bluuebunny/crossref_metadata_2025 huggingface dataset:
Alternate Gate Oxides for Silicon Mosfets Using High-k Dielectrics
Authors: Billman C. A. , Tan P. H. , Hubbard K. J. , Schlom D. G.
Published: April 2011

High K (dielectric constant) and silicon-compatibility are essential for an alternative gate dielectric for use in silicon MOSFETs. Thermodynamic data were used to comprehensively evaluate the thermodynamic stability of binary oxides and binary nitrides in contact with silicon at 1000 K. Using the Clausius-Mossotti equation and ionic polarizabilities, the K of all known inorganic compounds composed of Si-compatible binary oxides was estimated. A ranked list of alternate gate oxide candidates that are likely to possess both high K and silicon-compatibility is given.
Crystalline Oxides on Silicon – Alternative Dielectrics for Advanced Transistor Technologies
Authors: McKee Rodney , Walker Fred , Chisholm Matt
Published: April 2011

Since the advent of the integrated circuit in 1959 and the introduction of MOS capacitors in the early ‘60’s, electronic technology has relied on silica (SiO2) as the gate dielectric in a field effect transistor. However, silica-based transistor technology is approaching fundamental limits. Feature-size-reduction and the ever-demanding technology roadmaps have imposed scaling constraints on gate oxide thickness to the point where excessive tunneling currents make transistor design untenable; an alternative gate dielectric is needed. Crystalline oxides on silicon (COS), simply by virtue of their high dielectric constants, could fundamentally change the scaling laws for silicon-based transistor technology. More importantly, COS could provide the opportunity for an entirely new device physics based on anisotropic response of crystalline oxides grown commensurately on a semiconductor. In this paper, we report that high dielectric constant alkaline earth and perovskite oxides can be grown in perfect registry with silicon. Commensurate heteroepitaxy between the semiconductor and the oxide is established via a sequenced transition that uniquely addresses the thermodynamics of a layer-by-layer energy minimization at the interface. The perfection of the physical structure couples directly to the electrical structure, and we thus obtain the unparalleled result of an equivalent oxide thickness of less than I nm in a MOS capacitor. With this demonstration it is apparent that COS presents a functional alternative to SiO2. With COS, a transistor gate can not only exhibit a much higher dielectric response, but add entirely new capabilities such as logic-state retention with the anisotropic response of ferroelectric polarization in a ferro-gated device. COS is the basis for fundamental change in semiconductor technology.
Nitrogen (N2) Implantation to Suppress Growth of Interfacial Oxide in Mocvd Bst and Sputtered Bst Films
Authors: Nieh Renee , Qi Wen-Jie , Jeon Yongjoo , Lee Byoung Hun , Lucas Aaron , Kang Laegu , Lee Jack C. , Gardner Mark , Gilmer Mark
Published: April 2011

Ba0.5Sr0.5TiO3 (BST) is one of the high-k candidates for replacing SiO2 as the gate dielectric in future generation devices. The biggest obstacle to scaling the equivalent oxide thickness (EOT) of BST is an interfacial layer, SixOy, which forms between BST and Si. Nitrogen (N2) implantation into the Si substrate has been proposed to reduce the growth of this interfacial layer. In this study, capacitors (Pt/BST/Si) were fabricated by depositing thin BST films (50Å) onto N2 implanted Si in order to evaluate the effects of implant dose and annealing conditions on EOT. It was found that N2 implantation reduced the EOT of RF magnetron sputtered and Metal Oxide Chemical Vapor Deposition (MOCVD) BST films by ∼20% and ∼33%, respectively. For sputtered BST, an implant dose of 1×1014cm−;2 provided sufficient nitrogen concentration without residual implant damage after annealing. X-ray photoelectron spectroscopy data confirmed that the reduction in EOT is due to a reduction in the interfacial layer growth. X-ray diffraction spectra revealed typical polycrystalline structure with (111) and (200) preferential orientations for both films. Leakage for these 50Å BST films is on the order of 10−8 to 10−5 A/cm2—lower than oxynitrides with comparable EOTs.
Scanning Probe Microscopy (SPM) for the Investigation of Local Electrical Properties of High-K Dielectric/Ferroelectric Films
Authors: Landau S.A. , Weiß P.-A. , Junghans N. , Kolbesen B.O. , Adderton D. , Schindler G. , Hartner W. , Hintermaier F. , Dehm C. , Mazuré C.
Published: April 2011

Thin films of high-k dielectric/ferroelectric materials such as BaxSr1−xTiO3(BST), PbZrxTi1−xO3(PZT) and SrBi2Ta2O9(SBT) are currently investigated for integration into high-density CMOS technology. Characterization of these materials by SPM techniques combines imaging of the morphology and microstructure of these films and recording of various electrical parameters at the same local area. Using commercial equipment we have investigated electrical properties such as polarization and leakage current behavior of MOD/MOCVD SBT by applying electrostatic force microscopy (EFM) and conducting atomic force microscopy (CAFM). After applying bias voltages of a few volts across the SBT films between the scanning tip and the lower electrode completely polarized/reverse polarized SBT layers could be observed by EFM. Even single crystallite polarization was imaged. However, unexpectedly some films showed incomplete polarization, which may be caused by local electrical field effects. Images taken by C-AFM displayed enhancement of leakage currents in grain boundary regions, in particular at depressions between adjacent crystallites. The results achieved demonstrate that SPM techniques operated in a variety of imaging and measuring modes, provide a tremendous potential in the elucidation of the microscopic properties of high-k materials.
Formation of High Quality Oxynitride Gate Dielectrics by High Pressure Thermal Oxidation of Si in NO
Authors: Song S. C. , Lee C. H. , Luan H. F. , Kwong D. L. , Gardner M. , Fulford J. , Allen M. , Bloom J. , Evans R.
Published: April 2011

