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15 May 2000

Volume 87, Issue 10, pp. 7147-7597

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Optical grating recording in anisotropic photorefractive thin film: Dimensional resonance

V. Kalinin and L. Solymar

J. Appl. Phys. 87, 7147 (2000); http://dx.doi.org/10.1063/1.372961 (5 pages) | Cited 1 time

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A differential equation and boundary conditions are derived for the amplitude of the first harmonic of the space-charge field in the case of a lossy thin photorefractive film with anisotropic conductivity that is illuminated by a moving interference pattern. It is shown that for certain values of the anisotropy parameter, detuning, and film thickness, a new resonance phenomenon may occur. This resonance is distinct from and additional to the one that relies on the agreement between the speed of the interference pattern and that of the space charge wave, and has been known for a long time. © 2000 American Institute of Physics.
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42.40.Ht Hologram recording and readout methods
42.40.Eq Holographic optical elements; holographic gratings
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.79.Wc Optical coatings

Photonic band in two-dimensional lattices of micrometer-sized spheres mechanically arranged under a scanning electron microscope

Hideki T. Miyazaki, Hiroshi Miyazaki, Kazuo Ohtaka, and Tomomasa Sato

J. Appl. Phys. 87, 7152 (2000); http://dx.doi.org/10.1063/1.372962 (7 pages) | Cited 58 times

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Two-dimensional photonic crystals of dielectric spheres with a 2.1 μm diameter have been fabricated by arranging individual spheres using a micromanipulation technique in a scanning electron microscope. A buildup of photonic bands from whispering gallery modes has been observed as the number of spheres increased, by measuring the transmission spectra for lattices composed of various numbers of spheres. The photonic band dispersion curves were experimentally obtained for a finite system made of 91 spheres from the transmission spectra for oblique incidence in the near-infrared region. They were in good agreement with the results of a numerical calculation for an infinite lattice. Since this mechanical manipulation technique enables us to control the arrangement of individual optical wavelength-sized scatterers, it provides a new way to systematically investigate various photonic band effects. © 2000 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
78.30.Hv Other nonmetallic inorganics

Spectroscopic properties of nonlinear NdSc3(BO3)4

John B. Gruber, Thomas A. Reynolds, Douglas A. Keszler, and Bahram Zandi

J. Appl. Phys. 87, 7159 (2000); http://dx.doi.org/10.1063/1.372963 (5 pages) | Cited 6 times

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NdSc3(BO3)4 (NdSB) can be grown as a nonlinear optical crystal having hexagonal (huntite) structure. The crystal has important spectroscopic properties suitable for various applications in photonics. The observed crystal-field splitting of the energy levels of Nd3+(4f3) has been identified based on analyses of the fluorescence, absorption, and excitation spectra obtained at 13, 80, and 300 K. A detailed crystal-field splitting calculation in which initial crystal-field parameters Bnm are established from lattice–sum calculations gives good agreement to the observed splitting. Experimental branching ratios and fluorescence lifetimes are reported and are compared with calculated values. The spectroscopic properties of Nd3+ in NdSB are also compared with values obtained for Nd3+ as a dopant in the nonlinear crystal YAl3(BO3)4. © 2000 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
71.70.Ch Crystal and ligand fields
42.70.Mp Nonlinear optical crystals
78.40.Ha Other nonmetallic inorganics
78.30.Hv Other nonmetallic inorganics

Comparison of linewidth enhancement factors in midinfrared active region materials

J. T. Olesberg, Michael E. Flatté, and Thomas F. Boggess

J. Appl. Phys. 87, 7164 (2000); http://dx.doi.org/10.1063/1.372964 (5 pages) | Cited 6 times

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We report calculations of the linewidth enhancement factor for five midinfrared active region materials. The linewidth enhancement factors for two type-I quantum wells based on InAsSb are 2.5 and 5.4, which represent a reduction of up to a factor of 2.6 with respect to bulk InAs0.91Sb0.09. However, active region materials based on the type-II, InAs/GaInSb system have linewidth enhancement factors near 1.0, which is a factor of 2–5 reduction compared to the type-I quantum wells. The reduction of the linewidth enhancement factor is associated with both a reduction of the mismatch between the conduction and valence band densities of states and the presence of conduction band dispersion. We describe an additional optimization that is possible in the type-II materials: Carefully placed intersubband absorption features can be used to further reduce the linewidth enhancement factor. We show that linewidth enhancement values as low as 0.3 can be obtained in the type-II superlattices when fabricated into a distributed feedback structure. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
73.20.At Surface states, band structure, electron density of states
42.55.Ah General laser theory

