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15 Jul 1996

Volume 69, Issue 3, pp. 287-438

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Size effect upon emission dynamics of 1.5 μm quasi‐quantum wire distributed feedback semiconductor lasers

Jian Wang, Uwe A. Griesinger, Frank Adler, Heinz Schweizer, V. Härle, and F. Scholz

Appl. Phys. Lett. 69, 287 (1996); http://dx.doi.org/10.1063/1.118035 (3 pages) | Cited 5 times

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Emission dynamics of 1.5 μm InGaAs/InGaAsP quasi‐quantum wire lasers excited by ultrashort optical pulses were investigated. Wire distributed feedback lasers with different nanometer wire widths and distances between the wires, which were realized by dry‐etching technique, were compared in detail. The dependence of dynamic behavior on wire width was observed. Detailed theoretical simulations show that, the improvement of dynamic response with decrease of wire width is attributed to a superlinear increase of differential gain with decrease of wire width, which counteracts the negative effects due to decrease of packing density of the active region and increase of electron relaxation time.
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42.55.Px Semiconductor lasers; laser diodes
78.66.Fd III-V semiconductors

Propagation of sheet electron beam through a planar, five‐period electromagnetic wiggler

A. V. Ravi Kumar and K. K. Jain

Appl. Phys. Lett. 69, 290 (1996); http://dx.doi.org/10.1063/1.118036 (3 pages) | Cited 2 times

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An experimental study on the propagation of a sheet electron beam of energy ∼200 keV, current ∼80–250 A, and pulse duration of ∼100–150 ns through a planar five‐period electromagnetic wiggler has been carried out as a part of the development of a pulsed, high‐power mm wave free‐electron laser. Beam focusing is observed for peak wiggler magnetic fields up to 2.5 kG, and enhancements in propagated beam current efficiencies by 40%–65% are found for different values of the initial beam current. © 1996 American Institute of Physics.
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41.85.Lc Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles
41.60.Cr Free-electron lasers

Third‐order nonlinear optical susceptibilities of the Langmuir–Blodgett films of octa‐substituted metallophthalocyanines

M. A. Díaz‐García, J. M. Cabrera, F. Agulló‐López, J. A. Duro, G. de la Torre, T. Torres, F. Fernández‐Lázaro, P. Delhaes, and C. Mingotaud

Appl. Phys. Lett. 69, 293 (1996); http://dx.doi.org/10.1063/1.118037 (3 pages) | Cited 7 times

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The third‐order susceptibilities χ(3)(−3ω:ω,ω,ω) of Langmuir–Blodgett films of a series of octasubstituted metallophthalocyanines have been measured by third‐harmonic generation experiments at 1.064 and 1.904 μm. For the latter excitation wavelength a marked enhancement of the nonlinearity for the cobalt‐containing compound has been found, and χ(3) values are one order of magnitude larger than for the other systems. The effect has been associated to the role of two‐photon allowed metal (possibly d−d) transitions in the cobalt derivative. © 1996 American Institute of Physics.
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42.65.An Optical susceptibility, hyperpolarizability
78.66.Qn Polymers; organic compounds
68.18.-g Langmuir-Blodgett films on liquids

Phototransformation in visible and near‐IR femtosecond pump‐probe studies of C60 films

S. B. Fleischer, B. Pevzner, D. J. Dougherty, E. P. Ippen, M. S. Dresselhaus, and A. F. Hebard

Appl. Phys. Lett. 69, 296 (1996); http://dx.doi.org/10.1063/1.118038 (3 pages) | Cited 13 times

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The ultrafast non‐linear optical dynamics of C60 thin films were investigated at low excitation levels. The pump‐probe response observed at low power is found to differ significantly from the ultrafast non‐exponential behavior observed at higher intensity. It is determined that the ultrafast relaxation processes measured at higher fluence levels are affected by phototransformation of C60. © 1996 American Institute of Physics.
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78.66.Tr Fullerenes and related materials
61.46.-w Structure of nanoscale materials
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Solitary‐pulse regimes of solid‐state laser additively mode locked by a cascading nonlinearity

I. V. Mel’nikov and A. V. Shipulin

Appl. Phys. Lett. 69, 299 (1996); http://dx.doi.org/10.1063/1.118039 (3 pages)

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The steady‐state additive mode locking of a laser incorporating phase‐mismatched frequency converter in an external cavity is analyzed. The model includes a main cavity with a slowly bleaching lasing transition and a fiber with χ(2) grating, in the form of Fabry‐Pérot interferometer. The dependence of the parameters of the spectral‐limited pulse on the laser control parameter is investigated. © 1996 American Institute of Physics.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Rz Doped-insulator lasers and other solid state lasers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Thermodynamic and photochemical stability of low interface state density Ga2O3–GaAs structures fabricated by in situ molecular beam epitaxy

Matthias Passlack, Minghwei Hong, Joseph P. Mannaerts, Robert L. Opila, and Fan Ren

Appl. Phys. Lett. 69, 302 (1996); http://dx.doi.org/10.1063/1.118040 (3 pages) | Cited 19 times

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The thermodynamic and photochemical stability of Ga2O3–GaAs interfaces fabricated using in situ multiple‐chamber molecular beam epitaxy has been investigated. The Ga2O3 films were deposited on clean, atomically ordered (100) GaAs surfaces using a molecular beam of gallium oxide. Thermally induced degradation of electronic interface properties such as interface recombination velocity S (5750±1250 cm/s) and interface state density Dit(mid‐1010 cm−2 eV−1 range) has not been observed after rapid thermal annealing at 800 °C. Furthermore, no interface degradation has been detected during exposure to high intensity laser light. The preservation of excellent electronic interface properties and the absence of interfacial chemical reactions are attributed to AsxOy and elemental As free Ga2O3–GaAs interfaces. © 1996 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Analysis of parameters of multilayer carbon interference structures in the soft x‐ray range

P. E. Kondrashov, I. S. Smirnov, E. G. Novoselova, and A. M. Baranov

Appl. Phys. Lett. 69, 305 (1996); http://dx.doi.org/10.1063/1.118041 (3 pages) | Cited 4 times

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A new type of x‐ray interference mirrors using hydrogenated carbon films of various densities is described. The reflection coefficient and resolution of multilayer carbon structures obtained in the soft x‐ray range (1.54–44.7 Å) are investigated experimentally and theoretically. As is shown, hydrogenated carbon films can be used to create mirrors with high resolution. © 1996 American Institute of Physics.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
42.79.Bh Lenses, prisms and mirrors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Optical bistability in symmetrically strained (GaIn)As/Ga(PAs) superlattices

G. Bastian, G. von Plessen, J. Feldmann, J. Hader, T. Marschner, W. Stolz, and E. O. Göbel

Appl. Phys. Lett. 69, 308 (1996); http://dx.doi.org/10.1063/1.118042 (3 pages) | Cited 1 time

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We have studied the electroabsorptive properties of symmetrically strained (GaIn)As/Ga(PAs) superlattices consisting of 100 periods. Photocurrent measurements at 4 K reveal a pronounced pseudo‐blue shift and a Wannier–Stark splitting of the heavy‐hole exciton transition. A self‐electro‐optic effect device has been realized which makes use of the pseudo‐blue shift due to the Wannier–Stark localization and of the transparency of the GaAs substrate. The self‐electro‐optic effect devices show on–off contrast ratios of 2.1 at 77 K and of 1.3 at room temperature. © 1996 American Institute of Physics.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
81.40.Tv Optical and dielectric properties related to treatment conditions
78.20.Jq Electro-optical effects
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Periodic poling and waveguide frequency doubling in RbTiOAsO4

W. P. Risk and G. M. Loiacono

Appl. Phys. Lett. 69, 311 (1996); http://dx.doi.org/10.1063/1.118043 (3 pages) | Cited 13 times

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We report the demonstration of a guided‐wave nonlinear process in the material rubidium titanyl arsenate (RTA). Quasi‐phase‐matched frequency doubling of 874.5 nm light was achieved in a Cs:RTA waveguide, with a normalized conversion efficiency of 225%/W cm2. We also report phase matching characteristics for bulk periodically poled RTA. © 1996 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.82.Et Waveguides, couplers, and arrays
42.70.Mp Nonlinear optical crystals

