bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural, Optical and Electrical Properties of μc-SiC:H Thin Films Deposited by the VHF-GD
Authors: Fluckiger Roger , Meier J. , Shah A. , Pohl J. , Tzolov M. , Carius R.
Published: April 2011

In the present paper the authors present new results on thin (μc-SiC:H films deposited at low temperatures by the Very High Frequency - Glow Discharge technique (VHF-GD) at 70 MHz. The individual effects of each of the deposition parameters (methane and diborane gas phase ratios, input power, deposition temperature and pressure) are investigated with respect to the structural, optical and electrical properties of the films; the goal being the growth of optimised, thin μc-SiC:H layers for use as highly conductive and high gap window layers in solar cells.
Porous Silicon: A Possible Buffer Layer for Diamond Growth on Silicon Substrates
Authors: Liu Zhaohui , Zong B.Q. , Lin Zhangda
Published: April 2011

Continuous diamond films have been grown on porous silicon by hot filament chemical vapor deposition. The demonstration of diamond growth on porous silicon seems to suggest that porous silicon can act as a buffer layer for diamond growth on Si substrates, and that the nanoscale structures of porous silicon play an important role in nucleation and growth of diamond.
Characterization of Flame Grown Diamond Films by Luminescence and EPR
Authors: Pereira L. , Pereira E. , Tavares C. , Neto M. , Creades A. , Piqueras J. , Jimenez J. , Martin P.
Published: April 2011

Flame grown diamond films, depending on the growth conditions may present various amounts of diamond like carbon (DLC) besides the diamond phase. A correlation of the morphology with the secondary electron emission, cathodoluminescence, photoluminescence, EPR and Raman data is presented for samples grown using in different ratios of oxygen and acetylene.
Visible Light Emission in Silicon-Interface Adsorbed Gas Superlattices
Authors: Tsu Raphael , Morais Jonder , Bowhill Amanda
Published: April 2011

Having an indirect fundamental bandgap, unlike III-V or II-VI compound semiconductors, silicon has not played a role in optoelectronic applications such as injection lasers and light emitting diodes. In an attempt to introduce a sufficient quantum size effect, we present the experimental results on a new type of silicon based superlattices consisting of alternating layers of silicon and monolayers of adsorbed gases, Si/IAG multilayers (Si/Interface Adsorbed Gas), constructed by repeated interruptions of silicon deposition with adsorbed gases of oxygen and hydrogen. Fairly strong visible luminescence has been observed.
Surface Structure of Tetrahedral-Coordinated Amorphous Diamond-Like Carbon Films Grown by Pulsed Laser Deposition
Authors: Mercer T. W. , DiNardo N. J. , Martinez-Miranda L. J. , Fang F. , Friedmann T. A. , Sullivan J. P. , Siegal M. P.
Published: April 2011

The structure and composition of tetrahedral-coordinated amorphous diamondlike carbon films (a-tC) grown by pulsed laser deposition (PLD) of graphite has been studied with atomic force microscopy (AFM). The nanometer-scale surface structure has been studied as a function of growth parameters (e.g., laser energy density and film thickness) using contact-mode and tapping-mode AFM. Although the surfaces were found to be generally smooth, they exhibited reproducible structural features on several size scales which correlate with the variation of laser energy and the effects of excited ion etching.
Laser Doping and Crystallization of Amorphous Silicon Thin Films
Authors: Boyce J. B. , Anderson G. B. , Carey P. G. , Fork D. K. , Johnson R. I. , Mei P. , Ready S. E. , Smith P. M.
Published: April 2011

Fast-pulse laser crystallization of amorphous silicon thin films on non-crystalline substrates provides a low-temperature process for generating polycrystalline silicon. This process can be augmented by including laser doping to reduce the number of process steps in the fabrication of thin-film polysilicon devices. We have studied the simultaneous laser crystallization and laser doping process, starting with amorphous silicon on fused silica substrates and using the gas immersion technique for the doping. n-type and p-type doping employed PF5 and BF3 gases, respectively. Films were characterized both structurally and electrically. The grain size increases with increasing laser energy density as the film becomes fully melted and reaches a peak value, similar to laser crystallization without doping. The dopant concentration increases with the number of laser shots and, with 100 shots, achieves a high dose with a low sheet resistance below 1000 ohms/square, appropriate for devices. The dopant profile extends to a depth comparable to the melt depth, beyond which it falls off to the background level. Therefore, the doping depth and concentration can be controlled with the laser parameters.
Improved SiCr Resistor Performance by Means of Rapid Thermal Processing
Authors: Maghsoudnia Pirouz
Published: April 2011

New and improved processes for fabrication of SiCr thin film resistors are desirable to achieve precision circuits. Two major draw backs to conventional single target sputtered SiCr resistors are high temperature coefficient of resistance (TCR) and low sheet rho (ρ□). Depositing a very thin film to achieve a higher ρ□, generally degrades the film stability, TCR and manufacturability. Annealing the film at higher temperatures by means of hot air, does increase the film sheet rho but the anneal temperature is limited to below 500°C to avoid film decomposition.

