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15 Oct 1998

Volume 84, Issue 8, pp. 4033-4639

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Limitations on distinguishing between representations of relaxation data over narrow frequency ranges

Chad R. Snyder and Frederick I. Mopsik

J. Appl. Phys. 84, 4421 (1998); http://dx.doi.org/10.1063/1.368665 (7 pages) | Cited 4 times

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In this article, we examine the ability to distinguish between relaxation functions with data over a limited range of frequency. It is demonstrated that over these limited frequency ranges under a variety of conditions, the Cole–Cole equation can be used to fit data generated by the Havriliak–Negami equation. These results show that discerning between several very different broad relaxation functions fit to data obtained over narrow time or frequency ranges is nearly impossible within experimental accuracy. Therefore, the uniqueness of the fit parameters, and hence the ability to verify model predictions, is brought into question. Furthermore, as this conclusion is drawn from comparison of exact functions that experience no dispersion overlaps or instrumental systematic errors that can mask exact fits, the true situation with experimental data is even worse. The same conclusion can be applied to time domain data.
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77.22.Gm Dielectric loss and relaxation
06.20.Dk Measurement and error theory

Imprint failures and asymmetric electrical properties induced by thermal processes in epitaxial Bi4Ti3O12 thin films

B. H. Park, S. J. Hyun, C. R. Moon, Byung-Doo Choe, J. Lee, C. Y. Kim, W. Jo, and T. W. Noh

J. Appl. Phys. 84, 4428 (1998); http://dx.doi.org/10.1063/1.368666 (8 pages) | Cited 31 times

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Epitaxial Bi4Ti3O12 (BTO) thin films were deposited on MgO(001) substrates using Pt layers as top and bottom electrodes. In spite of the apparently symmetric capacitor structure, polarization–voltage measurements revealed strong imprint failures and current–voltage measurements showed rectifying behaviors. Imprint pulse tests with a 5 V dc bias and post-annealing treatments suggested that the asymmetric behaviors should be due to interfacial states induced by thermal processes. To probe the interfacial states, capacitance–voltage (C–V) measurements were performed. By fitting the C–V data with a model which describes the Pt/BTO/Pt structure as a series circuit composed of three capacitors, built-in voltages at the top and the bottom interfaces could be determined. Difference in the built-in voltages could explain the imprint failures and the rectifying behaviors. The interfacial states in the BTO capacitors were controlled by varying electrode materials. © 1998 American Institute of Physics.
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73.61.Ng Insulators
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
73.20.At Surface states, band structure, electron density of states
77.80.Dj Domain structure; hysteresis
77.55.-g Dielectric thin films
61.72.Cc Kinetics of defect formation and annealing

Comparative study of the relaxation behavior at very low frequencies of acrylate polymers with pendant 1,3-dioxane rings in their structure

R. Díaz-Calleja, M. J. Sanchís, J. Guzmán, and E. Riande

J. Appl. Phys. 84, 4436 (1998); http://dx.doi.org/10.1063/1.368698 (7 pages) | Cited 5 times

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The dielectric activity of poly {5-[(acryloxy)methyl]-5-methyl-1,3-dioxacyclohexane} (PAMMD), poly{5-[(acryloxy)methyl]-5-ethyl-1,3-dioxacyclohexane} (PAMED) and poly{5-[(acryloxy) methyl]-2-phenyl-5-ethyl-1,3-dioxacyclohexane} (PAEDP) is studied by thermostimulated discharge current (TSDC) techniques. The global TSDC curves corresponding to PAMMD, PAMED, and PAEDP exhibit subglass absorptions centered in the vicinity of −105, −100, and −120 °C, respectively. The dielectric activity of PAEDP in the glassy region is negligible in comparison with that of both PAMMD and PAEDP which have nearly similar relaxation strengths. Prominent peaks associated with the glass–rubber transition are located at 41, 38, and 57 °C for PAMMD, PAMED, and PAEDP, respectively. The real and loss components of the complex dielectric permittivity in the frequency domain (10−10–10−2 Hz) were calculated at several temperatures from elementary peaks obtained by partial TSDC curves in the glassy region. The differences observed in the spectra are discussed in terms of previous molecular dynamics studies carried out in model compounds of the flexible side groups of these polymers. © 1998 American Institute of Physics.
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77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)
77.84.Jd Polymers; organic compounds
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
77.22.Ej Polarization and depolarization
61.41.+e Polymers, elastomers, and plastics

