bluuebunny/crossref_metadata_2025 huggingface dataset:
Amorphization of Al10(Vx,Cr1-x) intermetallic phase
Authors: Radmilovic V. , Kilaas R. , Thomas G.
Published: June 2020

The stability of phases in alloy systems, including stability in irradiation environments, is conditio sine qua non of their engineering applications. Thus, investigations of different phenomena, such as compositional variation, segregation, order/disorder transitions and amorphization in different phases under irradiation, is of great importance.

In the present paper experiments are reported on using high resolution electron microscopy and electron diffraction to observe the stability of Al-V-Cr based intermetallic phase in Al based alloys which are considered potential material for aerospace applications. In addition, it is an attempt to establish a possible method for investigation of disordering and amorphization in intermetallic phases under the electron beam, as first observed by Thomas et al. in the Ni-Ti system.

The Al based alloy with chemical composition (in wt.%) Al - 2.3 Li - 1.0 Cu - 0.8 Mg - 1.0 Cr - 1.0 V - 0.5 Zr was solutionized at 530°C for 4 hours, water quenched, and aged for 48 hours at 148°C.
The effect of reactive elements on the segregation behavior and microstructure of α-Al2O3 scales on β-NiAl
Authors: Alexander K. B. , Pint B. A.
Published: June 2020

In order to improve oxidation resistance, small quantities of certain oxygen-active or “reactive” elements (RE) such as Y, Zr, Hf, or Ce are added to chromia- and alumina-forming high temperature alloys. Many theories have been proposed to explain the effects of RE additions, with a number of these theories including some aspect of the observed segregation of RE ions to oxide scale grain boundaries and the metalscale interface. The RE-ion segregation to the scale grain boundaries has been proposed to affect the oxidation behavior by suppressing cation transport along grain boundaries. It has been demonstrated that the quantity of RE segregation at α-Al2O3 scale grain boundaries varies with oxidation time and temperature and is greatly affected by the formation of RE-rich oxide particles in the scale (particularly at the gas interface). A previous study of scale formation on Y-implanted β-NiAl found that the Y implant had only a short-term (<1 h) effect at high temperatures.
Twin-induced kinetic shapes of Ge-precipitates in Al
Authors: Xiao S. Q. , Hinderberger S. , Westmacott K. H. , Dahmen U.
Published: June 2020

Twinning plays an important role in the growth of Ge precipitates from solid solution in dilute Al-Ge alloys. Previous work found a great variety of precipitate shapes and corresponding orientation relationships. At thermodynamic equilibrium only one of these has the lowest free energy, and is therefore the most stable shape. The symmetry of the equilibrium shape must conform to the bicrystal symmetry, i.e. the symmetry of precipitate and matrix superimposed by their orientation relationship. For a twinned precipitate the equilibrium shape is determined by the tricrystal symmetry, i.e. the intersection group of the symmetry of matrix, the precipitate and its twin. This shape is different from that of an untwinned precipitate. For the same reason, twinning can also change the precipitate-matrix interface structure, resulting in preferential growth along certain crystallographic directions. This effect induces non-equilibrium, growth or kinetic shapes. In this report a formation mechanism for the kinetic shapes of Ge precipitates due to twinning is proposed and preliminary TEM observations of the relationship between internal twinning and precipitate shape are presented.
Fabrication and characterization of dispersion-strengthened aluminum composite
Authors: Choi J. , Park K. , Sung C. , Czubarow P. , Seyferth D.
Published: June 2020

The excellent high-temperature mechanical properties of metal matrix composites (MMC) make it possible for potential high-temperature applications. Several methods have been used to make the MMC, i.e., plasma spray method, melted metal infiltration method, electroplate method, and foil metallurgy method. In this study, dispersion-strengthened Al composite has been fabricated by the pressing of Al powder and organosilicon preceramic polymer (polymethylsilane-PMS). The Al powder and PMS were pressed under uniaxial stress of 13.5 ksi for 1 hour, and then were pressed under isostatic stress of 40 ksi for 10 minutes at room temperature. Subsequently, it has been heated to 550°C for ∼2 hours under argon atmosphere. Two main chemical stages take place during the heating: pyrolysis of the PMS to create a ceramic (SiC or SiC/C) and solid state reaction of the Al powder and the ceramic at ∼660°C The microstructure of the composite was characterized using transmission electron microscopy in order to understand the relationship between the microstructural and mechanical properties.
Transmission Electron Microscopy of Mercury Sulfide Particles From A Mercury-Contaminated Soil
Authors: Stevenson R. , Harris L. , Turner R. , Barnett M.
Published: June 2020

Presently the East Fork Poplar Creek (EFPC) floodplain located in the city of Oak Ridge, Tennessee and adjacent to the Y-12 nuclear plant is reportedly contaminated with mercury. The metallic mercury which was used from 1955 to 1963 in the production of lithium enriched in the 6Li isotope, is the source of the present contamination.

Previous analyses of these soils using electron probe micro-analysis (EPM) and scanning electron microscopy (SEM) revealed mercury to be present principally as discrete micrometer and submicrometer size particles which were observed to coexist with sulfur. These observations suggested that mercury might be present as mercury sulfide (perhaps even in a crystalline form) which could then affect the level of remediation required for this soil since the toxicity and mobility of mercury is dependent upon its speciation.