In this paper, we report a novel low thermal budget process (<800°C) for engineered ultra thin oxynitride dielectrics with high nitrogen concentration (>5% a.c.) using vertical high pressure (VHP) process. VHP grown oxynitride films show >1 OX lower leakage current, higher drive current and superior hot-carrier reliability compared to control SiO2 of identical thickness (Tox,eq) grown by RTP in O2.
Ostwald Ripening of {113} Defects Precursors and Transient Enhanced Diffusion
Authors: Manninoo Giovanni , Cowem Nicholas E.B. , Stolk Peter A. , Roozeboom Fred , Huizing Hendrik G.A. , Berkum Jurgen G.M. van , Boer Wiebe B. de , Cristiano Filadelfo , Claverie Alain , Jaraiz Martin
Published: April 2011

The ripening of ion-beam generated point defects into extended defects has been investigated in detail. The interstitial supersaturation has been extracted from boron marker-layer diffusion after annealing under non-equilibrium defect conditions. We measured a very high initial supersaturation followed by a decrease over many orders of magnitude with a characteristic “plateau” related to the presence of {113} defects. A continuum inverse model has been used to properly describe the ripening of point defects into clusters and their evolution in the presence of a remote sink, e.g. the surface. It evidences that a nonconservative Ostwald ripening process takes place inside the defect band during the annealing and sustains the interstitial supersaturation. The model reveals moreover an oscillatory behaviour of dissociation energies of the nanometer-sized defects which are responsible for the initial high supersaturation. These defects are believed to be {113} precursors.
Ultra-Shallow Junctions by Ion Implantation and Rapid Thermal Annealing: Spike-Anneals, Ramp Rate Effects
Authors: Agarwal Aditya , Gossmann Hans-J. , Fiory Anthony T.
Published: April 2011

Over the last couple of years rapid thermal annealing (RTA) equipment suppliers have been aggressively developing lamp-based furnaces capable of achieving ramp-up rates on the order of hundreds of degrees per second. One of the driving forces for adopting such a strategy was the experimental demonstration of 30nm p-type junctions by employing a ramp-up rate of ≈400°C/s. It was subsequently proposed that the ultra-fast temperature ramp-up was suppressing transient enhanced diffusion (TED) of boron which results from the interaction of the implantation damage with the dopant. The capability to achieve very high temperature ramp-rates was thus embraced as an essential requirement of the next generation of RTA equipment.

In this paper, recent experimental data examining the effect of the ramp-up rate during spike-and soak-anneals on enhanced diffusion and shallow junction formation is reviewed. The advantage of increasing the ramp-up rate is found to be largest for the shallowest, 0.5-keV, B implants. At such ultra-low energies (ULE) the advantage arises from a reduction of the total thermal budget. Simulations reveal that a point of diminishing return is quickly reached when increasing the ramp-up rate since the ramp-down rate is in practice limited. At energies where TED dominates, a high ramp-up rate is only effective in minimizing diffusion if the implanted dose is sufficiently small so that the TED can be run out during the ramp-up portion of the anneal; for larger doses, a high ramp-up rate only serves to postpone the TED to the ramp-down duration of the anneal. However, even when TED is minimized at higher implant energies via high ramp-up rates, the advantage is unobservable due to the rather large as-implanted depth. It appears then that while spike anneals allow the activation of ULE-implanted dopants to be maximized while minimizing their diffusion the limitation imposed by the ramp-down rate compromises the advantage of very aggressive ramp-up rates.
In-Situ Optical Characterization of Titanium Nitride Thin Films for Applications in Microelectronics
Authors: Patsalas P. , Logothetidis S. , Dimitriadis C.A.
Published: April 2011

Titanium Nitride (TiNx) thin films were deposited on Si(100) by reactive magnetron sputtering. The varied deposition conditions were the substrate temperature (Td) (27 - 650 °C) and the negative bias voltage (Vb) applied to the substrate (0 - 200 V) in order to produce TiNx films with various compositions and structural characteristics. The deposition process was monitored in-situ by Spectroscopic Ellipsometry in the spectral range 1.5–5.5 eV. Determination of the film composition was made through the measured screened plasma energy ωps while the electrical resistivity of TiNx was studied in terms of the unscreened plasma energy ωpu. ωpu was calculated by an optical model including a Drude term and Lorentz oscillator terms and their dependence on Td and Vb was studied. The ωpu was found to increase with Vb until a saturation value was obtained. The saturation value of ωpu depends on the Td.ωpu describes better the TiNx films, since it is directly correlated with their metallic character in terms of the electrical resistivity.
Study of Natural Oxidation of Ultra-Thin Aluminum Layers with In-Situ Resistance Measurement
Authors: Fery C. , Bailey W.E. , Yamada K. , Wang S.X.
Published: April 2011

Exposure to oxygen (1 Torr) at room temperature of thin Al films deposited by UHV ion beam sputtering has been studied using an in-situ resistance measurement set-up. Two lock-in amplifiers allow low noise data acquisition. By monitoring the conductance during deposition and oxidation we can deduce the consumed Al thickness as a function of exposure time (t). It is found that the Al/vacuum interface is diffuse for electron scattering. A two-stage mechanism for natural oxidation is revealed: fast growth (for t<10s) followed by a slow logarithmic growth. A simple model based on interface reactions and place exchange describes the experimental results. The conductance drop after 5 minutes of oxidation is found to decrease for initial Al thicknesses below 30A. This suggests the oxidation rates slow down for thin initial Al thicknesses.
Secondary Grain Growth in Thin Films
Authors: Thompson C. V. , Smith Henry I.
Published: April 2011

