bluuebunny/crossref_metadata_2025 huggingface dataset:
XTEM analysis of buried layer structure of silicon-on-insulator materials
Authors: Rushan Ni , Chenglu Lin
Published: June 2020

It Is well known that a buried silicon nitride or silicon oxide layer in silicon can be formed by high dose >150 KeV nitrogen or oxygen implantation into single crystal silicon followed by high temperature annealing. This is one of the techniques to produce silicon-on-insulator (SOI) structures which is promising for a variety of potential application in VLSI, high-voltage devices, high density CMOS circuits and possibly 3-dimensional integration, etc. The main concern is how to produce a buried dielective layer with good insulating properties and with a high quality single crystal silicon overlayer on it.

In this paper the microstructures of buriea silicon nitride and silicon oxide layer of the SOI materials formed by N+ or O+ implantation in single-crystal silicon are studied oy means of cross-sectional transmission electron microscopy (XTEM) and infrared (IR) absorption measurements.
Formation of AlGaAs by ion beam mixing of Al films on GaAs
Authors: Deol R.S. , Kamil E.A. , Homewood K.P. , Kobayashi T.
Published: June 2020

There is considerable interest in the use of ion implantation for material synthesis. The synthesis of AlGaAs by dual implants of As+ and Al+ into GaAs followed by rapid thermal annealing (RTA) has been reported recently. In this paper results relating to the formation of AlxGa1-xAs by depositing thin Al films on GaAs substrates and irradiating with arsenic ions followed by RTA are presented.

Aluminium layers of 580Å or 650Å in thickness were deposited onto liquid encapsulated Czochralski (LEC) grown samples of semi-insulating <100> GaAs. The deposition was done using pure aluminium on a heated filament at a chamber pressure of ∽10−6 Torr with the thickness being measured using a talystep. Subsquently As+ implants were performed at room temperature using an energy of 150, 200 or 300 keV and a dose of 3x1016 or 1x1017 cm−2. The implantation energy was selected to ensure that the projected depth exceeded the thickness of the Al overlayer employed.
Nanostructure of semiconductor quantum dots in a borosilicate glass matrix by complementary use of HREM and AEM
Authors: Kim M.J. , Liu L.C. , Risbud S.H. , Carpenter R.W.
Published: June 2020

When the size of a semiconductor is reduced by an appropriate materials processing technique to a dimension less than about twice the radius of an exciton in the bulk crystal, the band like structure of the semiconductor gives way to discrete molecular orbital electronic states. Clusters of semiconductors in a size regime lower than 2R {where R is the exciton Bohr radius; e.g. 3 nm for CdS and 7.3 nm for CdTe) are called Quantum Dots (QD) because they confine optically excited electron- hole pairs (excitons) in all three spatial dimensions. Structures based on QD are of great interest because of fast response times and non-linearity in optical switching applications.

In this paper we report the first HREM analysis of the size and structure of CdTe and CdS QD formed by precipitation from a modified borosilicate glass matrix. The glass melts were quenched by pouring on brass plates, and then annealed to relieve internal stresses. QD precipitate particles were formed during subsequent "striking" heat treatments above the glass crystallization temperature, which was determined by differential thermal analysis.
A procedure for cross-sectioning materials for TEM analysis without ion milling
Authors: Benedict J.P. , Anderson Ron , Klepeis S. J.
Published: June 2020

Traditional specimen preparation procedures for non-biological samples, especially cross section preparation procedures, involves subjecting the specimen to ion milling for times ranging from minutes to tens of hours. Long ion milling time produces surface alteration, atomic number and rough-surface topography artifacts, and high temperatures. The introduction of new tools and methods in this laboratory improved our ability to mechanically thin specimens to a point where ion milling time was reduced to one to ten minutes. Very short ion milling times meant that ion milling was more of a cleaning operation than a thinning operation. The preferential thinning and the surface topography that still existed in briefly ion milled samples made the study of interfaces between materials such as platinum silicide and silicon difficult. These two problems can be eliminated by completely eliminating the ion milling step and mechanically polishing the sample to TEM transparency with the procedure outlined in this communication. Previous successful efforts leading to mechanically thinned specimens have shown that problems center on tool tilt control, removal of polishing damage, and specimen cleanliness.
Surface recombination effects on minority carrier diffusion length measurements using electron beam-induced current
Authors: Malta D.P. , Timmons M.L.
Published: June 2020

Measurement of the minority carrier diffusion length (L) can be performed by measurement of the rate of decay of excess minority carriers with the distance (x) of an electron beam excitation source from a p-n junction or Schottky barrier junction perpendicular to the surface in an SEM. In an ideal case, the decay is exponential according to the equation, I = Ioexp(−x/L), where I is the current measured at x and Io is the maximum current measured at x=0. L can be obtained from the slope of the straight line when plotted on a semi-logarithmic scale. In reality, carriers recombine not only in the bulk but at the surface as well. The result is a non-exponential decay or a sublinear semi-logarithmic plot. The effective diffusion length (Leff) measured is shorter than the actual value. Some improvement in accuracy can be obtained by increasing the beam-energy, thereby increasing the penetration depth and reducing the percentage of carriers reaching the surface. For materials known to have a high surface recombination velocity s (cm/sec) such as GaAs and its alloys, increasing the beam energy is insufficient. Furthermore, one may find an upper limit on beam energy as the diameter of the signal generation volume approaches the device dimensions.
The use of Scanning Tunneling Microscopy in combination with Scanning Electron Microscopy in the fabrication and imaging of microstructures
Authors: Gómez-Rodríguez J.M. , A.M. Baró
Published: June 2020

In the last few years, Scanning Tunneling Microscopy (STM), has proven to be a powerful and versatile technique to investigate the topographic and electronic structure of metals and semiconductors with an unprecedent vertical (0.01 nm) and lateral (0.2 nm) resolution. In this paper we are interested in the use of STM to study surfaces having microfabricated structures in the nanometer range, particularly those produced by the STM tip itself.

