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13 Nov 2000

Volume 77, Issue 20, pp. 3131-3302

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Optically induced propulsion of small particles in an evenescent field of higher propagation mode in a multimode, channeled waveguide

Takuo Tanaka and Sadahiko Yamamoto

Appl. Phys. Lett. 77, 3131 (2000); http://dx.doi.org/10.1063/1.1325397 (3 pages) | Cited 19 times

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We report experimental results in which Mie particles were optically propelled in an evanescent field generated in a multimode, channeled waveguide. Polystyrene latex spheres 4 μm in diameter were trapped laterally at the high intensity region of the evanescent field and were driven along the waveguide channel in the evanescent field of either fundamental or higher guided modes. © 2000 American Institute of Physics.
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37.10.Vz Mechanical effects of light on atoms, molecules, and ions
42.79.Gn Optical waveguides and couplers

Enhanced ultraviolet photoluminescence from SiO2/Ge:SiO2/SiO2 sandwiched structure

J. K. Shen, X. L. Wu, R. K. Yuan, N. Tang, J. P. Zou, Y. F. Mei, C. Tan, X. M. Bao, and G. G. Siu

Appl. Phys. Lett. 77, 3134 (2000); http://dx.doi.org/10.1063/1.1325399 (3 pages) | Cited 11 times

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SiO2/Ge:SiO2/SiO2 sandwiched structure was fabricated for exploring efficient light emission. After annealed in N2 (O2<1%), this structure shows three photoluminescence (PL) bands at 293, 395, and 780 nm. The intensity of the 395 nm band is largely enhanced in comparison with that from the monolayered Ge:SiO2 film. Spectral analyses suggest that the three PL bands originate from S1→S0, T∑(T∏)→S0, and T∏′→S0 optical transitions in GeO color centers, respectively. The improvement of the GeO density resulting from the confinement on Ge diffusion is responsible for the enhanced ultraviolet PL. This structure is expected to have important applications in optoelectronics. © 2000 American Institute of Physics.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing

Near-room-temperature continuous-wave operation of multiple-active-region 1.55 μm vertical-cavity lasers with high differential efficiency

J. K. Kim, S. Nakagawa, E. Hall, and L. A. Coldren

Appl. Phys. Lett. 77, 3137 (2000); http://dx.doi.org/10.1063/1.1325400 (3 pages) | Cited 21 times

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We present completely monolithic, single-step grown, bipolar cascade vertical-cavity surface-emitting lasers at 1.55 μm with a greater-than-unity differential quantum efficiency. A typical device had a threshold current density of 1 kA/cm2, a threshold voltage of 3.2 V, and demonstrated continuous wave operation up to 8 °C. Devices smaller than 10 μm in diameter lased single mode. Active regions in our device were epitaxially stacked in three stages. This technique of multiple-active regions enabled the greater-than-unity differential quantum efficiency operation, which is essential in constructing high-efficiency microwave optical links with gain. We report the device characteristics and a model on the scaling properties of active region stacking in multiple-active-region vertical-cavity lasers. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Aluminum and GaN contacts on Si(111) and sapphire

Z. M. Zhao, R. L. Jiang, P. Chen, W. P. Li, D. J. Xi, S. Y. Xie, B. Shen, R. Zhang, and Y. D. Zheng

Appl. Phys. Lett. 77, 3140 (2000); http://dx.doi.org/10.1063/1.1325402 (3 pages) | Cited 6 times

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Al and GaN contacts on both Si(111) and sapphire substrates were studied in this letter. After annealing at 450, 520, 600, and 650 °C for 35 min under a N2 flowing ambient, the current–voltage characteristics of Al/GaN contacts on Si(111) substrates were different from those on sapphire ones. The interfacial properties were discussed using the Schottky emission model in which the current is proportional to the square of the applied voltage. The metallurgical reactions were analyzed using photoluminescence (PL) spectra and x-ray diffraction (XRD). After annealing, blueshifts in the PL spectra and new peaks in the XRD data indicated that the wide-band gap interfacial phase AlGaN was formed at the Al/GaN interface. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Cg Contact resistance, contact potential
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.30.+y Surface double layers, Schottky barriers, and work functions

