Scanning electron microscopy and energy dispersive X-ray study of a recovered dental implant

A recovered dental implant has been studied for surface contamination using SEM and EDS microanalysis. The implant had been in place for 4 years in an adult male (age: 56 years), who had poor oral hygiene and was a smoker. Loosening had occurred, and the implant was removed accidentally during the taking of an impression. Using SEM, three distinct regions were identified, a clear one where the metal appeared shiny and unaffected, a discoloured one, where the surface appeared smooth and uncoated, and a region where there was a distinct deposit. All three regions gave elemental compositions of approximately 85% Ti, 12% Al, 3% V, which is a little richer in aluminium than the nominal overall composition of the usual alloy employed in implants. All three regions showed the presence of carbon, with the highest levels being associated with the surface deposit, and the lowest with the clear region. Oxygen was also present in substantial amounts, with most being found in the discoloured region. No nitrogen was detected, which suggests that the organic surface contamination is not due to interaction with proteins, despite their presence in saliva and crevicular fluid within the mouth.     

Transmission electron microscopy study of plastic deformation in NiZr2

Plastic deformation mechanisms in the body centred tetragonal (C16-structure) NiZr₂ compound have been studied using transmission electron microscopy. Dislocations, stacking faults and microtwins have been characterized. Four families of dislocations have been identified: screw-type (b=[0 0 1]), edge-type ([0 0 1](1 1 0) and [110] (1¯10) systems) and mixed-type (1/2[1¯11] (110) system). Partial dislocations associated with stacking faults have also been detected and analysed. The plane of the faults is shown to be (1¯10) and the fault vectors 1/4 [1 1 1] and 1/4 [11¯1]. A hard-sphere model illustrating the formation mechanism of these stacking faults is proposed. The microtwins are found to be 60° rotation twins around the [1¯10]^* direction and can be described by the stacking faults scheme.     

Transmission electron microscopy study of the cell–sensor interface

An emerging number of micro- and nanoelectronics-based biosensors have been developed for non-invasive recordings of physiological cellular activity. The interface between the biological system and the electronic devices strongly influences the signal transfer between these systems. Little is known about the nanoscopic structure of the cell-sensor interface that is essential for a detailed interpretation of the recordings. Therefore, we analysed the interface between the sensor surface and attached cells using transmission electron microscopy (TEM). The maximum possible resolution of our TEM study, however, was restricted by the quality of the interface preparation. Therefore, we complemented our studies with imaging ellipsometry.We cultured HEK293 cells on substrates, which had been precoated with different types of proteins. We found that contact geometry between attached cell membrane and substrate was dependent on the type of protein coating used. In the presence of polylysine, the average distance of the membrane-substrate interface was in the range of 35-40 nm. However, the cell membrane was highly protruded in the presence of other proteins like fibronectin, laminin or concanavalin-A. The presented method allows the nanoscopic characterization of the cell-sensor interface.     

Transmission electron microscopy on the microstructure of 7050 aluminium alloy in the T74 condition

The microstructure of 7050 aluminium alloy in the T74 condition has been investigated by transmission electron microscopy. It was found that the alloy contains the superlattice Al₃Zr phase, η′ phase and Al₇Cu₂Fe constituent phase. The η′ phase is proposed to have an orthorhombic crystal structure witha=0.492 nm,b=0.852 nm andc=0.701 nm. The orientation relationship between the matrix and η′ phase is [11−2]_m//[100]_η′; [1−]_m//[010]_η′;[−1−1−1]_m//[001]_η′. The phases on the small-angle grain boundary are found to be mainly η′ phase and Cu/Si-rich phase, whereas on the large-angle grain boundary there is only η phase.     

High-resolution electron microscopy study of a high-copper variant of weldalite 049 and a high-strength AI-Cu-Ag-Mg-Zr alloy

A high-resolution electron microscopy study was preformed on two high-strength aluminium alloys, an Al-6.2Cu-0.4Ag-0.4Mg-0.2Zr alloy and a similar alloy but having a low lithium addition (1.25 wt%), named Weldalite 049, in order to identify their principal strengthening phase. The lattice images of the principal strengthening phase in these alloys were found to be different. The former alloy had the so-called phase, which agrees with previous publications, whereas Weldalite 049 had a phase similar to, but not exactly like, the so-called T₁ phase which is the principal strengthening phase of some high lithium (2 wt%) AlCuLi alloys.     

