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Realising the artificial chemical cell with vesiclesPasparakis, George January 2009 (has links)
Responsive biomedical materials span a plethora of applications in the biomedical field, from stents, hydrogels, degradable implants to drug delivery systems, and are in constant further development to give properties that ultimately improve the quality of life and prevent disease. In an effort to develop cell-interacting constructs we sought to synthesize polymers with bioresponsive and even “life-like” properties. By exploiting living polymerization techniques we aim to build self-assembled capsule-mimicking structures (i.e. vesicles) that can serve as prototype copycats of natural cell membranes. Also, we aim to establish a primitive communication platform of the artificial structures with their natural counterparts (i.e. bacterial cells) by using the “glyco-code” as a means of biochemical language. First, model thermoresponsive polymers are utilized that bear carbohydrate moieties to study polymer-cell interactions via multivalency and ligand-receptor interactions. The glycopolymers were found to induce bacterial aggregation of a specific bacterial strain through specific molecular recognition effects. In chapter three, block-copolymer vesicles are synthesized that comprise sugar groups on their coronae and also interact with bacteria through multiple specific ligand-receptor interactions. Also, molecular transport of a model dye from the vesicles to the bacterial cells is facilitated by discrete vesicle-bacteria complex formation. Chapter four explores the communication networks employed by bacterial cells, that is quorum sensing, and simple polymers are tested as molecular quorum quenchers that modulate the quorum sensing response of bacteria through autoinducers scavenging. Ultimately, we seek for an integrated platform to set up an “imitation game” where artificial entities, such as the polymer vesicles, can act as prototype cell-mimics that can actively intervene to the bacterial communication networks. Aspects of the principles and practical requirements to prove the concept are discussed in the final chapter.
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Microwave assisted synthesis of chalcogenide glassesPrasad, Nupur January 2010 (has links)
Chalcogenide glasses have several potential uses for new photonic devices for two reasons: i) their infrared (IR) transparency and ii) viscous flow at the glass transition temperature (Tg). Because of the latter, these glasses can be drawn to optical fibre and polished glass discs can be patterned above Tg for instance as planar waveguides. The fibre or waveguide shaped chalcogenide glasses have several potential uses as chemical sensors, biosensors, laser power delivery etc. and hence efforts have been made to synthesise high optical quality chalcogenide glasses. The well-established melt-quenching method was used as a comparative to prepare chalcogenide glass-melts in this project. Conventionally, the chalcogenide glass-melts are prepared using a rocking resistance furnace but this process is very long and cumbersome. To make the glass-melting process fast, simple and cost effective microwave heating was investigated instead in this project, and this was the main aim of the project. As2S3,Ge33As12Se55, Te20As30Se50 glasses were made with partial success and As2S3, Gel7As18Se65 glasses successfully, for the first time to the author's knowledge, through microwave heating in a domestic microwave oven (DMO) working at a frequency 2.45 GHz in less than an hour while the resistance heating method took about 1.5 days. The DMO output power was 800 W or 1000 W, and co-heating using both the microwaves and convection current heating to 220°C enabled some glass preparations to be carried out in ca. 10 minutes. The reactants were crushed manually for the DMO preparation of chalcogenide products keeping in mind that electric current tends to flow at the surface of the material which is known as 'skin effect'. The size of the silica glass melt-ampoule was kept as small as possible (normally - 10 cm) so that the DMO chalcogenide-melt could collect at the bottom of the ampoule and form a DMO chalcogenide rod product. The increased rate of reaction in the DMO compared to the rate of reaction in the rocking resistance furnace was attributed to the formation of plasma which caused a very high temperature (> 1000°C) of the reaction system leading to the almost instant melting of the some reactants. The boiling DMO chalcogenide-melt was seen in several cases but As/S = 2:3 (at%) did not boil when exposed to microwaves. Visually homogenous DMO chalcogenide-products were formed in each of the above stated compositions except in the case of DMO As-S product when four distinct layers could be seen. The red transparent portion of the DMO As-S sample was X-ray amorphous and showed no crystal feature in SAED (Selected area electron diffraction) using TEM (Transmission electron microscopy) whereas the non-glassy portion showed some crystalline peaks in XRD (X-ray diffraction) but showed no crystalline features in SAED. The DMO Ge/As/Se=33/12/55 (at%) rod product showed a single crystalline peak in the XRD pattern but it was completely amorphous according to SAED. On the other hand, the DMO Te/As/Se = 20/30/50 (at %) rod product showed slight evidence of crystallinity from SAED but was completely amorphous in XRD. DMO As/Se = 40/60 (at %) rod product and DMO Ge/As/Se= 17/18/65 (at %) rod did not show any crystalline structure from XRD and from SAED. The inhomogeneity of the DMO As-S glass was further reflected in the multiple Tgs observed using DTA (Differential thermal analysis) viz.:166°C, -194°C (broad) and 300°C in the first DTA run. Though, the sample showed a single Tg value of 202°C during the second DTA run after quenching in-situ the sample from the first DTA run. The stoichiometry of this glass wasAs43.9Se56.1 when observed through EDX (Energy dispersive X-ray analysis) which was performed using ESEM (Environmental scanning electron microscopy) showing that the glass was inhomogeneous. The DMO As/Se = 2:3 (at %) rod product showed a single Tg value of 180°C ± 5°C and the stoichiometry was found to be As40.1Se59.9 from EDX analysis which was very close to the desired value. The DMO rod product obtained from the composition Ge/As/Se = 17/18/65 showed a single Tg value of 246°C ± 5°C and the observed stoichiometry of the DMO chalcogenide product was Gel7.6As19.2Se63.5. Whereas the Ge32.8As11.0Se56.4 DMO rod product could be made from the batch composition Ge/As/Se=33/12/55 with a Tg value of 368°C ± 5°C but the conventionally prepared glass exhibited a stoichiometry Ge33.8As12.5Se50.6 with Tg value 371 DC± 5°C showing that a slight increase in percentage of germanium in the glass composition increases the Tg value. The Te19.6As30.4Se50.0 DMO rod product was obtained from Te/As/Se = 30/20/50 batch composition having a Tg value of 371°C ± 5°C showing that the experimental values for the stoichiometry and Tg of the product were very close to the desired value. A sample of Te/As/Se = 20/30/50 was heated in the DMO only for 5 minutes when stoichiometry of the product was found to be Te19.6As32.6Se47.8 showing that prolonged exposure of microwaves, which facilitated boiling, was important for homogenisation of the product (note that DMO As-S product never boiled) since the ampoule was not rocked inside the DMO. It was observed that optical absorption at 2.9 urn wavelengths due to hydroxide contamination for the DMO As-S product was reduced to - 3% of that of the AS2S3 glass made through conventional heating. The absorption bands for -OH group at 2.9 urn and H20 at 6.3 mum were very low in almost all the DMO products. Some carbon and silica contamination was found to be slightly larger in DMO products than that present in the conventionally prepared products and the reasons for this are not known at present. The DMO chalcogenide products were obtained reproducibly except in the cases of the DMO As-S product.
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C60 and its derivatives at Si surfaces : experimental and theoretical studies of electronic structurePhillips, Michael Andrew January 2004 (has links)
There has been a considerable amount of research into the effects of the modifcation of C60 on its properties in the bulk and at metal surfaces. Strong covalent interactions between C60, its derivatives, and a silicon substrate, however, are not well understood, nor is their role in determining the electronic properties of a modified fullerene film. In conjunction with existing knowledge concerning the behaviour of unmodified C60 at silicon surfaces, the study of modified C60 at these surfaces may provide some insight into the nature of the adsorbate{substrate interactions. Furthermore, if the tunability o®ered by fullerene modification is to be exploited in the production of novel nanoscale devices, an understanding of the role of these interactions is of key importance. From a theoretical perspective, modelling a fullerene{substrate system can prove to be computationally costly, and an approach to the reduction of this expense has been tested. Relative stabilities of various binding geometries of C60 to the Si(100)-(2 x 1) surface have been determined. Additionally, an agreement between experimental results and a rather simplistic model of the C60/Si interaction suggests that the electronic structure of C60 adsorbed at Si surfaces is not strongly dependent upon adsorption geometry --- much of the structure in the valence region is inherent to the formation of localised covalent bonds. Photoemission spectroscopy has been used to study alkali- and noble-metal doping of C60 at Si surfaces, and the effects of functional groups on electronic structure and adsorption. An alternative method for the determination of charge transfer from a dopant to the fullerene cage has been proposed and tested. The results show that a metallic phase of KxC60 can exist at the Si(111)-(7x7) surface, but not at the Si(100)-(2x1) surface, and that the LUMO-derived band is split, in both cases. In contrast to the considerable charge transfer seen upon adsorption of C60 at noble-metal surfaces, a Si substrate severely limits the interaction of both Ag and Au with thin films of C60. Furthermore, Au demonstrates an interaction with the encapsulated Si surface that is su±ciently strong to displace adsorbed C60. A mechanism for this interaction is proposed. Finally, the addition of phenyl groups to C60 is observed to have a profound effect on the chemistry of the fullerene cage itself.