A new method of increasing the sheet rho of SiCr films has been established where the deposited film with a ρ□ of 400Ω/□ is annealed to 1400Ω/□. Silicon substrates with thermally grown oxide were deposited with SiCr using rf sputtering. The wafers were ran through a single wafer rapid thermal processor with the chamber filled with dry nitrogen. Anneal temperatures were varied and it was found that the highest sheet rho was obtained at a temperature of 650°C and anneal time of 60 seconds. Resistors were manufactured using the annealed film and electrical characteristics of the resistors evaluated. When compared to hot air annealed SiCr resistors, the RTA SiCr resistors showed improved stability, TCR and sheet rho performance.
Characterization of High Ge Content SiGe Heterostructures and Graded Alloy Layers Using Spectroscopic Ellipsometry
Authors: Heyd A. R. , Alterovitz S. A. , Croke E. T.
Published: April 2011

SixGe1–x heterostructures on Si substrates have been widely studied due to the maturity of Si technology. However, work on SixGe1–x heterostructures on Ge substrates has not received much attention. A SixGe1–x: layer on a Si substrate is under compressive strain while SixGe1–x on Ge is under tensile strain; thus the critical points will behave differently. In order to accurately characterize high Ge content SixGe1–x layers the energy shift algorithm, which is used to calculate alloy compositions, has been modified. These results have been used along with variable angle spectroscopic ellipsometry (VASE) measurements to characterize SixGe1–x/Ge superlattices grown on Ge substrates. The results are found to agree closely with high resolution x-ray diffraction measurements made on the same samples.

The modified energy shift algorithm also allows the VASE analysis to be upgraded in order to characterize linearly graded layers. In this work VASE has been used to characterize graded SixGe1–x layers in terms of the total thickness, and the start and end alloy composition. Results are presented for a 1 µm SixGe1–x layer linearly graded in the range 0.5 ≤ x ≤ 1.0.
Structure, Stability and Properties of Covalent C34, C20, and C22 Crystals
Authors: Benedek G. , Colombo L. , Corona B. , Galvani E. , Sanguinetti S. , Serra S.
Published: April 2011

Topological arguments indicate that an infinite number of covalent carbon crystals may exist with either diamond-like (sp3), graphitic-like (sp2)- or mixed (sp3/sp2) bonding structure. We investigate the structural, elastic and electronic properties of three prototypical structure: C34, C20 and C22, respectively. All of them form a face-centered cubic lattice. Their properties have been calculated by both Montecarlo and molecular dynamics simulations based on the Tersoff potential. Both the sp3-bonded C34 and the sp2-bonded C20 are found to have a cohesive energy per atom very close to that of diamond. A comparison of elastic and electronic properties to those ones of diamond and graphite are also presented and discussed.
Reaction Chamber and Cathode Configurations in Arc Production of Fullerenes
Authors: Pasqualini E. , Podesta C. , GarcÍa A. , Rafael A. , Dengra S. , Paulozzi M.
Published: April 2011

The reaction chamber in the arc production of fullerenes was redesigned with a nozzle surrounding the decomposition zone to allow for clean collection of soot in a filtering cartridge. Quantitative analysis in the region of 300–430 nm in UV-visible spectra permits determination of the abundance of C60 and C70 in the soot. Calibrated curves of absorptivity for both pure fullerenes were employed. In equivalent conditions of current and pressure, electrographites of different origins have different decomposition rates and yields. A mechanism to interpret the cathodic deposit formation is proposed. Decomposition inside a closed cathodic cylinder yields 100% deposit.
Effect of He Pressure on the Superconducting Transition Temperatures of Na2CsC60 and (NH3)4Na2CsC60
Authors: Schirber J.E , Bayless W.R. , Rosseinsky M.J. , Zhou O. , Fleming R.M. , Murphy D. , Fischer J.E.
Published: April 2011

The Na based mixed alkali doped C60 superconductors show anomalous behavior with respect to the “universal” superconducting transition temperature Tc vs lattice constant ao relation followed by most of the fcc A3C60 superconductors. We have measured dTc/dP for Na2CsC60 and (NH3)4Na2CsC60 using solid He as the pressure medium to ∼ 6 kbar finding dTc/dP equal to −0.88±(0.01) K/kbar and −1.0(±0.1) K/kbar for Na2CsC60 and Na2(NH3)4C60 respectively. Our value for Na2CsC60 differs markedly from that obtained by Mizuki et al of about −1.3 K/kbar. However, using N2 or Ar, we obtain values for dTc/dP in substantial agreement with Mizuki et al who used fluorinert to generate their pressure. This work emphasizes the need for compressibility measurements with the same pressure medium in the appropriate temperature range so that meaningful comparisons can be made between various pressure measurements and models which are based on lattice spacing.
Higher Fullerenes: Structure and Properties
Authors: Achiba Yohji , Kikuchi Koichi , Aihara Yuichi , Wakabayashi Tomonari , Miyake Yoko , Kainosho Masatsume
Published: April 2011

The structures of higher fullerenes are described based on 13C NMR measurements of isolated and purified samples. The most interesting aspect deduced from the present structural work on the higher fullerenes up to C90 is that among 19 kinds of fullerenes with different sizes and isomers, 18 fullerenes commonly have at least one C2 symmetry axis in their molecular frame. Only one exception is C90 fullerene with a C1 symmetry. The spectral feature of UV/Visible absorption obtained for the HPLC-isolated C120 fullerene gives, on the other hand, a strong indication that the numbers of co-existing isomer of very large fullerenes are extremely limited, probably one or two. Considering the huge numbers of IPR-(isolated pentagon rule) satisfying isomer of C120 (10,774), these experimental evidences may suggest the presence of very strong selectivity for the formation of stable higher fullerenes, which, in turn, is closely associated with the unknown growth process of a fullerene cage network.
Hreels Studies of KxC60 Thin Films
Authors: Lopinski G.P. , Mitch M.G. , Chase S.J. , Lannin J.S.
Published: April 2011

