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15 Sep 2010

Volume 108, Issue 6, Articles (06xxxx)

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back to top Lasers, Optics, and Optoelectronics

Slow and fast light in photorefractive GaAs–AlGaAs multiple quantum wells in transverse geometry

Fang Bo, Ze Liu, Feng Gao, Guoquan Zhang, and Jingjun Xu

J. Appl. Phys. 108, 063101 (2010); http://dx.doi.org/10.1063/1.3485829 (8 pages) | Cited 1 time

Online Publication Date: 16 September 2010

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We show theoretically that, based on the dispersive phase coupling effect during the wave mixing process, both slow and fast light can be achieved in GaAs–AlGaAs photorefractive multiple quantum wells (PRMQWs) films applied with a transverse direct-current electric field. The general formula for the group velocity of the diffracted beams in the Raman–Nath regime during the wave mixing process in a nonlinear thin film is derived and is then applied to the case of the PRMQWs films in the transverse geometry. The simulation results in the transverse-geometry PRMQWs films show that the group velocity and bandwidth of slow light can be on the order of centimeter per second and 100 kHz, respectively. The extremely low group velocity and the relatively broad bandwidth are mainly originated from the strong quadratic electro-optic effect and the fast response rate of the PRMQWs films, respectively. Our results show that the delay-bandwidth product of slow light can be significantly improved in PRMQWs films as compared to the reported results in other photorefractive materials.
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78.66.Fd III-V semiconductors
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.25.Fx Diffraction and scattering

The effect of thickness and/or doping on the nonlinear and saturable absorption behaviors in amorphous GaSe thin films

Ulaş Kürüm, Mustafa Yüksek, H. Gul Yaglioglu, Ayhan Elmali, Aytunç Ateş, Mevlüt Karabulut, and Gasan M. Mamedov

J. Appl. Phys. 108, 063102 (2010); http://dx.doi.org/10.1063/1.3486047 (8 pages) | Cited 3 times

Online Publication Date: 20 September 2010

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We investigated the nonlinear and saturable absorption characteristics of very thin amorphous undoped GaSe, Ge (0.01 at. %), and Sn (0.5 at. %) doped GaSe films by pump-probe and open aperture Z-scan techniques. Linear absorption measurements indicate blueshift in energy with increasing film thickness. Thinner films exhibit saturable absorption while thicker films exhibit nonlinear absorption for 4 ns and 65 ps pulse durations. The films exhibit competing effects between nonlinear and saturable absorption. Saturable absorption behavior weakens while nonlinear absorption appears with increasing film thickness. In addition to that, saturable absorption behavior is very sensitive to doping. Doping causes absorption behaviors to appear in thinner films compared to undoped films. These behaviors are attributed to increasing localized defect states with increasing film thickness and doping. To derive the transmission in open aperture Z-scan data, a theoretical model incorporating one photon, two photon, and free carrier absorptions and their saturations were considered. The experimental curves were fitted to the theory of open aperture Gaussian beam Z-scan based on the Adomian decomposition method. Nonlinear absorption coefficients and saturation intensity thresholds were extracted from the fitting of the experimental results for both pulse durations used for the experiments. Saturation intensity threshold values increased with increasing film thickness and doping. The lowest saturation intensity threshold for undoped GaSe film was found to be 1.9×10−3 GW/cm2 for 45 nm film thickness and increased about two orders of magnitude for 74 nm film thickness.
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78.66.Jg Amorphous semiconductors; glasses
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
71.55.Ht Other nonmetals

Light emission properties of planar source in multilayer structures with photonic crystal patterns

Yu Zhao, Gang Wang, and Xue-Hua Wang

J. Appl. Phys. 108, 063103 (2010); http://dx.doi.org/10.1063/1.3483941 (7 pages) | Cited 3 times

Online Publication Date: 22 September 2010

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Based on scattering matrix method, we investigate the light emission properties of planar source (i.e., an area current source) in multilayer structures with two-dimensional photonic crystal (PC) patterns. Our numerical results show that the outgoing power from planar source is good agreement with the experimental results of multilayer structures with PC patterns reported before, which clarifies the reason of the big differences between experimental results and theoretical simulations based upon point dipole source. Our studies should provide a deep insight into the underlying physics of quantum optoelectronic devices based upon PC structures.
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42.70.Qs Photonic bandgap materials
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Optical characterization of GaN/AlGaN bilayer by transmission and reflection spectra