Correlation between structural and optical properties of Si nanocrystals embedded in SiO2: The mechanism of visible light emission

B. Garrido, M. López, O. González, A. Pérez-Rodríguez, J. R. Morante, and C. Bonafos

Appl. Phys. Lett. 77, 3143 (2000); http://dx.doi.org/10.1063/1.1325392 (3 pages) | Cited 42 times

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The size distribution, band gap energy, and photoluminescence of silicon nanocrystals embedded in SiO2 have been measured by direct and independent methods. The size distribution is measured by coupling high-resolution and conventional electron microscopy in special imaging conditions. The band gap is calculated from photoluminescence excitation measurements and agrees with theoretical predictions. Their correlation allows us to report the experimental Stokes shift between absorption and emission, which is 0.26±0.03 eV, independent of average size. This is almost exactly twice the energy of the Si–O vibration (0.134 eV). These results suggest that the dominant emission is a fundamental transition spatially located at the Si–SiO2 interface with the assistance of a local Si–O vibration. © 2000 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
61.46.-w Structure of nanoscale materials
68.35.Ja Surface and interface dynamics and vibrations
63.20.Pw Localized modes

Circular photogalvanic effect induced by monopolar spin orientation in p-GaAs/AlGaAs multiple-quantum wells

S. D. Ganichev, H. Ketterl, W. Prettl, E. L. Ivchenko, and L. E. Vorobjev

Appl. Phys. Lett. 77, 3146 (2000); http://dx.doi.org/10.1063/1.1326488 (3 pages) | Cited 25 times

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The circular photogalvanic effect (CPGE) has been observed in (100)-oriented p-GaAs/AlGaAs quantum wells at normal incidence of far-infrared radiation. It is shown that monopolar optical spin orientation of free carriers causes an electric current which reverses its direction upon changing from left to right circularly polarized radiation. CPGE at normal incidence and the occurrence of the linear photogalvanic effect indicate a reduced point symmetry of studied multilayered heterostructures. As proposed, CPGE can be utilized to investigate separately spin polarization of electrons and holes and the symmetry of quantum wells. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.50.Pz Photoconduction and photovoltaic effects

Patterning of sub-50 nm dense features with space-invariant 157 nm interference lithography

M. Switkes, T. M. Bloomstein, and M. Rothschild

Appl. Phys. Lett. 77, 3149 (2000); http://dx.doi.org/10.1063/1.1326490 (3 pages) | Cited 7 times

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We have implemented a space-invariant interference lithography tool for 157 nm F2 lasers, capable of creating dense line and space patterns with a spatial period of 91 nm. No gratings or curved optics are required, allowing a simple and inexpensive tool for resist and process development at 157 nm. Initial patterning of several commercial and experimental resists has resulted in high contrast features with little line edge roughness and good cross-sectional profiles, indicating that the fundamental performance of acid-catalyzed resists patterned at 157 nm may meet lithography requirements for sub-50 nm features. © 2000 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
07.60.Ly Interferometers
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
42.55.Lt Gas lasers including excimer and metal-vapor lasers

Mode behavior of photopumped AlGaAs–GaAs lasers confined by oxide-semiconductor distributed Bragg reflectors

D. A. Kellogg, N. Holonyak, and R. D. Dupuis

Appl. Phys. Lett. 77, 3152 (2000); http://dx.doi.org/10.1063/1.1326485 (3 pages)

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Data are presented on photopumped AlGaAs–GaAs quantum-well (QW) heterostructure lasers with oxide-semiconductor distributed Bragg reflector (DBR) vertical confinement (and Fabry–Perot cleaved edges) that reduces the mode volume and influences the edge emission (EE) spectra. For narrow samples (≲20 μm), with the vertical DBRs “tuned” below the QW recombination transitions (E1 lowest, E2 higher), single mode EE operation occurs on E2 at a wavelength ∼77 meV above the lowest QW energy. For wide samples with an oxide-semiconductor vertical DBR located in a narrow band at the sample cleave edges, the DBR region acts as a spacial and spectral filter, thus increasing the possibility of single-mode EE operation. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Mode-locked operation of the copper-doped germanium terahertz laser

