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3 Jan 2000

Volume 76, Issue 1, pp. 1-128

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Two-photon fluorescence imaging and spectroscopy of nanostructured organic materials using a photon scanning tunneling microscope

Yuzhen Shen, Daniel Jakubczyk, Faming Xu, Jacek Swiatkiewicz, Paras N. Prasad, and Bruce A. Reinhardt

Appl. Phys. Lett. 76, 1 (2000); http://dx.doi.org/10.1063/1.125637 (3 pages) | Cited 25 times

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Photon scanning tunneling microscopy and spectroscopy using femtosecond two-photon excitation are demonstrated. The measurement of both intensity dependence and spectral dependence is performed on a two-photon chromophore. A subdiffraction-limited resolution is obtained, and the domain-size dependence of spatial and spectral features is observed, which indicates the high degree of molecular order in the isolated nanoparticle. It is shown that the light confinement due to a quadratic dependence of the fluorescence intensity leads to an optical contrast enhancement with a coated probe. © 2000 American Institute of Physics.
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07.60.Rd Visible and ultraviolet spectrometers
07.79.Cz Scanning tunneling microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
78.66.Vs Fine-particle systems
61.46.-w Structure of nanoscale materials
78.55.Kz Solid organic materials
07.79.Fc Near-field scanning optical microscopes

Efficient GaAs light-emitting diodes by photon recycling

E. Dupont, H. C. Liu, M. Buchanan, S. Chiu, and M. Gao

Appl. Phys. Lett. 76, 4 (2000); http://dx.doi.org/10.1063/1.125718 (3 pages) | Cited 13 times

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Heterostructure AlGaAs/GaAs light-emitting diodes (LEDs) with a thick active region have shown high external efficiencies, thanks to reabsorption in the active region. For high injection currents and low temperature, we report a 22% efficiency which corresponds to a 98% efficiency internally. We discuss the application of such LED when integrated with a quantum-well infrared photodetector for pixelless thermal imaging systems. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
85.60.Jb Light-emitting devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Thermal lensing effects in small oxide confined vertical-cavity surface-emitting lasers

M. Brunner, K. Gulden, R. Hövel, M. Moser, and M. Ilegems

Appl. Phys. Lett. 76, 7 (2000); http://dx.doi.org/10.1063/1.125638 (3 pages) | Cited 26 times

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The thickness and position of an oxide layer inside a vertical-cavity surface-emitting laser structure have been optimized for minimum optical scattering loss. In the resulting structure, the index guiding provided by the oxide aperture is very small. Consequently, for an oxide aperture radius <2 μm, the optical mode is only weakly confined. In devices using such small apertures, the formation of a thermal lens has a strong influence on optical guiding. The thermal lens leads to lower threshold currents and increased differential efficiency with continuous wave as compared to pulsed injection operation in devices with small apertures. © 2000 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

PbS quantum-dot-doped glasses for ultrashort-pulse generation

K. Wundke, S. Pötting, J. Auxier, A. Schülzgen, N. Peyghambarian, and N. F. Borrelli

Appl. Phys. Lett. 76, 10 (2000); http://dx.doi.org/10.1063/1.125639 (3 pages) | Cited 55 times

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We investigate the use of PbS quantum-dot-doped glasses as saturable absorbers for ultrashort-pulse lasers by means of absorption bleaching experiments and numerical analysis of the pulse shaping process using the Haus’ master equation. We explain the mode-locking mechanism and the limitations of these absorbers. The generation of transform-limited fs pulses is predicted by soliton mode locking initiated by the absorption saturation of higher excited states of the quantum-dot saturable absorber. © 2000 American Institute of Physics.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking
78.66.Li Other semiconductors
81.05.Hd Other semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
02.30.-f Function theory, analysis
06.60.Jn High-speed techniques (microsecond to femtosecond)
78.47.-p Spectroscopy of solid state dynamics
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.65.Tg Optical solitons; nonlinear guided waves

Electroluminescence of a cubic GaN/GaAs (001) p–n junction

D. J. As, A. Richter, J. Busch, M. Lübbers, J. Mimkes, and K. Lischka

Appl. Phys. Lett. 76, 13 (2000); http://dx.doi.org/10.1063/1.125640 (3 pages) | Cited 26 times