In order to study these samples we have used an STM integrated into a commercial Scanning Electron Microscope (SEM). This allows to address two problems which limit the operation of STM: (i) the limited STM scanning range (1-10 μm) which makes difficult the localization of microstructures on the sample; (ii) the undetermined size and shape of the STM probing tip.

Our STM/SEM combination has been described in detail earlier. In short, it consists of an STM placed on the sample stage of a commercial SEM allowing the simultaneous operation of both microscopes.
Magnetic micro structure evaluation by means of electron beam measuring techniques
Authors: Steck M.
Published: June 2020

The trend to micro miniaturization of magnetic devices with structure dimensions in the sub micrometer range at present necessitates more and more test techniques with a high spatial resolution. The electron beam techniques have been proved to be particularly suitable even ensuring high quality and reliability of these devices.

In principle, two different types of measurement can be distinguished. In the sample-hitting type, the e-beam hits the sample and interacts with certain magnetic properties of the specimen. Two categories can be divided: reflection mode and transmission mode. In reflection mode, secondary electrons (SE) and back scattered electrons (BSE) are created by the primary beam. These SE change their trajectories due to the magnetic micro field at the specimen’s surface yielding to different signals at the detector. This contrast is very well known as magnetic contrast type 1. Magnetic contrast type 2 uses the change in the BSE-generation volume due the internal magnetization of the sample. A very new and promising technique is secondary electron microscopy with polarization analysis (SEMPA). SEMPA analyses the SE-spin which depends on the direction of magnetization in the magnetic domains. In reflection mode, SEMPA offers the best spatial resolution (sub-0.1 μm) up to now.
The utilisation of electron-beam damage for the study of beam spreading in synthetic polymers
Authors: Haunton K. M. , Vesely D.
Published: June 2020

The knowledge of beam spreading is important for determination of spatial accuracy and volume calculation in quantitative X-ray analysis. It is also useful for determination of best conditions for electron beam lithography with high line resolution. The theoretical modelling of beam spreading is difficult as for example the Monte Carlo simulation is very demanding on computer time and many simplifications have to be made. The validity of the theoretical results must therefore be verified experimentally.

In this work some new techniques are utilised for evaluation of the spatial distribution of the deposited energy in synthetic polymers, namely the formation of isolated and conjugated double bonds, revealed by staining and by fluorescent microscopy.

Thick samples of PVC, PS and PMMA were coated with about 10 nm of carbon and exposed to an electron beam of 75 - 200 keV for different lengths of time. A Hitachi 700H transmission electron microscope (TEM) was operated in the scanning (STEM) mode. Currents of lxl0−9A and 2x10−10A were used. The stationary beam was convergent or parallel.
SEM-EDXA study of bronze/carbon steel interface in relation with adhesion measurements
Authors: de Castellar M.D. , Tura J.M. , Traveria A. , Pujadas J.
Published: June 2020

Water atomized bronze formed the basis of the powder metallurgy coating. The grain size distribution, its morphology and internal porosity have been previously investigated. The largest bronze particles have a very irregular shape. It becomes more spherical when the granulometry decreases. Figure 1 shows an image of a bronze particle.

The XPS analysis of the grain surface revealed a composition of Cu°/CuO being 87/13 and Sn°/SnO2 14.3/87.5. Powders with smallest granulometry show a deeper oxide layer. This is probably due to the larger specific surface shown by these particles.

The substrate was sintered carbon steel with 1.75 % Ni, 1 % Cu and 0.5 % Mo as minoritary elements.

An optimization of the layer substrate bond strength was carried out. A shear stress was applied on the coating and the force required to detach it from the substrate was measured. Cross sections of the samples obtained in every sintering cycle were observed by SEM.
Improved measurement of void swelling
Authors: Gelles D. S. , Claudson R. M. , Thomas L. E.
Published: June 2020

Irradiation of crystalline materials by neutrons or other energetic particles often causes swelling by formation of internal cavities, or voids. The swelling, or total void volume within a given sample volume, can be determined from transmission electron micrographs by simple measurement of the void images. However, errors of over 100% in the calculated void volumes are possible if the voids are approximated as spheres. The problem arises because the voids are usually polyhedral, crystallographically oriented features and no single size parameter has been defined for the spherical approximation. In austenitic stainless steels and other face-centered-cubic (fCC) alloys, voids range from octahedra with {111} faces to cubes with {100} faces and exhibit all intermediate (truncated) forms. Void truncation may also vary widely within a given field of view. Voids in ferritic steels and other body-centered-cubic (bcc) materials may range from octahedra with {111} faces to cubes with {100} faces to dodecahedra with {110} faces. The relationship between void shape on electron micrographs and void volume was therefore studied with the aim of improving the accuracy of swelling determination without requiring a separate shape determination for each void. Void volumes were determined as a function of a shape parameter and related to the various ‘size’ parameters available in different crystal orientations. Procedures were then defined to minimize the error in swelling measurement.
Butyl rubber slurry formation: Cold-stage SEM study
Authors: Ban L. L. , Powers K. W. , Wang H-C
Published: June 2020