J. N. Hovenier, R. M. de Kleijn, T. O. Klaassen, W. Th. Wenckebach, D. R. Chamberlin, E. Bründermann, and E. E. Haller

Appl. Phys. Lett. 77, 3155 (2000); http://dx.doi.org/10.1063/1.1326487 (3 pages) | Cited 6 times

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We have fabricated a copper-doped germanium laser using copper diffusion into commercially available pure germanium. The spectrum and the emission pulses of this laser were investigated. Active mode locking was achieved with pulse lengths of 160 ps at full width half maximum. The current Ge:Cu laser does not yet reach the performance of an earlier studied Ge:Ga laser although mode-locked Ge:Cu lasers promise much shorter pulse lengths and wavelength tunable pulses due to the absence of acceptor related absorption. Possibilities to optimize the laser will be discussed. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
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Temporal evolution of the shock wave and hot core air in laser induced plasma

Hugo Sobral, Mayo Villagrán-Muniz, Rafael Navarro-González, and Alejandro C. Raga

Appl. Phys. Lett. 77, 3158 (2000); http://dx.doi.org/10.1063/1.1324986 (3 pages) | Cited 57 times

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The temporal evolution of electric breakdown in air at atmospheric pressure by Nd:yttrium–aluminum–garnet Q-switched nanosecond laser pulses was studied from the nanosecond to the millisecond time scale by shadowgraphy and interferometry techniques. The results were modeled with a gasdynamic code with good agreement. It was possible to simultaneously model the whole evolution of the plasma, the shock wave, and the hot core air. The shock wave velocity was determined to be ≥ 60 km s−1 at 20 ns. The plasma temperature was found to reach about 1.7×104 K at 1 μs and the hot core air temperature was determined to be <103 K at 100 μs. This letter presents an experimental work that extends the study of laser induced plasmas to millisecond time scales. © 2000 American Institute of Physics.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.35.Tc Shock waves and discontinuities
52.25.-b Plasma properties
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Tensile strength of single-walled carbon nanotubes directly measured from their macroscopic ropes

F. Li, H. M. Cheng, S. Bai, G. Su, and M. S. Dresselhaus

Appl. Phys. Lett. 77, 3161 (2000); http://dx.doi.org/10.1063/1.1324984 (3 pages) | Cited 85 times

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20 mm long ropes consisting of soundly aligned single-walled carbon nanotube (SWNT) ropes, synthesized by the catalytic decomposition of hydrocarbons, were employed for direct tensile strength measurements. The average tensile strength of SWNT rope composites is as high as 3.6±0.4 GPa, similar to that of carbon fibers. The tensile strength of SWNT bundles was extrapolated from the strength of the composites to be 2.3±0.2 to 14.2±1.4 GPa after simply taking into account the volume fraction of SWNT bundles in the minicomposite, and the tensile strength of single SWNTs was estimated to be as high as 22.2±2.2 GPa. The excellent mechanical properties of SWNTs will make them an ideal reinforcement agent for high performance composite materials. © 2000 American Institute of Physics.
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62.20.F- Deformation and plasticity
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.05.ub Fullerenes and related materials
81.05.Cy Elemental semiconductors

Optical anisotropy of Langmuir–Blodgett sapphyrin films

C. Di Natale, C. Goletti, R. Paolesse, F. Della Sala, M. Drago, P. Chiaradia, P. Lugli, and A. D'Amico

Appl. Phys. Lett. 77, 3164 (2000); http://dx.doi.org/10.1063/1.1324983 (3 pages) | Cited 15 times