Compound semiconductor oxide antireflection coatings

K. J. Knopp, R. P. Mirin, K. A. Bertness, K. L. Silverman, and D. H. Christensen

J. Appl. Phys. 87, 7169 (2000); http://dx.doi.org/10.1063/1.372965 (7 pages) | Cited 2 times

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We report the development of high quality, broad-bandwidth, antireflection (AR) coatings using the low index provided by wet thermally oxidized Al0.98Ga0.02As. We address the design criteria, fabrication, and characterizations of AR coatings composed of surface and buried oxide layers on GaAs. We show, using native-oxide dispersion data, that surface oxide coatings can be designed to offer a nearly zero minimum of reflectance and a reflectance of <1% over bandwidths as large as 500 nm. Surface coatings having a reflectance minimum of 0.4% and a reflectance of <1% over >250 nm have been experimentally demonstrated at a design wavelength of 1 micrometer. Additionally, buried oxide coatings can be designed with an AlxGa1−xAs matching layer of any composition to exactly match the admittance of any substrate with effective index between 2.5 and 3.5. We have demonstrated buried oxide coatings, also designed for 1 micrometer, having a reflectance minimum of 0.4% and a reflectance of <1% over 21 nm. The calculated optical scattering loss from measured roughness data indicates that reflectance minima as low as 10−4 % are ultimately achievable with native-oxide antireflection coatings.
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81.05.Ea III-V semiconductors
81.65.Mq Oxidation
42.79.Wc Optical coatings
68.35.B- Structure of clean surfaces (and surface reconstruction)
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Ion dynamics model for collisionless radio frequency sheaths

Deepak Bose, T. R. Govindan, and M. Meyyappan

J. Appl. Phys. 87, 7176 (2000); http://dx.doi.org/10.1063/1.372966 (9 pages) | Cited 40 times

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Full scale reactor model based on fluid equations is widely used to analyze high density plasma reactors. It is well known that the submillimeter scale sheath in front of a biased electrode supporting the wafer is difficult to resolve in numerical simulations, and the common practice is to use results for electric field from some form of analytical sheath model as boundary conditions for full scale reactor simulation. There are several sheath models in the literature ranging from Child’s law to a recent unified sheath model [P. A. Miller and M. E. Riley, J. Appl. Phys. 82, 3689 (1997)]. In the present work, the cold ion fluid equations in the radio frequency sheath are solved numerically to show that the spatiotemporal variation of ion flux inside the sheath, commonly ignored in analytical models, is important in determining the electric field and ion energy at the electrode. Consequently, a semianalytical model that includes the spatiotemporal variation of ion flux is developed for use as boundary condition in reactor simulations. This semianalytical model is shown to yield results for sheath properties in close agreement with numerical solutions. © 2000 American Institute of Physics.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Dg Plasma kinetic equations

Precursors of fluorocarbon film growth studied by mass spectrometry

Kungen Teii, Masaru Hori, Toshio Goto, and Nobuo Ishii

J. Appl. Phys. 87, 7185 (2000); http://dx.doi.org/10.1063/1.372967 (6 pages) | Cited 18 times

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The precursor species of fluorocarbon film growth at the reactor wall irradiated by an electron cyclotron resonance C4F8 plasma have been studied by using a quadrupole mass spectrometer. The amount of polymeric neutral species [CmFn (m⩾2)] and absolute densities of CFx (x=1–3) radicals in the vicinity of the wall were measured by electron attachment and threshold ionization mass spectrometry, respectively. The trends in the film growth rate as a function of gas residence time, diluted hydrogen concentration, and microwave power were well accounted for by the competition between the incorporation of CFx radicals and positive ions and the removal by F and H atoms. The fluxes of CFx radicals and positive ions incident upon the wall were shown to be comparable with the net condensed carbon flux derived from the growth rate. In contrast, the trends in the amount of polymeric neutrals were not well correlated to the growth rate. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Aa Theory and models of film growth
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
82.35.-x Polymers: properties; reactions; polymerization
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Modeling a metal–vapor buffer-gas hollow cathode discharge

