bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ain Films Grown by Electric Field Induced Flux of al Cations
Authors: Johnson Matthew T , Mao Zhigang , Barry Carter C 
Published: July 2020

Abstract
The properties of aluminum nitride (A1N) make it an interesting material for applications in the microelectronics industry. These properties include: a large bandgap, good thermal conductivity, high-temperature stability and chemical inertness. Additionally, thin A1N films are used as buffer layers for the growth of GaN on alumina. In the present study, thin-films of A1N have been grown on (000l)-oriented α-Al2O3 through the use of an electric field. At elevated temperatures an electric field applied across a normally insulating oxide material will typically induce a flux of ions that carry current. In the case of Al2O3, since the more mobile species are the Al3+ cations, by applying an electric-field across the material, with an appropriate electrode material, a flux of 3+ cations can be induced toward the cathode surface (negative electrode).
Prospects For Imaging of Single Dopant Atoms in Silicon by ADF Stem
Authors: Vanfleet Richard R , Silcox John 
Published: July 2020

Abstract
The demands of the National Technology Roadmap for Semiconductors will necessitate measurement of dopant concentrations with greater spatial resolution than now possible. Current experimental and simulation experience indicate that Annular Dark Field (ADF) imaging in a Scanning Transmission Electron Microscope (STEM) should be able to determine dopant distributions with near atomic resolution. The ADF signal is derived from electrons diffusely scattered to high angles, resulting in contrast due to atomic number (Z-contrast) and defects in the crystal lattice. Thus, heavy atoms can be imaged by their Z-contrast and small atoms by the misfit strain induced in the silicon lattice. Atomic number scattering is proportional to Zn where n is between 1.5 and 1.9 depending upon the inner detector angle of the ADF detector.
Direct Transmission Electron Microscope Observations of Doping Variations in InP-Based Semiconductor Laser Diodes
Authors: Hull R 
Published: July 2020

Abstract
The ability to map semiconductor doping distributions with high spatial resolution (∽10 nm) and high compositional sensitivity (of order 1 ppm) is of enormous importance to the microelectronics and optoelectronics industry. Although several methods (e.g. scanning capacitance microscopy, masked secondary ion mass spectroscopy, secondary electron microscopy, electron holography) are under development, no technique currently offers the combination of sufficient resolution, sensitivity and reproducibility to fully address characterization requirements. In this paper, we describe development of a technique which utilizes focused ion beam (FIB) sputtering and transmission electron microscopy (TEM) to enable direct imaging of dopant distributions in InP-based semiconductor devices, with spatial resolution of order 10 - 30 ran, and compositional sensitivity of order 1017 cm-3 (i.e. 5 ppm).
Laser diode samples are prepared for TEM imaging using a FEI 200 30 kV Ga+ focused ion beam system. A schematic of the relevant structure is shown in Figure 1(a).
A New Method for Pin Point Failure Analysis Using Fib Combined Analytical Tem
Authors: Kamino T , Yaguchi T , Matsumoto H , Tomita M , Koike H 
Published: July 2020

Abstract
Recently, we developed the dedicated FIB system(FB-2000A) for the TEM specimen preparation. The system has ion optics with the maximum ion beam current density of 15 A/cm2 and the minimum ion probe size of l0nm. In the system, the side entry type specimen stage originally designed for high resolution TEM was employed, and the drift rate of the stage during FIB milling is less than lnm/min. The FIB-TEM compatible specimen holder has been developed it made milling of specimen in FIB system and observation of milled specimen in TEM without remounting the specimen possible.. The holder was designed to rotate the specimen around the axis of specimen holder so that both side of milled surfaces can be faced to incident electron beam in TEM.
To improve positional resolution in pin point TEM specimen preparation, it is important to know the inside structure of specimen before starting the milling.
Microstructural Characterization of Heteroepitaxial SiGeC Alloys
Authors: Smith David J , Chandrasekhar D , Laursen T , Mayer JW , Huffman J , Robinson McD , Croke ET , Hunter AT 
Published: July 2020

