Physics

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Open Access
Bepaling van die elastisiteitskonstantes van yster enkel-kristalle
(University of the Free State, 1966-10) Lombaard, J. C.
Abstract not available
Open Access
Mode identification in delta δ Scuti stars
(University of the Free State, 1998-10) Evers, Elizabeth Anne; Balona, L. A.; Meintjes, P. J.
This thesis discusses mode-identification from multicolour photometry. First, the need for a better mode identification technique for stars that have significant phase differences between the light curves in different colours is addressed. The necessary equation needed for modeidentification from photometry is then derived and briefly discussed. Then, a new, statistically based algorithm for mode-identification is developed by extending and adapting a method that has been applied to pulsating white dwarfs, to include the information provided by the different phases of the light curves in different wavelengths. This new algorithm allows the best estimate of the spherical harmonic degree l to be determined, as well as a confidence level from which the uniqueness of the mode-identification can be ascertained. The algorithm is then applied to a selection of well-observed 8 Seuti stars with the necessary multicolour photometry. It is found that it works well for high amplitude 8 Set stars, but that discrimination between the l = 0 and l = 1 modes is sometimes poor for the low amplitude stars. An algorithm to deduce the effective temperature, luminosity and equatorial velocity from the observed frequencies is also proposed. It is found that some mode-identification is necessary to obtain a unique solution of the stellar parameters. The method is applied to a subset of the 8 Set stars which have a suitable number of frequencies and suitable mode identifications.
Open Access
The determination of ternary segregation parameters using a linear heating method
(University of the Free State, 2000-11) Asante, Joseph Kwaku Ofori; Roos, W. D.; Du Plessis, J.
In this study the segregation behaviour of the ternary system Cu(lll ), Sb, Sn is investigated experimentally, as well as with the modified Darken segregation model. The model, which describes the kinetics as well as the equilibrium of segregation, had been used successfully in various studies of binary systems. A computer program based on this model was developed for ternary systems. A Cu(lll) single crystal was doped with low concentrations of 0,180 at% Sb and 0.133 at% Sn using evaporation and diffusion process.' The experimental results were gathered with the Auger electron spectroscopy technique. This technique was combined with a linear temperature ramp that makes it possible to obtain the segregation parameters in a single run. The traditional method requires various runs at different temperatures. The overlapping of Sb and Sn Auger peaks in the energy regions of interest necessitated the development of a method to successfully extract the true contributions of the elements from the measured spectra. It is clearly shown that the combination of Auger peaks is not linear and that the true contributions of Sb and Sn can be calculated if the peaks overlap in two energy regions and the standard spectra are available. The segregation profiles resulted from the Auger data show clearly the sequential segregation of the two elements (Sn and Sb). From the equilibrium conditions, it is also concluded that an interaction energy between Sb and Sn is present. By simulating the experimental results, using the theoretical Darken model, values for the segregation parameters can be obtained. The initial values for the fits are found mathematically (highenergy regions) and manually (low energy regions). The calculated profiles fit the experimental results very well. The present study confirms that Sn segregate first to the surface with Do = 1.58x10-5 m²s-¹ and E = 170 kJ/mol. Sb with a lower dimsion coefficient (Do = 1.93x10-8 m²s-¹ and E = 150 kJ/mol) segregates at higher temperatures. A further increase in temperature results in the stronger segregate Sb, (with a higher segregation energy ∆G = -74.6 kJ/mol) to displace the Sn (∆G = -59.0 kJ/mol) from the surface. From the simulations, it is clear that the maximum surface coverage for Sn is determined mainly by the attractive interaction (ΩSnCu = -8.25 kJ/mol) between Sn and Cu. The desegregation rate of Sn in this system is determined by the segregation rate of Sb. The segregation profile of Sb is similar to that in a binary system (Cu,Sb) with the desegregation rate of Sb much slower than the segregation rate. The study also shows definite attractive interaction between Sb and Cu (ΩSbCu= -17.05 kJ/mol) This trend was not observed in the studies of binary systems. There is, however, repulsive interaction between the segregates (ΩSnSb = 3.62 kJ/mol). The repeatability of the segregation parameters at different heating rates shows that this experimental method can be used successfully.
Open Access
'n ISS studie van die (110), (111) en (100)-enkel-kristalvlakke van NiAI
(University of the Free State, 2000-11) Mostert, Jacob Cornelis; Van Wyk, G. N.; Roos, W. D.
English: In this study the [110]-, the [111]- and the [1OO]-single crystal surfaces of Ni Al were investigated. The aim was to firstly harmonize the existing knowledge of these surfaces and secondly to create a clear and coherent overview of their properties. The essence of a problem of this kind is the determination of the structure and composition of the surface of a material. In this study, low energy ion scattering (LEISS) was used as primary investigative technique. Other techniques such as ICISS ("Impact Collision" ISS", Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) were used in conjunction with LEISS. Several intensive investigations of the NiAI(IIO)-surface were launched in recent times. The results of these investigations were largely similar and are widely accepted. In this study the results of several previous investigations are discussed. It is shown that the surface is largely a simple truncation of the bulk in the (110)-direction, but that the surface exhibits a ripple effect due to the particular way in which the Al and Ni atoms in the surface and second layer relaxes. In contradiction with the NiAI(ll O)-surface, there is still a measure of uncertainty regarding the properties of the NiAI(ll I)-surface. As part of this study, the NiAI(111)-surface was investigated using LEISS. The results of this investigation are given and is compared with the results of previous studies of the surface from the literature. It is shown that the surface consists of small Al-areas on top of a Ni-layer. One of the studies showed that the Al-areas could be removed by heating the surface to 1300 K. From other studies however, including this one, it seems that the removal of the Al-atoms from the surface may be inhibited or prevented by the presence of oxygen. As in the case of the NiAI(110)- and NiAI(l1 l j-surfaces, a large number of investigations were done on the NiAI( 1OO)-surface. Contradictory results were however a commonplace occurrence. In this study, the NiAI(lOO)-surface was subjected to a comprehensive LEED, LEISS, ICISS and AES investigation with the aim of clarifying the structure and composition of the surface. An overview of results of previous, as well as this investigation is given. It is shown that the NiAI(100)-surface is very sensitive to changes in temperature and that the surface composition and sometimes also the surface structure undergo several changes during heating. At low temperatures (approximately 500 K), a largely AItermination can be found, but with heating from 500 K to 873 K the surface composition changes to 65 at. % Al and 35 at. % Ni and voids. At this temperature the surface undergoes a reconstruction process so that it exhibits a c (Ji x 3.J2)R45°- LEED pattern. Further heating leads to another change in composition to 75 at. % Al and 25 at. % Ni and voids at 1073 K. At this temperature the surface exhibits a p(1 x 1)-LEED pattern. At temperatures above 1073 K the Al concentration in the surface starts to decline until the Al atoms are complete removed at approximately 1300 K. After this point the surface consists of only Ni atoms.