Characterization of Cu–Na ion‐exchanged glass waveguides

Francesco Gonella

Appl. Phys. Lett. 69, 314 (1996); http://dx.doi.org/10.1063/1.118044 (2 pages) | Cited 19 times

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Copper–sodium ion‐exchanged glass waveguides are fabricated and characterized. Optical absorption and m‐lines spectroscopy analyses are presented. No stress‐induced birefringence is observed from refractive index profiles reconstruction, and the Cu+ oxidation state is shown to mostly determine the refractive index change. Comparison between compositional in‐depth profiles and index profiles is allowed to obtain the variation in the electronic polarizability due to the Cu+–Na+ exchange. The diffusion coefficient of Cu+ in soda‐lime glass is also calculated. © 1996 American Institute of Physics.
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42.70.Ce Glasses, quartz
42.82.Et Waveguides, couplers, and arrays
66.30.Ny Chemical interdiffusion; diffusion barriers

Carrier transport in a photorefractive multiple quantum well device

Ergun Canoglu, Ching‐Mei Yang, Elsa Garmire, Daniel Mahgerefteh, A. Partovi, T. H. Chiu, and G. J. Zydzik

Appl. Phys. Lett. 69, 316 (1996); http://dx.doi.org/10.1063/1.118045 (3 pages) | Cited 17 times

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Using picosecond time‐resolved four‐wave mixing we have investigated the turn‐on and turn‐off mechanisms in a photorefractive multiple quantum well spatial light modulator with Stark geometry. We show that holes contribute to the turn‐on time as a slower rise (∼300 ps) of the diffraction efficiency. Furthermore, the diffraction grating is dominated by either electrons or holes, depending on the applied voltage polarity relative to the diffraction of illumination. The grating decays in 0.4–8.5 ns, depending on the grating spacing. We show that the decay is due to lateral transport of carriers at the multiple quantum well/dielectric interfaces, where low‐temperature grown layers can increase the diffraction efficiency and device resolution. © 1996 American Institute of Physics.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.79.Hp Optical processors, correlators, and modulators

Formation and control of phosphorus buried layers in silicon using a pulsed XeCl excimer laser

G. Verma, S. Talwar, and T. W. Sigmon

Appl. Phys. Lett. 69, 319 (1996); http://dx.doi.org/10.1063/1.118046 (3 pages)

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In this letter, we report fabrication of pulsed‐shaped phosphorus doping profiles in Si, using a XeCl (λ=380 nm) pulsed excimer laser. Phosphorus buried layers as shallow as 750 Å and as deep as 3200 Å, with peak full width at half‐maximums as narrow as 100 Å and as broad as 900 Å are demonstrated. It is also demonstrated that the sample is free of point defects and full electrical activation is achieved by using a rapid thermal anneal at 800 °C for 30 s after the laser processing. This process, we demonstrate, afford simplicity, versatility, and independent control over the depth, width, and height of the phosphorus buried layer. Phosphorus buried layers have potential application in the fabrication of metal–oxide–semiconductor field effect transistors and BiPOLAR electronic devices. © 1996 American Institute of Physics.
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42.62.Cf Industrial applications
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.S- Impurities in crystals

γ‐radiation resistance of aluminum‐coated all‐silica optical fibers fabricated using different types of silica in the core

D. L. Griscom, K. M. Golant, A. L. Tomashuk, D. V. Pavlov, and Yu. A. Tarabrin

Appl. Phys. Lett. 69, 322 (1996); http://dx.doi.org/10.1063/1.118047 (3 pages) | Cited 17 times

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Induced loss spectra in four Al‐coated large‐core optical fibers are measured in the range 380–1000 nm during and after 60Co γ irradiation. These fibers had F‐doped‐silica claddings and synthetic silica core materials produced by different technologies. Measurements were carried out independently in Washington and Moscow using differing techniques but yielding very similar results. The highest radiation resistance is exhibited by two fibers with extremely low OH and Cl contents in their cores, one with a core material containing 0.5 mass % of fluorine, fabricated specially for this study, and one based on KS‐4V silica, an original technology developed in Russia. The latter fiber demonstrates a rather flat induced loss spectrum in the visible region at a level of 2–2.5 dB/m for γ‐ray doses of ∼10 MGy(Si). © 1996 American Institute of Physics.
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42.81.Bm Fabrication, cladding, and splicing
42.88.+h Environmental and radiation effects on optical elements, devices, and systems
61.72.Cc Kinetics of defect formation and annealing
28.52.Lf Components and instrumentation