Abstract
Heteroepitaxial growth of Group IV elements on Si is attracting increased attention because of the possibility of strain compensation in addition to bandgap engineering. The incorporation of the smaller C atom into Si1-xGex binary alloys to compensate for the larger size of the Ge atom offers the prospect of lattice matching and hence strain-free growth. In our early work, ternary SiGeC alloy films with up to ∽ 2% C were epitaxial with excellent crystallinity and very few interfacial defects. However, with increased C content, the films developed considerable disorder away from the substrate and finally became amorphous. Moreover, even at low C contents (∽2-3%), it appears that substantial C is being incorporated interstitially rather than substitutionally into the covalent lattice.2 Our recent work has therefore been aimed at establishing growth conditions that enable the amount of substitutional C to be maximized while still maintaining high crystal quality.
Direct Observation of Threading Dislocations in Gan by High Resolution z-contrast imaging
Authors: Xin Y , Browning ND , Pennycook SJ , Nellist PD , Sivananthan S , Faurie J-P , Gibart P 
Published: July 2020

Abstract
Wide gap nitride semiconductors have attracted significant attention recently due to their promising performance as short-wavelength light emitting diodes (LEDs) and blue lasers. One interesting issue concerning GaN is that the material is relatively insensitive to the presence of a density of dislocations which is six orders of magnitude higher than that for III-V arsenide and phosphide based LEDs. Although it is well known that these dislocations originate at the film-substrate interface during film growth, thread through the whole epilayer with line direction along &lt;0001&gt; and are perfect dislocations with Burgers vectors of a, c, or c+a, the reason why they have such a small effect on the properties of GaN is unclear.
To develop a fundamental understanding of the properties of these dislocations, the core structures are studied here by high resolution Z-contrast imaging in a 300kV VG HB603 scanning transmission electron microscope (STEM) with a resolution of 0.13nm.
Atomic Structure of Twinned As Precipitates in Lt-GaAs
Authors: Ruvimov S , Dicker Ch , Washburn J , Liliental-Weber Z 
Published: July 2020

Abstract
Low-temperature GaAs (LT-GaAs) of a high resistivity and a short carrier lifetime (0.2-20 ps) is promising for device applications. High temperature annealing of LT-GaAs often leads to formation of twinned As precipitates in the GaAs matrix. Here high resolution electron microscopy has been applied to study the structure of As precipitates formed in MBE grown LT-GaAs layers during rapid thermal annealing at 850 and 950 °C. Twinning in the rhombohedral As was a special focus of this study.
Fig. 1 shows a HREM image of a typical As precipitate formed in a LT-GaAs layer after annealing at 850 °C. The precipitate has a rhombohedral structure with a=0.376 nm and c= 1.055 nm and a polyhedral shape with distinct facets. The long facets bounded by the {111}A planes of the GaAs are planar while the others have a high density of steps.
Microstructure Of Au/Ti Ohmic Contacts On n-GaN
Authors: Liu R-J , Smith L L , Kim M J , Carpenter R W , Davis R F 
Published: July 2020

Abstract
GaN is a semiconductor with a direct band-gap of 3.4 eV which has a potential application in optoelectronic devices such as UV-emitting lasers and blue light emitting diodes. Extensive efforts have been made to develop low-resistance, thermally stable and uniform ohmic contacts on GaN. In this study, n-GaN films (Si-doped) with an intermediate A1N buffer layer were grown on 6H-SiC substrates via MOVPE. The contacts were formed by depositing Ti and then Au films on GaN by e-beam evaporation at room temperature. Current-voltage measurements as a function of temperature showed that the ohmicity of the Au/Ti contact improved upon annealing, corresponding to changes in the microstructure of the contact interfaces involving a redistribution of nitrogen and gold.
Fig. 1 shows the microstructure of the as-deposited Au/Ti/GaN films. The nanocrystalline Ti film was about 50 nm thick. Au film was polycrystalline, containing many growth twins. The thickness of Au film varied from 260 to 350 nm.
Structure of Low- And High-Angle Grain Boundaries In YBCO/MgO Films
Authors: Oktyabrsky S , Kalyanaraman R , Jagannadham K , Narayan J 
Published: July 2020

