
42.79.Gn Optical waveguides and couplers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.86.+b Optical workshop techniques

Large improvement of pumping rate in the He–CuCl–NiBr2 laser system

H. Saito, Y. Shiraiwa, T. Ishikawa, K. Uno, and K. Fujii

Appl. Phys. Lett. 78, 2113 (2001); http://dx.doi.org/10.1063/1.1358849 (3 pages) | Cited 2 times

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A Ni atom is employed as the energy donor to a Cu upper laser level. After the energy transfer is done by collision between Ni and Cu atoms, the population of the Cu upper laser level is enhanced via a cascading decay resulting in a four-level excitation loop. The peak value of the lasing pulse was increased by a rate of 400%, whereas the pulse width was not changed. The near-infrared spectra, λ = 809.3 and 793.3 nm, emitted via this cascading decay method, were also observed and the intensity properties agreed with that of the lasing lines. © 2001 American Institute of Physics.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
32.80.Xx Level crossing and optical pumping
32.50.+d Fluorescence, phosphorescence (including quenching)

Correlation between dark spot growth and pinhole size in organic light-emitting diodes

Shuang Fang Lim, Lin Ke, Wei Wang, and Soo Jin Chua

Appl. Phys. Lett. 78, 2116 (2001); http://dx.doi.org/10.1063/1.1364658 (3 pages) | Cited 29 times

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Our in situ experimental observations of dark spot growth in organic light-emitting diodes using optical microscopy show a linear rate of growth for the area of all the dark spots. We used uniformly sized silica micro particles to intentionally create size-controllable pinholes on the cathode protective layer. Subsequently, we observed initial formation of dark spots as a result of these pinholes and then monitored their growth. Due to usage of particles of various diameters, we were able to linearly correlate the growth rate with pinhole size. This allows us to estimate the original pinhole sizes that gave rise to the dark spots, which we believe were initiated by “dust” particles. Our studies verify that dark spot formation is due to pinholes on the protective layer that creates pathways for water or oxygen permeation, and that dark spot growth is dependent on the pinhole sizes. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices

Reduction in surface recombination of GaInAsP microcolumns by CH4 plasma irradiation

Hiroyuki Ichikawa, Kyoji Inoshita, and Toshihiko Baba

Appl. Phys. Lett. 78, 2119 (2001); http://dx.doi.org/10.1063/1.1364506 (3 pages) | Cited 20 times

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We evaluated the surface recombination velocity vs of 1.55 μm GaInAsP microcolumns through the measurement of carrier lifetime using the phase-resolved spectroscopy. We investigated various surface treatments and confirmed that vs was reduced to nearly half of that for as-etched microcolumns by CH4 electron cyclotron resonance plasma irradiation. This result was ensured by the two- to fivefold increase in photoluminescence intensity. The secondary ion mass spectroscopy analysis suggested that the reduction in vs was attributable to the deposition of a polymer, the hydrogenated hard carbon, etc., and/or a carbon deep level formed near the surface. © 2001 American Institute of Physics.
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73.25.+i Surface conductivity and carrier phenomena
78.55.Cr III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
73.63.-b Electronic transport in nanoscale materials and structures

Near-infrared electroluminescence of polymer light-emitting diodes doped with a lissamine-sensitized Nd3+ complex

L. H. Slooff, A. Polman, F. Cacialli, R. H. Friend, G. A. Hebbink, F. C. J. M. van Veggel, and D. N. Reinhoudt

Appl. Phys. Lett. 78, 2122 (2001); http://dx.doi.org/10.1063/1.1359782 (3 pages) | Cited 69 times

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We report 890 nm luminescence from a neodymium-doped polymer light-emitting diode. The active layer is a blend of poly(dioctylfluorene-co-benzothiadiazole), F8BT, and a lissamine-functionalized terphenyl-based neodymium complex. We detect electroluminescence from both the lissamine (580 nm) and the Nd3+ complex (890 nm). By comparison with lissamine-free devices we show that the lissamine is crucial to infrared emission. The neodymium/lissamine luminescence intensity ratio is higher under electrical excitation than under optical excitation, showing that more triplets reach Nd3+ under electrical excitation. High turn-on voltages provide a clear indication for charge trapping onto the lissamine, and we consider direct triplet formation on the lissamine to be competing efficiently with respect to slower Dexter-type triplet transfer from the F8BT to the lissamine. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds

Photosensitivity in phosphate glass doped with Ag+ upon exposure to near-ultraviolet femtosecond laser pulses

Yuichi Watanabe, Gaku Namikawa, Teppei Onuki, Keishi Nishio, and Toshio Tsuchiya

Appl. Phys. Lett. 78, 2125 (2001); http://dx.doi.org/10.1063/1.1361284 (3 pages) | Cited 23 times

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We report on a photosensitivity in soda-alumino-phosphate glass doped with silver ions Ag+ upon exposure to near-ultraviolet femtosecond laser pulses. The photosensitivity, i.e., formation of color centers such as Ag0 and Ag2+ in the glass is found to be associated with intensity-dependent nonlinear optical process induced by extremely high irradiance up to ∼ TW/cm2 of the femtosecond pulses. We demonstrate a bright orange fluorescence from the induced color centers inside the glass, that should be applicable to a functional optical device. © 2001 American Institute of Physics.
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42.70.Gi Light-sensitive materials
42.70.Ce Glasses, quartz
61.43.Fs Glasses
78.55.Hx Other solid inorganic materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
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Hydrogen storage in aligned carbon nanotubes

Yan Chen, David T. Shaw, X. D. Bai, E. G. Wang, C. Lund, W. M. Lu, and D. D. L. Chung

Appl. Phys. Lett. 78, 2128 (2001); http://dx.doi.org/10.1063/1.1341224 (3 pages) | Cited 38 times

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Aligned carbon nanotubes (CNTs) with diameters of 50–100 nm, synthesized by plasma-assisted hot filament chemical vapor deposition, were employed for hydrogen adsorption experiments in their as-prepared and pretreated states. Quadruple mass spectroscopy and thermogravimetric analysis show a hydrogen storage capacity of 5–7 wt% was achieved reproducibly at room temperature under modest pressure (10 atm) for the as-prepared samples. Pretreatments, which include heating the samples to 300 °C and removing of the catalyst tips, can increase the hydrogen storage capacity up to 13 wt% and decrease the pressure required for storage. The weight gains were measured after the samples moved out of the hydrogen environment. The release of the adsorbed hydrogen can be achieved by heating the samples up to 300 °C. © 2001 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
68.43.Mn Adsorption kinetics
84.60.-h Direct energy conversion and storage
81.07.De Nanotubes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Enhancement of the molecular nitrogen dissociation levels by argon dilution in surface-wave-sustained plasmas

M. Tabbal, M. Kazopoulo, T. Christidis, and S. Isber

Appl. Phys. Lett. 78, 2131 (2001); http://dx.doi.org/10.1063/1.1359775 (3 pages) | Cited 10 times

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In this work, the nitrogen molecular dissociation level in Ar/N2 surface-wave plasma is evaluated as a function of plasma parameters such as Ar percentage in the gas mixture, power absorbed in the plasma, and total pressure in order to design an efficient N-atom source that can be used for various applications such as thin-film deposition and materials surface modification. This plasma is operated at 40.68 MHz and the nitrogen dissociation rate is determined, in the remote plasma, by analyzing the optical emission of the first positive molecular nitrogen band. For all operating conditions, the dissociation rate ([N]/[N2]) of N2 molecules was enhanced, as the percentage of Ar in the mixture increased from 0 to ∼95%, and dissociation rates higher than 2.5% were measured. This gain in the dissociation rate became more pronounced when the plasma power and total pressure increased from 40 to 120 W and from 4 to 7.5 Torr, respectively. These results are discussed in terms of the kinetics of the electrons, nitrogen atoms, and molecules and confirm theoretical kinetic models presented in the literature. © 2001 American Institute of Physics.
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52.50.Dg Plasma sources
82.37.Np Single molecule reaction kinetics, dissociation, etc.
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
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Electron energy loss near-edge structures of cubic Si3N4

Isao Tanaka, T. Mizoguchi, T. Sekine, Hongliang He, K. Kimoto, T. Kobayashi, Shang-Di Mo, and W. Y. Ching

Appl. Phys. Lett. 78, 2134 (2001); http://dx.doi.org/10.1063/1.1360232 (3 pages) | Cited 35 times

