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15 Aug 2010

Volume 108, Issue 4, Articles (04xxxx)

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J. Appl. Phys. 108, 041901 (2010); http://dx.doi.org/10.1063/1.3474648 (2 pages)

Sergei V. Kalinin, Nava Setter, and Andrei L. Kholkin
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back to top Interdisciplinary and General Physics

Hydrogen refinement during solid phase epitaxy of buried amorphous silicon layers

D. J. Pyke, J. C. McCallum, and B. C. Johnson

J. Appl. Phys. 108, 044901 (2010); http://dx.doi.org/10.1063/1.3465547 (6 pages) | Cited 1 time

Online Publication Date: 16 August 2010

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The effect of hydrogen on the kinetics of solid phase epitaxy (SPE) have been studied in buried amorphous Si layers. The crystallization rate of the front amorphous/crystalline (a/c) interface is monitored with time resolved reflectivity. Secondary ion mass spectrometry (SIMS) is used to examine H implanted profiles at selected stages of the anneals. The H retardation of the SPE rate is determined up to a H concentration of 2.3×1020 cm−3 where the SPE rate decreases by 80%. Numerical simulations are performed to model the H diffusion, the moving a/c interfaces and the refinement of the H profile at these interfaces. Despite the high H concentration involved, a simple Fickian diffusion model results in good agreement with the SIMS data. The segregation coefficient is estimated to be 0.07 at 575 °C. A significant fraction of the H escapes from the a-Si layer during SPE especially once the two a/c interfaces meet which is signified by the lack of H-related voids after a subsequent high temperature anneal.
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68.55.ag Semiconductors
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.35.Fx Diffusion; interface formation
02.60.-x Numerical approximation and analysis

Thermal conductivity of pure silica MEL and MFI zeolite thin films

Thomas Coquil, Christopher M. Lew, Yushan Yan, and Laurent Pilon

J. Appl. Phys. 108, 044902 (2010); http://dx.doi.org/10.1063/1.3462500 (6 pages) | Cited 1 time

Online Publication Date: 16 August 2010

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This paper reports the room temperature cross-plane thermal conductivity of pure silica zeolite (PSZ) MEL and MFI thin films. PSZ MEL thin films were prepared by spin coating a suspension of MEL nanoparticles in 1-butanol solution onto silicon substrates followed by calcination and vapor-phase silylation with trimethylchlorosilane. The mass fraction of nanoparticles within the suspension varied from 16% to 55%. This was achieved by varying the crystallization time of the suspension. The thin films consisted of crystalline MEL nanoparticles embedded in a nonuniform and highly porous silica matrix. They featured porosity, relative crystallinity, and MEL nanoparticles size ranging from 40% to 59%, 23% to 47% and 55 nm to 80 nm, respectively. PSZ MFI thin films were made by in situ crystallization, were b-oriented, fully crystalline, and had a 33% porosity. Thermal conductivity of these PSZ thin films was measured at room temperature using the 3ω method. The cross-plane thermal conductivity of the MEL thin films remained nearly unchanged around 1.02±0.10 W m−1 K−1 despite increases in (i) relative crystallinity, (ii) MEL nanoparticle size, and (iii) yield caused by longer nanoparticle crystallization time. Indeed, the effects of these parameters on the thermal conductivity were compensated by the simultaneous increase in porosity. PSZ MFI thin films were found to have similar thermal conductivity as MEL thin films even though they had smaller porosity. Finally, the average thermal conductivity of the PSZ films was three to five times larger than that reported for amorphous sol-gel mesoporous silica thin films with similar porosity and dielectric constant.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
68.55.-a Thin film structure and morphology
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.16.-c Methods of micro- and nanofabrication and processing
82.70.Kj Emulsions and suspensions

Effects of yttrium doping on the thermoelectric properties of Hf0.6Zr0.4NiSn0.98Sb0.02 half-Heusler alloys

T. J. Zhu (朱铁军), K. Xiao (肖凯), C. Yu (蔚翠), J. J. Shen (沈俊杰), S. H. Yang (杨胜辉), A. J. Zhou (周爱军), X. B. Zhao (赵新兵), and J. He (贺健)

