bluuebunny/crossref_metadata_2025 huggingface dataset:
Single Crystal X-Ray Diffraction Study of the Phase Transitions in Graphite-Bromine Intercalation Compounds
Authors: Ghosh D. , Chung D.D.L.
Published: March 2011

Reported here is the first observation of an incommensurate-commensurate phase transition at 316 ± 1 K upon heating stage-2 graphite-bromine prepared in bromine liquid. The transition during heating involved the movement of the 300 reflection toward a lower q value and the sharpening of the 010 reflection, thereby resulting in the commensurate structure characteristic of stage-2 prepared in bromine vapor. The transition was reversible. The previously reported comtmensurate-incommensurate transition occurred at 326, 329, 332, 338 and 348 K for stage 2 (in bromine liquid), stage 2 (in bromine vapor), stage 3, stage 4, and desorbed material, respectively. Disordering was observed upon completion of this transition.
C-Axis Resistivity of SbCl5-Graphite in Hopg and Single Crystal Forms
Authors: Uher C. , Morelli D.T.
Published: March 2011

C-axis electrical resistivities were measured from 2-300K on SbCl5-graphite intercalation compounds, using both HOPG and single crystals as host materials. The resistivity of these compounds is up to an order of magnitude higher (˜10−2Ωm) than that of pure HOPG graphite. Yet, for stage n≤3 (in the case of HOPG), a metallic temperature dependence of ρC is observed throughout the entire investigated range. Higher stage compounds show metallic behavior at high temperatures, but exhibit a crossover to an activated dependence as the temperature is lowered. All samples show hysteretic behavior with cycling. A model, based on defect-mediated short-circuiting channels, is proposed to account for the existence of a metallic temperature dependence in conjunction with large resistivity.
Thermodynamics Of Intercalation of Bromine in Graphite
Authors: Anderson S. H. , Chung D. D. L.
Published: March 2011

The thermodynamics of intercalation of bromine in highly oriented pyrolytic graphite had been studied by determining the pressure-temperature equilibrium diagram for stages 2–4. The standard heat and entropy of reaction for the transformation from stage n to stage n−l (n=5, 4, 3) were found to be roughly the same, though the enthalpy of reaction became slightly more negative as the stage number increased. The heat and entropy of formation from pure graphite were thus found to be −10.9 kcal mol-1 Br2 and −30.4 cal mol−1 Br2 K−1 respectively for stage 2, −11.32 kcal mol−1 Br2 and −30.6 cal mol−1 Br2 K−1 respectively for stage 3, and −11.5 kcal mol−1 Br2 and −30.6 cal mol−1 Br2 K−1 respectively for stage 4.
Intercalation-Desorption Studies of Graphite Nitrate
Authors: Dziemianowicz T. , Leong K. , Forsman W.C.
Published: March 2011

A new model for intercalation kinetics is presented whick takes into account both nucleation of the interlaminar spaces and intercalant layer growth. For nitric acid intercalation, the nucleation constant, β, ranges from 1.25×10−3 to 10−4 sec−1 depending on graphite type (HOPG > powder > fibers); the corresponding range of effective diffusivities, D, is 2.5×10−5 to 10−10 cm2/sec. It is emphasized that effective diffusivities obtained from sorption kinetics are reaction enhanced.

Stepwise isothermal desorption experiments show that the diffusivities of HNO3 neutrals are lower than the effective diffusivities on sorption. At desorptive equilibrium, intercalant retention is in the order HOPG > fibers > powder. In HOPG, resistance is constant over the desorptive transition stage II → III → IV; during the stage IV → V → VI regime (dynamic vacuum), resistance doubles. A similar resistance gain is noted on desorption of neturals from nitrated graphite fibers.
Binary and Ternary Alkali Graphite Intercalation Compounds: In-Situ X-Ray Study Of Elastic And Electrostatic Effects on Staging
Authors: Misenheimer M.E. , Chow P. , Zabel H.
Published: March 2011

We have studied stage transformations of binary potassium-graphite intercalation compounds by in-situ x-ray (00ℓ) scans. In the transition region of stages one and two, both stages coexist and all Bragg reflections exhibit resolution limited widths. The characteristics of the stage transformation are identical in intercalated HOPG and single crystals. This implies that the stage transformation is a direct process with no need of forming intermediate structures, favoring electrostatic interaction as the dominant stabilizer for pure stage donor compounds. We have also studied the elastic distortion due to potassium atoms substitutionally dissolved in rubidium intercalant layers. From the interlayer spacing variation we find a double force tensor Pzz = 0.36 eV for potassium defects in RbC8 in the small defect concentration region.
Ultrasonic Velocity Studies of Graphite and Its Intercalation Compounds
Authors: Hwang D. M.
Published: March 2011

The c-axis sound velocities and attenuations for HOPG, stage 3 and stage 4 SbCl5-graphite were determined by ultrasonic techniques in the temperature range between 4 and 325 *K. The temperature variation of C33 for HOPG agrees closely with the theoretical prediction based on the Lennard-Jones interlayer potential. In SbCl5-graphite, the longitudinal sound attenuation increases sharply and the transverse sound cannot propagate for temperatures above 200 °K, indicating a commensurate-to-incommensurate in-plane phase transition. The stage dependence of C33 at low temperatures indicates that the interlayer forces beyond the nearest layers can not be neglected.
Second-Order Raman Scattering in Graphite Intercalation Compounds
Authors: Giergiel J. , Eklund P. C.
Published: March 2011