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Electron energy loss near-edge structures of the newly discovered cubic-Si3N4 at the Si L2,3, edge and N K edge have been measured. The same edges were calculated using a first-principles supercell approach, including the core–hole interaction. The experimental spectra at the two edges were satisfactorily reproduced by the calculations, confirming that the present calculation has sufficient predictive power. The difference in spectral shapes between c-Si3N4 and β-Si3N4 is more clear for the Si L2,3, edge. However, the difference cannot be simply explained by the difference in coordination numbers of Si. © 2001 American Institute of Physics.
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79.20.Uv Electron energy loss spectroscopy
71.20.Ps Other inorganic compounds

Compositional dependence of the strain-free optical band gap in InxGa1−xN layers

S. Pereira, M. R. Correia, T. Monteiro, E. Pereira, E. Alves, A. D. Sequeira, and N. Franco

Appl. Phys. Lett. 78, 2137 (2001); http://dx.doi.org/10.1063/1.1358368 (3 pages) | Cited 50 times

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The effect of strain on the compositional and optical properties of a set of epitaxial single layers of InxGa1−xN was studied. Indium content was measured free from the effects of strain by Rutherford backscattering spectrometry. Accurate knowledge of the In mole fraction, combined with x-ray diffraction measurements, allows perpendicular strain (ϵzz) to be evaluated. Optical band gaps were determined by absorption spectroscopy and corrected for strain. Following this approach, the strain free dependence of the optical band gap in InxGa1−xN alloys was determined for x ⩽ 0.25. Our results indicate an “anomalous,” linear, dependence of the energy gap on the In content, at room temperature: Eg(x) = 3.39–3.57x eV. Extension of this behavior to higher concentrations is discussed on the basis of reported results. © 2001 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
61.66.Bi Elemental solids
61.66.Dk Alloys
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
68.55.Nq Composition and phase identification

Semimagnetic self-organized Cd1−xMnxTe quantum dots generated by postgrowth thermal annealing

G. Prechtl, W. Heiss, S. Mackowski, and E. Janik

Appl. Phys. Lett. 78, 2140 (2001); http://dx.doi.org/10.1063/1.1362199 (3 pages) | Cited 13 times

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We demonstrate the possibility to fabricate self-organized semimagnetic quantum dots by the growth of two-dimensional layers and subsequent thermal annealing. In particular, CdTe/CdMgTe quantum-well samples containing four narrow MnTe barriers are characterized by optical methods. After annealing well above the growth temperature, from time-resolved photoluminescence (PL), PL experiments under selective excitation, as well as micro-PL measurements, we find clear evidence for the presence of quantum dots. For a sample with a average Mn content of 5%, the dot luminescence shows a redshift of 18 meV under an applied magnetic field of 4 T, due to the giant Zeeman effect. © 2001 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
75.50.Pp Magnetic semiconductors
78.67.Hc Quantum dots
61.72.Cc Kinetics of defect formation and annealing
78.55.Et II-VI semiconductors
78.47.-p Spectroscopy of solid state dynamics
78.20.Ls Magneto-optical effects

Near infra-red radiation squeezing through 20 nm voids in obliquely deposited metal films

G. B. Smith, A. K. M. Hossain, and A. Gentle

Appl. Phys. Lett. 78, 2143 (2001); http://dx.doi.org/10.1063/1.1359489 (2 pages) | Cited 1 time

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Obliquely deposited metal films which are nearly continuous, displaying several unexpected solar optical properties. Transmittance intensity, spectral character, preferred direction of incidence, and polarization sensitivity, infer processes which effective-medium models based solely on “interior” properties cannot describe. Amplified transmittance through voids around 20 nm wide involving near surface excitations can explain the data. © 2001 American Institute of Physics.
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78.66.Bz Metals and metallic alloys
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
42.50.Dv Quantum state engineering and measurements
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
61.72.Qq Microscopic defects (voids, inclusions, etc.)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Kinetics of the glass-transition and crystallization process of Fe72−xNbxAl5Ga2P11C6B4 (x = 0, 2) metallic glasses

N. Mitrovic, S. Roth, and J. Eckert

Appl. Phys. Lett. 78, 2145 (2001); http://dx.doi.org/10.1063/1.1361099 (3 pages) | Cited 37 times