Poly(isobutylene-co-isoprene) or butyl rubber was invented in 1937 and has been used in many technologically important applications during the ensuing years. Its physical properties such as air-retention encouraged its uses in tire inner tubes, and played an important part in the tubeless tire development. The halogenated derivative is now predominantly used in tubeless radial tires.

Butyl rubber is made by a slurry polymerization process with aluminum chloride catalyst at -95°C in methyl chloride diluent. Typical reactor runs only last from 18-60 hours because of fouling of the reactor. Fouling and agglomeration occur because only weak electrostatic repulsion forces exist, but recent patents describe the use of block copolymer stabilizer agents which create steric (entropic) repulsion forces between slurry polymer particles and prevent

To better understand the mechanism of reactor fouling, a method was developed to collect samples from within the reactor.
Crystal chemistry of calcium oxalate formed in plants
Authors: Ishii Yuuko , Takiyama Kazuyoshi
Published: June 2020

Calcium oxalate crystals, which were produced in plants to protect protoplasm from the toxic action of oxalic acid formed by metabolism, were observed with an optical microscope. In the present investigation, calcium oxalate crystals isolated from many plants were studied from the viewpoint of crystal chemistry.

Leaves of spinach, begonia, begonia lucerna, garden sorrel, goose foot, camellia, tea-plant, agave, et al., stem of aloe, and barks of cherry-tree, plum-tree, fir, camphor-tree et al. were used in the investigation. Plants were cut into small pieces and pulverized in water with a food blender. The mixture was filtered through gauze and water was sprinkled onto the residue. Many small crystalline particles sank in the filtrate. Particles were carefully gathered into a beaker. Dried particles were observed with a scanning electron microscope(SEM) and analyzed with an X-ray diffraction(XRD).
Microstructure of resistance spot welding of maraging steels
Authors: Neuman I. , Dirnfeld S.F. , Minkoff I.
Published: June 2020

Experimental work on the spot welding of Maraging Steels revealed a surprisingly low level of strength - both in the as welded and in aged conditions. This appeared unusual since in the welding of these materials by other welding processes (TIG,MIG) the strength level is almost that of the base material. The maraging steel C250 investigated had the composition: 18wt%Ni, 8wt%Co, 5wt%Mo and additions of Al and Ti. It has a nominal tensile strength of 250 KSI. The heat treated structure of maraging steel is lath martensite the final high strength is reached by aging treatment at 485°C for 3-4 hours. During the aging process precipitation takes place of Ni3Mo and Ni3Ti and an ordered solid solution containing Co is formed.

Three types of spot welding cycles were investigated: multi-pulse current cycle, bi-pulse cycle and single pulsle cycle. TIG welded samples were also tested for comparison.

The microstructure investigations were carried out by SEM and EDS as well as by fractography. For multicycle spot welded maraging C250 (without aging), the dendrites start from the fusion line towards the nugget centre with an epitaxial growth region of various widths, as seen in Figure 1.
An EM study of carbides in double austenitized AISI M2 high-speed steel
Authors: Ögel Bilgehan , Tekin Erdoĝan
Published: June 2020

Multiple austenitization is not a conventional heat treatment process in tool steel industry and has only recently attracted some attention. Several workers who studied multiple austenitized high speed steels reported a fine carbide precipitation in the matrix of double austenitized specimens. However, the metallography of this precipitation is not well documented and needs further investigation. In this study, the microstructure of AISI M2 high speed steel and the effect of double austenitization on carbide distribution is investigated using SEM.

The heat treated specimens were prepared by conventional metallographic methods for SEM examination. Polishing with diamond paste gave better results as much less carbides were extracted from their sites. Picral was used as an etchant.

It is known that in M2 steels, undissolved carbides are either M6C or MC type. However, in the present investigation some of the massive undissolved M6C carbides contained small dark regions within them (Fig.l). X-ray mapping for W, Mo and V of such a carbide has shown that it is mainly a M6C carbide,whereas the dark regions on it is rich in vanadium implying that these regions represent V4C3(Fig.2).
Precipitation at the transformation interface of pearlite in steel
Authors: Khalid F. A. , Edmonds D. V.
Published: June 2020

The austenite/pearlite growth interface in a model alloy steel (Fe-1lMn-0.8C-0.5V nominal wt%) is being studied in an attempt to characterise the morphology and mechanism of VC precipitation at the growth interface. In this alloy pearlite nodules can be grown isothermally in austenite that remains stable at room temperature thus facilitating examination of the transformation interfaces. This study presents preliminary results of thin foil TEM of the precipitation of VC at the austenite/ferrite interface, which reaction, termed interphase precipitation, occurs in a number of low- carbon HSLA and microalloyed medium- and high- carbon steels. Some observations of interphase precipitation in microalloyed low- and medium- carbon commercial steels are also reported for comparison as this reaction can be responsible for a significant increase in strength in a wide range of commercial steels.

