The aim of this study is to synthesize a material with high thermal conductivity and a low coefficient of thermal expansion (CTE), useful as a heat sink. Carbon nanofibres (CNF) are first coated with copper by an electroless plating technique and then sintered to a solid sample by either spark plasma sintering (SPS) or hot pressing (HP). The final product is a carbon nanofibre reinforced copper composite. Two different fibre structures are considered: platlet (PL) and herringbone (HB). The influence of the amount of CNF reinforcement (6-24 %wt), on the thermal conductivity and CTE is studied. CNF has an excellent thermal conductivity in the direction along the fibre while it is poor in the transverse direction. The CTE is close to zero in the temperature range of interest. The adhesion of Cu to the CNF surface is in general poor and thus improving the the wetting of the copper by surface modifications of the fibres are of interest such that thermal gaps in the microstructure can be avoided. The poor wetting results in CNF agglomerates, resulting in an inhomogeneous microstructure. In this report a combination of three different types of surface modifications has been tested: (1) electroless deposition of copper was used to improve Cu impregnation of CNF; (2) heat treatment of CNF to improve wetting; and (3) introduction of a Cr buffer layer to further enhance wetting. The obtained composite microstructures are characterized in terms of chemical composition, grain size and degree of agglomeration. In addition their densities are also reported. The thermal properties were evaluated in terms of thermal diffusivity, thermal conductivity and CTE. Cr/Cu coated platelet fibres (6wt% of CNF reinforcement) sintered by SPS is the sample with the highest thermal conductivity, ~200 W/Km. The thermal conductivity is found to decrease with increasing content of CNFs.

This work examines the selective deposition of metallic and semiconductor materials onto DNA templates for the fabrication of nanodevices. DNA origami provides a simple and robust method for folding DNA into a variety of shapes and patterns and makes it possible to create the complex templates needed for nanodevices, such as nanoelectronic circuits, plasmonics, and nanosensors. Metallization of DNA origami templates is essential for the fabrication of such nanodevices. In addition, selective deposition of semiconductor materials onto the DNA template is of importance for making many nanodevices such as nanocircuits. Metallization of DNA origami presents several challenges beyond those associated with the metallization of other DNA templates such as λ-DNA. All of these challenges were addressed in this study. DNA origami templates were seeded with Ag and then plated with Au via electroless deposition. Selective continuous metal deposition was achieved, with an average metallized height as small as 32 nm. The structure of T-shaped DNA origami was also retained after metallization. Following the metallization of complete origami, site-specific metallization of branched DNA origami was also demonstrated. To achieve this, staple strands at select locations on origami were replaced with staple strands modified with binding sites at the end. These binding sites then attached to thiolated DNA coated Au nanoparticles through base pairing. The continuous Au nanowires formed at designated sites on DNA origami after Au plating had an average width of 33 nm, with the smallest ones ~20 nm wide. The continuity of nanowires was verified by conductivity tests- the only tests of this nature of which I am aware. Moreover, predesigned sites on "circuit-shaped" DNA origami were successfully metallized. The selective deposition of a variety of materials onto DNA templates for the formation of continuous DNA-templated nanowires was also demonstrated. Specifically, an electroless Ni plating solution was developed to enable the fabrication of uniform and continuous DNA-templated Ni nanowires. Tests showed that these DNA-templated Ni nanowires were conductive. Moreover, continuous DNA-templated Bi2Te3 and/or Te nanowires have been fabricated through galvanic displacement of DNA-templated Ni and Cu nanowires. Altogether, these results represent important progress toward the realization of DNA-templated nanofabrication.