Open Access
Oxidation of a segregated MoN layer grown on Fe(100)-3.5wt%Mo-N
(University of the Free State, 2001-06) Conradie, Rochelle; Roos, W. D.; Swart, H. C.
English: The oxidation behaviour of the segregated MoN layer on the Fe(100)-3.5wt% Mo-N substrate was investigated in this study. Previous studies suggested the synergetic segregation of the Mo and N from the Fe(100)-3.5wt% Mo-N specimen. It has also been shown that the segregated Mo and N form a MoN surface compound. As an alloy element in stainless steels, the Mo aids in the inhibition of the oxidation and thus prevents corrosion Auger electron spectroscopy (AES) was used to obtain the experimental results. For this study the oxidation of a Fe(100) specimen and a Fe(100)-3.5wt% Mo-N specimen were investigated to establish a point of reference to describe the oxidation behaviour of the segregated MoN layer. Linear temperature ramping was used to segregate the Mo and N from the Fe(100)-3.5wt% Mo-N specimen. The specimens were exposed to an oxygen environment at various temperatures. The partial pressure of the oxygen was monitored with a mass spectrometer and was kept constant at 2 x 10-10 torr. The Auger peak-to-peak heights for the relevant elements in the specimens were measured as a function of the exposure time. Upon oxidation, the low energy Fe AES peak (47 eV) undergoes shape changes. The iron oxide has a dual peak with 42 eV and 52 eV kinetic energy respectively. The Fe(100) specimen surface reacted rapidly with the oxygen environment at room temperature to form an iron oxide, as depicted by the change in the low energy Fe AES peak. The exposures performed at 100°C and 200°C also resulted in oxide formation although the extent of the oxidation decreased with an increase in the temperature. Above 300°C indication of the Mo and N reacting with the oxygen environment. At 100°C and 200°C less oxide formation was detected and above 300°C there was only oxygen adsorption. The segregated MoN layer had a markedly different response to the oxygen exposure. The oxygen exposure performed at room temperature had a strikingly different course of the 0 Auger peak-to-peak height increase compared to that of the Fe(100) and Fe(100)- 3.5wt% Mo-N specimens exposure at the same temperature. The segregated MoN layer retards the surface reaction. A hypothesis formulated describes the MoN layer as a perforated layer that has some Fe exposed. The oxygen reacts rapidly with the exposed Fe. Longer exposures result in the dissociation of the MoN layer and the desorption of the Mo03 and NxOy compounds from the surface. Once the layer has dissociated completely the Fe will continue to react as for the other specimens. Oxidation occurs up to 300°C and at higher temperatures no oxide formation is detected. The changes in the low energy Fe AES peak are used to calculate the fraction oxide and metal contributing to the peak by using the Linear Least Squares method. The low energy Fe AES peak cannot be used for thickness calculations as it is subject to the backscattering term. The experimental data suggests that the backscattering term is a function of the exposure time. A first approximation is to assume a linear change with time. This approximation was applied successfully to the room temperature oxidation of the segregated MoN layer, but the same function could not be applied to the other two specimens, The thickness of the oxide was calculated using the change in the high energy Fe AES peak intensity. The O2 sticking coefficient for the exposure of the Fe(100) and the exposure of the segregated layer was also calculated and the differences in the values were attributed to the effect of the dissociation of the MoN layer on the adsorption of the O2 on the specimen surface. there was no oxide formation detected and therefore there is only oxygen adsorption at these temperatures. The Fe(100)-3.5wt% Mo-N specimen showed similar oxidation behaviour as was seen for the Fe(100) specimen. At room temperature the surface of the specimen reacted rapidly with the oxygen environment to form an iron oxide. There was no
Open Access
Degradation of ZnS:Cu,Au,Al phosphor powder and thin films under prolonged electron bombardment
(University of the Free State, 2001-10) Hillie, Kenneth Thembela; Swart, H. C.; Berning, G. L. P.
Auger electron spectroscopy (AES) and cathodoluminescence (CL), both excited by the same electron beam, were used to monitor changes in surface composition and luminous efficiency during electron bombardment. ZnS:Cu,Al,Au phosphor powders and thin films were subjected to prolonged electron beam bombardment of varying beam energies and different electron beam current densities in two different (O2 and CO2) vacuum gas ambients. The thin film phosphors were grown on Si (100) substrates by using XeCl (308nm) pulsed laser deposition (PLD) method. X-ray diffraction (XRD) measurements revealed that ZnS (100) films were preferentially grown on a Si (100) substrate. The RBS results show that the growth rate, increased with an increase of the N2 pressure in the deposition chamber during deposition. Degradation on both the powder and the thin film phosphors was manifested by a nonluminescent ZnO layer that formed on the surface of the phosphor according to the electron stimulated surface chemical reactions (ESSCR) mechanism. Lower current densities lead to a higher surface reaction rate, due to a lower local temperature beneath the beam, which resulted into a more severe CL degradation. A lower temperature beneath the electron beam may lead to an increase in the surface reaction rate due to the longer time spent by the adsorbed molecules on the surface, with a direct increase in the ESSCR probability. Low current densities would also lead to surface charging due to a lower electron conductivity of the phosphor resulting in an increase in the CL degradation rate due to band-bending. In the studies conducted between room temperature and 310 oC, an increase in the temperature led to a decrease in the surface reaction rate due to a decrease in the mean surface lifetime of the oxygen molecules on the surface, with a direct decrease in the ESSCR probability. Without the presence of the electron beam no chemical reactions, up to 310 oC, occurred on the surface. Therefore, local heating due to the electron beam irradiation is not responsible for the chemical reactions on the ZnS phosphor surface. At -125 °C the degradation was controlled by the residual small amount of water vapour in the system that is frozen at this low temperature. The thermoluminescence (TL) curves of the phosphor powder before and after degradation showed the influence of the O substitutional atoms that are created during electron bombardment in an O2 ambient. The O substitutional atoms acted as electron traps. On the electron beam bombardment of thin film phosphors, the degradation was more severe under O2 ambient compared to the same partial pressure of CO2 during electron beam bombardment, which is attributed to the free energy of formation of ZnO from ZnS when these respective gases are used. The degradation rate also depended on the energy of the electron beam, decreasing with increasing beam energy. This was interpreted according to the ionisation energy cross-section profile. The CL brightness increased exponentially with the increasing energy beam as more free carriers that will subsequently recombine yielding CL, are excited at higher beam energies. The thin film phosphor was also subjected to the electron beam bombardment after the phosphor film was coated with a CdO film by using a chemical bath deposition (CBD) method. The surface reactions were electron beam stimulated, resulting in the desorption of both Cd and S from the surface which happened as soon as the surface adventitious C was depleted. Sulphur from the ZnS accumulated on the surface but was soon depleted as volatile SOx compounds. The CdO was reduced by an electron beam assisted mechanism in the presence of non-reducible ZnO in the CdO-ZnO system as the Zn from the underlying ZnS layer emerged to the surface. The CL intensity degradation of the coated film showed a dependence on the surface composition. The intensity remained constant until the Cd was reduced on the surface before a slight decrease was observed. The effect of the CdO capping layer on the intensity of the phosphor was evident until the CdO eventually disintegrated.