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The polarization dependence of the optical reflectivity for sapphyrin layers deposited by the Langmuir–Blodgett technique onto a gold substrate has been measured. The experimental results show that characteristic reflectance anisotropy spectroscopy (RAS) spectra are related to layers of different thicknesses. In order to interpret the measured spectral features, the anisotropy of the optical properties of the sapphyrin molecule has been evaluated by using a semi-empirical quantum chemistry approach. The results show clearly that the main RAS structures are related to the electronic properties of the sapphyrin molecules. In particular, two different regimes are observed. Below one (true) monolayer, the optical signal remains very low and structureless, in agreement with the sapphyrin molecules being stacked with their planes almost perpendicular to the substrate plane. Above one monolayer, instead, a strong RAS signal related to the Soret band develops, suggesting that sapphyrin molecules lay more parallel to the substrate surface, in an ordered fashion. © 2000 American Institute of Physics.
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78.20.-e Optical properties of bulk materials and thin films
78.66.Qn Polymers; organic compounds

Effects of growth conditions on the incorporation of oxygen in AlGaN layers grown by plasma assisted molecular beam epitaxy

C. R. Elsass, T. Mates, B. Heying, C. Poblenz, P. Fini, P. M. Petroff, S. P. DenBaars, and J. S. Speck

Appl. Phys. Lett. 77, 3167 (2000); http://dx.doi.org/10.1063/1.1325398 (3 pages) | Cited 20 times

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Using secondary ion mass spectroscopy we have shown that oxygen incorporation in AlGaN films is dependent upon the III/V growth conditions and the growth temperature of the films. AlGaN films grown under excess group III conditions (Ga-rich) exhibited step flow growth and at least a factor of 3 less oxygen incorporation than films grown under excess group V (N-rich conditions). We found that oxygen incorporation into AlGaN decreases as the growth temperature is increased. The lowest oxygen levels were achieved by growing at 750 °C under Ga-rich growth conditions. Possible sources of unwanted oxygen are discussed. © 2000 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Influence of Ti on CoSi2 nucleation

C. Detavernier, R. L. Van Meirhaeghe, F. Cardon, K. Maex, W. Vandervorst, and B. Brijs

Appl. Phys. Lett. 77, 3170 (2000); http://dx.doi.org/10.1063/1.1325401 (3 pages) | Cited 21 times

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Evidence is presented that impurities present in the precursor phase may influence the nucleation of a new phase. In case of the CoSi→CoSi2 transition, it is found that the presence of small amounts of Ti (originating from either a Ti capping layer or interlayer) causes an increase in the CoSi2 nucleation temperature. Moreover, for an increasing amount of Ti, we observed a transition from polycrystalline CoSi2 over preferential (220) orientation towards epitaxial (400) CoSi2. The model that we propose entails a new point of view on the mechanism of Ti interlayer mediated epitaxy. © 2000 American Institute of Physics.
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64.60.Q- Nucleation
68.55.-a Thin film structure and morphology

Well-defined nanostructure nucleation sites provided by the faceted TiC(111) surface

J. Günster, J. G. Heinrich, S. Dieckhoff, H. van Eys-Schäfer, S. Otani, and R. Souda

Appl. Phys. Lett. 77, 3173 (2000); http://dx.doi.org/10.1063/1.1326034 (3 pages) | Cited 1 time

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Reproducible growth of well-aligned nanostructures with an average nearest-neighbor distance of a few hundred nanometers is achieved on an array of strong nucleation sites provided by the facetted TiC(111) surface. The growth of the complex shaped nanostructures, composed out of carbon encapsulated TiCx crystallites interconnected by nanorods, 25 nm in diameter, is fed by the thermal decomposition of TiC. The length of the nanorods and the shape of the nanocrystallites is determined by the applied annealing program. © 2000 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
61.46.-w Structure of nanoscale materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.Cy Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
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As-cast quasicrystalline phase in a Zr-based multicomponent bulk alloy

U. Kühn, J. Eckert, N. Mattern, and L. Schultz

Appl. Phys. Lett. 77, 3176 (2000); http://dx.doi.org/10.1063/1.1326036 (3 pages) | Cited 41 times

