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22 Jan 2001

Volume 78, Issue 4, pp. 393-559

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Stimulated emission depletion microscopy with an offset depleting beam

T. A. Klar, M. Dyba, and S. W. Hell

Appl. Phys. Lett. 78, 393 (2001); http://dx.doi.org/10.1063/1.1338491 (3 pages) | Cited 10 times

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We demonstrate that an offset stimulated emission depletion (STED) beam breaks the diffraction barrier of fluorescence microscopy in both the lateral and the axial directions. A 2.5-fold axial reduction of the focal spot is accomplished through the ear-shaped lobes of the diffraction maximum of the STED beam. The effect of the minima and side maxima of the STED beam on the lateral and axial resolution is shown to be in remarkable agreement with theory. Conditions are given for which a regular STED beam reduces the axial extent of a confocal spot from 490±36 to 175±18 nm, and simultaneously from 183±12 to 70±8 nm along the direction of the offset. The latter establishes the lowest reported value in far-field fluorescence microscopy. © 2001 American Institute of Physics.
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07.60.Pb Conventional optical microscopes
42.30.Va Image forming and processing
07.05.Pj Image processing

High-temperature operation of distributed feedback quantum-cascade lasers at 5.3 μm

Daniel Hofstetter, Mattias Beck, Thierry Aellen, and Jérôme Faist

Appl. Phys. Lett. 78, 396 (2001); http://dx.doi.org/10.1063/1.1340865 (3 pages) | Cited 76 times

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High-temperature operation of a low-threshold 5.3 μm quantum-cascade distributed feedback laser is presented. The emission spectrum was single mode with more than 20 dB side mode suppression ratio for all investigated temperatures and up to thermal rollover. For 1.5% duty cycle and at 0 °C, the laser emitted 1.15 W of single mode peak power; at 120 °C, a value of 92 mW was seen. For a 3 mm long device, we observed a room-temperature threshold current density of 3.6 kA/cm2. This remarkable performance is mainly due to a 4 quantum-well active region using a double phonon resonance for the lower laser level. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Submilliwatt operation of AlGaN-based ultraviolet light-emitting diode using short-period alloy superlattice

T. Nishida, H. Saito, and N. Kobayashi

Appl. Phys. Lett. 78, 399 (2001); http://dx.doi.org/10.1063/1.1338964 (2 pages) | Cited 29 times

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Over 0.1 mW ultraviolet output was achieved by an AlGaN-based light-emitting diode. To realize a highly conductive and ultraviolet-transparent layer, a short-period alloy superlattice was introduced. The device was fabricated on SiC substrate. Low electric resistivity due to the short-period alloy superlattice and the high thermal conductivity of the SiC substrate enabled large current injection of up to 1.7 kA/cm2. The emission was monochromatic band-edge emission about 350 nm in wavelength without significant D–A and/or deep emissions. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
73.21.Cd Superlattices

SiGe/Si THz laser based on transitions between inverted mass light-hole and heavy-hole subbands

L. Friedman, G. Sun, and R. A. Soref

Appl. Phys. Lett. 78, 401 (2001); http://dx.doi.org/10.1063/1.1341221 (3 pages) | Cited 23 times

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We have investigated a SiGe/Si quantum-well laser based on transitions between the light-hole and heavy-hole subbands. The lasing occurs in the region of k space where the dispersion of ground-state light-hole subband is so nonparabolic that its effective mass is inverted. This kind of lasing mechanism makes total population inversion between the two subbands unnecessary. The laser structure can be electrically pumped through tunneling in a quantum cascade scheme. Optical gain as high as 172/cm at the wavelength of 50 μm can be achieved at the temperature of liquid nitrogen, even when the population of the upper laser subband is 15% less than that of the lower subband. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.Fg Quantum wells
78.45.+h Stimulated emission

BeCdSe as a ternary alloy for blue-green optoelectronic applications

S. V. Ivanov, O. V. Nekrutkina, S. V. Sorokin, V. A. Kaygorodov, T. V. Shubina, A. A. Toropov, P. S. Kop’ev, G. Reuscher, V. Wagner, J. Geurts, A. Waag, and G. Landwehr

Appl. Phys. Lett. 78, 404 (2001); http://dx.doi.org/10.1063/1.1342202 (3 pages) | Cited 12 times