Open Access
A comparative study between the simulated and measured cathodoluminescence generated in ZnS phosphor powder
(University of the Free State, 2003-08) Chen, Sheng-Hui; Greeff, A. P.; Swart, H. C.
In the past few decades cathode ray tubes (CRTs) have dominated the display market because of their excellent image quality, ease and economy of manufacture. However their bulky packaging and high power consumption make them unsuitable for portable electronic devices. Field emission displays (FEDs) show the most potential amongst all other types of flat panel displays (FPDs). These FEDs have several advantages over the FPD market, which is currently dominated by active matrix liquid crystal displays (AMLCDs) and plasma displays (PDPs). FEDs generate their own light by a process referred to as cathodoluminescence (CL) in which phosphor powders inside the screen are excited in a similar manner to those used in CRTs. However, in contrast to CRTs, the accelerating voltage of electrons in FEDs is lowered in order to reduce the bulky packaging and the power consumption. Electrons with the reduced accelerating voltage have a shallower penetration depth and therefore the surface condition of the phosphor powder is critical in order to ensure proper functioning of the display. During the prolonged exposure of the phosphors to an electron beam, the phosphor surface is oxidised to form a non-luminescent layer. This electron stimulated oxide formation is due a chemical reaction between the phosphor and the residual gases in the sealed vacuum, e.g. oxygen and water vapour. Since the CL is dependent upon the energy loss of electrons in the phosphors, the CL decreases with the growth of the oxide layer on the phosphor surface. For high acceleration voltages, this oxide layer has little effect on the brightness of the CL, but as the accelerating voltage decreases as for FEDs, the layer has a much more profound effect. The ZnS:Cu,Al,Au (P22G) is a standard green phosphor commonly found in CRTs. In this study the P22G phosphor powder was bombarded by an electron beam in an oxygen ambient, argon ambient and other mixture of gases. These mixtures consisted of varying concentrations of oxygen, carbon monoxide and argon gas. Auger electron spectroscopy (AES) and cathodoluminescence spectroscopy were used to monitor changes in surface composition and luminescent properties of the P22G phosphor during electron bombardment. When the P22G phosphor powder was exposed to an electron beam in water-rich oxygen gas, a chemically-limited ZnO layer was formed on the surface. The CL intensity generated from carbon free P22G phosphor decreased linearly with the thickness of the ZnO layer. The experimentally measured thickness of the ZnO layer agrees very well with the calculated value of the theoretical simulation. The theoretical simulation of electron trajectories into the ZnO/ZnS powders was based on a Monte Carlo simulation and the CL intensity was quantified from the electron energy loss profile generated during the simulation. According to the results of the simulation, the effect of a ZnO layer on the CL is minimised by the use of a high energy electron beam at a low incident angle. The electron exposure of P22G phosphor powder was also performed in dry oxygen gas. A layer of ZnSO4 was formed on the surface after electron exposure. The sulphate formation decayed exponentially with time and it is postulated that this was due to the diffusion of the charge reactants through the sulfate film to reaction interfaces. The P22G phosphor exposed to the electron beam in argon gas and gas mixtures degraded more slowly than in oxygen gas. Argon gas and carbon monoxide gas may suppress the degradation of the P22G phosphor powder.
Open Access
'n Ondersoek na die segregasie van fosfor en ander onsuiwerhede in 3Cr12 vlekvrye staal
(University of the Free State, 2003-11) Vermaak, Christiaan; Roos, W. D.; Terblans, J. J.
English: One of the main reasons for temper embrittlement in steel is the segregation of impurities like P to the grain boundaries. Segregation can be defined as the diffusion of atoms from the bulk to the surface and grain boundaries in such a way that the total Gibbs free energy is minimized. This means that segregation can take place against the concentration gradient, from a low concentration in the bulk to a high surface concentration. The chemical potential gradient is the driving force behind segregation. The aim of this study is to investigate the segregation behaviour of P and other impurities like S and Sn in 3Cr12 steel. A background theory is founded by using: (i) The semi infinite solutions to the Fick equations (ii) t½ and modified t½ models (iii) the modified Darken model. One of the advantages of the Darken model is that it supported both segregation kinetics and equilibrium behaviour. The multi component model for ternary alloys could be expanded to quaternary alloy systems in this study. Segregation kinetics as well as the equilibrium was described by making use of constant and linear temperature heating. Auger electron spectroscopy was used to investigate the S, P, Cr, N, and Sn segregation behaviour in a Fe matrix. A personal computer was used to control the Auger spectrometer as well as the constant and linear heating runs. Three commercial 3Cr12 samples was investigated during the study. They were numbered according to their P contend as 26P for the sample with 0.026wt% P, 32P for 0.032wt% P and 62P for the sample containing 0.062wt% P. The constant temperature runs indicate that Sn competes with Cr, N and Pin sample 26P. A definite correlation is visible between Cr and N in sample 32P while Sn and S compete with P in sample 62P. The constant and linear heating Darken simulation model was used to give a qualitative description of the experimental segregation behaviour. The behaviour of two segregating species were simulated in a Fe matrix, from which the influence of the segregation parameters could be demonstrated, namely. If the surface concentration of species 1 is higher than that of species 2 during segregation kinetics, it can be said that the diffusion coefficient of species 1 is higher than that of species 2. If the surface concentration of species 1 is less than that of species 2, then the diffusion coefficient of species 1 is less than that of species 2. If the surface concentration of species 1 is less than that of species 2 at equilibrium, then the segregation energy of species 1 is less than that of species 2. If the equilibrium surface concentrations are equal, the segregation energies are equal. When the surface concentration of species 1 is higher than that of species 2, then the segregation energy of species 1 is higher than that of species 2. It is possible to sort the segregation parameters in order of magnitude from the results of the experimental work and the constant and linear heating simulations. The diffusion coefficients of the species could be arranged from high to low (DN > DP > DSn = DS). The segregation energies of samples 26P and 32P could be arranged in the same order, namely ?GS < ?GS n< ?GP
Open Access
A Monte Carlo program for simulating segregation and diffusion utilizing chemical potential calculations
(University of the Free State, 2004) Joubert, Heinrich Daniel; Terblans, J. J.; Swart, H. C.
