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3 Jul 2000

Volume 77, Issue 1, pp. 1-153

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Germanium/carbon core–sheath nanostructures

Yiying Wu and Peidong Yang

Appl. Phys. Lett. 77, 43 (2000); http://dx.doi.org/10.1063/1.126871 (3 pages) | Cited 35 times

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Germanium/carbon core–sheath nanostructures and junctions are produced when Ge nanowires are subject to a thermal treatment in an organic vapor doped vacuum. The organic molecules pyrolyze on the surface of the Ge nanowires and form a continuous graphitic coating. The carbon-sheathed Ge nanowires undergo melting and evaporation at high temperature, which results in the formation of germanium/carbon junctions. These core–sheath nanostructures and junctions generally have diameters of 5–100 nm, sheath thickness of 1–5 nm, and lengths up to several micrometers. This process may prove to be an effective approach to prevent the nanowire surface oxidation and create nanowires with chemically inert surface. © 2000 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.65.Mq Oxidation
68.35.Ct Interface structure and roughness
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
61.46.-w Structure of nanoscale materials

Ductility of bulk nanocrystalline composites and metallic glasses at room temperature

Cang Fan and Akihisa Inoue

Appl. Phys. Lett. 77, 46 (2000); http://dx.doi.org/10.1063/1.126872 (3 pages) | Cited 101 times

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Mechanical properties of bulk Zr60Cu20Pd10Al10 nanocrystalline composite and Zr55Ni5Cu30Al10 metallic glass were measured by compression tests at room temperature. The Zr60Cu20Pd10Al10 as-quenched alloy obviously exhibits plastic strain while no distinct plastic deformation is recognized in the Zr55Ni5Cu30Al10 metallic glass. Moreover, the plastic strain increased by increasing the volume fraction of nanocrystals and achieved maximum value in the early stage of the nanocrystallization. High-resolution electron microscopy showed that, different from the microstructure of Zr55Ni5Cu30Al10 metallic glass, nanocrystals with main grain sizes of about 2 nm were embedded in the amorphous matrix of the bulk Zr60Cu20Pd10Al10 alloy which showed the maximum plastic strain. © 2000 American Institute of Physics.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.43.Fs Glasses
61.46.-w Structure of nanoscale materials
81.05.Kf Glasses (including metallic glasses)
81.07.-b Nanoscale materials and structures: fabrication and characterization
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations

On the possibility of diamond wafer bonding in ultrahigh vacuum

D. Conrad, K. Scheerschmidt, and U. Gösele

Appl. Phys. Lett. 77, 49 (2000); http://dx.doi.org/10.1063/1.126873 (3 pages) | Cited 1 time

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The possibility of bonding clean diamond surfaces covalently in ultrahigh vacuum is investigated by molecular dynamics simulations based on a tight binding model. Our simulations predict that strong covalent bonding is possible for C(001)-2×1 surfaces. C(111)-2×1 surfaces will bond very weakly and debond already at moderate temperatures. © 2000 American Institute of Physics.
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81.05.ub Fullerenes and related materials
81.05.Cy Elemental semiconductors
68.35.Gy Mechanical properties; surface strains

Thermoelectric properties of Sn-filled skutterudites

G. S. Nolas, H. Takizawa, T. Endo, H. Sellinschegg, and D. C. Johnson

Appl. Phys. Lett. 77, 52 (2000); http://dx.doi.org/10.1063/1.126874 (3 pages) | Cited 59 times

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Thermal conductivity, resistivity, Seebeck coefficient, and structure measurements of CoSb3 with tin interstitially placed in the voids are reported. These tin-filled skutterudites were synthesized under high pressure and temperature conditions; they cannot be synthesized under “normal” synthesis approaches. The tin atoms exhibit very large atomic displacement parameters indicating a large “rattling” motion inside their atomic “cages.” The disorder induced by the Sn atoms is a very good phonon scattering mechanism. The thermal conductivity of these compounds is very low with a temperature dependence that is atypical of simple solids. The tin-filled compounds exhibit n-type semiconducting behavior with relatively high Seebeck coefficients for compounds whose electronic properties have not been optimized. The potential for thermoelectric applications is discussed. © 2000 American Institute of Physics.
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72.20.Pa Thermoelectric and thermomagnetic effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
61.72.Qq Microscopic defects (voids, inclusions, etc.)
63.20.K- Phonon interactions
72.80.Jc Other crystalline inorganic semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance

Band-tail photoluminescence in nanocrystalline Si

A. Kaan Kalkan, S. J. Fonash, and Shang-Cong Cheng

Appl. Phys. Lett. 77, 55 (2000); http://dx.doi.org/10.1063/1.126875 (3 pages) | Cited 4 times