High resolution electron energy loss spectroscopy has been used to investigate the vibrational and electronic excitations of single-phase, crystalline AxC60 films. Substantial changes in intramolecular mode frequencies and intensities with alkali concentration arise from charge transfer effects as well as free carrier screening. For x=4, splitting of the t1u band is observed, resulting in an insulating phase with an estimated gap of 0.3-0.4eV. Screening in the x=3 phase results in enhanced surface sensitivity and deviations from bulk stoichiometry at the surface of metallic films are observed.
Structure Sequence and Physical Properties of Rubidium Fulleride C70Rbx
Authors: Kobayashi Mototada , Fukuda Masao , Akahama Yuichi , Kawamura Haruki , Saito Yahachi , Shinohara Hisanori
Published: April 2011

A structure sequence of doped fcc, bct, bcc and Rb-saturated fcc phases was observed in C70Rbx with increasing Rb concentration using x-ray-diffraction measurements. The composition of the Rb-saturated phase was estimated to be C70Rb9.4±0.4 from a weight measurement. A model for the structure of C70Rb9 is proposed. Superconductivity in each phase was checked using ac magnetic-susceptibility measurements. All these phases were nonsuperconducting down to 1.3 K.
Polyhydroxylated C60 as an Hypercross-Linking Agent
Authors: Chiang Long Y. , Wang Lee Y. , Wu Rong-Shen , Hsieh Kuo-Huang
Published: April 2011

Polyhydroxylated fullerene derivatives (fullerenols) were utilized as an efficient hypercross-linking agent for the synthesis of elastic poly(tetramethylene oxide)-based polyurethane networks with excellent thermal mechanical properties. Polyhydroxylated fullerenes were synthesized from the hydrolysis of polycyclosulfated fullerene derivatives in the presence of water at 85-90 °C or in aqueous NaOH solution at ambient temperature.
Characterization of Ferromagnetic Nanoparticles Produced by A Carbon Arc
Authors: Brunsman E. M. , Anna S. , Majetich S. A. , Mchenry M. E.
Published: April 2011

The effect of increasing metal fraction on carbon arc nanoparticle production is examined for 10–50 weight percent cobalt starting materials. With 500 Torr of helium buffer gas, the carbon arc process yields carbon-coated FCC Co nanoparticles of similar sizes throughout this range. The saturation magnetization is believed to scale linearly with the relative abundance of Co. The variation in the coercivity with abundance is small compared to the dramatic changes which can arise from changes in the size of fine particles. The approach to magnetic saturation is more rapid in high abundance samples. This is attributed to interparticle interactions which align the easy axes when the nanoparticles crystallize within interconnected carbon shells. The switching field distribution as a function of Co abundance arises from both rotational barriers and from barriers due to the particle size distribution.
Functionalization of C60 by Cycloaddition Reactions
Authors: Wilson Stephen R. , Cao Jingrong , Lug Qingyi , Wu Yunhui , Kaprinidas Nikolaos , Lem George , Saunders Martin , Jimenez-Vasquez Hugo A. , Schuster David I.
Published: April 2011

Functionalization of C60 has been achieved by [2+2] photocycloaddition reactions of enones and [2+4] cycloaddition reactions of dienes, the course of these reactions can be followed using electrospray mass spectrometry using a special tagging reagent. Using tagged C60 it was shown that cis and trans cycloadducts are formed from ketones such as 3-methylcyclohexenone. We have also employed the new technique of 3He NMR spectrometry. 3He is an NMR-active nucleus. Fullerenes containing an endohedral 3He atom can be examined by NMR to obtain structural information and potentially determine isomer distributions. Examples, of helium spectra of fullerene hydrides are presented.
Morphology of Nanoparticles and Fullerene Blacks Produced in A Carbon Arc
Authors: Scott John Henry J. , Majetich S. A. , Derrington S.
Published: April 2011

Using X-ray powder diffraction and transmission electron microscopy we examine the morphology and crystallographic structure of carbon-coated nanoparticles produced in a modified Huffman-Kratschmer carbon arc process. Graphite rods containing Ho were consumed in the arc and soots sampled from both the reactor walls and the inner core of the cathode deposit are compared. The inner core soot displays increased crystallinity and less amorphous carbon than wall-deposited soot, and nanoparticles in the inner core have more graphitic layers in the encapsulating shells, more gaps between the carbon coating and the core, and exhibit a greater degree of facetting than particles harvested from the reactor walls. These differences are interpreted as manifestations of the high temperature post-formation environment of the inner core of the cathode deposit.
Low Temperature Internal Friction of thin Fullerene Films
Authors: White B. E. , Freund J. E. , Topp K. A. , Pohl R. O.
Published: April 2011

The lattice vibrations of crystalline solids are generally described by traveling elastic waves. However, the vibrations of fullerene solids are expected to be quite different from typical crystalline solids because of the large molecular mass. In fact, based on measurements of thermal conductivity and specific heat, it appears that the vibrations of compacted fullerene solids are best described as localized. Only below a few Kelvin has evidence for elastic waves been found in these solids where they exist along with the localized tunneling states that are characteristic of amorphous solids. In order to verify the existence of these tunneling defects, the low temperature internal friction of thin fullerene films deposited on a silicon substrate has been measured. Fullerene films were prepared under a variety of conditions with substrate temperatures ranging from 300 K to 500 K. Film grain sizes were characterized using atomic force microscopy, as well as, scanning tunneling microscopy. Grain sizes were found to range between 100 nm and 400 nm. We find that while localized tunneling defects appear to be present in these films, they do not appear to be intrinsic to the fullerene solid. Instead, the tunneling states may be the result of residual disorder that is present in the grain boundaries of the solids.
13C Isotopic Effect on the Raman Spectrum and Structure of C60 Fullerene
Authors: Huong Pham V. , JÉrÔme Denis , Auban-Senzier Pascale , Bernier Patrick
Published: April 2011

The Raman spectrum of 13C enriched C60 samples is recorded and analyzed in comparison with that of undoped 12C60. Comparison with the isotopic effect in diamond and in other infinite solid networks is also made.