The limited concentration of mercury in the EFPC soils (3000-100 mg/kg) and the relatively small size of these mercury bearing particles makes transmission electron microscopy (TEM) the ideal analytical method for unequivocally identifying these particles with micro-chemistry and select area electron diffraction (SAED).
Structure identification of a new superconducting phase
Authors: Mao Z. Q. , Fan C. G. , Lu B. , Li F. H. , Zhang Y. H.
Published: June 2020

Four superconducting phases have been found in cuprates with Bi bilayers. The ideal chemical compositions of these phases are identified as Bi2Sr2Can-1CunO2n+4+δ, n=l,2,3,4.The Tc of n=l,2,3 phasesis 20, 80, 110K respectively. The n=4 phase wasonly observed in the study ofconvergentbeam electrondiffraction and its bulk superconductivity has never been reported. These phases possess similar average structure. They are all tetragonal body-centered lattice with the space group of I4/mmm and adoptlayered structures composed of Bi2O2 layer between which perovskite structure are sandwiched. The lattice parameters are a=b=5.4Å, c=24.4 Å for n=l phase (2201), a=b=5.4 Å,c=30.9 Å for n=2 phase (2212), a=b=3.8 Å, c=37.1 Å for n=3 phase (2223). Recently, we successfully synthesizeda newcuprate withBi bilayers, which has a c-centered orthorhombic unit cell with lattice parameters of a=5.39 Å, b=23.46 Å, c=33.96 Å. And this new structure exhibited superconductivity at about 45 K. In this article, we report on the structure identification of such a new superconducting phase.
Recent developments of the tomographic atom probe
Authors: Deconihout B. , Menand A. , Blavette D.
Published: June 2020

Today material science requires the use of increasingly powerful tools in materials analysis. The last twenty years have witnessed the development of a number of analytical techniques. However, though the arsenal of these techniques is large today, only a few instruments allow both observation and analysis of materials at the nanometer level. One can mention secondary ions mass spectrometry technique (SIMS), scanning transmission electron microscopy coupled with electron energy loss spectrometry (STEM-EELS) and atomprobe techniques. In the SIMS technique, only in-depth spatial resolution can reach one nanometer since lateral spatial resolution is related to the incident ions beam diameter namelya few tenth of micrometers. On the contrary, in the STEM-EELS technique, the lateral spatial resolution can be as good as one nanometer while the in-depth spatial resolution is rather poor ; this last resolution is determined by the specimen thickness and therefore strongly depends on samples preparation.

Atom-probe techniques makes it possible to investigate a material with both a high lateral and in-depth spatial resolution. Indeed, the spatial resolution reached with the atom-probe can be lower than one nanometer at the sample surface while being strictly equal to an atomic layer in-depth.
Faster turnaround time for TEM by using a multiple-sample approach
Authors: Alvis Roger , Tracy Bryan
Published: June 2020

The many advantages of transmission electron microscopy (TEM) over other microscopy techniques areoften offset only by one drawback: slow turnaround time. Because of the fact that the time required to complete a multi-sample analysis is directly proportional to the number of samples submitted, TEM is often not a viable tool to analyze an entire fabrication process run or a multi wafer process development experiment. However, we have developed a technique that has allowed a single person to prepareas many as six cross-sectional TEM samples in one day thereby affording the opportunity for the investigation of an entire experimental matrix in a relatively short time.

This improvement in throughput is achieved by our approach to sample preparation which combines features of the Bravman-Sinclair method with the Tripod polishing technique developed by Benedict and wide tool dimpling described by Humiston. In essence, the standard dummy dice of the Bravman techniqueare replaced by "real" device dice which have been thinned to less than 50°m using the Tripod polisher. This type of mechanical back lapping was first suggested by Marcus and Sheng. Our experiments with this type of sample preparation have been applied to both failure analysis and process development applications.
Recent advances in heteroepitaxial Ge/Si(100) and Ge/Si(l 11)
Authors: Posthill J. B. , Malta D. P. , Pickett R. , Timmons M. L. , Humphreys T. P. , Markunas R. J.
Published: June 2020

Heteroepitaxial Ge-on-Si could have many applications which include: high mobility p-channel fieldeffect transistors (FETs), large area Ge-based IR or X-ray detectors, or as a substrate for the growth of other epitaxial semiconductors. In particular, the close lattice match between Ge and GaAs and Ge and ZnSe offers a potential for Ge to be used as an interlayer for a GaAs/Si or ZnSe/Si technology.Additionally, with the Si substrate as the "foundation" for further epitaxial semiconductors, thereisa built-in thermal match for any device that must be intimately bonded to Si-based circuitry. Thisis particularly critical in the case of HgCdTe IR focal plane arrays that are indium bump-bonded to aSi multiplexer which will experience thermal cycling in use. This contribution briefly reviews some ofour recent results in the high temperature growth of Ge epitaxial films on Si(100) and Si(l 11) substrates which are being developed for use as a template for HgCdTe/CdZnTe growth.
TEM characterization of SiGeC material system
Authors: Chandrasekhar D. , Smith David J. , Kouvetakis J. , Robinson McD.
Published: June 2020

The IV-IV material system, specifically Si1-xGex/Si, has generated considerable interest in the scientific community in recent years. The built-in compressive strain and composition of pseudomorphic Si1-xGex epilayers on Si substrates affect the band structure and energy gap, which are fundamental to bandgap engineering. This property has been used in demonstrating a heterojunction bipolar transistor with SiGe base, resulting in improved high-frequency performance over conventional transistors with Si bases. However, the thermal instability and lower critical thickness of Si1-xGex layers limits applications, in turn prompting investigation of the Si1-x-yGexCy system. Substitutional carbon incorporation in Si1-xGex is expected to relieve the strain in the epilayer and increase the energy gap, the latter being an important consideration in revolutionizing transistor technology. Recently, growth and characterization of pseudomorphic Si1-x-yGexCy and its photoluminescence properties have been reported.