Transmission electron microscopy of partially crystallised glasses

The early stages of crystallisation in a Li₂O-SiO₂-P₂O₅ glass were studied by transmission electron microscopy using thin sections prepared from the bulk material by chemical thinning. Small crystalline regions of lithium disilicate were formed, often as several small single crystals joined together around a central core. Possible explanations of the core are discussed in terms of a region of different chemical composition or a central region of disorder. The observations are also compared with the growth of crystal spherulites in polymers.     

Transmission electron microscopy of a transformation toughened white cast iron

Transmission electron microscopy has been used to study the microstructure of an experimental white cast iron, in which a combination of modified alloy composition and unconventional heat treatment has resulted in a fracture toughness of 40 MPa m-1/2. Microstructural features of the alloy that contribute to the toughness improvement and hence distinguish it from conventional white irons have been investigated. In the as-cast condition the dendrites are fully austenitic and the eutectic consists of M7C3 carbides and martensite. During heat treatment at 1130 °C the austenite is partially destabilized by precipitation of chromium-rich M7C3 carbides. This results in a dendritic microconstituent consisting of bulk retained austenite and secondary carbides which are sheathed with martensite. The martensite sheaths, which contain interlath films of retained austenite, are irregular in shape with some laths extending into the bulk retained austenite. Emphasis has been placed on the morphology, distribution, and stability of the retained austenite and its transformation products in the dendrites. The implications of these findings on the transformation toughening mechanism in this alloy are discussed.     

Transmission electron microscopy study of dislocations and interfaces in CdTe solar cells

We report on our transmission electron microscopy study of dislocations and interfaces in CdTe solar cells. The atomic structure of dislocations formed inside CdTe grains have been determined by atomic-resolution transmission electron microscopy. We discuss the electronic properties of the dislocations and explore the effects of oxygen on the interdiffusion at CdS/CdTe interface. We find that the presence of oxygen in either CdS or CdTe suppresses the interdiffusion at the CdS/CdTe interface. We have further investigated interdiffusion at the CdS/Zn₂SnO₄ interface. We find that Zn diffuses into CdS from Zn₂SnO₄ and Cd diffuses into Zn₂SnO₄ from CdS. The possible effects of the interdiffusion are discussed. Finally, we have examined the distribution of intentionally introduced Cu at the CdTe/CdS junction, and we find that Cu is distributed uniformly in the CdS layer.     

Transmission electron microscopy study of 180° domain structure in PbZrO3

Abstracts are not published in this journal     

Transmission electron microscopy study of defect-selective etched (010) ScN crystals

The origin of etch pits, formed in (010) scandium nitride single crystals etched in molten potassium hydroxide KOH, is reported. Transmission electron microscopy (TEM) with weak beam condition and large area convergent beam electron diffraction technique were used to identify the nature of dislocations associated with etch pits. The top edge of the etch pits was a square inverted pyramid with the bottom point deviating from the center. TEM investigation demonstrated that a mixed dislocation terminated at the bottom of each etch pit. The Burgers vector of the mixed dislocation is ½ [01¯1¯] and the vector of the dislocation line is [1¯91].     

Transmission electron microscopy study of carbon nanophases produced by ion beam implantation

The formation of carbon nanocrystals, produced by ion implantation of carbon ions into fused SiO₂ substrates, followed by 1 h thermal annealing at 1000 °C, in an Ar + 5% H atmosphere has been studied. Combined high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) have been employed for structural characterization of carbon nanophases embedded in the quartz substrate. The dependence of grain size and sample morphology of the carbon nanophases on implantation dose was studied. The carbon nanocrystals formed by the implantation for a dose of 1 × 10¹⁶ C/cm² at 320 keV have been identified as a mixture of c-diamond nanophase and a modified diamond nanophase known as n-diamond. For a higher implantation dose, 5 × 10¹⁶ C/cm², besides n-diamond, another solid carbon nanophase was observed, with a structure known as i-carbon. Following the highest implantation dose 1 × 10¹⁷ C/cm² the sample contained the i-carbon nanophase only. A least-square refinement of SAED patterns was employed for the calculation of unit-cell parameters of identified carbon nanophases.     

Transmission electron microscopy study of 180° domain structure in PbZrO3

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.