Normal grain growth in thin films leads to columnar grains with sizes roughly equal to the film thickness. In subsequent grain growth, a minor fraction of the grains continue to grow at appreciable rates, leading initially to a bimodal grain size distribution and ultimately to a monomodal distribution of grains with sizes much larger than the film thickness. Those grains which continue to grow, secondary grains, often have uniform or restricted texture, suggesting that in such cases surface energy minimization plays an important role in driving their preferential growth. Surface-energy-driven secondary grain growth can, in principle, lead to single crystal films. Turnbull and co-workers were among the first to apply rate theory to the analysis of grain boundary motion, grain growth, and recrystallization. These models have been adapted to describe surface-energy-driven secondary grain growth in thin films. Recent experiments on secondary grain growth in thin metallic and semiconductor films are reviewed. It has been shown that film thickness, film composition and surface topography have pronounced effects on growth rates, final grain sizes and orientations.
Formation of Metallic Nanoclusters in SiC by MeV Ion Implantation
Authors: Ila D. , Williams E. K. , Elsamadicy A. , Gasic B. , Poker D. B. , Hensley D. K. , George M. A. , Ayoub M. A. , Larkin David J.
Published: April 2011

We present the results of our investigation of producing nanoclusters of gold, silver, copper and tin in 6H-SiC. This is accomplished by implanting 1.0 MeV Au, 2.0 MeV Ag, 2.0 MeV Cu, and 160 keV Sn into the Si face of SiC at room or elevated temperature followed by annealing at various temperatures. Using optical absorption spectrophotometry, we determined the location of the absorption band for each metal nanocluster in SiC. Elevated temperature implantation reduces optical absorption due to ion implantation induced defects. Using the Mie theory, we determined the index of refraction in the implanted volume.
Z-Contrast Stem Imaging and Eels of CdSe Nanocrystals: Towards the Analysis of Individual Nanocrystal Surfaces
Authors: Kadavanich A.V. , Kippeny T. , Erwin M. , Rosenthal S. J. , Pennycook S. J.
Published: April 2011

We have applied Atomic Number Contrast Scanning Transmission Electron Microscopy (Z-Contrast STEM) and STEM/EELS (Electron Energy Loss Spectroscopy) towards the study of colloidal CdSe semiconductor nanocrystals embedded in MEH-PPV polymer films. Z-Contrast images are direct projections of the atomic structure. Hence they can be interpreted without the need for sophisticated image simulation and the image intensity is a direct measure of the thickness of a nanocrystal. Our thickness measurements are in agreement with the predicted faceted shape of these nanocrystals.

Our unique 1.3Å resolution STEM has successfully resolved the sublattice structure of these CdSe nanocrystals. In [010] projection (the polar axis in the image plane) we can distinguish Se atom columns from Cd columns.

EELS measurements on individual nanocrystals indicate a significant amount (equivalent to 0.5–1 surface monolayers) of oxygen on the nanocrystals, despite processing in an inert atmosphere. Spatially resolved measurements at 7Å resolution suggest a surface oxide layer.
YMnO3 and YbMnO3 Thin Films for fet type FeRam Application
Authors: Fujimura Norifumi , Yoshimura Takeshi , Ito Daisuke , Ito Taichiro
Published: April 2011

We have been proposing the use of RMnO3 (R: rare earth elements) films for metalferroelectric- semiconductor field effect transistor (MFSFET)-type ferroelectric random access memories (Ferroelectric RAMs). This report describes the progress of YMnO3 and YbMnO3 films for FET type FeRAM application. Although highly (0001)-oriented YMnO3 films are easily obtained on a MgO, ZnO/Sapphire, Pt/Sapphire and Pt/Si substrates, it was very hard to obtain the crystalline films directly on Si or on SiO2/Si substrate. A Y-Mn-O buffer layer improved the crystallinity of the YMnO3 films on Si, and we got the C-V curve with ferroelectric hysteresis. The real ferroelectric component responsible for the C-V hysteresis was calculated to be just 8.4 nC/cm2 by pulse measurements. On the other hand, Y2O3 buffer layer drastically improved the dielectric properties. The window width of the C-V hysteresis does not change by changing the sweep rate and measurement frequency.
Improvement of Hydrogen Degradation in Pt/SrBi2Ta2-xNbxO9/Pt Capacitor
Authors: Furuya Akira , Cuchiaro Joe D.
Published: April 2011