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Bulk BeCdSe layer lattice-matched to a GaAs substrate, as well as a BeCdSe/ZnSe quantum well (QW) structure have been grown using the submonolayer digital alloying mode of molecular beam epitaxy. The structures have demonstrated bright photoluminescence up to room temperature and good structural quality. Stimulated emission under optical pumping has been obtained for a 2 nm BeCdSe/ZnSe multiple QW structure at 80 K. The bowing parameter of the energy gap of this ternary alloy has been estimated as about 4.5 eV. © 2001 American Institute of Physics.
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78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
71.20.Nr Semiconductor compounds
78.67.De Quantum wells
78.45.+h Stimulated emission
68.55.-a Thin film structure and morphology
68.65.Fg Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.07.St Quantum wells

Ultraviolet-emitting ZnO nanowires synthesized by a physical vapor deposition approach

Y. C. Kong, D. P. Yu, B. Zhang, W. Fang, and S. Q. Feng

Appl. Phys. Lett. 78, 407 (2001); http://dx.doi.org/10.1063/1.1342050 (3 pages) | Cited 476 times

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ZnO nanowires were mass produced using a physical vapor deposition approach. The ZnO nanowire monocrystallites have an average diameter around 60 nm and length up to a few micrometers. The unidirectional growth of the ZnO nanowires was controlled by the conventional vapor-liquid-solid mechanism. Intensive UV light emission peaked around 3.27 eV was observed at room temperature, which was assigned to emission from free exciton under low excitation intensity. The observed room temperature UV emission was ascribed to the decrease in structure defects as compared to bulk ZnO materials, and in particularly to the size effect in the ZnO wires. © 2001 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
73.22.Lp Collective excitations
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Very-low-operating-voltage organic light-emitting diodes using a p-doped amorphous hole injection layer

X. Zhou, M. Pfeiffer, J. Blochwitz, A. Werner, A. Nollau, T. Fritz, and K. Leo

Appl. Phys. Lett. 78, 410 (2001); http://dx.doi.org/10.1063/1.1343849 (3 pages) | Cited 152 times

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We demonstrate the use of a p-doped amorphous starburst amine, 4, 4′, 4″-tris(N, N-diphenyl- amino)triphenylamine (TDATA), doped with a very strong acceptor, tetrafluoro- tetracyano-quinodimethane by controlled coevaporation as an excellent hole injection material for organic light-emitting diodes (OLEDs). Multilayered OLEDs consisting of double hole transport layers of p-doped TDATA and triphenyl-diamine, and an emitting layer of pure 8-tris-hydroxyquinoline aluminum exhibit a very low operating voltage (3.4 V) for obtaining 100 cd/m2 even for a comparatively large (110 nm) total hole transport layer thickness. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices

Decreasing the emission wavelength of GaAs–AlGaAs quantum cascade lasers by the incorporation of ultrathin InGaAs layers

L. R. Wilson, J. W. Cockburn, M. J. Steer, D. A. Carder, M. S. Skolnick, M. Hopkinson, and G. Hill

Appl. Phys. Lett. 78, 413 (2001); http://dx.doi.org/10.1063/1.1343841 (3 pages) | Cited 11 times

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We demonstrate that the emission wavelength of GaAs–Al0.33Ga0.67As quantum cascade lasers can be decreased significantly by incorporating InGaAs layers within the active regions. InAs monolayers are deposited during growth, with segregation effects resulting in the formation of thin InGaAs layers within the GaAs active region quantum wells of the laser. The InGaAs layers are positioned close to the antinodes of the lower laser level wave function, thus decreasing its confinement energy. The small spatial overlap of the InGaAs layers with the upper laser level minimizes the perturbation of the upper state. Consequently, the energy separation between the upper and lower laser levels increases, reducing the emission wavelength. The measured operating wavelength of 7.4 μm is the shortest reported for a GaAs–AlGaAs quantum cascade laser and is approximately 2 μm less than for an identical structure without InGaAs layers in the active regions. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
68.35.Dv Composition, segregation; defects and impurities

High-performance quantum cascade lasers (λ ∼ 11 μm) operating at high temperature (T  ≥ 425 K)

A. Tahraoui, A. Matlis, S. Slivken, J. Diaz, and M. Razeghi

Appl. Phys. Lett. 78, 416 (2001); http://dx.doi.org/10.1063/1.1343848 (3 pages) | Cited 21 times

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We report record-low threshold current density and high output power for λ ∼ 11 μm Al0.48In0.52As/Ga0.47In0.53As quantum cascade lasers operating up to 425 K. The threshold current density is 1.1, 3.83, and 7.08 kA/cm2 at 80, 300, and 425 K, respectively, for 5 μs pulses at a 200 Hz repetition rate. The cavity length is 3 mm with a stripe width of 20 μm. The maximum peak output power per facet is 1 W at 80 K, 0.5 W at 300 K, and more than 75 mW at 425 K. The characteristic temperature of these lasers is 174 K between 80 and 300 K and 218 K in the range of 300–425 K. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
81.05.Ea III-V semiconductors
42.55.Sa Microcavity and microdisk lasers
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.66.Fd III-V semiconductors
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
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Silicon microdischarge devices having inverted pyramidal cathodes: Fabrication and performance of arrays

S.-J. Park, J. Chen, C. Liu, and J. G. Eden

Appl. Phys. Lett. 78, 419 (2001); http://dx.doi.org/10.1063/1.1338971 (3 pages) | Cited 43 times

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Microdischarge devices having inverted, square pyramidal cathodes as small as 50 μm×50 μm at the base and 35 μm in depth, have been fabricated in silicon and operated at gas pressures up to 1200 Torr. For the polyimide dielectric incorporated into these devices (εr = 2.9), the discharges produced exhibit high differential resistance ( ∼ 2×108 Ω in Ne), ignition voltages for a single device of ∼260–290 V, and currents typically in the μA range. Arrays as large as 10×10 have been fabricated. For an 8 μm thick polyimide dielectric layer, operating voltages as low as 200 V for a 5×5 array have been measured for 700 Torr of Ne. Array lifetimes are presently limited to several hours by the thin (1200–2000 Å) Ni anode. © 2001 American Institute of Physics.
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85.30.-z Semiconductor devices
81.05.Cy Elemental semiconductors
77.22.Jp Dielectric breakdown and space-charge effects

Experimental investigation of electron oscillation inside the filter of a vacuum arc plasma source

D. T. K. Kwok, T. Zhang, P. K. Chu, M. M. M. Bilek, A. Vizir, and I. G. Brown

Appl. Phys. Lett. 78, 422 (2001); http://dx.doi.org/10.1063/1.1342779 (3 pages) | Cited 5 times

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We report here experimental evidence of electron oscillation within the toroidal-section magnetic duct of a filtered vacuum arc plasma source. Our results clearly demonstrate that electrons can oscillate inside the duct under the combined effects of the electric and magnetic fields. In another experiment, we observe that, under the influence of the electron motion, the trajectories of the plasma ions are more or less unchanged except in the intensity when the Bilek plate is biased. Finally, our time-of-flight experiments show that the effects due to collisional scattering between plasma ions and oscillating electrons are masked by those associated with the metal plasma flow through the duct, and collisional scattering does not give rise to an increase of the mean charge state of the plasma ions. We conclude that the application of a bias voltage to the duct not only perturbs the ions but also influences the plasma electrons. Our results demonstrate that electrons at the central axis are one of the major reasons leading to improved plasma transport through the duct. © 2001 American Institute of Physics.
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52.50.Dg Plasma sources
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Vp Discharge in vacuum
52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.20.Fs Electron collisions
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Helix unwinding of doped cholesteric liquid crystals

W. C. Yip and H. S. Kwok

Appl. Phys. Lett. 78, 425 (2001); http://dx.doi.org/10.1063/1.1342781 (3 pages) | Cited 5 times

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By introducing benzoyl–benzene into a cholesteric liquid crystal, the helix unwinding voltage was reduced. This reduction was roughly proportional to the concentration of the dopant and was present for driving frequencies across the audio spectrum. It is believed that this voltage reduction is primarily due to a perturbation of the intermolecular coupling in the liquid crystal mixture. It was found that so long as the long-range order was not destroyed, the helix unwinding voltage could be reduced by as much as 24% at 60 Hz. © 2001 American Institute of Physics.
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61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
64.70.M- Transitions in liquid crystals

Raman-spectroscopic evaluation of the long-range order in Ba(B1/3′B2/3″)O3 ceramics

Roberto L. Moreira, Franklin M. Matinaga, and Anderson Dias

Appl. Phys. Lett. 78, 428 (2001); http://dx.doi.org/10.1063/1.1339254 (3 pages) | Cited 32 times

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Ordered Ba(B1/3′B2/3″)O3 ceramics are currently used as dielectric resonators for microwave and millimeter wave technologies. The degree of ordering is generally determined by x-ray techniques. In this work, we demonstrate that Raman spectroscopy can be used to evaluate the degree of long-range order of these materials. We also show how varying the degree of order of samples allows partial assignment of the optical vibrational modes. © 2001 American Institute of Physics.
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78.30.Hv Other nonmetallic inorganics
63.20.-e Phonons in crystal lattices