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An icosahedral quasicrystalline phase is obtained directly from the melt by copper mold casting of a Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 alloy. On the other hand, rapid quenching of the alloy leads to an amorphous phase. Upon annealing, the amorphous structure precipitates quasicrystals in the first stage of crystallization. The microstructure of the quasicrystalline state is quite different for the two preparation routes, which is correlated with the asymmetry of the nucleation and growth rate upon cooling or heating. The quasicrystals formed upon slow cooling from the melt have a size of about 1 μm. In contrast, the quasicrystals formed by annealing do not exceed a size of 5–10 nm. © 2000 American Institute of Physics.
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61.44.Br Quasicrystals
81.30.Fb Solidification
64.70.D- Solid-liquid transitions
81.40.Gh Other heat and thermomechanical treatments

Mode transition between growth and decomposition of oxides on Si(001): Kinetically determined critical coverage for oxidation

Maki Suemitsu, Yoshiharu Enta, Youichi Takegawa, and Nobuo Miyamoto

Appl. Phys. Lett. 77, 3179 (2000); http://dx.doi.org/10.1063/1.1326037 (3 pages) | Cited 6 times

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Effects of preoxidation on the reaction kinetics of oxygen molecules at Si(001) surface have been investigated by real-time ultraviolet photoelectron spectroscopy. A mode transition from decomposition to growth of surface oxides was found to exist at a certain initial oxide coverage, which is kinetically, not energetically, determined. By considering a change of balance between Si adatom and oxygen-monomer fluxes at the perimeter of oxide clusters, this mode transition is quantitatively described as a bifurcation of an autocatalytic-reaction rate equation. © 2000 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.65.Mq Oxidation
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Analyses of electroluminescence spectra of silicon junctions in avalanche breakdown using an indirect interband recombination model

M. Lahbabi, A. Ahaitouf, E. Abarkan, M. Fliyou, A. Hoffmann, J.-P. Charles, Bharat L. Bhuva, S. E. Kerns, and D. V. Kerns

Appl. Phys. Lett. 77, 3182 (2000); http://dx.doi.org/10.1063/1.1326038 (3 pages) | Cited 6 times

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Light emission from a p-n junction biased in avalanche breakdown has been modeled over the range 1.4–3.4 eV. The model emphasizes indirect interband processes and Si self-absorption. Comparisons between measured and simulated spectra for sample junctions from multiple devices demonstrate that the model is simple, accurate, and consistent with fundamental physical device characteristics. © 2000 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.60.Fi Electroluminescence
73.50.Fq High-field and nonlinear effects
73.61.Cw Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
73.25.+i Surface conductivity and carrier phenomena
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.20.At Surface states, band structure, electron density of states

Electronic states of intrinsic layers in n-i-p solar cells near amorphous to microcrystalline silicon transition studied by photoluminescence spectroscopy

Guozhen Yue, Daxing Han, D. L. Williamson, Jeffrey Yang, Kenneth Lord, and Subhendu Guha

Appl. Phys. Lett. 77, 3185 (2000); http://dx.doi.org/10.1063/1.1325391 (3 pages) | Cited 18 times

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Thin film n-i-p solar cells were prepared using decomposition of disilane-hydrogen mixtures by plasma-enhanced chemical vapor deposition. By increasing either the H dilution ratio or the thickness, the i-layer structure showed a transition from amorphous to microcrystalline silicon characterized by x-ray diffraction. The electronic states of the i layer were examined by photoluminescence (PL) spectroscopy, which showed that: (a) below the onset of microcrystallinity, a blueshift of the 1.4 eV PL peak energy along with a decrease of the band width occur as the structural order is improved; (b) above the onset of microcrystallinity, the PL efficiency decreases by a factor of 4–5 and the PL peak energy is redshifted toward 1.2 eV as the μc-Si volume fraction is increased. In addition, the solar cell open circuit voltage shows first an increase and then a decrease, correlating with the PL peak energy position. We conclude that the PL spectroscopy is a sensitive tool for characterizing the gradual amorphous-to-microcrystalline structural transition in thin film solar cells. © 2000 American Institute of Physics.
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84.60.Jt Photoelectric conversion
61.43.Dq Amorphous semiconductors, metals, and alloys
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
71.55.Jv Disordered structures; amorphous and glassy solids
78.55.Ap Elemental semiconductors
78.66.Jg Amorphous semiconductors; glasses
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Db Elemental semiconductors and insulators

