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1 Mar 2009

Volume 105, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 105, 051101 (2009); http://dx.doi.org/10.1063/1.3081635 (17 pages)

Kraig E. Sheetz and Jeff Squier
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Ultrafast optics: Imaging and manipulating biological systems

Kraig E. Sheetz and Jeff Squier

J. Appl. Phys. 105, 051101 (2009); http://dx.doi.org/10.1063/1.3081635 (17 pages) | Cited 12 times

Online Publication Date: 3 March 2009

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The rapid evolution of ultrafast optics technology over the past two decades has opened the window to a broad range of applications in biology and medicine. Compact, reliable, and turn-key ultrafast laser systems are enabling cutting-edge science to take place in everyday laboratories and clinics. Led by the discovery of two-photon excitation fluorescence microscopy nearly 20 years ago, the biological imaging community is exploring unique image contrast mechanisms and pushing spatial and temporal resolution to new limits. Concurrent with advancements in imaging are developments in the precision application of extremely high peak intensities available in ultrashort pulses for disrupting or manipulating targeted locations in biological systems on the submicron scale while leaving surrounding tissue healthy. The ability for scientists to selectively discriminate structures of interest at the cellular and subcellular levels under relevant physiological conditions shows tremendous promise for accelerating the path to understanding biological functions at the most fundamental level.
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87.63.lt Laser imaging
87.64.M- Optical microscopy
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Crystal-field split levels of Nd3+ ions in GaN measured by luminescence spectroscopy

Grace D. Metcalfe, Eric D. Readinger, Hongen Shen, Nathaniel T. Woodward, Volkmar Dierolf, and Michael Wraback

J. Appl. Phys. 105, 053101 (2009); http://dx.doi.org/10.1063/1.3082500 (5 pages) | Cited 4 times

Online Publication Date: 3 March 2009

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We present the Stark energy sublevels of Nd3+ ions in GaN grown by plasma-assisted molecular beam epitaxy as determined by luminescence spectra. We correlate the photoluminescence spectra with transitions from the 4F3/2 excited state to the 4I9/2, 4I11/2, and 4I13/2 multiplets of the Nd3+ ion for above and below bandgap excitation, with the strongest emission occurring at 1.12 eV (1106 nm). We determine a splitting of the 4F3/2 excited state to be 4.1 meV. From photoluminescence excitation spectra, we also identify the Stark sublevels of the upper states 4F5/2, 2H9/2, 4F7/2, 4S3/2, 2G7/2, and 4G5/2. Photoluminescence excitation spectra reveal an optimal excitation energy of 1.48 eV (836 nm). Site-selective spectroscopy studies using combined excitation-emission spectroscopy with confocal microscopy indicate enhanced substantial doping at the Ga site.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
71.70.Ch Crystal and ligand fields
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
52.77.Dq Plasma-based ion implantation and deposition
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors

Femtosecond laser-induced formation of nanometer-width grooves on synthetic single-crystal diamond surfaces

Masataka Shinoda, Rafael R. Gattass, and Eric Mazur

J. Appl. Phys. 105, 053102 (2009); http://dx.doi.org/10.1063/1.3079512 (4 pages) | Cited 11 times

Online Publication Date: 3 March 2009

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We form periodic linear grooves in synthetic single-crystal diamond with femtosecond pulses at 800 nm. The grooves are 40 nm wide, 500 nm deep, up to 0.3 mm long, and have an average spacing of 146±7 nm. The grooves are perpendicular to the direction of the laser polarization and are formed below the threshold for ablation throughout the focal volume. The submicrometer periodicity is caused by interference between a laser-induced plasma and the incident laser beam, which locally enhances the field at the surface so the ablation threshold is exceeded. Using Raman spectroscopy we find that the structures retain the original diamond composition.
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81.05.U- Carbon/carbon-based materials
81.16.-c Methods of micro- and nanofabrication and processing
81.16.Rf Micro- and nanoscale pattern formation

Gain characteristics of the InGaAs strained quantum wells with GaAs, AlGaAs, and GaAsP barriers in vertical-external-cavity surface-emitting lasers