J. Appl. Phys. 108, 044903 (2010); http://dx.doi.org/10.1063/1.3475719 (5 pages) | Cited 11 times

Online Publication Date: 17 August 2010

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The (Y,Sb) codoped (Hf0.6Zr0.4)1−xYxNiSn0.98Sb0.02 (x = 0, 0.01, 0.015, 0.02, and 0.025) half-Heusler alloys were prepared by levitation melting and spark plasma sintering. The effects of Y doping on the electrical conductivity, the Seebeck coefficient, and the thermal conductivity have been investigated in the temperature range of 300–900 K. It was found that the Y doping decreased the carrier concentration and electrical conductivity due to the introduction of hole carriers. The thermal conductivity was also reduced upon Y doping, mainly due to the reduced carrier thermal conductivity. The Y-doping substantially increased the Seebeck coefficient because of the decrease in carrier concentration. Pisarenko plot showed that the measured room temperature Seebeck coefficients agrees well with the predicted single parabolic band behavior as a function of the carrier concentration, suggesting that no additional mechanisms cause the extra enhancement of Seebeck coefficient in the Y–Sb codoped half-Heusler alloys. The figure of merit ZT of 1% Y-doped sample was increased by a factor of about 25% than that of the undoped sample.
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72.15.Jf Thermoelectric and thermomagnetic effects
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
64.70.dj Melting of specific substances

Influence of surface migration on the spatial resolution of pulsed laser atom probe tomography

B. Gault, M. Müller, A. La Fontaine, M. P. Moody, A. Shariq, A. Cerezo, S. P. Ringer, and G. D. W. Smith

J. Appl. Phys. 108, 044904 (2010); http://dx.doi.org/10.1063/1.3462399 (6 pages) | Cited 20 times

Online Publication Date: 17 August 2010

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The impact of laser pulsing on the field evaporation process is investigated for Al and W by pulsed laser atom probe tomography. Quantitative analysis reveals the influence on the spatial resolution of the peak temperature reached by the specimen following light absorption from the laser pulse. It is concluded that surface migration processes induce significant degradation of the lateral resolution, changing by 100% and 20%, respectively, for Al and W when the specimen temperature is increased from 4% to 7% of the material’s melting point, while the in-depth resolution is shown to remain nearly constant for both materials.
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79.20.Ds Laser-beam impact phenomena
79.70.+q Field emission, ionization, evaporation, and desorption
68.37.Vj Field emission and field-ion microscopy
68.35.Fx Diffusion; interface formation

Tensile properties of helical auxetic structures: A numerical study

J. R. Wright, M. R. Sloan, and K. E. Evans

J. Appl. Phys. 108, 044905 (2010); http://dx.doi.org/10.1063/1.3465378 (8 pages) | Cited 3 times

Online Publication Date: 18 August 2010

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This paper discusses a helical auxetic structure which has a diverse range of practical applications. The mechanical properties of the system can be determined by particular combinations of geometry and component material properties; finite element analysis is used to investigate the static behavior of these structures under tension. Modeling criteria are determined and design issues are discussed. A description of the different strain-dependent mechanical phases is provided. It is shown that the stiffnesses of the component fibers and the initial helical wrap angle are critical design parameters, and that strain-dependent changes in cross-section must be taken into consideration: we observe that the structures exhibit nonlinear behavior due to nonzero component Poisson’s ratios. Negative Poisson’s ratios for the helical structures as low as −5 are shown. While we focus here on the structure as a yarn our findings are, in principle, scaleable.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dj Poisson's ratio
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
02.70.Dh Finite-element and Galerkin methods

Preparation, characterization, emission (Eu3+), and electron spin resonance (Gd3+) studies of Y2−xLnxTi2O7 (Ln = Eu and Gd, x = 0.0,0.05)

B. Vijaya Kumar, Radha Velchuri, V. Rama Devi, G. Prasad, B. Sreedhar, C. Bansal, and M. Vithal

J. Appl. Phys. 108, 044906 (2010); http://dx.doi.org/10.1063/1.3476057 (9 pages) | Cited 5 times

Online Publication Date: 18 August 2010

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Bulk and nanopyrochlore materials of composition Y2−xLnxTi2O7 (Ln = Eu and Gd, x = 0.0,0.05) have been prepared by sol-gel method via peroxo titanium complex precursor. All the samples were characterized by powder x-ray diffraction (XRD), Raman spectra, and transmission electron microscopy (TEM). The unit cell parameters were obtained from Rietveld analysis of XRD patterns. The influence of particle size on the emission of Eu3+ (in Y2−xEuxTi2O7), the electron spin resonance (ESR) of Gd3+ (in Y2−xGdxTi2O7) and optical absorption spectra have been studied. The band gap energy of Y1.95Ln0.05Ti2O7 (Ln = Eu and Gd) was determined and compared with parent Y2Ti2O7. The variation in the emission intensity of Eu3+ is accounted with the particle size and short range order. The spin-Hamiltonian parameters of Gd3+ were obtained from the powder ESR spectra. The single-ion anisotropy was taken in to account in the analysis of powder ESR spectra. The crystallite size was obtained from powder XRD and TEM images.
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81.07.Bc Nanocrystalline materials
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.40.Ha Other nonmetallic inorganics
78.30.Hv Other nonmetallic inorganics
76.30.Kg Rare-earth ions and impurities