A. J. Lichtenberg and M. A. Lieberman

J. Appl. Phys. 87, 7191 (2000); http://dx.doi.org/10.1063/1.372968 (7 pages) | Cited 6 times

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The operation of a metal–vapor buffer-gas hollow cathode discharge is re-examined using modeling techniques that have been developed for electronegative plasma discharges. It is shown that a previously developed global model can be extended to give spatially resolved densities as well as more accurate values for the plasma parameters. A numerical calculation for a neon–copper (Ne–Cu) discharge is used to illustrate the results of the modeling technique. The density profiles of the neutral and ion components, and their variation with the buffer gas pressure, are similar to those found by numerical solution of the complete equations. © 2000 American Institute of Physics.
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52.80.Hc Glow; corona
52.65.-y Plasma simulation
52.25.-b Plasma properties

Effect of sputter heating in ionized metal physical vapor deposition reactors

Junqing Lu and Mark J. Kushner

J. Appl. Phys. 87, 7198 (2000); http://dx.doi.org/10.1063/1.372969 (10 pages) | Cited 23 times

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Ionized metal physical vapor deposition (IMPVD) is a process in which sputtered metal atoms from a magnetron target are ionized by a secondary plasma, accelerated into the substrate, and deposited with moderately anisotropic fluxes. The momentum and energy transfer from the sputtered metal atoms and ion-produced reflected neutrals to the background gas, sputter heating, produces rarefaction which influences the operating characteristics of the discharge. To address these processes, a model was developed to simulate the sputtering of metal atoms and their transport in IMPVD reactors. The model accounts for the ion-energy-dependent yield and kinetic energy of the sputtered and reflected atoms, and for sputter heating. The model was validated by comparing its results to experimentally measured metal atom densities and the ionization fraction of the deposition flux. Sputter heating as a function of auxiliary ionization and magnetron power in an inductively coupled plasma IMPVD reactor for Al deposition was then investigated. Sputter heating produces rarefaction of the buffer gas which results in a redistribution of Al species in the reactor compared to the absence of sputter heating. Consequently, the ionization fraction of the depositing metal flux decreases, while the magnitude of the flux increases. The minimum Ar density due to sputter heating is regulated by heat transfer to the target. The electron density increases significantly with the addition of a small amount of metal atoms to the plasma. © 2000 American Institute of Physics.
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81.15.Cd Deposition by sputtering
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
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Magnetic, Mössbauer and magnetostrictive studies of amorphous Tb(Fe0.55Co0.45)1.5 films

T. M. Danh, N. H. Duc, H. N. Thanh, and J. Teillet

J. Appl. Phys. 87, 7208 (2000); http://dx.doi.org/10.1063/1.372970 (5 pages) | Cited 13 times

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The Tb(Fe0.55Co0.45)1.5 films were fabricated by rf magnetron sputtering from a composite target. Samples were investigated by means of x-ray diffraction, vibrating sample magnetometer, conversion electron Mössbauer spectra, and magnetostriction measurements. The as-deposited film is an amorphous alloy with a perpendicular magnetic anisotropy and an intrinsic magnetostriction λ=1080×10−6 in an applied field of 0.7 T. In this state, it was determined that the hyperfine field Bhf=23.5 T and the cone-angle between the Fe moment direction and the film-normal direction β=12°. After annealing in the temperature range of TA=250–450 °C the amorphous structure still remained, however the anisotropy was changed to a parallel one. The soft magnetostrictive behavior has also been improved by these heat treatments: the parallel magnetostriction λ∥=465×10−6 was almost developed in low applied fields of less than 0.1 T and, especially, a huge magnetostrictive susceptibility χλ=dλ∥/d(μ0H)=1.8×10−2 T−1 was obtained at μ0H=15 mT. © 2000 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Kj Amorphous and quasicrystalline magnetic materials
81.05.Bx Metals, semimetals, and alloys
75.80.+q Magnetomechanical effects, magnetostriction
68.55.-a Thin film structure and morphology
76.80.+y Mössbauer effect; other γ-ray spectroscopy
75.30.Gw Magnetic anisotropy
81.40.Rs Electrical and magnetic properties related to treatment conditions
81.40.Gh Other heat and thermomechanical treatments
71.70.Jp Nuclear states and interactions
75.30.Cr Saturation moments and magnetic susceptibilities
61.43.Dq Amorphous semiconductors, metals, and alloys

Synthesis and reactivity of Fe nanoparticles embedded in a semi-insulating matrix

D. N. McIlroy, D. Zhang, M. Grant Norton, W. L. O’Brien, M. M. Schwickert, and G. R. Harp

J. Appl. Phys. 87, 7213 (2000); http://dx.doi.org/10.1063/1.372971 (5 pages) | Cited 2 times

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The technique of plasma enhanced chemical vapor deposition has been used to synthesize Fe nanoparticles in an amorphous boron carbide matrix. The nanoparticles range in size from approximately 0.7 to 4.5 nm. It has been demonstrated that the size of the nanoparticles is proportional to the density of the Fe precursor (ferrocene) in the vapor. The matrix films have been found to be extremely hygroscopic. Upon absorption of moisture the films buckle and delaminate from the Si substrate. The buckling is a consequence of induced strain arising from the transformation of the Fe nanoparticles into α-Fe2O3. The formation of α-Fe2O3 has been verified by electron diffraction and near edge x-ray absorption fine structure measurements. Examination of the magnetic properties of the α-Fe2O3 using the technique of magnetic circular dichroism indicate that the nanoparticles are not ferromagnetic. © 2000 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Kj Amorphous and quasicrystalline magnetic materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.46.-w Structure of nanoscale materials
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
78.70.Dm X-ray absorption spectra

X-ray absorption fine structure study of short-range order of iron in Fe/Al multilayers

Dirk C. Meyer, Kurt Richter, Peter Paufler, Peter Gawlitza, and Thomas Holz

J. Appl. Phys. 87, 7218 (2000); http://dx.doi.org/10.1063/1.372972 (9 pages) | Cited 10 times

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Results of quantitative analysis of fluorescence x-ray absorption fine structure (XAFS) experiments at the Fe–K absorption edge are presented for a 6∗(4.3 nm Fe/10.4 nm Al) multilayer prepared by pulsed laser deposition. Fluorescence XAFS experiments have been combined with excitation of x-ray standing waves. This combination in one experiment allowed for a depth-controlled excitation of Fe fluorescence and hence for a depth-resolved analysis of short-range order. Depth-resolved analysis showed that instead of sharp Fe/Al or Al/Fe interfaces extended interlayer regions exist. The structure retained that of bulk α-Fe. In the upper half of the Fe layer 37 at. % Al as nearest and next nearest neighbors of Fe were found, whereas in the lower half 80 at. % Al atoms occur. Thus the Fe/Al interface (deposition of Fe on Al) should be characterized by an intermixing zone significantly larger in comparison to that of the Al/Fe interface (deposition of Al on Fe). By conventional XAFS measurement carried out at a fixed angle of incidence of the exciting beam an average Fe neighborhood for the entire Fe layer of 58 at. % Al atoms was found. This value agrees with the average obtained when the analysis of the layer was performed separately for two sublayers by shifting the wave field through the layer. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Fg Pulsed laser ablation deposition
78.70.Dm X-ray absorption spectra
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.