Chao Li, Xichang Bao, Jintong Xu, Yan Zhang, and Xiangyang Li

J. Appl. Phys. 108, 063104 (2010); http://dx.doi.org/10.1063/1.3483952 (6 pages) | Cited 1 time

Online Publication Date: 23 September 2010

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A method has been proposed to study optical characteristics of GaN/Al0.45Ga0.55N bilayer on sapphire substrate at room temperature. Utilizing the incomplete absorption between 270 and 365 nm, absorption spectrum and extinction coefficient of wurtzite GaN both below and above energy gap were determined. Energy gaps of GaN and Al0.45Ga0.55N were located at 3.4 and 4.62 eV, respectively, in the same spectrum. Right above absorption edge (354 nm), the extinction coefficient was 0.269. Average total thickness calculated from transmission and reflection spectra was 1413 and 1407 nm, respectively, and thickness of GaN was calculated as 268.5 nm from the envelope of maximum reflection resulted from GaN/AlGaN interface. By comparison of two spectra, it was deduced that reflection curve had much larger oscillation amplitude than transmission spectrum, thanks to the larger contrast of interference fringes V. Additional half-wave loss was deduced at air/GaN interface, which resulted in the reverse of interference extrema.
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78.66.Fd III-V semiconductors
78.40.Fy Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.05.Ea III-V semiconductors
71.20.Nr Semiconductor compounds

Light output enhancement of GaN-based flip-chip light-emitting diodes fabricated with SiO2/TiO2 distributed Bragg reflector coated on mesa sidewall

K. H. Baik, B. K. Min, J. Y. Kim, H. K. Kim, C. Sone, Y. Park, and H. Kim

J. Appl. Phys. 108, 063105 (2010); http://dx.doi.org/10.1063/1.3478740 (4 pages) | Cited 1 time

Online Publication Date: 24 September 2010

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We report on the enhanced light output of GaN-based flip-chip light-emitting diodes (LEDs) fabricated with SiO2/TiO2 distributed Bragg reflector (DBR) on mesa sidewall. At the wavelength of 400 nm, five pairs of SiO2/TiO2 DBR coats on the GaN layer showed a normal-incidence reflectivity as high as 99.1%, along with an excellent angle-dependent reflectivity. As compared to the reference LED, the LED fabricated with the DBR-coated mesa sidewall showed an increased output power by a factor of 1.32 and 1.12 before and after lamp packaging, respectively. This could be attributed to an efficient reflection of the laterally guided mode at the highly reflective mesa sidewall, enhancing the subsequent extraction of light through the sapphire substrate.
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85.60.Jb Light-emitting devices
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
42.79.Bh Lenses, prisms and mirrors
42.82.Cr Fabrication techniques; lithography, pattern transfer

Guided-mode resonance excitation on multimode planar periodic waveguide

Tianyu Sun and Dongmin Wu

J. Appl. Phys. 108, 063106 (2010); http://dx.doi.org/10.1063/1.3483958 (5 pages) | Cited 3 times

Online Publication Date: 24 September 2010

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Planar periodic waveguides are applied to design numerous passive guided-mode resonance (GMR) elements. Key to achieving these devices with desired spectral properties is placement and manipulation of the resonance peaks. It has been shown that, the resonance locations closely track the dispersion curves of the leaky modes. In this paper, taking Bragg reflection due to periodicity and coupling between different modes into account, we investigate the dispersion relations of leaky modes in multimode planar periodic waveguides, both for s-polarized (TE mode) and p-polarized (TM mode) incident waves. Exploiting the characteristics of leaky mode dispersions in full range of the first Brillouin zone, we offer the ways to construct some novel optical elements, for example, polarization independent and angular tolerant GMR filters.
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42.79.Gn Optical waveguides and couplers
42.82.-m Integrated optics
42.79.Ci Filters, zone plates, and polarizers

Improvement in output power of a 460 nm InGaN light-emitting diode using staggered quantum well

Chih-Teng Liao, Miao-Chan Tsai, Bo-Ting Liou, Sheng-Horng Yen, and Yen-Kuang Kuo

J. Appl. Phys. 108, 063107 (2010); http://dx.doi.org/10.1063/1.3471804 (6 pages) | Cited 22 times

Online Publication Date: 24 September 2010

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Staggered quantum well structures are studied to eliminate the influence of polarization-induced electrostatic field upon the optical performance of blue InGaN light-emitting diodes (LEDs). Blue InGaN LEDs with various staggered quantum wells which vary in their indium compositions and quantum well width are theoretically studied and compared by using the APSYS simulation program. According to the simulation results, the best optical characteristic is obtained when the staggered quantum well is designed as In0.20Ga0.80N (1.4 nm)–In0.26Ga0.74N (1.6 nm) for blue LEDs. Superiority of this novelty design is on the strength of its enhanced overlap of electron and hole wave functions, uniform distribution of holes, and suppressed electron leakage in the LED device.
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85.60.Jb Light-emitting devices
85.35.-p Nanoelectronic devices

Plasmonic inverse rib waveguiding for tight confinement and smooth interface definition

H. Benisty and M. Besbes

J. Appl. Phys. 108, 063108 (2010); http://dx.doi.org/10.1063/1.3478746 (8 pages) | Cited 5 times

Online Publication Date: 24 September 2010

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A plasmonic inverse rib optical waveguide geometry is proposed and investigated, inspired by the recent CdS-nanorod-on-silver plasmonic laser. The proposed technology is suitable for large scale fabrication. It only uses a single wet resist development and several coatings onto a flat metal surface to define the waveguide geometry. It thus relieves the need to etch or lift-off a noble metal. High-index sol-gel inverse ribs are privileged candidates for the tightest confinement. We investigate and explain the guidance mostly for the case of Au and the wavelengths around λ = 633 nm. We get spot sizes down to ∼ 25×60 nm2. We notably describe how easily the tight confinement is granted and the reasons why only a single critical step defines the modal geometry. We finally detail how the classical building-blocks of integrated optics such as distributed reflectors and couplers can be made within the very same approach and integrated into devices for which losses are described.
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42.82.Et Waveguides, couplers, and arrays
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.82.-m Integrated optics

Achieving optical gain in waveguide-confined nanocluster-sensitized erbium by pulsed excitation

Gerald M. Miller, Ryan M. Briggs, and Harry A. Atwater

J. Appl. Phys. 108, 063109 (2010); http://dx.doi.org/10.1063/1.3465120 (5 pages) | Cited 8 times

Online Publication Date: 27 September 2010

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We use a rate equation approach to model the conditions for optical gain in nanocluster sensitized erbium in a slot waveguide geometry. We determine the viability of achieving net gain for the range of reported values of the carrier absorption cross section for silicon nanoclusters. After accounting for the local density of optical states modification of the emission rates, we find that gain is impossible in continuous wave pumping due to carrier absorption, regardless of the carrier absorption cross section. We, therefore, propose a pulsed electrical operation scheme which mitigates carrier absorption by taking advantage of the short lifetime of silicon nanoclusters compared to erbium. We show that pulsed excitation of a 10 nm layer achieves a modal gain of 0.9 dB/cm during each pulse. Furthermore this gain can be increased to 2 dB/cm by pumping a 50 nm layer.
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42.79.Gn Optical waveguides and couplers
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.22.-f Electronic structure of nanoscale materials and related systems

Plasmonic implementation of a quantum eraser for imaging applications

J. Ajimo, M. Marchante, A. Krishnan, A. A. Bernussi, and L. Grave de Peralta

J. Appl. Phys. 108, 063110 (2010); http://dx.doi.org/10.1063/1.3485810 (3 pages) | Cited 4 times

Online Publication Date: 27 September 2010

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We describe the use of a plasmonic version of a quantum eraser for imaging applications. Two perpendicular surface plasmon polariton (SPP) beams were excited in a glass-metal sample using a leakage radiation microscope. The polarization state of the SPP-coupled radiation leaked to the sample substrate permits to identify the path of photons along the metal-air interface of the sample. Introduction of a linear polarizer after the microscope high numerical aperture lens erases the which-path information. This enabled us to image on the microscope charge coupled device camera the interference pattern formed in the sample surface.
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42.50.Ex Optical implementations of quantum information processing and transfer
07.60.Pb Conventional optical microscopes
07.60.Ly Interferometers
42.30.-d Imaging and optical processing
back to top Plasmas and Electrical Discharges