In our present study, we have characterized Si1-x-yGexCy samples grown on Si substrates by chemical vapor deposition. Different precursors and flow rates were used tovary the relative elemental compositions. Rutherford backscattering and secondary ion mass spectroscopy techniques were employed for compositional analysis and transmission electron microscopy was used to determine microstructure. Electron transparent specimens were prepared in cross-section by a standard technique, involving mechanical grinding, dimpling and argon ion-milling. TEM observations were made with JEOL 2000FX and JEOL 4000EX microscopes. Selected area diffraction patterns and optical diffractograms were used in determining the structure and lattice constants.
Transmission Electron Microscopy of polysilicon microresistor
Authors: Duan J. Z. , Thomas B. , Sidhwa A. , Chopra S.
Published: June 2020

The electrical properties of electronic materials are greatly affected by their microstructure, which in turn is determined by the processes used for fabrication. Transmission Electron Microscopy (TEM) is one of the most powerful analytical techniques to provide localized information about microstructure as it relates to process control parameters. This information is used for process development and failure diagnoses as well as QA/QC control. In this study, the microstructures within the devicesof polysilicon microresistors were analyzed using TEM to understand different resistances.

The TEM samples were prepared from the devices to be analyzed by the mechanical polishing method using the tripod polisherTM. The selected area polishing technique was used to find the area of interest within one micron range. Figure 1 shows the specimen preparation process. The low and high magnification optical micrographs in Figures 1a and 1b indicate the region of interest within the die. Figure 1c is the optical image of the cross section along the line A-A in Figure lb.
Columnar microstructures of preferred oriented Aluminum Nitride films prepared by reactive sputtering
Authors: Kim Geun-Hong , Lee Hwan-Chul , Chun Chang-Hwan , Lee Jai-Young
Published: June 2020

Aluminum nitride (AIN) thin films have drawn much attention as piezoelectric materials for generation and detection of surface acoustic wave (SAW) owing to high ultrasonic velocity and fairly large piezoelectric coupling factors. Since the piezoelectric properties are strongly dependent upon the c-axis orientation of AIN films, it is important to control the crystallographic orientation with deposition parameters. Though many reports have been presented, the mechanism of crystallographic orientation change with deposition parameters still remains unknown and the microstructure analysis of AIN films have been scarcely carried out. In this paper, we present the effect of sputtering pressure on thecrystallographic orientation and the microstruclure of the deposited AIN films, using X-ray diffraction (XRD) and transmission electron microscopy (TEM) study.

AIN films have been deposited on Si (100) wafers by reactive RF magnetron sputtering in Ar-N2 gas mixture without substrate heating. The base pressure of vacuum chamber was below 1.5X10-6 Torr, RF power was 200 W and the ratio of gas flow rate (Ar:N2) was 3:1. Processing pressures ranged from 5 to 12 mTorr. Crystal structure of as-deposited films examined with XRD (Rigaku, D/MAX-RC, 12 kW) and microstructure analyses were carried out using crosssectional and plan-view TEM (JEOL 4000FX, 400 kV).
Preparation of Transmission Electron Microscopy specimens of integrated circuits usinga modified tripod polisher
Authors: Shishido Howard , Su David
Published: June 2020

With the continuous decrease in the critical dimensions of integrated circuit (IC) devices, transmission electron microscopy (TEM) has become an important tool for the study of these devices. Two reasons account for the new emphasis in TEM - small fabrication imperfections that did not affect the performance of devices in the past can no longer be ignored and thus need to be addressed, the dimensions of some features, such as gate oxide thicknesses, have become so small that only TEM can be used reliably to study them. However, as the need for TEM increases, the requirements for specimen preparation also has become more stringent. No longer is it acceptable to blindly prepare samples of blanket films or of any one of an array of devices, the ability to "hit" a specific area in a very short period of time has become a necessity. Fortunately, recent advances in the preparation of TEM specimens of IC devices has relieved some of the pressure of performing these jobs.
Correlative imaging of surfactant aggregates in emulsion polymers by optical, scanning- electron, and atomic-force microscopies
Authors: Neilly J. P. , Salvata L. , Johnson R. W. , Miller M. F. , Kozlowski J. , Schapira T.
Published: June 2020