The stage dependence of various second-order Raman features observed for acceptor (FeCl3, SbCl5) and donor (Rb) Graphite Intercalation Compounds is reported and discussed in terms of recent Born-von Kármán lattice dynamics calculations of Al-Jishi and Dresselhaus.
High Resolution Electron Microscopy of A Nicl2 – Intercalated Graphite
Authors: Dorignac D. , Lahana M.J. , Jagut R. , Jouffrey B. , Flandrois S. , Hauw C.
Published: March 2011

High resolution electron imaging supported by computer image simulation has been carried out for a nominal “second–stage” NiCl2 graphite compound. The resulting local structure information underlines the statistical nature of the stage ordering, rarely perfectly regular. It also shows the interpenetration of differently staged regions.
Cesium State, Thermal Evolution In Csc24
Authors: Estrade-Szwarckopf H. , Conard J. , Lauginie P. , Van Der Klink J. , Lagrange P. , Guerard D. , Rousseauxl F. , Nancy L.C.M.A. , Maaroufi A. , Hermann G.
Published: March 2011

By 133Cs and 13C NMR, EPR, susceptibility anisotropy and X-Ray diffraction,we studied the thermal evolution of Cs24 from 100 to 500 K. A smooth transition is observed near 300 K which can be interpreted in structural and electronic terms: at lower temperatures, the Cs atoms are located in a disordered manner on graphitic hexagonal sites and are almost completely ionized; in the high temperature state, the Cs atoms are completely disordered relatively to the graphitic lattice and their electrons are at least partly relocalized on the metallic s-function.
151Eu Mössbauer Studies on Graphite-EuC13
Authors: Boolchand P. , Lemon G. , Bresser W. , Mcdaniel D. , Heinz R.E. , Eklund P.C. , Stumpp E. , Nietfeld G.
Published: March 2011

151Eu Mössbauer experiments on EuC13-Alcl3 graphite flakes and HOPG samples have been performed as a function of temperature in the range 4.2K < T < 300K and indicate the presence of a narrow line characteristic of Eu3+. No evidence of Eu2+ was found. This suggests that enhanced conductivity of graphite upon intercalation with rare earth chlorides derives from a transfer of charge to the co-intercalated Cl.
X-Ray Diffraction Studies of Structural Dimensionality in Carbon Fibers
Authors: Stamatoff James , Goldberg Harris , Kalnin Ilmar
Published: March 2011

Diffraction patterns of carbon fibers have been recorded photographically using monochromatized MoKα radiation. <001> and  reflections are observed for fibers pyrolyzed at lower temperatures. The absence of  reflections suggests that the graphite planes are turbostratic. A three-dimensional structural transition is manifest in the appearance of  reflections. The results suggest that the degree of three dimensionality increases progressively through the sample as a function of increasing temperature of pyrolysis. There is no evidence for coexistence of three dimensional and tubostratic phases. It is further demonstrated that turbostratic carbon fibers may be intercalated to stage two with AsF5.
XPS Study of Alkali Graphite Intercalation Compounds
Authors: Wertheim G. K. , Dicenzo S. B.
Published: March 2011

Carbon 1s X-ray photoemission spectra of alkali graphite intercalation compounds are shown to provide detailed information about the distribution of charge among the carbon layers and atoms. The interior layers of higher stage compounds contain little charge and remain similar to graphite. The charge in the bounding layers is strongly localized to screen the alkali intercalate ions. The c-axis charge distribution in KC12n is in reasonable accord with the electrostatic screening model of Safran and Hamann.
Microstructure Characterization of Ferroelectric Thin Films used in Non-Volatile Memories - Optical and Scanning Electron Microscopy
Authors: Chapin Leo N. , Myers Sharon A.
Published: March 2011

Lead zirconate titanate ferroelectric thin films have been fabricated and fully integrated with standard CMOS semiconductor technology to produce non-volatile IC memory devices, now being tested in the marketplace. Starting with an organo-metallic sol-gel and using standard IC spin-on glass and annealing technologies, perovskite type ferroelectric thin films are formed. A variety of techniques have been under study for characterizing the crystalline microstructumre of the ferroelectric layer. Presented here are observations made with optical and scanning electron microscopy, and X-ray diffraction analysis of the effects of ferroelectric composition and sinter temperatures on crystal structure.
Characterization of Chemically Prepared PZT Thin Films
Authors: Tuttle Bruce A. , Schwartz R.W. , Doughty D.H. , Voigt J.A. , Carim A.H.
Published: March 2011

We have systematically varied processing parameters to fabricate PZT 53/47 thin films. Polycrystalline PZT thin films were fabricated by spin depositing Pt coated Sio2/Si substrates with alkoxide solutions. Our study focused on two process parameters: 1) heating rate and 2) excess Pb additions. We used rapid thermal processing techniques to vary heating rates from 3°C/min to 8400°C/min. Films were characterized with the following excess Pb additions: 0, 3, 5, and 10 mol% For all process variations, films with greater perovskite content had better ferroelectric properties. Our best films were fabricated using the following process parameters: an excess Pb addition of 5 mol%, a heating rate of 8400°C/min and annealing conditions of 700°C for 1 min. Films fabricated using these process conditions had a remanent polarization of 0.27 C/m2and a coercive field of 3.4 MV/m.
TEM Investigation of the Ferroelectric Domain Structure in Sputtered PZT Thin Films
Authors: Goral J.P. , Huffman Maria , Al-Jassim M.M.
Published: March 2011