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Metal-organic frameworks for platinum group metal extractionTrenholme, W. J. F. January 2016 (has links)
This Thesis describes the synthesis and characterisation of a variety of functionalised metal-organic frameworks (MOFs). These MOFs have been used for the extraction of platinum group metal (PGM) compounds from aqueous and organic solvents and for the storage of gases such as CO2, CH4 and the C2 hydrocarbons. Chapter 1 contains an introduction to PGM properties and uses with specific focus on the chemical properties which allow for separation of PGMs from base metal compounds and for separation between different PGM compounds. The synthesis and structure prediction of MOFs is then introduced, leading into an overview of the use of functionalised MOFs, especially those used for the encapsulation and extraction of metal ions from solution. General experimental techniques and details are described, as is the theory behind inductively coupled plasma optical emission spectrometry (ICP-OES), the most widely used analytical technique reported in this work. Chapter 2 describes the synthesis of chemically stable amine-functionalised Zr(IV) MOFs; UiO-68-NH2 and UiO-66-NH2, for extraction of PGM anions from aqueous and acidic solutions. ICP-OES was used to show that both materials exhibit close to 100% uptake of PtCl62- when present in just 3.5 equivalents per anion, comparable to the best materials reported for PtCl62- extraction. Furthermore, UiO-66-NH2 exhibited consistently higher PtCl62- uptake from aqueous solutions than four industrially used materials supplied by Johnson Matthey. Back-extraction of PtCl62- was demonstrated simply by heating the doped MOF in 4 M HCl, removing 99% of the PGM while maintaining the phase and crystallinity of UiO-66-NH2. Separation of PdCl62- from PtCl62- from acidic HCl solutions was exhibited by UiO-66-NH2, showing an exceptional selectivity of 20:1 for Pd:Pt from 2 M HCl. Likewise, 100% selectivity for PtCl62- and PdCl62- over CuCl2 and CuSO4 from acidic solutions was demonstrated, even in cases in which Cu was in 100-fold excess. Solid state NMR was employed to confirm the interaction between the framework and the PGM anions, with XPS results suggesting that the encapsulated Pt species within UiO-66-NH2 may be PtCl3(NH2)3 or PtCl4(NH2)2. Chapter 3 describes the synthesis and characterisation of a series of functionalised Cu(II) MOFs, NOTT-151, -155, -125 and -150, for the removal of neutral PGM complexes, Pd(OAc)2, PtCl4 and Rh2(OAc)4, from THF. The design of the MOFs allowed for an investigation into the effect of different topologies (ssa and fof), cage sizes and functional groups (amine, oxamide and methyl) on the uptake of each PGM complex. ICP-OES analysis showed that the MOFs were capable of extracting each PGM complex. The oxamide-functionalised NOTT-125 exhibited the most consistent uptake of Pd(OAc)2 with a maximum capacity of 35 mg g-1 (7 NH(CO)2NH groups per PtCl4). The amine-functionalised NOTT-155 showed the highest uptake of PtCl4, with a maximum capacity of 73 mg g-1 (4 NH2 groups per PtCl4). Uptake of Rh2(OAc)4 was generally low, however NOTT-125 showed a maximum extraction of 87 mg g-1 (3 NH(CO)2NH groups per PGM). The larger pore fof MOFs, NOTT-155 and NOTT-125, were more effective for each extraction than the MOFs of ssa topology, NOTT-151 and NOTT-150. However, of the ssa MOFs, amine-functionalised NOTT-151 was shown to give higher uptake of each PGM than the isostructural methyl-functionalised NOTT-150. This demonstrated the importance of incorporating a functional group capable of coordinating to the metal complex. Chapter 4 introduces the use of a nitrogen-rich triazine core in the synthesis of a variety of organic linkers to prepare MOFs for gas storage applications. The preparation of a novel 3,24-connected Cu(II) MOF of rht topology, denoted NOTT-160, is described and the structure characterised using X-ray crystallography. The material is shown to exhibit good uptake of C2 hydrocarbons with uptake of 128 cc g-1, 115 cc g-1, 110 cc g-1 for C2H2, C2H4, C2H6 respectively at 298 K and 1 bar (this becomes 212 cc g-1, 175 cc g-1 and 201 cc g-1 at 273 K and 1 bar). The selectivities of 79:1 and 70:1 calculated using Henry’s law for the separations of C2H2:CH4 and C2H4:CH4 respectively at 298 K are the third and second highest reported values for a MOF under these conditions. Ideal adsorbed solution theory (IAST) was also employed to calculate and predict these selectivities and shows agreement with the results obtained using Henry’s law. In addition, NOTT-160 shows an exceptional volumetric working capacity for CH4 of 221 cm3 cm-3 at 80 bar and 298 K. This is the second highest working capacity reported for a MOF under these conditions, with the excellent performance attributed to the high porosity and comparatively high crystal density of the material. Chapter 5 contains a summary of the work presented in this thesis.