Formation of In– and Au–In0.52Al0.48As(100) interfaces: A soft x-ray photoemission spectroscopy study

D. S. Cammack, S. A. Clark, P. R. Dunstan, Min Pan, S. P. Wilks, and M. Elliott

J. Appl. Phys. 84, 4443 (1998); http://dx.doi.org/10.1063/1.368667 (5 pages)

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We have examined the physical and chemical reactions occurring during the formation of intimate In– and Au–InAlAs(100) at room temperature. In deposition results in a two-dimensional mode of growth, followed by clustering. Au deposition however, perturbs the interface with As diffusing into the Au overlayer. A Fermi shift is evident following the deposition of In and Au, but in both cases this is lower than barrier heights measured by transport techniques. Possible mechanisms for the observed adaptation of pinning position are discussed in the light of current models of Schottky barrier formation. © 1998 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
73.40.Ns Metal-nonmetal contacts
73.61.Ey III-V semiconductors
73.61.At Metal and metallic alloys
79.60.Jv Interfaces; heterostructures; nanostructures
73.30.+y Surface double layers, Schottky barriers, and work functions

Positron beam studies of argon irradiated CdS thin films

G. Amarendra, K. L. Narayanan, G. Venugopal Rao, B. Viswanathan, K. G. M. Nair, and K. P. Vijayakumar

J. Appl. Phys. 84, 4448 (1998); http://dx.doi.org/10.1063/1.368668 (4 pages) | Cited 1 time

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Depth profiling studies of defects in CdS thin films using a low energy positron beam are reported. CdS films of 1 μm thickness on a glass substrate have been grown using the chemical bath deposition method and irradiated with 140 keV Ar ions to doses of 5×1014 and 5×1016 cm−2, respectively. The Doppler broadening line shape S parameter in as-grown and irradiated films has been monitored as a function of positron beam energy Ep. S vs Ep curves have been analyzed, using a positron diffusion model in terms of annihilations at surface, epithermal and bulk states. The S parameter at the surface (Ss) is found to be significantly higher than that in the bulk. This is understood as due to positron trapping at a large concentration of Cd vacancies in the surface region, which act as acceptors. The observed reduction of Ss with increasing Ar ion dose seems to indicate the formation of antisite defects in the surface region, brought about by irradiation. At sample depths corresponding to the peak damage layers, the observed behavior of the S parameter indicates that no large vacancy clusters are formed. Isochronal annealing studies have been carried out to investigate the thermal stability of defects in irradiated and as-grown samples. © 1998 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.70.Bj Positron annihilation
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors

Optical properties of InxGa1−xN alloys grown by metalorganic chemical vapor deposition

W. Shan, W. Walukiewicz, E. E. Haller, B. D. Little, J. J. Song, M. D. McCluskey, N. M. Johnson, Z. C. Feng, M. Schurman, and R. A. Stall

J. Appl. Phys. 84, 4452 (1998); http://dx.doi.org/10.1063/1.368669 (7 pages) | Cited 77 times

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We present the results of optical studies of the properties of InxGa1−xN epitaxial layers (0<x<0.2) grown by metalorganic chemical vapor deposition. The effects of alloying on the fundamental band gap of InxGa1−xN were investigated using a variety of spectroscopic techniques. The fundamental band-gap energies of the InxGa1−xN alloys were determined using photomodulation spectroscopy measurements and the variation of the fundamental band gap was measured as a function of temperature. The effects of pressure on the band gap for InxGa1−xN samples with different alloy concentrations were examined by studying the shift of photoluminescence (PL) emission lines using the diamond-anvil pressure-cell technique. The results show that PL originates from effective-mass conduction-band states. Anomalous temperature dependence of the PL peak shift and linewidth as well as the Stokes shift between photoreflectance and PL lines is explained by composition fluctuations in as-grown InGaN alloys. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
78.20.-e Optical properties of bulk materials and thin films