Bulk-to-surface segregation plays a major role in the engineering of alloy surfaces. An increase in surface sensitive analysis techniques in recent years have led to big advances in the engineering of surface properties. The focus of this study is the development of a Chemical Potential Monte Carlo (CPMC) model which is based on the modified Darken model. This model is capable of simulating diffusion and segregation in crystals with a uniform concentration as well as crystals consisting of thin layers. The chemical potential equations used for the calculations by the modified Darken model are rewritten to include the segregation energy associated with the surface layer. The change in chemical potential directs atomic motion and simulations involving the change in chemical potential are performed on a 2-dimensional matrix containing two elements: the solute and the solvent elements. A random selection of an atom inside the matrix initiates the model. The change in chemical potential due to an atomic jump of a randomly selected atom to an adjacent layer is calculated. The largest change in chemical potential directs the atomic motion, complying with the conditions associated with the lowering of the Gibbs free energy; the driving force of atomic motion is therefore the lowering of the total crystal energy. Inclusion of the segregation energy (for jumps involving the surface layer) limits the number of atomic jumps from the surface layer to the bulk. Simulated segregation profiles generated by the CPMC model were compared with profiles calculated with both the modified Darken and Fick model. The comparisons show that the CPMC successfully describes both the kinetic and equilibrium conditions associated with surfa ce segregation. A reduction in calculation time was also achieved by implementing the CPMC model in parallel.
Open Access
Simulating ion sputtered depth profiles in Auger electron spectroscopy
(University of the Free State, 2004-05) Yohannes Tesfamicael, Biniam; Roos, W. D.; Terblans, J. J.; Wang, J. Y.
Recent developments in advanced materials technology are mainly based on the progress in surface and interface science. These surface and interface properties of materials greatly affect and control the overall properties of the materials. The reliable performance of multilayered thin- film structures in many technological applications like microelectronics, for instance depends upon the mechanical and chemical stability of the interfaces. Hence, appropriate study and analysis of the interfaces is an important aspect that has to be carried out with great precision. Depth profiling is one of the most powerful mechanisms in the analysis of surface and interfaces of thin multilayered structures. This depth profiling is accomplished by surface analytical techniques like AES and XPS accompanied by ion sputtering. The principal aim of this depth profiling is to investigate the distribution of elemental concentration with depth. The ion etching of the sample during the depth profiling, however, imposes some effects on the shape of the profile. The major causes for the profile distortion comes from Atomic mixing, Interface roughness, Information depth of the secondary emission and preferential sputtering in multicomponent systems. A model (MRI) that is often used in literature to simulate depth profiles in Auger electron spectroscopy takes into account the effect of atomic mixing, interface roughness and information depth. One of the radiation-induced factors limiting depth resolution is preferential sputtering. In this study the model was modified to incorporate the effect of preferential sputtering on the distortion of the depth profile. Although preferential sputtering is an exponential function it was treated as independent of the other contributing functions and in such a way as to add to the total depth resolution in quadrature, according to an error propagation law. One application of the model is in the determination of interdiffusion parameters in annealed multilayered thin film structures. In the experimental part of this study a Cu/Ni multilayer structure was evaporated onto a silicon substrate. The samples were annealed for different times in the temperature range 250 to 350ºC. This was followed by Auger depth profiling using Ar + sputtering with 3 keV primary ions at an angle 60º to the surface normal. Deconvolution of the overlapping Cu and Ni Auger spectra were performed followed by the calibration of the depth and concentration scales. In the process of simulating the measured depth profile the modified model yielded the contributions of atomic mixing, information depth, interface roughness and the ratio of the sputtering yields of Cu and Ni. The value of the interface roughness, expected to be a function of annealing temperature and time, was used to calculate the interdiffusion coefficient. The diffusion parameters Do = 4x10 -14 m 2 /s and the activation energy Q=69kJ/mol agrees excellently with values available in literature where grain boundary diffusion is the dominant diffusion process. These results confirm the successful modification of the MRI model.
Open Access
Secondary star surface magnetic activity and mass transfer in cataclysmic variables
(University of the Free State, 2005) Jurua, Edward; Meintjes, P. J.
In this study it is shown that secondary star magnetic fields influence the mass transfer process in close interacting binaries, especially cataclysmic variables (CVs) and thus play a fundamental role in the whole mass transfer process, and evolution of these systems. The Mestel and Spruit (1987) stellar wind theory is used to model the surface magnetic field of the secondary star in CVs, particularly the intermediate polars, constraining the angular momentum that is required to drive the observed mass transfer rate through Roche lobe overflow. This in turn allows solving for the mass transfer rates, via magnetic braking, and the surface polar magnetic field of these stars. These field strengths are used to study and constrain magnetic advection from the secondary star to the primary star, and its effect on the mass flow in the funnel in magnetic CVs. This has important consequences for the so-called magnetic viscosity in the accretion discs of disc accreting magnetic cataclysmic variables, which are fed by these magnetic secondary stars. It is shown that the mass transfer rates in these systems vary with orbital period, with lower mass transfer rates in more compact systems than in the wider systems. It is also shown that advection of magnetic flux into the funnel results in severe magnetic viscosity at the L1 region. The advected magnetic field into the funnel flow results in a magnetized flow and enhanced magnetic pressure in the L1 region. Since the magnetic pressure in the L1 region exceeds the flow ram pressure, continuous flow of material through the L1 region is prevented. It is shown that matter can easily cross the funnel if pressure builds up behind the barrier. This therefore implies that the mass transfer in these systems is not continuous but fragmented in the form of blobs.
Open Access
Surface segregation of Sn and Sb in the low index planes of Cu
(University of the Free State, 2005-05) Asante, Joseph Kwaku Ofori; Roos, W. D.; Terblans, J. J.