Spatial and temporal evolution of ion energies in high power impulse magnetron sputtering plasma discharge

A. Hecimovic and A. P. Ehiasarian

J. Appl. Phys. 108, 063301 (2010); http://dx.doi.org/10.1063/1.3486018 (8 pages) | Cited 11 times

Online Publication Date: 16 September 2010

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High power impulse magnetron sputtering (HIPIMS) is a novel deposition technology successfully implemented on full scale industrial machines. HIPIMS utilizes short pulses of high power delivered to the target in order to generate high amount of metal ions. The life-span of ions between the pulses and their energy distribution could strongly influence the properties and characteristics of the deposited coating. In modern industrial coating machines the sample rotates on a substrate holder and changes its position and distance with regard to the magnetron. Time resolved measurements of the ion energy distribution function (IEDF) at different distances from the magnetron have been performed to investigate the temporal evolution of ions at various distances from target. The measurements were performed using two pressures, 1 and 3 Pa to investigate the influence of working gas pressure on IEDF. Plasma sampling energy-resolved mass spectroscopy was used to measure the IEDF of Ti1+, Ti2+, Ar1+, and Ar2+ ions in HIPIMS plasma discharge with titanium (Ti) target in Ar atmosphere. The measurements were done over a full pulse period and the distance between the magnetron and the orifice of the mass spectrometer was changed from 25 to 215 mm.
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81.15.Cd Deposition by sputtering
78.47.D- Time resolved spectroscopy (>1 psec)
52.80.-s Electric discharges
52.77.Dq Plasma-based ion implantation and deposition
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
81.15.Jj Ion and electron beam-assisted deposition; ion plating

Plasma sheath criterion in thermal electronegative plasmas

Hamid Ghomi, Mansour Khoramabadi, Padma Kant Shukla, and Mahmod Ghorannevis

J. Appl. Phys. 108, 063302 (2010); http://dx.doi.org/10.1063/1.3475508 (5 pages) | Cited 2 times

Online Publication Date: 16 September 2010

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The sheath formation criterion in electronegative plasma is examined. By using a multifluid model, it is shown that in a collisional sheath there will be upper as well as lower limits for the sheath velocity criterion. However, the parameters of the negative ions only affect the lower limit.
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52.40.Kh Plasma sheaths
52.40.Hf Plasma-material interactions; boundary layer effects

Particle simulation of femtosecond laser stimulation of electrical discharges in small gaps

J. Chen, L. N. He, D. F. Farson, and S. I. Rokhlin

J. Appl. Phys. 108, 063303 (2010); http://dx.doi.org/10.1063/1.3486057 (5 pages) | Cited 1 time

Online Publication Date: 20 September 2010

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A particle-in-cell/Monte Carlo collision simulation study of femtosecond laser stimulation of electrical discharges in submicron gaps between platinum scanning tunneling microscope cathode tips and gold film anodes in atmospheric pressure argon gas is described. The breakdown potential of gaps containing either preloaded electrons or preloaded neutral and ionized platinum atoms and electrons at various densities were compared to the breakdown potential of gaps with background argon gas alone. It was found that gaps preloaded with sufficient densities of either electrons or partially ionized electrode materials broke down at cathode potential of −80 V while gaps with background argon gas alone required applied cathode potentials between −200 to −250 V to cause a breakdown. Also, partially ionized material was much more effective at stimulating breakdown than electrons alone. The density of preloaded partially ionized platinum required to lower breakdown cathode potential to −80 V was approximately 12.5 times smaller than that required for the preloaded electrons alone in the same size gap. Analysis of the mechanism by which the preloaded partially ionized material promoted breakdown showed that laser ablated ions located near the cathode tip increased the local field at the cathode surface and the field-emitted electron flux from the cathode. This higher electron flux ionized background argon gas and preloaded platinum which resulted in gap breakdown. The threshold density of partially ionized platinum for gap breakdown varied approximately linearly with applied cathode potential.
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52.40.Mj Particle beam interactions in plasmas
82.45.Fk Electrodes
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
78.47.J- Ultrafast spectroscopy (<1 psec)
52.80.-s Electric discharges
52.65.Rr Particle-in-cell method
52.65.Pp Monte Carlo methods