Relaxation process of excited carriers in luminescent and nonluminescent porous silicon

Masato Ohmukai and Yasuo Tsutsumi

J. Appl. Phys. 84, 4459 (1998); http://dx.doi.org/10.1063/1.368670 (3 pages) | Cited 3 times

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We investigated photoluminescence (PL) and photoacoustic spectra of several porous silicon samples and proposed a relaxation process for excited carriers in luminescent and nonluminescent porous silicon. The carriers, generated by the exciting light, relax through a nonradiative process and then recombine resulting in light emission in the energy range from 1.7 to 2.2 eV. From the fact that PL peak energy depends linearly on the excitation energy, light emission occurs through radiative centers such as surface-localized states. If the nonradiative centers are distributed in this energy range, PL efficiency is noticeably quenched. © 1998 American Institute of Physics.
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78.55.Ap Elemental semiconductors
81.65.-b Surface treatments
73.20.Fz Weak or Anderson localization

Absorption measurements of liquid crystals in the ultraviolet, visible, and infrared

Shin-Tson Wu

J. Appl. Phys. 84, 4462 (1998); http://dx.doi.org/10.1063/1.368671 (4 pages) | Cited 23 times

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Complete absorption spectra of three liquid crystals with different conjugation length were measured in the 0.185–20 μm spectral range. In the ultraviolet region, the absorption is dependent on whether σ or π electrons are involved. In the mid and long infrared regions, several localized molecular vibration bands exist. The saddle absorption minimum occurs at around λ ∼ 0.8 μm that is far from the electronic resonance and is right before the overtone molecular vibration begins. © 1998 American Institute of Physics.  
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78.30.Jw Organic compounds, polymers
78.40.Me Organic compounds and polymers
61.30.-v Liquid crystals

Luminescence properties of thin film Ta2Zn3O8 and Mn doped Ta2Zn3O8

Philip D. Rack, Michael D. Potter, Santosh Kurinec, Wounjhang Park, John Penczek, Brent K. Wagner, and Christopher J. Summers

J. Appl. Phys. 84, 4466 (1998); http://dx.doi.org/10.1063/1.368672 (5 pages) | Cited 15 times

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Blue luminescence from Ta2Zn3O8 and green luminescence from Mn doped Ta2Zn3O8 has been observed under low voltage cathodoluminescent excitation. In this article, the luminescence mechanisms of Ta2Zn3O8 and Mn doped Ta2Zn3O8 are discussed in detail. The results suggest that the intrinsic blue luminescence of Ta2Zn3O8 results from a metal-to-ligand transition, whereas the green luminescence of Mn doped Ta2Zn3O8 results from the Mn 4T1–6A1 transition. The suppression of the blue intrinsic luminescence in Mn doped Ta2Zn3O8 suggests that efficient energy transfer from the host material to the Mn occurs. This energy transfer phenomenon is also discussed by comparing the photoluminescence excitation spectra of both thin film materials. Finally, the relative efficiency versus voltage and current density is demonstrated and discussed pertaining to field emission device operation. © 1998 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Nk Insulators

Evaluation of the energy-transfer rate between an Er 4f shell and a Si host in Er-doped Si