The experimental alloy was made as 50 g argon arc melts using high purity materials and homogenised. Samples were solution treated at 1300 °C for 1 hr and WQ. Specimens were then solutionised at 1300 °C for 15 min. and isothermally transformed at 620 °C for 10-18hrs. and WQ. Specimens of microalloyed commercial steels were studied in either as-rolled or as- forged conditions. Detailed procedures of thin foil preparation for TEM are given elsewhere.
Sensitization of manganese-stabilized austenitic steels
Authors: Kenik E. A. , Bell G. E. C. , Tortorelli P. F.
Published: June 2020

In an earlier study of the phase stability of manganese-stabilized austenitic steels based on Fe-12 Cr-20 Mn-0.25 C (wt %), significant precipitation of tau carbides (M23C6) was found to occur both in the matrix and at grain boundaries during aging near 600°C. Because of the similarity of the observed microstructures to those of sensitized steels and the evidence of preferential grain boundary attack in extraction replicas, the susceptibility of these alloys to sensitization relative to a type 304L nickel-stabilized stainless steel was investigated with the use of corrosion tests and analytical electron microscopy. Four Mn-stabilized steels (IT-2 - IT-5) were prepared with different minor additions (Table 1). These alloys and the type 304L steel were solution annealed at 1150°C (SA) and subsequently aged for 2 h at 650°C. The steels were checked for sensitization in both the SA and aged conditions by immersion in a boiling, acidified CuSO4 solution for 48 h (modified-Strauss test, ASTM A 262-E). The degree of sensitization was indicated by the extent of grain boundary attack and the tendency for grain boundary failure during immersion or post-immersion bending. The type 304L steel was not sensitized in the SA condition and only mildly sensitized as aged (only slight intergranular cracking during bending). On the other hand, though not sensitized in the SA conditions, the aged Mn-stabilized steels were severely attacked during the modified-Strauss test. They generally fractured intergranularly under their own weight or internal stresses after removal from the solution. This indicated a high degree of sensitization at 650°C.
Microstructural evolution of a nickel-based superalloy
Authors: Monteiro Waldemar A. , Dos Santos Ingrid A.
Published: June 2020

Superalloys are indispensable for the superior perfomance and efficien of jet engine turbine disks,turbine blades,combustors,roket shells and many other devices and components used in various industries, in Cluding nuclear, space and aeronautics.

Over the last thirty years,nickel-base superalloys has undergone more structural studies than any other superalloy as a result of attempts to correlate its properties to microstructure and heat treatment. To avoid contradictory or inconsistent findings, it is also necessary a carefully microstructural observation of the employed starting materials. In the present paper,we report morphologies relating to the as cast , forged and heat-treated Ni-base superalloy by transmission and scanning electron microscopy. This superalloy contain intermettallic compounds and carbides. The alloy in study was an as cast and also forged Ni-Fe based superalloy with the following chemical composition:
Effect of titanium addition on a Ni-Al-Co alloy
Authors: Lin L. S. , Levan G. W. , Russell S. M. , Law C. C.
Published: June 2020

AEM examinations of a NiAlCo alloy of composition Ni-29 at.% Al-21 at.% Co after room temperature compression show that the microstructure consists of a twinned tetragonal matrix (L10, marked A in Figure 1a) and ordered fcc gamma prime precipitates (L12, marked B in Figure 1a) along grain boundaries. The compressive yield strengths of this alloy at room temperature and 760°C are 754 MPa and 163 MPa respectively. It also has superior room temperature ductility as compared to binary NiAl. An addition of 5 at.% Ti at the expense of Ni was made to this alloy in order to increase the yield strengths. The quarternary alloy shows compressive yield strengths of 976 MPa and 403 MPa at room temperature and 760°C, respectively, indicating that the Ti addition is having the desired effect.

Comparison of the microstructures of the two alloys after room temperature compression (Figures la and lb) shows that the Ti containing alloy has a smaller grain size. X-ray diffraction data indicate that the gamma prime volume fraction increases from 10% to 20% as the result of the Ti addition. Titanium was also found to stabilize the B2 matrix (marked A in Figure lb) as no tetragonal L10 phase was found. All precipitates along grain boundaries were identified by micro-diffraction to be gamma prime.
Effect of hafnium addition on a Ni-Al-Co Alloy
Authors: Lin L. S. , Levan G. W. , Russell S. M. , Law C. C.
Published: June 2020

Recent efforts at P&W have shown that the addition of cobalt to binary NiAl results in an appreciable increase in room temperature ductility. One version of this ternary alloy, designated VIM A, has a composition of Ni-30 at.% Al-35 at.% Co. The addition of 0.5 at.% Hf to this alloy (designated VIM AH) results in an improvement in yield strength at 760°C. Room temperature properties were not found to be significantly affected by the Hf addition. This discussion will focus on the microstructures of alloys VIM A and VIM AH and their relationship to the mechanical properties observed in compression at room temperature and 760°C.