Peng Zhang, Yanrong Song, Jinrong Tian, Xinping Zhang, and Zhigang Zhang

J. Appl. Phys. 105, 053103 (2009); http://dx.doi.org/10.1063/1.3081974 (8 pages) | Cited 5 times

Online Publication Date: 4 March 2009

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InGaAs strained quantum wells (QWs) with GaAs, AlGaAs, and GaAsP barriers are widely used in optically pumped vertical-external-cavity surface-emitting lasers operating at 1 μm wavelength band. Compared with the reported data, the model-solid theory, which is more suitable for the studied materials, is selected to calculate the band offset. The band structures and the gain characteristics of the three different QWs are computed and compared, and the theoretical results are in good agreement with the recent experimental reports. The numerical simulation shows that the QW with the GaAs barrier has the highest absorption but the lowest peak gain, while for the AlGaAs barrier, it has the lowest absorption but the highest peak gain, and for the GaAsP barrier, it has a moderate absorption and peak gain. GaAsP is the most appropriate candidate for the barrier of InGaAs strained QW when the low-threshold, large-gain, and high-temperature characteristics are demanded simultaneously.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Strong plasmon absorption in InN thin films

A. Dixit, C. Sudakar, J. S. Thakur, K. Padmanabhan, Sanjiv Kumar, R. Naik, V. M. Naik, and G. Lawes

J. Appl. Phys. 105, 053104 (2009); http://dx.doi.org/10.1063/1.3088879 (5 pages) | Cited 2 times

Online Publication Date: 9 March 2009

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We have fabricated InN thin films using rf magnetron sputtering from an indium (In) metal target. Optical and electrical measurements show that these as-grown films are n-type with carrier concentrations ranging from 1020 to 1021 cm−3. This variation in carrier density is produced by controlling the conditions during the deposition. We used Rutherford backscattering spectrometry to identify possible sources for n-type carriers. We found that in addition to strong direct bandgap optical absorption ranging from 1.4 to 2.0 eV, a large plasmon absorption peak in the infrared region (0.45–0.8 eV) is also observed. This tunable IR absorption suggests that these highly degenerate InN films could be used for a number of applications, including optical filters and infrared devices.
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71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
71.20.Nr Semiconductor compounds
72.80.Ey III-V and II-VI semiconductors
81.15.Cd Deposition by sputtering
68.55.ag Semiconductors

Temperature dependence of refractive index and electronic polarizability of KNbGeO5 glass and its nanocrystallized glasses

Tsuyoshi Honma, Noriko Ito, Vesselin Dimitrov, and Takayuki Komatsu

J. Appl. Phys. 105, 053105 (2009); http://dx.doi.org/10.1063/1.3079790 (6 pages) | Cited 1 time

Online Publication Date: 11 March 2009

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The refractive indices (n) and densities (ρ) of a glass and transparent nanocrystallized glasses with the composition of 25K2O-25Nb2O5–50GeO2 (i.e., KNbGeO5) are measured in the temperature range of 30–150 °C in order to clarify the temperature dependences of the electronic polarizability of oxide ions (αO2−) and optical basicity (Λ). It is found that the values of n, αO2−, and Λ increase almost linearly with increasing temperature, and the values of the temperature dependence of these properties, i.e., dn/dT, dαO2−/dT, and dΛ/dT, tend to decrease slightly due to the nanocrystallization. It is clarified that the temperature dependence of the electronic polarizability of oxide ions in the precursor glass and nanocrystallized glasses has a large contribution for the temperature dependence of the refractive index in comparison with the contribution of density (volume thermal expansion). The features in the temperature dependences of αO2− and Λ in the present glass system is related to the large optical basicities of the constituent oxides of K2O, Nb2O5, and GeO2.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.43.Fs Glasses
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
73.63.Bd Nanocrystalline materials

Near-infrared two-color intersubband transitions in AlN/GaN coupled double quantum wells

L. B. Cen, B. Shen, Z. X. Qin, and G. Y. Zhang

J. Appl. Phys. 105, 053106 (2009); http://dx.doi.org/10.1063/1.3091280 (4 pages) | Cited 2 times

Online Publication Date: 12 March 2009

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A study on a four-energy-level system in asymmetric AlN/GaN coupled double quantum wells has been performed by solving Schrödinger and Poisson equations self-consistently. It is found that the transition selection rule is recovered when the first two subband pairs resonate in the four-energy-level system. The anticrossing gap between the second excited state (2odd) and the third excited state (2even) can be up to 135 meV when the Al composition of the central barrier is 0.80. The absorption coefficient of intersubband transition (ISBT) between the ground state (1odd) and the 2even subband is approximately equal to that between the first excited state (1even) and the 2odd subband. The wavelengths of the 1odd-2even and the 1even-2odd ISBTs are 1.31 and 1.55 μm, respectively. The results give possible application to the ultrafast two-color optoelectronic devices operating within optical communication wavelength range.
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68.65.Fg Quantum wells
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.21.Fg Quantum wells
78.47.J- Ultrafast spectroscopy (<1 psec)