Detecting excess ionizing radiation by electromagnetic breakdown of air

Victor L. Granatstein and Gregory S. Nusinovich

J. Appl. Phys. 108, 063304 (2010); http://dx.doi.org/10.1063/1.3484044 (5 pages) | Cited 13 times

Online Publication Date: 24 September 2010

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A scheme is proposed for detecting a concealed source of ionizing radiation by observing the occurrence of breakdown in atmospheric air by an electromagnetic wave whose electric field surpasses the breakdown field in a limited volume. The volume is chosen to be smaller than the reciprocal of the naturally occurring concentration of free electrons. The pulse duration of the electromagnetic wave must exceed the avalanche breakdown time (10–200 ns) and could profitably be as long as the statistical lag time in ambient air (typically, microseconds). Candidate pulsed electromagnetic sources over a wavelength range, 3 mm>λ>10.6 μm, are evaluated. Suitable candidate sources are found to be a 670 GHz gyrotron oscillator with 200 kW, 10 μs output pulses and a Transversely Excited Atmospheric-Pressure (TEA) CO2 laser with 30 MW, 100 ns output pulses. A system based on 670 GHz gyrotron would have superior sensitivity. A system based on the TEA CO2 laser could have a longer range >100 m.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma

Experimental studies on the plasma bullet propagation and its inhibition

Erdinc Karakas and Mounir Laroussi

J. Appl. Phys. 108, 063305 (2010); http://dx.doi.org/10.1063/1.3483935 (6 pages) | Cited 18 times

Online Publication Date: 24 September 2010

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Plasma bullets generated by atmospheric pressure low temperature plasma jets have recently been an active research topic due to their unique properties and their enhanced plasma chemistry. In this paper, experimental insights into the plasma bullet lifetime and its velocity are reported. Data obtained from intensified charge-coupled device camera and time-resolved optical emission spectroscopy (OES) elucidated the existence of a weakly ionized channel between the plasma bullet and its source (such as the plasma pencil). Factors responsible for the inhibition of the propagation of the bullet, such as low helium mole fraction, the magnitude of the applied voltage, and the secondary discharge ignition time, are also revealed. A new technique is discussed to accurately measure the plasma bullet velocity, using time-resolved OES. This new technique shows that during its lifetime the plasma bullet goes through launching, propagation, and ending phases. In addition, it is noted that the plasma bullet exhibits an unstable behavior at the early beginning and late ending of the propagation.
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52.80.Yr Discharges for spectral sources (including inductively coupled plasma)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.75.-d Plasma devices
52.50.Dg Plasma sources
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Analysis of atomic and ion debris features of laser-produced Sn and Li plasmas

R. W. Coons, S. S. Harilal, D. Campos, and A. Hassanein

J. Appl. Phys. 108, 063306 (2010); http://dx.doi.org/10.1063/1.3486209 (8 pages) | Cited 12 times

Online Publication Date: 28 September 2010

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Tin and lithium plasmas emit efficiently in the in-band region (13.5 nm with 2% bandwidth) necessary for extreme ultraviolet (EUV) lithography. We have made a detailed comparison of the atomic and ionic debris, as well as the emission features of Sn and Li plasmas under identical experimental conditions. Planar slabs of pure Sn and Li were irradiated with 1064 nm, 9 ns neodymium-doped yttrium aluminum garnet laser pulses for producing plasmas. A suite of diagnostics were used to analyze the emission and debris features, including optical emission spectroscopy (OES), a Faraday cup, an EUV pinhole camera, the absolute measurement of EUV conversion efficiency (CE), etc. Our results show that Sn plasmas provide a CE nearly twice that of Li. However, the kinetic energies of Sn ions are considerably higher, though with a lower flux. OES studies have showed that the kinetic energies of neutral species are substantially lower compared to that of the charged particle species.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.25.Tx Emission, absorption, and scattering of particles
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Ion flux characteristics and efficiency of the deposition processes in high power impulse magnetron sputtering of zirconium