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The characteristic subgap photoluminescence (PL) observed in nanocrystalline Si films was found to shift to higher energies with increasing optical gap and decreasing crystallite size. This behavior, along with the temperature dependence of the PL, is consistent with transitions between band-tail states in the energy gap of the crystallites. The PL bandwidth is too broad to be explained by the tail width as deduced from the temperature behavior. Hence, the broadening is ascribed to electron–phonon coupling, while the related Stokes shift was found to increase with decreasing crystallite size, possibly due to decreasing exciton size. © 2000 American Institute of Physics.
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78.55.Ap Elemental semiconductors
71.20.Mq Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.46.-w Structure of nanoscale materials
73.22.-f Electronic structure of nanoscale materials and related systems
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
63.20.K- Phonon interactions
71.38.-k Polarons and electron-phonon interactions

Large optical nonlinearity and fast response time in low-temperature grown GaAs/AlAs multiple quantum wells

Tsuyoshi Okuno, Yasuaki Masumoto, Masashi Ito, and Hiroshi Okamoto

Appl. Phys. Lett. 77, 58 (2000); http://dx.doi.org/10.1063/1.126876 (3 pages) | Cited 8 times

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We have investigated optical nonlinearity in low-temperature (LT) molecular-beam-epitaxy-grown GaAs/AlAs multiple quantum wells (MQWs). Minimum saturation intensity, that is, maximum optical nonlinearity, is observed at around the excitonic absorption peak. The saturation intensity of the LT MQW is smaller by an order of magnitude than that of LT bulk GaAs. The response time of the LT MQW is 1/4–1/2 of the LT GaAs, and becomes less than 1 ps, corresponding to ∼1/400 of the standard-temperature-grown MQW. These results demonstrate a clear advantage of the room-temperature excitons in the LT MQW having large optical nonlinearity as well as fast response time. © 2000 American Institute of Physics.
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42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Effect of charge carriers on the barrier height for vacancy formation on InP(110) surfaces

U. Semmler, Ph. Ebert, and K. Urban

Appl. Phys. Lett. 77, 61 (2000); http://dx.doi.org/10.1063/1.126877 (3 pages) | Cited 6 times

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We determine the energy barrier height for the formation of positively charged phosphorus vacancies in InP(110) surfaces using the rate of formation of vacancies measured directly from scanning tunneling microscope images. We found a barrier height in the range of 1.15–1.21 eV. The barrier height decreases with increasing carrier concentration. These results are explained by a charge separation during the vacancy formation process. © 2000 American Institute of Physics.
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61.72.J- Point defects and defect clusters
68.35.B- Structure of clean surfaces (and surface reconstruction)
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Ey III-V and II-VI semiconductors

Formation of amorphous nanostructured materials by liquid state spinodal decomposition

C. C. Leung, W. H. Guo, and H. W. Kui

Appl. Phys. Lett. 77, 64 (2000); http://dx.doi.org/10.1063/1.126878 (3 pages) | Cited 12 times

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As molten Pd40.5Ni40.5P19 is undercooled to a temperature T that is well below its liquidus Tl, liquid state spinodal decomposition takes place. If T is far away from Tl, wavelength λ of the liquid spinodals can be less than 100 nm. At this point, if water quenching is applied, upon solidification the final morphology consists of multiple amorphous networks intertwined with each other. © 2000 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
61.43.Fs Glasses
81.05.Kf Glasses (including metallic glasses)
61.46.-w Structure of nanoscale materials
64.75.-g Phase equilibria
64.70.D- Solid-liquid transitions
81.30.Fb Solidification
81.05.Bx Metals, semimetals, and alloys

Blue–violet photoluminescence from large-scale highly aligned boron carbonitride nanofibers

X. D. Bai, E. G. Wang, J. Yu, and Hui Yang

Appl. Phys. Lett. 77, 67 (2000); http://dx.doi.org/10.1063/1.126879 (3 pages) | Cited 45 times

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We report on the strong blue–violet photoluminescence (PL) at room temperature from the large-scale highly aligned boron carbonitride (BCN) nanofibers synthesized by bias-assisted hot filament chemical vapor deposition. The photoluminescence peak wavelength shifts in the range of 470–390 nm by changing the chemical composition of the BCN nanofibers, which shows an interesting blue and violet-light-emitting material with adjustable optical properties. The mechanism for the shift of the PL peaks at room temperature is also discussed. © 2000 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
78.66.Vs Fine-particle systems