Diffusion of boron in silicon carbide: Evidence for the kick-out mechanism

H. Bracht, N. A. Stolwijk, M. Laube, and G. Pensl

Appl. Phys. Lett. 77, 3188 (2000); http://dx.doi.org/10.1063/1.1325390 (3 pages) | Cited 23 times

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We report diffusion experiments of implanted boron (B) in nitrogen-doped 4H- and aluminum-doped 6H-SiC which were performed at temperatures between 1700 and 1800 °C. Transient enhanced B diffusion caused by implantation damage was effectively suppressed by annealing of the B-implanted samples at 900 °C prior to the diffusion anneal. Concentration profiles of B measured with secondary ion mass spectrometry are accurately described on the basis of the kick-out mechanism. This provides strong evidence that Si self-interstitials mainly mediate B diffusion. © 2000 American Institute of Physics.
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66.30.J- Diffusion of impurities
61.72.up Other materials
61.72.Cc Kinetics of defect formation and annealing
61.72.Yx Interaction between different crystal defects; gettering effect
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
61.72.J- Point defects and defect clusters
61.72.S- Impurities in crystals

Improvement of interface formation between metal electrode and polymer film by polymer surface modification using ion sputtering

L. S. Liao, M. K. Fung, L. F. Cheng, C. S. Lee, S. T. Lee, M. Inbasekaran, E. P. Woo, and W. W. Wu

Appl. Phys. Lett. 77, 3191 (2000); http://dx.doi.org/10.1063/1.1325389 (3 pages) | Cited 6 times

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The surface of poly (9,9-dioctylfluorene) (PFO) film was modified by 1.0 keV Ar+ irradiation with a dose of 6.5×1014 ions/cm2 prior to Ca deposition. Ultraviolet and x-ray photoelectron spectroscopic studies indicated that the modified surface could effectively block Ca diffusion into the PFO film and prevent the formation of doping-induced bipolaron states in the former forbidden energy gap. As a result, a sharper metal contact on the surface of the PFO film could be formed, compared to that on the surface without Ar+ irradiation. The results suggest that the judicial surface modification of polymer surfaces may be useful for the improvement of metal/polymer contacts and thus device performance. © 2000 American Institute of Physics.
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79.60.Jv Interfaces; heterostructures; nanostructures
61.41.+e Polymers, elastomers, and plastics
68.35.Ct Interface structure and roughness
73.40.Ns Metal-nonmetal contacts
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.80.Jh Ion radiation effects

Scanning tunneling spectroscopy study of silicon and platinum assemblies in an opal matrix

C. Díaz-Guerra, J. Piqueras, V. G. Golubev, D. A. Kurdyukov, A. B. Pevtsov, and M. V. Zamoryanskaya

Appl. Phys. Lett. 77, 3194 (2000); http://dx.doi.org/10.1063/1.1325387 (3 pages) | Cited 12 times

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Scanning tunneling microscopy and scanning tunneling spectroscopy (STS) are used to investigate the local electronic behavior of Pt–Si nanostructures fabricated in an opal matrix formed by silica spheres of 250 nm diameter. Si and Pt are regularly distributed inside the opal pores and form nanoscale metal-semiconductor-metal junctions. Normalized differential conductance curves enable us to study the distribution of Pt and Si and to detect the presence of regions showing a surface band gap in the range 0.5–0.8 eV, possibly associated with the formation of silicides. STS appears as a suitable technique for the electrical characterization of opal-based nanostructures. © 2000 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
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
73.40.Sx Metal-semiconductor-metal structures
73.50.Fq High-field and nonlinear effects
68.35.Fx Diffusion; interface formation
73.61.Cw Elemental semiconductors