Water based emulsion polymers are utilized in a wide variety of industrial applications. Because of the hydrophobic nature of the monomers utilized as starting materials for these polymers, surfactants arc typically used to facilitate polymer synthesis. One of the problems associated with the use of surfactants in these systems is the phenomenon of surfactant migration to the polymer surface. Migration, which can occur over variable time periods, often interferes with the desired performance properties of the finished product. However, tests for migration are often empirical and highly subjective. Imaging of surfactant aggregates can provide valuable information that allows the researcher to correlate performance properties with the amount and type of surfactant present at the surface. In this paper we describe correlative imaging of surfactant aggregates by optical, scanning electron and atomic force microscopies and the types of information they provide. In addition, X-ray photoelectron spectroscopy was used to determine the chemical composition of the aggregates.
Investigation of the microstructure effect on the magnetoresistance of heterogeneous Au1-xCox melt-spun ribbons
Authors: Hütten A. , Bernardi J. , Friedrichs S. , Thomas G.
Published: June 2020

Giant magnetoresistance (GMR) of up to 65% at room temperature has been achieved in Cu/Co multilayers, far exceeding the 2.5% arising from permalloy, which is presently used in magnetoresistive read heads. The GMR effect is not restricted to multilayered structures only and has been also discovered in heterogeneous CulxCox thin films. At present, experimentally determined and statistically significant microstructural parameters, e.g., Co particle size distribution, composition of Co particles and Co matrix concentration, are still not available for Cu1-xCox films or melt-spun ribbons because of two reasons. First, the small difference in atomic scattering factors of Cu and Co and secondly, the Ashby-Brown contrast, which is expected for coherent precipitates, is not observed. The large volume fraction of Co precipitates results in overlap and cancellation of their strain fields. To overcome limitations in imaging Co precipitates, melt-spun AU1-xCox ribbons have been investigated regarding their GMR. AuCo has a similar phase diagram (Fig. 1) compared with CuCo, but it has the advantage of a large difference in atomic scattering factors of Au and Co. As a consequence Co-rich precipitates can be directly identified by their mass contrast.
A new technique for measuring the separation of closely spaced dislocations using residual-contrast conditions
Authors: Angelo J. E. , Mills M. J.
Published: June 2020

In order to measure the spacing of closely spaced dislocations, a method with sufficient spatial resolution must be used. High resolution imaging provides one method of determining the spacing of paired dislocations, but care must be taken since these authors have shown that thin film effects can give rise to structures not present in bulk materials. To date, the most widely used method of determining the spacing of paired dislocations is the weak-beam dark field method. This method has proved extremely useful in the study of many systems, see Cockayne3 for a review. One of the difficulties of the weak-beam method is that the observed peak positions do not generally correspond to the actual position of the partial dislocation cores. Correlation of the peak positions with the true position depends on the deviation parameter, foil thickness, and position of the dislocations within the foil.
Characterization of constitutional liquid-film migration in Alloy 718
Authors: Acoff V. L. , Griffin R. D. , Thompson R. G.
Published: June 2020

Alloy 718 is a nickel-based superalloy which consists of an FCC solid solution of Ni, Fe, and Cr strengthened with γ″ precipitates. The composition of the alloy is shown in Table 1. It has excellent high temperature mechanical properties and oxidation resistance. However, Alloy 718 is susceptible to hot cracking in weld heat affected zones (HAZ) as a result of the formation of intergranular liquid. This metastable grain boundary liquid may be due to “constitutional liquation” of second phase particles, known as constitutional liquid film migration (CLFM). Radhakrishnan and Thompson report that CLFM can occur in situ in the weld HAZ of alloy 718 as a result of constitutional liquation.

Constitutional liquation can be described in terms of a binary alloy with a phase diagram such as theone shown in Figure 1. If an alloy of composition C° is rapidly heated above theeutectic temperature, TE, to temperature T, the AB particles will not have sufficient time to dissolve, as dictated by equilibrium.
Four-fold aperture synthesis, three-fold astigmatism, and two-fold resolution improvement: Computer-aided microscopy comes of age
Authors: Saxton W. O.
Published: June 2020

Virtually no electron microscopes are now without internal computer control at least, and externalcomputer support continues to play a more important part every year, fuelled by the hundred-fold increase in computing power over the past five years and the continuing if slow advance in the availability of CCD camera systems for TEM. High resolution electron microscopy is within sight of becoming a well-defined, reproducible, technique in which the variability will be restricted at last to the specimen under investigation. The choice of computer systems has narrowed to Macs, Windows on PCs, or Unixworkstations; the future may be with Windows NT.

Image restoration (recovering the specimen exit plane wavefunction) is again the subject of considerable interest as a route to higher resolution, in parallel with biprism holography, and incoherent imaging and ptychography in STEM; and the inverse scattering problem (deducing atomic positions from the scattered wave leaving the specimen) is under active investigation.
Direct retrieval of crystal structures by maximum-entropy analysis of incoherent Z-contrast images
Authors: McGibbon A. J. , Pennycook S. J.
Published: June 2020

Z-contrast imaging of crystalline specimens in a scanning transmission electron microscope (STEM) can provide directly interpretable images of crystal structures at atomic resolution with strong compositional sensitivity. The key feature of the technique is that, by recording images using high-anglethermally diffuse scattered electrons, the resultant image is incoherent, and can be interpreted as aconvolution between the incident electron probe and the projected crystal structure of the specimen. Consequently, the technique is ideally suited to the application of deconvolution routines which enable the retrieval of the original crystal lattice by means of an incident electron probe approximation, and with no prior assumption of the nature of the crystal itself. Here, we show that by applying the image processing technique of maximum entropy, such a retrieval can be achieved with high accuracy,enhancing spatial resolution whilst preserving Z-sensitivity.