Nonuniform bulk second-order optical nonlinearity in PbO/B2O3 glass

Zhiling Xu, Liying Liu, Yue Fei, Peng Yang, Zhanjia Hou, Lei Xu, Wencheng Wang, Jong Wook Lim, Mario Affatigato, and Steve Feller

Appl. Phys. Lett. 77, 70 (2000); http://dx.doi.org/10.1063/1.126880 (3 pages) | Cited 3 times

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Second-order nonlinearity (SON) of thermally poled PbO/B2O3 glass was investigated. The SON distribution within the glass was obtained by repeatedly grinding the poled glass and measuring its Maker fringes. After grinding away up to one third of the thickness of the poled sample, i.e., about 300 μm, clear fringes with the interference minimum not equal to zero could still be observed, indicating that the area of SON was not confined within thin layers near the two surfaces. Cathode side grinding and anode side grinding had quite different influences on the SON of the poled sample. A model of the anode-charge-layer dependent bulk electric field distribution was proposed and this electric field was regarded as playing a key role in the generation of a nonuniform bulk SON distribution in PbO/B2O3 glass. © 2000 American Institute of Physics.
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42.65.-k Nonlinear optics
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.20.Jq Electro-optical effects
81.05.Kf Glasses (including metallic glasses)
42.70.Ce Glasses, quartz

Nanoscale icosahedral quasicrystalline phase formation in a rapidly solidified Zr80Pt20 binary alloy

Junji Saida, Mitsuhide Matsushita, and Akihisa Inoue

Appl. Phys. Lett. 77, 73 (2000); http://dx.doi.org/10.1063/1.126881 (3 pages) | Cited 44 times

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It is found that an icosahedral quasicrystalline phase is directly formed in a Zr80Pt20 binary alloy during rapid solidification from the melt. The size of the icosahedral particles lies in the diameter range below 10 nm, and the particles are distributed homogeneously. The formation of the nanoscale icosahedral phase indicates that the icosahedral short-range order exists in the melted state of Zr–Pt binary alloy. The strong chemical affinity between Zr and Pt contributes to the restraint of the long-range rearrangement of constitutional elements to form a stable crystalline phase, which is the important factor of the stabilization of an icosahedral phase. © 2000 American Institute of Physics.
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61.44.Br Quasicrystals
81.30.Fb Solidification
81.05.Bx Metals, semimetals, and alloys

Protection of SrBi2Ta2O9 ferroelectric capacitors from hydrogen damage by optimized metallization for memory applications

Suk-Kyoung Hong, Chung Won Suh, Chang Goo Lee, Seok Won Lee, Eung Youl Kang, Nam Soo Kang, Cheol Seong Hwang, and Oh Seong Kwon

Appl. Phys. Lett. 77, 76 (2000); http://dx.doi.org/10.1063/1.126882 (3 pages) | Cited 12 times

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The degradation behavior of integrated Pt/SrBi2Ta2O9/Pt capacitors by hydrogen impregnation during the intermetal dielectric deposition and passivation is investigated. The hydrogen ions generated as a reaction byproduct from the SiH4-based deposition processes of the dielectric films induce reduction in the remanent polarization (Pr) as well as the imprint behavior of the small size capacitors (2×2 μm2). The degree of degradation is quite dependent on the size of the individual capacitors. The smaller capacitors underwent more serious degradation implying that the hydrogen ions impregnate into the SBT layer mainly along the etched side area of the capacitors not through the top Pt electrode. Metallization adopting TiN/Al/TiN/Ti multilayer is very effective in suppressing the hydrogen impregnation. In particular, the Ti layer appears to block the hydrogen penetration. Therefore, the optimized metallization scheme, wider metal lines than the top electrode area by 1 μm, successfully protects the integrated capacitors from the hydrogen damage. 12 μC/cm2 of 2Pr and 1.1 V of 2Vc (coercive voltage) with an imprinting voltage of 0.16 V were obtained from the passivated 2×2 μm2 array capacitors by the optimized metallization. © 2000 American Institute of Physics.
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84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
85.40.Ls Metallization, contacts, interconnects; device isolation
84.30.Sk Pulse and digital circuits
77.22.Ej Polarization and depolarization

Dispersion of metal nanoparticles for aligned carbon nanotube arrays

Hiroki Ago, Toshiki Komatsu, Satoshi Ohshima, Yasunori Kuriki, and Motoo Yumura

Appl. Phys. Lett. 77, 79 (2000); http://dx.doi.org/10.1063/1.126883 (3 pages) | Cited 51 times