Effect of van der Waals forces on axial buckling of a double-walled carbon nanotube

C. Q. Ru

J. Appl. Phys. 87, 7227 (2000); http://dx.doi.org/10.1063/1.372973 (5 pages) | Cited 115 times

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An elastic model is presented to study infinitesimal buckling of a double-walled carbon nanotube under axial compression. A simple formula is derived for the critical axial strain, which clearly indicates the role of the van der Waals forces between the inner and outer tubes characterized by two parameters. In particular, the analysis shows that inserting an inner tube into a single-walled nanotube does not increase the critical axial strain as compared to the single-walled nanotube under otherwise identical conditions, despite the fact that the total critical axial force of the double-walled nanotube could be increased due to an increase in the cross-sectional area. © 2000 American Institute of Physics.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
62.20.F- Deformation and plasticity

Metastable phases induced by ion irradiation in the equilibrium immiscible Fe–Cu system

G. W. Yang, W. S. Lai, C. Lin, and B. X. Liu

J. Appl. Phys. 87, 7232 (2000); http://dx.doi.org/10.1063/1.372974 (10 pages) | Cited 7 times

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Anomalous structural evolution was induced by room-temperature 200 keV xenon ion irradiation and it results in the formation of various new metastable phases in the equilibrium immiscible Fe–Cu system. First, nanosized quasicrystals were formed in an amorphous matrix through a two-step transition of crystal to amorphous to quasicrystal in Fe70Cu30 multilayered films. The real compositions of the amorphous matrix and quasicrystals were determined to be close to Fe70Cu30 and Fe50Cu50, respectively. Moreover, the same icosahedral phase was also obtained in another similarly designed Fe50Cu50 multilayered sample upon 850 °C thermal annealing, confirming the existence of such a metastable state. Second, amorphous alloys were formed in a composition range of 30–50 at. % of Cu. Third, a Cu-based face-centered-cubic (fcc) solid solution was formed at an alloy composition of about Fe30Cu70 and, interestingly, another fcc structured metastable crystalline phase was obtained at a composition very close to that of Fe50Cu50. A Gibbs free energy diagram of the Fe–Cu system was calculated, with special consideration of excess interfacial free energy stored in the multilayered films, within the framework of Miedema’s model and it gives a reasonable thermodynamic explanation to the metastable phase formation observed. The amorphous-to-quasicrystal transition is also discussed in terms of the similarity in the atomic configuration between the icosahedral and amorphous short-range orders. Furthermore, molecular dynamics study showed that Fe and Cu could be mixed on an atomic scale in the metastable phases observed. © 2000 American Institute of Physics.
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61.80.Jh Ion radiation effects
61.44.Br Quasicrystals
61.82.Bg Metals and alloys
61.43.Dq Amorphous semiconductors, metals, and alloys
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
64.75.-g Phase equilibria

Thermodynamics of Cu47Ti34Zr11Ni8, Zr52.5Cu17.9Ni14.6Al10Ti5 and Zr57Cu15.4Ni12.6Al10Nb5 bulk metallic glass forming alloys

S. C. Glade, R. Busch, D. S. Lee, W. L. Johnson, R. K. Wunderlich, and H. J. Fecht

J. Appl. Phys. 87, 7242 (2000); http://dx.doi.org/10.1063/1.372975 (7 pages) | Cited 68 times

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The differences in the thermodynamic functions between the liquid and the crystalline states of three bulk metallic glass forming alloys, Cu47Ti34Zr11Ni8, Zr52.5Cu17.9Ni14.6Al10Ti5, and Zr57Cu15.4Ni12.6Al10Nb5, were calculated. The heat capacity was measured in the crystalline solid, the amorphous solid, the supercooled liquid, and the equilibrium liquid. Using these heat capacity data and the heats of fusion of the alloys, the differences in the thermodynamic functions between the liquid and the crystalline states were determined. The Gibbs free energy difference between the liquid and the crystalline states gives a qualitative measure of the glass forming ability of these alloys. Using the derived entropy difference, the Kauzmann temperatures for these alloys were determined. © 2000 American Institute of Physics.
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65.40.-b Thermal properties of crystalline solids
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
81.05.Kf Glasses (including metallic glasses)
65.20.-w Thermal properties of liquids
65.40.gd Entropy
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
81.05.Bx Metals, semimetals, and alloys
64.70.D- Solid-liquid transitions