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A cubic GaN p–n diode has been grown on n-type GaAs (001) substrates by plasma assisted molecular epitaxy. For p- and n-type doping, elemental Mg and Si beams have been used, respectively. The optical properties are characterized by photoluminescence at room temperature and 2 K. Current–voltage and capacitance–voltage measurements of the cubic GaN n+–p junction are performed at room temperature. The electroluminescence at 300 K is measured through a semitransparent Au contact. A peak emission at 3.2 eV with a full width at half maximum as narrow as 150 meV is observed, indicating that near-band edge transitions are the dominating recombination processes in our device. A linear increase of the electroluminescence intensity with increasing current density is measured. © 2000 American Institute of Physics.
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78.60.Fi Electroluminescence
78.66.Fd III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uj III-V and II-VI semiconductors

Efficiency enhancement of free electron Maser oscillator by mode selection with a prebunched electron beam

A. Abramovich, H. Kleinman, A. Eichenbaum, Y. M. Yakover, A. Gover, and Y. Pinhasi

Appl. Phys. Lett. 76, 16 (2000); http://dx.doi.org/10.1063/1.125641 (3 pages) | Cited 3 times

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We present a method for enhancing the efficiency of a Free Electron Laser Maser oscillator by locking it to a preferred resonator mode. This is done by prebunching of the e beam before injection into the wiggler. In a free running oscillator, the longitudinal mode that dominates the mode competition process during the oscillation buildup period is usually the highest gain mode. However, this mode does not extract the highest energy from the e beam. Lower eigenfrequency modes would provide a higher efficiency if they could dominate the mode competition process. By prebunching the e beam at a frequency near any one of the longitudinal eigenfrequencies of the resonator (having a gain>1), we can make that mode dominant at saturation. The eigenfrequency for which the maximum efficiency is obtained is the lowest eigenfrequency of the resonator for which the net small signal gain is greater than 1. Employing an experimental setup of a prebunched beam Free Electron Maser, we demonstrated efficiency enhancement of 30% for this lowest eigenfrequency mode (as compared to the highest gain mode). Simulation results predict an efficiency enhancement of up to 50%. © 2000 American Institute of Physics.
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84.40.Ik Masers; gyrotrons (cyclotron-resonance masers)
41.60.Cr Free-electron lasers
42.60.Fc Modulation, tuning, and mode locking
41.85.Ct Particle beam shaping, beam splitting
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Magnetic-field-enhanced quantum-cascade emission

J. Ulrich, R. Zobl, K. Unterrainer, G. Strasser, and E. Gornik

Appl. Phys. Lett. 76, 19 (2000); http://dx.doi.org/10.1063/1.125642 (3 pages) | Cited 42 times

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We have observed an enhancement of terahertz intersubband electroluminescence in a quantum cascade structure in the presence of a magnetic field applied normal to the epitaxial layers. At a field of B = 7.2 T the emission efficiency doubles. This effect is attributed to the suppression of nonradiative Auger–intersubband transitions caused by Landau-quantization of the in-plane electron motion. The magnetic field dependence of the luminescence intensity shows strong oscillations. These magnetointersubband oscillations are caused by the modulation of the transition rate via resonant inter-Landau-level transfer. © 2000 American Institute of Physics.
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78.60.Fi Electroluminescence
78.66.Fd III-V semiconductors
73.23.-b Electronic transport in mesoscopic systems
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.70.Di Landau levels
42.55.Px Semiconductor lasers; laser diodes

Blue InGaN-based laser diodes with an emission wavelength of 450 nm

Shuji Nakamura, Masayuki Senoh, Shin-ichi Nagahama, Naruhito Iwasa, Toshio Matsushita, and Takashi Mukai

Appl. Phys. Lett. 76, 22 (2000); http://dx.doi.org/10.1063/1.125643 (3 pages) | Cited 114 times

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Blue InGaN single-quantum-well-structure laser diodes (LDs) with an emission wavelength of 450 nm were grown on an epitaxially laterally overgrown GaN substrate by a metalorganic chemical vapor deposition method. The threshold current density and voltage were 4.6kA cm−2 and 6.1 V, respectively. The estimated lifetime was approximately 200 h under room-temperature continuous-wave operation at an output power of 5 mW. When the number of InGaN well layers of the LDs with emission wavelengths longer than 435 nm varied from one to three, the lowest threshold current density was obtained when the number of well layers was one. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Second-harmonic imaging of poled silica waveguides

Jesper Arentoft, Kjeld Pedersen, Sergey I. Bozhevolnyi, Martin Kristensen, Ping Yu, and Christian B. Nielsen