A. Taguchi, K. Takahei, M. Matsuoka, and S. Tohno

J. Appl. Phys. 84, 4471 (1998); http://dx.doi.org/10.1063/1.368673 (8 pages) | Cited 10 times

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We estimated the energy-transfer rate between an erbium (Er) 4f shell and a Si host by using two independent measurements. The first method involved measuring the temperature dependence of the decay time of Er 4f-shell luminescence and obtaining the energy-transfer rate by assuming that the energy transfer is assisted by nonradiative multiphonon processes and that thermal quenching is due to an energy back-transfer mechanism. The estimated value was 2×108 s−1. The second method involved measuring the time response for luminescence intensity after pulsed host photoexcitation. Although some tens of μs luminescence delay after host excitation has been reported, we found that the slow response time of the detection system may cause spurious delay. We measured the luminescence decay curve using a system with a fast response time and analyzed the data, taking into account the system response time. The energy transfer rate was estimated to be at least 107 s−1. This estimation is consistent with the result obtained by the first method, mentioned above, confirming a rather large energy-transfer rate between the Er 4f shell and Si host. © 1998 American Institute of Physics.
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78.55.Ap Elemental semiconductors
63.20.K- Phonon interactions

Electronic characterization of N,N′-bis(2-phenylethyl)perylene-3,4:9, 10-bis(dicarboximide) and its application to optical disks

Jin Mizuguchi

J. Appl. Phys. 84, 4479 (1998); http://dx.doi.org/10.1063/1.368699 (8 pages) | Cited 22 times

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The title compound is a commercial black pigment based on the perylene skeleton. As evaporated, it exhibits a brilliant red color (absorption maximum: 500 nm). However, it undergoes a color change from red to black (absorption maxima: 473 and 610 nm) when exposed to acetone vapor or heated above 100 °C for several seconds. The electronic spectra have been characterized on the basis of the crystal structure and intermolecular interactions. The red color (500 nm) is due to randomly oriented, individual molecules in the amorphous phase; whereas the black phase is characterized by a quasiordered system which gives two absorption bands: one is due to individual molecules (473 nm) and the other is due to exciton coupling effects (610 nm). The color change is attributed to the appearance (on state) or disappearance (off state) of the absorption band around 610 nm and is applicable to optical disk systems based on an AlGaInP diode laser of 635 nm. An information storage system has been developed in which the absorption at 635 nm is switched on (red–black) or switched off (black–red) on irradiation with laser in the presence of a hydrazone compound that induces a phase change. © 1998 American Institute of Physics.
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42.70.Jk Polymers and organics
42.79.Vb Optical storage systems, optical disks
78.40.Me Organic compounds and polymers
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.66.Hq Organic compounds

Dual electroluminescence of an amino substituted 1,3,5-triphenylbenzene

J. Rommens, A. Vaes, M. Van der Auweraer, F. C. De Schryver, H. Bässler, H. Vestweber, and J. Pommerehne

J. Appl. Phys. 84, 4487 (1998); http://dx.doi.org/10.1063/1.368704 (8 pages) | Cited 22 times

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The electroluminescent properties of 5′-[4-[bis(4-ethylphenyl)amino]phenyl] -N,N,N′,N′-tetrakis(4-ethylphenyl) -[1,1′:3′,1″-terphenyl]-4,4″-diamine (pEFTP) were investigated in a vapor deposited layer and dispersed in a polymer matrix. Blue–violet electroluminescence was observed, after applying voltages beyond 12 V for the single layer devices and 22 V for the double layer devices. The electroluminescence (EL) spectrum shows two maxima, of which one corresponds to that of the photoluminescence spectrum. Either direct radiative recombination of the hole and the electron residing at two neighboring molecules or phosphorescence is causing this red shifted electroluminescence maximum. Transient electroluminescence measurements allow us to estimate the mobilities of the charge carriers in the different transport layers. The occurrence of an EL overshoot after switching off a voltage pulse, confirms the importance of detrapping and interfacial phenomena in the radiative recombination in pEFTP. © 1998 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
78.60.Fi Electroluminescence

Analysis of the temperature evolution from the time resolved thermo-optical interferometric measurements with few Fabry–Pérot peaks