The ferroelectric domain structure in sputtered lead zirconate titanate (PZT) thin films has been investigated using transmission electron microscopy (TEM) and transmission electron diffraction (TED). The individual ferroelectric domains occur as {110}-type microtwins as is observed in the bulk ceramic. The arrangement and size of the ferroelectric domains is strongly dependent on the microstructure of the sputtered film.
Microstructural Characterization of Ferroelectric Thin Films for Non-Volatile Memory Applications
Authors: Myers Sharon A. , Chapin Leo N.
Published: March 2011

Ferroelectric thin films are now being used in conjunction with semiconductor CMOS technology to produce non-volatile IC memory devices. Three film compositions across the lead-zirconate-titanate (PZT) phase diagram were examined by transmission electron microscopy (TEM). The films are produced using organo-metallic sol-gels and sintered using standard semiconductor processing techniques. The grain structure of these thin films differ greatly from bulk ceramic crystals and thin films prepared using other deposition techniques. For two compositions, Pb1.1 (Zr0.75Ti0. 25)O3 and Pb1.1 (Zr0.50Ti0.50)O3, the perovskite structure was found in large rosettes surrounded by the polycrystalline pyrochlore phase. In the Pb1.1(Zr0.25Ti0.75)O3 sample, perovskite grains were found with no evidence of the pyrochlore phase. Ferroelectric domains were imaged in all three samples.
Measuring Fatigue in PZT Thin Films
Authors: Johnson D. J. , Amm D. T. , Griswold E. , Sreenivas K. , Yi G. , Sayer M.
Published: March 2011

Small signal dielectric response is reported for a variety of PZT thin film samples. Small and large signal responses, recorded simultaneously during the fatiguing of PZT thin films, are used to identify distinct fatigue mechanisms. Microcracking or electrode delamination less than 100 Å is sufficient to explain the high correlation between the dielectric permittivity and remanent polarization during fatigue.
Electrical and Mechanical Properties of PZT Films
Authors: Etzold K. F. , Roy R. A. , Saenger K. L. , Cuomo J. J.
Published: March 2011

PZT is a well known ferroelectric material which has been investigated in thin film form for memory, electro-optical and actuator applications. The electrical and electro-mechanical properties of thin PZT films deposited by opposed target RF-sputtering and laser ablation were determined. The targets were sintered and one of them had a composition near the morphotropic phase boundary (48% Ti and 52% Zr) while the other one was on the tetragonal side of the phase diagram with 60% Ti and 40% Zr. Both types had 25% excess lead. The thin films were deposited on a number of substrates (MgO, CaF2, Al2O3 and Spinel. Platinum electrodes were e-beam evaporated on Si/SiO2 as well as on the above single crystal materials). We have measured the relative dielectric constant ε, the polarization P and the electrical field to mechanical strain conversion factor d33. The values which were obtained are compatible with bulk materials but an annealing step at 575°C in oxygen is necessary after deposition. The values before anneal are often significantly lower and we have attributed the reduction to interface layers between the electrodes and the perovskite film or a surface layer on the grains. The d33 coefficients were determined by an interferometric technique which directly detects the surface displacement of the electrode dot.
Electrical Measurement of Ferroelectric Capacitors for Non-Volatile Memory Applications
Authors: Abt Norman
Published: March 2011

Modified lead titanate ferroelectdc thin films are currently utilized in conjunction with silicon CMOS technology for non-volatile memory applications. The electrical measurement of ferroelectric films has been common practice for many years but the parameters necessary for optimizing their use as memory have not been routinely recorded. Remanent polarization, spontaneous polarization and their change through fatigue and ageing are still the dominant parameters but the pulsing conditions of interest are driven by the circuit requirements. The operation of a memory circuit will be discussed along with implications for testing. Memory is written by applying a pulse to the capacitor. It is read by applying a pulse and sensing whether or not the polarization switched. Read and write pulses will apply different voltages to the ferroelectric capacitor in the circuit because a sense capacitor will be in series with it during the read. A new test, pulsed hysteresis, which is based on circuit operation will be presented. Parameter space of interest will also be discussed.
Electrical Characterization of Ferroelectric Thin Films of Lithium Niobate on Silicon Substrates
Authors: Baumann Robert C. , Rost Timothy A. , Rabson Thomas A.
Published: March 2011

Thin films (.1-.6 μm) of LiNbO3 have been deposited on silicon substrates by rf reactive sputtering. MFS (metal-ferroelectric-semiconductor) capacitor structures were created by a liftoff process which physically isolated small areas of LiNbO3. Standard MOS (metal-oxide-semiconductor) electrical characterization techniques were used to determine the resistivity and dielectric constant of the films. Short-circuit photocurrent measurements revealed both transient and steady state components attributed to a pyroelectric effect and a bulk photovoltaic effect respectively. The conduction processes in these films were examined and found to exhibit Frenkel-Poole characteristics. Ferroelectric switching at room temperature has also been observed in these films, however, the reversed orientation was not stable.
Ferroelectric Thin Films by Metal Organic Chemical Vapour Deposition
Authors: Ainger F.W. , Brierley C.J. , Hudson M.D. , Trundle C. , Whatmore R.W.
Published: March 2011

There is a growing interest in thin films of ferroelectric oxides because of their electronic and optoelectronic applications. Various growth processes are being explored, but here, we review progress with chemical vapour deposition in a purpose built low pressure reactor. The two ferroelectric perovskites selected for our initial studies were lead titanate and lead scandium tantalate which have necessitated the synthesis of proprietary precursors. These compounds are based on metal alkoxides and β-diketonates, and are suitably modified to exhibit the required volatility and necessary thermal and hydrolytic stabilities.