Appl. Phys. Lett. 76, 25 (2000); http://dx.doi.org/10.1063/1.125644 (3 pages) | Cited 10 times

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Electric-field poled silica-based waveguides are characterized by measurements of second-harmonic generation (SHG) and of the linear electro-optic effect (LEO). A SHG scanning technique allowing for high-resolution imaging of poled devices is demonstrated. Scans along the direction of the poling field show that the second-order optical nonlinearity is located near the interface between differently doped glass layers. Both SHG and LEO measurements indicate that the ratio between the main elements of the second-order nonlinear optical susceptibility tensor, χ33(2) and χ31(2), is significantly smaller than three. © 2000 American Institute of Physics.
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42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.20.Jq Electro-optical effects
42.65.An Optical susceptibility, hyperpolarizability
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Breakdown of the high-voltage sheath in metal plasma immersion ion implantation

André Anders

Appl. Phys. Lett. 76, 28 (2000); http://dx.doi.org/10.1063/1.125645 (3 pages) | Cited 11 times

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It is suggested that breakdown of a space-charge sheath obeys similar breakdown laws as known for vacuum breakdown. When metal plasmas of vacuum arcs are used, the sheath between a biased substrate and plasma is very thin and the electric-field strength is very high. Field enhancement (e.g., at sharp edges of the substrate) leads to thermal instability of electron emission centers, followed by dense plasma formation which, in turn, electrically short circuits the sheath (breakdown). Theoretical and experimental evidence for this mechanism is presented. © 2000 American Institute of Physics.
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
61.72.up Other materials
61.80.Jh Ion radiation effects
52.40.Hf Plasma-material interactions; boundary layer effects
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Vp Discharge in vacuum
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Dynamics of an air breakdown plasma on a solid surface during picosecond laser ablation

Samuel S. Mao, Xianglei Mao, Ralph Greif, and Richard E. Russo

Appl. Phys. Lett. 76, 31 (2000); http://dx.doi.org/10.1063/1.125646 (3 pages) | Cited 25 times

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Using picosecond time-resolved shadowgrams and interferograms, we measured the lateral expansion of an early stage ablation plasma induced by a 1064 nm, 35 ps laser pulse on a copper target. The plasma was found to have an electron density on the order of 1020 cm−3 near the target surface. Prior to the expanding material vapor plume, this high density plasma originates from the breakdown of air, assisted by laser-induced electron emission from the target surface. The longitudinal expansion of the plasma was suppressed due to the development of a strong space-charge region. At postpulse times, the relation r ∼ t1/2 was found for the temporal lateral expansion of the radius of the plasma. Measurements of energy absorption by the plasma provide an interpretation for the experimentally measured reduction in ablation efficiency as the laser fluence increases beyond approximately 100 J/cm2. © 2000 American Institute of Physics.
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79.20.Ds Laser-beam impact phenomena
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
06.60.Jn High-speed techniques (microsecond to femtosecond)

Prepulse-enhanced narrow bandwidth soft x-ray emission from a low debris, subnanosecond, laser plasma source

P. Dunne, G. O’Sullivan, and D. O’Reilly

Appl. Phys. Lett. 76, 34 (2000); http://dx.doi.org/10.1063/1.125647 (3 pages) | Cited 11 times

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Soft x-ray emission from 170 ps laser-produced plasmas formed on cerium-doped borosilicate glasses has been recorded in the 7–17 nm region using a 2 m grazing incidence vacuum spectrograph. Broadband spectra have been recorded on photographic plates, while intensity comparisons have been made using an absolutely calibrated, extreme ultraviolet sensitive photodiode. The use of a laser prepulse to prime the target has been seen to enhance the emission with the maximum flux produced at an interpulse delay of 5.1 ns. The peak conversion efficiency is found to be 4.8%±1.5% into 3% bandwidth, centered at 8.8 nm. In addition, the level of debris emitted by the target is greatly reduced by comparison with solid metallic targets. © 2000 American Institute of Physics.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
79.20.Ds Laser-beam impact phenomena
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
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Effect of high magnetic field on the two-step martensitic-phase transition in Ni2MnGa

Yanwei Ma, S. Awaji, K. Watanabe, M. Matsumoto, and N. Kobayashi

Appl. Phys. Lett. 76, 37 (2000); http://dx.doi.org/10.1063/1.125648 (3 pages) | Cited 17 times

