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1 Feb 2005

Volume 97, Issue 3, Articles (03xxxx)

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Manipulation and detection of single electrons for future information processing

Yukinori Ono, Akira Fujiwara, Katsuhiko Nishiguchi, Hiroshi Inokawa, and Yasuo Takahashi

J. Appl. Phys. 97, 031101 (2005); http://dx.doi.org/10.1063/1.1843271 (19 pages) | Cited 34 times

Online Publication Date: 19 January 2005

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The ultimate goal of future information processing might be the realization of a circuit in which one bit is represented by a single electron. Such a challenging circuit would comprise elemental devices whose tasks are to drag, transfer, and detect single electrons. In achieving these tasks, the Coulomb blockade, which occurs in tiny conducting materials, plays an important role. This paper describes the current status of research on such single-charge-control devices from the viewpoints of circuit applications.
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85.35.Gv Single electron devices
85.30.Tv Field effect devices
85.35.Ds Quantum interference devices
84.30.Sk Pulse and digital circuits
73.23.Hk Coulomb blockade; single-electron tunneling
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Theory of bright-field scanning transmission electron microscopy for tomography

Zachary H. Levine

J. Appl. Phys. 97, 033101 (2005); http://dx.doi.org/10.1063/1.1828604 (12 pages) | Cited 4 times

Online Publication Date: 5 January 2005

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Radiation transport theory is applied to electron microscopy of samples composed of one or more materials. The theory, originally due to Goudsmit and Saunderson, assumes only elastic scattering and an amorphous medium dominated by atomic interactions. For samples composed of a single material, the theory yields reasonable parameter-free agreement with experimental data taken from the literature for the multiple scattering of 300-keV electrons through aluminum foils up to 25 μm thick. For thin films, the theory gives a validity condition for Beer’s law. For thick films, a variant of Molière’s theory [ V. G. Molière, Z. Naturforschg. 3a, 78 (1948) ] of multiple scattering leads to a form for the bright-field signal for foils in the multiple-scattering regime. The signal varies as [t ln(e1−2γt/τ)]−1 where t is the path length of the beam, τ is the mean free path for elastic scattering, and γ is Euler’s constant. The Goudsmit–Saunderson solution interpolates numerically between these two limits. For samples with multiple materials, elemental sensitivity is developed through the angular dependence of the scattering. From the elastic scattering cross sections of the first 92 elements, a singular-value decomposition of a vector space spanned by the elastic scattering cross sections minus a delta function shows that there is a dominant common mode, with composition-dependent corrections of about 2%. A mathematically correct reconstruction procedure beyond 2% accuracy requires the acquisition of the bright-field signal as a function of the scattering angle. Tomographic reconstructions are carried out for three singular vectors of a sample problem with four elements Cr, Cu, Zr, and Te. The three reconstructions are presented jointly as a color image; all four elements are clearly identifiable throughout the image.
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68.37.Lp Transmission electron microscopy (TEM)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Photonic states deep into the waveguide cutoff frequency of metallic mesh photonic crystal filters

Hong-Yi Sang, Zhi-Yuan Li, and Ben-Yuan Gu

J. Appl. Phys. 97, 033102 (2005); http://dx.doi.org/10.1063/1.1850993 (7 pages) | Cited 8 times

Online Publication Date: 18 January 2005

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We examine the optical properties of three-dimensional metallic photonic crystals made from a periodic stacking of thin metallic mesh layers separated by homogeneous dielectric films by means of a combination of the plane-wave-based transfer-matrix method and analytical modal solution approach. Although each metallic mesh layer can serve as a frequency-selective surface and involves an intrinsic long-wavelength waveguide cutoff to electromagnetic waves, pass bands and new band gaps can exist far below the cutoff frequency due to the global coupling effect among different mesh layers. The results for the transmission spectra and photonic band structures are in good agreement with existing experimental measurements. It is found that the position of the pass bands and band gaps strongly depends on the thickness and composite of the separation layer between the adjacent metallic mesh layers.
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42.70.Qs Photonic bandgap materials
41.20.Jb Electromagnetic wave propagation; radiowave propagation
78.70.Gq Microwave and radio-frequency interactions