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Carbon dioxide as a reagent and solventStreng, Emilia S. January 2017 (has links)
The work described in this Thesis has been carried out within the Erasmus Mundus framework for Sustainable Industrial Chemistry (SINCHEM). The work concentrates on the possible utilisation of carbon dioxide as a solvent and as a starting material. Chapter 1 introduces carbon dioxide and its utilisation. In addition, the 12 Principles of CO2 Chemistry are presented, as well as continuous flow chemistry and self-optimising reactors. The relevant aspects of these reactors are discussed further in Chapter 2. The results of the research are presented in Chapters 3-6. A self-optimising reactor with FT-IR analysis was employed for the methylation of alcohols as explained in Chapter 3. Chapters 4-6 concentrate on N-alkylation reactions. In Chapter 4, the reactivity between aniline, tetrahydrofuran and dimethyl carbonate in supercritical carbon dioxide is discussed. This research led to the discovery of novel transformations. In Chapters 5 and 6, methanol was employed to methylate amines. A ruthenium triphosphate catalyst, which can produce methanol from carbon dioxide and hydrogen, was used to catalyse the reactions between methanol and aliphatic amines, as described in Chapter 5. Also the cyclisation and subsequent methylation of amino alcohols was studied. This reactivity is also the topic of Chapter 6, where γ-alumina was used as catalyst and supercritical carbon dioxide as solvent. Finally, Chapter 7 summarises the work described in this Thesis and evaluates the progress made towards achieving the aims that are introduced at the end of Chapter 1. One of these aims is to evaluate the work carried out in this Thesis according to the 12 principles of CO2 Chemistry. This evaluation is shown in Chapter 7.
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Structure and surface reactions of iodine and cadmium iodide on fcc(111) metal surfacesFisher, Christopher John January 1999 (has links)
Structural studies using the synchrotron based Normal Incidence X-Ray Standing Wave (NIXSW) technique of the copper(III)- √3x√3))R30 grad.-Iodine and copper(111)- √3x√3)R30grad.-1/2(CdI2) surfaces are presented. For the copperiodine system, the iodine was shown to adsorb in a mixture of fcc and hcp hollow sites at a distance of 2.16 ± 0.05A from the copper surface, in a (√3x√3))R30 grad. mesh. The hollow site ratio observed was 50 ± 3 % in fcc sites and 50 ± 3 % in hcp sites. For the copper-cadmium iodide system, the iodine was again shown to adsorb in a mixture of the three fold hollows, at a slightly smaller distance of 2.10 ± 0.05A from the copper surface, again in a (√3x√3)R30 grad. mesh. The ratio of occupation of the hollow sites was determined to be 37 ± 3 % in fcc sites and 63 ± 3 % in hcp sites. The copper(111)-( √3x√3)R30 grad.-Iodine surface produced by annealing the copper(111)- 1/2(CdI2) surface, was shown to have a different ratio again, at 80± 3 % in fcc sites and 20 ± 3 % in hcp sites. Possible explanations for the changing ratios are discussed including sample temperature during surface preparation, step density of the crystal, co-adsorption of adsorbate or contamination and surface coverage. The cadmium in the copper-1/2(CdI2) surface was shown to be adsorbed randomly in a mixture of the three fold hollow sites, at 2.25 ± 0.05A from the copper surface. The ratio was found to be 48 ± 3 % in fcc sites and 52 ± 3 % in hcp sites. Both studies were found to be affected by the presence of non-dipole effects in the angular distribution of the core level photoelectrons used to collect some of