Luminescence mechanisms of silicon-rich nitride films fabricated by atmospheric pressure chemical vapor deposition in N2 and H2 atmospheres

Chia-Hung Lin, Wu-Yih Uen, Shan-Ming Lan, Yen-Chin Huang, Sen-Mao Liao, Zhen-Yu Li, Tsun-Neng Yang, Chien-Te Ku, Meng-Chu Chen, and Yu-Hsiang Huang

J. Appl. Phys. 105, 053107 (2009); http://dx.doi.org/10.1063/1.3086620 (6 pages) | Cited 2 times

Online Publication Date: 12 March 2009

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This work examines possible luminescence mechanisms of silicon-rich nitride (SRN) films that were fabricated by atmospheric pressure chemical vapor deposition (APCVD). Under an ambient gas of either H2 or N2, two SRN films were deposited using the same precursors of Si and N. While photoluminescence (PL) measurements of both as-deposited specimens revealed an intense luminescence band (1.8–3.8 eV), which was observable by the naked eye, a detailed examination of the high energy band of the PL spectra over 2.8 eV yielded different results for those samples that were fabricated in different ambiences. To determine the reason for these differences, Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy were conducted, suggesting unique chemical bonds and elemental ratio of nitrogen to silicon in SRN films. Further analysis involving plan-view high-resolution transmission electron microscopic observations of SRN films demonstrated the embedding of Si quantum dots (Si QDs), but with some differences depending on the deposition environment. Analyses of the results obtained suggest that the emission from SRN films that were deposited by APCVD is not only dominated by the quantum confinement effect of Si QDs, but also subordinately affected by the surface states around these Si QDs.
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78.55.Hx Other solid inorganic materials
78.66.Nk Insulators
78.30.Hv Other nonmetallic inorganics
73.21.La Quantum dots
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.60.Dp Adsorbed layers and thin films

Electrical tuning of intersubband transition in a semiconductor quantum ring

S. Bhattacharyya, N. R. Das, and Susmita Sen

J. Appl. Phys. 105, 053108 (2009); http://dx.doi.org/10.1063/1.3087480 (5 pages) | Cited 1 time

Online Publication Date: 12 March 2009

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In this paper, the intersubband transition energy in an n-type semiconductor quantum ring has been investigated in the presence of an electric field perpendicular to the plane of the ring. The analysis has been done considering the effect of band nonparabolicity of the semiconductor. The results show that at high electric field energy varies nonlinearly with field and the optical transition between the two lowest quantized subbands can be controlled by the electric field. It has also been shown how this fine wavelength tuning by electric field depends on the band gap of the semiconductor.
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78.67.Hc Quantum dots
73.63.Kv Quantum dots
73.21.La Quantum dots
78.20.Jq Electro-optical effects

Ultrafast nonlinear optical properties of alkyl-phthalocyanine nanoparticles investigated using Z-scan technique

S. Venugopal Rao, N. Venkatram, L. Giribabu, and D. Narayana Rao

J. Appl. Phys. 105, 053109 (2009); http://dx.doi.org/10.1063/1.3079801 (6 pages) | Cited 11 times

Online Publication Date: 13 March 2009

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We report our results on the femtosecond nonlinear optical studies of alkyl-phthalocyanine nanoparticles dispersed in water and dissolved in chloroform. Nonlinear refractive and absorptive properties were investigated using the closed and open aperture Z-scan techniques. The nonlinear optical coefficients obtained for nanoparticles suspended in water are compared with those dissolved in chloroform, which resulted in simple phthalocyanine solutions. Our studies clearly demonstrate the nonlinear refractive index of nanoparticles to be positive, while that of the nanoparticles in chloroform was negative. Our results and analysis point out a high nonlinearity in the ultrafast domain for both the nanoparticles and solutions indicating their potential in optical signal processing and limiting applications.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
42.65.Pc Optical bistability, multistability, and switching, including local field effects
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
82.70.Kj Emulsions and suspensions
78.47.-p Spectroscopy of solid state dynamics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.07.Bc Nanocrystalline materials

On the fabrication of all-glass optical fibers from crystals

J. Ballato, T. Hawkins, P. Foy, B. Kokuoz, R. Stolen, C. McMillen, M. Daw, Z. Su, T. M. Tritt, M. Dubinskii, J. Zhang, T. Sanamyan, and M. J. Matthewson

J. Appl. Phys. 105, 053110 (2009); http://dx.doi.org/10.1063/1.3080135 (9 pages) | Cited 8 times

Online Publication Date: 13 March 2009

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The highly nonequilibrium conditions under which optical fibers conventionally are drawn afford considerable, yet underappreciated, opportunities to realize fibers comprised of novel materials or materials that themselves cannot be directly fabricated into fiber form using commercial scalable methods. Presented here is an in-depth analysis of the physical, compositional, and selected optical properties of silica-clad erbium-doped yttrium aluminosilicate glass optical fibers derived from undoped, 0.25, and 50 wt % Er3+-doped yttrium aluminum garnet (YAG) crystals. The YAG-derived fibers were found to be noncrystalline as evidenced by x-ray diffraction and corroborated by spectroscopic measurements. Elemental analysis across the core/clad interface strongly suggests that diffusion plays a large role in this amorphization. Despite the noncrystalline nature of the fibers, they do exhibit acceptable low losses ( ∼ 0.15–0.2 dB/m) for many applications, broad-band emissions in the near-infrared, and enhanced thermal conductivity along their length while maintaining equivalent mechanical strength with respect to conventional silica optical fibers. Further, considerably higher rare-earth doping levels are realized than can be achieved by conventional solution or vapor-phase doping schemes. A discussion of opportunities for such approaches to nontraditional fiber materials is presented.
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42.81.Bm Fabrication, cladding, and splicing
42.81.Dp Propagation, scattering, and losses; solitons
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The dynamics of microscopic bubbles in viscous insulating liquids

F. Jomni, A. Denat, and F. Aitken

J. Appl. Phys. 105, 053301 (2009); http://dx.doi.org/10.1063/1.3082001 (9 pages) | Cited 3 times

Online Publication Date: 3 March 2009

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The dynamics of microscopic bubbles in low viscosity insulating liquids has been widely investigated. It has been shown that the bubble motion (growth, collapse, and rebounds) in such liquids is governed by inertial forces. In this paper, the results of an experimental study of the dynamics of microscopic bubbles in viscous liquids (μ ≥ 3 mPl) are presented. It is shown that, according to the conditions (injected energy, liquid viscosity, and applied pressure), the bubble motion is greatly modified. For example, no bubble rebound is observed in the higher viscosity liquids (e.g., Napvis XD110, μ = 83.5 mPl) and, for a given injected energy, the ratio of the expansion time of the bubble to its implosion time drops with increasing in liquid viscosity. The bubble dynamics are then governed by liquid viscosity. Moreover, the transition of the bubble dynamics from the inertial regime to the viscous one has been experimentally observed (as far as the present authors are aware) for the first time. This transition can be explained by a refined analysis of the Rayleigh–Plesset model of bubble dynamics. The bubble dynamics regime can be deduced from a Reynolds number (ReTp) versus elasticity number (Σ) diagram, where four zones can be distinguished. Each zone corresponds to a particular regime: inertial regime with only one growth and collapse stage, inertial regime with at least one bubble rebound, viscous regime, and finally, a regime where a jet of hot liquid is produced. All experimental results are well distributed into the good part of this diagram.
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47.55.D- Drops and bubbles
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
66.20.-d Viscosity of liquids; diffusive momentum transport

Effects of long pulse width and high pulsing frequency on surface superhydrophobicity of polytetrafluoroethylene in quasi-direct-current plasma immersion ion implantation

Dixon T. K. Kwok, Huaiyu Wang, Yumei Zhang, Kelvin W. K. Yeung, and Paul K. Chu

J. Appl. Phys. 105, 053302 (2009); http://dx.doi.org/10.1063/1.3082122 (4 pages) | Cited 3 times

Online Publication Date: 3 March 2009

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Long pulse, high frequency quasi-direct-current (dc) oxygen plasma immersion ion implantation (PIII) is utilized to create a superhydrophobic polytetrafluoroethylene (PTFE) surface with a water contact angle of over 150°. This technique allows the use of a high duty cycle without deleterious effects such as extensive sample heating encountered in conventional PIII. Scanning electron microscopy images review submicrometer-nanometer structures on the PTFE surface after long pulse, high frequency PIII indicative of ion implantation. On the other hand, plasma modification is the dominant effect in short pulse, low frequency PIII. Quasi-dc PIII is demonstrated to offer adjustable synergistic plasma and ion beam effects.
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52.77.Dq Plasma-based ion implantation and deposition
61.72.up Other materials
61.41.+e Polymers, elastomers, and plastics

