Andy Horsewell

Critical factors in SEM 3D stereo microscopy

This work addresses dimensional measurements performed with the scanning electron microscope (SEM) using 3D reconstruction of surface topography through stereo-photogrammetry. The paper presents both theoretical and experimental investigations, on the effects of instrumental variables and measurement parameters on reconstruction accuracy. Investigations were performed on a novel sample, specifically developed and implemented for the tests. The description is based on the model function introduced by Piazzesi and adapted for eucentrically tilted stereopairs. Two main classes of influencing factors are recognized: the first one is related to the measurement operation and the instrument set-up; the second concerns the quality of scanned images and represents the major criticality in the application of SEMs for 3D characterizations.

Quantification of the EELS near‐edge structures to study Mn doping in oxides

The L3 to L2 white‐line intensity ratios of Mn in solid solution in yttria‐stabilized zirconia and in Mn oxide standards are measured using different approaches. We show that the L3/L2 ratio alone cannot be used as a means of deducing the oxidation state and that a combined analysis of this ratio and the normalized white‐line intensity is required to retrieve the ionicity and magnetic state of the Mn dopant with respect to reference standards. Changes as a function of composition are measured and these are discussed in terms of variations in crystal field parameters associated with possible vacancy interaction. From the oxygen near‐edge structure we analyse the localization of the extra electron charge introduced by the dopant and discuss the possible effects of the association of this extra charge with oxygen vacancies in relation to the macroscopic ion conductivity.

Microstructural and microchemical characterization of the interface between La0.85Sr0.15MnO3 and Y2O3-stabilized ZrO2

La0.85Sr0.15MnO3 and Y2O3-stabilized ZrO2 may be used as cathode and electrolyte materials, respectively, in solid oxide fuel cells. One of the requirements of the cathode-electrolyte interface is that high impedance phases are not formed at the interface during manufacture or operation of the SOFC. The interfaces of interest were prepared as a diffusion couple and by sintered powder mixtures of La0.85Sr0.15MnO3 and Y2O3-stabilized ZrO2. The structures at the interfaces were examined by transmission electron microscopy. Chemical analyses were made by energy dispersive X-ray spectroscopy. A Zr, La-based pyrochlore-type crystalline phase has been observed at some of the interfaces between La0.85Sr0.15MnO3 and Y2O3-stabilized ZrO2. In the present paper, changes in element ratios are used to obtain knowledge on how the elements diffuse with respect to each other at the interface. It was found that the formation of pyrochlore depends on the content of Mn in the La0.85Sr0.15MnO3 and on the ratio between La0.85Sr0.15MnO3 and Y2O3-stabilized ZrO2.

Dislocation and void segregation in copper during neutron irradiation

Abstract High-purity (99·999%) and fully annealed copper specimens have been irradiated in the DR-3 reactor at Ris⊘ to doses of 1 × 1022 and 5 × 1022 neutrons (fast)m−2 (2 × 10−3 dpa and 1 × 10−2 dpa, respectively); the irradiation experiments were carried out at 250°C. The irradiated specimens were examined by transmission electron microscopy. At both doses, the irradiation-induced structure was found to be highly segregated; the dislocation loops and segments were present in the form of irregular walls and the voids were distributed between these walls. The dislocation walls were practically free of voids and generally had a void-denuded zone along them. The density of dislocations (loops and segments) was very low in the region containing voids (i.e. between the dislocation walls). Even with this low dislocation density, the void swelling rate was very high (∼2·5% per dpa). The implications of the segregated distribution of sinks for void formation and growth are briefly discussed. It is pointed out th...

On texture formation of nickel electrodeposits

Electrodeposited nickel has been investigated by cross-sectional transmission electron microscopy and X-ray diffraction. The <100> fibre texture and fine-grained, dislocated columnar microstructure has been considered with respect to the mechanisms of growth during electrodeposition. Fine, codeposited nickel oxide hydroxide precipitates which have formed on the {111} planes appear not to have influenced texture formation. Although strong inhibition by adsorbed hydrogen or organic species is suggested from the work of others, this has not resulted in any codeposition of other species, either crystalline or amorphous.

Multimodal Electrothermal Silicon Microgrippers for Nanotube Manipulation

Microgrippers that are able to manipulate nanoobjects reproducibly are key components in 3-D nanomanipulation systems. We present here a monolithic electrothermal microgripper prepared by silicon microfabrication, and demonstrate pick-and-place of an as-grown carbon nanotube from a 2-D array onto a transmission electron microscopy grid, as a first step toward a reliable and precise pick-and-place process for carbon nanotubes.

Free-volume evolution and its temperature dependence during rolling of Cu60Zr20Ti20 bulk metallic glass

The free-volume evolution during rolling Cu60Zr20Ti20 bulk metallic glass at room and cryogenic temperatures has been investigated by differential scanning calorimetry. When the specimen is rolled at cryogenic temperature, the free-volume content increases as the rolling proceeds first, and then saturates accompanied by the occurrence of phase separation as the thickness reduction exceeds 89%. If the rolling is performed at room temperature, although the free-volume content also rises in the earlier stage, it tends to decrease rather than saturate when the thickness reduction exceeds 87%, accompanied by partial crystallization. Phase separation does not change the annihilation rate of free volume, while the appearance of crystal/amorphous boundaries can enhance the annihilation.

On texture formation of chromium electrodeposits

The microstructure, texture and hardness of electrodeposited hard, direct current (DC) chromium and pulsed reversed chromium has been investigated. These investigations suggest that the growth and texture of hard chromium is controlled by inhibition processes and reactions. Further, it has been established that codeposition of Cr2O3 nanoparticles is a general feature of DC chromium electrodeposition.

Microstructure in electrodeposited copper layers, the role of the substrate

The microstructures of Cu layers, ranging in thickness from 3 to 12 µm, were investigated. The layers were electrodeposited from an acidic copper electrolyte onto two distinct substrate materials i ...

Mechanical properties of low-density polyethylene filled by graphite nanoplatelets

The mechanical properties of GNP/LDPE nanocomposites (graphite nanoplatelets/low density polyethylene) have been investigated, in order to establish the effect of nanoscale reinforcement within the polymer matrix. Results show that the presence of the filler does not involve a change in the microscopic structure of the polymer. However, on a macroscopic scale, GNPs limit the mobility of the polymer chains, resulting in an increase in stiffness for the final composite. Orientation of GNPs within the LDPE matrix is also an important issue that affects mechanical properties and it has been evaluated by testing nanocomposites made by different manufacturing techniques (compression moulding and blown extrusion). The comparison between the experimental data and the Halpin-Tsai model shows that the orientation of GNPs due to the extrusion process leads to values of tensile modulus higher than that obtained with the randomly oriented disposition resulting from the compression moulding technique.