Abstract
Grain boundaries (GBs) in laser deposited YB2Cu3O7-δ/MgO(001) thin films have been investigated by high-resolution transmission electron microscopy (TEM) and scanning TEM (STEM). We report both statistics and atomic structure of low-angle and high-angle [001] tilt grain boundaries resulting from almost perfect c-axis textured YBCO films.
Atomic structure of low-angle GBs was analyzed using a dislocation model. These boundaries have been found to be aligned primarily along (100) and (110) interface planes. For (100) boundary plane, the GB consists of a periodic array of [100] dislocations (Fig.l). For (110) boundary plane, the array is also periodic but every [110] dislocation is split by ∼ 1.5 nm into two [100] and [010] dislocations (Fig.2). We have calculated energy of various configurations and shown that the energy of the (110) boundary with dissociated dislocations is comparable to that of (100) boundary, which explains the coexistence of (100) and (110) interface facets along the boundary.
The Atomic-Scale Origins of Grain Boundary Superconducting Properties
Authors: J. Pennycook S , Buban J , Prouteau C , Chisholm M F , Nellist P D , Browning N D 
Published: July 2020

Abstract
Due to the extemely short coherence lengths of the high-Tc superconductors (around 30 Å in the a-b plane), defects such as grain boundaries are obvious barriers to the flow of supercurrent. Within a few months of the discovery of these materials, it was shown how the critical current dropped four orders of magnitude as the grain boundary misorientaion increased from zero to 45°. Even today, there is no quantitative understanding of this behavior. A qualitative understanding is however possible through atomic resolution Z-contrast imaging on YBa2cu3O7-δ and SrTiO3 bicrystal grain boundaries, combined with bond-valence-sum analysis.
The Z-contrast image of a YBa2cu3O7-δ low angle grain boundary in Fig. 1 shows the same kind of reconstructed dislocation cores as seen in SrTiO3, containing reconstructions on both the Cu and Y/Ba sublattices.
Investigation of the Local Superconducting Properties at Grain Boundaries in High-Tc Superconductors
Authors: Prouteau C , Duscher G , Browning N D , Pennycook S J , Verebelyi D , Christen D K , Chisholm M F , Norton D P 
Published: July 2020

Abstract
Developing an atomic scale study of the structure-property relationships of grain boundaries in high-Tc superconductors is essential to understand their current dissipation mechanism and for incorporating these materials into viable devices. Thin YBa2Cu3O7-δ films have been deposited by pulsed laser deposition (PLD) on SrTiO3 symmetric bicrystals. Transport measurements in a magnetic field have been conducted across the grain boundaries through a wide bridge. The data obtained are consistent with microstructural observation in a VG Microscopes HB603 U and a VG HB501 UX dedicated STEM. Of particular interest in the study of high-Tc materials is the use of EELS, which can highlight the presence of non-superconducting regions through interpretation of the onset positions and finestructure (ELNES) of characteristic core-edge features.
The V(I) curves recorded across a 24° boundary for several magnetic fields (fig. 1 - left) show an onset critical current density followed by a linear differential ohmic behavior which gives a negative intercept.
Anisotropy of Electronic Structure and Transport Properties of Oxide Superconductors
Authors: Dravid Vinayak P 
Published: July 2020

Abstract
High temperature superconductivity in cuprates has become a fairly mature field now that more than a decade has passed by since its discovery. While scientific appeal of the field continues, the technological implications have faced harsh realities. Although the transition temperatures are high, the coherence length in oxide superconductors is awfully short and thus inhomegeneity or perturbation at the length scale of a few nanometers proves extremely detrimental to their properties, especially transport. Further, slight changes in the oxygen stoichiometry in cuprates have a profound effect on their superconducting properties and it is often not clear whether the nonstoichiometry at defect sites (e.g. grain boundaries- GBs) is intrinsic or extrinsic.
The anisotropy of electronic structure is well reflected in low loss EELS spectra of these materials. Figure 1 shows low loss EELS spectra from Y124: one taken with momentum transfer confined to the Cu-02 planes, and the other normal to them. These observations are in accord with the fact that conduction is predominantly along the ab-planes, within single crystals.
Structure in Amorphous Network Solids and its Evidence in Electron Diffraction
Authors: Hobbs Linn W 
Published: July 2020

Abstract
A cubic millimeter (10-9 m3) of condensed matter contains typically ∼1020 atoms, and a complete solution to the general structure problem requires finding ∼3 ×l020 atom coordinates. For crystals, long-range translational periodicity immensely simplifies the structure elucidation problem to something like a 101-102 problem (further reduced by the symmetry accompanying orientational order), because only the contents of the unit cell (&lt; 100 atoms for most inorganic structures) and the unit cell geometry need be determined. Amorphous is the epithet traditionally bestowed on structures with neither orientation nor translational order, a more precise term for which is topologically disordered [1], A structural average for an amorphous solid can be established with a good many fewer than 1020 atoms, because many atom-atom correlations nevertheless exist in topologically-disordered structures due to bonding, packing and associated topological constraints. In fact, assemblies with less than 200 atoms can usually adequately represent characteristic structural topologies [1].
Experimental and Theoretical Characterisation of Structure in Thin Disordered Films
Authors: McCulloch DG , McKenzie DR , Cockayne DJH , Goringe CM 
Published: July 2020

Abstract
The electron microscope provides an ideal environment for the structural analysis of small volumes of amorphous and polycrystalline materials by collecting scattering information as a function of energy loss and momentum transfer. The scattering intensity at zero energy loss can be readily processed to a reduced density function G(r), providing information on nearest neighbour distances and bond angles[l]. Figure 1(a) shows the G(r) for glassy carbon, a turbostratic form of graphite. The three nearest neighbours in glassy carbon (labelled 1-3 in figure 1) are at 1.42 Å, 2.44 Å and 3.75 Å respectively. These distances correspond to the first three nearest neighbours in a graphite sheet and are expected in glassy carbon which is know to have good in-plane graphitic order. In figure 1(b) the G(r) of cathodic arc deposited tetrahedral amorphous carbon is shown. This material contains a high fraction of diamond-like bonding[2] and has a 1st nearest neighbour peak at 1.52 Å.
An Investigation Into Beam Damage of Mesoporous Materials
Authors: Blanford C F , Bentley J , Stein A , Carter C B 
Published: July 2020

Abstract
In 1992, researchers at Mobil Research and Development created a new class of porous silicates, most notably mesoporous MCM-41.2-3 This material features a hexagonal arrangement of linear pores and surface areas in excess of 1000 m2 g-1. MCM-41 exhibits narrow pore size distributions in the nanometer range. The walls of MCM-41 are essentially amorphous silica, but its porous nature makes it about 3 kJ mol-1 less stable than the collapsed form. Particles of MCM-41 are beam sensitive and it appears that they cannot withstand the large current densities required to obtain reliable analytical data at the nanometer scale in the transmission electron microscope (TEM). For example, low beam currents were used to preserve the pore structure but resulted in energy-filtered TEM elemental maps of oxygen K and Ti L2,3 edge intensities that were too noisy to reveal structure at 5 nm resolution.
A BCC Superlattice of Passivated Gold Nanocrystals
Authors: Harfenist SA , Wang ZL , Schaaff TG , Whettent RL 
Published: July 2020

Abstract
A recent development in the study of nanocrystalline materials has been the self-assembly of passivated nanometer scale building blocks into larger, well ordered structures reaching the micron scale. Nanocrystal supercrystals (NCS) have been observed in metallic, semiconductor, and magnetic materials. In most cases the nanocrystals (NXs) are encapsulated in some inert medium that effectively protects the nanocrystal core and its unique electronic and optical properties. Here we describe the self-assembly of gold nanocrystals (∼4.5 nm core diameter), passivated with hexanethiol self-assembled-monolayers into ordered regions exhibiting a body-centered-cubic (bcc) superstructure. Transmission Electron Microscopy (TEM) imaging and Electron Diffraction (ED) experiments were used to characterize the NCSs and their resulting superstructures.
A large agglomeration of NCSs can be seen in figure 1. One can clearly see regions of periodicity within the nanocrystal aggregation.
Growth Mechanism of Ag Nanocrystal Supercrystals
Authors: Harfenist SA , Wang ZL , Vezmar I , Alvarez MM , Whetten RL 
Published: July 2020

Abstract
Of recent interest in the science of nano-scale materials is the production and characterization of substances composed of ordered lattices of up to millions of identical nanometer scale particles. Silver nanocrystals of ∼ 4.5 nm diameter passivated with dodecanthiol surfactant were produced in the aerosol phase. Characterization of the individual particles and the subsequent supercrystals (SXs) resulting from their periodic packing was brought about using Mass Spectrometry, Transmission Electron Microscopy (TEM)/Electron Diffraction (ED), Scanning Electron Microscopy and Atomic Force Microscopy (AFM). It was determined that the micrometer and greater sized faceted SXs exhibited an hexagonal-close-packed (HCP) superstructure (fig.l) resulting in triangular shapes bounded by ﹛1100﹜ facets (fig. la); their platlet-like nature (∼20 nanocrystal layers thick) owing to their particular growth pattern. Knowledge of the growth mechanism is important to production of these materials on a macroscopic scale. Here we report a proposed growth model for these supercrystals.
Energy-Filtered Imaging of Zirconia Pillars in Montmorillonite
Authors: Crazier P A , Pan M , Bateman C , Alcaraz J J , Holmgren J S 
Published: July 2020