Excitation of the l = 3 diocotron mode in a pure electron plasma by means of a rotating electric field

G. Bettega, B. Paroli, R. Pozzoli, and M. Romé

J. Appl. Phys. 105, 053303 (2009); http://dx.doi.org/10.1063/1.3086619 (4 pages) | Cited 2 times

Online Publication Date: 3 March 2009

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The l = 3 diocotron mode in an electron plasma confined in a Malmberg–Penning trap has been resonantly excited by means of a rotating electric field applied on an azimuthally four-sectored electrode. The experimental observations are interpreted with a theory based on the linearization of the drift-Poisson equations and by means of two-dimensional particle-in-cell simulations. The experimental technique presented in this paper is able to selectively excite different diocotron perturbations and can be efficiently used for electron or positron plasma control and manipulation.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.65.Vv Perturbative methods
52.65.Rr Particle-in-cell method

Terahertz laser modulation of electron beams

J. G. Neumann, R. B. Fiorito, P. G. O’Shea, H. Loos, B. Sheehy, Y. Shen, and Z. Wu

J. Appl. Phys. 105, 053304 (2009); http://dx.doi.org/10.1063/1.3075563 (11 pages) | Cited 10 times

Online Publication Date: 4 March 2009

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The study of modulated electron beams is important because they can be used to produce coherent radiation, but the modulations can cause unwanted instabilities in some devices. Specifically, in a free electron laser, proper prebunching at the desired emission frequency can enhance performance, while bunching resulting from instabilities and bunch compression schemes can degrade performance. In a photoinjector accelerator, tailoring the shape of the drive laser pulse could be used as a technique to either enhance or mitigate the effect of these modulations. This work explores the possibility of creating deeply modulated electron beams at the photocathode by using a modified drive laser designed to produce multiple subpicosecond pulses repeated at terahertz frequencies. Longitudinal space charge forces can strongly influence the evolution of modulations by converting density modulations to energy modulations. Experiments at the Source Development Laboratory electron accelerator at Brookhaven National Laboratory and PARMELA simulations are employed to explore the dynamics of electron beams with varying charge and with varying initial modulation. Finally, terahertz light generated by a transition radiator is used to confirm the structure of the electron beam.
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41.60.Cr Free-electron lasers
42.60.By Design of specific laser systems
41.75.Fr Electron and positron beams
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Ion-energy distributions at a substrate in reactive magnetron sputtering discharges in Ar/H2S from copper, indium, and tungsten targets

S. Seeger, K. Harbauer, and K. Ellmer

J. Appl. Phys. 105, 053305 (2009); http://dx.doi.org/10.1063/1.3086618 (8 pages) | Cited 4 times

Online Publication Date: 6 March 2009

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Ion-energy distributions from copper, indium, and tungsten targets were measured during reactive sputtering in argon-hydrogen sulfide (H2S) mixtures, since reactive magnetron sputtering of sulfides from metallic targets is of increasing interest, especially for photovoltaic applications (buffer and absorber layers, i.e., CuInS2, In2S3, or WS2). The mass spectra of the ions show a wide range of molecules HxSn derived from H2S by plasma-assisted attachment both for positive (n ≤ 9) and for negative (n ≤ 6) ions. From the copper and the indium targets metallic ions (Cu+, In+) could be detected. While tungsten and indium sulfur compounds were found, copper does not form compounds with sulfur, caused by its lower chemical reactivity. Positive (Ar+, S+, W+, Cu+, In+, etc.) as well as negative ions (S−, InS−, WS3−) were measured for dc and rf (27 MHz) plasma excitations. The positive ions originate mainly from the plasma in front of the substrate and exhibit energies of about 12 eV for the dc and 18 eV for the rf discharge for the substrate at floating potential. The energy difference is caused by the higher electron temperature in the rf compared to the dc discharge. The ion-energy distributions of negative ions exhibit two distinct peaks. The high-energetic peak can be attributed to ions accelerated in the cathode dark space to a high energy (up to more than 400 eV) corresponding to the cathode (target) voltage. The second peak has its maximum at zero energy decreasing steeply up to energies of about 100 eV. These ions are generated by charge-exchange collisions of energetic species from the target (reflected neutral argon, negative sulfur ions, etc.) on their passage from the target to the substrate caused by the high charge-exchange cross section. rf magnetron sputtering leads to significantly lower energies of negative ions from the target, caused by the lower discharge voltages, which could be advantageous for the deposition of active semiconducting sulfide films.
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81.15.Cd Deposition by sputtering
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.55.-a Thin film structure and morphology
52.80.Pi High-frequency and RF discharges