The addition of hafnium reduced the grain size of VIM AH alloy. After room temperature compression, both alloys show an ordered bcc (B2) matrix and precipitates which are distributed primarily along grain boundaries. These precipitates were identified by microdiffraction to be ordered fcc (L12) gamma prime for VIM A and hexagonal (A3) for VIM AH.
Compendium of alloy phases observed after low temperature aging of Ni-rich NiAl
Authors: Locci Ivan E. , Khadkikar P. S. , Noebe R. D. , Vedula K.
Published: June 2020

An overwhelming amount of research has been performed on Ni3Al (γ’) and NiAl (β) intermetallic alloys over the last decade. Yet, very little is known about the two phase field between these ordered compounds, including the occurrence and stability of phases other than γ’ or β Identifying and understanding these other phases are important since one approach to improving the ductility and toughness of NiAl is to design an alloy with a dual phase microstructure (i.e. NiAl + Ni3Al). Preliminary alloying attempts have encountered varying degrees of success. They range from powder metallurgy alloys with significantly increased fracture strengths over single phase (β-alloys to directionally solidified γ’ + β crystals which exhibit up to 9% tensile ductility at room temperature. Unfortunately, aging of these alloys at low temperature (<973 K) results in the formation of several complex, stable and metastable phases which may negate any original improvements in mechanical behavior.
A TEM study of ternary hydrides formed in the Ti3Al intermetallic
Authors: Xiao H. Z. , Robertson I. M. , Birnbaum H. K.
Published: June 2020

The intermetallic compound Ti3Al (DO19’, an ordered hexagonal structure) has, because of its high strength to weight ratio, stimulated extensive studies. As a consequence of the improved ductility through the addition of niobium, Ti3Al can be considered for use at both high and low temperatures. Since many applications for this material also involve high hydrogen fugacity environment, the mechanism of hydrogen embrittlement (related to the hydride formation) must be understood. In the present study of the interaction of Ti3Al with gaseous hydrogen we have applied the methods of TEM, electron diffraction, X-ray scattering and gas chromatographic H analysis. Specimens of Ti3Al were equilibrated with gaseous H2 at a pressure of 700 torr at temperatures of 373 K and 323 K for two and seven days, respectively. This resulted in H/metal values of 0.59 and 1.67, respectively. The specimens fractured severely during the gaseous charging and were subsequently ground into fine powders under pure ethyl alcohol. These powders were used for the TEM studies. TEM examinations were performed at 120 kV using a Philips 420 electron microscope.
Microstructrures of the rapidly solidified Nd2Co14B alloys
Authors: He L.L. , Li J.H. , Ye H.Q.
Published: June 2020

It is known that the Nd2Co14B compound belongs to the Nd2Fe14B-type crystal structure ( 2:14 phase ), and has higher values of coercivity Hci and Cruie temperature Tc of about 1000K. The properties of this compound are sensitive to cooling velocity. In this presentation, we will study the chemical twins and other defects in the phases formed at different cooling velocities. Two kinds of rapidly solidified samples were examined: No.l with low cooling velocity of about 102-103 °C/s and No.2 with high cooling velocity of about 105-106 °C/s. The foils prepared by ion thinning were observed in a JEOL-200CX microscope for high resolution imaging.

The main phase in the sample No. 1 was the 2:14 phase. The electron diffraction analysis demonstrated that the lattice parameter of this phase was a=0.88 nm, c=1.21 run with the space group P42/mΩm ( the insert in fig.l ).
The beginnings of graphitic alignment in the matrix of carbon-carbon composites
Authors: Payne Robin S , Bradsky Gina Von , Gray Gavin , Savage Gary
Published: June 2020

Carbon-Carbon composites (C-C) may prove to be critical materials for high temperature applications, as they retain their mechanical properties well above 2000°C1. The development of a graphitic structure in the matrix of C-C composites is crucial to the understanding of their mechanical properties. To date very few transmission electron microscope (TEM) studies of these materials have been performed: as a result production often occurs without a full understanding of structural changes which occur during manufacture. X-ray diffraction has indicated that the degree of matrix alignment is greater in C-C composites than in the matrix carbon alone given same thermal history, in addition, the matrix graphitisation can occur in an orientation close to that of the long axis of the carbon fibres. These phenomena are thought to be the result of; a) the fibre-matrix interface acting as a nucleation site for graphitic domains forming in the matrix, and/or b) the difference in the coefficients of thermal expansion of the matrix and the fibres being sufficient to cause stresses which encourage graphitisation.
Characterization of silicon carbide platelet-reinforced alumina
Authors: Alexander K. B. , Becher P. F. , Waters S. B.
Published: June 2020

The incorporation of silicon carbide whiskers into ceramic matrices has been shown to result in significant increases in toughness, strength, resistance to thermal shock, slow crack growth, and creep. The health hazards associated with the handling of silicon carbide whiskers, however, can be considerable. Silicon carbide platelets are therefore being considered as an alternative to whiskers for reinforcing ceramic composites.

The silicon carbide platelets used in this study were supplied by Alcan International Ltd. The platelets varied from 1 to 5 μm in thickness and 5 to 45 μm in diameter. Sumitomo alumina powder was mixed with the platelets and the composites were fabricated by hot-pressing in vacuum at 1600°C for 1.5 h. The resultant composites had the platelet faces oriented primarily perpendicular to the hot-pressing axis. Specimens containing 7 vol% SiC platelets had a fracture toughness of 6.6 MPa m½, which is about the same value as observed for alumina of equivalent grain size containing 7 vol% SiC whiskers. Considerable porosity was observed in specimens with platelet volume fractions larger than 7 vol%.
AEM-investigation of ceramic coatings on hard metals
Authors: Warbichler P. , Hofer F.
Published: June 2020

To improve their working life, hard metal tools are coated with ceramic protective coatings by means of chemical vapour deposition (CVD). Generally, several layers are deposited, e.g. titaniumcarbide, titaniumnitride, titaniumcarbonitride and aluminiumoxide with thicknesses ranging from some 10 nm to some μm.

The understanding of mechanical properties of the coatings is dependent on gaining a knowledge of both the interfaces and the structure of the coatings involved. The coating properties are, in turn, dependent on the coating deposition parameters. A detailed understanding of the influence of these parameters on the mechanical and chemical properties of the multilayer/substrate combination is therefore required.

The structure and morphology of the multilayer coatings have been already investigated by using optical and scanning electron microscopy (SEM), whereas transmission electron microscopy (TEM) was hitherto only applied to the study of single TiC or Al2O3coatings.

For TEM-investigations cross-sections must be taken through the multilayer coating and the cemented carbide substrate. In our investigations, a method of preparation described by Newcomb et al.
Microstructure of bioceramic chloroapatite
Authors: Feng Jingwei , Wen Shulin , Ravaglioli A.
Published: June 2020

Bioceramics has drawn the attention of scientists working at the solid state field. The main constituent of bone and teeth in human body is Ca10(PO4)6(OH)2. So this compound and its derivatives form a first important class of particular bioceramic materials. Chloroapatite is a member of this compound family. We synthesized a series of chloroapatite at increasing content of chlorine in comparison with the hydroxyl- apatite in order to search better bioceramics which has not only large biological compatibility with human tissues, but also exert bioactive properties. We found that in comparison with hydroxylapatite all the structures are very similar among them at the level of atomic arrangement. However, in the case of high chlorinated compound, like Ca10(PO4)Cl2, the structure would transform to monoclinic system with space group P21/a from original hexagonal system with space group P63/m. Only in the case of low chlorinated compound, the structure would be kept to be hexagonal system with space group P63/m.
A new sulphide Ag8S formed in the early stage of sulfurization of silver
Authors: Yu Y.D. , Guan R. , Kuo K.H. , Hashimoto H.
Published: June 2020

Metal sulphuration, like oxidation, is a basic problem in metal corrosion. For silver the sulphuration is more important than oxidation in materials engineering such as in microelectronic applications. In the present note, we report the formation of Ag8S prior to Ag2S, like copper and nickel oxidation, in the initial sulphuration stage.

A block of 99.99% silver was rolled into sheets of about 50 μm thick and was then electrolytically thinned by the window method in dilute nitric acide. Then these films were sulphurated at 300°C in a tube with some trace sulphur left on the tube wall in a vacuum of about 10”4 Torr. The thin film was somewhat sulphurized and many microcrystallites grew up at the edge of the film. From the electron diffraction patterns it is clear that these crystallites are not silver, nor the Ag2S sulphide, indicating that they may belong to a new silver sulphide. Figure 1 is the low magnification electron microscopic images of these sulphide crystallites. Figure 2 shows its energy dispersive X-ray (EDS) peaks, indicating that it contains sulphur of about 2-3 wt%, which is much lower than the sulphur content (12.9 wt%) in Ag2S. Fig. 3 shows the HREM image in which region B is much thinner than region A and shows a higher resolution. The distance between the imaging spots in region B is half of that in region A. By analysing the EDPs and the HREM images we came to conclusion that the structure of the crystal is body- centered orthorhombic with a=0.59, b=0.64 and c=0.87 nm. Each unit cell has 16 Ag atoms and 2 S atoms. Fig.4 is the [010] projection of the structure. Fig.5a shows the magnified image of region A of Fig.3 and Fig.6a shows that of region B. Figs.5b and 6b show the simulated images which were obtained from the suggested model for Ag8S with thicknesses of 185A and 20A, respectively. The agreement between the observed and the calculated images is rather good indeed. Comparing Figs.5b and 6b with Fig.4, we can see that the imaging spots in Fig.5a correspond to the projected S atoms, while those in Fig.6a to the projected Ag atoms. In the thicker area (region A), only S atoms can be imaged as shown in Fig.5a, while in the thinner area (region B), Ag atoms can be observed as in Fig. 6a. This phenomenon can easily be made clear by the variation of the diffraction amplitudes of (400) and (004) planes with Ag atoms as the dominating scatters, and of (200), (002) and (101) planes with S atoms as the dominating scatters, as shown in Fig.7.
Polymer characterization via FT-IR microspectroscopy
Authors: Wihlborg William T. , Reffner John A.
Published: June 2020

FT-IR microspectroscopy systems have been used for a wide range of polymer applications. Reffner et al reported a quantitative reflectance technique for the determination of ethylene/vinyl acetate copolymer. Chase, using an infrared polarizer with the microscope, studied single polymer fibers and was able to determine the orientation of functional groups relative to the fiber axis. Brasch and Lustiger also used FT-IR microspectroscopy in conjunction with an IR polarizer to determine the percentage of tie molecules in polyethylene. The relative amount of tie molecules is an important parameter for understanding the mechanical failure of polyethylene and the FT-IR microscope improves the sensitivity of this measurement by confining the analysis to the areas of the sample which undergo the greatest change.

In the present study the IRμs™ microanalysis system was used to explore the effects of environmental and mechanical stresses upon the molecular structure of polymers. A sample of polypropylene which was weathered for two years was microtomed and the cross section studied for indications of degradation.
New Direct Methods for Phase and Structure Retrieval in HREM
Authors: Van Dyck D. , Op de Beeck M.
Published: June 2020

Reliable interpretation of high resolution electron micrographs is only possible by comparison with computer simulations. However, simulation is a tedious trial and error technique which can only be successful if the experimental parameters are known and if the number of plausible structure models is small. For instance the interpretation of images of amorphous objects by simulation is hopeless. This makes the power of HREM very much dependent on the amount of prior information available from other techniques such as X-ray diffraction. HREM would be much more powerful and independent if a direct method could be established to retrieve the structural information of the object directly from the electron micrographs.

We present a new “focus variation method” in which the phase is retrieved in the image plane in a deterministic way from a combination of images at closely spaced focus values, as inspired on the method proposed in [1] [2]. In a sense the whole information is used in the 3D image area of the electron microscope. The method allows to correct for chromatic aberration, spherical aberration and focus and is robust against noise. In a second stage we retrieve the projected structure of the object directly from the knowledge of the wavefunction at the exit face, using the channelling theory proposed in [3]. The first results are very promising.
High-Resolution Electron Microscopy Study of Enamel Crystal Growth in Human Foetus
Authors: Cuisinier F.J.G. , Steuer P. , Voegel J.C. , Frank R. M.
Published: June 2020

The mineral component of human dental enamel is formed by nonstoichiometric carbonated hydroxyapatite crystals. The presence of relatively large amounts of impurities in mature enamel crystals as well as their external shape are related to their growing mechanism. Enamel crystal growth was investigated previously directly with low resolution electron microscopy or by comparison with synthetic apatite crystal growth. The growing process of enamel crystals is still unknown and the aim of this study was to investigate foetal enamel growth during secretory stage by high resolution transmission electron microscopy.

Developing enamel from 5 month-old human foetuses was fixed for 3 hours in a 2% glutaraldehyde and 2% paraformaldehyde solution in 0.1 M sodium cacodylate buffer. After 2 hour postfixation in 1% OsO4in the same buffer and embedding in Epon, non decalcified ultrathin sections were obtained with a Sorvall-Porter MT-2C microtome equipped with a diamond knife and floated on demineralized water saturated against hydroxyapatite (200mg/l). The sections were observed in a Philips EM 430 transmission electron microscope operating at 300 kV equipped with a double tilt specimen holder. This microscope possessed a Sherzer resolution of 0.19 nm and the absence of drift and astigmatism was checked for each micrograph by an optical diffraction.
Analysis of Image Contrast in High-Resolution Images of n-Paraffin Recorded at 400 kV and -167°C
Authors: Brink J. , Chiu W.
Published: June 2020

Images of radiation-sensitive two-dimensional crystals quite often fail to display the same resolution visible in electron diffraction patterns of these crystals. It is now generally accepted that besides the microscope's envelope functions, radiation damage and the MTF of the film and cryo-holder, beam-induced specimen motion is a major contrast degrading factor. Minimization of this movement proved possible through use of narrow electron beams, i.e. in spot-scanning. Routine high resolution imaging, however, remains a difficult task. We have investigated the possibilities of enhancing the effeciency this goal by using 400 keV electrons. Based upon overall less attenuation from the envelope functions at 400 kV, structure factors at around 3Å resolution would show amplitudes easily twice as large as compared to 100 kV. Further, at 400 kV inelastic scattering would be reduced relative to 100 kV. Moreover, it has been suggested that image contrast would increase roughly proportional to β. Additional advantages concerning for instance Ewald sphere curvature and depth of field have been put forward in Chiu et al.
Developments in Processing Multisignal Imaging in STEM
Authors: Jeanguillaume C. , Ballongue P. , Tencé M. , Colliex C.
Published: June 2020

In an electron microscope, it is most important to optimize , for a given irradiation dose, the information extracted from the specimen . The STEM configuration is quite suited for such developments because it can easily be equipped with a set of detectors for recording simultaneous signals . When associated with novel processing modes, this multisignal imaging approach affords interesting developments in many fields of applications, as illustrated here on a simple example . A VG STEM with a magnetic spectrometer for energy loss studies, has been fitted with four different detection channels, as shown in Fig 1 . These are : the beam current measurement (Icur), the annular dark field image (Iadf), the unscattered (Iun ), and total inelastic signal (Iin ). These latter contributions are discriminated on two separate detectors after magnification of the EELS spectrum with a dedicated double gap electron lens, see (1) for complete description of the design. Before introducing these different data in the appropriate analytical expressions which involve sums, differences or ratios, it is necessary to evaluate their relative weights, i.e the ratios of their detection efficiencies. Following the general principle described in (2), a reconstructed image of the primary beam current is obtained as a suitable linear combination of the three other signals . New images can then be generated for : a) the enhancement of the signal to noise ratio in low dose condition; b) the separation of the elastic and inelastic contributions; c) the improvement of the Z contrast; d) the development of mass thickness measurements. These latter two aspects are illustrated in the present abstract.
Evolutionary Developments in X-Ray and Electron Energy Loss Microanalysis Instrumentation for the Transmission Electron Microscope
Authors: Zaluzec Nestor J.
Published: June 2020