the data. This caused incorrect values for the standing wave structural parameters to be determined, A novel experiment was performed using two analyser geometries which enabled the importance of including the non-dipole terms in the standing wave equations to be confinned. An updated version of the standing wave equations is presented which allows quantification of and correction for the non-dipole terms. The surface reactions of iodine and cadmium iodide on an aluminium(111) surface at room temperature are shown to result in etching of the surface and the production of aluminium iodide (A1I3). For both systems, iodine forms a close-packed chemisorbed layer that has a (..J7x-..J7)R19.1° symmetry, with an iodine coverage of 3/7 of a monolayer. For the cadmium iodide surface, the cadmium is proposed as being located randomly above the chemisorbed iodine layer. With the sample liquid nitrogen cooled to low temperatures, iodine produced physisorbed multilayers, and cadmium iodide adsorbs intact, but with no ordered growth. A novel technique, Line Of Sight Sticking Probability (LOSSP), which allows the measurement of sticking and reaction probabilities is presented and applied to the I/Al system. The initial sticking probability for iodine at 300 K was determined as 0.8 ± 0.1. Under steady state etching conditions at 300 K the overall reaction probability for I2 to form AlI3, was, Rss = 0.36 ± 0.07. The surface consisted of a majority of chemisorbed iodine, with a minority of coadsorbed AlI3, with a total iodine coverage of ~ 0.6 ML. The sticking probability of I2, to solid iodine at 103 K was measured as Sphys = 0.98 ± 0.02, while the sticking probability on the halogenated surface at 300 K was measured as ~ys > 0.8 ± 0.1 Variable temperature measurements gave an activation energy for the desorption of All, of approximately 57 kJmol-1.
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Continuous hydrothermal synthesis of inorganic nanoparticlesEvans, Edward January 2006 (has links)
In Chapter 1, the special properties of nanoparticles are discussed, followed by different methods of nanoparticle synthesis, particularly the hydrothermal flow synthesis. Finally, factors thought to affect particle size are identified, and the aims of the Thesis are stated. In Chapter 2, hydrothermal flow reactors used by different research groups are discussed. Modelling of the reactor mixing point leads to a new nozzle design, to improve mixing and avoid blockages, which is incorporated into the Nottingham reactor. In Chapter 3, it is explained how initial problems of reactor blocking are solved, and that formation of CuO is seen to be affected by reaction temperature and which precursor is used. Chapter 4 details how Ru02 and anatase Ti02 are made separately, and unsuccessful attempts are made to produce rutile Ti02 and a single-phase mixed-metal (Ru-Ti) oxide compound. Chapter 5 describes how an efficient method of separating CexZr1-x02 particles from suspension was found. This allowed the identification of a dependence of particle size upon reaction temperature. In Chapter 6, the effect of increasing temperature upon formation of α-Fe203 particles was investigated, and found to give larger particles and greater yields. Particles with different size distributions were then used as catalyst for the growth of carbon nanofibres, leading to the formation of different nanofibre structures. Chapter 7 reports how successful preliminary experiments were made to form Ag and CdS nanoparticles using the hydrothermal flow method. Finally, in Chapter 8, the achievements of this Thesis are summarised and ideas are put forward for future work.