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We report that Co metal nanoparticles (an average diameter of 4 nm) chemically synthesized by a reverse micelle method catalyzes the growth of multiwall carbon nanotubes (MWNTs) aligned perpendicular to a substrate. The surface of the nanoparticles is covered with surfactants so that the nanoparticles can be dispersed in organic solvent. The dispersion of the nanoparticles was cast directly onto a plane Si substrate for thermal pyrolysis of acetylene. We have found that the pretreatment of the metal nanoparticles with hydrogen sulfide before the pyrolysis straightens the MWNTs, suggesting sulfurization of the nanoparticle catalyst plays an important role in regular growth of the MWNTs. The dispersion of the nanoparticles offers a conventional and processible approach to synthesize large area aligned MWNT arrays. © 2000 American Institute of Physics.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.05.ub Fullerenes and related materials
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Origin of hexagonal-shaped etch pits formed in (0001) GaN films

S. K. Hong, T. Yao, B. J. Kim, S. Y. Yoon, and T. I. Kim

Appl. Phys. Lett. 77, 82 (2000); http://dx.doi.org/10.1063/1.126884 (3 pages) | Cited 39 times

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We report the origin of hexagonal-shaped etch pits generally observed by conventional wet etching processes on (0001) GaN-based films based on the investigation with transmission electron microscopy on GaN films after being etched with molten KOH. The origin of hexagonal-shaped etch pits is identified as nanopipes through careful characterization of abnormal contrast of nanopipe (open-core screw dislocation), “lobe contrast” of end-on edge and screw (full-core) dislocations, visible and invisible conditions of edge and screw dislocations. Consideration of energetics of these defects also suggests preferential etch pit formation at nanopipes because of much higher energy. © 2000 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations

Polarized luminescence in CdS/ZnSe quantum-well structures

M. Schmidt, M. Grün, S. Petillon, E. Kurtz, and C. Klingshirn

Appl. Phys. Lett. 77, 85 (2000); http://dx.doi.org/10.1063/1.126885 (3 pages) | Cited 15 times

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The photoluminescence from type II CdS/ZnSe quantum-well structures is found to be polarized with respect to the 〈110〉 directions with polarization degrees up to 20%. The absolute polarization direction is related to the interface bond directions in samples with differently prepared interfaces. The observations are explained by the detailed analysis of the epitaxial growth process and polarization sensitive luminescence experiments. © 2000 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors

Effective surface Debye temperature for NiMnSb(100) epitaxial films

C. N. Borca, Takashi Komesu, Hae-kyung Jeong, P. A. Dowben, D. Ristoiu, Ch. Hordequin, J. Pierre, and J. P. Nozières

Appl. Phys. Lett. 77, 88 (2000); http://dx.doi.org/10.1063/1.126886 (3 pages) | Cited 30 times

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The surface Debye temperature of the NiMnSb (100) epitaxial films has been obtained using low energy electron diffraction, inverse photoemission, and core-level photoemission. The normal dynamic motion of the (100) surface results in a value for the effective surface Debye temperature of 145±13 K. This is far smaller than the bulk Debye temperature of 312±5 K obtained from wave vector dependent inelastic neutron scattering. The large difference between these measures of surface and bulk dynamic motion indicates a soft and compositionally different (100) surface. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
68.35.Ja Surface and interface dynamics and vibrations
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Single titanium crystals encapsulated in carbon nanocages obtained by laser vaporization of sponge titanium in benzene vapor

Hong Chen, Rong-bin Huang, Zi-chao Tang, Lan-sun Zheng, Guang-wen Zhou, and Ze Zhang

Appl. Phys. Lett. 77, 91 (2000); http://dx.doi.org/10.1063/1.126887 (3 pages) | Cited 3 times

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A technique, laser vaporization by ablating at a solid target in the vapor phase, is developed to produce encapsulated titanium nanocrystals. By vaporizing sponge titanium in benzene vapor, the single titanium crystals encapsulated in carbon nanocages have been synthesized in good yields. The sizes of the encapsulated crystals are around 5–15 nm and the numbers of the wrapped graphitic layers are on the order of 3–10 layers. Characteristic lattice spacings and angles observed by high-resolution transmission electron microscopy identify two phases of the nanocrystals inside the carbon onion cavities as α-Ti and β-Ti. The latter has never been stable below 850 °C until the experiment. The encapsulated titanium crystals adsorbed a large amount of hydrogen released in the synthesis. © 2000 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
73.22.-f Electronic structure of nanoscale materials and related systems
64.70.Hz Solid-vapor transitions
79.20.Ds Laser-beam impact phenomena
81.05.Bx Metals, semimetals, and alloys
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