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30 Nov 1998

Volume 73, Issue 22, pp. 3181-3305

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Controlled doping of phthalocyanine layers by cosublimation with acceptor molecules: A systematic Seebeck and conductivity study

M. Pfeiffer, A. Beyer, T. Fritz, and K. Leo

Appl. Phys. Lett. 73, 3202 (1998); http://dx.doi.org/10.1063/1.122718 (3 pages) | Cited 17 times

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We investigate the doping of vanadyl–phthalocyanine by a fluorinated form of tetracyano-quinodimethane as an example of controlled doping of thin organic dye films by cosublimation of matrix and dopant. The electrical parameters of the films derived from conductivity and Seebeck measurements show that the results largely follow standard models used to describe the doping of crystalline semiconductors; e.g., a smooth shift of the Fermi level towards the valence states with increasing doping is observed. Other effects, like the superlinear increase of conductivity with the molar doping ratio, need the inclusion of additional effects like percolation. © 1998 American Institute of Physics.
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73.61.Ph Polymers; organic compounds
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.50.Lw Thermoelectric effects
61.72.up Other materials

Termination, surface structure and morphology of the molecular beam epitaxially grown HgTe(001) surface

S. Oehling, M. Ehinger, T. Gerhard, C. R. Becker, G. Landwehr, M. Schneider, D. Eich, H. Neureiter, R. Fink, M. Sokolowski, and E. Umbach

Appl. Phys. Lett. 73, 3205 (1998); http://dx.doi.org/10.1063/1.122719 (3 pages) | Cited 5 times

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The surface structure of molecular beam epitaxially grown HgTe(001) has been studied under in situ ultrahigh vacuum conditions. The as-grown samples were investigated by means of x-ray photoelectron spectroscopy (XPS), spot profile analysis of low-energy electron diffraction, reflection of high-energy electron diffraction and scanning tunneling microscopy (STM). They exhibited a c(2×2) surface reconstruction with an additional weak (2×1) component in both diffraction experiments. The surface was shown by XPS to be terminated with Hg atoms. In addition, by means of STM experiments, we have been able to resolve the atomic structure of the reconstructed surface and to detect domain boundaries along the [1math0] direction whose local symmetry is twofold and, therefore, the probable cause of the weak (2×1) reconstruction. © 1998 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
79.60.Bm Clean metal, semiconductor, and insulator surfaces

“Contact epitaxy” observed in supported nanoparticles

M. Yeadon, M. Ghaly, J. C. Yang, R. S. Averback, and J. M. Gibson

Appl. Phys. Lett. 73, 3208 (1998); http://dx.doi.org/10.1063/1.122720 (3 pages) | Cited 38 times

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We have observed the formation of heteroepitaxial interfacial layers between silver nanoparticles and a single crystal copper surface by a phenomenon we term “contact epitaxy.” Upon depositing Ag nanoparticles (5–20 nm diameter) onto clean (001) Cu in an ultrahigh vacuum in situ transmission electron microscope, a thin (111)-oriented layer of Ag was detected at the interface between the substrate and particles. Molecular dynamics simulations reveal that the epitaxial layers form within picoseconds of impact, with rapid alignment arising from mechanical relaxation of the highly stressed interface formed upon initial contact. The simulations also show that multiple grains form in the nanoparticle as a consequence of this relaxation process. The unique structure of the nanoparticles, induced by contact epitaxy, is expected to significantly influence physical properties such as interfacial bonding, diffusion, chemical activity, and electrical transport, as well as forming a nucleus for grain growth and epitaxy which we also observe. Due to its simple origin, the phenomenon should also apply to materials systems beyond the field of nanoparticles with implications for cluster deposition, adhesion, rheology, and catalysis. © 1998 American Institute of Physics.
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68.35.Ct Interface structure and roughness
61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.Cd Deposition by sputtering
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Multistable antiferroelectric liquid-crystal optical modulator

Valery Vorflusev and Satyendra Kumar

Appl. Phys. Lett. 73, 3211 (1998); http://dx.doi.org/10.1063/1.122721 (3 pages) | Cited 1 time

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An electro-optical element based on antiferroelectric liquid crystal (AFLC) has been prepared by photopolymerization-induced anisotropic phase separation of a solution of an AFLC and a prepolymer. It consists of two adjacent layers, one comprised of the isotropic polymer and the other of the AFLC aligned by surface treatment of the adjacent substrate. The electro-optical properties show that these devices are either optically monostable or multistable (at zero field) with maximum memory angle of ∼15°. A qualitative model to describe the origin of memory in these AFLC/polymer composites is discussed. © 1998 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
42.79.Hp Optical processors, correlators, and modulators
42.70.Df Liquid crystals
42.70.Jk Polymers and organics
64.75.-g Phase equilibria
64.70.M- Transitions in liquid crystals
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Aluminum-induced crystallization of amorphous silicon on glass substrates above and below the eutectic temperature

Oliver Nast, Tom Puzzer, Linda M. Koschier, Alistair B. Sproul, and Stuart R. Wenham

Appl. Phys. Lett. 73, 3214 (1998); http://dx.doi.org/10.1063/1.122722 (3 pages) | Cited 84 times