Evanescent modes in sonic crystals: Complex dispersion relation and supercell approximation

V. Romero-García, J. V. Sánchez-Pérez, and L. M. Garcia-Raffi

J. Appl. Phys. 108, 044907 (2010); http://dx.doi.org/10.1063/1.3466988 (6 pages) | Cited 11 times

Online Publication Date: 20 August 2010

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Evanescent modes in complete sonic crystals (SCs) and SC with point defects are reported both theoretically and experimentally in this paper. Plane wave expansion (PWE) and in general, ω(k) methods have been used to calculate band structures showing gaps that have been interpreted as ranges of frequencies where no real k exists. In this work, we extend PWE to solve the complex k(ω) problem applied to SC, introducing the supercell approximation for studying one vacancy. Explicit matrix formulation of the equations is given. This k(ω) method enables the calculation of complex band structures, as well as enabling an analysis of the propagating modes related with real values of the function k(ω), and the evanescent modes related with imaginary values of k(ω). This paper shows theoretical results and experimental evidences of the evanescent behavior of modes inside the SC band gap. Experimental data and numerical results using the finite elements method are in very good agreement with the predictions obtained using the k(ω) method.
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63.20.Pw Localized modes

Modeling of transport phenomena during the coaxial laser direct deposition process

Shaoyi Wen and Yung C. Shin

J. Appl. Phys. 108, 044908 (2010); http://dx.doi.org/10.1063/1.3474655 (9 pages) | Cited 7 times

Online Publication Date: 23 August 2010

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Laser direct deposition is widely used for rapid freeform fabrication of fully dense components with good metallurgical properties directly from computer-aided design drawings. Because of complex physics involved such as laser powder interaction, laser substrate interaction, track interface evolution, and melt-solid interaction, it is important to develop simulation models to better understand the characteristics and mechanisms in the process so that optimization and control of a laser direct deposition process are possible. In this paper, a new comprehensive three-dimensional self-consistent transient model is presented for a coaxial laser direct deposition process, which considers physical behaviors such as laser particle interaction, mass addition, heat transfer, fluid flow, melting, and solidification. A continuum model is built to deal with different phases (gas, liquid, solid, and mushy zone) in the calculation domain. An improved level-set method, which takes the conservative form while being implicitly solved with other governing equations, is proposed to track the evolution of free liquid/gas interface during the deposition process. To make the model more physically complete than those in the literature, a newly derived mass source term, which considers the rate of the gas phase being replaced by the deposited material due to the moving interface in some control volumes, is incorporated into the continuity equation. Corresponding new source terms of enthalpy and momentum due to the moving interface are also derived and embedded in the energy and momentum equations. The governing equations are discretized using the finite volume approach to better predict the fluid motion mainly driven by capillary and thermocapillary forces. The simulated track heights, widths, molten pool depths, and track profiles agree well with the experimental results.
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81.10.Fq Growth from melts; zone melting and refining
81.30.Fb Solidification

Hugoniot of shocked liquid deuterium up to 300 GPa: Quantum molecular dynamic simulations

Cong Wang, Xian-Tu He, and Ping Zhang

J. Appl. Phys. 108, 044909 (2010); http://dx.doi.org/10.1063/1.3467969 (5 pages) | Cited 2 times

Online Publication Date: 23 August 2010

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Quantum molecular dynamic (QMD) simulations are introduced to study the thermophysical properties of liquid deuterium under shock compression. The principal Hugoniot is determined from the equation of states, where contributions from molecular dissociation and atomic ionization are also added onto the QMD data. At pressures below 100 GPa, our results show that the local maximum compression ratio of 4.5 can be achieved at 40 GPa, which is in good agreement with magnetically driven flyer and convergent-explosive experiments; At the pressure between 100 and 300 GPa, the compression ratio reaches a maximum of 4.95, which agrees well with recent high power laser-driven experiments. In addition, the nonmetal-metal transition and optical properties are also discussed.
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64.30.Jk Equations of state of nonmetals
05.70.Ce Thermodynamic functions and equations of state
61.20.Ja Computer simulation of liquid structure
71.30.+h Metal-insulator transitions and other electronic transitions
64.70.Tg Quantum phase transitions
62.50.Ef Shock wave effects in solids and liquids