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The kinetics of the glass-transition and the crystallization process of multicomponent ferromagnetic Fe72−xNbxAl5Ga2P11C6B4 (x = 0, 2) metallic glasses have been investigated by constant-rate heating differential scanning calorimetry at different heating rates. The glass-transition temperature Tg and the crystallization peak temperature Tp shift to higher temperatures with increasing heating rate. The apparent activation energy and the frequency factor are evaluated by the Kissinger method, and the rate constant of the crystallization process is estimated by an Arrhenius law. The kinetics of the glass-transition process have been analyzed in terms of a Vogel–Fulcher–Tammann equation describing the heating rate dependence of the glass-transition temperature. The effect of the niobium addition on the glass-forming ability has been investigated with respect to the glass-transition and crystallization kinetics, revealing that substitution of Nb for Fe does not improve the glass-forming ability and it lowers the thermal stability of the material. © 2001 American Institute of Physics.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.43.Fs Glasses

Photoluminescence of nanostructured PbTiO3 processed by high-energy mechanical milling

E. R. Leite, L. P. S. Santos, N. L. V. Carreño, E. Longo, C. A. Paskocimas, J. A. Varela, F. Lanciotti, C. E. M. Campos, and P. S. Pizani

Appl. Phys. Lett. 78, 2148 (2001); http://dx.doi.org/10.1063/1.1362200 (3 pages) | Cited 25 times

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This letter reports on a process to prepare nanostructured PbTiO3 (PT) at room temperature with photoluminescence (PL) emission in the visible range. This process is based on the high-energy mechanical milling of ultrafine PbTiO3 powder. The results suggest that high-energy mechanical milling modifies the particle’s structure, resulting in localized states in an interfacial region between the crystalline PT and the amorphous PT. These localized states are believed to be responsible for the PL obtained with short milling times. When long milling times are employed, the amorphous phase that is formed causes PL behavior. An alternative method to process nanostructured wide-band-gap semiconductors with active optical properties such as PL is described in this letter. © 2001 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.20.Wk Machining, milling
81.07.Wx Nanopowders
73.22.-f Electronic structure of nanoscale materials and related systems
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
71.55.Jv Disordered structures; amorphous and glassy solids

Argon inclusion in sputtered films and the effect of the gas on molybdenum field emitter arrays

Babu R. Chalamala and Robert H. Reuss

Appl. Phys. Lett. 78, 2151 (2001); http://dx.doi.org/10.1063/1.1361281 (3 pages) | Cited 6 times

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Residual gas analysis of a number of field emission displays showed that argon desorbed from molybdenum metal lines was the dominant gas in sealed vacuum packages. We present experimental results on the emission characteristics of molybdenum field emitter arrays in argon ambient. In argon, the emission current dropped rapidly similar to that in oxygenic gas ambients. Existing degradation models do not provide an adequate explanation for this behavior. Rather, we suggest a model based on shallow implantation of argon into the field emitter tips that increases the effective width of the tunneling barrier. Experimental support for this model comes from the following observations: emission current degraded only when the device was turned on; after gas exposure, significant current recovery which followed diffusion type behavior was noted; degradation and recovery rates were functions of partial pressure; and no detectable effects associated with sputtering were observed. This mechanism is also consistent with ion pumping known to occur in field emission displays. © 2001 American Institute of Physics.
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85.45.Fd Field emission displays (FEDs)
68.43.Mn Adsorption kinetics
79.70.+q Field emission, ionization, evaporation, and desorption
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
82.80.-d Chemical analysis and related physical methods of analysis

Multiplet structures of tetrahedrally coordinated Cr4+ and Cr5+ in Y3Al5O12

Takugo Ishii, Kazuyoshi Ogasawara, Hirohiko Adachi, and Isao Tanaka

Appl. Phys. Lett. 78, 2154 (2001); http://dx.doi.org/10.1063/1.1364655 (3 pages) | Cited 2 times