D. Pogany, N. Seliger, E. Gornik, M. Stoisiek, and T. Lalinský

J. Appl. Phys. 84, 4495 (1998); http://dx.doi.org/10.1063/1.368674 (7 pages) | Cited 3 times

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A mathematical method is proposed to calculate the temperature evolution in semiconductor layers from the measurements of Fabry–Pérot (FP) interferences in the reflected or transmitted intensity of a probing laser beam. The changes in the optical intensity are caused by the temperature induced changes in the refractive index and thermal expansion of the semiconductor layer. The method is particularly suitable in cases where the intensity curve exhibits few (at least two) FP intensity extrema. The unknown temperature evolution is obtained from a comparison of mathematical representations of the intensity–time and intensity–temperature dependences and using a symmetry property of the FP intensity–temperature function around the intensity extremum. Expressions for polynomial and exponential approximations of the temperature evolution are given together with empirical rules to maximize the accuracy of output parameters as thermal time constant, polynomial expansion coefficients, and temperature amplitudes. The applicability of the method is demonstrated by time resolved optical reflectivity measurements on semiconductor devices with the active layer forming a FP resonator: smart power devices prepared by silicon-on-insulator technology and power sensors fabricated on GaAs micromachined cantilevers. The temperature evolution in the former and latter devices is studied in the μs and ms time scale up to the temperature increase of 200 and 350 K, respectively. The relative error in both the extracted temperature evolution and time constants is about 15%. © 1998 American Institute of Physics.
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07.60.Ly Interferometers
78.47.-p Spectroscopy of solid state dynamics
07.20.Dt Thermometers

Electroreflectance measurements of electric fields in ordered GaInP2

J. D. Perkins, Y. Zhang, J. F. Geisz, W. E. McMahon, J. M. Olson, and A. Mascarenhas

J. Appl. Phys. 84, 4502 (1998); http://dx.doi.org/10.1063/1.368675 (7 pages) | Cited 3 times

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Ordered Ga0.52In0.48P alloys (GaInP2 for simplicity) grown on miscut [001] GaAs resemble monolayer superlattices with alternating Ga- and In-rich layers along either the [111] or [111] directions. Recent calculations suggest that, in fully ordered GaInP2, an intrinsic ordering-induced electric field of order 1600 kV/cm should exist. In partially ordered samples, as can actually be grown, the expected field is reduced to 400 kV/cm. For such a strong internal electric field, clear Franz–Keldysh Oscillations (FKOs) would be expected in an electroreflectance measurement. We report electroreflectance measurements of ordered GaInP2 layers measured at T = 100 K. For all samples measured, no FKOs are observed in the absence of an additional external dc bias voltage. At the lowest bias voltages for which FKOs are seen, the internal electric field in the GaInP2 layer, determined from the FKOs, is ∼60 kV/cm along the [001] direction corresponding to ∼100 kV/cm along the ordering direction. Hence, we conclude that, at least in the organometallic vapor phase epitaxy grown samples studied here, any net macroscopic internal electric field in the GaInP2 layer is less than ∼100 kV/cm along the ordering direction. © 1998 American Institute of Physics.
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78.20.Jq Electro-optical effects
78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors

Spectroscopic ellipsometry of composite thin films with embedded Bi nanocrystals

R. Serna, J. C. G. de Sande, J. M. Ballesteros, and C. N. Afonso

J. Appl. Phys. 84, 4509 (1998); http://dx.doi.org/10.1063/1.368676 (8 pages) | Cited 31 times

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Spectroscopic ellipsometry together with an effective medium model is used to determine simultaneously the effective refractive index, thickness, and metal volume fraction of thin nanocomposite films. The films are formed by Bi nanocrystals embedded in amorphous matrices, either semiconducting (Ge) or dielectric (Al2O3). For the Bi:Ge films (metal in an absorbing host), the values obtained for both the real and imaginary parts of the refractive index vary continuously from that of Ge to that of Bi. The metal contents determined from the ellipsometry analysis are in excellent agreement with those obtained from direct measurements of the composition. For the Bi:Al2O3 films (metal in a nonabsorbing host), the extinction coefficient (k) exhibits a maximum around 360 nm which is related to the metal plasmon resonance frequency of Bi nanocrystals. The metal content determined from the ellipsometry analysis in this case is underestimated, probably due to interaction of the Bi crystals with the Al2O3 host. © 1998 American Institute of Physics.
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78.66.Jg Amorphous semiconductors; glasses
78.66.Nk Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
07.60.Fs Polarimeters and ellipsometers
81.07.-b Nanoscale materials and structures: fabrication and characterization
68.55.-a Thin film structure and morphology

Optical functions from 0.02 to 6 eV of AlxGa1−xSb/GaSb epitaxial layers

R. Ferrini, M. Patrini, and S. Franchi

J. Appl. Phys. 84, 4517 (1998); http://dx.doi.org/10.1063/1.368677 (8 pages) | Cited 15 times

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The complex refractive index = n+ik and the dielectric function math = ε1+iε2 at room temperature of AlxGa1−xSb films with 0 ⩽ x ⩽ 0.5, grown by molecular beam epitaxy on a GaSb substrate, were determined from 0.02 to 6 eV by using the complementary data from fast Fourier transform far-infrared, dispersive, and ellipsometric spectrometry. The effect of the native oxide was accounted for and the self-consistency of the optical functions was checked in the framework of the Kramers–Kronig causality relations. In the restrahlen region the dielectric function was well fitted by classical Lorentz oscillators; in the transparent region below the fundamental gap E0, the refractive index was modeled by a Sellmeier dispersion relation, and in the interband region the dielectric function near the critical points was analyzed through standard line shapes. Interpolating the fitting parameters or the interband dielectric spectra, it was possible to obtain the optical functions for any concentration x between 0.0 and 0.5. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
78.30.Fs III-V and II-VI semiconductors

Photoluminescence from SiO2 films containing Si nanocrystals and Er: Effects of nanocrystalline size on the photoluminescence efficiency of Er3+

Minoru Fujii, Masato Yoshida, Shinji Hayashi, and Keiichi Yamamoto

J. Appl. Phys. 84, 4525 (1998); http://dx.doi.org/10.1063/1.368678 (7 pages) | Cited 122 times

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SiO2 films containing Si nanocrystals (nc-Si) and Er were prepared and their photoluminescence (PL) properties were studied. The samples exhibited PL peaks at 0.8 and 1.54 μm, which could be assigned to the electron-hole recombination in nc-Si and the intra-4f transition in Er3+, respectively. Correlation between the intensities of the two PL peaks was studied as functions of the size of nc-Si, Er concentration, excitation power and excitation wavelength. It was found that the 1.54 μm PL of Er3+ is strongly enhanced by incorporating nc-Si in films. Furthermore, the intensity of the 1.54 μm peak was found to depend strongly on the size of the incorporated nc-Si. © 1998 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.66.Jg Amorphous semiconductors; glasses
61.46.-w Structure of nanoscale materials

Surface plasmon enhanced second harmonic response from gold clusters embedded in an alumina matrix

R. Antoine, M. Pellarin, B. Palpant, M. Broyer, B. Prével, P. Galletto, P. F. Brevet, and H. H. Girault

J. Appl. Phys. 84, 4532 (1998); http://dx.doi.org/10.1063/1.368679 (5 pages) | Cited 35 times

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The second order nonlinear response from 4 nm diam gold clusters embedded in an alumina matrix deposited on a pure silica substrate has been recorded as a function of the wavelength of the fundamental incident beam. The spectrum exhibits a narrow resonance band peaked at 520 nm as a result of the coupling of the second harmonic field with the surface plasmon of the particles. The nonlinear second harmonic response of gold clusters is found to be blueshifted compared to the bulk, due to the finite size effects on the cluster optical properties, as already observed with the linear response. Furthermore, this nonlinear response appears to be well described with a simple free electron model where the valence electrons only participate through the screening of the ionic cores, owing to the weakness of the interband transition contribution. © 1998 American Institute of Physics.
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73.22.-f Electronic structure of nanoscale materials and related systems
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
61.46.-w Structure of nanoscale materials

Ga2+ hole centers and photostimulated luminescence in the x-ray storage phosphor RbBr:Ga+

U. Rogulis, S. Schweizer, S. Assmann, and J.-M. Spaeth

J. Appl. Phys. 84, 4537 (1998); http://dx.doi.org/10.1063/1.368680 (6 pages) | Cited 6 times

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It was previously shown that RbBr doped with Ga+ is an efficient x-ray storage phosphor with a figure of merit comparable to that of the commercially used BaFBr:Eu2+. The paramagnetic hole centers generated upon x-irradiation involved in the storage and read-out process were investigated by measuring the magnetic circular dichroism of the optical absorption (MCDA), the MCDA-detected electron paramagnetic resonance (MCDA-EPR) and the photostimulated luminescence (PSL). Two different Ga2+ hole centers with a hyperfine interaction with 69Ga of 69A = 8.2 GHz and 69A = 6.0 GHz, respectively, were found. No superhyperfine interaction was resolved. Therefore, the structural difference between the two Ga2+ centers could not be established from EPR. The PSL effect is correlated only to one of the two Ga2+ centers, namely that with A = 8.2 GHz. The generation mechanism of the two hole centers is investigated. It is proposed that the PSL-active Ga2+ center is an isolated Ga2+ on a Rb+ site, whereas the other center is a Ga2+-cation vacancy complex. © 1998 American Institute of Physics.
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78.55.Fv Solid alkali halides
61.80.Cb X-ray effects
78.20.Ls Magneto-optical effects
76.30.Lh Other ions and impurities
71.70.Jp Nuclear states and interactions

Determination of secondary electron yield from insulators due to a low-kV electron beam

Y. C. Yong, J. T. L. Thong, and J. C. H. Phang

J. Appl. Phys. 84, 4543 (1998); http://dx.doi.org/10.1063/1.368700 (6 pages) | Cited 18 times

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A technique for the accurate determination of secondary electron (SE) yield of insulators due to low-kV electron beam is presented. It is based on a capacitatively coupled charge measurement by subjecting the insulating film to a controlled pulsed electron beam in a scanning electron microscope. SE emissions from several insulating materials employed in integrated circuit manufacturing including wet and sputtered silicon dioxide (SiO2), polyimide, and AZ1350J photoresist, have been investigated for a range of primary energies between 0.5 and 2.5 keV. Comparisons are made between experimental data for SiO2 and polyimide with previous results. The dependence of SE emission on incidence angle and topography for SiO2 was investigated. Experimental results indicate that the dependence of SE emission on surface tilt for SiO2 is in good agreement with the power law for tilt angles below 70°, while emission saturation is observed at higher tilt angles. The SE yield from sputtered oxide was found to be higher than that of wet oxide, which is related to differences in topography between the two materials. © 1998 American Institute of Physics.
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79.20.Hx Electron impact: secondary emission

Trajectory displacement effect in particle projection lithography systems: Modifications to the extended two-particle theory and Monte Carlo simulation technique

G. H. Jansen

J. Appl. Phys. 84, 4549 (1998); http://dx.doi.org/10.1063/1.368681 (19 pages) | Cited 18 times

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The extended two-particle model for statistical interactions in particle beams, developed by Jansen [Coulomb Interactions in Particle Beams (Academic, Boston, 1990)], has been refined to improve the accuracy of the predictions of the trajectory displacement effect in particle beam projection systems. The original theory was developed for probe forming systems, such as electron and ion scanning microscopes and Gaussian or shaped beam lithography systems. Fit functions are used within the theory to express part of the numerical output into explicit analytical prescriptions. These functions were found to become inaccurate for the relatively wide beams typically used in the more recently developed projection type lithography systems. New fit functions are presented which extend the applicability of the theory to the wide beams and doublet configurations used in projection systems. The Monte Carlo program MONTEC, used to verify the results of the analytical theory, has been modified as well to account for the first order space charge magnification effect. This effect could be ignored for the relatively small spots of Gaussian and shaped beam systems, but would yield a significant overestimation of the trajectory displacement effect—assumed to be identical to the remaining blur after refocusing—for the wide images used in projection type of systems. The refined analytical theory and the modified MONTEC program have been used to evaluate the impact of statistical interactions on the performance of the SCALPEL electron projection system and a hypothetical ion projection lithography system, representing a simplified model of the IMS ALG-1000 (He+) system. The analytical predictions are in good agreement with the Monte Carlo results. An estimate of the total system resolution, determined by the combined effect of statistical interactions and geometrical aberrations, indicates that maximum attainable beam current for a 0.18 μm design rule is about 25 μA for the SCALPEL and 0.2–0.3 μA for the ion projection system, leading to an ∼10× higher throughput for the former taking the difference in resist sensitivities for electrons and ions into account. © 1998 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer

Atomic hydrogen cleaning of InP(100) for preparation of a negative electron affinity photocathode

K. A. Elamrawi, M. A. Hafez, and H. E. Elsayed-Ali

J. Appl. Phys. 84, 4568 (1998); http://dx.doi.org/10.1063/1.368701 (5 pages) | Cited 7 times

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Atomic hydrogen cleaning is used to clean InP(100) negative electron affinity photocathodes. Reflection high-energy electron diffraction patterns of reconstructed, phosphorus-stabilized, InP(100) surfaces are obtained after cleaning at ∼ 400 °C. These surfaces produce high quantum efficiency photocathodes (∼8.5%), in response to 632.8 nm light. Without atomic hydrogen cleaning, activation of InP to negative electron affinity requires heating to ∼ 530 °C. At this high temperature, phosphorus evaporates preferentially and a rough surface is obtained. These surfaces produce low quantum efficiency photocathodes (∼0.1%). The use of reflection high-energy electron diffraction to measure the thickness of the deposited cesium layer during activation by correlating diffraction intensity with photoemission is demonstrated. © 1998 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
85.60.Ha Photomultipliers; phototubes and photocathodes

Alignment of a nematic liquid crystal induced by anisotropic photo-oxidation of photosensitive polyimide films

Yinghan Wang, Chunying Xu, Akihiko Kanazawa, Takeshi Shiono, Tomiki Ikeda, Yasuo Matsuki, and Yasumasa Takeuchi

J. Appl. Phys. 84, 4573 (1998); http://dx.doi.org/10.1063/1.368682 (6 pages) | Cited 11 times

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The alignment of a nematic liquid crystal (LC) could be induced by three polyimide (PI) films exposed to linearly polarized ultraviolet (UV) light of long wavelength (366 nm). The alignment could also be modified by changing the direction of polarization of the linearly polarized light (LPL). Infrared (IR) and UV-visible spectroscopy indicated that among the three PI films the PI with a benzophenone moiety and the PI with a diphenyl methane moiety were sensitive to UV radiation and susceptible to remarkable ablation after irradiation with LPL in air. Polarized UV-visible spectroscopy indicated that dichroism of the PI films was caused by LPL and altered by changing the polarization of the LPL. Furthermore, the PI films irradiated under vacuum showed little reduction in intensity of IR bands, which is in sharp contrast to the marked decreases in samples irradiated in atmospheres containing oxygen. This proves that oxygen is necessary to the ablative process of the PI films. Our results indicate that the mechanism of LC alignment on the photosensitive PI films is photoinduced anisotropic oxidative ablation of the PI films. In contrast, the PI film with a diphenyl ether moiety was quite stable under similar irradiation conditions even though the irradiated PI film could also induce alignment of the LC molecules. © 1998 American Institute of Physics.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
78.66.Qn Polymers; organic compounds
78.30.Jw Organic compounds, polymers
78.40.Me Organic compounds and polymers
78.20.Fm Birefringence
81.65.Mq Oxidation
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
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