Viscous flow of the Cu47Ti34Zr11Ni8 glass forming alloy

S. C. Glade and W. L. Johnson

J. Appl. Phys. 87, 7249 (2000); http://dx.doi.org/10.1063/1.373411 (3 pages) | Cited 30 times

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The viscosity of the Cu47Ti34Zr11Ni8 glass forming alloy was determined by beam bending experiments and by a noncontact oscillating drop technique. These viscosity data can be described with the Vogel–Fulcher–Tammann relation. Using the strong/fragile classification of glasses, Cu47Ti34Zr11Ni8 is more fragile than the strong Zr–Ti–Cu–Ni–Be metallic glass formers. © 2000 American Institute of Physics.
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66.20.-d Viscosity of liquids; diffusive momentum transport
81.05.Kf Glasses (including metallic glasses)
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
62.10.+s Mechanical properties of liquids

Physically trapped oxygen in sputter-deposited MoO3 films

T. J. Vink, R. G. F. A. Verbeek, J. H. M. Snijders, and Y. Tamminga

J. Appl. Phys. 87, 7252 (2000); http://dx.doi.org/10.1063/1.372976 (3 pages) | Cited 7 times

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In the present study, we show that the stoichiometry of sputtered molybdenum oxide films can be changed from oxygen deficient to, more surprisingly, oxygen rich. O/Mo ratios as high as 3.2 were measured, depending on the oxygen partial pressure in the sputtering atmosphere. It is shown that a substantial part of the excess oxygen is physically trapped in the film while the remaining part is chemically bonded in the form of H2O groups. The presence of physically trapped oxygen is demonstrated through a hydration reaction of the film resulting in the controlled detrapping of both excess oxygen and argon. The quantities of released oxygen are electrochemically measured and compared with the elemental composition of the film as determined by means of Rutherford backscattering spectroscopy (Mo, O, and Ar) and elastic recoil detection (H). © 2000 American Institute of Physics.
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68.55.Nq Composition and phase identification
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

X-ray scattering study of interfacial roughness correlation in Mo/Si multilayers fabricated by ion beam sputtering

A. Ulyanenkov, R. Matsuo, K. Omote, K. Inaba, J. Harada, M. Ishino, M. Nishii, and O. Yoda

J. Appl. Phys. 87, 7255 (2000); http://dx.doi.org/10.1063/1.372977 (6 pages) | Cited 15 times

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Specular and diffuse x-ray scattering are used to probe the mesoscopic structure of interfaces within two 30-period Mo/Si superlattices, grown on silicon and glass substrates by ion beam sputtering. The data are evaluated qualitatively and quantitatively on the basis of a distorted-wave Born approximation, which includes a correlating behavior of interface roughness in both the lateral and vertical directions. Different initial conditions of the substrate’s surface result in distinguishable characters of roughness replications in the direction of growth. The average value, lateral correlation and fractal dimension of roughness are found to be different in the two samples, which leads to differences in the reflective properties of multilayer mirrors. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.05.cf X-ray scattering (including small-angle scattering)
68.35.Ct Interface structure and roughness
81.15.Cd Deposition by sputtering
42.79.Bh Lenses, prisms and mirrors

Simulation and growth of gold on silicon oxide in one-dimensional and quasi-one-dimensional arrays

M. Boero, J. K. Vincent, J. C. Inkson, M. Mejias, C. Vieu, H. Launois, and P. A. Mulheran

J. Appl. Phys. 87, 7261 (2000); http://dx.doi.org/10.1063/1.372978 (5 pages)

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The granular film deposition of gold atoms by means of thermal evaporation on silicon oxide surfaces is known to produce nanometer-scale islands which show electrical characteristics dominated by Coulomb blockade. Here we report on the growth and the simulation of structures produced by a combination of evaporation and lithography. A lithographic technique is used to define a region of a width of several nm that is surrounded by polymethylmethacrylate (PMMA). The PMMA confines the diffusion of the atoms, and the growth process is characterized by different boundary conditions compared with the case where atoms are deposited on a macroscopic surface. This method enables us to create quasi-one-dimensional (quasi-1D) and 1D structures in which the gold islands are arranged in a single row where the lateral size is only a few nanometers. Such structures offer the possibility of studying Coulomb blockade in 1D arrays and a signature of self-organized growth is observed in such structures. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
73.61.At Metal and metallic alloys
73.23.Hk Coulomb blockade; single-electron tunneling
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Bx Metals, semimetals, and alloys