In this study, the segregation parameters for Sn and Sb in Cu were determined for the first time using novel experimental procedures. Sn was first evaporated onto the three low index planes of Cu(111), Cu(110) and Cu(100) and subsequently annealed at 920°C for 44 days to form three binary alloys of the same Sn concentration. Experimental quantitative work was done on each of the crystals by monitoring the surface segregation of Sn. Auger electron spectroscopy (AES) was used to monitor the changes in concentration build up on the surface by heating the sample linearly with time (positive linear temperature ramp, PLTR) from 450 to 900 K and immediately cooling it linearly with time (negative linear temperature ramp, NLTR) from 900 to 650 K at constant rates. The usage of NLTR, adopted for the first time in segregation measurements, extended the equilibrium segregation region enabling a unique set of segregation parameters to be obtained. The experimental quantified data points were fitted using the modified Darken model. Two supportive models - the Fick integral and the Bragg- Williams equations - were used to extract the starting segregation parameters for the modified Darken model that describes surface segregation completely. The Fick integral was used to fit part of the kinetic section of the profile, yielding the pre-exponenrial factor and the activation energy. The Bragg- Williams equations were then used to fit the equilibrium profiles yielding the segregation and interaction energies. For the first time, a quantified value for interaction energy between Sn and Cu atoms through segregation measurements was determined (ΩCuSn = 3.8 kJ/mol). The different Sn segregation behaviours in the three Cu orientations were explained by the different vacancy formation energies (that make up the activation energies) for the different orientations. The profile of Sn in Cu(110) lay at lowest temperature which implies that Sn activation energy was lowest in Cu(110). Sb was evaporated onto the binary CuSn alloys and annealed for a further 44 days resulting in Cu(111)SnSb and Cu(100)SnSb ternary alloys. Sn and Sb segregation measurements were done via AES. The modified Darken model was used to simulate Sn and Sb segregation profiles, yielding all the segregation parameters. Guttman equations were also used to simulate the equilibrium segregation region that was extended by the NLTR runs to yield the segregation and interaction energies. These segregation values obtained from the modified Darken model for ternary systems completely characterize the segregation behaviours of Sn and Sb in Cu. For the ternary systems, it was found that Sn was the first to segregate to the surface due to its higher diffusion coefficient, which comes about mainly from a smaller activation energy (ESn(100)= 175 kJ/mol and ESb(100) 186 kJ/mol). A repulsive interaction was found between Sn and Sb (ΩSnSb = - 5.3 kJ/mol) and as a result of the higher segregation energy of Sb, Sn was displaced from the surface by Sb. This sequential segregation was found in Cu(100) (∆GSb(100)= 84 kJ/mol; ∆GSn(100)= 65 kJ/mol) and in Cu(111) (∆GSb(111) = 86 kJ/mol; ∆GSn(l1l) = 68 kJ/mol). It was also found that the profile of Sn in the ternary systems lay at lower temperatures due the higher pre-exponential factor (DoSn(binary) = 9.2 x 10-4 m2/mol and DoSn(ternary) = 3.4 X 10³ m2/mol) if compared to the binary systems. This study successfully and completely describes the segregation behaviour of Sn and Sb in the low index planes of Cu.
Open Access
Surface segregation of Sn and Sb in the low index planes of Cu
(University of the Free State, 2005-05) Asante, Joseph Kwaku Ofori; Roos, W. D.; Terblans, J. J.
In this study, the segregation parameters for Sn and Sb in Cu were determined for the first time using novel experimental procedures. Sn was first evaporated onto the three low index planes of Cu(111), Cu(110) and Cu(100) and subsequently annealed at 920 oC for 44 days to form three binary alloys of the same Sn concentration. Experimental quantitative work was done on each of the crystals by monitoring the surface segregation of Sn. Auger electron spectroscopy (AES) was used to monitor the changes in concentration build up on the surface by heating the sample linearly with time (positive linear temperature ramp, PLTR) from 450 to 900 K and immediately cooling it linearly with time (negative linear temperature ramp, NLTR) from 900 to 650 K at constant rates. The usage of NLTR, adopted for the first time in segregation measurements, extended the equilibrium segregation region enabling a unique set of segregation parameters to be obtained. The experimental quantified data points were fitted using the modified Darken model. Two supportive models – the Fick integral and the Bragg-Williams equations - were used to extract the starting segregation parameters for the modified Darken model that describes surface segregation completely. The Fick integral was used to fit part of the kinetic section of the profile, yielding the pre-exponential factor and the activation energy. The Bragg-Williams equations were then used to fit the equilibrium profiles yielding the segregation and interaction energies. For the first time, a quantified value for interaction energy between Sn and Cu atoms through segregation measurements was determined (Ω.CuSn = 3.8 kJ/mol). The different Sn segregation behaviours in the three Cu orientations were explained by the different vacancy formation energies (that make up the activation energies) for the different orientations. The profile of Sn in Cu(110) lay at lowest temperature which implies that Sn activation energy was lowest in Cu(110). Sb was evaporated onto the binary CuSn alloys and annealed for a further 44 days resulting in Cu(111)SnSb and Cu(100)SnSb ternary alloys. Sn and Sb segregation measurements were done via AES. The modified Darken model was used to simulate Sn and Sb segregation profiles, yielding all the segregation parameters. Guttman equations were also used to simulate the equilibrium segregation region that was extended by the NLTR runs to yield the segregation and interaction energies. These segregation values obtained from the modified Darken model for ternary systems completely characterize the segregation behaviours of Sn and Sb in Cu. For the ternary systems, it was found that Sn was the first to segregate to the surface due to its higher diffusion coefficient, which comes about mainly from a smaller activation energy (ESn(100) = 175 kJ/mol and ESb(100) = 186 kJ/mol). A repulsive interaction was found between Sn and Sb (Ω.SnSb = - 5.3 kJ/mol) and as a result of the higher segregation energy of Sb, Sn was displaced from the surface by Sb. This sequential segregation was found in Cu(100) (ΔGSb(100) = 84 kJ/mol; ΔGSn(100) = 65 kJ/mol) and in Cu(111) (ΔGSb(111) = 86 kJ/mol; ΔGSn(111) = 68 kJ/mol). It was also found that the profile of Sn in the ternary systems lay at lower temperatures due the higher pre-exponential factor (DoSn(binary) = 9.2 × 10-4 m2/mol and DoSn(ternary) = 3.4 × 10-3 m2/mol) if compared to the binary systems. This study successfully and completely describes the segregation behaviour of Sn and Sb in the low index planes of Cu.