Light‐induced expansion of fiber tips in near‐field scanning optical microscopy

Ch. Lienau, A. Richter, and T. Elsaesser

Appl. Phys. Lett. 69, 325 (1996); http://dx.doi.org/10.1063/1.118048 (3 pages) | Cited 30 times

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The emission profiles of laser diodes working at 780 nm and 1300 nm are studied by near‐field scanning optical microscopy. As the near‐field probe is scanned across the laser mirror facet, the laser emission induces a transient expansion of the probe tip which is monitored using shear force microscopy. The thermal expansion of the tips reaches absolute values of up to 100 nm per mW of emitted laser power. A fully metallized near‐field probe tip is shown to serve as a local bolometer with a spatial resolution of better than 1 μm. © 1996 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
42.55.Px Semiconductor lasers; laser diodes

The influence of demixing on the properties of a free‐burning arc

A. B. Murphy

Appl. Phys. Lett. 69, 328 (1996); http://dx.doi.org/10.1063/1.118049 (3 pages) | Cited 7 times

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Demixing in an atmospheric‐pressure free‐burning welding arc was investigated using a two‐dimensional numerical model. Simulations of arcs in argon–nitrogen and argon–helium mixtures demonstrated that demixing can have a major influence on the composition of the arc in both the central and edge regions. Convection suppressed the change in composition in the central 0.5 mm of the argon–nitrogen arc only. Furthermore, demixing was found to have only a relatively minor effect on temperature and axial velocity, but it significantly altered thermal transport in the argon–nitrogen mixture. It is concluded that demixing can be important in both chemical and thermal applications of mixed‐gas arcs. © 1996 American Institute of Physics.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
51.20.+d Viscosity, diffusion, and thermal conductivity

Atom transport in nickel by displacement cascades for spatially dependent displacement rate and sink strength

P. Fielitz, M.‐P. Macht, V. Naundorf, and H. Wollenberger

Appl. Phys. Lett. 69, 331 (1996); http://dx.doi.org/10.1063/1.118050 (3 pages) | Cited 8 times

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Diffusion coefficients D were measured in nickel under 600 keV Kr++ ion irradiation at 77 K and at 800 K using multilayer specimens. At 77 K the diffusion coefficient closely follows the calculated depth dependence of the displacement rate K indicating that athermal atomic mixing with an efficiency of Dmix/K=0.6 nm 2/dpa is responsible for the observed transport at this temperature. At 800 K considerable diffusion is observed far from the irradiated surface in a region where the displacement rate is zero. The exponential slope of the diffusion coefficient measured here indicates annihilation of mobile defects in a microstructure with a sink strength of 7×1013 m−2. An upper limit of the fraction of freely migrating defects of 0.05 is estimated. © 1996 American Institute of Physics.
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61.80.Jh Ion radiation effects
66.30.Fq Self-diffusion in metals, semimetals, and alloys
61.82.Bg Metals and alloys

Coexistence of wurtzite GaN with zinc blende and rocksalt studied by x‐ray power diffraction and high‐resolution transmission electron microscopy

Yi Xie, Yitai Qian, Shuyuan Zhang, Wenzhong Wang, Xianming Liu, and Yuheng Zhang

Appl. Phys. Lett. 69, 334 (1996); http://dx.doi.org/10.1063/1.118051 (3 pages) | Cited 9 times