Interface dilution and morphology of CdTe/MnTe superlattices studied by small- and large-angle x-ray scattering

J. Eymery, J. M. Hartmann, and G. T. Baumbach

J. Appl. Phys. 87, 7266 (2000); http://dx.doi.org/10.1063/1.372979 (9 pages) | Cited 3 times

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We have performed small- and large-angle x-ray scattering experiments on CdTe/MnTe superlattices. The Fresnel optical method and the distorted wave Born approximation were used to extract from small-angle measurements out-of-plane and in-plane information about the interfaces. Specular reflectivity shows that the interface roughness is quite high (about 7 Å) for all superlattices. The effective MnTe concentration, directly determined from the refractive index profile, is successfully used to simulate the structured nonspecular scattering, and to determine the lateral correlation length of the interface roughness (about 1500±750 Å). Moreover, it is shown that the layers are almost completely correlated over the sample thickness. The thickness fluctuations along the growth direction are estimated from the analysis of the large-angle (004) reflection, and the effective MnTe profile is also checked by dynamical simulation. It is shown that the small- and large-angle results are in good agreement. The MnTe profile width deduced from x-ray reflectivity is slightly overestimated due to the large integration area of this technique. An estimation of the local MnTe profile is given. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.Fx Diffusion; interface formation
68.35.Ct Interface structure and roughness
81.05.Dz II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.70.Ck X-ray scattering
78.66.Hf II-VI semiconductors

Size distribution and electroluminescence of self-assembled Ge dots

L. Vescan, T. Stoica, O. Chretien, M. Goryll, E. Mateeva, and A. Mück

J. Appl. Phys. 87, 7275 (2000); http://dx.doi.org/10.1063/1.372980 (8 pages) | Cited 34 times

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In this article we study the electroluminescence of p-i-n diode structures with Ge dots consisting of coherent three-dimensional small (pyramids) and larger (dome) islands. The Ge dots are formed through strain-induced islanding. The diode structures, including one layer with Ge dots, were deposited on Si mesas with variable areas in order to study the influence of limited area deposition on self-assembling. It was observed that the reduction of deposited area improves island uniformity. The combined analysis of island distribution and electroluminescence spectra has lead to the conclusion that domes in small diodes have a smaller Si content or are less relaxed than domes in larger diodes. The diodes are found to emit up to room temperature near the optical communication wavelength of 1.3 microns. © 2000 American Institute of Physics.
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78.60.Fi Electroluminescence
78.66.Db Elemental semiconductors and insulators
85.30.Kk Junction diodes
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Direct quantitative detection of the sp3 bonding in diamond-like carbon films using ultraviolet and visible Raman spectroscopy

K. W. R. Gilkes, S. Prawer, K. W. Nugent, J. Robertson, H. S. Sands, Y. Lifshitz, and X. Shi

J. Appl. Phys. 87, 7283 (2000); http://dx.doi.org/10.1063/1.372981 (7 pages) | Cited 65 times

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The bonding in a series of unhydrogenated amorphous carbon films has been analyzed quantitatively using Raman spectroscopy excited by laser light in both the visible and ultraviolet regions of the spectrum. The asymmetry of the peak near 1550 cm−1 in the visible Raman spectra is correlated with the percentage of sp3 bonding in the films. The ultraviolet Raman spectra exhibit two broad Raman peaks at 1650 and 1100 cm−1, due to sp2 and sp3 vibrational modes, respectively. The former is a resonance feature associated with a large proportion of paired sp2 sites, while the latter is a weighted phonon density-of-states for the distorted random network of sp3 sites. The position and relative intensity of the two peaks are shown to be strongly correlated with the percentage of sp3 sites in the films, providing a reliable measure of sp3 bonding which is both semiquantitative and nondestructive. © 2000 American Institute of Physics.
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61.43.Er Other amorphous solids
81.05.ub Fullerenes and related materials
78.35.+c Brillouin and Rayleigh scattering; other light scattering
63.50.-x Vibrational states in disordered systems
68.55.-a Thin film structure and morphology