A frequency shift depending on the amount of 13C is observed for the C=C stretching vibration, without any splitting. This effect is unusual and is a proof that the C=C is not localized and its double bond character is not isolated but strongly coupled with other bonds in the cage. If the CC bond was independent as in small or non-spherical molecules such as organic compounds, an isotopic effect of Δv ≃ 30 cm-1 for 12C=13C and Δv ≃ 60 cm−1 for 13C=13C could be expected and a splitting could appear in the case of uncompleted 13C substitution and variable relative intensities could be observed. It is not the case of 13C60.

In isotopic C60, all C=C vibrations in the spherical network are stronglycoupled ; an average isotopic mass must be considered for the randomly distributed isotopic atoms in the material to interpret the experimental result. C60 has thus more solid than molecule behavior.
Micro-Ftir and Theoretical Study of C60 Single-Crystal Vibrational Modes
Authors: Guizzetti G. , Marabelli F. , Patrini M. , Manfredini M. , Milani P. , Benedek G. , Sanguinetti S.
Published: April 2011

Reflectance (R) and trasmittance (T) of C60 single-crystals have been measured in the 400-5000 cm-1 range, at room temperature, by using micro-Fourier transform IR spectroscopy. The frequencies of the peaks, appearing in both R and T spectra, are compared with the IR active ones calculated for the simple cubic structure with the bond charge model. It appears that all modes which are expected from symmetry arguments to give a dipole activity are actually observed and the corresponding frequencies are in good agreement with the experimental findings.
Laser and oxygen induced damage of C60 single crystal observed by scanning electron microscopy
Authors: Milani P. , Manfredini M.
Published: April 2011

Modifications induced by laser heating of C60 single crystal are examined by scanning electron microscopy (SEM). The fullerite surface is etched in the presence of oxygen, whereas no substantial change is observed under inert atmosphere. The formation of three dimensional micro-structures is observed depending on laser annealing conditions. Energy dispersive X-ray (EDX) spectroscopy shows that oxygen concentration substantially increases in the irradiated regions.
13C NMR Study of Oxygen Intercalation in C60
Authors: Bernier P. , Luk'yanchuk I. , Belahmer Z. , Ribet M. , Firlej L.
Published: April 2011

High resolution 13C NMR has been used to investigate the properties of solid C60 after intercalation of molecular oxygen, which does not induce charge transfer with the host molecules. We show that, via the magnetic characteristics of the intercalant, information can be gained on its position and movement in the structure. In particular, molecular oxygen is found to occupy the middle of the octahedral site in the fcc structure of solid C60.
Neutron Scattering Studies of C61H2
Authors: Neumann D. A. , Fischer J. E. , Copley J. R. D. , Heiney P. A. , Rush J. J. , Strongin R. M. , Brard L. , Smith Amos B.
Published: April 2011

We report neutron diffraction measurements of orientational ordering, and inelastic neutron scattering measurements of the inter- and intra-molecular excitations, for the 6:5 annulene isomer (C3 symmetry) of C61H2. We confirm previous x-ray measurements[1] which have shown that above 290K this isomer has an fcc structure, with the molecules orientationally disordered such that the methylene groups preferentially occupy “octahedral” sites. Below 290K, the diffraction pattern can be indexed on a simple cubic lattice, in direct analogy with the orientational ordering transition of C60. The observed low energy dynamics reflect this behavior. A peak corresponding to molecular librations is observed below the transition, at ∼2.5meV, while above the transition the peak collapses into a quasielastic line characteristic of rotational diffusion. The intramolecular spectra show several pronounced peaks. The assignments of these modes are discussed.
Thermal Conductivity of C60 Under High Pressure
Authors: Andersson O. , Soldatov A. , Sundqvist B.
Published: April 2011

We have measured the thermal conductivity λ of highly pure polycrystalline C60 in the range 50 to 300 K under pressures up to 1 GPa. The results are discussed in terms of the lattice structure and dynamics. In particular, we discuss the phase diagram as delineated by anomalies observed in λ and cp at the f c.c.-to-s.c. transition at 260 K and the glass transition at Tg = 90 K, and also the effect on λ of the orientational motion in the s.c. phase. The results are found to be compatible with p-T phase diagram recently suggested by us.
Thermophysical Properties of C70 Up to 1 GPa
Authors: Lundin A. , Soldatov A. , Sundqvist B.
Published: April 2011

We have measured the thermal conductivity λ and the compressibility of highly pure C70 in the range 90 to 450 K under pressures up to 1.2 GPa. Our results for the thermal conductivity indicate molecular rotation in C70 above 280 K at zero pressure. The phase boundary for the rotationally disordered phase has an approximate slope dT/dp = 75 K GPa−1. The bulk modulus B increases linearly with increasing p above 0.1 GPa, with an extrapolated zero pressure value at 296 K of B(0) = 8.3 GPa. Unexpected anomalies are found in both B and λ near 100 MPa, and we tentatively suggest that orientational ordering is responsible.
Diffusion Separation of Fullerenes in Solution
Authors: Eletskii Alexander V. , Okun Michael V. , Stepanov Eugene V.
Published: April 2011

The diffusion of fullerenes in solution is studied taking into account the recently established fact of the formation of clusters containing some number of aggregated fullerene molecules. Based on a droplet model of a cluster, the distribution function of fullerene clusters by size is obtained for various concentrations of solution. It is shown that dissolved fullerene is present mainly in the form of clusters at saturation conditions, but the contribution of clusters decreases as concentration drops down. Since the diffusion mobility of clusters is much less than that of molecules, it leads to the dependence of an effective diffusion coefficient on concentration, which is computed for the case of fullerene C60. The feasibility of the use of this dependence as a basis for a diffusion method of the separation and enrichment of the fullerene extract with a small addition of higher fullerenes is analyzed. Possible schemes for enrichment are discussed.
Optical Band Gap Implications for Ferroelectric Memory Applications
Authors: Klein J.D. , Clauson S.L.
Published: April 2011

Metallic perovskite contact layers enable fatigue-resistant ferroelectric memory capacitors to be obtained. LaNiO3 films atop (100) LaAlO3 substrates exhibit metallic resistivity over a wide range of temperature and oxygen partial pressure. Subsequent deposition of PZT and LaNiO3 thin films atop LaNiO3/LaAlO3 provides parallel-plate ferroelectric capacitor structures. However, the quality of the PZT thin films cannot be reliably indicated by conventional means such as x-ray diffraction. Optical properties of the PZT layers were examined to discern differences in otherwise similar films. The suitability of Au/LaNiO3/PZT/LaNiO3/LaAlO3 devices for nonvolatile memory applications was surveyed through pulsed voltage testing. Observed 1-second remanent polarization (PR [1 sec]) exceeded 35μC/cm2. Long-term memory was demonstrated for up to sixteen hours. No decrease in remanent polarization was apparent after more than 2 × 1010 switching cycles.
Optical Losses in Ferroelectric Oxide Thin Films: Is There Light at the End of the Tunnel?
Authors: Fork D. K. , Armani-Leplingard F. , Kingston J. J.
Published: April 2011

Optical losses are a barrier to use of ferroelectric waveguide thin films. Losses of about 2 dB/cm will reduce the efficiency of a frequency doubler by over 50%. Achieving losses on this order in conjunction with other essential film properties is difficult. The optical loss has several origins, including absorption, mode leakage, internal scattering and surface scattering. When the film surface morphology is accurately known, it is possible to estimate the surface scattering component of the loss. We have employed atomic force microscopy and computer modeling to compute, and correlate the optical loss as a function of film thickness and wavelength. The results suggest upper limits to the morphological roughness for various device applications. For lithium niobate films on sapphire which are intended to frequency double into the blue part of the spectrum, the optimal film thickness is about 400 nm and the RMS roughness is constrained below about 1.0 nm, with some weak dependence on grain size. Although present growth techniques do not appear to achieve this level of surface flatness intrinsically, an understanding of the morphological development of the film structure may lead to improvements.
Pulsed Laser Deposition of Epitaxial Sr0.61Ba0.39Nb2O6 Thin Films for Waveguide Applications
Authors: Youden K.E. , Schwyn Thöny S. , Hesselink L. , Harris J.S.
Published: April 2011

We report the epitaxial growth of Sr0.6iBa0.39Nb2O6 (SBN) thin films on MgO substrates by pulsed laser deposition. Rutherford backscattering analysis shows that the films have stoichiometric composition, identical to the target, and thicknesses in the range 200–400 nm. X-ray diffraction 2θ-scans indicate layers with the (001) orientation perpendicular to the substrate plane, and phi scans on the (221) plane reveal that the films have two pairs of in-plane orientations. The orientations correspond to a rotation of the SBN unit cell relative to the MgO unit cell of ± 18.6° and ± 30.9° respectively. Waveguide characterization shows waveguides supporting up to four modes and film refractive indices which compare well with those of bulk SBN.
Influence of the Ferroelectric Phase Transition on the Photoelectrical Properties of the P-N Junctions
Authors: Lupu Anatol T. , Grishechkina Svetlana P.
Published: April 2011

Photoelectrical properties of the p-n junctions on the base of Pb1−xGexTe were investigated. A number of anomalous phenomena below Tc such as: the change of the photovoltage sign, low frequency maximum in the temperature dependence of the junction capacitance and feature near the edge of the spectral dependence were observed.

To explain the obtained results a model considering screening of spontaneous polarization outside the junction was proposed. This work gave for the first time experimental evidence concerning the model of polarization switching in ferroelectric with p-n junction.
Electrode Contacts on PZT Thin Films and Their Influence on Fatigue Properties
Authors: Lee J.J. , Thio C.L. , Bhattacharya M. , Desu S.B.
Published: April 2011

The degradation (fatigue) of dielectric properties of ferroelectric PZT (Lead Zirconate Titanate) thin films during cycling was investigated. PZT thin films were fabricated by metal-organic decomposition (MOD). Samples with electrodes of platinum (Pt) and ruthenium oxide (RuO2) were studied. The interfacial capacitance (if any) at the Pt/PZT and RuO2/PZT interfaces was determined from the thickness dependence of low-field dielectric permittivity (εr) measurements. It was observed that a low εrlayer existed at the Pt/PZT interface but not at the RuO2/PZT interface. The dielectric permittivity of this interfacial layer degrades with increasing fatigue while the εrof the bulk PZT film remains constant. This indicates that fatigue increases the interfacial layer thickness but does not change the bulk properties. For the capacitors with RuO2/PZT/RuO2 structure, however, the εdoes not change with thickness and fatigue cycling. This implies no interfacial layer exists between RuO2/PZT and, therefore, no fatigue was observed. Additionally, an impedance spectroscopie technique has been proposed for possible use in analyzing the nature of the interfacial layer during the fatigue process.
Effects of A.C. Stress on Charge and Voltage Decay Rates of PZT Thin Film Capacitors for DRAM Applications
Authors: Khamankar Rajesh B. , Kim Jiyoung , Jiang Bo , Lee Jack
Published: April 2011

A PZT thin film capacitor displays a reduction in the charge storage density (Qc') after the device has undergone pulsed electrical stress. This changes the charge-voltage relationship for the devices. The effect of this change in the Q-V relationship on the DRAM READ time is described. Measurements of the charge and voltage decay rates have been previously identified as ideal techniques for characterizing signal loss. For the first time the effects of electrical stress on these rates have been studied. While the charge decay rate decreases with an increase in the number of stress cycles for both the bipolar and unipolar stress, the voltage decay rate decreases after unipolar stress but it increases for bipolar stress at lower stress voltages. The implications of these results on the DRAM performance shall be discussed.
Microstructural and Electrical Characterization of Barium Strontium Titanate Thin Films
Authors: Wu Yujing , Jacobs Elizabeth G. , Pinizzotto Russell F. , Tsu Robert , Liu Hung-Yu , Summerfelt Scott R. , Gnade Bruce E.
Published: April 2011

The kinetics of BST thin film grain nucleation and growth caused by rapid thermal annealing have been investigated. A series of Ba0.67Sr0.33Tii0.5O3 films were deposited on Pt electrodes using a metal-organic decomposition process. The effects of anneal time and temperature on BST grain sizes were studied by altering the processing conditions during RTA. A series of films were annealed by RTA at temperatures ranging from 550°C to 950°C for times ranging from 30 to 120 seconds. Crystallographic and microstructural characterization were done using XRD and TEM. The XRD results indicated that BST grain size increased with increasing anneal temperature, but was not affected by anneal time. Plan-view TEM indicated that BST grains were imbedded in an amorphous matrix. The average grain size was on the order of 200 Å.
Pulsed Laser Deposition of Bi4Ti3O12 Thin Films on Sapphire Substrates
Authors: Jo William , Noh T.W.
Published: April 2011

Using pulsed laser deposition, Bi4Ti3O12 thin films were grown on (0001) and (1102) surfaces of Al2O3. Substrate temperature from 700 to 800 °C and oxygen pressure from 50 to 1000 mtorr were varied, and their effects on Bi4Ti3O12 film growth behavior was investigated. Only for a narrow range of deposition parameters, can highly oriented Bi4Ti3O12(104) films be grown on Al2O3(0001). Further, epitaxial BTO(004) films can be grown on Al2O3(1102). The growth behavior of preferential BTO film orientations can be explained in terms of atomic arrangements in the Bi4Ti3O12 and the Al2O3 planes.
Correlations of Ba1−xSrxTiO3 Materials and Dielectric Properties
Authors: Tsu Robert , Liu Hung-Yu , Hsu Wei-Yung , Summerfelt Scott , Aoki Katsuhiro , Gnade Bruce
Published: April 2011

Thin film barium strontium titanate, Ba1−xSrxTiO3 (BST), has been deposited on Pt bottom electrodes using metal-organic decomposition (MOD). Optimization of BST electric properties, including capacitance density and leakage current, can be achieved by altering the chemical and microstructural attribute of the films. Dielectric properties of BST are strongly dependent on processing temperature, film thickness, composition, and microstructure, which are closely correlated with each other. Nucleation temperatures of BST range from 580°C – 650°C depending on film thicknesses. The chemical composition giving the highest dielectric constant is explained in terms of microstructure; capacitance increases with increasing grain size for the BST films in this study. Capacitance density of 50 fF/μ m2 and leakage current density < 100 nA/cm2 at 1.6 V can be achieved by optimizing BST materials properties. In addition, leakage conduction through the Pt/BST/Pt capacitor is shown to consist of polarization current resulting from Debye relaxation and true leakage current attributed to Schottky electron emission.
SrTiO3 Films Prepared by MOCVD Using Novel Sr Source
Authors: Yamauchi Hideaki , Kimura Takafumi , Yamada Masao
Published: April 2011

SrTiO3 thin films have been prepared by MOCVD. A novel Sr source of Sr(DPM)2-tetraen2 was used to stabilize source delivery and to reduce the vaporization temperature of Sr source. Films were deposited on Pt/Ta/Si substrates at deposition temperatures from 450 °C to 600 °C. The relative dielectric constant was about 220 at the deposition temperatures from 550 °C to 600 °C for as-deposited 90-nm-thick films. The leakage current density was in the range of 10−7 A/cm2, typically.
Improved Electrical Properties of SrTiO3, Thin Films by Electron Cyclotron Resonance Plasma Chemical Vapor Deposition
Authors: Yabuta Hisato , Takemura Koichi , Yamaguchi Hiromu , Sone Shuji , Sakuma Toshiyuki , Yoshida Masaji
Published: April 2011

SrTiO3 thin films with various compositions have been prepared on Pt coated sapphire substrates by electron cyclotron resonance plasma chemical vapor deposition at 450 °C and 600 °C. The stoichiometric (Sr/(Sr+Ti)=0.50) films have maximum dielectric constants (εr) of 190 for the 600 °C deposition and 170 for the 450 °C deposition. The dielectric constant decreases abruptly with increasing or decreasing the Sr/(Sr+Ti) value from the stoichiometry, especially for the 450 °C deposition. The Ti-rich films include titanium suboxide (TiOx). In the Sr-rich films, excess SrO is thought to be inserted into the SrO plane and TiO2 plane in SrTiO3. In addition, SrCO3 is included in Sr-rich films. The concentration of these impurities is greater for the 450 °C deposition than for the 600 °C deposition. The leakage current density increases with increasing the Sr/(Sr+Ti) value, and the leakage current density for the 450 °C deposition is larger than for the 600 °C deposition in the Sr-rich composition region. These impurity phases may be related to the higher leakage current density. These results suggest that precise composition control in stoichiometry is necessary to deposit SrTiO3 films with superior electrical properties.
Structural and Leakage Current Behavior of Bi4Ti3O12 Thin Films on La0–5Sr0–5jCoO3 Bottom Electrodes Grown by Pulsed Laser Deposition
Authors: Jo William , Kim K.H. , Noh T.W. , Kwon S.D. , Choe B.D. , You B.D.
Published: April 2011

Using La0.5Sro.5CoO3 bottom electrode layers, Bi4Ti3O12 thin films were grown on LaAlO3(001), Al2O3(0001), and Si(001) substrates. Crystalline orientation of the Bi4Ti3O12 thin films was examined by x-ray diffraction techniques. The cross-sectional microstructures of Bi4Ti3O12/La0.5Sr0.5CoO3 heterostructures are investigated. It is found that the crystalline orientation and the microstructure affect leakage current behavior of the Bi4Ti3O12 layers.
Growth and Characterization of PbTiO3 and Pb(Zr,Ti)O3 Thin Films by MOCVD
Authors: Gao Y. , Dong W. , Turtle B.A.
Published: April 2011

Ferroelectric PbTiO3 and Pb(Zr,Ti)O3 thin films with a perovskite structure were grown on MgO and Pt/Ti/SiO2/Si by MOCV.D. The microstructure and composition of the films were characterized by x-ray diffraction, SEM, and AES. Preferred orientation of either (111) or (100)/(001) was obtained on the Pt/Ti/SiO2/Si substrates at temperatures from 600 °C to 650 °C The preferred (111) orientation was attributed to the formation of the Pt3Ti phase in the Pt layer of the substrates, whereas the (100)/(001) orientations were inferred as the growth rate effect. AES depth profiling indicated a uniform composition through the thickness of the PZT films. However, SEM showed different topography and microstructure of the PZT films deposited in different oxygen partial pressure. Electrical properties of the PZT films appear varied as a function of the oxygen partial pressure in the reactor.
Effects of Acetylacetone Additions on PZT Thin Film Processing
Authors: Schwartz Robert W. , Assink R.A. , Dimos D. , Sinclair M.B. , Boyle T.J. , Buchheit C.D.
Published: April 2011

Sol-gel processing methods are frequently used for the fabrication of lead zirconate titanate (PZT) thin films for many electronic applications. Our standard approach for film fabrication utilizes lead acetate and acetic acid modified metal alkoxides of zirconium and titanium in the preparation of our precursor solutions. This report highlights some of our recent results on the effects of the addition of a second chelating ligand, acetylacetone, to this process. We discuss the changes in film drying behavior, densification and ceramic microstructure which accompany acetylacetone additions to the precursor solution and relate the observed variations in processing behavior to differences in chemical precursor structure induced by the acetylacetone ligand. Improvements in thin film microstructure, ferroelectric and optical properties are observed when acetylacetone is added to the precursor solution.
Rapid Thermal Processing and Crystallization Kinetics in Lead Zirconate Titanate (PZT) Thin Films
Authors: Griswold E.M. , Weaver L. , Calder I.D. , Sayer M.
Published: April 2011

Rapid thermal processing (RTP) has been used to examine the crystallization kinetics of lead zirconate titanate (PZT) fabricated using a sol gel process. Depth profiling of PZT films was performed with glancing angle x-ray diffraction and transmission electron microscopy. The films were annealed using RTP ramp rates from 10°C/s to 200°C/s and hold temperatures from 525°C to 650°C. The effect of ramp rate on the phase transformation is presented, and the growth of oriented columnar structures is demonstrated. Films subjected to RTP at 650°C for 1s using a ramp of 10°C/s began to transform to perovskite and were ferroelectric while a ramp of 100°C/s (same hold) produced a linear material which was pyrochlore. Longer hold conditions such as 650°C for 30s produced ferroelectric films with Pr in excess of 20μC/cm2 and relative permittivities ε > 600.
The Pyrochlore-to-Perovskite Transformation in Solution-Derived Lead Zirconate Titanate Thin Films
Authors: Voigt James A. , Tuttle B.A. , Headley T.J. , Lamppa D.L.
Published: April 2011

We have characterized the pyrochlore-to-perovskite crystallization process in solution-derived Pb(Zr0.20Ti0.80)O3 thin films on (100) MgO single crystal substrates. It has been determined that the perovskite phase nucleated preferentially at the film/MgO interface out of a nanocrystalline (≈100Å grains) pyrochlore matrix. During the early stages of the pyrochlore-to-perovskite conversion process, perovskite growth proceeded nearly isotropically from the substrate to form hemispherically shaped grains. Deviations from isotropie growth were shown to result from a growth dependence based on the crystallographic orientation of a growing perovskite grain relative to the orientations of pyrochlore grains being transformed. The volume change that occurs during the pyrochlore-to-pervoskite transformation along with two-dimensional grain growth has been used to develop a mechanism for formation of porosity that commonly is concentrated in grain boundary regions.
Effect of Microstructure on the Electrical Characteristics of Sol-Gel Derived PZT Thin Films
Authors: Kim Jiyoung , Khamankar Rajesh , Jiang Bo , Mamar Papu , Moazzami Reza , Jones Robert E. , Lee Jack C.
Published: April 2011

The effects of the microstructure of PZT sol-gel thin films, processed using different solutions, on their material and electrical properties have been studied. The films have different degrees of preferred orientation of the perovskite crystals as well as different grain size. The material characteristics are evaluated using SEM micrographs and XRD. Correlation of these material properties with the electrical properties for both NVRAM and DRAM applications is made.
Construction of Strained SrTiO3/BaTiO3 Superlattices and Their Dielectric Properties
Authors: Tabata Hitoshi , Tanaka Hidekazu , Kawai Tomoji
Published: April 2011