Maximum entropy is an image processing routine based on Bayesian probability which produces a ‘most likely’ reconstruction of the original image given a particular point spread function, or in this case, electron probe current density distribution.
Quantitative analysis of silicon oxide using EELS
Authors: Kim M. J.
Published: June 2020

Silicon oxide exists as a continuous solid solution of Si and O (i.e., Si to SiO2), and its band gap energy (Eg) depends on the oxygen content in the system. Si is a semiconductor (Eg=1.1eV) but SiO2is an insulator (Eg=9eV). Substoichiometric oxide SiOx, where 0<x<2, is a semi-insulator. With its extensive applications in electronic and photonic devices, quantitative analysis for the structure and composition of silicon oxide synthesized by various methods becomes increasingly important to understand its structure/properties relationships. EELS, when coupled to a TEM with a field emission source, is a powerful analytical technique for obtaining a host of spatially resolved information from nanoscale solids. In this paper, several examples of applications of high spatial resolution EELS for quantitative analysis of silicon oxides will be illustrated, with brief descriptions of experimental and data quantification procedure.
Elemental mapping of segregation in stainless steels with an imaging filter
Authors: Bentley J. , Kenik E. A.
Published: June 2020

Elemental mapping in a TEM equipped with an imaging filter is expected to become an important microanalysis technique in materials science. The efficacy of the technique for studying solute segregation and composition gradients is not as well established as for mapping precipitate distributions. We have therefore undertaken a preliminary investigation of two types of solute segregation in 300-series austenitic stainless steels.

Elemental mapping was performed at 200 kV with Gatan Imaging Filters (GIF™) attached to JEM 2010 and Philips CM20 electron microscopes operating with probe currents of > 100 nA. Further work will also use a GIF on a Philips CM30 at ORNL. Images were recorded (exposure times of 15-50 s) with the slow scan CCD camera of the filter for 30- or 40-eV-wide windows before and after ionization edges of interest, including Cr-, Fe-, and Ni-L23 edges (see the spectrum shown in Fig. 1), and were processed with Gatan Digital Micrograph™ software.
Detection of ultrafine particles in the lung macrophages of healthy people
Authors: Hatch V. , Hauser R. , Hayes G. B. , Stearns R. , Christiani D. , Godleski J. J.
Published: June 2020

Modern environmental air pollution control strategies are designed to reduce airborne particulate mass by reducing the size of effluent particles to less than lOOnm. Recently, Dockery et al have clearly shown that fine-particulate air pollution (<2.5(μm) can be directly related to excess mortality in humans. Although ultrafine metal fumes (<100nm) have been shown to produce adverse effects in occupational settings, little is known of the extent to which they contribute to ambient environmental particulate air pollution. The purpose of this study is to determine to what extent ultrafine particles are present in lung macrophages of healthy human volunteers studied by electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI).

Lung macrophages were obtained by bronchoalveolar lavage from 14 current non-smokers, 7 of whom work at an oil-fired power plant but were not considered to have significant occupational exposure, 4 of whom were welders at the power plant with the possibility of metal fume (ultrafine particulate) exposure, and 3 of whom were university employees with no known occupational or environmental exposure.
Progress in biological cryo-SEM
Authors: Hermann R. , Hohenberg H. , Bauer H. H. , Muller M.
Published: June 2020

Field-emission SEM's of the in-lens type generate electron beam diameters of less than 1 nm at high accelerating voltages and of ca. 3-5 nm at 1 kV. These instruments, combined with a proper understanding of the involved signal generation and detection processes, represent one of the means to investigate biological surfaces with a structural information at the macromolecular level. In order to obtain this information, the biological structures have to be preserved as close as possible to the native state. This can be achieved with cryotechniques, e.g. cryoimmobilization, eventually followed by freeze-drying of the sample, metal coating at low specimen temperatures and lowtemperature observation in the SEM.

Thin beam transparent samples can be visualized in this way with a structural resolution of ca. 3 nm. Fig. 1 shows a micrograph of differently polymerized human calcitonin: (a) a single fibril of ca. 8 nm diameter, exhibiting helical windings, and (b) a ribbon-like higher order structure, which is composed of individual fibrils.
Ultra-high-resolution low-voltage imaging of polymers
Authors: Butler J. H.
Published: June 2020

We have been using an LVSEM with an immersion-type objective lens extensively for the examination of polymers at low (<2 keV) incident beam energies. Because of this instrument's field emission source, the incident probe can be demagnified down to subnanometer dimensions and still provide enough incident beam current to stimulate detectable image forming signals, esp. secondary electrons. Also, the incident beam penetration depth at low voltages is less than the SE escape depth (=200Å) for carbonaceous materials), so the sample/beam interaction volume is correspondingly smaller. The combination of these two factors suggest that the attainable resolution at low voltages for polymeric materials can be significantly higher than that which can be obtained via conventional SEM, all while the beam induced radiation damage is correspondingly reduced.