In situ observation of surface processes in InAs/GaAs(001) heteroepitaxy: The role of As on the growth mode

Akihiro Ohtake and Masashi Ozeki

Appl. Phys. Lett. 78, 431 (2001); http://dx.doi.org/10.1063/1.1342216 (3 pages) | Cited 10 times

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Surface processes of the growing thin films of InAs on GaAs(001) substrates have been studied as a function of substrate temperature and As to In flux ratio. They have been observed by reflection high-energy electron diffraction and total-reflection-angle x-ray spectroscopy in real time. At temperatures lower than ∼480 °C, InAs grows in a Stranski–Krastanov mode irrespective of the As/In flux ratio, while the growth mode of InAs strongly depends on the flux ratio above ∼500 °C. We have found that the sticking probability of In decreases as the As flux is decreased above ∼500 °C, which results in the changes in the growth mode of InAs. © 2001 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.70.Ck X-ray scattering

Excitonic properties and band alignment in lattice-matched ZnCdSe/ZnMgSe multiple-quantum-well structures

B. Bonanni, E. Pelucchi, S. Rubini, D. Orani, A. Franciosi, A. Garulli, and A. Parisini

Appl. Phys. Lett. 78, 434 (2001); http://dx.doi.org/10.1063/1.1342043 (3 pages) | Cited 1 time

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Lattice-matched Zn0.85Cd0.15Se/Zn0.74Mg0.26Se multiple-quantum-well structures were obtained on GaAs(001) using graded-composition InyGa1−yAs layers to match the II–VI lattice parameter to the III–V substrate. Cross-sectional transmission electron microscopy studies show that the effect of the crosshatch pattern of the InyGa1−yAs surface is limited to long-period coherent undulations of quantum well and barrier layers. Optical measurements of the excitonic properties as a function of well thickness, complemented by self-consistent calculations of the transition energies, indicate good quantum confinement in the well, with a 68% conduction band contribution to the 0.482 eV band gap difference. © 2001 American Institute of Physics.
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78.67.De Quantum wells
78.55.Et II-VI semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.21.Fg Quantum wells

Effects of the morphologies and structures of light-emitting layers on the performance of organic electroluminescent devices

D. S. Qin, D. C. Li, Y. Wang, J. D. Zhang, Z. Y. Xie, G. Wang, L. X. Wang, and D. H. Yan

Appl. Phys. Lett. 78, 437 (2001); http://dx.doi.org/10.1063/1.1342203 (3 pages) | Cited 23 times

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Organic electroluminescent devices with a structure of ITO/ploy (9-vinylcarbazole)/tris (8-hydroxyquinoline) aluminum (Alq3)/Mg:Ag are fabricated at different substrate temperatures (77, 298, and 438 K) during Alq3 deposition. It is found that the surface morphologies of Alq3 thin films greatly affect the I–V characteristics of the devices by the contact area between metal cathode and light-emitting layer. There is an increase in the luminous efficiency of the devices in the order 77 K<298 K<438 K. We attribute this trend to different structures of Alq3 thin films. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.70.Jk Polymers and organics
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.60.Fi Electroluminescence

On “radiation-free” states in transient motion of dislocations

Xanthippi Markenscoff

Appl. Phys. Lett. 78, 440 (2001); http://dx.doi.org/10.1063/1.1339852 (3 pages) | Cited 3 times

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The existence of "radiation-free" states in transient motion of dislocations is investigated. By analyzing an edge dislocation jumping from rest to a supersonic speed, we see that the Mach fronts disappear at vd = mathc2 because at this dislocation velocity, the pole singularity in the complex plane is replaced by a removable one. However, there exist radiated stress waves propagating with velocity c2, as well as c1. Also, due to radiated longitudinal waves, there is a “force” required to be supplied to sustain such a motion. © 2001 American Institute of Physics.
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61.72.Bb Theories and models of crystal defects
66.30.Lw Diffusion of other defects

X-ray scattering from misfit dislocations in heteroepitaxial films: The case of Nb(110) on Al2O3

R. I. Barabash, W. Donner, and H. Dosch

Appl. Phys. Lett. 78, 443 (2001); http://dx.doi.org/10.1063/1.1342215 (3 pages) | Cited 12 times