J. Lazar, J. Vlček, and J. Rezek

J. Appl. Phys. 108, 063307 (2010); http://dx.doi.org/10.1063/1.3481428 (9 pages) | Cited 4 times

Online Publication Date: 28 September 2010

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High power impulse magnetron sputtering of zirconium was investigated at the average target power density of up to 2.22 kW cm−2 in a pulse. The depositions were performed using a strongly unbalanced magnetron with a planar zirconium target of 100 mm diameter at the argon pressure of 1 Pa. The repetition frequency was 500 Hz at duty cycles ranging from 4% to 10%. Time-averaged mass spectroscopy was carried out at the substrate positions of 100 and 200 mm from the target. The increase in the average target power density from 0.97 kW cm−2 to 2.22 kW cm−2 in shortened voltage pulses (from 200 to 80 μs) at an average target power density of 100 W cm−2 in a period led to high fractions (21%–32%) of doubly charged zirconium ions in total ion fluxes onto the substrate located 100 mm from the target. However, the respective fractions of singly charged zirconium ions decreased from 23% to 3%. It was observed that ion energy distributions were extended to high energies (up to 100 eV relative to the ground potential) under these conditions. The increased target power densities during the shortened voltage pulses resulted in a reduced deposition rate of films from 590 to 440 nm/min and in a weakly decreasing ionized fraction (from 55% to 49%) of the sputtered zirconium atoms in the flux onto the substrate. The doubly charged zirconium ions became strongly predominant (up to 63%) in the total ion flux onto the substrate at the distance of 200 mm from the target. Model calculations were carried out to explain the complicated deposition processes.
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81.15.Cd Deposition by sputtering
68.55.at Other materials
61.80.Jh Ion radiation effects
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
61.82.Bg Metals and alloys
81.05.Bx Metals, semimetals, and alloys

Simulated plasma immersion ion implantation processing of thin wires

A. Lejars, D. Manova, S. Mändl, D. Duday, and T. Wirtz

J. Appl. Phys. 108, 063308 (2010); http://dx.doi.org/10.1063/1.3485812 (4 pages) | Cited 1 time

Online Publication Date: 30 September 2010

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In plasma immersion ion implantation, the dependencies of sheath expansion and ion flux density on substrate geometry are well established. However, effects of extreme diameter variations have not been investigated explicitly. Using an analytical simulation code assuming an infinite mean free path, the sheath expansion, ion flux density, and resulting substrate temperature are explored down to wire diameters of 150 μm. Comparing the results for planar substrates and cylindrical, thin wires, a reduction in the sheath width up to a factor of 10, a faster establishing of a new equilibrium sheath position, and an increase in the ion fluence by a factor of 100 is encountered. The smaller plasma sheath allows for a denser packing of wires during the treatment than for planar substrates. Additionally, the implantation time is reduced, allowing a fast wire transport through the chamber, further increasing the throughput.
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52.77.Dq Plasma-based ion implantation and deposition
52.65.-y Plasma simulation
52.40.Kh Plasma sheaths
52.25.Fi Transport properties
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Kinetic and thermodynamic studies of the fragility of bulk metallic glass forming liquids

Isabella Gallino, Jan Schroers, and Ralf Busch

J. Appl. Phys. 108, 063501 (2010); http://dx.doi.org/10.1063/1.3480805 (8 pages) | Cited 7 times

Online Publication Date: 16 September 2010

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The thermodynamic functions of the bulk metallic glass (BMG) forming Pd43Ni10Cu27P20 alloy are determined calorimetrically as a function of temperature. Along with eight other BMG forming alloys, the available experimental thermodynamic and viscosity data are reassessed. For each alloy, consistent Vogel–Fulcher–Tammann (VFT) fits of the viscosity measurements are established, and the temperature dependence of the configurational entropy is calculated from thermodynamic data. Together with the VFT fits, fits to the Adam–Gibbs equation are performed using this configurational entropy change. We find remarkable agreement between the Adam–Gibbs and VFT fits. Moreover, the temperature T0 is obtained from the VFT fits at which the viscous flow diverges. This T0 matches very well the temperature where the configurational entropy vanishes in the corresponding Adam–Gibbs fits.
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61.43.Fs Glasses
66.20.-d Viscosity of liquids; diffusive momentum transport
65.40.gd Entropy

Single crystalline Sc2O3/Y2O3 heterostructures as novel engineered buffer approach for GaN integration on Si (111)

L. Tarnawska, A. Giussani, P. Zaumseil, M. A. Schubert, R. Paszkiewicz, O. Brandt, P. Storck, and T. Schroeder

J. Appl. Phys. 108, 063502 (2010); http://dx.doi.org/10.1063/1.3485830 (7 pages) | Cited 7 times

Online Publication Date: 16 September 2010

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The preparation of GaN virtual substrates on Si wafers via buffer layers is intensively pursued for high power/high frequency electronics as well as optoelectronics applications. Here, GaN is integrated on the Si platform by a novel engineered bilayer oxide buffer, namely, Sc2O3/Y2O3, which gradually reduces the lattice misfit of ∼ −17% between GaN and Si. Single crystalline GaN(0001)/Sc2O3(111)/Y2O3(111)/Si(111) heterostructures were prepared by molecular beam epitaxy and characterized ex situ by various techniques. Laboratory-based x-ray diffraction shows that the epitaxial Sc2O3 grows fully relaxed on the Y2O3/Si(111) support, creating a high quality template for subsequent GaN overgrowth. The high structural quality of the Sc2O3 film is demonstrated by the fact that the concentration of extended planar defects in the preferred {111} slip planes is below the detection limit of synchrotron based diffuse x-ray scattering studies. Transmission electron microscopy (TEM) analysis reveal that the full relaxation of the −7% lattice misfit between the isomorphic oxides is achieved by a network of misfit dislocations at the Sc2O3/Y2O3 interface. X-ray reflectivity and TEM prove that closed epitaxial GaN layers as thin as 30 nm can be grown on these templates. Finally, the GaN thin film quality is studied using a detailed Williamson–Hall analysis.
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68.55.-a Thin film structure and morphology
68.55.ag Semiconductors
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.55.A- Nucleation and growth

Heterogeneous nucleation and metal-insulator transition in epitaxial films of NdNiO3

Devendra Kumar, K. P. Rajeev, A. K. Kushwaha, and R. C. Budhani

J. Appl. Phys. 108, 063503 (2010); http://dx.doi.org/10.1063/1.3481396 (7 pages) | Cited 2 times

Online Publication Date: 16 September 2010

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We have investigated the temperature driven first order metal-insulator (M-I) transition in thin films of NdNiO3 and have compared it with the bulk behavior. The M-I transition of thin films is sensitive to epitaxial strain and its partial relaxation creates an inhomogeneous strain field in the films which broadens the M-I transition. Both the thin film and the bulk samples exhibit nonequilibrium features in the transition regime which are attributed to the presence of high temperature metallic phases in their supercooled state. The degree of supercooling in the thin films is found to be much smaller than in the bulk which suggests that the M-I transition in the thin film occurs through heterogeneous nucleation.
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68.55.at Other materials
64.60.Q- Nucleation
72.60.+g Mixed conductivity and conductivity transitions
71.30.+h Metal-insulator transitions and other electronic transitions
68.60.Bs Mechanical and acoustical properties
73.61.-r Electrical properties of specific thin films

Reaction pathway analysis for dislocation nucleation from a sharp corner in silicon: Glide set versus shuffle set

Koichi Shima, Satoshi Izumi, and Shinsuke Sakai

J. Appl. Phys. 108, 063504 (2010); http://dx.doi.org/10.1063/1.3486465 (3 pages) | Cited 6 times

Online Publication Date: 17 September 2010

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Using reaction pathway sampling, we have investigated the shear stress dependences of the activation energies of shuffle-set and glide-set dislocation nucleation from a sharp corner in silicon. The gradient of the glide-set dislocation curve is lower than that of the shuffle-set dislocation, and the athermal stress of glide-set dislocation is largely higher than that of shuffle-set dislocation. As a result, the two curves have a cross point, which means that shuffle-set dislocation is likely nucleated at high stress and low temperature and glide-set dislocation is likely nucleated at low stress and high temperature. Our result clearly explains the mechanism of recent molecular dynamics on these two types of dislocation nucleation at different temperatures and stress regimes. With increased compressive stress on the slip plane, the activation energy of the shuffle-set dislocation nucleation is greatly decreased, while that of glide-set dislocation nucleation is slightly increased. That would explain why shuffle-set dislocations were found under compressive stress fields.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Magneto-optical enhancement in magnetophotonic crystals based on cholesteric liquid crystals