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X‐ray powder diffraction and high‐resolution transmission electron microscopy (HRTEM) have found coexistence of three structures of GaN: wurtzite, zinc blende, and rocksalt in the samples prepared through benzene thermal process at 280–300 °C under pressure about 5 MPa. Previously, GaN with rocksalt structure only appeared at high pressure more than 37 GPa. HRTEM showed that there was a transitional region between the two cubic phases of GaN with zinc blende and rocksalt. X‐ray photoelectron spectra analysis of the sample gave the average composition of Ga0.95N. © 1996 American Institute of Physics.
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61.05.cp X-ray diffraction
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
61.50.Ks Crystallographic aspects of phase transformations; pressure effects

Determination of lattice polarity for growth of GaN bulk single crystals and epitaxial layers

F. A. Ponce, D. P. Bour, W. T. Young, M. Saunders, and J. W. Steeds

Appl. Phys. Lett. 69, 337 (1996); http://dx.doi.org/10.1063/1.118052 (3 pages) | Cited 128 times

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The polarity of the lattice of bulk single GaN crystals and the polarity of homoepitaxial and heteroepitaxial‐on‐sapphire GaN thin films has been studied using convergent beam electron diffraction. Diffraction patterns obtained at 200 kV for the 〈1–100〉 projection of GaN were matched with calculated patterns. The lattice orientations of two commonly observed bulk single‐crystal facets were identified. It is shown that the smooth facets in single crystals correspond to the (0001), Ga‐terminated, lattice planes, whereas the rough facets correspond to the (0001), N‐terminated, planes. It is also shown that metalorganic chemical vapor deposition epitaxy retains the polarity of the substrate, i.e., no inversion boundaries were observed. Heteroepitaxy on sapphire is shown to grow in the (0001), Ga‐terminated orientation. © 1996 American Institute of Physics.
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61.05.jm Convergent-beam electron diffraction, selected-area electron diffraction, nanodiffraction
68.55.-a Thin film structure and morphology
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation

UV irradiation effects in Al chemical vapor deposition on titanium nitride

Toshinari Nitta and Mitsugu Hanabusa

Appl. Phys. Lett. 69, 340 (1996); http://dx.doi.org/10.1063/1.118053 (3 pages) | Cited 2 times

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UV irradiation effects on Al chemical vapor deposition on titanium nitride (TiN) was investigated by using dimethylaluminum hydride at 150 °C. Al films grew thermally at a rate of 6.3 nm/min, while the UV light generated by a deuterium lamp reduced the rate to 5.2 nm/min. When TiN surfaces were oxidized, Al films started to grow only under UV irradiation. Using x‐ray photoelectron spectroscopy (XPS), we showed that the adsorbates formed on the oxidized surfaces could be dissociated only when the UV light was irradiated. The XPS results also suggested involvement of photoinduced desorption in reducing the growth rate. © 1996 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.60.Jv Interfaces; heterostructures; nanostructures

Room‐temperature operation of InTlSb infrared photodetectors on GaAs

J. D. Kim, E. Michel, S. Park, J. Xu, S. Javadpour, and M. Razeghi

Appl. Phys. Lett. 69, 343 (1996); http://dx.doi.org/10.1063/1.118054 (2 pages) | Cited 6 times

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Long‐wavelength InTlSb photodetectors operating at room temperature are reported. The photo‐ detectors were grown on (100) semi‐insulating GaAs substrates by low‐pressure metalorganic chemical vapor deposition. Photoresponse of InTlSb photodetectors is observed up to 11 μm at room temperature. The maximum responsivity of an In0.96Tl0.04Sb photodetector is about 6.64 V/W at 77 K, corresponding to a detectivity of about 7.64×108 cm Hz1/2/W. The carrier lifetime in InTlSb photodetectors derived from the stationary photoconductivity is 10–50 ns at 77 K. © 1996 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.61.Ey III-V semiconductors

A method for synthesizing large quantities of carbon nanotubes and encapsulated copper nanowires

A. A. Setlur, J. M. Lauerhaas, J. Y. Dai, and R. P. H. Chang

Appl. Phys. Lett. 69, 345 (1996); http://dx.doi.org/10.1063/1.118055 (3 pages) | Cited 63 times