Few modes in infrared photonic crystal fibers

E. Rave, S. Sade, A. Millo, and A. Katzir

J. Appl. Phys. 97, 033103 (2005); http://dx.doi.org/10.1063/1.1845583 (6 pages) | Cited 3 times

Online Publication Date: 19 January 2005

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Photonic crystal fibers guide light by trapping it in a periodic array of elements in the cladding area. We fabricated photonic crystal fibers by multiple extrusions of silver halide (AgClxBr1−x) crystals which are highly transparent in the middle infrared. The core of such a fiber consisted of pure silver bromide AgBr (n = 2.16 at 10.6 μm), and the cladding area consisted of concentric rings of fiber-optic elements made of pure silver chloride AgCl (n = 1.98 at 10.6 μm), which lowered the refractive index of the clad. Two types of photonic crystal fibers were fabricated, one with two concentric rings and one with five concentric rings of fiber-optic elements around the core. The characterization of the fibers, such as the power distribution, the attenuation, and the numerical aperture were measured. Both fibers behaved like regular core-clad structures. Simulations on these structures showed that each of these fibers guided a small number of modes and that adding rings to the structure lowered the number of bound modes in the core. This would pave the way for the fabrication of single-mode fibers. Photonic crystal fibers offer many advantages compared to conventional fibers, and they will be extremely useful for many applications in the middle and far infrared.
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42.81.Bm Fabrication, cladding, and splicing
42.70.Qs Photonic bandgap materials
42.81.Dp Propagation, scattering, and losses; solitons
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics
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Noninvasive monitoring of ion energy drift in an inductively coupled plasma reactor

Mark A. Sobolewski

J. Appl. Phys. 97, 033301 (2005); http://dx.doi.org/10.1063/1.1834977 (12 pages) | Cited 7 times

Online Publication Date: 30 December 2004

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A noninvasive method for monitoring ion current and ion kinetic energy has been used to monitor drift in an inductively coupled, rf-biased plasma reactor. The technique detects a slow decrease in ion current over time caused by the deposition of a conductive layer on the dielectric window of the inductive source. Accompanying this drift in ion current are changes in ion energy which, depending on conditions, may be large or small, increasing or decreasing. The changes in ion energy are explained by three different kinds of mechanisms: bias voltage effects, sheath impedance effects, and ion transit-time effects. For each mechanism, a simple analysis is given that allows one to estimate the resulting drift in ion energy for a given drift in ion current. The mechanisms of ion energy drift, and the monitoring technique itself, are not limited to the particular experimental conditions of this study; rather, they apply to a wide range of plasmas and reactors. Drifts in ion energy caused by the mechanisms reported here have undoubtedly occurred in many plasma reactors but have gone largely or entirely unnoticed for lack of any reliable method to detect them.
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52.70.Ds Electric and magnetic measurements
52.35.Kt Drift waves
52.25.Fi Transport properties
52.40.Kh Plasma sheaths
52.58.-c Other confinement methods
52.75.-d Plasma devices

Excessive Balmer line broadening in a plane cathode abnormal glow discharge in hydrogen

N. Cvetanović, M. M. Kuraica, and N. Konjević

J. Appl. Phys. 97, 033302 (2005); http://dx.doi.org/10.1063/1.1846139 (8 pages) | Cited 25 times

Online Publication Date: 18 January 2005

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Results of a Doppler spectroscopy study of the hydrogen Balmer alpha line in an abnormal glow discharge operated in pure hydrogen are reported. Measurements of line shapes are performed side-on to the discharge axis in a low electric field region of negative glow. The excessive Balmer alpha broadening is detected and its presence and linewidth is related to the collisions of fast hydrogen atoms with molecular hydrogen. The collision model enabled also an estimation of effective cross section data from the Balmer alpha axial intensity decay curves. Large excessive Balmer alpha line broadening in pure hydrogen and its dependence upon the direction of observation with respect to the electric field is in contradiction to the resonance transfer model, proposed byMills et al. in several publications [see, e.g., IEEE Trans. Plasma Sci. 31, 338 (2003)].
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52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.80.Hc Glow; corona
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Raman study of phonons in bismuth triborate BiB3O6 crystal