Ferroelectric SrBi2(Ta1-xNbx)2O9 (SBTN) thin films are under evaluation for IC memory applications. It has been reported that SrBi2(Ta1-xNbx)2O9 has higher fatigue endurance and imprint resistance than other common ferroelectric materials such as lead zirconate titanate (PZT). One of the most important technical issues for integrating ferroelectric oxide materials into IC memory applications is the degradation of ferroelectric capacitor properties from the oxide reduction from hydrogen. Hydrogen annealing processes performed to terminate dangling bonds in silicon, or, elevated temperature processes, which dissociate hydrogen, are expected to reduce the ferroelectric oxide thereby degrading the dielectric properties. Therefore, in this work, we have investigated reducing degradation of Pt/SBTN/Pt capacitors due to hydrogen exposure by evaluating the compositional dependence of the Ta/Nb ratio and incorporating TiN as a hydrogen diffusion barrier. To investigate compositional dependence, the Pt/SBTN/Pt capacitors with the desired composition were fabricated from enhanced metal organic decomposition solutions that were spin deposited and delineated with a conventional patterning and etching techniques. Post annealing the samples in H2 (1%)-N2 ambient at 200°C for 10–60min, hysteresis and current-voltage measurements were conducted to evaluate any degradation to pre-anneal measurements. This experimental condition revealed that the best electrical characteristics were obtained with the Ta/Nb ratio of 1.5/0.5. Therefore, Pt/SBTN/Pt capacitors with a Ta/Nb ratio of 1.5/0.5 were evaluated using a TiN barrier and its effect characterized. After depositing a TiN film on the Pt/SBTN/Pt capacitors, the samples were annealed in H2 (5%)-N2 at 400°C for 10–60 min. The TiN was removed with NH4OH: H2O2: H2O = 1: 3: 1, respectively, at 60 - 70°C and the hysteresis and current-voltage characteristics of the capacitors measured. It was found that the degradation was extremely reduced by incorporating a TiN barrier. Moreover, the degradation effects decreased with increased density of the deposited TiN film. TiN densities greater than 3.8g/cm3 in these experiments kept the leakage current degradation to less than 10−6A/cm2 while the degradation in remanent polarization is less than 20%.
The Influence of 5- and 6-Atom Rings on the Optical Properties of Amorphous Silicon Nitride. A Cluster Simulation
Authors: Valladarest R.M. , Calles A.G. , Valladares Alexander , Valladares Ariel A.
Published: April 2011

We simulate α - Si21 –N2: H that contains 6-atom boat-type rings and a – Si17–iNi: H that contains 5-atom planar rings, where i = 0, 1 or 4. The simulations were carried out using the DFT-LDA approximation contained in the DMol code of MSI. We report calculations of impurity levels and relate these to the size of the gap and to the optical absorption curves for each cluster. A comparison is made between the two α – SiN clusters studied to analyze the effect of the ring topology.
Local Basis Gw Calculations and the Dielectric Response of Si and C Clusters
Authors: Yu Ming , Ulloa Sergio E. , Yang Sang H.
Published: April 2011

We describe our progress in developing an ab initio computational scheme for the calculation of the dielectric response function of solids, with special emphasis here on Si and C clusters. All calculations are carried out employing a basis of localized atomic-like orbitals and include the evaluation of quasiparticle corrections. The self-energy operator is evaluated in the GW approximation, with a full frequency dependence for the dielectric matrix. The approach is convenient and computationally optimal for the calculation of optical properties of complex systems lacking full periodicity, such as surfaces and clusters. We present here the dielectric response functions of clusters with structures found after full equilibration via molecular dynamical simulations, and discuss the sensitivity of the optical properties to quasiparticle corrections.
Effect of Preparation and Impurities on The Size and Shape of The Crystallites and on The Crystal Symmetry of Superionic PbSnF4
Authors: Dénès Georges , Cecilia Madamba M.
Published: April 2011

The highest performance fluoride ion conductor, PbSnF4, has been applied for the fabrication of an ambient temperature amperometric oxygen sensor, where it is used in the polycrystalline form. However, the structure of this material is highly anisotropic, thus one could expect polycrystalline samples to give a performance strongly dependent on crystallite direction. We have shown that the tin electronic structure has a very strong influence on the local structure, which determines the preferred direction of crystal growth, which is itself responsible for the crystal shape. This, in turn, determines the direction of preferred orientation, which can dramatically alter the properties relative to a randomly oriented sample. The effect of minor impurities on the size of the crystallites and on the crystalline symmetry has been studied.
Influence of The Electrochemical Environment on Diffusion Processes Near Step and Island Edges: Ag(111) and Ag(100)
Authors: Haftel Michael I. , Einstein T. L.
Published: April 2011

The electrochemical cell provides a potentially powerful means of altering morphology and islanding phenomena on metallic surfaces. Diffusion and attachment processes on terraces and near step and island edges are known to profoundly affect island sizes, shapes and coarsening kinetics. Using the surface-embedded-atom-model (SEAM) for describing metallic surfaces in the electrolytic environment, we calculate the dependence of the activation energies for the aforementioned diffusion processes on the deposited surface charge for the Ag(111) and Ag(100) surfaces in an electrolytic environment. While all these processes show some degree of dependence on the potential, the step-edge barrier and the edge diffusion processes are the most sensitive. Step-edge barriers increase (to over 1 eV) with large positive potential (0.85 V), while edge diffusion barriers monotonically decrease with positive surface charge on Ag(100) and Ag(111). We assess the effect these diffusion barriers have on island size/shapes and coarsening dynamics and discuss the implications on electrochemical tuning of islanding phenomena.
Interrogation of Alumina Grain Boundaries using Atomic Force Microscopy
Authors: Tibble P.A. , Heywood B.R. , Richardson R. , Barnes P.
Published: April 2011

A number of MgO doped (3wt%) polycrystalline alumina samples were prepared. The preparation of these samples varied; different regimes for annealing (1500 – 1600°C) and a range of dwell times were examined. Atomic force microscopy (AFM) was used to study surface features. Information on grain boundary dimensions (depth, width) is presented along with a study of grain particle size. The growth of the grain boundaries was found to contradict Mullins' theory of uniform growth with time. We also present evidence for Ostwalds' ripening and the preferential growth of [001] oriented grains.
Modelling Solid Nucleation and Growth In Supercooled Liquid
Authors: Leonard J.P. , Im James S.
Published: April 2011

In this paper, we present a numerical model that incorporates algorithms to simulate nucleation and growth in supercooled liquid in a manner that properly accounts for the stochastic nature of nucleation. The basis of our model relies on a discretization of space and time to address thermal evolution, rapid growth of the undercooled interface, and nucleation in supercooled liquid. The present formulation of nucleation permits the spatially and temporally random nature of the phenomenon to be manifested in the transformation and resultant microstructure. This is accomplished by (1) calculating the probability of nucleation in each and every liquid node during each time step using the Poisson expression, and (2) triggering nucleation if and only when the random number assigned to a node for the time step is less than the calculated nucleation probability. No empirical or deterministic conditions for nucleation are imposed; nucleation occurs spontaneously and solely based on nucleation kinetics. We demonstrate the effectiveness of the overall model by analyzing conditions similar to those encountered in pulsed laser-induced crystallization of thin Si films, and discuss the generality of the proposed stochastic formulation of nucleation.
Morphology Control of Sulfide in Fe-Cr-S alloys during the solidification
Authors: Oikawa Katsunari , Ikeshoji Tamio , Mitsui Hajime , Ishida Kiyohito
Published: April 2011

The evolution of sulfide morphology in the Fe- (0.3 to 18) mass% Cr -0.3 mass% S alloys during solidification and its modification by additions of elements such as Mn, Ti, Zr and C have been investigated by means of optical microscopy, scanning electron microscopy and X-ray diffraction. The sulfide morphologies in the Fe-Cr-S ternary alloy are classified under three types: (i) cellwall (ii) fine particle and (iii) globular sulfides. The iron-rich cellwall sulfide is formed in the Fe-(0.3-1) %Cr-0.3 %S alloys. This sulfide morphology changes to the globular type with increasing Cr content and the size of that is more than 51gm. Fine sulfide particles of size smaller than 2 gtm also coexist in the Fe-(0.3-5) %Cr-0.3 %S alloys. Zr or Ti additions change this morphology from the globular type to the rod-like type in the Fe-18 %Cr-0.3 %S alloy, but Mn addition does not have the same effect. The mechanism of the formation of different sulfide morphologies is discussed on the basis of phase diagram information.
A Molecular Dynamics Study of Implant-Induced Erosion of A (100)-Silicon Stepped Surface
Authors: Mazzone A. M.
Published: April 2011

The purpose of these simulations is to study the mechanisms leading to surface damage during low-energy implants. Therefore the bombarded surface has a realistic vicinal structure and contains one step edge, SA or SB. The damaging event is produced by an atom, Ar or Si, of a low kinetic energy (≤ 30eV), moving on the surface or below it. The simulation indicates a total etching of the first two layers of silicon and the ejection of the implanted Ar. These features are independent on the step structure, on the direction of motion of the moving atom and they hold over a broad range of temperatures. However. if Ar and Si move below this critical depth, they may remain in the lattice as interstitials. The preferred location of these defects is the tetrahedral location at the center of the hexagonal rings. In addition to the formation of interstitials, also a corrugation of the atomic rows on the surface is observed. This effect has a characteristic dependence on the step structure and it is remarkably more pronounced for the SB non-rebonded steps than in the other cases.
Molecular Dynamics Simulations of Growth and Low-Energy Ion Polishing of Thin Molybdenum Films for EUV Multilayer Mirrors
Authors: Klaver Peter , Goedheer Wim , Bijkerk Fred , Thijsse Barend J.
Published: April 2011

We report on the simulation of the growth and subsequent krypton ion polishing of thin molybdenum films, required for extreme ultraviolet multilayer mirror fabrication. We have used a comprehensive Molecular Dynamics (MD) code, principally enabling a simulation of the deposition, ion bombardment and annealing processes. Ion energies used are in the sub-keV range, and the ion angle of incidence is varied between 30 and 60 degrees off-normal.

The effects of ion polishing on the surface roughness are discussed, as well as the increase in (surface) atom mobility. We also report data on sputtering yields, ion penetration depths, trapping, energy transfer and krypton implantation and saturation.

The results are compared with TRIM results, and the relevance of MD and TRIM simulations for specific purposes is discussed. Also, the effects of short-time, high-temperature annealing of an amorphous film are investigated.
Growth of Co ON Ag(100): A Comparison of Ultra Low Energyion Beam Deposition and Thermal Deposition
Authors: Degroote B. , Dekoster J. , Degroote S. , Pattyn H. , Vantomme A. , Langouche G. , Hou M.
Published: April 2011

We have investigated the growth of Co deposited on Ag(100) with ultra low energy ion beam deposition. The preferred sites of nucleation, the island densities and heights are determined with scanning tunneling microscopy. Submonolayers of Co were ion beam deposited at 300 K using energies between 5 and 30 eV. Preferential growth of islands on the upper side of the mono-atomic Ag steps (i.e. step decoration) is observed for deposition energies of 5 and 15 eV. In addition, 3–4 ML deep holes are formed in the Ag substrate for deposition at 5 eV. At higher deposition energies, the number of holes per surface area decreases. The results are compared with experiments on thermal deposition of Co on Ag(100) as a function of substrate temperature, performed in a previous study.
Electron Holography of Nanostructured Magnetic Materials
Authors: Dunin-Borkowski R. E. , Kardynal B. , Mccartney M. R. , Scheinfein M. R. , Smith David J.
Published: April 2011

Off-axis electron holography and micromagnetic calculations that involve solutions to the Landau-Lifshitz-Gilbert equations are used to study magnetization reversal processes in lithographically patterned submicron-sized Co and Co/Au/Ni magnetic elements.
In-Situ Annealing Transmission Electron Microscopy Study of Pd/Ge/Pd/GaAs Interfacial Reactions
Authors: Radulescu F. , Mccarthy J.M. , Stach E. A.
Published: April 2011