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Multiplet structures of tetrahedrally coordinated Cr4+ and Cr5+ in Y3Al5O12 (yttrium aluminum garnet) were calculated with use of the ab initio electronic-structure calculation method. The calculated absorption spectrum of Cr4+ showed that two bands at the near-infrared and visible spectral regions originated from the same 3T1 parent multiplet term. The calculated levels originating from Cr5+ in the near-infrared region overlapped with the levels originating from Cr4+. Both the lowest-spin-allowed transitions of Cr4+ and Cr5+ were revealed to have the same polarization dependence. The result indicated that confusion on the assignment of the peaks could be ignored if the Cr5+ state really exists. © 2001 American Institute of Physics.
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75.50.Gg Ferrimagnetics
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
71.55.Ht Other nonmetals

Transmission electron microscopy studies of the effect of A-site cation size mismatch and disorder on charge ordering behavior in (La1−xYx)0.5(Ca1−ySry)0.5MnO3

Y. Q. Wang, X. F. Duan, Z. H. Wang, and B. G. Shen

Appl. Phys. Lett. 78, 2157 (2001); http://dx.doi.org/10.1063/1.1364505 (3 pages) | Cited 6 times

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The effects of A-site cation mismatch and disorder on the charge ordering (CO) behavior in the manganites (La1−xYx)0.5(Ca1−ySry)0.5MnO3 have been studied by transmission electron microscopy. The presence of the size mismatch and disorder suppresses the CO transition. Incommensurate CO modulations are observed in three samples with 0 ⩽ σ2 ⩽ 0.003. Structural models, based on the selected area electron diffraction and high-resolution electron microscopy observation, are suggested for such kinds of incommensurate modulations. © 2001 American Institute of Physics.
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64.70.Rh Commensurate-incommensurate transitions
71.45.-d Collective effects
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Si single-electron transistors with in-plane point-contact metal gates

T. H. Wang, H. W. Li, and J. M. Zhou

Appl. Phys. Lett. 78, 2160 (2001); http://dx.doi.org/10.1063/1.1359777 (3 pages) | Cited 3 times

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We report on the operation of Si single-electron transistors with in-plane point-contact metal gates. These in-plane gates are fabricated by a self-aligned process, which are used to squeeze the channel and to form a single dot at the constriction of the channel. The characteristics of such single-electron transistors strongly depend on the channel width and the voltage of the in-plane gates. A few dips are observed at the less positive gate voltages for a device with a 70 nm wide channel. Applying negative voltages to the in-plane gates leads to the formation of a single dot in the conducting channel. These in-plane gates facilitate fabricating Si single-electron transistors with single dot structures. © 2001 American Institute of Physics.
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85.35.Gv Single electron devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Radiative recombination from InP quantum dots on (100) GaP

F. Hatami, W. T. Masselink, and L. Schrottke

Appl. Phys. Lett. 78, 2163 (2001); http://dx.doi.org/10.1063/1.1361277 (3 pages) | Cited 16 times

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We describe the growth and optical emission from strained InP quantum dots grown on GaP using gas-source molecular beam epitaxy. Self-organized island formation takes place for InP coverage greater than 1.8 monolayers on the (100) GaP surface. Intense photoluminescence from the dots is peaked at about 2.0 eV, blueshifted by 0.6 eV from the band gap of bulk InP due to strain, quantum size effects, and possibly Ga interdiffusion. © 2001 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots

Effects of Mg doping on photoelectrical properties of hydrogenated GaN films grown at 380 °C

Shigeru Yagi and Seiji Suzuki

Appl. Phys. Lett. 78, 2166 (2001); http://dx.doi.org/10.1063/1.1350900 (3 pages) | Cited 7 times

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The effects of Mg doping on hydrogenated GaN films grown at 380 °C are investigated in terms of the photoelectrical properties of simple sandwich-type cells. The photocurrent increases with Mg until it reaches maximum and the dark current decreases monotonically with Mg doping. The photovoltaic current of the cells using transparent conductive glass substrates exhibits excellent linearity with an optical power. The peak responsivity at a 0 V bias is 0.02 A/W at 340 nm, which corresponds to an internal quantum efficiency of approximately 0.3. This simple cell functions as a visible-blind ultraviolet detector and also a transparent solar cell. © 2001 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.50.Pz Photoconduction and photovoltaic effects
84.60.Jt Photoelectric conversion
85.60.Gz Photodetectors (including infrared and CCD detectors)
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
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