Developments in instrumentation for both X-ray Energy Dispersive and Electron Energy Loss Spectroscopy (XEDS/EELS) over the last ten years have given the experimentalist a greatly enhanced set of analytical tools for characterization. Microanalysis have waited for nearly two decades now in the hope of getting a true analytical microscope and the development of 300-400 kV instruments should have allowed us to attain this goal. Unfortunately, this has not generally been the case. While there have been some major improvements in the techniques, there has also been some devolution in the modern AEM!

In XEDS, the majority of today's instruments are still plagued by the hole count effect, which was first described in detail over a fifteen years ago. Figure 1 shows that the magnitude of this problem can still reach the 20% level for medium atomic number species in a conventional off-the-shelf intermediate voltage AEM. This is an absurd situation and the manufacturers should be criticized, however, part of the blame here also rests on the AEM community for not having come up with a universally agreed upon standard test procedure. Fortunately, such a test procedure is in the early stages of refinement. On the quantitative side, after corrections for the hole count, we understand the effects of the higher voltage to the intensity variation and hence to quantification (figure 2). Windowless x-ray detector systems have opened up the low-energy, light-element regime to the x-ray analyst (figure 3), however, spectral overlaps are a recurring problem in complex systems.
Stereo Imaging System for High-Voltage Electron Microscopy
Authors: Malecki Marek
Published: June 2020

An analysis of three-dimensional ultrastructure is especially efficient when performed on stereo images. The high voltage electron microscope (HVEM) providing high beam penetration and low radiation damage to specimens has been shown to be the most effective instrument for such studies. The successive HVEM stereo images recorded on films are subsequently photoprinted or stored in an image processor memory can be observed on an RGB monitor. Successful stereo imaging must meet several requirements regarding magnification, specimen thickness, tilt axis and angle. In particular, the optimal tilt for stereo perception depends on the thickness and microscopical magnification. Ultramicrotome settings can provide only approximate information on section thickness; however, their sectioning compression, procedural etching or beam induced shrinkage has to be considered. The situation becomes even more difficult when extractable media are used because an amount of extracted material may seriously affect final thickness. An estimation of an exact thickness of whole cell mounts is practically impossible, and therefore, optimal tilt difficult to predict. Then the most reliable way is the laborious recording of series of images at different tilt angles and selection of the most effective. To overcome this constraint, I designed a very reliable system for AEI HVEM 7MkII allowing exact prediction of the perfect tilt angle. The diagram of the system is presented on Fig. 1 and a photograph of the assembly on Fig. 2. It consists of a low light level TV camera with two independent outputs-SIT/TVC/, image processor-Quantex/QIP/, two high resolution flat square monitors-Hitachi/H1 & H2/ and stereo viewer-Nikon/SN/. A signal from the first TV camera output goes to the QIP, after processing is displayed on monitor H1. A signal from the second output goes directly to the second monitor, H2. Prerequisites for using this system are axis-centered or eucentric goniometer and a rotation-free imaging system of HVEM. The recording procedure happens as follows. The specimen is tilted 1/2 of the value of the roughly predicted optimal angle and the resulting image is stored in the Quantex memory followed by recording on the film sheet. The left monitor displays the stored image from QIP, while the right monitor provides the live image. Then the specimen is tilted while being observed with a stereo viewer. When the strongest stereo effect is noticed, then tilting is stopped and an image recorded. If + and − tilt values differ, then perfectly symmetrical values can be calculated followed by image recording. Figs. 3 and 4 represent the stereo images of a human melanoma cell grown on a film grid. An optimal stereo perception was obtained for different magnifications, at different tilt angles determined using the system I have designed.
Stem Holography
Authors: Leuthner Thomas , Lichte Hannes , Herrmann Karl-Heinz , Sum Jürgen
Published: June 2020

Electron optical imaging is a wave optical process. Therefore, to obtain the whole information about the object structure, one must record both amplitude and phase of the electron in the detector plane, e.g. in the Fourier plane or in the image plane. In the general case, an electron image detected only by its intensity is in principle incomplete [1]. This is true in particular in face of the lens aberrations which scramble amplitude and phase hence limit resolution and interpretability of an electron image.

Following Gabor’s proposal of electron holography, these problems are being solved in the TEM [2], and in the STEM we try to tackle them in the following way [3] (fig.l): Two coherent waves, produced by means of the Mollenstedt electron biprism, are focused in the object plane. One of them is transmitted through the object and modulated in amplitude a(x,y) and phase φ(x,y) whereas the other one instead goes through empty space. Subsequently they are superimposed and give rise to an interference pattern (spatial frequency Rc) in the detector plane (coordinate u ) as