Hai-Xia Da, Zi-Qiang Huang, and Zhen-Ya Li

J. Appl. Phys. 108, 063505 (2010); http://dx.doi.org/10.1063/1.3481444 (4 pages) | Cited 3 times

Online Publication Date: 17 September 2010

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The magneto-optical features in a one-dimensional magnetophotonic crystal based on cholesteric liquid crystals are explored theoretically by employing the Muller matrix method. It is unveiled that the intrinsic nonreciprocity-derived magneto-optical effect exhibits an enhancement, which origins from the strong photonic localization in the defect layers. Meanwhile, the oscillation behavior in the transmission spectrum with the linearly polarized angle indicates its polarization-dependent characteristic due to the breaking of time reversal symmetry in the magnetic materials. This novel scheme presents an opportunity of developing new hybrid structures for technological applications.
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61.30.-v Liquid crystals
42.70.Qs Photonic bandgap materials
42.70.Df Liquid crystals
78.20.Ls Magneto-optical effects
78.15.+e Optical properties of fluid materials, supercritical fluids and liquid crystals

A yellow phosphor K2SiF6 activated by Mn2+ ions

Takahiro Arai, Yusuke Arai, Toru Takahashi, and Sadao Adachi

J. Appl. Phys. 108, 063506 (2010); http://dx.doi.org/10.1063/1.3481856 (7 pages) | Cited 5 times

Online Publication Date: 17 September 2010

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A unique Mn2+-activated phosphor has been synthesized by wet chemical etching of Si wafers in HF/K2Cr2O7 mixed solution with the addition of pure Mn metal. The x-ray diffraction pattern suggests that the synthesized compound is a Mn2+-activaed K2SiF6 phosphor having cubic structure (space group = Oh5−Fm3m). The Mn2+-activated K2SiF6 phosphor emits light in the yellow or yellowish green region, depending on the quantity of the Mn additive. This phosphor shows unique photoluminescent properties that have not yet been reported previously. The electronic states of the 3d5 (Mn2+) electrons in the K2SiF6:Mn2+ phosphor are identified together with those of the 3d3 (Mn4+) electrons in the conventional K2SiF6:Mn4+ red phosphor. The temperature-dependent photoluminescent properties are explained by the aid of the electronic energy-band diagram of K2SiF6 with taking into account the effects of thermal emission of electrons in the Mn2+ excited states.
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81.05.Cy Elemental semiconductors
61.66.Fn Inorganic compounds
81.65.Cf Surface cleaning, etching, patterning
78.55.Hx Other solid inorganic materials
71.20.Ps Other inorganic compounds
71.55.Ht Other nonmetals

Transmission electron microscopy and in situ Raman studies of glassy sanbornite: An insight into nucleation trend and its relation to structural variation

Yoshihiro Takahashi, Minoru Osada, Hirokazu Masai, and Takumi Fujiwara

J. Appl. Phys. 108, 063507 (2010); http://dx.doi.org/10.1063/1.3487473 (5 pages) | Cited 1 time

Online Publication Date: 17 September 2010

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In situ observation of Raman scattering in glassy sanbornite (BaSi2O5) showing homogeneous nucleation was performed during heating to investigate the structural variation in the glassy/supercooled-liquid phase in the pre- and postnucleation regimes. It was observed that the formation of Q2 units accelerates around 400 °C, which is well below Tg, just after structural relaxation in the Ba-enriched/-cohesive region. The relation between the structural variation and the nucleation trend in glassy sanbornite was also discussed on the basis of transmission electron microscopy and in situ Raman results and previous Boson observation [ Takahashi et al. Appl. Phys. Lett. 94, 211907 (2009)] .
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61.43.Fs Glasses
81.40.Gh Other heat and thermomechanical treatments
78.35.+c Brillouin and Rayleigh scattering; other light scattering
64.70.ph Nonmetallic glasses (silicates, oxides, selenides, etc.)
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