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We apply the Krivoglaz theory of x-ray scattering to thin epitaxial films containing misfit dislocations and reanalyze the seemingly puzzling x-ray scattering phenomena observed in several heteroepitaxial films. We show that the two-line shape scattering distribution and its dependence upon film thickness and momentum transfer can be understood in natural way and on a quantitative level. Extended diffuse x-ray scattering maps have been obtained from Nb(110)/Al2O3(11math0) which are discussed within the framework of this theory disclose a particular dislocation network at the Nb–Al2O3 interface. © 2001 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.05.cf X-ray scattering (including small-angle scattering)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Neutron transmutation of 10B isotope-doped diamond

K. Jagannadham, K. Verghese, and J. E. Butler

Appl. Phys. Lett. 78, 446 (2001); http://dx.doi.org/10.1063/1.1342207 (2 pages) | Cited 4 times

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Diamond samples grown by microwave plasma chemical vapor deposition and doped with 10B have been irradiated under thermal neutron flux of 1013 cm−2 s−1 for 76 h to examine transmutation of 10B to 7Li and the attendant lattice damage to diamond. To prevent graphitization and formation of diamond-like carbon, continuous cooling in water is provided during irradiation. Characterization of the diamond samples using Raman spectroscopy, photoluminescence spectroscopy, and secondary ion mass spectrometry showed that diamond remained crystalline without a major damage. Formation of vacancies due to neutron irradiation is inferred from photoluminescence spectroscopy. © 2001 American Institute of Physics.
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81.05.U- Carbon/carbon-based materials
61.80.Hg Neutron radiation effects
61.82.Fk Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.up Other materials
85.40.Ry Impurity doping, diffusion and ion implantation technology
52.77.Dq Plasma-based ion implantation and deposition
61.80.Jh Ion radiation effects
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.30.Am Elemental semiconductors and insulators
78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Comparison of aluminum and sodium doped poly(vinylidene fluoride-trifluoroethylene) copolymers by x-ray photoemission spectroscopy

B. Xu, Jaewu Choi, C. N. Borca, P. A. Dowben, A. V. Sorokin, S. P. Palto, N. N. Petukhova, and S. G. Yudin

Appl. Phys. Lett. 78, 448 (2001); http://dx.doi.org/10.1063/1.1340858 (3 pages) | Cited 4 times

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The chemical interaction between the simple metals, aluminum and sodium, and crystalline copolymer thin films of vinylidene fluoride (70%) with trifluoroethylene (30%), has been studied using x-ray photoemission spectroscopy. Aluminum and sodium metalize the polymer differently and different binding sites for the two metals can be inferred from the corresponding core level shifts. Aluminum leads to enhanced screening of final photoemission states associated with the polymer, while sodium doping strongly influences the fluorine, but perturbs the carbon backbone only slightly. © 2001 American Institute of Physics.
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61.41.+e Polymers, elastomers, and plastics
79.60.Fr Polymers; organic compounds
71.55.Jv Disordered structures; amorphous and glassy solids
71.20.Rv Polymers and organic compounds
71.15.Nc Total energy and cohesive energy calculations

Local structure of uncapped and Si-capped Ge/Si(100) self-assembled quantum dots

Alexander V. Kolobov, Hiroyuki Oyanagi, Karl Brunner, Peter Schittenhelm, Gerhard Abstreiter, and Kazunobu Tanaka

Appl. Phys. Lett. 78, 451 (2001); http://dx.doi.org/10.1063/1.1339841 (3 pages) | Cited 11 times

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Local structure of uncapped and Si-capped Ge quantum dots on Si(100) has been probed by extended x-ray absorption fine structure and x-ray absorption near-edge structure spectroscopy. It is found that the uncapped Ge dots are partially oxidized and partially alloyed with Si. The amount of Ge present in the Ge phase is found to be about 20–30%. In the Si-capped sample, Ge is found to be dissolved in silicon, the fraction of Ge atoms existing as a Ge phase being less than 10%. © 2001 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
78.70.Dm X-ray absorption spectra

Compliant effect of low-temperature Si buffer for SiGe growth

Y. H. Luo, J. Wan, R. L. Forrest, J. L. Liu, G. Jin, M. S. Goorsky, and K. L. Wang

Appl. Phys. Lett. 78, 454 (2001); http://dx.doi.org/10.1063/1.1337633 (3 pages) | Cited 19 times