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Using a low-temperature x-ray diffraction apparatus in a high field, a systematic study was performed of the stoichiometric Ni2MnGa alloys in a wide temperature range from 10 K to room temperature and in fields up to 5 T. X-ray diffraction data at different fields clearly show the martensitic-phase transition is a two-step process. It is found that the martensitic-transition temperature Tm increases and the premartensitic-transition temperature Tp decreases with increasing magnetic fields up to 2 T, and then both remain unchanged in fields up to 5 T. © 2000 American Institute of Physics.
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81.30.Kf Martensitic transformations
64.70.K- Solid-solid transitions
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Subgap optical absorption and recombination center efficiency in bulk GaAs irradiated by light or heavy ions

J. Mangeney, J. Lopez, N. Stelmakh, J.-M. Lourtioz, J.-L. Oudar, and H. Bernas

Appl. Phys. Lett. 76, 40 (2000); http://dx.doi.org/10.1063/1.125649 (3 pages) | Cited 10 times

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This letter reports the results of a comparative study on heavy- and light-ion-irradiated semiconductors for fast saturable absorbers. The linear absorption of bulk GaAs irradiated either by Au+ ions or protons was measured over a wide range of wavelengths below the gap. Good correspondence was found between the absorption measurements and the calculated elementary defect concentrations. Defect clustering is evidenced in the heavy-ion case. Pump–probe experiments were used to measure the time-resolved absorption variations for weakly irradiated GaAs samples under intense illumination. Much shorter carrier recombination times are estimated for the heavy-ion case. © 2000 American Institute of Physics.
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72.80.Ey III-V and II-VI semiconductors
61.80.Jh Ion radiation effects
78.40.Fy Semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.82.Fk Semiconductors

Quantum confinement of E1 and E2 transitions in Ge quantum dots embedded in an Al2O3 or an AlN matrix

C. W. Teng, J. F. Muth, R. M. Kolbas, K. M. Hassan, A. K. Sharma, A. Kvit, and J. Narayan

Appl. Phys. Lett. 76, 43 (2000); http://dx.doi.org/10.1063/1.125650 (3 pages) | Cited 13 times

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Alternating layers of Ge quantum dots embedded in either Al2O3 or AlN matrices were deposited on sapphire substrates by pulsed-laser deposition. The characteristics of the dots are shown to be independent of the surrounding matrix. The dots size (73, 130, 160, and 260 ű5%) was controlled by the laser energy density and deposition time, and was characterized by high-resolution transmission electron microscopy. The dots were single crystalline with no apparent GeOx interfacial layers. Transmission spectroscopy at room temperature and 77 K was used to probe the above-band-edge absorption of the Ge nanodots. The spectral positions of both E1/E1+Δ1 and E2 transitions were found to shift to higher energy in the absorption spectra with decreasing nanodot sizes. This indicates that strong quantum-confinement effect permits the optical properties of Ge dots to be modified in a controlled manner. © 2000 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Cw Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Fg Pulsed laser ablation deposition
81.05.Cy Elemental semiconductors

Thin-film metrology of silicon-on-insulator materials

S. Zollner, T.-C. Lee, K. Noehring, A. Konkar, N. D. Theodore, W. M. Huang, D. Monk, T. Wetteroth, S. R. Wilson, and J. N. Hilfiker

Appl. Phys. Lett. 76, 46 (2000); http://dx.doi.org/10.1063/1.125651 (3 pages) | Cited 5 times

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Spectroscopic rotating-analyzer ellipsometry employing a compensator was used to measure the ellipsometric angles and depolarization from 0.73 to 5.4 eV of commercial separation by implantation of oxygen wafers. The data were analyzed to find the thicknesses of the native oxide cap, the top Si layer, and the buried oxide (BOX). From the depolarization in the spectral region of interference fringes, we determine layer thickness nonuniformities. Although a reasonable agreement between the data can be found by describing the BOX with the optical constants of thermal oxide, it can be improved by modeling the BOX as an effective medium consisting of thermal oxide and amorphous Si. The physical justification for this model is the presence of Si islands near the BOX/substrate interface. We compare our ellipsometry results with a destructive analysis using electron microscopy and secondary ion mass spectrometry. © 2000 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.60.-p Physical properties of thin films, nonelectronic
68.55.-a Thin film structure and morphology

Self-ordered pore structure of anodized aluminum on silicon and pattern transfer

D. Crouse, Yu-Hwa Lo, A. E. Miller, and M. Crouse

Appl. Phys. Lett. 76, 49 (2000); http://dx.doi.org/10.1063/1.125652 (3 pages) | Cited 150 times

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A practical approach of transferring a hexagonal array of nanosized pores produced in porous alumina into silicon and other substrates is discussed. The alumina pores have dimensions of 25–250 nm pore diameters and 50–300 nm pore spacings depending on the anodization conditions used. The characteristics of the alumina pores and the alumina–silicon interface are studied for different substrate materials and anodizing conditions. The unique structure of the barrier layer allows for the alumina to be directly used as an etch mask for pattern transfer into the silicon substrate. © 2000 American Institute of Physics.
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61.43.Gt Powders, porous materials
85.40.Hp Lithography, masks and pattern transfer
81.05.Rm Porous materials; granular materials
82.45.-h Electrochemistry and electrophoresis
81.65.Cf Surface cleaning, etching, patterning
81.05.Cy Elemental semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
61.46.-w Structure of nanoscale materials
68.35.Ct Interface structure and roughness

Use of x-ray reflectivity techniques to determine structural parameters of some silicide structures for microelectronics applications

S. Santucci, A. V. la Cecilia, A. R. Phani, R. Alfonsetti, G. Moccia, and M. De Biase

Appl. Phys. Lett. 76, 52 (2000); http://dx.doi.org/10.1063/1.125653 (3 pages) | Cited 4 times

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X-ray reflectivity measurements have been carried out on TiN/Ti/Si- and WSix/Si-deposited and -annealed structures. The results show that for the as-deposited samples there are periodic oscillations due to a well-defined interface roughness, while for the annealed samples the disappearance of the oscillations due to increase in surface and interface roughness of the formed silicide layers is observed. We demonstrate that the analysis of x-ray reflectivity measurements collected both in the specular and in the off-specular way, even for the samples with very high surface and interface roughness, allows the determination of structural parameters of the films and interfaces. © 2000 American Institute of Physics.
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68.35.Ct Interface structure and roughness
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
85.40.Ls Metallization, contacts, interconnects; device isolation
68.35.Fx Diffusion; interface formation

Direct evidence for oxygen stabilization of icosahedral phase during crystallization of Zr65Cu27.5Al7.5 metallic glass

B. S. Murty, D. H. Ping, K. Hono, and A. Inoue

Appl. Phys. Lett. 76, 55 (2000); http://dx.doi.org/10.1063/1.125654 (3 pages) | Cited 76 times

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The present letter reports the formation of the icosahedral phase during crystallization of amorphous Zr65−xCu27.5Al7.5Ox (x = 0.43% and 0.82%) alloys. Three-dimensional atom probe studies have revealed that the quasicrystalline phase is enriched in oxygen. This, together with the fact that no icosahedral phase forms at low oxygen level (0.14%), clearly establishes that the quasicrystalline phase in Zr-based metallic glasses is stabilized by oxygen. © 2000 American Institute of Physics.
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61.44.Br Quasicrystals
61.43.Fs Glasses
64.75.-g Phase equilibria

The use of ionic salt dyes as amorphous, thermally stable emitting layers in organic light-emitting diodes

Konstantinos Chondroudis and David B. Mitzi

Appl. Phys. Lett. 76, 58 (2000); http://dx.doi.org/10.1063/1.125655 (3 pages) | Cited 5 times

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The conversion of two neutral dye molecules (D) to ionic salts (H2N–D–NH2⋅2HX) and their utilization as emitting layers in organic light-emitting diodes (OLEDs) is described. The dye salts, AEQT⋅2HCl and APT⋅2HCl, can be deposited as amorphous films using conventional evaporation techniques. X-ray diffraction and scanning electron microscopy analysis, coupled with thermal annealing studies, demonstrate the resistance of the films to crystallization. This stability is attributed to strong ionic forces between the relatively rigid molecules. OLEDs incorporating such salts for emitting layers exhibit better thermal stability compared with devices made from the corresponding neutral dyes (H2N–D–NH2). These results suggest that ionic salts may more generally enable the formation of thermally stable, amorphous emitting, and charge transporting layers. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.70.Jk Polymers and organics
68.60.Dv Thermal stability; thermal effects
78.66.Qn Polymers; organic compounds
78.60.Fi Electroluminescence

Determination of the mesostructure of lead borate glasses using laser photoionization mass spectroscopy

D. Stentz, S. Blair, C. Goater, S. Feller, and M. Affatigato

Appl. Phys. Lett. 76, 61 (2000); http://dx.doi.org/10.1063/1.125656 (3 pages) | Cited 3 times