Efficiency enhancement of a high power microwave generator based on a relativistic backward wave oscillator with a resonant reflector

Renzhen Xiao, Changhua Chen, Xiaowei Zhang, and Jun Sun

J. Appl. Phys. 105, 053306 (2009); http://dx.doi.org/10.1063/1.3086635 (3 pages) | Cited 14 times

Online Publication Date: 11 March 2009

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A high power microwave generator based on a relativistic backward wave oscillator with a resonant reflector (BWO-RR) has been proposed in order to improve microwave conversion efficiency. In this device, the slow wave structure is separated by a modulation cavity, which significantly decreases the energy spread of the modulated beam electrons. At the end of the slow wave structure, an extraction cavity is employed to increase the beam-wave interaction and optimize the extraction of the output power. Particle-in-cell simulations show that a microwave efficiency of 46% has been obtained compared with that of 34% obtained with the BWO-RR.
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84.30.Ng Oscillators, pulse generators, and function generators
84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)

Temperature measurement of an atmospheric pressure arc discharge plasma jet using the diatomic CN (B 2Σ+-X 2Σ+, violet system) molecular spectra

Se Youn Moon, D. B. Kim, B. Gweon, and W. Choe

J. Appl. Phys. 105, 053307 (2009); http://dx.doi.org/10.1063/1.3087537 (4 pages) | Cited 2 times

Online Publication Date: 11 March 2009

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The CN (B 2Σ+-X 2Σ+) molecular emission spectrum is used to measure both the vibrational and rotational temperatures in atmospheric pressure arc jet discharges. The vibrational and rotational temperature effects on the synthetic diatomic molecular spectra were investigated from the (v′,v″) = (0,0) band to the (5,5) band. The temperatures obtained from the synthetic spectra compared with the experimental result of a low-frequency arc discharge show a vibrational temperature of (4250–5010) K and a rotational temperature of (3760–3980) K for the input power in the range of (80–280) W. As the (0,0) band is isolated from other vibrational transition bands, determination of the rotational temperature is possible based only on the (0,0) band, which simplifies the temperature measurement. From the result, it was found that the CN molecular spectrum can be used as a thermometer for atmospheric pressure plasmas containing carbon and nitrogen.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
33.20.Lg Ultraviolet spectra
52.75.-d Plasma devices
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.25.-b Plasma properties

Vacuum-ultraviolet-induced charge depletion in plasma-charged patterned-dielectric wafers

G. S. Upadhyaya, J. B. Kruger, and J. L. Shohet

J. Appl. Phys. 105, 053308 (2009); http://dx.doi.org/10.1063/1.3088889 (9 pages) | Cited 6 times

Online Publication Date: 12 March 2009

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Plasma-induced charging of patterned-dielectric structures during device fabrication can cause structural and electrical damage to devices. In this work, we report on vacuum-ultraviolet (VUV) radiation-induced charge depletion in plasma-charged patterned-silicon-oxide dielectric wafers. Charge depletion is studied as a function of photon energy and the aspect ratio of hole structures. The wafers were charged in a plasma and subsequently exposed to monochromatic-synchrotron-VUV. Surface-potential measurements after VUV exposure showed that photon energies less than 11 eV were beneficial in depleting the plasma-induced charge from the patterned-dielectric wafers. In addition, for a given photon-flux density and for photon energies less than 11 eV, VUV-induced charge depletion decreases with increasing hole aspect ratio. The results are explained with a physically plausible equivalent-circuit model, which suggests that both electron photoinjection from Si into the oxide and oxide surface conductivity play an important role in the charge-depletion process.
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72.40.+w Photoconduction and photovoltaic effects
73.25.+i Surface conductivity and carrier phenomena
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
52.77.-j Plasma applications

Mechanism for low-etching resistance and surface roughness of ArF photoresist during plasma irradiation

Butsurin Jinnai, Koji Koyama, Keisuke Kato, Atsushi Yasuda, Hikaru Momose, and Seiji Samukawa

J. Appl. Phys. 105, 053309 (2009); http://dx.doi.org/10.1063/1.3089245 (6 pages) | Cited 8 times

Online Publication Date: 12 March 2009

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ArF excimer laser lithography was introduced to fabricate nanometer-scale devices and uses chemically amplified photoresist polymers including photoacid generators (PAGs). Because plasma-etching processes cause serious problems related to the use of ArF photoresists, such as line-edge roughness and low etching selectivity, we have to understand the interaction between plasma and ArF photoresist polymers. Investigating the effects of surface temperature and the irradiation species from plasma, we have found that ion irradiation by itself did not drastically increase the roughness or etching rate of ArF photoresist films unless it was combined with ultraviolet/vacuum ultraviolet (UV/VUV) photon irradiation. The structures of ArF photoresist polymers were largely unchanged by ion irradiation alone but were destroyed by combinations of ion and UV/VUV-photon irradiation. Our results suggested that PAG-mediated deprotection induced by UV/VUV-photon irradiation was amplified at surface temperatures above 100 °C. The etching rate and surface roughness of plasma-etched ArF photoresists are affected by the irradiation species and surface temperature during plasma etching. UV/VUV-photon irradiation plays a particularly important role in the interaction between plasma and ArF photoresist polymers.
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81.16.Nd Micro- and nanolithography
68.35.bg Semiconductors
85.40.Hp Lithography, masks and pattern transfer
61.80.Jh Ion radiation effects
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
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Evolution of mechanical properties in ErT2 thin films

J. A. Knapp, J. F. Browning, and G. M. Bond

J. Appl. Phys. 105, 053501 (2009); http://dx.doi.org/10.1063/1.3082011 (7 pages) | Cited 1 time

Online Publication Date: 3 March 2009

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The mechanical properties of rare earth tritide films evolve as tritium decays into 3He, which forms bubbles that influence long-term film stability in applications such as neutron generators. Ultralow load nanoindentation, combined with finite-element modeling to separate the mechanical properties of the thin films from their substrates, has been used to follow the mechanical properties of model ErT2 films as they aged. The size of the growing 3He bubbles was followed with transmission electron microscopy, while ion beam analysis was used to monitor total T and 3He content. The observed behavior is divided into two regimes: a substantial increase in layer hardness but elasticity changed little over ∼ 18 months, followed by a decrease in elastic stiffness and a modest decease in hardness over the final 24 months. We show that the evolution of properties is explained by a combination of dislocation pinning by the bubbles, elastic softening as the bubbles occupy an increasing fraction of the material, and details of bubble growth modes.
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68.60.Bs Mechanical and acoustical properties
61.80.Jh Ion radiation effects
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
62.20.dq Other elastic constants
81.40.Jj Elasticity and anelasticity, stress-strain relations

From supercritical hydrodynamic expansion to explosive phase change: Thermodynamic evolution of water during its interaction with high-intensity infrared nanosecond-pulsed laser

Benxin Wu

J. Appl. Phys. 105, 053502 (2009); http://dx.doi.org/10.1063/1.3082120 (5 pages) | Cited 1 time

Online Publication Date: 3 March 2009

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A predictive hydrodynamic model has been developed for high-intensity infrared nanosecond laser-water interactions. The model is first tested by comparing with experimental measurements for laser-induced pressure and shock wave propagation. Then the verified predictive model is applied to quantitatively understand the water thermodynamic state evolution, which has not been sufficiently studied in literature. It has been found that for the studied intense infrared nanosecond laser-water interaction, the major phase change process during the early stage is the supercritical hydrodynamic expansion followed by an explosive phase change process that occurs as the water thermodynamic-state curve approaches (from outside the binodal curve) and starts touching the critical point in the phase diagram. The model shows that the explosive phase change occurs at a delay time of ∼ 150 ns after laser pulse starts, which is quantitatively consistent with previous experimental observations.
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62.50.Ef Shock wave effects in solids and liquids
81.30.Dz Phase diagrams of other materials

