Bonding of rubber to brass-plated steel wire

This research is based on a study of the parameters affecting the adhesion of styrene–butadiene rubber (Solprene 1204) and polyisoprene (Natsyn 2200) to monofilament brass-plated steel wire. Investigations are concentrated on the influence of compounding ingredients and coupling agents on the adhesion between the rubber and wire using H-shape specimens. X-Ray Photo Electron Spectroscopy (ESCA) and Scanning Electron Microscopy (SEM) techniques have been used to identify residues on the wire surface and to interpret the chemical and physical roles of carbon black and silica on the mechanism of bonding rubber to brass-plated wire. [Continues.

Graphene-Capped Liquid Thin Films for Electrochemical Operando X-ray Spectroscopy and Scanning Electron Microscopy

Electrochemistry is a promising building block for the global transition to a sustainable energy market. Particularly the electroreduction of CO2 and the electrolysis of water might be strategic elements for chemical energy conversion. The reactions of interest are inner-sphere reactions, which occur on the surface of the electrode, and the biased interface between the electrode surface and the electrolyte is of central importance to the reactivity of an electrode. However, a potential-dependent observation of this buried interface is challenging, which slows the development of catalyst materials. Here we describe a sample architecture using a graphene blanket that allows surface sensitive studies of biased electrochemical interfaces. At the examples of near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and environmental scanning electron microscopy (ESEM), we show that the combination of a graphene blanket and a permeable membrane leads to the formation of a liquid thin film between them. This liquid thin film is stable against a water partial pressure below 1 mbar. These properties of the sample assembly extend the study of solid–liquid interfaces to highly surface sensitive techniques, such as electron spectroscopy/microscopy. In fact, photoelectrons with an effective attenuation length of only 10 Å can be detected, which is close to the absolute minimum possible in aqueous solutions. The in-situ cells and the sample preparation necessary to employ our method are comparatively simple. Transferring this approach to other surface sensitive measurement techniques should therefore be straightforward. We see our approach as a starting point for more studies on electrochemical interfaces and surface processes under applied potential. Such studies would be of high value for the rational design of electrocatalysts

Growth and chemical characterisation studies of Mn silicate barrier layers on SiO2 and CDO

This thesis investigates the suitability of manganese silicate (MnSiO3) as a possible copper interconnect diffusion barrier layer on both a 5.4 nm thick thermally grown SiO2 and a low dielectric constant carbon doped oxide (CDO), with the focus of understanding the barrier formation process. The self forming nature of this diffusion barrier layer resulting from the chemical interaction of deposited Mn with the insulating substrate has potential application in future generations of copper interconnect technologies as they are significantly thinner than the conventional deposited barrier layers. The principle technique used to study the interface chemistry resulting from the interaction of deposited manganese with the insulating substrates to form a MnSiO3 layer was x-ray photoelectron spectroscopy (XPS). Transmission electron microscopy (TEM) measurements provided information on the structure of the barrier layers which could be correlated with the XPS results. Significant differences in the extent of the interface interaction which resulted in the formation of the MnSiO3 barrier layer were found to depend on whether the deposited Mn was partially oxidised. The studies performed on the 5.4 nm thermally grown SiO2 confirmed that the growth of the MnSiO3 resulted in a corresponding reduction in the SiO2 layer thickness. Interactions between residual metallic Mn and subsequently deposited copper layers were also investigated and showed that in order to reduce the width of the barrier layer, it was preferable that all the deposited Mn was fully incorporated into the silicate. TEM measurements were also used to investigate thicker thermally deposited Mn/Cu heterostructures on SiO2 which were subsequently annealed in order to study the diffusion interactions between copper and manganese. The formation of Mn silicate layers on low dielectric constant carbon doped oxide (CDO) was also investigated and compared with the formation characteristics on the thermally grown SiO2

Carbon nanomaterial based vapor sensors.