Deposition has been studied over the temperature range 400–800°C and, in general, amorphous films result which can be converted by subsequent annealing to crystalline perovskites. However, the inclusion of hydroxyl group compounds (H2O or alcohols) in the vapour train catalyses the crystallisation process and enhances the growth rates at temperatures in excess of 600°C. In order to deposit the perovskite phase, it is important to maintain the gas phase composition throughout the growth. Deposition rates of up to 10μm/hour can be achieved, but the best thin films, in terms of density and morphology, are formed at lower deposition rates. The crystallite size of the deposit may vary from 0.1μm up to 2μm, depending on temperature. The choice of precursors, gas compositions and the growth conditions will be discussed in conjunction with the electrical and structural properties of the layers grown.
Effect of Thermal Processing Conditions on Ferroelectric PZT Thin Films
Authors: Kwok Chi K. , Desu Seshu B. , Kammerdiner Lee
Published: March 2011

Ferroelectric and transparent lead–zirconate–titanate thin films were fabricated by rf sputtering. The substrates used were Pt–coated single crystal silicon. The deposition temperatures were relatively low (≅ 200°C). Annealing at high temperatures yielded first pyrochlore type and finally perovskite with good switching characteristics. The phase structure, microstructure, surface composition, and properties were measured as a function annealing time and temperature. In general, the Pb concentration on the surface decreased with increasing annealing temperature or time, whereas Zr concentration increased. It was observed that the grain size of perovskite PZT did not show any significant changes with increasing either anneal temperature or time.
Characterization of Ferroelectric Thin Film PLZT(9/65/35) on R-Plane Sapphire
Authors: Krishnakumar S. , Esener S.C. , Fan C. , Ozguz V.H. , Title M.A. , Cozzolino C. , Lee S.H.
Published: March 2011

The deposition of ferroelectric PLZT on r-plane sapphire using R-F Triode Magnetron Sputtering is reported. R-plane (1102) sapphire is chosen, in spite of its large lattice mismatch to PLZT, because of its capability of integrating MOS silicon circuits with PLZT modulators. Perovskite PLZT films with the desired composition (9/65/35) are obtained using co-deposition techniques around 500°C and post deposition annealing at 650°C. The deposited films exhibit good optical and electro-optical properties. The room temperature dielectric constant of the films was 1800 at 10 Khz. The refractive index of the films was in the range 2.2–2.5. The films showed a quadratic E-O effect with R=0.6×10−16 m2/V2. The films are promising for smart Spatial Light Modulators (SLM) applications.
Substrate Temperature Effects on Properties of Silicon Nitride Films Deposited by Ion Beam Assisted Deposition
Authors: Donovan E. P. , Carosella C. A. , Grabowski K. S. , Coleman W. D.
Published: March 2011

Silicon nitride films (Si1−x,.Nx) have been deposited on silicon by simultaneous evaporation of silicon and bombardment of nitrogen ions. Films approximately 1 μm thick were deposited in an ambient nitrogen pressure of 50 μTorr. The substrate temperature (TSUB) ranged from nominally room temperature to 950° C for films with X between 0 and 0.6. Nitrogen atom fraction, X, was measured with Rutherford backscattering spectrometry (RBS). Refractive index was measured with near-IR reflection spectroscopy. Differences in film structure were measured by FT1R on the Si-N bond bending absorption mode, and by x-ray diffraction (XRD). X was found to depend upon the incident flux ratio of energetic nitrogen atoms to vapor silicon, and upon TSUB. Refractive index depends upon X and TSUB. XRD found evidence of the presence of amorphous structure, poly-crystalline silicon and (101) oriented β-Si3N4 depending on X and TSUB. The Si-N absorption signal increases with X and shows some structure at high TSUB.
Reactive Ion Etching of Copper with SiCl4 and CCl2F2
Authors: Howard B. J. , Wolterman S. K. , Yoo W. J. , Gittleman B. , SteinbrÜchel CH.
Published: March 2011

Copper may become an alternative to aluminum as an interconnect material in future multilevel metallization schemes if it is possible to pattern Cu by dry etching in a manufacturable process. Here we report results on the reactive ion etching of Cu in SiCl4 /Ar, SiCl4/N2, and CCl2F2/Ar plasmas. Etch rates have been investigated as a function of various plasma parameters, such as gas composition, pressure, etc., and substrate temperature. We have obtained etch rates as high as 850 Å /min with SiCl4/N2 and a substrate temperature of ∼ 200 ° C. Also, it appears feasible to pattern Cu anisotropically using either polyimide or amorphous carbon as a high-temperature etch mask.
Optimization of Reactive Ion Etching Parameters Via Material Characterization
Authors: Cole M. W. , Cooper C. B. , Dutta M. , Wrenn C. S. , Saliman S. , Lee H. S. , Fotiadis L. , Saunders M-L. , Chang W. H.
Published: March 2011

This study evaluates variations in SiCl4 reactive ion etching (RIE) process parameters in order to optimize the fabrication of lateral quantum well arrays (QWA) used in III–V semiconductor laser and detector designs. Since fabrication involves MBE regrowth on SiCl4 etched surfaces, material quality of both the etched surface and GaAs regrowth are evaluated. The variation of RIE parameters involved power levels, DC bias and etch times (10 Watts, -30V, 8 min.; 25 Watts, -100V, 5 min.; 95 Watts,-340V, 2 min.) while material removal was held constant (400nm). Evaluation of the etched surfaces revealed that the lattice damage depth exceeded lOOnm for all power levels. The extent of disorder beneath the etched surface was less for the low power long etch time. Etching at higher power levels for shorter time periods resulted in smoother surfaces and enhanced electrical characteristics, which in turn yielded a higher quality GaAs regrowth region. For the RIE parameters examined in this study, the variation in defect densities seemed to have a lesser effect on device performance as compared to the extreme differences in surface morphologies. Thus, for the parameters evaluated in this work, we suggest that QWA fabrication is optimized via SiClif RIE at the high power level for a short time period.
Fabrication of a-Si:H/a-Al1−xOx Superlattice by Excimer Laser MOCVD and its Properties
Authors: Uwasawa K. , Ishihara F. , Wada J. , Matsumoto S.
Published: March 2011

a-Si:H/a-A11−xOx superlattice structures have been fabricated by ArF excimer laser MOCVD. Periodic variation of composed elements in multilayers with quite uniform layer thickness was clearly shown by SIMS analysis. Optical band gap was increased with the decrease of the well layer thickness, indicating the quantum size effect. With the advantage of the inherent digital process, very sharp interface was obtained, which was confirmed by both XPS and cross sectional TEM analyses.
Silicon Homoepitaxy at 300°C Using ArF Excimer Laser Photolysis of Disilane
Authors: Fowler B. , Lian T. , Bullock D. , Banerjee S.
Published: March 2011

Photolysis of Si2H6 by an ArF excimer laser has been used to deposit Si homoepitaxial layers at temperatures as low as 300°C. The chemical vapor deposition process at growth rates from 0.5-4 Å/minute is performed in an ultra-high vacuum chamber which, along with an ex situ HF dip and a novel in situ hydrogen clean using laser excitation, results in minimization of oxygen and carbon contamination which inhibits Si epitaxy. The growth involves photolytic decomposition of Si2H6 and the generation and adsorption of SiH2 precursors on the hydrogenated Si surface, which is the rate limiting step. Growth rates are observed to vary proportionally with laser power. Very low defect density films in terms of stacking faults and dislocation loops (less than 105 cm−2), and excellent crystallinity have been deposited as confirmed by Schimmel etching and Nomarski microscopy, transmission electron microscopy, electron diffraction and in situ reflection high energy electron diffraction.
Effect of Laser Heating on Compositions of Films Deposited from the Metal Hexacarbonyls
Authors: Singmaster K. A. , Houle F. A.
Published: March 2011

A systematic study of the composition of metal films thermally deposited by laser heating (cw 514 nm) of the group VI hexacarbonyls is described. The films are found to contain significantly lower levels of carbon and oxygen than photochemically deposited films, and are spatially inhomogeneous. Estimates of temperature to determine the extent of laser heating permit the kinetics of this process to be compared to ∞ desorption from single crystal surfaces.
Characterization of BaTiO3 Thin Films Deposited by Pulsed-Laser Ablation
Authors: Scarfone Christopher , Grant Norton M. , Barry Carter C. , Li Jian , Mayer James W.
Published: March 2011

Thin films of barium titanate (BaTiOs) have been deposited by pulsed-laser ablation onto (001)-oriented MgO substrates. The films were epitactic as evidenced by both x-ray diffraction and ion-channeling techniques. The film surface appeared smooth and contained a low density of particulates. This latter feature is believed to be due to the formation of target pellets having a very high density.
Collision Cascades in Zr3Al
Authors: Howe L. M. , Rainville M. H.
Published: March 2011

Zr3Al is an ordered f.c.c. alloy of the L12 type, which under various irradiation conditions can be disordered and then eventually amorphized. In the present transmission-electron-microscopy (TEM) investigation, the nature of the damaged regions formed in individual collision cascades was investigated using low fluence (< 1 × 1011 ions cm−2) bombardments at 290 K with 15 − 120 keV 63Cu ions.

Imaging under dynamical conditions with the fundamental 111, 200, 220 and 113 reflections revealed damaged regions (5.1 - 8.1 nm average diameter) that exhibited black-white strain contrast features. These damaged regions have essentially a spherically symmetrical strain field and probably are three-dimensional clusters of point defects. Imaging with 110 superlattice reflections revealed additional damaged regions (2.4 - 3.7 nm average diameter), which appeared as black spots, that represent disordered regions in the ordered lattice. For both the strain-contrast regions and the disordered regions, as the incident ion energy increased, the number of damaged regions produced per incident ion increased and the fraction of the theoretical collision cascade volume occupied by these regions decreased.
Modeling of Damage Enhanced Diffusion of Implanted Boron in Silicon
Authors: Lo V. C. , Wong S. P. , Lam Y. W.
Published: March 2011

Modeling of the damage enhanced diffusion (DED) behaviors of implanted boron in silicon of Powell’s experiment [1] has been performed. In his experiment, Powell showed that the diffusion of implanted boron in silicon was dependent on implantation dosage as well as on the annealing conditions. For low dose boron implantation, the extent of boron diffusion after 15 second RTP is less than that of furnace annealing at 900°C for 30 minutes. But the reverse is true for the high dose case, and a two-step annealing leads to least and minimal diffusion. In this work, implantation induced excess self-interstitials which generate mobile boron atoms at the intersititial sites are considered the dominant point defect species responsible for the DED. Both the local relaxation and diffusion of these excess self-interstitials are considered. The features of the DED reported by Powell are successfully reproduced and explained.
The Use of 2-Mev He+ Microbeams for Ion-Beam Mixing of Bi-Layer Systems
Authors: Davis John B , Benenson R.E.
Published: March 2011