Influence of Mn doping on structural, optical, and magnetic properties of Zn1−xMnxO nanorods

The-Long Phan, S. C. Yu, R. Vincent, H. M. Bui, T. D. Thanh, V. D. Lam, and Y. P. Lee

J. Appl. Phys. 108, 044910 (2010); http://dx.doi.org/10.1063/1.3478709 (7 pages) | Cited 12 times

Online Publication Date: 24 August 2010

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We prepared Zn1−xMnxO nanorods by thermal diffusion. These samples were then studied the structural, optical, and magnetic properties. The structural analyses basing on x-ray diffraction and transmission electron microscope revealed the absence of Mn-related secondary phases. The study of photoluminescence spectra revealed the blueshift in the UV emission when the Mn doping concentration was increased, as a consequence of the extension of the band gap energy. Besides this situation, the increase in emission intensity associated with extrinsic defects at about 680 nm also took place. Concerning the Raman scattering spectra, apart from conventional phonon modes related to the ZnO wurtize-type structure, there were some additional modes introduced by the doping. Their origin was assessed carefully. Particularly, the shift in peak position of E2(high) toward low frequencies due to the increase in the Mn doping concentration could be explained well by means of the spatial correlation model. Magnetic measurements proved the samples with Mn concentrations above 1.15 at. % exhibiting the weak-ferromagnetic order at low temperatures. The nature of the ferromagnetism was discussed by means of the results of the structural and optical investigations.
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81.16.-c Methods of micro- and nanofabrication and processing
78.55.Et II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
78.66.Hf II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
78.40.Fy Semiconductors
75.50.Pp Magnetic semiconductors

Influence of nozzle random side loads on launch vehicle dynamics

Nilabh Srivastava, Peter T. Tkacik, and Russell G. Keanini

J. Appl. Phys. 108, 044911 (2010); http://dx.doi.org/10.1063/1.3457887 (19 pages) | Cited 2 times

Online Publication Date: 24 August 2010

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It is well known that the dynamic performance of a rocket or launch vehicle is enhanced when the length of the divergent section of its nozzle is reduced or the nozzle exit area ratio is increased. However, there exists a significant performance trade-off in such rocket nozzle designs due to the presence of random side loads under overexpanded nozzle operating conditions. Flow separation and the associated side-load phenomena have been extensively investigated over the past five decades; however, not much has been reported on the effect of side loads on the attitude dynamics of rocket or launch vehicle. This paper presents a quantitative investigation on the influence of in-nozzle random side loads on the attitude dynamics of a launch vehicle. The attitude dynamics of launch vehicle motion is captured using variable-mass control-volume formulation on a cylindrical rigid sounding rocket model. A novel physics-based stochastic model of nozzle side-load force is developed and embedded in the rigid-body model of rocket. The mathematical model, computational scheme, and results corresponding to side loading scenario are subsequently discussed. The results highlight the influence of in-nozzle random side loads on the roll, pitch, yaw, and translational dynamics of a rigid-body rocket model.
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89.20.Kk Engineering
89.40.Dd Air transporation
02.50.Ey Stochastic processes

Enhancement of silicon solar cell efficiency by upconversion: Optical and electrical characterization