Xiaobo Hu, Jiyang Wang, Bing Teng, Chun-Keung Loong, and Marcos Grimsditch

J. Appl. Phys. 97, 033501 (2005); http://dx.doi.org/10.1063/1.1823573 (5 pages) | Cited 4 times

Online Publication Date: 30 December 2004

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A Raman-scattering study of the vibrational modes in a BiB3O6 crystal was conducted at room temperature. The numbers of external and internal modes obtained in experiment are consistent with the results of a group theoretical analysis. The Raman lines below ∼ 300 cm−1 and from ∼ 300 to 1600 cm−1 are assigned to the external modes of the lattice and internal vibrations of the BO3 and BO4 subunits of the BiB3O6 structure, respectively.
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42.70.Mp Nonlinear optical crystals
78.30.Hv Other nonmetallic inorganics
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
61.66.Fn Inorganic compounds

Interface and confined optical-phonon modes in wurtzite multi-interface heterostructures

J. T. Lü and J. C. Cao

J. Appl. Phys. 97, 033502 (2005); http://dx.doi.org/10.1063/1.1829142 (5 pages) | Cited 13 times

Online Publication Date: 30 December 2004

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Interface and confined optical-phonon modes in wurtzite multi-interface heterostructures are studied numerically based on the dielectric continuum model and Loudon’s uniaxial crystal model. The phonon dispersion relation and electrostatic potential are calculated using the transfer matrix method. The anisotropic characteristics of wurtzite phonons are demonstrated. The electron-optical-phonon Fröhlich interaction is studied in a fully numerical manner. The dispersion relation is taken into account in the derivation of Fermi’s golden rule. The method presented here is general and can be easily applied to the design and simulation of optoelectronic devices based on wurtzite multi-interface heterostructures.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
63.20.K- Phonon interactions
68.35.Ja Surface and interface dynamics and vibrations

Discerning between bulk diffusion and surface crossing in diffusion measurements

Z. Burshtein and M. Sinder

J. Appl. Phys. 97, 033503 (2005); http://dx.doi.org/10.1063/1.1832746 (5 pages)

Online Publication Date: 30 December 2004

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We propose a method for experimentally discerning between impurity bulk diffusion and surface crossing by a systematic study of diffusion in bulk samples of varying dimensions: varying thickness for the case of plane-parallel plates and varying radii for spheres and long cylinders.
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46.70.De Beams, plates, and shells
66.30.J- Diffusion of impurities
61.72.S- Impurities in crystals
68.35.Fx Diffusion; interface formation

Influence of gaseous annealing environment on the properties of indium-tin-oxide thin films

R. X. Wang, C. D. Beling, S. Fung, A. B. Djurišić, C. C. Ling, and S. Li

J. Appl. Phys. 97, 033504 (2005); http://dx.doi.org/10.1063/1.1834984 (5 pages) | Cited 23 times

Online Publication Date: 30 December 2004

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The influence of postannealing in different gaseous environments on the optical properties of indiu-tin-oxide (ITO) thin films deposited on glass substrates using e-beam evaporation has been systematically investigated. It is found that the annealing conditions affect the optical and electrical properties of the films. Atomic force microscopy, x-ray diffraction, and x-ray photoemission spectroscopy (XPS) were employed to obtain information on the chemical state and crystallization of the films. These data suggest that the chemical states and surface morphology of the ITO film are strongly influenced by the gaseous environment during the annealing process. The XPS data indicate that the observed variations in the optical transmittance can be explained by oxygen incorporation into the film, decomposition of the indium oxide phases, as well as the removal of metallic In.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
61.72.Cc Kinetics of defect formation and annealing
78.66.Nk Insulators
73.61.Ng Insulators
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.50.Dn Low-field transport and mobility; piezoresistance
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.37.Ps Atomic force microscopy (AFM)
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Dp Adsorbed layers and thin films

Near-field second-harmonic imaging of magnetic domains

W. Dickson, S. Takahashi, D. McHugh, R. Atkinson, R. Pollard, and A. V. Zayats

J. Appl. Phys. 97, 033505 (2005); http://dx.doi.org/10.1063/1.1841465 (7 pages) | Cited 2 times

Online Publication Date: 30 December 2004

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The principles and mechanisms of scanning near-field microscopy of second-harmonic generation from ferromagnetic films have been investigated. Magnetic domain image formation in near-field second-harmonic microscopy is discussed and the role of the probe tip is considered. It is shown that magnetic contrast can be achieved in the second-harmonic intensity measurements in both the transverse and longitudinal magnetization configurations for both polarizations of the fundamental light. This is related to the electromagnetic near-field properties in the vicinity of the probe tip and the electromagnetic interaction between a tip and a surface. The capabilities of this imaging approach have been illustrated using magnetic domain structures in thin Co and Ni films. The near-field second-harmonic distributions obtained with p-polarized excitation light are strongly correlated to the topography of the films. At the same time, the images obtained with s-polarized excitation light are much less sensitive to the topography.
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75.50.Cc Other ferromagnetic metals and alloys
68.55.-a Thin film structure and morphology
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.20.Ls Magneto-optical effects
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ch Domain walls and domain structure
75.60.Jk Magnetization reversal mechanisms
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Uv Near-field scanning microscopy and spectroscopy
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Creation and annihilation of free volume during homogeneous flow of a metallic glass

Marc Heggen, Frans Spaepen, and Michael Feuerbacher

J. Appl. Phys. 97, 033506 (2005); http://dx.doi.org/10.1063/1.1827344 (8 pages) | Cited 44 times

Online Publication Date: 30 December 2004

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Bulk samples of Pd41Ni10Cu29P20 glass were tested at constant true stress (20–636 MPa) in compression at 550, 555, and 565 K to study the transition from steady-state creep at low stress to deformation-induced softening at high stress. In the high-stress regime strongly accelerating creep was observed. All deformation was homogeneous. The activation volume was 106 Å3. The isoconfigurational activation energy was 9.03±0.64 eV. The disordering rate is proportional to the applied power density (stress×strain rate). The disordering process is inefficient in energy and in the production of free volume.
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81.40.Lm Deformation, plasticity, and creep
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.Hg Creep
62.20.F- Deformation and plasticity

Raman-scattering and structure investigations on porous SiC layers

T. V. Torchynska, A. Vivas Hernandez, A. Diaz Cano, S. Jiménez-Sandoval, S. Ostapenko, and M. Mynbaeva

J. Appl. Phys. 97, 033507 (2005); http://dx.doi.org/10.1063/1.1840095 (4 pages) | Cited 9 times

Online Publication Date: 30 December 2004

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Raman scattering spectroscopy, scanning electron microscopy, and scanning acoustic microscopy were studied on porous SiC layers prepared by different technological routes and subjected to reactive ion treatment. The Raman spectra revealed a number of features specific for nanocrystallite materials, which can be used for characterization and diagnostics of porous SiC layers for technological applications.
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68.55.-a Thin film structure and morphology
78.30.Hv Other nonmetallic inorganics
61.43.Gt Powders, porous materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Tj Acoustic force microscopy

Suppression of oxygen diffusion by thin Al2O3 films grown on SrTiO3 studied using a monoenergetic positron beam

A. Uedono, M. Kiyohara, N. Yasui, and K. Yamabe

J. Appl. Phys. 97, 033508 (2005); http://dx.doi.org/10.1063/1.1836010 (5 pages) | Cited 3 times

Online Publication Date: 30 December 2004

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The annealing behaviors of oxygen vacancies introduced by the epitaxial growth of thin SrTiO3 and Al2O3 films on SrTiO3 substrates were studied by using a monoenergetic positron beam. The films were grown by molecular-beam epitaxy without using an oxidant. The Doppler broadening spectra of the annihilation radiation were measured as a function of the incident positron energy for samples fabricated under various growth conditions. The line-shape parameter S, corresponding to the annihilation of positrons in the substrate, was increased by the film growth, suggesting diffusion of oxygen from the substrate into the film and a resultant introduction of vacancies (mainly oxygen vacancies). A clear correlation between the value of S and the substrate conductivity was obtained. From isochronal annealing experiments, the Al2O3 thin film was found to suppress the penetration of oxygen from the atmosphere for annealing temperatures below 600 °C. Degradation of the film’s oxygen blocking property occurred due to the annealing at 700 °C, and this was attributed to the oxidation of the Al2O3 by the atmosphere and the resultant introduction of vacancy-type defects.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.35.Fx Diffusion; interface formation
61.80.Fe Electron and positron radiation effects
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.70.Bj Positron annihilation
78.66.Nk Insulators
73.61.Ng Insulators
61.72.J- Point defects and defect clusters
81.40.Gh Other heat and thermomechanical treatments

Impact of oxygen on carbon precipitation in polycrystalline ribbon silicon

Jinggang Lu, George Rozgonyi, Axel Schönecker, Astrid Gutjahr, and Zhenxian Liu

J. Appl. Phys. 97, 033509 (2005); http://dx.doi.org/10.1063/1.1847699 (4 pages) | Cited 3 times

Online Publication Date: 5 January 2005

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This article reports experimental evidence for the effect of oxygen on carbon precipitation in polycrystalline ribbon silicon. Four sets of wafers subject to various heat treatments have been examined by infrared spectroscopy. It is found that carbon precipitation in an oxygen-containing wafer consists of two distinct steps, namely, an initial rapid oxygen–carbon coprecipitation in the very first hour annealing, followed by slow precipitation during subsequent prolonged annealing. A high oxygen content enhances carbon precipitation throughout the two steps. It is shown that the formation of interstitial carbon in the presence of excess silicon self-interstitials generated during oxygen precipitation plays an important role in increasing the carbon precipitation rate in the first hour annealing. Because of the absence of interstitial injection during the following slow precipitation process, the enhancement effect of oxygen can only arise from an increase in precipitation sites. It is proposed that the oxygen–carbon coprecipitates formed in the very first hour annealing provide sites for continuous carbon precipitation. This explains why carbon impurities precipitate faster in a high oxygen-containing wafer, even after removal of all the interstitial oxygen from the silicon matrix.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
64.75.-g Phase equilibria
61.72.Cc Kinetics of defect formation and annealing
78.66.Db Elemental semiconductors and insulators
78.30.Am Elemental semiconductors and insulators
61.72.J- Point defects and defect clusters
61.72.S- Impurities in crystals
66.30.J- Diffusion of impurities
66.30.Lw Diffusion of other defects

Interlayer-related paramagnetic defects in stacks of ultrathin layers of SiOx, Al2O3, ZrO2, and HfO2 on (100)Si

A. Stesmans and V. V. Afanas’ev

J. Appl. Phys. 97, 033510 (2005); http://dx.doi.org/10.1063/1.1818718 (8 pages) | Cited 20 times

Online Publication Date: 5 January 2005

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An electron spin resonance (ESR) study has been carried out of the influence of postdeposition heating on stacks of (100)Si with nanometer-thick dielectric layers of SiOx and atomic-layer-deposited Al2O3, ZrO2, and HfO2. This reveals upon postdeposition oxidation (PDO) in the range 650–800 °C the appearance of various SiO2-characteristic defects, including E′, EX, and a 95-G doublet, in different intensities with increasing anneal temperature, attesting to significant modification and∕or additional SiOx interlayer growth. The revealed defects enable probing of the quality of the interlayer on atomic level. In terms of the E′ criterion, it is found that the SiOx interlayer formed in (100)Si/SiOx/ZrO2 is drastically inferior to standard thermal (100)Si/SiO2, exhibiting over one order of magnitude more O-deficiency (E′) centers. The (100)Si/Al2O3 and (100)Si/HfO2 systems appear more robust with better interlayer properties. Particularly in the (100)Si/HfO2 structure, both the E′ and EX densities remain small (<1.6×1011 cm−2) after PDO, which comes as one more favorable property for the application of HfO2 as an alternative gate dielectric. Yet, the Si/Al2O3 entity exhibits the largest EX density, and there appears evidence for an additional Si∕dielectric interface defect. No obvious ESR-active defect inherent to the metal oxide layers could be detected.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
76.30.Mi Color centers and other defects
61.72.J- Point defects and defect clusters
81.40.Gh Other heat and thermomechanical treatments
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Enhanced photoluminescence of Ga2O3:Dy3+ phosphor films by Li+ doping