In-situ TEM annealing experiments on the Pd (20 nm) / a-Ge (150 nm) / Pd (50 nm) GaAs ohmic contact system have permitted real time determination of the evolution of contact microstructure. As-deposited cross-sectional samples of equal thickness were prepared using a focused ion beam (FIB) method and then subjected to in-situ annealing at temperatures between 130-400 °C. Excluding Pd-GaAs interactions, four sequential solid state reactions were observed during annealing of the Pd:Ge thin films. First, interdiffusion of the Pd and Ge layers occurred, followed by formation of the hexagonal Pd2Ge phase. This hexagonal phase then transformed into orthorhombic PdGe, followed by solid state epitaxial growth of Ge at the contact / GaAs interface. The kinetics of the solid state reactions, which occur during ohmic contact formation, were determined by measuring the grain growth rates associated with each phase from the videotape observations. These data agreed with a previous study that measured the activation energies through a differential scanning calorimetry (DSC) method. We established that the Ge transport to the GaAs interface was dependent upon the grain size of the PdGe phase. The nucleation and growth of this phase was demonstrated to have a significant effect on the solid phase epitaxial growth of Ge on GaAs. These findings allowed us to engineer an improved two step annealing procedure that would control the shape and size of the PdGe grains. Based on these results, we have established the suitability of combining FIB sample preparation with in-situ cross-sectional transmission electron microscopy (TEM) annealing for studying thin film solid-state reactions.
Electron Microscopy of Single Molecules
Authors: Luzzi D.E. , Smith B.W.
Published: April 2011

We report on the imaging of single C60 molecules adsorbed on the surface of carbon nanotubes. In the course of the work, the efficacy of carbon nanotubes as substrates for the high signal-to-noise observation of molecules is examined. The stability of nanotubes as a function of temperature, chemical environment and irradiation environment is explored. Carbon nanotubes are found to have a threshold energy for ballistic irradiation damage of approximately 85 keV. Finally, the use of nanotubes as in-situ reaction chambers and for other in-situ experimentation is demonstrated.
Combined HRTEM and EFTEM Study of Precipitates in Tungsten and Chromium-Containing TiB2
Authors: Mader W. , Freitag B. , Kelm K. , Telle R. , Schmalzried C.
Published: April 2011

The structure and chemical composition of two types of precipitates in the system TiB2-WB2-CrB2 were studied by means of high-resolution TEM and energy filtering TEM. Type I particles (W2B5 structure) are precipitated at the basal plane of the hexagonal matrix whereas type II precipitates are thin platelets lying parallel to the {1100} prism planes. Lattice imaging yields displacements of the metal positions with respect to the matrix. Information on the chemical composition at high lateral resolution is obtained from elemental maps of all chemical constituents using electron spectroscopic imaging (ESI). The type II precipitates show a decrease in the B and Ti concentration, whereas the tungsten concentration increases and the Cr is homogeneously distributed. The HRTEM results combined with the results of the elemental maps allow to develop a structural model based on the intergrowth of the β-WB structure in the TiB2-rich matrix. The two deficient boron layers in W0.5Ti0.5B with a spacing of 0.38 nm can be used to examine the resolution limit of ESI.
Microstructural Characterization of Longitudinal Magnetic Recording Media
Authors: Sinclair Robert , Park Dong-Won , Habermeier Claus , Ma Kai
Published: April 2011

The optimization of disc manufacturing conditions is required to increase the storage capacities of magnetic recording media, which is strongly related to both magnetic properties and microstructural features. Analyzing the microstructure requires transmission electron microscopy (TEM), since the small grain sizes of the media prevent other tools from characterizing them. This paper discusses several fascinating characteristics of TEM in understanding and analyzing the properties of the recording media.
Synthesis of Multiwalled Carbon Nanotubes
Authors: Jacques David , Villain Stephane , Rao Apparao M. , Andrews Rodney , Derbyshire Frank , Dickey Elizabeth C. , Qian Dali
Published: April 2011

In a recent publication we have described the synthesis of multiwalled carbon nanotubes (MWNTs) by the reaction of a hydrocarbon vapor over a dispersed iron catalyst that is deposited in situ on quartz substrates. Our system configuration involves entraining a mixture of xylene and ferrocene into an inert gas stream. Decomposition of the ferrocene at temperatures in the range 625-775 °C, and at atmospheric pressure, produces a coating of iron nanoparticles on the quartz surfaces, and these metal sites function as catalysts for the formation and growth of MWNTs. In this study, we report the influence of operating conditions on MWNT purity and yield. These parameters include the feed injection temperature, furnace temperature, hydrocarbon partial pressure, reaction time, space velocity, and iron to carbon ratio in the feed. We observed that the quality of the MWNTs dependc sensitively on the growth parameters and a window for the operating conditions is identified for the growth of high purity aligned MWNTs. Characterization of the MWNTs by electron microscopy has shown that there is a relationship between metal particle size and MWNT diameter.
Synthesis of Novel Mesoporous Carbons and Their Applications to Electrochemical Double-Layer Capacitors
Authors: Hyeon Taeghwan , Oh Seung M. , Lee Jinwoo , Yoon Songhun
Published: April 2011