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Relaxed SiGe attracted much interest due to the applications for strained Si/SiGe high electron mobility transistor, metal-oxide-semiconductor field-effect transistor, heterojunction bipolar transistor, and other devices. High-quality relaxed SiGe templates, especially those with a low threading dislocation density and smooth surface, are critical for device performance. In this work, SiGe films on low-temperature Si buffer layers were grown by solid-source molecular-beam epitaxy and characterized by atomic force microscope, double-axis x-ray diffraction, and photoluminescence spectroscopy. It was demonstrated that, with the proper growth temperature and Si buffer thickness, the low-temperature Si buffer became tensily strained and reduced the lattice mismatch between the SiGe and the Si buffer layer. This performance is similar to that of the compliant substrate: a thin substrate that shares the mismatch strain in heteroepitaxy. Due to the smaller mismatch, misfit dislocation and threading dislocation densities were lower. © 2001 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Hd Other semiconductors
68.55.A- Nucleation and growth
68.60.Bs Mechanical and acoustical properties
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
78.66.Li Other semiconductors
78.55.Hx Other solid inorganic materials

Nanofractography of shocked RDX explosive crystals with atomic force microscopy

J. Sharma, R. W. Armstrong, W. L. Elban, C. S. Coffey, and H. W. Sandusky

Appl. Phys. Lett. 78, 457 (2001); http://dx.doi.org/10.1063/1.1342046 (3 pages) | Cited 8 times

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Examination with atomic force microscopy has revealed apparent shear-type cleavage steps with heights as small as 0.05 nm, smaller than the size of cyclotrimethylenetrintramine (RDX) molecules, on the fracture surfaces of crystals that were subjected to aquarium shocks of 61.6 or 129 kbar, both greater than the pressure (38 kbar) required for the alpha-to-gamma phase transformation. The shocked centimeter size, originally transparent crystals became opaque and white from prolific fractures and internal cracks that are associated with their breakup into nanocrystallites of sizes extending from 500 down to 20 nm. The submolecular steps are related geometrically to the macroscale (K∥) fracture mechanics mode of shear fracturing that has obvious consequences at the nanoscale level for nonregistry between molecules across the crack surfaces. The results are of interest in relation to lattice trapping of crack fronts and as a contribution to the possibility of deformation-induced chemical decomposition/detonations. © 2001 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
82.40.Fp Shock wave initiated reactions, high-pressure chemistry
62.20.M- Structural failure of materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.33.Vx Reactions in flames, combustion, and explosions
68.37.Ps Atomic force microscopy (AFM)
61.46.-w Structure of nanoscale materials
62.25.-g Mechanical properties of nanoscale systems

Oxidation kinetics in SrTiO3 homoepitaxy on SrTiO3(001)

X. D. Zhu, Weidong Si, X. X. Xi, and Qidu Jiang

Appl. Phys. Lett. 78, 460 (2001); http://dx.doi.org/10.1063/1.1338497 (3 pages) | Cited 14 times

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Using an oblique-incidence optical reflectivity difference technique, we investigated kinetic processes in SrTiO3 homoepitaxy on SrTiO3(001) under pulsed-laser deposition conditions. Depending upon growth temperature and oxygen ambient pressure, we found that the oxidation of an as-grown SrTiO3 monolayer may take a much longer time to complete than the recrystallization of the monolayer. The oxidation reaction was found to be characterized by an effective activation energy barrier of 1.35 eV and a large preexponential factor. © 2001 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
78.66.Nk Insulators
81.65.Mq Oxidation
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
82.20.Pm Rate constants, reaction cross sections, and activation energies

Chemical ordering in AlGaN alloys grown by molecular beam epitaxy

E. Iliopoulos, K. F. Ludwig, T. D. Moustakas, and S. N. G. Chu

Appl. Phys. Lett. 78, 463 (2001); http://dx.doi.org/10.1063/1.1341222 (3 pages) | Cited 23 times

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Aluminum gallium nitride alloys were grown by molecular beam epitaxy and their film composition, structure, and microstructure were investigated by Rutherford backscattering spectroscopy, atomic force microscopy, x-ray diffraction, and transmission electron microscopy. It was found that the ratio of group-III to group-V fluxes influences the relative incorporation of gallium and aluminum in the films. The transmission electron microscopy and x-ray diffraction studies revealed the existence of three types of spontaneously formed superlattice structures with periodicities of 2, 7, and 12 ML. While the 2 ML ordering is preferred under group-V rich conditions of growth, the 7 and 12 ML orderings were observed under group-III rich conditions of growth. © 2001 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Nq Composition and phase identification
61.66.Bi Elemental solids
61.66.Dk Alloys
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