ISSN:1059-910X    

DOI:10.1002/jemt.1070310402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe methodology and one of the first attempts to produce transmission electron microscopic (TEM) specimens of nanocrystalline metals, alloys and ceramics by ultramicrotomy are presented. Samples of the pure elements Co, Pd; alloys of Y‐12 at.% Fe, Al‐7 at.% Ag and W‐30 at.% Ga; and ZnO ceramic, were found to section successfully to varying degrees. Advantages of sections prepared through ultramicrotomy over ion beam methods include extensive electron‐transparent regions of uniform thickness and absence of ion beam damage. Typical artefacts were observed (knife marks, tearing, pull‐out, shear lamellae, section curling, and anodic dissolution) but did not impede TEM analysis significantly. A potentially important effect observed was that of a texture development upon sectioning of the Co and Pd samples. It is thought that this unusual phenomenon results from the extremely fine scale of the microstructure and the purity of the Co and Pd samples, and may be enhanced by frictional heating effects and the state of the knife edge. © 1995 Government of Canada.Exclusive worldwide publication rights in the article have been transferred to Wiley‐Liss, Inc., i

ISSN:1059-910X    

DOI:10.1002/jemt.1070310403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractUltramicrotomy has found novel application in materials research using transmission electron microscopy, for both analytical and high resolution work. Specimens 20–50 nm in thickness with lateral dimensions of up to 100 microns may routinely be prepared, with the additional advantage of precise area location for cross‐sectional samples from real devices (e.g., VLSI structures). Much of this work is possible through the availability of diamond knives with various included angles and lengths at reasonable cost. This paper reports on various applications of ultramicrotomy, in particular, lattice imaging of surfaces and interface regions from epilayers of II–VI compound semiconductors and related materials. Ultramicrotomed cross‐sections have enabled modern electron beam imaging, diffraction and analytical techniques to be brought to bear near surfaces and across interfaces of multilayer structures, yielding high spatial resolution information on crystallography, defect structure and composition. © 1995 Wiley

ISSN:1059-910X    

DOI:10.1002/jemt.1070310404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractA recent advance in metallurgical technology has been the application of rapid solidification techniques to Al alloy production. FVS0812 is the designation given to a microcrystalline Al‐based alloy consisting of 8 wt% Fe, 1 wt% V and 2 wt% Si. It is a two‐phase alloy, consisting of ca. 27 vol percent of approximately spherical Fe‐V‐Si‐rich dispersoids in an essentially pure Al matrix. The high strength, low density properties of this advanced material, and other related alloys, have not yet been realized, however, due, in part, to the inability of the alloy to form a thick, adherent, abrasion‐resistant outer surface oxide film, a feature readily achieved at conventional Al alloys by normal anodizing methods. The present research has involved an electro‐chemical study of oxide film growth at the 812 alloy, with the specific goals being to seek an understanding of the origin of the oxide film growth problem and ultimately to propose alternative approaches to the formation of a thick, stable oxide film at this material. The techniques used in this research have included electrochemical methodologies such as cyclic voltammetry and electrochemical impedance spectroscopy. Crucial information has been obtained through transmission electron microscopy (TEM) of ultramicrotomed specimens. Experiments were carried out initially in neutral borate solutions to characterize the compact barrier oxide film formed in this environment and expected to be present beneath the porous oxide film formed in the normal sulfuric acid anodizing medium. In borate solutions, the electrochemical results implied oxide film thicknesses which were less than seen subsequently by TEM work, suggesting either that the barrier film at the 812 alloy can be penetrated by solution in very fine pores (not resolvable by conventional TEM) at its outer surface or that dispersoids trapped in the oxide film cause differential oxide film thicknesses to develop across the alloy surface. In sulfuric acid solutions, dissolution of Fe and V occurs from the 812 alloy during anodization. Both impedance and TEM studies reveal the absence of a barrier film at the 812 alloy surface. Also, the thick oxide overlayer has a tortuous and more open pore structure than formed at Al and the oxide film is also substantially thinner than it should be. It is suggested that the absence of a barrier oxide film indicates that the sulfuric acid anodizing medium is too aggressive for oxide film formation at the 812 alloy, resulting in excessive dissolution and poor oxide film qualities. © 1995 W

ISSN:1059-910X    

DOI:10.1002/jemt.1070310405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe formability of galvanneal steel sheets used in the automotive industry is influenced by the presence and distribution of brittle and difficult to distinguish Zn‐Fe intermetallics in the coating. Characterization of these intermetallics requires a high spatial resolution technique such as analytical transmission electron microscopy (ATEM). Sample preparation by ion milling is impossible due to iron redeposition, and traditional ultramicrotomy using water affects the coating chemistry. A technique based on dry ultramicrotomy has therefore been developed.To optimize the technique, different parameters (knife angle, cutting medium, thickness setting on the ultramicrotome, cutting speed) have been investigated for the preparation of galvanneal coatings and pure Al sections. Results show that dry cutting does not affect the coating chemistry but shortens the life of the knife. Knife quality (cleanliness, sharpness and absence of defects) is a major factor to obtain good dry sections. The best results for the more ductile pure Al are obtained with a 35° knife whilst for the harder galvanneal coating it is recommended to use a 55° knife. These results suggest that the sectioning mechanism for the harder material involves more a cleavage‐fracture mechanism whilst a greater amount of shear is involved when sectioning relatively ductile Al. The optimum parameters for sectioning galvanneal coatings are established and results obtained by parallel electron energy loss spectrum imaging and energy dispersive X‐ray spectrometry in the TEM are given. This study shows that with a good control of all the sectioning parameters it is possible to obtain good sections repeatedly and rapidly. © 1995 Wiley