We have observed ion-beam mixing in three bi-layer targets, Sb/Si, Cu/Si and Cu/Al, using 2-MeV He+ beams of 4 – 9 urn width. Detailed investigation of Cu/Al revealed that 1) the depth of the mixed layer exhibits a linear dependence on dose, equivalent to 80 A for every 1018 He+ ions/cm2; 2) there is evidence of lateral diffusion of the mixed atoms away from the line of application of the beam; and 3) the sputtering coefficient for 2.0-MeV He+ on Cu is 0.07 sputtered atoms per ion.
Temperature Dependence of DC Conductivity in Ion-Beam-Irradiated Glassy Carbon
Authors: McCulloch Dougal , Prawer Steven
Published: March 2011

The electrical conductivity of ion beam irradiated Glassy Carbon has been investigated in the temperature range 100 to 300 K. Ion species used were C+ and N+ with doses between 1014 and 1018 ions/cm2. Ion beam irradiation was found to lower the conductivity of Glassy Carbon by up to six orders of magnitude. The temperature dependence of the conductivity in ion beam modified Glassy Carbon has been measured. The functional dependence was found to remain largely unchanged by ion irradiation despite the large overall decrease in the conductivity. The results are interpreted in terms of a model which includes a variable range hopping and strongly scattering metallic components.
Reactive Ion Etching of III-V Semiconductors Using Hydrogenated Chlorofluorocarbon Mixtures
Authors: Pearton S. J. , Hobson W. S. , Chakrabarti U. K. , Derkits G. E. , Perley A. P.
Published: March 2011

There are two basic gas chemistries used for dry etching of III-V semiconductors. The most common discharges contain chlorine, but these generally give rise to somewhat rough surface morphologies for In-containing compounds. More recently methane/hydrogen mixtures have been demonstrated to give low rate, smooth etching of In-based materials. In this work we describe the use of gas mixtures containing both CH and CI species. The hydrochlorofluorocarbons CHCl2F and CHCIF2 with O2 or H2 addition were used to reactively ion etch GaAs, InP, AlGaAs, GaSb, InGaAs and AlInAs as a function of etch time, plasma power density, pressure and gas composition. At moderate power densities (0.56 W · cm−2) the etch rates are in the range 125 Å · min−1 (AlInAs) to 1000 A · min−1 (GaAs). All of the materials exhibit smooth surface morphologies over a wide range of RIE parameters and there is no significant lattice disorder introduced for low power RIE as evidenced by PL and diode I-V measurements. Thin (≤40 Å) surface residue layers of CI (3–9 at. %) and F(≤3 at. %) for all materials except AlInAs are present after dry etching, but these can be removed by simple solvent cleaning.
Influence of Temperature and Electron Energy on Solid-Phase Epitaxy of Implanted Si Induced at Low Temperature by Electron Irradiation in the Electron Microscope
Authors: Lulli G. , Merli P. G. , Garulli A. , Antisari M. Vittori
Published: March 2011

Electron beam induced solid-phase epitaxy has been obtained on cross sections of implanted Si layers, by in-situ irradiation in the electron microscope, with electrons of energies of 200 and 300 keV, in the temperature range −170≤T≤20°C. The rate of the induced transformation is shown to depend very weakly on temperature (activation energies of the order of 10−2 eV ), and to be basically related to the nuclear energy loss of electrons, even if the ratio of the rates observed for irradiation at 300 and 200 keV slightly increases with T, thus deviating from the exact theoretical ratio between displacement cross sections. These facts are likely to be related to a temperature dependence of the rate of defect production and to the effect of a ionization-enhanced diffusion mechanism, rather than to a thermal mechanism of defect migration. Furthermore, the linear dependence of epitaxial rate from the dose rate leads, in the framework of a simple diffusion model, to infer that mutual interaction (recombination, clustering) between defects must be negligible. These features are discussed and compared with the results and models of ion-beam induced crystallization, which occurs in the range 200≤T≤400°C. It is concluded that different assumptions on defect kinetics must be made in the different temperature ranges where electron and ion-beam induced epitaxy occur, in order to reproduce their dependence on the main irradiation parameters.
Measured Lattice Damage and Optical Index Change in KNbo3
Authors: Irmscher R. , Fluck D. , Buchal CH. , Stritzker B. , GÜnter P.
Published: March 2011

We have used 2-MeV and 200-KeV He implantation into KNbO3 and LiNbO3 single crystals to generate a damaged layer of reduced optical index. MeV implantation enables the formation of optical waveguides of several µm thickness, which have been analyzed by dark and bright line spectroscopy in order to determine the refractive index profiles. In addition, 200-keV implants have been used to model the end-of-range-damage, which was measured by RBS/Channeling. KNbO3 and LiNbO3 show a distinctly different sensitivity of the radiation damage.
Crystallisation and Diffusion in <001> Oriented Sapphire Amorphised by Zinc Ion Implantation
Authors: Bunn L. A. , Sood D. K.
Published: March 2011

High dose zinc implantation (1×1016 to 6×1016 ions/cm2) into c-axis sapphire at 770K produces amorphous surface layers. Post-implantation annealing at temperatures at and above 800°C show that the modes of recrystallisation are strongly dependant on ion dose. At low doses formation of crystallites of α and γ phase Al2O3 is seen, with no evidence of any planar epitaxial growth at the original crystalline-amorphous interface. The zinc is seen to diffuse isotropically within the crystallised layer and becomes partially substitutional within the crystallites. At high doses, however, the formation of crystallites is inhibited, with the layer remaining amorphous. A more rapid diffusion of zinc is seen in the amorphous Al2O3, with some of the zinc being lost at the surface.
Low Fragmentation Laser Desorption of Thermally Labile Molecules
Authors: Atkinson Ian M. , Shorter Jeffrey A. , Karaiste Timo , Keene F. Richard , Steinfeld Jeffrey I. , Knight Alan E.W.
Published: March 2011

Thermally labile involatile inorganic complexes and biomolecules have been laser desorbed from silver doped emulsions without significant fragmentation. The silver doped emulsions are saturated with the molecule of interest and then mounted in the source chamber of a skimmed molecular beam apparatus. A pulsed frequency doubled Nd:YAG laser is used to desorb the molecules. The desorbed molecules are entrained in a pulsed supersonic expansion of argon, and are thereby cooled rotationally and vibrationally. A pulsed tunable dye laser is used to ionize the desorbed molecules (either resonantly or non-resonantly) between the acceleration grids of a Wiley-McLaren configuration time-of-flight mass spectrometer. Mass-resolved detection of the ions created from the desorbed species reveals that the desorption process causes almost no fragmentation for all the species studied (various aromatic amino acids and inorganic coordination compounds such as the [Ru(2,2’bipyridyl)3] moiety). While other techniques are successful for introducing relatively involatile materials into mass spectrometers, they often lead to substantial fragmentation of the molecular species of interest. Laser desorption combined with laser ionization can minimize fragmentation during both the vaporization process and the ionization step. Furthermore, a specific merit of our sample handling technique involving silver doped emulsions is that the number density of desorbed species is found to remain sufficiently stable on a shot-to-shot basis so as to permit the recording of wavelength scanned resonance enhanced multiphoton ionization spectra. The combination of laser desorption with resonance enhanced multiphoton ionization spectroscopy has thus provided for the first time a means of recording electronic spectra for a range of vibrationally and rotationally cooled involatile materials.
Maskless Laser Etching of Alumina and Ceramic Substrates
Authors: Khan Jamal
Published: March 2011

Maskless patterning of alumina (A12O3) films of various thicknesses and ceramic (TiC-Al2O3) substrate material was accomplished by using pulsed excimer and Nd:YAG laser systems. Etched structure size was defined through the computer software which also controls the workpiece position and laser operating parameters. Etch profile, materials removal rate and surface roughness was found to be dependent on laser emission wavelength, fluence, pulse rate and relative scan speed. Smoother etching was obtained with the excimer lasers. The etch characteristics are compared with those of the polymeric and metallic materials. Various potential applications of this laser based etching process in microelectronic and micromagnetic device fabrication are identified.
Laser Rapid Sintering of Metallo-Organic Derived Oxide Films
Authors: Louh Rong-Fuh , Buchanan Relva C.
Published: March 2011

Oxide films of ZrO2, Y2O3, yttria stabilized zirconia (YSZ), and high Tc superconducting YBa2Cu3O7-x and Bi-Sr-Ca-Cu-O films were produced by spin coating metallo-organic precursors onto Si, ZrO2 and MgO single crystal substrates. Densification of these oxide films, after pyrolysis of organic constituents, was achieved by scanning a Nd:YAG laser beam across the film surface. Surface morphology, microstructures, spatial grain size distribution, compositional variations, defects and physical properties of laser sintered films were characterized using SEM, EDS, TEM, SIMS, XRD and 4-point electrical resistivity probe. Laser processing parameters, deposited film thickness and organic burn-off showed strong influences on the film densification behavior. This paper focuses on pursuing optimum conditions for obtaining dense, uniform sintered patterns in oxide films and on understanding the film-substrate interaction and dynamics of nucleation and growth via the laser rapid sintering process.
In Situ Laser Ablation Plasma Diagnostics in the Film Growth Regime - Effects of Ambient Background Gases
Authors: Geohegan D. B.
Published: March 2011

The propagation of the laser-induced plasma formed by KrF irradiation of Y1Ba2Cu3O7 has been characterized in background pressures of oxygen and argon typically used for thin film growth. The ion current transmitted through the background gases was recorded along the normal to the irradiated pellet as a function of distance in order to measure the decreasing velocity and magnitude of the expanding plasma current due to collisional slowing and attenuation of the laser plume. The integrated ion charge delivered to a substrate at low pressures can be described by elastic scattering giving a general integral cross sections of σc[O2] = 3.2 × 10−16 cm2 and σc[Ar] = 2.7 × 10−16 cm2. At higher pressures, inelastic-scattering leads to increased recombination and reactive conversion of ions indicated by increased fluorescence of all the species, which becomes dominated by fluorescence of YO and BaO. Spatially resolved fluorescence measurements indicate that the luminous boundary to the plasma follows a weak shock front which coincides with the ion flux propagation. The ion transmission is found to drop exponentially with distance and background pressure, in agreement with a simple scattering model which yields general scattering cross sections for ion-argon σi-Ar = 2.1 × 10−16 cm2 and ion-oxygen σi-O2 = 2.3 × 10−16 cm2 interactions in background pressures up to 300 mTorr. The general features of the plume deceleration are described in terms of a drag force model.
Real Time Optical Diagnostics in Laser Etching and Deposition
Authors: Herman Irving P. , Tang Hua , Leong Patrick P.
Published: March 2011