The discovery of carbon nanotubes and subsequently graphene has led to an interest in carbon materials as sensing elements due to their unique properties. Graphene is a 2-dimensional material that has a large surface area that can be exposed to surface adsorbates from a target gas. This enables studies on the interaction of gas molecules with the graphene surface and subsequent changes in its properties. Graphene also exhibits high conductivity and low noise and has low crystal defects. Due to its high electron mobility at room temperature, graphene exhibits high sensitivity (in tune of detecting ppm) which is a required trait in environmental and industrial sensing applications, making graphene a good candidate for sensors. Several models of sensors based on graphene as sensing element have been put forth previously based on high-resolution lithographic techniques and for individual electrode attachment to the sensing film with e-beam lithography. These techniques can produce small numbers of devices that explore the limits of molecular scale sensing, but the methods are currently impractical for large scale production of low cost sensors. The work presented here counters this labor-intensive process and puts forth a practical lowcost sensor. Graphene sheets grown using chemical vapor deposition are transferred onto an acrylic chip designed for gas sensing. The working principle of the sensor is the electrical conductivity change exhibited by the graphene when molecules adsorb onto the material while the sensor chip is exposed to the target gas in a controlled environment. We present our graphene based sensor with the focus on designing small, cost effective and reliable sensors with high sensitivity towards the target gas, detailing the assembly of graphene/acrylic based devices, their characterization and investigation of their performance as resistive chemical sensors using different substrates as graphene supports

Electrodeposition and characterisation of nickel-niobium-based diffusion barrier metallisations for high temperature electronics interconnections

The control of interfacial microstructural stability is of utmost importance to the reliability of liquid solder interconnects in high temperature electronic assemblies. This is primarily due to excessive intermetallic compounds (IMCs) that can form and continuously grow during high temperature operation, which practically renders conventional barrier metallisations inadequate. In this study, electrically conducting, NbOx containing Ni coatings were developed using electrodeposition. Their suitability as a solder diffusion barrier layer was assessed in terms of the electrical conductivity and barrier property. The present work explores a novel electrochemical route to produce Ni-NbOx composite coatings of good uniformity, compactness and purity, from non-aqueous glycol-based electrolytes consisting of NiCl2 and NbCl5 as metal precursors. The effects of cathodic current density and NaBH4 concentrations on the surface morphology, composition and thickness of the coatings were examined. A combined study of Scanning Transmission Electron Microscopy (STEM) and Electrochemical Quartz Crystal Microbalance (EQCM) was conducted to understand the fundamental aspects of this novel electrodeposition process. The composite coatings generally exhibited good electrical conductivity. The reaction behaviour between a liquid 52In-48Sn solder and Ni-NbOx, with Nb contents up to 6 at.%, were studied at 200ºC. The results indicate that, Ni-NbOx with sufficient layer thickness and higher Nb content, offered longer service lifetime. Nb enrichment was generally observed at or close to the reaction front after high temperature storage, which suggests evident effectiveness of the enhanced diffusion barrier characteristics

Tin Catalyst preparation for Silicon Nanowire synthesis

>Magister Scientiae - MScSolar cells offer SA an additional energy source. While Si cells are abundantly available they are not at an optimal efficiency and the cost is still high. One technology that can enhance their performance is SiNW. However, material properties such as the diameter, porosity and length determine their effectiveness during application to solar cell technology. One method of growing SiNW uses Sn catalysts on a Si substrate. As the properties of the Sn nanoparticle govern the properties of the SiNW, this thesis investigates their formation and properties by depositing a Sn layer on a Si wafer and then subjecting it to different temperatures, during process the layer forms into nanoparticles. At each temperature the morphology, composition and crystallinity will be determined using XPS, SEM, TEM and EDS. Thus, in Chapter 1 there is an overview, Chapter 2 deals with techniques used in this study, Chapter 3 will give the quantitative and qualitative results on the XPS analysis and Chapter 4 will illustrate the structural behaviour of the annealed Sn film samples