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A method using a hydrogen arc for synthesizing large quantities of carbon nanotubes filled with pure copper is reported. The interaction of small copper clusters with polycyclic aromatic hydrocarbons (PAHs) is shown to form carbon nanotubes and encapsulated copper nanowires. The effectiveness of this model is demonstrated by showing that no copper filled nanotubes are formed in a helium arc that does not generate PAHs. A direct proof of this model is demonstrated by using pyrene, a PAH molecule, to grow carbon nanotubes and encapsulated copper nanowires. © 1996 American Institute of Physics.
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81.20.-n Methods of materials synthesis and materials processing
81.05.ub Fullerenes and related materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures

Evidence of diffusion characteristics of field emission electrons in nanostructuring process on graphite surface

Chen Wang, Chunli Bai, Xiaodong Li, Guangyi Shang, Imshik Lee, Xinwen Wang, Xiaohui Qiu, and Fang Tian

Appl. Phys. Lett. 69, 348 (1996); http://dx.doi.org/10.1063/1.118056 (3 pages) | Cited 6 times

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The characteristics of the nanostructure on the surface of highly oriented pyrolytic graphite (HOPG) involving field emitted electrons is examined with scanning tunneling microscopy (STM). A simple model based on the continuum electron diffusion is proposed and is compared with the experimental results. It suggests that the process could be associated with the diffusion of electrons at the vicinity of the injection position. It also implies that the characteristics of the as‐produced nanometer sized craters could be correlated to the anisotropy degree of the transport properties of HOPG. © 1996 American Institute of Physics.
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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
73.25.+i Surface conductivity and carrier phenomena
79.70.+q Field emission, ionization, evaporation, and desorption

MoS2 as microtubes

M. Remskar, Z. Skraba, F. Cléton, R. Sanjinés, and F. Lévy

Appl. Phys. Lett. 69, 351 (1996); http://dx.doi.org/10.1063/1.118057 (3 pages) | Cited 39 times

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We report on the existence of MoS2 hollowed microtubes, several mm in lengths and less than 0.1 μm wall thickness, grown from the vapor phase. Scanning electron microscopy studies reveal that instability of thin weakly bonded sheets against folding causes the tube growth directly or indirectly beyond the formation of turbulent gas flow. Electron diffraction of a single tube wall proves a parallel growth mode of successive layers while the crystal lattices of both tube walls are mutually rotated. A spiral growth mode is proposed. © 1996 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.46.-w Structure of nanoscale materials
61.66.Fn Inorganic compounds
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Direct visualization of the oscillation of Au (111) surface atoms

T. Hesjedal, E. Chilla, and H.‐J. Fröhlich

Appl. Phys. Lett. 69, 354 (1996); http://dx.doi.org/10.1063/1.118058 (3 pages) | Cited 16 times

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A high frequency oscillating Au (111) surface was measured with atomic resolution using a modified scanning tunneling microscope. On the atomic scale propagating surface acoustic waves lead to oscillations of atoms on elliptical trajectories, with the axes being determined by the material parameters of the surface. Since those oscillation frequencies are much higher than the scan frequencies the topography contrast is reduced. This basic problem is solved by measuring a stroboscopic snapshot seeing a defined state of oscillation. The atomic resolution of the phase and the amplitude contrast is explained by the superposition of the surface topography and the oscillation trajectory. © 1996 American Institute of Physics.
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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
68.35.Ja Surface and interface dynamics and vibrations
62.30.+d Mechanical and elastic waves; vibrations
43.35.Pt Surface waves in solids and liquids

Size effects on the phonon spectra of quantum dots in CdTe‐doped glasses

A. M. de Paula, L. C. Barbosa, C. H. B. Cruz, O. L. Alves, J. A. Sanjurjo, and C. L. Cesar

Appl. Phys. Lett. 69, 357 (1996); http://dx.doi.org/10.1063/1.118059 (3 pages) | Cited 28 times

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We studied the confinement effects on the phonon spectra of CdTe quantum dots by means of resonant Raman scattering measurements. The spectra show clearly longitudinal optical phonons, surface phonons and some of their overtone combinations. We show that the scattering due to surface phonons increases as the quantum dot size decreases. The results are obtained by tuning the laser excitation energy to resonance for quantum dots of different sizes inside the broad size distribution in CdTe‐doped glasses. © 1996 American Institute of Physics.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.66.Hf II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
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