Artificial dielectric superlattices of SrTiO3/BaTiO3(STO/BTO) and CaTiO3/BaTiO3 (CTO/BTO) have been formed by a pulsed laser ablation technique with an in situ monitoring of RHEED (reflection high energy electron diffraction) oscillation. The crystal structures can be controlled with atomic order accuracy and a large stress of 400–500 MPa is introduced at the interface between the BTO and STO layers. Xhe superlattices show higher dielectric constant than that of (Sr0.5Ba0.5)TiO3 films against the change of temperature or applied frequency. A large dielectric constant of 900 was observed for the superlattices with a stacking periodicity of 2 unit cells / 2 unit cells. Xhe superlattices show drastically different electrical behavior from that of the solid solution (Sr,Ba)XiO3 films, both with changing temperature and applied frequency. Broad maxima of the dielectric constants occur around 40–50 °C and the values remain large even for the temperature above 200 °C. On the contrary, in the case of CTO/BTO superlattices, lattice constants and dielectric constant do not change so much compared with STO/BTO cases. Lattice mismatch in the STO/BTO and the CTO/BTO superlattices are 2.5% and 5.5%, respectively. In the case of CTO/BTO, misfit dislocations such as stacking faults may occur at the interface between CTO and BTO layers owing to large lattice mismatch. Therefore, lattice strain is introduced effectively below the lattice mismatch of about 3%.
Thickness Dependence of Induced Ferroelectricity in Epitaxially Grown Ba0.44Sr0.56TiO3 Thin Films
Authors: Abe Kazuhide , Komatsu Shuichi
Published: April 2011

Ba0.44Sr0.56TiO3 (BST) thin films with various thicknesses were epitaxially grown on Pt/MgO(100) substrates with rf magnetron sputtering. The thickness dependence of lattice constant, D-E hysteresis and dielectric constant were evaluated for the BST films. The lattice constant in the thickness direction is elongated through the thickness range (33 to 221 nm), whereas the ferroelectric and the dielectric properties had strong thickness dependencies. The mechanism of the induced ferroelectricity is discussed in terms of the thickness dependence and deposition technique.
Effects of Excess Pb on Crystallization and Electrical Properties of Ferroelectric PZT Films Deposited by Reactive RF Magnetron Sputtering
Authors: Bernstein S.D. , Wong T.Y. , Collins S.R. , Kisler Yanina , Tustison R.W.
Published: April 2011

Films were deposited onto unheated, Ti/Pt coated Si substrates by reactive sputtering in an argon-oxygen atmosphere from a sintered PZT target, and subsequently crystallized at temperatures between 550 and 650 °C. Pt/PZT/Pt capacitors were formed by ion beam sputtering of top electrodes through a shadow mask. Electrical properties were found to depend on gas pressure during deposition. This effect is interpreted in terms of variations in film stoichiometry (particularly Pb content). Films with large excesses of Pb were found to exhibit high leakage currents and poor ferroelectric behavior, whereas films with lower excesses of Pb had low leakage currents, and good ferroelectric properties. Films with the largest Pb excess had a random orientation, while the film with the lowest Pb excess had a preferred (111) orientation. With 550 °C crystallization temperatures the films consist of a mixture of ferroelectric perovskite phase and either PZT pyrochlore or PbO. At higher crystallization temperatures no pyrochlore is detected.
Liquid Phase Epitaxy of Na1−yKyTa1−xNbxO3 for Pyroelectric Applications
Authors: Sitar Z. , Gutmann R. , Pierhöfer H. , Günter P.
Published: April 2011

The epitaxial growth of para- and ferroelectric KTa1−xNbxO3 (KTN) thin films was achieved in an in-house built liquid phase epitaxy (LPE) apparatus. Films were grown from a KF/NaF/KTN solution on KTaO3 substrates. Growth rates of several μ/min were achieved at a growth temperature of 1200 K. Up to 150 μm thick, smooth KTN films with different compositions were grown and characterized. Almost perfect lattice matching was achieved by the addition of NaF to the KF flux. Partial replacement of K by Na did not result in a significant change of physical properties of KTN.

The investigation of the dielectric properties revealed a sharp change of the dielectric constant at the ferroelectric phase transition. The ferroelectric domain structure was modified by poling at 1kV/cm. Pyroelectric studies yielded a pyroelectric coefficient of up to 5.2 mC/m2K while the frequency dependence of the pyroelectric response showed a maximum at 230 Hz.
Imprint of La-Sr-Co-O/Pb-La-Zr-Ti-O/La-Sr-Co-O Heterostructures Grown by Pulsed Laser Deposition
Authors: Lee J. , Ramesh R. , Keramidas V.G.
Published: April 2011

La-Sr-Co-O(LSCO)/Pb-La-Zr-Ti-O(PLZT)/La-Sr-Co-O heterostructures with different crystalline quality have been grown on LaAlO3 and Si with a bismuth titanate template layer. Imprint of the heterostructures are investigated in comparison with fatigue and retention. Oxygen ambient during cooling the heterostructures was also varied to investigate the imprint. With consideration of the switching behavior caused by imprint, imprint behavior was deconvoluted from fatigue and retention. In epitaxial PLZT capacitors grown on LaAlO3, imprint behavior was found to be significantly dependent on the oxygen ambient. As the oxygen ambient became more reducing, the capacitors developed more voltage asymmetry in hysteresis loops and a more preferred polarization state directed towards the top electrode. On the other hand, oriented PLZT capacitors exhibited less pronounced effect of the oxygen ambient on the imprint behavior.