Evidence of a phase transition induced in zirconia by high energy heavy ions

A. Benyagoub, F. Levesque, F. Couvreur, C. Gibert-Mougel, C. Dufour, and E. Paumier

Appl. Phys. Lett. 77, 3197 (2000); http://dx.doi.org/10.1063/1.1326483 (3 pages) | Cited 20 times

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Monoclinic zirconia samples were irradiated with 300 MeV Ge and Ni ions at increasing ion fluences. Their structural evolution was monitored in situ by x-ray diffraction and ex situ by Raman spectroscopy. No amorphization of zirconia was observed in both cases. However, a transition from the monoclinic to the tetragonal phase was found in the case of Ge ion irradiation. On the contrary, no such effect was detected upon Ni ion irradiation. A comparison of these experiments indicates that the electronic energy loss released by swift heavy ion irradiation needs to be quite in excess of ∼12 keV nm−1 in order to induce a monoclinic to a tetragonal phase transition in pure (i.e., unstabilized) zirconia. © 2000 American Institute of Physics.
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61.80.Jh Ion radiation effects
61.82.Ms Insulators
61.50.Ks Crystallographic aspects of phase transformations; pressure effects
64.70.K- Solid-solid transitions
78.30.Hv Other nonmetallic inorganics

IrSiN films with superior oxygen-diffusion barrier effect for stacked ferroelectric capacitors

Shigeharu Matsushita, Mitsuaki Harada, Tatsuro Gueshi, and Yoshifumi Matsushita

Appl. Phys. Lett. 77, 3200 (2000); http://dx.doi.org/10.1063/1.1326480 (3 pages) | Cited 1 time

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IrSiN films (including IrSi film) formed by the reactive co-sputtering of Ir and Si targets have been investigated with regard to their oxygen-diffusion barriers in an application to stacked ferroelectric capacitors. The film properties and barrier effect were examined with relation to the N2/(Ar+N2) deposition flow ratio. In IrSiN films formed with a N2/(Ar+N2) flow ratio of 0.06 or 0.12, a shallow oxygen penetration depth of less than 20 nm was attained even under annealing in O2 at 800 °C for 40 min, and no reaction was observed with polycrystalline silicon (poly-Si) films. These films also adhered well to both poly-Si and SiO2 films. Therefore, the barriers are likely to prove extremely useful for integrated ferroelectric capacitors. © 2000 American Institute of Physics.
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77.55.-g Dielectric thin films
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
81.15.Cd Deposition by sputtering
68.35.Fx Diffusion; interface formation
84.32.Tt Capacitors
61.72.Cc Kinetics of defect formation and annealing

Direct observation of a local structural transition for molecular recording with scanning tunneling microscopy

D. X. Shi, Y. L. Song, H. X. Zhang, P. Jiang, S. T. He, S. S. Xie, S. J. Pang, and H.-J. Gao

Appl. Phys. Lett. 77, 3203 (2000); http://dx.doi.org/10.1063/1.1326481 (3 pages) | Cited 13 times

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We present a direct observation of a structural transition at molecular scale in an organic p-nitrobenzonitrile (PNBN) thin film using scanning tunneling microscopy (STM). STM images clearly show an ordered molecular structure of unrecorded regions in the films, while the PNBN molecular arrangements are disordered in the recorded regions. The current–voltage (I–V) measurements from the STM demonstrate a great increase of the conductance transition in the recorded regions after the voltage pulses. Those results suggest that the recording mechanism may be due to a crystalline structural transition, which is consistent with our previously proposed mechanism in another organic system for ultrahigh density data storage. © 2000 American Institute of Physics.
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64.70.K- Solid-solid transitions
68.55.Nq Composition and phase identification
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
85.65.+h Molecular electronic devices
72.60.+g Mixed conductivity and conductivity transitions
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