Another reason that higher resolution can be obtained at low voltages is that, for all materials, a surface charge balance situation (wherein the incident beam current is equal to the summed SE and backscattered currents) exists for a particular incident beam energy, E2.
AFM: The art of touching molecules
Authors: Moy V. T. , Hofmann U. G. , Benoit M. , Wagner D. , Ludwig M. , Florin E. L. , Holstein T. , Gaub H. E.
Published: June 2020

During recent years the atomic force microscopy (AFM) has evolved into an extremely useful instrument in life sciences. Particularly the option of this novel technique to operate under quasi physiological conditions and in real time has initiated a broad spectrum of new experiments. As a result, structural and micro-mechanical properties of supramolecular arrangements like molecular films and protein complexes were elucidated. Dynamic processes in live cells were recorded at unparalleled resolution and molecular interactions were investigated. Selected examples of such aspects will be the topic of this lecture.

The AFM has improved drastically the understanding of the molecular structure of Langmuir-Blodgett films. LB films have in turn evolved into standards for the improvement of the understanding of the fundamental imaging mechanisms because of several reasons: they may be formed from a broad variety of substances and their molecular packing can be varied and controlled to a large degree at the air water interface prior to transfer, allowing the intelligent design of certain surface properties like roughness and charge density or micro-mechanical properties.
Using STM to characterize interactions at metal-ceramic interfaces
Authors: Bonnell D. , Liang Y. , Carroll D.
Published: June 2020

The atomic interactions at metal/ceramic interfaces are often the limiting factor in mechanical and electrical properties. As such, much attention has been devoted to the issue. Experimental approaches include high resolution transmission electron microscopy, Auger electron spectroscopy, low energy electron diffraction, photoemission, etc. Scanning probe microscopies have yielded considerable insight into similar studies concerning semiconductors. Here we demonstrate how the spatial localization of scanning tunneling microscopy (STM) and tunneling spectroscopy (STS) can be exploited to elucidate atomic interactions at initial stages of metal/ceramic interface formation.

A SrTiO3 single crystal is doped with 0.1% niobium so that the oxide will be conductive even when fully oxidized. The (001) surface was prepared with standard polishing techniques, then annealed at 1000 C in a UVH chamber backfilled with oxygen. This treatment results in a surface that consists of terraces 50-100 nm wide and several 100 nm long. The steps separating the terraces are 0.4 - 0.8 nm, i.e. one or two unit cells in height.
Scanning-probe microscope analysis of optical thin films: A new analytical tool in a manufacturing environment
Authors: Sapers S. P. , Clark R. , Somerville P.
Published: June 2020

OCLI is a leading manufacturer of thin films for optical and thermal control applications. The determination of thin film and substrate topography can be a powerful way to obtain information for deposition process design and control, and about the final thin film device properties. At OCLI we use a scanning probe microscope (SPM) in the analytical lab to obtain qualitative and quantitative data about thin film and substrate surfaces for applications in production and research and development. This manufacturing environment requires a rapid response, and a large degree of flexibility, which poses special challenges for this emerging technology. The types of information the SPM provides can be broken into three categories:

(1)

Imaging of surface topography for visualization purposes, especially for samples that are not SEM compatible due to size or material constraints;

(2)

Examination of sample surface features to make physical measurements such as surface roughness, lateral feature spacing, grain size, and surface area;

(3)

Determination of physical properties such as surface compliance, i.e. “hardness”, surface frictional forces, surface electrical properties.
Quasi-epitaxial orientations of grains and structure of grain boundaries in YBa2Cu3O7−x thin films
Authors: Shin D. H. , Silcox J. , Russek S. E. , Lathrop D. K. , Moeckly B. , Buhrman R. A.
Published: June 2020

When a thin film is grown on a substrate with a large difference in lattice constants, the interface energy as a function of relative orientation shows several cusped minima. If the lattice mismatch is small, or if the growth temperature is high and the deposition rate is slow, most of the nucleated islands assume the orientation corresponding to the minimum interface energy, and a nearly single crystalline film is obtained. If the growth conditions are not so favorable, a polycrystalline film is obtained in which each of the grains may take a variety of orientations corresponding to local minima of interface energy. These relative orientations between the film and substrate determine the tilt angles at the grain boundaries.

YBCO films grown on MgO at high temperatures or on SrTiO3 where the lattice mismatch is minimal are found to be nearly single crystal.
Investigation of ultra-thin films of YBa2Cu3O7−δ grown on MgO
Authors: Streiffer S.K. , Eom C.B. , Bravman J.C. , Geballet T.H.
Published: June 2020

The study of very thin (<15 nm) YBa2Cu3O7−δ (YBCO) films is necessary both for investigating the nucleation and growth of films of this material and for achieving a better understanding of multilayer structures incorporating such thin YBCO regions. We have used transmission electron microscopy to examine ultra-thin films grown on MgO substrates by single-target, off-axis magnetron sputtering; details of the deposition process have been reported elsewhere. Briefly, polished MgO substrates were attached to a block placed at 90° to the sputtering target and heated to 650 °C. The sputtering was performed in 10 mtorr oxygen and 40 mtorr argon with an rf power of 125 watts. After deposition, the chamber was vented to 500 torr oxygen and allowed to cool to room temperature. Because of YBCO’s susceptibility to environmental degradation and oxygen loss, the technique of Xi, et al. was followed and a protective overlayer of amorphous YBCO was deposited on the just-grown films.
A study of twinning in YBa2Cu3O7−x by large-angle convergent-beam electron diffraction
Authors: Midgley P.A. , Vincent R. , Cherns D.
Published: June 2020

The oxygenation of YBa2Cu3O7−x (YBCO) leads to an orthorhombic distortion of the unit cell to accommodate the extra oxygen atom. This makes the formation of twins energetically favourable with CuO4 planar unit chains running alternately along the a and b axes of the parent tetragonal structure. The geometry of this twinning is such that four possible twin variants may co-exist with the twin boundaries lying in the (110) or (110) planes of the deformed structure. The traces of these planes are not mutually perpendicular and thus the crystal is strained to allow for the mismatch. It is to the nature of this strain field that this work has been addressed.