M. L. Pang, W. Y. Shen, and J. Lin

J. Appl. Phys. 97, 033511 (2005); http://dx.doi.org/10.1063/1.1849829 (5 pages) | Cited 20 times

Online Publication Date: 5 January 2005

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Ga2O3:Dy3+ and Li+-doped Ga2O3:Dy3+ phosphor films were prepared by a Pechini sol-gel process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy, and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting thin films (and powder samples for comparison). The results of the FTIR and XRD indicated that the films began to crystallize at 700 °C and the crystallinity increased with the elevation of annealing temperatures. Upon excitation into band gap of β-Ga2O3 at 250 nm, the Ga2O3:Dy3+ and Li+-doped Ga2O3:Dy3+ films show similar emission spectra, which mainly consist of the characteristic emission bands of Dy3+ ions (math–math transition at 492 nm and math–math transition at 580 nm) due to an efficient energy transfer from the β-Ga2O3 host lattice to the doped Dy3+ ions. The incorporation of Li+ ions into the Ga2O3:Dy3+ film have enlarged the grain size and enhanced the photoluminescence intensities. The highest emission intensity was observed in Ga1.86Dy0.04O3:0.1Li+ film, whose PL intensity is more than twice that of the Ga1.96Dy0.04O3 film.
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82.50.-m Photochemistry
82.45.Mp Thin layers, films, monolayers, membranes

Polarization-dependent Raman spectra of thin crystalline silicon films

Z. Q. Lu, T. Quinn, and H. S. Reehal

J. Appl. Phys. 97, 033512 (2005); http://dx.doi.org/10.1063/1.1844613 (6 pages) | Cited 3 times

Online Publication Date: 6 January 2005

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Polarization-dependent Raman spectra are presented to analyze the structural properties of epitaxial, quasiepitaxial, and microcrystalline silicon films deposited on (100) single-crystal silicon substrates by electron cyclotron resonance plasma-enhanced chemical-vapor deposition. We rotate the sample with respect to the polarization direction of the incident laser light and observe the changes in Raman scattering. The measurements are very effective in differentiating between films with a preferred orientation and those that are randomly oriented or amorphous. An interesting anisotropy has been observed for quasiepitaxial films for which the spectra resemble those of single-crystal wafers under normal measurement conditions. However, at sample orientations where the scattering intensity is minimized, additional structure on the low-energy side of the main silicon TO-phonon peak becomes visible. This is tentatively attributed to scattering from crystalline and amorphouslike grain-boundary regions. Polarization-dependent Raman spectra are able to provide useful information on the structure of these films which would normally be masked by the main silicon optical-phonon peak.
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68.55.-a Thin film structure and morphology
81.05.Cy Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
78.30.Am Elemental semiconductors and insulators
61.72.Mm Grain and twin boundaries

Fluence, flux, and implantation temperature dependence of ion-implantation-induced defect production in 4H–SiC

J. Slotte, K. Saarinen, M. S. Janson, A. Hallén, A. Yu. Kuznetsov, B. G. Svensson, J. Wong-Leung, and C. Jagadish

J. Appl. Phys. 97, 033513 (2005); http://dx.doi.org/10.1063/1.1844618 (7 pages) | Cited 8 times

Online Publication Date: 6 January 2005

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Vacancy-type defect production in Al- and Si-implanted 4H–SiC has been studied as a function of ion fluence, ion flux, and implantation temperature in the projected ion range region by positron annihilation spectroscopy and Rutherford backscattering techniques. Ion channeling measurements show that the concentration of displaced silicon atoms increases rapidly with increasing ion fluence. In the ion fluence interval of 1013–1014 cm−2 the positron annihilation parameters are roughly constant at a defect level tentatively associated with the divacancy VCVSi. Above the ion fluence of 1014 cm−2 larger vacancy clusters are formed. For implantations as a function of ion flux (cm−2 s−1), ion channeling and positron annihilation measurements behave similarly, i.e., indicating increasing damage in the projected range region with increasing ion flux. However, for samples implanted at different temperatures the positron annihilation parameter S shows a clear minimum at approximately 100 °C, whereas the normalized backscattering yield decrease continuously with increasing implantation temperature. This is explained by the formation of larger vacancy clusters when the implantation temperature is increased.
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61.72.up Other materials
61.80.Jh Ion radiation effects
61.72.J- Point defects and defect clusters
71.55.-i Impurity and defect levels
61.82.Fk Semiconductors
78.70.Bj Positron annihilation

Optical properties of self-assembled ZnTe quantum dots grown by molecular-beam epitaxy