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The achievement of high-quality continuous polycrystalline silicon (poly-Si) layers onto glass substrates by using aluminum-induced crystallization is reported. The crystallization behavior of dc sputtered amorphous silicon on glass induced by an Al interface layer has been investigated above and below the eutectic temperature of 577 °C. Secondary electron micrographs in combination with energy-dispersive x-ray microanalysis show that annealing below this temperature leads to the juxtaposed Al and Si layers exchanging places. The newly formed poly-Si layer is fully crystallized and of good crystalline quality, according to Raman spectroscopy and transmission electron microscopy investigations. At 500 °C, the time needed to crystallize a 500-nm-thick Si layer is as short as 30 min. By annealing above the eutectic temperatures, layer exchange is not as pronounced and the newly formed Al layer is found to contain a network of crystallized Si. © 1998 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.43.Dq Amorphous semiconductors, metals, and alloys
61.72.Cc Kinetics of defect formation and annealing
81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
78.66.Db Elemental semiconductors and insulators
78.30.Am Elemental semiconductors and insulators

Diagnostics of “colossal” magnetoresistance manganite films by Raman spectroscopy

V. B. Podobedov, D. B. Romero, A. Weber, J. P. Rice, R. Schreekala, M. Rajeswari, R. Ramesh, T. Venkatesan, and H. D. Drew

Appl. Phys. Lett. 73, 3217 (1998); http://dx.doi.org/10.1063/1.122723 (3 pages) | Cited 24 times

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Polarized Raman scattering by phonons is used to characterize thin films prepared by laser ablation of La1−xCaxMnO3 targets. It was found that, in the temperature range from 6 to 300 K, phonon spectra of La0.7Ca0.3MnO3 films exhibit observable differences from those in bulk materials (microcrystalline ceramics and single crystals). A significant difference was found in the spectra of “as-grown” films compared to those annealed in oxygen at 800 °C. The observed Raman peaks and their linewidths exhibit an irregular temperature dependence near Tc. A correlation of Raman data with magnetization of the sample was also found. © 1998 American Institute of Physics.
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75.47.De Giant magnetoresistance
78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
72.20.My Galvanomagnetic and other magnetotransport effects
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Diffusion coefficient of Al in metastable, amorphous Al–Pt phase

Z. Radi, J. L. Lábár, and P. B. Barna

Appl. Phys. Lett. 73, 3220 (1998); http://dx.doi.org/10.1063/1.122724 (3 pages) | Cited 4 times

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Diffusion data for amorphous binary alloys are scarce in the literature. There are no data available for the diffusion of Al in Al–Pt amorphous phase known to the authors. High-temperature successive deposition of components was used in the present experiments to reveal the elementary processes of reactive diffusion forming the metastable amorphous phase and to determine the diffusion coefficient of Al in this phase: D(α) = (1.2±0.4)×10−10×exp[−(6.9±0.1)×104J mol−1/RT]m2 s−1. This value, taken from thin film experiments, can be considered as a good approximation to the bulk diffusion coefficient. © 1998 American Institute of Physics.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.55.Nq Composition and phase identification
68.35.Fx Diffusion; interface formation

Sub-5 nm gold dot formation using retarding-field single ion deposition

M. Hori, R. G. Woodham, and H. Ahmed

Appl. Phys. Lett. 73, 3223 (1998); http://dx.doi.org/10.1063/1.122725 (3 pages)

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Gold dots of 2.5 nm mean diameter and 0.8 nm standard deviation have been fabricated successfully on chromium oxide (CrOx) thin films. The CrOx thin films were deposited on Si substrates by sputtering and gold dots were subsequently deposited by a retarding-field single ion deposition (RSID) technique. The formation of gold dots has been investigated systematically with landing energies from 100 to 900 eV and doses from 10 to 40 C/m2. The dot diameter and density could be controlled by varying the landing energy and dose of gold ions arriving on the surface. The formation of single electron devices, quantum dots, nanopillars, and other nanoscale device structures is proposed using the RSID technique. © 1998 American Institute of Physics.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.55.-a Thin film structure and morphology
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Effect of the hydrogen on the intrinsic stress in hydrogenated amorphous carbon films deposited from an electron cyclotron resonance plasma

B. Racine, M. Benlahsen, K. Zellama, P. Goudeau, M. Zarrabian, and G. Turban

Appl. Phys. Lett. 73, 3226 (1998); http://dx.doi.org/10.1063/1.122726 (3 pages) | Cited 13 times

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The intrinsic stresses have been investigated in detail in particular diamondlike carbon films prepared by chemical vapor deposition assisted by electron cyclotron resonance plasma, as a function of the substrate bias and sample thickness in relation with the H content and bonding. Combined infrared absorption, elastic recoil detection analysis, and residual stress measurements are used to fully characterize the films in their as deposited state. The results indicate clearly that both the low and high biased samples exhibit compressive stresses. The stresses are found to be higher in the high biased films and are affected not only by the [H]/[C] ratio but also by the C–H and C–C volumetric distortions. © 1998 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.66.-w Optical properties of specific thin films

Nanometer-scale imaging of domains in ferroelectric thin films using apertureless near-field scanning optical microscopy

Charles Hubert and Jeremy Levy

Appl. Phys. Lett. 73, 3229 (1998); http://dx.doi.org/10.1063/1.122727 (3 pages) | Cited 26 times

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Images of nanometer-scale ferroelectric domains in BaxSr1−xTiO3 thin films are obtained with 30 Å spatial resolution using apertureless near-field scanning optical microscopy (ANSOM). The images exhibit inhomogeneities in the ferroelectric polarization over the smallest scales that can be observed, and are largely uncorrelated with topographic features. The application of an in-plane static electric field causes domain reorientation and domain-wall motion over distances as small as 40 Å. These results demonstrate the promise of ANSOM for imaging near-atomic-scale polarization fluctuations in ferroelectric materials. © 1998 American Institute of Physics.
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77.55.-g Dielectric thin films
77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
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