Open Access
The development of a UFS-Boyden Photometric pipeline to facilitate the observational study of accretion driven systems
(University of the Free State, 2005-05-30) Calitz, Johannes Jacobus; Meintjes, P. J.
After the retirement of professor A. Jarrett in 1986, the 1.5-m telescope at Boyden Observatory stood idle for a decade. With the appointment of Dr P. Meintjes, steps were taken to refurbish the telescope with an updated drive control and camera system, which would eventually enable the telescope to be operated as an astrophysical research instrument. After funding became available, upgrading of the drive mechanisms were undertaken by DFM during August and September 2001 and the new SpectraVision 1k 1k CCD camera, that was on loan from Lawrence Livermore National Laboratory (LLNL), was installed during February 2002. After 16 years, the telescope was ready to be used for gathering data for research projects. The camera was installed with only demonstration software. Software was needed to control the camera and also for data reduction and a photometry pipeline. During this project, the problems encountered with the baes, electronics and collimation in the telescope were analized and xed where needed and possible. Manuals were written for the general use of the telescope, as well as the reduction and photometry pipeline. Extinction coecients for Boyden Observatory were determined. Software were developed to control the PixelVision CCD camera. A CCD reduction routine that is easy and automatic as far as possible was written and implemented. A photometry pipeline that can be used with vast amounts of data, while producing a high level of accuracy were developed. The research elds that are making use of the software include gravitational microlens observations, accreting compact objects and Gamma Ray Burst afterglows. A brief overview of these elds are given.
Open Access
The effect of nitrogen on the cosegregation of molybdenum in a Fe-3.5wt%Mo-N (100) single crystal
(University of the Free State, 2006) Jordaan, Werner Albert; Terblans, J. J.; Swart, H. C.
In this study the cosegregation of molybdenum and nitrogen to the (100) plane of an iron single crystal was investigated. Ternary systems are considerably more complex than binary systems in that there are seven segregation parameters to determine, as opposed to three. However, a novel approach was undertaken to minimize the amount of variables, by first analysing a similar binary system that was exposed to a nitrogen ambient. Two single crystal were selected for this purpose, i.e. a Fe- 3.5wt%Mo(100) binary system and a Fe-3.5wt%Mo-N ternary system. By exposing the binary crystal to a nitrogen ambient at high temperatures it was observed that molybdenum segregated to the surface. The segregation profiles of the two systems were acquired at constant temperatures from 797 K - 888 K and Auger Electron Spectroscopy was used to monitor the surface concentrations of the relevant species. Since accurate surface temperature measurements are essential to segregation studies, a calibrated infrared thermometer was used. The segregation profiles were generated by measuring time and the Auger signal simultaneously. From the segregation profiles, initial estimates for the diffusion coefficients of Mo were first determined for the binary system by applying Fick’s equation to the segregation profiles. From these values the pre-exponential factor, D0, was determined to be 1.2x10−4±2 m2/s and the activation energy, E, as 258±33 kJ/mol. The diffusion coefficients determined thus, were used as estimates for obtaining the Darken seggregation profiles. In this case the D0 value was found to be 2.4x100±1 m2/s and the E value, 323±16 kJ/mol. The segregation energy, G, of Mo was calculated as -38 kJ/mol. In both cases it was observed that the diffusion coefficient of Mo deviated from the expected value at high temperatures due to the desorption of nitrogen from the surface. Using thermodynamic theory, an expression for the segregation energy of Mo in terms of the nitrogen surface concentration was derived. The Darken fits were repeated and it was found that the high temperature diffusion coefficient values fell on the the Arrhenius linear regression lines. For this special case, the D0 value was calculated as 5.5x101±1 m2/s, the E value as 345±18 kJ/mol. The segregation parameters determined for the binary system were then used as initial values for fitting the experimental data of the ternary system. Using Fick’s equation, the diffusion coefficients of Mo and N in Fe were determined. From the Arrhenius linear regression, the pre-exponential factor for Mo was calculated as 3.6x10−2±1 m2/s and that of N as 4.1x10−1±2 m2/s. The activation energies were 308±20 kJ/mol and 210±40 kJ/mol for Mo and N, respectively. The segregation parameters of the ternary system were then determined via the Darken method. In this case the pre-exponential factors were 1.9x10−4±1 m2/s for Mo and 2.8x100±3 m2/s for N. The activation energies were 271±11 kJ/mol and 323±43 kJ/mol. The segregation energy of Mo was calculated as -32 kJ/mol and for N, -19 kJ/mol. The interaction coefficient between Mo and N was calculated as -19 kJ/mol.
Open Access
Influence of the shape and size of a quantum struture on its energy levels
(University of the Free State, 2006-05) Harris, Richard Anthony; Terblans, J. J.; Swart, H. C.
In this study the importance of the luminescent properties of low-dimensional quantum structures are investigated focusing on the change in the exciton binding energy with a change in the size of the low dimensional QuantumWell or Wire. With a reduction in dimensionality, moving from bulk semiconductor materials through Quantum Wells, Wires and ultimately Quantum Dots, the band structure as well as the density of states for these low-dimensional structures change appreciably going from quasi-continuous in bulk semiconductors to discrete in Quantum Dots. This leads to an increase in the energy gap (compared to the bulk material), with a decrease in size for a low-dimensional structure. An interacting electron-hole pair in a Quantum Well-Wire is studied within the framework of the Effective-Mass Approximation. A mathematical technique is presented which investigates the quasi-two-dimensional, quasi-one-dimensional behavior of a confined exciton inside a semiconductor as the bulk material is reduced in dimensions to form a Quantum Well and Wire. The technique is applied to an infinite Well-Wire confining potential. The Envelope Function Approximation is employed in the approach, involving a three parameter variational calculation in which the symmetry of the component of the wave function representing the relative motion is allowed to vary from the one- to the two- and three-dimensional limits. A quasi–two-dimensional behavior occurs on reducing the well width as the average electron-hole distance decrease leading to an increase in the binding energy. However, when the well width is smaller than a critical value, the leakage of the wave function into the barriers becomes more important and the binding energy is reduced until it reaches the value appropriate to the bulk barrier material for which L = 0. As the electronic industry progress from micro-technologies to nanotechnologies whereby devices are designed in the nanometer range, it becomes increasingly necessary to address the concern of the exciton losing its enhanced effects in the ultra- small quantum structures, due to the increased penetration of the exciton wave function into the barrier regions in the direction of diminishing spatial confinement. A trial wave function is employed; written as a product of three wave functions. The first two are corresponding to the single particle wave function of an electron and a hole in the Quantum Well-Wire and the third represents a free exciton whose radius is adjusted as a variational parameter. This method can be suitably adapted for any particular choice of variational wave function. The choice of this wave function is only limited by the users’ qualitative knowledge of the system under consideration and how this knowledge is imbedded into this trial wave function. Results to this numerical calculation are presented. Quantitative comparisons with previous calculations for quantum wells was made (in the wire limit where Lz → ∞) and it was found that there exists a good agreement between this infinite- and other finite- as well as infinite - potential models up to a point of 100 Å. A plot of the binding energy vs. the variational parameter λ revealed that the electron in the exciton has a very similar behavior than the electron in the Hydrogen atom (or for that matter any particle trapped inside a radial decreasing (i.e. V~1/r) potential field). However on reducing the size and dimensions of the quantum structure, it seems that the screening of the other electrons surrounding the hole start to play a very important role and the shape of a plot of binding energy versus λ is very similar to that of an alpha particle trapped in an atomic nucleus. It is concluded from this that for accurately predicting the behavior of systems like these it is important to include in such a model not only the different dielectric constants for the barrier and the well-wire materials, but also to include the change in dielectric constant due to a change in size, i.e. ε = ε (L), i.e. to take into account the decrease in the amount of electrons in the valence band due to a decrease in size of the Quantum Well-Wire.