Sintered samples were prepared by crushing and dispersing the resultant powder onto a very fine Cu mesh grid. Single crystals were chemically thinned to perforation. No discernible artefacts were seen and similar results were obtained with either method.
Processing and characterization of YBa2Cu3O7−x/Ag composites
Authors: Javadpour Jafar , Thiel Bradley L. , Mehmet Sarikaya , Aksay Ilhan A.
Published: June 2020

Practical applications of bulk YBa2Cu3O7−x materials have been limited because of their inadequate critical current density (jc) and poor mechanical properties. Several recent reports have indicated that the addition of Ag to the YBa2Cu3O7−x system is beneficial in improving both mechanical and superconducting properties. However, detailed studies concerning the effect of Ag on the microstructural development of the cermet system have been lacking. Here, we present some observations on the microstructural evolution in the YBa2Cu3O7−x/Ag composite system.

The composite samples were prepared by mixing various amounts (2.5 - 50 wt%) AgNO3 in the YBa2Cu3O7−x nitrate precursor solution. These solutions were then spray dried and the resulting powders were either cold pressed or tape cast. The microstructures of the sintered samples were analyzed using SEM (Philips 515) and an analytical TEM (Philips 430T).

The SEM micrographs of the compacts with 2.5 and 50 wt% Ag addition sintered at 915°C (below the melting point of Ag) for 1 h in air are displayed in Figs. 1 and 2, respectively.
Transmission Electron Microscopy study of Bi-based superconducting phases
Authors: Wen J.G. , Fung K.K.
Published: June 2020

Bi-based superconducting phases have been found to be members of a structural series represented by Bi2Sr2Can−1Cun−1On+4, n=1,2,3, and are referred to as 2201, 2212, 2223 phases. All these phases are incommensurate modulated structures. The super space groups are P2/b, NBbmb 2201, 2212 phases respectively. Pb-doped ceramic samples and single crystals and Y-doped single crystals have been studied by transmission electron microscopy.

Modulated structures of all Bi-based superconducting phases are in b-c plane, therefore, it is the best way to determine modulated structure and c parameter in diffraction pattern. FIG. 1,2,3 show diffraction patterns of three kinds of modulations in Pb-doped ceramic samples. Energy dispersive X-ray analysis (EDAX) confirms the presence of Pb in the three modulated structures. Parameters c are 3 0.06, 38.29, 30.24Å, ie 2212, 2223, 2212 phases for FIG. 1,2,3 respectively. Their average space groups are all Bbmb.
Imaging of BaCuO2 impurity in solution-grown YBa2Cu3O7−δ
Authors: Dufner D. C. , Mohan Ram R.A. , Clearfield A.
Published: June 2020

Solid state reactions are the most commonly employed processes for the preparation of high-Tc superconducting ceramic oxides. However, there has been considerable effort expended to prepare the YBa2Cu3O7−δ (1-2-3) superconductor by low-temperature methods in order to obtain a more homogeneous oxide mixture resulting in products with superior superconducting properties. In our investigations, TEM was used to characterize the microstructure of these materials as a function of various processing parameters.

The precursors for the (1-2-3) superconductors were prepared by precipitating hydroxides of Y, Ba, and Cu and heating the precipitates at various temperatures in the 750-930°C range for 12-60 hours in flowing O2. Crystals for electron microscopy were crushed, suspended in acetone, and dispersed onto holey carbon grids. TEM characterization was carried out on the Philips 400T operating at 120kV or on the JEOL 2000FX at the Texas Center for Superconductivity at the University of Houston.

In this work, one of the impurity phases was observed and identified as BaCuO2.
Investigation of the atomic structure of crystal/amorphous interfaces in Pd80Si20 Alloy by HRTEM and image simulations
Authors: Shieh P.C. , Howe J.M.
Published: June 2020

Determining the atomic structures of solid/liquid interfaces is important for understanding mechanisms of solidification of crystalline materials. To date, research in this area has largely been theoretical in nature because of the difficulty of determining the atomic structure of a solid/liquid interface experimentally. This study has employed HRTEM and image simulations to investigate the atomic structure of crystalline/amorphous interfaces in directionally crystallized Pd80Si20 amorphous ribbons. The crystalline/amorphous interface is similar to a solid/liquid interface in many respects. The HRTEM analyses of directionally crystallized samples have shown that the amorphous Pd80Si20 alloy crystallizes into a lamellar mixture of faceted Pd3Si and nonfaceted Pd9Si2. Interpretation of the HRTEM images requires knowledge of the visibility of ordered structures imbedded in amorphous surroundings. This paper reports the results of a computer simulation study undertaken to determine this visibility.