S. Fischer, J. C. Goldschmidt, P. Löper, G. H. Bauer, R. Brüggemann, K. Krämer, D. Biner, M. Hermle, and S. W. Glunz

J. Appl. Phys. 108, 044912 (2010); http://dx.doi.org/10.1063/1.3478742 (11 pages) | Cited 26 times

Online Publication Date: 24 August 2010

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Upconversion (UC) of subband-gap photons is a promising possibility to enhance solar cell efficiency by making also the subband-gap photons useful. For this application, we investigate the material system of trivalent erbium doped sodium yttrium fluoride (NaYF4:20%Er3+), which shows efficient UC suitable for silicon solar cells. We determine the optical UC efficiency by calibrated photoluminescence measurements. Because these data are free from any influence of losses associated with the application of the upconverter to the solar cell, the obtained values constitute the upper limit that can be achieved with an optimized device. Subsequently, we compare the results of the optical measurements with the results obtained by using solar cells as detectors on which the upconverter material is applied. We find an optical UC quantum efficiency of 5.1% at a monochromatic irradiance of 1880 W m−2 (0.27 cm2 W−1) at 1523 nm. The device of silicon solar cell and applied upconverter showed an external quantum efficiency of 0.34% at an irradiance of 1090 W m−2 (0.03 cm2 W−1) at 1522 nm. The differences are explained by the optical losses occurring in the upconverter solar cell device, which are dominated by the transmission of the solar cell and the incomplete absorption of the upconverting layer, and the nonlinear behavior of the upconverter.
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88.40.H- Solar cells (photovoltaics)
85.30.De Semiconductor-device characterization, design, and modeling
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.55.Hx Other solid inorganic materials

Demonstration of a plasma mirror based on a laminar flow water film

Dmitriy Panasenko, Anthony J. Shu, Anthony Gonsalves, Kei Nakamura, Nicholas H. Matlis, Csaba Toth, and Wim P. Leemans

J. Appl. Phys. 108, 044913 (2010); http://dx.doi.org/10.1063/1.3460627 (4 pages) | Cited 1 time

Online Publication Date: 25 August 2010

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A plasma mirror based on a laminar water film with low flow speed (0.5–2 cm/s) has been developed and characterized, for use as an ultrahigh intensity optical reflector. The use of flowing water as a target surface automatically results in each laser pulse seeing a new interaction surface and avoids the need for mechanical scanning of the target surface. In addition, the breakdown of water does not produce contaminating debris that can be deleterious to vacuum chamber conditions and optics, such as is the case when using conventional solid targets. The mirror exhibits 70% reflectivity, while maintaining high-quality of the reflected spot.
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52.30.-q Plasma dynamics and flow
68.15.+e Liquid thin films
47.15.gm Thin film flows

Scaling laws for electrical contact resistance with dissimilar materials

Peng Zhang and Y. Y. Lau

J. Appl. Phys. 108, 044914 (2010); http://dx.doi.org/10.1063/1.3457899 (9 pages) | Cited 4 times

Online Publication Date: 26 August 2010

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This paper attempts to quantify the effects of contaminants on electrical contact resistance. Based on an idealized model, simple and explicit scaling laws for the electrical contact resistance with dissimilar materials are constructed. The model assumes arbitrary resistivity ratios and aspect ratios in the current channels and their contact region, for both Cartesian and cylindrical geometries. The scaling laws have been favorably tested in several limits, and in sample calculations using a numerical simulation code. From the scaling laws and a survey of the huge parameter space, some general conclusions are drawn on the parametric dependence of the contact resistance on the geometry and on the electrical resistivity in different regions.
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73.40.Cg Contact resistance, contact potential

Charge separation and recombination in radial ZnO/In2S3/CuSCN heterojunction structures

Julian Tornow, Klaus Schwarzburg, Abdelhak Belaidi, Thomas Dittrich, Marinus Kunst, and Thomas Hannappel

J. Appl. Phys. 108, 044915 (2010); http://dx.doi.org/10.1063/1.3466776 (7 pages) | Cited 3 times

Online Publication Date: 31 August 2010

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A ZnO-nanorod/In2S3/CuSCN radial heterostructure has recently shown promising photovoltaic conversion efficiencies. In this work, the charge separation and recombination in single ZnO/In2S3 and In2S3/CuSCN interfaces as well as the complete ZnO/In2S3/CuSCN structure were studied by time resolved microwave photoconductivity. Photoconductivity transients were measured for different thicknesses of the In2S3 light absorbing layer, under variation in the exciting light flux and before and after annealing of the ZnO nanorods at 450 °C. Upon excitation with 532 nm light, a long lived (millisecond) charge separation at the In2S3/ZnO interface was found, whereas no charge separation was present at the In2S3/CuSCN interface. The presence of the CuSCN hole conductor increased the initial amplitude of the time resolved microwave conductivity signal of the In2S3/ZnO interface by a factor of 8 for a 6 nm thick In2S3 layer, but the enhancement in amplitude dropped strongly for thicker films. The measurements show that the primary charge separation is located at the In2S3/ZnO interface but the charge injection yield into ZnO depends critically on the presence of CuSCN.
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73.40.Ty Semiconductor-insulator-semiconductor structures
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
72.40.+w Photoconduction and photovoltaic effects
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