ISSN:1059-910X    

DOI:10.1002/jemt.1070310406

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractIndustrial materials, such as alumina, often pose difficulties in their preparation for TEM examination. Composite and particulate materials are particularly difficult to prepare using conventional thinning techniques, i.e., ion beam and chemical jet thinning. Ultramicrotomy (UM) can be used to produce TEM specimens with a uniform thickness and an unaltered composition.Some crystalline materials, i.e., alumina hydrate, were difficult to section due to conflict between the cutting direction and cleavage planes. Sectioning was successful when these two directions were mutually parallel or perpendicular. At other orientations shattering occurred. Microcrystalline particulate materials, i.e., calcined alumina, were sectioned successfully in particles<70 μm in diameter.The phases found in industrial alumina particles were gamma, delta, theta, and alpha alumina. Gamma alumina consisted of fine‐grained, equiaxed crystallites. The selected area electron diffraction (SAED) patterns indicated poor crystallinity with a distinct hexagonal texture. Delta and theta alumina appeared as an undifferentiated intermediary microstructure of elongated grains. The SAED patterns indicated poor crystallinity, but without a distinct texture. Alpha alumina was found to be a coarse‐grained crystalline phase with high diffraction contrast. SAED patterns consisted of fine, randomly oriented spots.Considerable variation was observed in the distribution of phases. In some specimens, discrete particles of gamma and alpha predominated. In others, particles were a mixture of phases repre‐sentative of the bulk composition. To characterise these samples, TEM of numerous whole particles was required. Ultramicrotomy was the only preparation technique capable of producing such samples. © 1995 Wiley‐

ISSN:1059-910X    

DOI:10.1002/jemt.1070310407

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractUltramicrotomy has been used to prepare TEM cross‐sections of typical hard dielectric, semiconductor, and metal coatings, providing a critical capability in the study of structure‐property relationships of thin films. Ultramicrotomy of thin film coatings requires meticulous attention to technique and handling. The sample to be microtomed must be very small, well bonded to the epoxy embedding medium, and precisely oriented. In this article we report the ability to microtome TEM cross‐sections of diamond and cubic boron‐nitride (cBN) coatings. © 1995 Wiley

ISSN:1059-910X    

DOI:10.1002/jemt.1070310408

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractUsing back projection for reconstruction and tilt series of Epon or Lowicryl embedded and sectioned material, we demonstrated: (1) a reduction in thickness of 50% for Epon and 80% for Lowicryl sections, and (2) a non‐uniform density distribution along the electron‐optical axis in sections. The highest density was found at the vacuum exposed side of the section. The formvar side of the section showed a similar increase in density, but not to the same extent. Minimalization of electron exposure, even without pre‐exposure, did not affect the reconstructed thickness, nor did it affect the non‐uniform density distribution. However, parallax measurements showed that at 150K, collapse of Epon sections does not take place. For EM‐tomography of plastic embedded material our findings imply that at the top and bottom portion of the sections the dimensions of the reconstructed structures are distorted, but that in the middle portion the dimensions are reliably retained. © 1995 Wiley

ISSN:1059-910X    

DOI:10.1002/jemt.1070310409

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractFour different methods for calcium precipitation are compared in the optic tectum and the inner ear of the cichlid fish,Oreochromis mossambicus. Several parameters are investigated concerning their influences on the reaction product. Three procedures (bichromate, fluoride, and oxalate‐pyroantimonate) produce fine‐grained deposits, often flocculent in the latter method. The fourth method (potassium‐pyroantimonate) generates predominantly coarse‐grained reaction product. The calcium content of the deposits is always proven with energy‐filtering transmission electron microscopy (EFTEM). In both tissues fine‐grained reaction product is found in endoplasmic reticulum and synaptic vesicles, and in addition in some mitochondria and at the cytoskeleton. The coarse‐grained deposits of the potassium‐pyroantimonate method have a more unspecific distribution. This is the only method which produces extracellular deposits in the inner ear, whereas in the optic tectum extracellular precipitates are always present except with the oxalate‐pyroantimonate procedure. Two factors have an influence on the reaction product: the duration of fixation and the type of resin. The prolongation of the fixation time up to 24 hours leads to an increase of the reaction product, which also becomes coarse‐grained. These observations are corroborated by quantification with image analysis. Furthermore the use of an epoxy resin compared to acrylic resins decreases the amount of reaction product produced. We show that the application of several methods is meaningful in order to understand the calcium properties of the investigated tissue, but it is necessary to optimize a certain method for a given tissue. ©

ISSN:1059-910X    

DOI:10.1002/jemt.1070310410

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractTechniques to extract focus properties of microscopy images are many and varied. Many of them, however, rely on the summation of local statistical properties. Presented here is an examination of conventional focus determination algorithms, and a new method based on planar histograms of these local statistical properties. It is shown that this new method provides finer discernment of the focus properties of an image, and provides a means to extend the focus of an optical microscopy system. © 1995 Wiley‐Liss, I

ISSN:1059-910X    

DOI:10.1002/jemt.1070310411

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY