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13 Nov 2000

Volume 77, Issue 20, pp. 3131-3302

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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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