Annealing effects on optical properties of low temperature grown ZnO nanorod arrays

L. L. Yang, Q. X. Zhao, M. Willander, J. H. Yang, and I. Ivanov

J. Appl. Phys. 105, 053503 (2009); http://dx.doi.org/10.1063/1.3073993 (7 pages) | Cited 23 times

Online Publication Date: 4 March 2009

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Vertically well-aligned ZnO nanorods on Si substrates were prepared by a two-step chemical bath deposition method. The structure and optical properties of the grown ZnO nanorods were investigated by Raman and photoluminescence spectroscopy. The results showed that after an annealing treatment at around 500 °C in air atmosphere, the crystal structure and optical properties became much better due to the decrease in surface defects. The resonant Raman measurements excited by 351.1 nm not only revealed that the surface defects play a significant role in the as-grown sample, which was supported by low temperature time-resolved photoluminescence measurements, but also suggested that the strong intensity increase in some Raman scatterings was due to both outgoing resonant Raman scattering effect and deep level defect scattering contribution for ZnO nanorods annealed from 500 to 700 °C.
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61.72.Cc Kinetics of defect formation and annealing
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.05.Dz II-VI semiconductors
78.55.Et II-VI semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
78.30.Fs III-V and II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
71.55.Gs II-VI semiconductors

Fe-Al interface intermixing and the role of Ti, V, and Zr as a stabilizing interlayer at the interface

W. Priyantha, R. J. Smith, H. Chen, M. Kopczyk, M. Lerch, C. Key, P. Nachimuthu, and W. Jiang

J. Appl. Phys. 105, 053504 (2009); http://dx.doi.org/10.1063/1.3079521 (5 pages) | Cited 1 time

Online Publication Date: 4 March 2009

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Fe-Al bilayer interfaces with and without interface stabilizing layers (Ti, V, Zr) were fabricated using dc magnetron sputtering. Intermixing layer thickness and the effectiveness of the stabilizing layer (Ti, V, Zr) at the interface were studied using Rutherford backscattering spectrometry (RBS) and x-ray reflectometry (XRR). The result for the intermixing thickness of the AlFe layer is always higher when Fe is deposited on Al as compared to when Al is deposited on Fe. By comparing measurements with computer simulations, the thicknesses of the AlFe layers were determined to be 20.6 Å and 41.1 Å for Al/Fe and Fe/Al bilayer systems, respectively. The introduction of Ti and V stabilizing layers at the Fe-Al interface reduced the amount of intermixing between Al and Fe, consistent with the predictions of model calculations. The Zr interlayer, however, was ineffective in stabilizing the Fe-Al interface in spite of the chemical similarities between Ti and Zr. In addition, analysis suggests that the Ti interlayer is not effective in stabilizing the Fe-Al interface when the Ti interlayer is extremely thin ( ∼ 3 Å) for these sputtered metallic films.
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68.35.Ct Interface structure and roughness
81.05.Bx Metals, semimetals, and alloys
81.15.Cd Deposition by sputtering
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.65.Ac Multilayers

Optical and microstructural study of a single layer of InGaN quantum dots

J. Bai, Q. Wang, T. Wang, A. G. Cullis, and P. J. Parbrook

J. Appl. Phys. 105, 053505 (2009); http://dx.doi.org/10.1063/1.3079525 (5 pages) | Cited 10 times

Online Publication Date: 4 March 2009

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Two typical kinds of InGaN quantum dots (QDs) have been grown on sapphires under different conditions through modifying the NH3 flow rate using metal-organic chemical vapor deposition: small spherical dots with a high dot density and large truncated pyramidal dots with a low dot density. The small dots have been found typically coherent and defect-free, while a strain relaxation has often been observed in the large dots. Consequently, this leads to a massive difference in optical properties between them. The optical properties have been investigated by means of temperature-dependent and excitation power-dependent microphotoluminescence measurements. It has been found that the small spherical QDs show higher optical quantum efficiency and much weaker piezoelectric field induced quantum-confined Stark effect than the large truncated QDs. Based on the energy balance between the strain and surface energy, the influence of V/III ratio on the transition from two-dimensional to three-dimensional growth mode during the QD growth has been discussed.
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78.67.Hc Quantum dots
81.07.Ta Quantum dots
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Cr III-V semiconductors
78.20.Jq Electro-optical effects
68.35.Md Surface thermodynamics, surface energies
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