We have developed a new synthetic procedure to fabricate mesoporous carbons using mesoporous inorganic materials as templates. Mesoporous carbons with regular 3-dimensionally interconnected ∼ 2 nm pore arrays have been synthesized using aluminum substituted MCM-48 and HMS mesoporous silicas as templates. The polymerization of phenol and formaldehyde inside the nanopores of the mesoporous silica templates generated phenol-resin/luminosilicate nanocomposites. The carbonization followed by the removal of silicate templates generated mesooporous carbons with regular pore dimensions. The mesoporous carbons exhibited excellent performance for electrochemical double layer capacitors (EDLC). They revealed ideal rectangular shaped cyclovoltammograms up to the high scan rate of 20 mV/sec, which is important for the future applications.
Synthesis of C60 Chains Contained Within Carbon Nanotubes
Authors: Smith Brian W. , Luzzi David E.
Published: April 2011

We have recently discovered self-assembled chains of C60 molecules contained within single wall carbon nanotubes (SWNTs). Using in situ transmission electron microscopy studies, we show a route by which such ‘peapod’ structures can be synthesized. The results indicate that exterior C60 molecules arrive at the nanotubes from the vapor phase and subsequently enter, presumably through open ends or sidewall defects. The methods discussed in this work provide a means for the bulk production of these molecular assemblies.
Field Emission and Nanostructure of Carbon Films
Authors: Merkulov V. I. , Lowndes D. H. , Baylor L. R.
Published: April 2011

The results of field emission measurements of various forms of carbon films are reported. It is shown that the films' nanostructure is a crucial factor determining the field emission properties. In particular, smooth, pulsed-laser deposited amorphous carbon films with both high and low sp3 contents are poor field emitters. This is similar to the results obtained for smooth nanocrystalline, sp2 - bonded carbon films. In contrast, carbon films prepared by hot-filament chemical vapor deposition (HF-CVD) exhibit very good field emission properties, including low emission turn-on fields, high emission site density, and excellent durability. HF-CVD carbon films were found to be predominantly sp2 -bonded. However, surface morphology studies show that these films are thoroughly nanostructured, which is believed to be responsible for their promising field emission properties.
Filtered Cathodic Arc Deposited Diamond-Like Carbon: Electron Spin Resonance (ESR) and Raman Spectroscopy
Authors: Druz B. , Zaritskiy I. , Yevtukhov Y. , Konchits A. , Valakh M. , Kolesnik S. , Shanina B. , Visotski V.
Published: April 2011

Tetrahedral diamond like carbon (ta-C) films were deposited onto Si substrates using Filtered Cathodic Vacuum Arc (FCVA) process. Stress of deposited films was varied in the range 3.5÷8.5 GPa. The ESR (stationary and pulse) and Raman techniques were used to analyze sp2 related defects in the pseudo-gap of undoped, as deposited 20 – 100 nm thick films. The results are compared with data for direct ion beam deposited from CH4 plasma hydrogenated DLHC films and nature of paramagnetic defects in DLC is discussed.
Mechanisms of Single-Wall Carbon Nanotube Growth by the Laser Vaporization Technique: In Situ Imaging and Spectroscopy
Authors: Geohegan D. B. , Puretzky A. A. , Fan X. , Guillorn M. A. , Simpson M. L. , Merkulov V. I. , Pennycook S. J.
Published: April 2011

Single-wall carbon nanotubes are formed by Nd:YAG laser vaporization of a graphite/(1 at. % Ni, 1 at. % Co) target into flowing argon (500 Torr) within a quartz tube furnace (1000 °C). Here, this process is investigated for the first time with time-resolved laser-induced luminescence imaging and spectroscopy of Co atoms, C2 and C3 molecules, and clusters. These measurements under actual synthesis conditions show that the plume of vaporized material is segregated and confined within a vortex ring which maintains a ˜1 cm3 volume for several seconds. Using time-resolved spectroscopy and spectroscopic imaging, the time for conversion of atomic and molecular species to clusters was measured for both carbon (200 μs) and cobalt (2 ms). This rapid conversion of carbon to nanoparticles, combined with transmission electron microscopy analysis of the collected deposits, indicate that nanotube growth occurs during several seconds of time from a feedstock of mixed nanoparticles in the gas-suspended plume. Using these in situ diagnostics to adjust the time spent by the plume within the high-temperature zone, single-walled nanotubes of controlled length were grown at an estimated rate of 0.2 μm/s.
Elastic Constants of Diamond-Like Carbon Films by Surface Brillouin Scattering
Authors: Ferrari A.C. , Robertson J. , Pastorelli R. , Beghi M.G. , Bottani C.E.
Published: April 2011

The elastic constants of thin Diamond-Like Carbon (DLC) films supply important information, but their measurement is difficult. Standard nanoindentation does not directly measure the elastic constants and has strong limitations particularly in the case of hard thin films on softer substrates, such as tetrahedral amorphous carbon on Si. Surface acoustic waves provide a better mean to investigate elastic properties. Surface Brillouin scattering (SBS) intrinsically probes acoustic waves of the wavelength which is appropriate to test the properties of films in the tens to hundreds of nanometers thickness range. SBS can be used to derive all the isotropic elastic constants of hard-on-soft and soft-on-hard amorphous carbon films of different kinds, with thickness down to less than 10 nm. The results help to resolve the previous uncertainties in mechanical data. The Young's modulus of tetrahedral amorphous carbon (ta-C) turns out to be lower than that of diamond, while the moduli of hydrogenated ta-C (ta-C:H) are considerably lower than those of ta-C because of the weakening effect of C-H bonding.
Observation of Blue Emission from ECR-CVD Deposited Amorphous Hydrogenated Silicon Carbide
Authors: Rusli J. Cui , Yoon S. F. , Yu M. B. , Chew K. , Ahn J. , Zhang Q.
Published: April 2011