Open Access
CL degradation of Y2SiO5:Ce thin films coated with SnO2
(University of the Free State, 2006-05) Coetsee, Elizabeth; Swart, H. C.; Terblans, J. J.
The degradation of the cathodoluminescence (CL) intensity of cerium-doped yttrium silicate (Y 2SiO 5:Ce) phosphor thin films and commercially available Y2SiO5:Ce phosphor powders from Phosphor technology, England, were investigated for possible application in low voltage field emission displays (FEDs). Thin films of Y2SiO5:Ce were pulsed laser ablated on Si (100) substrates by using a XeCl (308 nm) excimer laser, in an oxygen (O) ambient gas pressure of 7.5 x 10-4 Torr, with laser energy of 81.81 mJ, repetition rate of 10 Hz, substrate temperature of 400°C, target to substrate distance of 3.7 cm and by using 6600 pulses. Some of the phosphor thin films were coated with tin oxide (SnO2), with the same deposition parameters as for the Y2SiO5:Ce phosphor layer except for the amount of pulses that was reduced to 1200 pulses. A SnO2 layer was ablated onto some of the thin films in order to investigate the effect of the coated layer on the surface and on the degradatio n of the CL intensity. Rutherford backscattering (RBS) was used to measure the film thicknesses. The results showed a non uniform Y2SiO5:Ce layer covered with a 58 nm thick SnO2 layer. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and energy dispersive spectroscopy (EDS) were use to study the surface morphology of the thin films. The results indicated that the Y2SiO5:Ce phosphor was ablated onto the Si (100) substrate surface as micron-sized spherical particles and that the SnO2 layer was ablated as a uniform coated layer covering the surface of the substrate and the randomly distributed spherical Y2SiO5:Ce particles. SEM was also use to study the surface morphology of the Y2SiO 5:Ce phosphor powders and the results showed that the particles were agglomerated. X-ray diffraction (XRD), that was used to measure the crystal planes of both the thin films and the powders, revealed the monoclinic crystal structure of Y2SiO5:Ce. Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and CL spectroscopy were used to monitor changes in the surface chemical composition and luminous efficiency of the Y2SiO5:Ce phosphor powders and thin films (coated and uncoated) . AES and CL spectroscopy measurementswere done with 2 keV energy electrons and with beam current densities between 26.3 mA.cm-2 and 52.63 mA.cm-2 , in high vacuum and in oxygen pressures of 1 x 10-8, 1 x 10-7 and 1 x 10-6 Torr. AES indicated adventitious carbon (C) on the surface before CL measurements were made. C was depleted from the surface during electron bombardment. Residual gas mass analysis (RGA) showed that C was removed from the surface as volatile gas species. RGA with the electron beam on resulted in a higher intensity of CO2, CO and H2O gas specie s, compared to when the electron beam was off. This is consistent with the electron stimulated surface chemical reaction (ESSCR) model, whereby the electron beam dissociates the oxygen gas species into reactive atomic species, which then reacts with the carbon on the surface to form the volatile CO2 and CO gas species. Auger peak to peak heights (APPH) for oxygen and silicon on both the uncoated thin film and the powder surface stayed almost constant. The CL intensity (measured at 440 nm) increased within the first 300 C.cm-2, which is the result of the depletion of the carbon from the surface, and then it stayed constant for prolonged electron bombardment. The carbon results in an extra layer on the thin film surface that increases the energy loss of the incoming electrons. This results in the creation of fewer electron – hole pairs for photon emission during radiative recombination. The CL emission spectrum resulted in the characteristic double shoulder peak of Y2SiO5:Ce with the two main peak positions at 440 and 500 nm (blue light) before and after 24 hr s of electron bombardment for the uncoated thin film, coated thin film and for the powders. Light emission in the rare earth, Ce3+, is due to the 5d ? 4f transition due to the splitting effects of the 4f energy level. The 4f energy level splits due to the effect of the crystal field in Y2SiO5 as the host material, into the 2F7/2 and the 2F5/2 energy levels. The broad band emission of Y2SiO5:Ce is the result of the different splitting effects due to the crystal field. The relatively high CL intensity of the thin films is attributed to the spherically shaped phosphor particles grown on the surface of the Si (100) substrate. The SnO2 was also successfully ablated as a coating layer. The SnO 2 coating layer increases the energy loss of the incoming electrons which results in a lower CL intensity. The CL intensity for the uncoated thin film was therefore higher than for the coated thin film. The CL intensity stayed almost constant for the 24 hr s of electron bombardment of both the coated and uncoated thin films. The CL intensity for the phosphor powders, however, behaved differently. The intensity showed an increase after about 300 C.cm-2. The CL emission spectrum showed an increase in a second broad band at a wavelength of 650 nm after 24 hr electron bombardment. It was proved with XPS that this second broad band is due to the formation of a luminescent silicon dioxide (SiO2) layer on the surface of the Y2SiO5:Ce phosphor powders, as a result of the electron surface stimulated reactions (ESSCR). The increase in the CL intensity is thus due to the luminescent SiO2 layer that was formed as a result of electron beam irradiation that causes the Si-O bonds to break and to form intrinsic defects at 1.9 eV (650 nm) and 2.7 eV (459 nm). XPS also indicated that the Ce concentration on the surface layer increased during the degradation process and the formation of CeO2 and CeH3 also resulted from the degradation process. The phosphor powders degraded from a blue light emitting phosphor before electron bombardment to a whit ish light emitting phosphor after 24 hr, as a result of the luminescent SiO2 layer formed during degradation.