C. S. Yang, Y. J. Lai, W. C. Chou, W. K. Chen, M. C. Lee, M. C. Kuo, J. Lee, J. L. Shen, D. J. Jang, and Y. C. Cheng

J. Appl. Phys. 97, 033514 (2005); http://dx.doi.org/10.1063/1.1834985 (7 pages) | Cited 6 times

Online Publication Date: 6 January 2005

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The morphology and the size-dependent photoluminescence (PL) spectra of the type-II ZnTe quantum dots (QDs) grown in a ZnSe matrix were obtained. The coverage of ZnTe varied from 2.5 to 3.5 monolayers (MLs). The PL peak energy decreased as the dot size increased. Excitation power and temperature-dependent PL spectra are used to characterize the optical properties of the ZnTe quantum dots. For 2.5- and 3.0-ML samples, the PL peak energy decreased monotonically as the temperature increased. However, for the 3.5-ML sample, the PL peak energy was initially blueshifted and then redshifted as the temperature increased above 40 K. Carrier thermalization and carrier transfer between QDs are used to explain the experimental data. A model of temperature-dependent linewidth broadening is employed to fit the high-temperature data. The activation energy, which was found by the simple PL intensity quenching model, of the 2.5, 3.0, and 3.5 MLs were determined to be 6.35, 9.40, and 18.87 meV, respectively.
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81.05.Dz II-VI semiconductors
81.07.Ta Quantum dots
78.67.Hc Quantum dots
73.63.Kv Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
78.55.Et II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
72.20.Fr Low-field transport and mobility; piezoresistance

Growth of N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine dome structures

Y. H. Leung, A. B. Djurišić, C. H. Cheung, M. H. Xie, and W. K. Chan

J. Appl. Phys. 97, 033515 (2005); http://dx.doi.org/10.1063/1.1847722 (5 pages) | Cited 4 times

Online Publication Date: 6 January 2005

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N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine samples exhibiting interesting nano/microstructure were fabricated by thermal evaporation in a tube furnace under Ar gas flow. We investigated the influence of the substrate type, substrate temperature, source temperature, and the gas flow rate on the obtained morphology. The deposited material was investigated using scanning electron microscopy, x-ray diffraction, and photoluminescence. We found that the substrate temperature was the factor which significantly affected the obtained morphology, while other factors such as substrate type, source temperature, and gas flow mainly affected the size distribution of the features but not the type of morphology observed.
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85.60.Jb Light-emitting devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.55.Kz Solid organic materials
78.60.Fi Electroluminescence
78.66.Li Other semiconductors
78.66.Qn Polymers; organic compounds
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Quantum wires and dots induced in a semiconductor by charged metallic filaments separated by an isolating barrier

Z. S. Gribnikov and G. I. Haddad

J. Appl. Phys. 97, 033516 (2005); http://dx.doi.org/10.1063/1.1849827 (12 pages) | Cited 1 time

Online Publication Date: 6 January 2005

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A very thin positively charged metallic filament separated from a surface of a semiconductor (S) by a thin nontunneling potential barrier (B) induces a quantum wire (QWr) in the semiconductor at the B/S interface. Single-electron quantum states of this QWr are controlled by a potential (and a charge) of the metallic filament. Two close parallel metallic filaments placed over such a B/S interface form a double-quantum wire with the ground and the first excited electron states, which appear as a result of a symmetric–antisymmetric splitting of the ground electron state in the single QWr. Two crossed metallic filaments, which are parallel to the B/S interface, form a quantum dot with completely localized electron states under the crossing point of the metallic filaments. The analogous crossing of a metallic filament by a pair of close metallic filaments forms a double-quantum dot (DQD). The latter can serve as a two-level qubit cell. Such qubits can be controlled by potentials of three independent metallic filaments inducing the above-mentioned DQD. Besides this “outside” metallic wire control, the DQDs can be connected to each other across the “inside” quantum wires, which have formed these DQDs by crossing.
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73.21.La Quantum dots
73.21.Hb Quantum wires
73.23.Hk Coulomb blockade; single-electron tunneling
73.20.Fz Weak or Anderson localization

Investigation of phase-separated electronic states in 1.5 μm GaInNAs∕GaAs heterostructures by optical spectroscopy