Amorphous hydrogenated silicon carbide (a-Sil-xCx:H) thin films have been deposited by the electron cyclotron resonance chemical vapor deposition (ECR-CVD) technique at different microwave powers from 100W to 1000W. The films were characterized in terms of their optical absorption and photoluminescence (PL). Their optical band gap E04 ranged from 3.06eV to 3.54eV and when excited at 363.8nm from an Ar+ ion laser, the PL peak emission energy Epl, was found to range from 2.44eV to 2.79eV, corresponding to green to blue emission. The effects of excitation energy Eex, on Epl, and FWHM of the PL spectra were also investigated. A linear relation between the FWHM and Urbach tail width E0was noted, suggesting that the PL bandwidth is mainly contributed by static disorder. The blue emission observed in these a-S1-x-Cx:H films is promising for their applications in large area flat panel displays.
Structure, Properties, and Applications of Single Crystalline Films of Vinylidene Fluoride and Trifluoroethylene Copolymers
Authors: Ohigashi H.
Published: April 2011

The single crystalline (SC) film of copolymer of vinylidene fluoride and trifluoroethylene is a highly crystallized; highly double-oriented, and optically transparent ferroelectric film, which can be prepared by annealing a uniaxially drawn film in the paraelectric phase with its ends being clamped and its surfaces free. The SC film is composed of endlessly extended chain crystals whose c-axis aligns along the stretching direction almost perfectly and the polar b-axis is oriented ±π/6 off the film normal. It does not contain lamellar crystals nor amorphous phase. Owing to such unique structure, the SC film exhibits the ferroelectricity and related properties inherent to the crystal more clearly than the films composed of lamellar crystals. In this paper, we present the results of our recent studies on the SC films: (1) the structure and morphology studied by POM and X-ray diffiractions; (2) the ferroelectric, piezoelectric, and mechanical properties in the ferroelectric phase; (3) molecular chain motions in the paraelectric phase as revealed by dielectric, X-ray diffraction and shear mechanical studies; and (4) applications to shear ultrasonic transducers. The followings are the main results to be emphasized: (A) the Young's modulus in the direction along the stretching axis is much larger (120 GPa at 10K) than that of LC films (15 GPa); (B) the SC film is the most effective piezoelectric polymer film among piezoelectric polymers; (C) the SC film in the paraelectric phase is a liquid crystal of ID-liquid and 2D-solid, and each chain molecule of TGTG' conformation undergoes rotational and flip-flop motions independently of neighboring chains in a highly regular hexagonal crystal lattice, which leads to anomalous dielectric behaviors in the paraelectric phase; (D) SC film transducers for shear ultrasonic waves are effectively usable for NDE.
Effects of Sample Processing and High-Energy Electron Irradiation Conditions on the Structural and Transitional Properties of P(VDF-TrFE) Copolymer Films
Authors: Bharti Vivek , Cheng Z.-Y , Xu H. S. , Shanthi G. , Xu T.-B. , Mai T. , Zhang Q. M.
Published: April 2011

Recently it has been demonstrated that using a high electron energy irradiation, the electromechanical properties of polyvinylidene fluoride - trifluoroethylene, P(VDF-TrFE) copolymers can be improved significantly for example; high electric field induced strain (∼ 4.5%) with high elastic energy density, high dielectric constant (∼ 65 with loss less than at 1kHz), high piezoelectric coefficient (∼ 350 pm/V ) and high electro-mechanical coupling coefficient (∼0.45). It was found, depending on sample processing and electron irradiation conditions these properties can be controlled. In this talk we will present the experimental data on the effect of processing and irradiation conditions on structural and transitional behavior of copolymers. These structural information coupled with the electro-mechanical properties will be presented in order to show the possibilities for further improvement.
Analysis of Ferroelectric Switching Process in VDF/Trfe Copolymers
Authors: Kano Kenji , Kodama Hidekazu , Takahashi Yoshiyuki , Furukawa Takeo
Published: April 2011

The ferroelectric switching curve of vinylidene fluoride / trifluoroethylene copolymer exhibits a characteristic time evolution consisting of two processes; an initial gradual increase in proportion to t0 5 followed by a rapid increase according to an exponential function with particularly large exponent 6. Such a switching curve was analyzed by means of computer simulation based on a modified nucleation-growth mechanism. It was found that the initial gradual increase is attributed to generation of considerably large nuclei that grow according to a random-walk scheme. Once such nuclei gain a critical size, they start to grow automatically either one or two dimensionally. The time required to generate critical nuclei serves as an incubation time for the later growth process to result in the large exponent.
Grain Boundary Structure and Sliding of Alumina Bicrystals
Authors: Ikuhara Y. , Watanabe T. , Yarnamoto T. , Saito T. , Yoshida H. , Sakuma T.
Published: April 2011

Alumina bicrystals were fabricated by a hot joining technique at 1500°C in air to obtain ten kinds of [0001] symmetric tilt grain boundaries which included small angle, CSL and high angle grain boundaries. Their grain boundary structures were investigated by high-resolution electron microscopy (HREM), and the respective grain boundary energies were systematically measured by a thermal grooving technique. It was found that grain boundary energy strongly depended on the grain boundary characters, e.g., there were large energy cusps at low Σ CSL grain boundaries. But, main part of grain boundary energy is likely to be due to the strain energy around the grain boundary, and the contribution of atomic configuration is not so large. Small angle grain boundaries were consisted of an array of partial dislocation with Burgers vector of 1/3[1100] to form the stacking faults between the dislocations. The behavior of grain boundary sliding was also investigated for typical grain boundaries by high-temperature creep test at 1400°C. As the result, the occurrence of grain boundary sliding was found to depend on the grain boundary atomic structure.