Open Access
Oxygen-induced segregation during batch annealing of industrial steel coils
(University of the Free State, 2006-05) Wurth, Etienne; Swart, H. C.; Terblans, J. J.
The development of diffusion welds between spirals of steel coils, during batch annealing, is of particular interest because it preve nts the coils from being unwound for further use. The physical metallurgy of iron and steel is exceedingly complicated and many of the complications arise from the behaviour of solutes, which segregate to surfaces and interfaces, which alter the mechanical behaviour. Segregation studies were done by measuring the APPH’s (Auger Peak to Peak Heights) of the segregating species (P, S, C and Ti) against annealing time during the annealing of an ultra low carbon (ULC) Ti stabilized steel between 550 and 800oC. The modified Darken model was used to describe the complex segregation behaviour of the species involved during annealing of the industrial steel. This was done by comparing the initial changes in fractional surface concentration of the segregating species against annealing time to the trends in the surface concentration changes as describe by the Darken model for a ternary alloy. Calculations were done, using Langmuir-McClean equations, to determine the change in effective segregation energy as a function of oxygen surface coverage. Oxidation was allowed after sputtered cleaning and segregation, these oxidation results were compared with each other. No C segregation occurred without oxygen in the system. Oxygen induced-segregation of Ti and C occurred at 700oC and 800oC. Oxidation occurred at 700oC and 800oC. It was found that the adsorption of oxygen on the surface profoundly influence the segregation rate of the species involved. The modified Darken model was successfully used to describe the oxygen induced-segregation process. The induced segregation may act as a possible source of the diffusion welds during batch annealing.
Open Access
Kinetic Monte Carlo simulation of the growth of gold nanostructures on a graphite substrate
(University of the Free State, 2006-06) Claassens, Christina Hester; Hoffman, M. J. H.; Terblans, J. J.
Nanotechnology has, without a doubt, ushered in a new era of technological convergence and holds the promise of making a profound impact on the way research in physics, chemistry, materials science, biotechnology etc. are conducted. The novel properties of materials at the nanoscale (or nanostructures) make them useful in a variety of applications, from catalysis to the medical field and electronics industry. However, to exploit these properties at the nanoscale, precise control over the morphology and size of nanostructures is required. One strategy that may be explored to tailor nanostructure morphology and size is vapour deposition. A lot of further insight can be gained from computer simulations of the processes governing the growth of nanostructures during vapour deposition. A method that shows promise in simulating thin film growth through vapour deposition is kinetic Monte Carlo (KMC). Therefore, in this study, a KMC model was developed to describe growth through vapour deposition. A gold on graphite system was simulated to test the model. In this KMC model, substantial effort was devoted to developing the model in different stages, each stage being more robust than the previous one. The assumptions made at each stage and possible artefacts (unphysical consequences) arising from them are discussed in order to distinguish real physical effects from artificial ones. In the model, data structures, search algorithms and a random number generator were developed and employed in an object-orientated code to simulate the growth. Several simulations were performed at different growth conditions for each of the stages. The results are interpreted based on the kinetic constraints imposed during the growth.
Open Access
Surface analysis of white spot formation on industrial electrogalvanised automotive steel
(University of the Free State, 2006-11-30) Conradie, Rochelle; Swart, H. C.; Terblans, J. J.; Roos, W. D.
MSSA (Mittal Steel South Africa), which produces electrogalvanised steel for the local automobile industry, experiences a problem with white spot formation when their steel is phosphated. The addition of nickel inhibits white spot formation but produces an unacceptable discolouration of the surface layer. Furthermore the locally produced steel exhibits blister formation when heated to 300ºC. The substrates, electrogalvanised coatings, phosphated samples and annealed samples are studied with Glow Discharge Optical Emission Spectroscopy, Scanning Electron Microscopy, Energy Dispersive Spectroscopy, as well as X-ray diffraction. Combining the results allows for an interpretation of the morphology, topography, composition, crystalline structure, quantitative depth profile as well as the spatial distribution of the elements The white spot formation on the electrogalvanised surfaces is closely related to the presence of contaminants on the electrogalvanised surface and at the interface between the substrate and the electrogalvanised coatings. The accelerated phosphate reaction results in complete dissolution of the electrogalvanised surface, thereby exposing the iron substrate. The white spot consists of an anomalous protruding perimeter with elongated crystals that grow towards the centre of the spot, present inside the spot. Partial dissolution is required in order for the phosphate process to occur. Complex phosphates deposit on the surface comprised of various cations, such as zinc, manganese and nickel. The zinc dissolution is the preferred reaction and therefore there is a slight enrichment of nickel in the sublayers of the phosphate. The manganese deposited on the surface must not be confused with the manganese present in the substrate. The addition of other cations to the electrogalvanised layer results in a change in the structure of the phosphated layer. The presence of cobalt and copper in the electrolyte results in an increase in the deposition of manganese phosphates on the surfaces. The manganese phosphates grow upward, away from the surface as opposed to the zinc phosphates that grow along the sample surface. The growth of the zinc phosphates only continues until the surface is covered. The structure of the electrogalvanised deposits changes with changes in the composition of the electrolyte. The morphology changes from a well-defined rigid structure (as for the zinc electrolyte) to a complex structure consisting of both grains and a fine intricate network of small deposits as various cations such as nickel, copper and cobalt are added to the electrolyte. The surface of the steel substrate clearly shows the rolling direction, as well as numerous dislocations. This compromises the epitaxial growth of the electrogalvanised layer. The alloy elements added to the steel are also present on the surface. These react differently compared to the steel and will therefore impact on the nature of the deposition at these sites. The annealing of the electrogalvanised samples causes both structural and compositional changes in the samples. The movement of the zinc and possible dezincification are most likely responsible for the blister formation. This is further affected by the presence of hydrogen in the sample and the subsequent hydrogen blistering. It is of paramount importance for all the surfaces and parameters to be controlled and monitored carefully to ensure the best coating quality. The presence of any contamination on the surfaces or in the solutions will cause adverse reactions and compromise the final product.