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We have investigated the structure of lead borate glasses up to high lead contents using a high-resolution reflectron time-of-flight mass spectrometer. The glasses showed the repeatable presence of intermediate-range units, which varied in relative abundance depending on composition. This direct measurement of the network showed a high abundance of (B3O5) and (PbB3O6) groups, which are likely to arise from metaborate rings, as well as the rise of ortho- and pyroborate units. Smaller quantities of entire diborate units (B4O9, with added lead and boron atoms for charge compensation) were also observed. © 2000 American Institute of Physics.
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61.43.Fs Glasses

Sheet resistance modeling of the Ti/SiO2 system upon high temperature annealing

Yuxiao Zeng, Linghui Chen, and T. L. Alford

Appl. Phys. Lett. 76, 64 (2000); http://dx.doi.org/10.1063/1.125657 (3 pages) | Cited 6 times

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The reaction of Ti/SiO2 structure at elevated temperatures has been studied by measuring the sheet resistance as a function of annealing temperature for different initial Ti thicknesses. A sheet resistance model has been developed to account for the effects of the thickness and resistivity variations of the reaction products [Ti(O) and Ti5Si3]. The simulated sheet resistance values varying with the Ti5Si3 thickness are in good agreement with the general trend as obtained from the experimental measurements for different initial Ti thicknesses. The approach used in modeling can be applied to other thin film structures with similar reaction mechanism to simulate the overall sheet resistance variation. © 2000 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
61.72.Cc Kinetics of defect formation and annealing
73.61.At Metal and metallic alloys

Improved performance of electroluminescent devices based on an europium complex

C. J. Liang, D. Zhao, Z. R. Hong, D. X. Zhao, X. Y. Liu, W. L. Li, J. B. Peng, J. Q. Yu, C. S. Lee, and S. T. Lee

Appl. Phys. Lett. 76, 67 (2000); http://dx.doi.org/10.1063/1.125658 (3 pages) | Cited 61 times

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Electroluminescent (EL) devices using an europium complex Eu(DBM)3 bath as the electron-transport emitting layer were fabricated. The quenching effect of the metal cathode and the unstable nature of the Eu complex under EL operation markedly influence the EL efficiency. By keeping the emitting area far from the metal cathode and partly doping the Eu(DBM)3 bath layer with a hole-transport material, the EL performance was significantly improved. Sharp-band red emissions with turn-on voltage of 3 V, brightness of 820 cd/m2, and external quantum efficiency of 1% were achieved. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds

Fusion bonding of Si wafers investigated by x ray diffraction

S. Weichel, F. Grey, K. Rasmussen, M. Nielsen, R. Feidenhans’l, P. B. Howes, and J. Vedde

Appl. Phys. Lett. 76, 70 (2000); http://dx.doi.org/10.1063/1.125659 (3 pages) | Cited 6 times

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The interface structure of bonded Si(001) wafers with twist angle 6.5 ° is studied as a function of annealing temperature. An ordered structure is observed in x-ray diffraction by monitoring a satellite reflection due to the periodic modulation near the interface, which results from the formation of a regular array of screw dislocations. This satellite reflection first appears at an annealing temperature of 800 °C, and increases abruptly up to temperatures of 1000 °C. We propose that this transition occurs when there is sufficient mobility for the reorganization of atomic steps and terraces in the interface region. © 2000 American Institute of Physics.
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81.05.Cy Elemental semiconductors
68.35.Ct Interface structure and roughness
61.72.Cc Kinetics of defect formation and annealing
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.35.Gy Mechanical properties; surface strains

Room-temperature photoluminescence spectroscopy of self-assembled In0.5Ga0.5As single quantum dots by using highly sensitive near-field scanning optical microscope

K. Matsuda, T. Saiki, H. Saito, and K. Nishi

Appl. Phys. Lett. 76, 73 (2000); http://dx.doi.org/10.1063/1.125660 (3 pages) | Cited 34 times

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We have studied the optical properties of self-assembled In0.5Ga0.5As single quantum dots (QDs) at room temperature with a near-field scanning optical microscope. Successful detection of a weak photoluminescence (PL) signal from a single QD at room temperature could be achieved by using a double-tapered fiber probe having the advantages of both high collection efficiency and high spatial resolution. Through the precise examination of PL spectra of many QDs, including broadening and saturation behaviors, the homogeneous linewidth of the ground state emission is evaluated as from 9.8 to 14.5 meV. © 2000 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
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