Abstract
The ability to vary the plane spacing in different clays is becoming increasingly important in catalysis and other technological applications [Baker and Murrell, 1990]. Considerable effort is now being devoted to understanding the mechanisms involved in pillaring such materials with a view to being able to fine-tune parameters such as the plane spacing and active sites for the application of interest. We have been able to use analytical electron microscopy to directly image the pillars in zirconia pillared montmorillonite. By using a combination of TEM techniques, we are able to correlate morphological information with elemental composition and conclusively identify the location of the zirconia pillars.
A sample of natural montmorillonite clay, trade name HPM-20, was obtained from American Colloid and used as received. Zirconia pillared clays were prepared following published procedures [Bartley, 1988]. The Z1O2 pillars were prepared by using hydroxyzirconium cations produced by the solvation of zironyl chloride.
Kinetically Controlled Growth And Shape Formation Mechanism Of Platinum Nanoparticles
Authors: Petroski Janet M , Wang Zhong L , Green Travis C , El-Sayed Mostafa A 
Published: July 2020

Abstract
Many studies on colloidal nanoparticles have focused on the control of nanoparticle size and correlated this to the catalytic activity. Recently, our group has reported for the first time a technique that controlled the shape distribution of Pt nanoparticles. This was done by varying the concentration of the capping polymer and the platinum ion ratio used in the reductive synthesis of colloidal nanoparticles at room temperature. Cubic, tetrahedral and truncated octahedral (TO) particles have been prepared, making it possible to study the catalytic activities of nanoparticles with different shapes and facets.
Using transmission electron microscopy (TEM), we imaged the shapes and determined the shape distribution of platinum nanoparticles at different stages of their growth as a function of time. The small nanoparticles formed during the early stages of growth or at high polymer concentration displayed distributions with a dominance of tetrahedral shapes (see Figure la).
Cu Nanoparticle Formation: Copper Redistribution During NaCl Solution Corrosion of Al-Cu-Mg Alloys
Authors: Ford R G , Carpenter R W , Sieradzki K 
Published: July 2020

Abstract
Aluminum-copper-magnesium alloys also containing manganese and iron (commercial designation 2024) are susceptible to marine corrosion and stress corrosion cracking. Susceptibility depends on heat treatment, and is thought to involve redistribution of copper from within the microstructure onto the surface of the corroding alloy, but few direct observations of the mechanism have been made. Copper can be distributed in several ways throughout the microstructure, which complicates mechanism studies. The primary age-hardening phase is Al2CuMg (orthorhombic; a=4.01, b=9.25, c=7.15 Å) which appears as more or less large equiaxed S particles at equilibrium, and as metastable S’ plates after aging for shorter times at lower temperature (∼190°C). In addition, ubiquitous so-called “dispersoids” containing copper and manganese (prolate spheroid morphology) or iron (irregular “blocky” morphology) do not go into solution when the alloy is solid state homogenized (-495 °C) and are always present in the microstructure. All of these phases are copper-rich sources for surface redistribution relative to the matrix during corrosion.
Z-Contrast Scanning Transmission Electron Microscopy Of Nanometer-Scale Coated Particulate Materials
Authors: Gao HJ , Yan Y , Fitz-Gerald J , Kumar D , Singh RK , Pennycook SJ 
Published: July 2020

Abstract
Particulate materials with unique functional properties have been the focus of much attention in recent years. Of particular interest, due to their considerable scientific and technological importance, are particles coated with nanoparticles. These have greatly stimulated interest for their novel structure and properties. In these kinds of particulate materials, the interface structures between the support particle and the nanoparticle play a crucial role in controlling their properties. Consequently, imaging of the atomic structures at the interfaces can provide deep understanding of the relationship between the particulate and the corresponding properties. Z-contrast scanning transmission electron microscope (STEM) provides a new view of materials on the atomic scale, a direct image of atomic structure composition which can be interpreted without the need for any preconceived model structure. Therefore it is a powerful tool in the study of particulate materials. In this report, we will present the structures of 18 micron diameter alumina particles coated with Ag nanoparticles.