H. D. Sun, A. H. Clark, S. Calvez, M. D. Dawson, P. Gilet, L. Grenouillet, and A. Million

J. Appl. Phys. 97, 033517 (2005); http://dx.doi.org/10.1063/1.1836856 (5 pages) | Cited 7 times

Online Publication Date: 11 January 2005

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We report on the comparative electronic state characteristics of particular GaInNAs∕GaAs quantum well structures that emit near 1.3 and 1.5 μm wavelength at room temperature. While the electronic structure of the 1.3 μm sample is consistent with a standard quantum well, the 1.5 μm sample demonstrate quite different characteristics. By using photoluminescence (PL) excitation spectroscopy at various detection wavelengths, we demonstrate that the macroscopic electronic states in the 1.5 μm structures originate from phase-separated quantum dots instead of quantum wells. PL measurements with spectrally selective excitation provide further evidence for the existence of composition-separated phases. The evidence is consistent with phase segregation during the growth leading to two phases, one with high In and N content which accounts for the efficient low energy 1.5 μm emission, and the other one having lower In and N content which contributes metastable states and only emits under excitation in a particular wavelength range.
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73.21.Fg Quantum wells
64.75.-g Phase equilibria
78.67.De Quantum wells
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Near-edge x-ray absorption fine-structure study of ion-beam-induced phase transformation in Gd2(Ti1−yZry)2O7

P. Nachimuthu, S. Thevuthasan, V. Shutthanandan, E. M. Adams, W. J. Weber, B. D. Begg, D. K. Shuh, D. W. Lindle, E. M. Gullikson, and R. C. C. Perera

J. Appl. Phys. 97, 033518 (2005); http://dx.doi.org/10.1063/1.1840097 (5 pages) | Cited 8 times

Online Publication Date: 11 January 2005

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The structural and electronic properties of Gd2(Ti1−yZry)2O7 (y = 0–1) pyrochlores following a 2.0-MeV Au2+ ion-beam irradiation ( ∼ 5.0×1014 Au2+/cm2) have been investigated by Ti 2p and O 1s near-edge x-ray absorption fine structure (NEXAFS). The irradiation of Gd2(Ti1−yZry)2O7 leads to the phase transformation from the ordered pyrochlore structure (Fd3m) to the defect fluorite structure (Fm3m) regardless of Zr concentration. Irradiated Gd2(Ti1−yZry)2O7 with y ⩽ 0.5 are amorphous, although significant short-range order is present. Contrasting to this behavior, compositions with y ≥ 0.75 retain crystallinity in the defect fluorite structure following irradiation. The local structures of Zr4+ in the irradiated Gd2(Ti1−yZry)2O7 with y ≥ 0.75 determined by NEXAFS are the same as in the cubic fluorite-structured yttria-stabilized zirconia (Y–ZrO2), thereby providing conclusive evidence for the phase transformation. The TiO6 octahedra present in Gd2(Ti1−yZry)2O7 are completely modified by ion-beam irradiation to TiOx polyhedra, and the Ti coordination is increased to eight with longer Ti–O bond distances. The similarity between cation sites and the degree of disorder in Gd2Zr2O7 facilitate the rearrangement and relaxation of Gd, Zr, and O ions∕defects. This inhibits amorphization during the ion-beam-induced phase transition to the radiation-resistant defect fluorite structure, which is in contrast to the ordered Gd2Ti2O7.
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
61.80.Jh Ion radiation effects
61.82.Ms Insulators
78.55.Hx Other solid inorganic materials
78.70.Dm X-ray absorption spectra

Superposition of patterns in cross-linked liquid crystals

N. Stich and H.-S. Kitzerow

J. Appl. Phys. 97, 033519 (2005); http://dx.doi.org/10.1063/1.1832744 (5 pages) | Cited 7 times

Online Publication Date: 11 January 2005

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Patterns appearing in liquid crystals due to electrohydrodynamic convection can be permanently stored by in situ photopolymerization. After curing, the respective pattern is fixed in a glasslike state which is stable even if the entropy production becomes zero. If a small amount of photoreactive mesogenic monomers is dissolved in a cholesteric liquid crystal, the reaction can result in the formation of either separate polymer walls or a polymer film with a regularly modulated surface. The symmetry and the orientation of the pattern depend essentially on the ratio between the sample thickness and the helical pitch of the cholesteric phase, while the cross section of the polymer walls or the topography of the polymer film depend on the ultraviolet radiation and the concentration of the reactive monomer.
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61.30.Vx Polymer liquid crystals
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
82.50.Hp Processes caused by visible and UV light
82.40.Ck Pattern formation in reactions with diffusion, flow and heat transfer
42.70.Df Liquid crystals
82.35.Lr Physical properties of polymers
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