Computer simulations were performed in two parts: 1) construction of a model atomic structure, and 2) simulation of HRTEM images of the model structure. The atomic model was started with a crystalline seed of Pd3Si several unit-cells thick and new atoms were deposited on to the seed according to the dense random packing model for metal-metalloid systems. A unit cell of appropriate size was cut from the resulting composite structure and sliced into layers for input into the image simulations. The HRTEM images were calculated using the TEMPAS multislice program with the following parameters for a JEOL 4000EX: 400kV accelerating potential, 1.0 mm spherical aberration coefficient, 5.0 nm half-width of Gaussian spread of defocus, 0.5 mrad semi-angle of beam convergence, 6.5 nm−1 objective aperture radius, −50.0 nm defocus (near Scherzer defocus) and diffracted beams out to 4.0 nm−1
Electron diffraction investigation of the incommensurate modulation in Ba1−xKxBiO3
Authors: Verwerft M. , Van Tendeloo G. , Hinks D.G. , Dabrowski B. , Richards D.R. , Mitchell A.W. , Marx D.T. , Pei Shiyou , Jorgensen J.D.
Published: June 2020

The perovskite system Ba1−xKxBiO3 has been studied by different techniques since the discovery of superconductivity at an onset temperature of ≈ 30 K for the compound Ba6K4BiO3. Structural phase transitions (between commensurate structures) occur as function of both composition and temperature. Electron diffraction and high resolution experiments revealed an extra modulation induced by electron beam irradiation (fig. 1 and fig.2) of which the wavevector varies with composition and irradiation amount. For this modulation, different models have been proposed: ordering of oxygen / vacancies, of Ba/K or of Bi3+/Bi5+, but direct evidence for any of these models has not been found yet.

In order to determine the symmetry and nature of this modulation, electron diffraction tilting experiments were performed (fig. 2) on the Ba.75K.25BiO3 sample. Extinction of the satellite reflections is observed for reflections (hkl) with 1 = n+1/2 (n = integer).In order to obtain the symmetry restrictions on the modulation, these diffraction results are interpreted using the superspace concept.
Continuous transformation of decagonal quasicrystal to a related crystalline phase
Authors: Kuo K.H. , Zhang H.
Published: June 2020

Decagonal quasicrystal is a two-dimensional one with a periodicity of about 1.2 or 1.6 nm along its tenfold rotation axis. It is known to exist in rapidly solidified Al-rich Al-Mn-Si and Al-Cr-Si alloys, sometimes coexisting with the bcc α-AlMnSi or cubic Al13Cr4Si4 phase. Both these two crystalline phases are known to have many icosahedral units in them. The structural similarity between the decagonal phase and the related bcc α-AlMnSi has been studied extensively lately.

However, recently we have found a new base-centered orthorhombic phase with a=1.24, b=3.79, and c=1.23 nm coexisting with the decagonal phase to these alloys. Moreover, evidence of a continuous transformation from the latter to the former has been found by selected area electron diffraction. Fig. la is the tenfold electron diffraction pattern (EDP) of the decagonal quasicrystal with strong spots forming a series of concentric decagons. However, in the region close to the boundary to the crystal, the circle on which the inner 10 strong spots lie becomes an ellipse with its long axis in the arrowed direction (Fig. 1b). The closer to the boundary, the more the distortion of this decagon (Fig. 1c) and finally the EDP changes almost to a 2D crossgrid pattern of a base-centered crystal (a reciprocal unit cell is outlined in Fig. 1d).
HREM images of phason-defected quasicrystals
Authors: Li F.H. , Yokota Y. , Pan G.Z. , Hashimoto H.
Published: June 2020

The firstly published electron diffraction patterns(EDPs) of icosahedral(I) quasicrystal in Al-Mn alloy show a perfect I symmetry. The high resolution electron microscope images of I quasicrystals are in agreement with the Penrose tiling. However, in most cases the quasicrystals have a special kind of defect caused by the quenched phason strain so that the I symmetry breaks down. It was demonstrated that a special linear phason strain makes the Al-Cu-Mg and Al-Cu-Li quasicrystals distorted such that they turn into some intermediate states between I phase and body centered cubic(bcc) phase. In this abstract three images of quasicrystals with phason strain of different strength are shown.

Fig.1 is an image of Al-Cu-Fe quasicrystal taken along the five-fold axis with an EM-4000 electron microscope equipped with the side entry goniometer. The lower part shows a more or less perfect five-fold symmetry, and the arrangement of all points having equivalent enviroment obeys the golden ratio.
TEM study on the diffraction streaks caused by initial phase disorder in a displacive modulation structure
Authors: Wu X. J. , Horiuchi S.
Published: June 2020

Recently it was found in some electron diffraction patterns from one-dimensional displacive modulation structure that some streaks pass through the satellite spots. Fig.1 taken from a mineral Ankangite shows that the streaks always appear when the crystal was tilted along b*. This means than in this crystal there must be some reflection planes parallel to (a*, b*) plane in the reciprocal space. The similar EDPs are also observed in a crystal (Sr, Ca)3Cu5Ox. The streaks always pass through the satellite spots, which is quite different from the case where streaks are caused by conventional lattice defects like a stacking fault. It implies that in this kind of crystal the streaks must be produced by a new diffraction mechanism.

An initial phase disorder model has been proposed to explain this diffraction phenomenon. So-called initial phase disorder means that the modulation wave is not a plane wave.