Optical probing of laser-assisted chemical reactions on surfaces in real time can help explain and control these processes. Raman microprobe spectroscopy and micro laser induced fluorescence are the two optical probes employed here to investigate several examples of localized laser surface reactions. Raman microprobe analysis is used to monitor in real time the CuCl and CuCl2 products on the surface during local laser etching of copper films by Cl2 and the concomitant loss of the Cu2O passivation layer. It is also used to follow the production of Cu2O during the laser oxidation of Cu. Polarization Raman analysis is utilized to identify and analyze partially molten silicon during laser heating in vacuum and during the etching of silicon by chlorine. Laser induced fluorescence is used as a real time microprobe of desorbed products during local laser-assisted etching of Si and Al surfaces.
Selective Suppression of Carrier-Driven Photochemical Etching: Raman Spectroscopy as a Diagnostic Tool
Authors: Ashby C. I. H. , Myers D. R. , Vawter G. A. , Biefeld R. M. , Klem J. F.
Published: March 2011

Carrier-driven photochemical etching of semiconductors can be selectively suppressed by altering the near-surface region to enhance carrier recombination, thereby reducing the supply of carriers that drive the surface etching reaction. Two methods for enhancing recombination and decreasing the etch rate at a given phonon flux include ion implantation and localized Zn diffusion. Raman spectroscopy can be employed to determine whether sufficient alteration of electronic properties has occurred to suppress etching.

Carrier-driven photochemical reactions, which require direct participation of free carriers for the chemical reaction to proceed, can be selectively suppressed by increasing the minority carrier recombination rate, thereby reducing the supply of carriers that drive the surface etching reaction. Two methods for enhancing recombination and decreasing the etching quantum yield, which is the number of atoms removed per incident photon, include ion implantation and localized Zn diffusion. For ion implantation, recombination-promoting defect concentrations depend on ion species, fluence, and annealing both during and after the implantation process. Other recombination processes related to carrier scattering from ionized impurities from in-diffusion of dopants or following implant activation can control etching.

Raman spectroscopy can be employed to detect changes in electronic properties that correlate with etching suppression. Changes that occur in the LO-phonon lineshape, such as those associated with phonon confinement and ionized impurity scattering, can be diagnostic of the carrier-driven etching behavior following a specific treatment. We have demonstrated two applications of Raman spectroscopy as a diagnostic for suppression of the carrier-driven photochemical etching of GaAs.
Tem, Raman, and Langmuir Probe Studies of the Heteroepitaxial Growth of Metastable Cd(x)pb (1–X) Te Alloys Deposited on BaF2 by Low-Energy Bias Sputtering
Authors: Das Suhit R. , Cook John G. , Lockwood David J.
Published: March 2011

Metastable Cd(x)Pb(1–x)Te films with x values from 0 to 0.47, well past the range of bulk thermodynamic solubility, have been grown on single crystal (lll) BaF2 by co-deposition from CdTe and PbTe r.f. magnetron sputter targets. Cross-sectional transmission electron microscopy and transmission electron diffraction revealed epitaxial growth across the interface. However, the lattice of the deposited epilayers was observed to be typically rotated 180°C about the surface normal <111> axis of the substrate. Raman spectra of the alloys showed no evidence of segregation. Langmuir probe diagnostics were employed to estimate the energy of the ions incident on the substrate during growth which promote extended miscibility in the alloy epilayers.
Simulation of Microstructural Evolution in Polycrystalline Films
Authors: Frost H. J.
Published: March 2011

This paper will review the topic of computer simulation of the evolution of grain structure in polycrystalline thin films, with particular attention to the modelling of the grain growth process. If the grain size is small compared to the film thickness, then the grain structure is three-dimensional. As the grains grow to become larger than the film thickness, so that most grains traverse the entire thickness of the film, the microstructure may approach the conditions for a two-dimensional grain structure. Both two- and three-dimensional grain growth have been simulated by various authors.

When the grains become large enough for the microstructure to be two-dimensional, the surface energy associated with the two free surfaces of the film becomes comparable to the surface energy of the grain boundaries. In this condition, the free surface may profoundly effect the grain growth. One effect is that grooves may develop along the lines where the grain boundaries meet the free surfaces. This grooving may pin the boundaries against further migration and lead to grain-growth stagnation. Another possible effect is that differences in the free surface energy for grains with different crystallographic orientation may provide a driving force for the migration of the boundaries which is additional to that provided by grain boundary capillarity. Grains with favorable orientations will grow at the expense of grains with unfavorable orientations. The coupling of grain-growth stagnation with an additional driving force can produce abnormal or secondary grain growth in which a few grains grow very large by consuming the normal grains.
Effects of Surface Energy on the Microstructures of Thin Sb Films
Authors: Chou L. H. , Kuo M. C.
Published: March 2011

Thin Sb films have been prepared on glass substrates by rapid thermal evaporation. Films with thicknesses varied from 260 Å to 1300Å were used for the study. X-ray diffraction data showed that for films deposited at room substrate temperature, an almost random grain orientation was observed for films of 1300 Å thick and a tendency for preferred grain orientation was observed as films got thinner. For films of 260 Å thick, only two x-ray diffraction peaks--(003) and (006) were observed. After thermal annealing, secondary grains grew to show preferred orientation in all the films. This phenomenon was explained by surface-energy-driven secondary grain growth. This paper reports the effects of annealing time and film thickness on the secondary grain growth and the evolution of thin Sb film microstmctures. Transmission electron microscopy (TEM) and x-ray diffraction were used to characterize the films.