Photoluminescence of donor–acceptor carbazole-based molecules in amorphous and powder forms

D. Adès, V. Boucard, E. Cloutet, A. Siove, C. Olivero, M. C. Castex, and G. Pichler

J. Appl. Phys. 87, 7290 (2000); http://dx.doi.org/10.1063/1.372982 (4 pages) | Cited 13 times

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We present absorption and photoluminescence features of four samples of carbazole molecules substituted with various electron–acceptor groups. These molecules named 1-(N-ethylcarbazolyl)-2-substituted-2-cyanovinylene contain in their structure the electron–donor carbazole nucleus and cyanovinylene bearing either another nitrile function, an ethylester, a phenyl, or a para-nitrophenyl groups. It is shown that depending on the strength of the donor–acceptor internal charge transfer, both the absorption and emission spectra are more or less redshifted. It is found that the ethyl-ester derivative displays the best relative photoluminescence efficiency among all the samples and its peak is measured at 490 nm when taking amorphous thin film. The microcrystalline powder form of the same material exhibits spectral narrowing and shift of the peak emission. We obtain further narrowing of the emission band and further redshifting of the emission when we illuminate, transversely, a glass capillary containing the crystalline sample by an ultraviolet light-emitting diode. © 2000 American Institute of Physics.
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78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds
42.79.Wc Optical coatings

Optical properties of CuGaSe2 and CuAlSe2 layers epitaxially grown on Cu(In0.04Ga0.96)Se2 substrates

Sho Shirakata, Shigefusa Chichibu, Hideto Miyake, and Kohichi Sugiyama

J. Appl. Phys. 87, 7294 (2000); http://dx.doi.org/10.1063/1.372983 (9 pages) | Cited 3 times

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Photoluminescence (PL) study has been performed on epitaxial layers of CuGaSe2 and CuAlSe2 grown by metalorganic chemical vapor epitaxy on CuGa0.96In0.04Se2 substrates prepared by the traveling heater method. PL properties of epilayers are compared with each other for those grown on GaAs (100), CuGa0.96In0.04Se2 (100), CuGa0.96In0.04Se2 (112), and randomly oriented CuGa0.96In0.04Se2 substrates. PL results are discussed in terms of the lattice mismatches and stress in the epilayers. © 2000 American Institute of Physics.
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78.66.Li Other semiconductors
78.55.Hx Other solid inorganic materials
68.60.Bs Mechanical and acoustical properties

Change of TO and LO mode frequency of evaporated SiO2 films during aging in air

A. Brunet-Bruneau, S. Fisson, G. Vuye, and J. Rivory

J. Appl. Phys. 87, 7303 (2000); http://dx.doi.org/10.1063/1.372984 (7 pages) | Cited 11 times

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The microstructural modifications, induced by atmospheric water vapor, in the silica network of porous amorphous SiO2 films, evaporated by electron gun and capped by a nonporous TiO2 layer, have been investigated. We have taken advantage of infrared ellipsometric measurements to extract the infrared complex dielectric function of the SiO2 films in the 600–5000 cm−1 range, from which we deduce the actual values of the frequencies of the Si–O–Si stretching vibrational modes [transverse optic (TO) and longitudinal optic (LO)]. The TO and LO frequency shifts are studied experimentally and reproduced by simulation. Experimental data show the increase as a function of time in air of both TO and LO frequencies, and of the refractive index in the visible range. The film is modeled as a mixture of two constituents: a silica matrix, with variable density, and pores, into which water can penetrate. We show that the TO frequency is mainly sensitive to the silica matrix density, while the LO frequency gives information about the pore volume fraction. We first demonstrate that our deposition method leads to films having initially a dense silica matrix, characterized by a high visible refractive index (1.543 as compared to 1.458 for fused silica). Second, we show that the strong relaxation of the silica network (characterized by the decrease of the silica matrix refractive index from 1.543 to 1.475), due to the water penetration in the pores, is accompanied by a decrease of the pore volume fraction (from ∼30% before venting down to ∼15% after air exposure). © 2000 American Institute of Physics.
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68.60.Wm Other nonelectronic physical properties
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.66.Nk Insulators
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
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