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The detection and measurement of hydrogen sulphideDeuchar, Christopher Norton January 2003 (has links)
Gas measurement techniques for hydrogen sulphide (H2S) have been investigated, with particular reference to the monitoring of average ambient concentrations and also the rapidly changing concentrations which may be associated with vehicle pollution. Two new techniques have been identified, and new equipment built and tested, for H2S determination. The first of these is designed to measure long term average concentrations of H2S and the second to evaluate rapidly changing peak concentrations over very short periods of time. The implementation of catalytic converters in modern petrol driven motor vehicles has resulted in undesirable emissions of hydrogen sulphide gas. The reasons for these emissions are discussed. Ambient concentrations of H2S have been measured at the roadside and the average contribution originating from vehicular emissions on major roads determined. Results are presented which confirm the elevation of hydrogen sulphide concentrations at the road side of an average of single figure parts per billion. Peak H2S concentrations of up to 100 ppb were also measured at the roadside and within motor vehicles. The peaks were of very short duration and therefore of only minimal contribution to average ambient concentrations. Measurements of H2S concentrations at a variety of locations have also been made,and results are presented, of comparisons between areas with no source of H2S nearby, roadside sites and other possible H2S sources such as sewage treatment works and landfill sites. Known H2S concentrations, in excess of 500 ppm from a point source on a landfill site, were found to diminish rapidly toward zero, within 150 m of the source. This demonstrated the high reactivity of H2S and therefore the importance of measuring H2S concentration as closely as possible to the emission source. Consequently, this high reactivity is particularly important in the consideration of roadside and 'on-road' monitoring of H2S.
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Environmental and biological tin and lead chemistryHealy, Michael Anthony January 1980 (has links)
Tin and lead are metals of considerable commercial importance and are used in many forms in the environment. Heat and light stabilization of polyvinylchloride polymer by organotins is now a principle application of that metal. The spectroscopic properties and crystal structures are determined for some estertin precursors of these stabilizers: mono and bis-(beta-carbomethoxyethyl) tin chlorides, as well as the bis-(beta-carbomethoxyethyl) tin dichloride analogue. The feasibility of using Mössbauer spectroscopy to determine the fate of the organotin species within the PVC is also assessed. The INDOR technique is used to obtain tin-119 n. m. r. data for a series of trimethyl and dimethyltin(IV) compounds and the results interpreted in a manner illustrating the use of this method as a structural probe for the solution chemistry of organotin systems. In the case of lead, attention is given to the effects of use of that metal in petrol by examining its overall distribution pattern in the dust, soil, grasses, plants and fruit of a roadside environment. Additionally a new aetiology of lead poisoning involving some traditional Asian medicines and cosmetics is also described and a route for gastrointestinal absorption of lead sulphide from this source proposed. The effect of particle size on uptake rate is established. A chemical model for interaction between body-phosphate systems and lead derived from such sources as those studied is designed. The reactions found to occur between lead acetate, lead nitrate and dimethylphosphite and trimethylphosphate are interpreted. Preliminary studies show reaction between lead and adenosine di- and triphosphate and the data obtained from the model systems are used to elucidate the reaction pathway with these body-phosphate systems.
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A structural study of mercury adsorbed on single crystal metal surfacesBastow, Sarah Louise January 1997 (has links)
The Normal Incidence X-Ray Standing Wavefield technique has been used to study the adsorption of mercury on two single crystal metal surfaces, Ni(111) and Cu(100). The three Hg/Ni(111) structures studied were (√3x√3)R30°-0.33ML, p(2x2)-0.SML and "c(2√3x2√3)R30°"-0.64ML. A well-ordered, commensurate mercury adlayer is postulated, which has a low frequency (or soft) phonon mode parallel to the surface. Such a surface is well ordered and will give good LEED patterns, but the large distribution of distances relative to the (111) set of planes leads to a low coherent fraction, in agreement with the (111) NIXSW data. The Hg/Cu(100) structures studied were two equilibrium structures, c(2x2)-0.SOML and c(4x4)-0.62ML and two nonequilibrium structures, (3x3)-0.66ML and c(2x6)-0.83ML. In agreement with the literature, the NIXSW analysis of the lowest coverage Cu(100)/Hg-c(2x2)-0.SOML structure indicated mercury adsorption into the most energetically stable four-fold hollow sites. However, the NIXSW analysis of the Cu(100)/Hg-c(4x4)-0.62ML structure appears to disprove the mercury coincidence net proposed by previous authors. Our model proposes that some of the mercury atoms adsorb exactly in energetically favourable four-fold hollow sites whilst some reside in sites slightly off the four-fold hollow position. The Cu(100)/Hg-(3x3)-0.66ML structure is found to consist of two domains, each containing mercury atoms adsorbed equally in both bridge and four-fold hollow sites and differing only in the type of bridge sites occupied by the mercury adsorbate atoms. Finally, the NIXSW data of the highest coverage Cu(100)/Hg-c(2x6)-0.83ML structure, was found to indicate a model combining a slightly rumpled overlayer with more than a monolayer of adsorbate atoms to fit the experimental NIXSW data presented here.
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