Composite thin Pd/Ag alloy membranes with long-term thermal and chemical stabilities have potential applications for H2 separation via catalytic membrane reactors and may be one of the key determinants to achieve the 21st century's global hydrogen economy. This work provides a detailed microstructure characterization study and a better understanding of the fundamental principles involved in the synthesis of a novel Pd/Ag intermetallic diffusion barrier formed by the bi-metal multi-layer (BMML) deposition technique. The BMML deposition technique formed an extremely effective Pd/Ag intermetallic diffusion barrier and significantly improved the thermal and long-term stability of the composite Pd and Pd/alloy membranes over a temperature range of 500-600oC. In addition, high temperature annealing studies over a temperature range of 500-800oC in H2 atmosphere led a thorough understanding of the surface interactions and the phase changes between the Pd and Ag metals and the porous metal support elements (Fe, Cr and Ni) and it was shown by the SEI, EDX and X-ray phase analyses that the Ag/Fe and Ag/Ni binary systems exerted complete immiscibility compared to the completely miscible solid solutions of Pd/Fe and Pd/Ni phases. A novel characterization method of in-situ time-resolved high temperature X-ray diffraction (HTXRD) analysis was used to elucidate the mechanistic details of the isothermal nucleation and growth kinetics of the Pd/Ag alloy phase over a temperature range of 500-600oC in H2. The nucleation of the Pd/Ag alloy phase was instantaneous where the growth mechanism was through diffusion-controlled one-dimensional thickening of the Pd/Ag alloy layer. The Pd/Ag alloy phase growth was strongly dependent upon the deposition morphology of the as-synthesized Pd and Ag layers due to the presence of the heterogeneous nucleation sites. Based on the empirical rate constants derived from the solid-state reaction models, the estimated activation energies for the Pd/Ag alloy phase transformation were 236.5 and 185.6 kJ/mol and in good agreement with the literature values of 183-239.5 kJ/mol. The successful utilization of surface modification techniques and modified plating conditions led to the synthesis of several dense Pd/Ag layers, which were as thin as 5-15 µm with a bulk Ag content in the 10-40 wt% range. The long-term testing of the composite Pd/Ag membranes (5-15 µm) at 500oC showed stable hydrogen permeances as high as 30 to 54 m3/m2-h-atm0.5 with H2/He selectivities ranging from 200 to 14000. Furthermore, the atomic absorption flame analysis was used for the first time to elucidate the effects of temperature, initial metal ion concentration, initial hydrazine concentration and bath agitation on the electroless plating rates of Pd and Ag. The electroless plating of both Pd and Ag were strongly affected by the external mass transfer in the absence of bath agitation. The external mass transfer limitations for both Pd and Ag deposition have been overcome at or above an agitation rate of 400 rpm, resulting in a maximum conversion of the plating reaction and dramatically shortened plating times with the added advantage of uniform deposition morphology as evidenced by the SEI micrographs. Finally, the agitation rate of 400 rpm was successfully employed for the synthesis of composite Pd and Pd/Ag membranes. The H2 permeance for a 4.7 µm thick pure-Pd membrane at 400oC was as high as 61 m3/m2-h-atm0.5 with H2/He selectivity over 310 after a total testing period of 690 hours.

Magnesium and its alloys are extensively used for various industries such as aerospace, automobile and electronics due to their excellent properties such as low density, high strength and stiffness and electromagnetic shielding. However, the wide spread applications of these alloys are limited due to the undesirable properties such as poor corrosion, wear and creep resistance and high chemical reactivity. These alloys are highly susceptible to galvanic corrosion in sea water environment due to their high negative potential (-2.37 V vs SHE). The effective way of preventing corrosion is through the formation of a protective coating, which acts as a barrier between the corrosive medium and the substrate. Many surface modification methods such as electro/ electroless plating, conversion coating, physical and chemical vapour depositions, thermal spray coating etc., are available currently to improve the corrosion resistance of Mg alloys. Of these methods, the electroless nickel plating has gained considerable importance because of its excellent properties such as high hardness, good wear and corrosion resistance. The properties of binary electroless nickel coating have been further improved by the addition of a third element such as cobalt, tungsten, tin and copper etc. It has been reported that the addition of tungsten as the third element in the Ni-P improves the properties such as hardness, wear and corrosion resistance, thermal stability and electrical resistance. Magnesium alloys are categorized as a “difficult to plate metal”, because of their high reactivity in the aqueous solution. They react vigorously with atmospheric oxygen and water, resulting in the formation of the porous oxide/ hydroxide film which does not provide any protection in the corrosive environment. Further, the presence of this oxide film prevents the formation of a good adhesive bond between the coating and the substrate. The surface treatment process for removal of the oxide layer is very much essential before plating the Mg alloy. Currently two processes such as zinc immersion and direct electroless nickel plating are adopted to plate Mg alloys. Etching in a solution of chromate and nitric acid followed by immersion in HF solution to form a conversion film is necessary for direct electroless nickel (EN) plating of Mg alloy. However, strict environmental regulations restrict their usage because of hazardous nature. Expensive palladous activation treatment is a well-known process as a replacement for chromate-HF pretreatments for Mg alloys. It has been reported that EN plating has been carried out over Mg alloys by using conversion coating followed by HF treatment. Formation of an intermediate oxide layer by electrolytic methods is also one of the ways these toxic pretreatments can be avoided. Microarc oxidation (MAO) is an environment friendly surface treatment technique which provides high hardness, better corrosion and wear resistance properties for the Mg alloys. EN coating has been prepared on MAO layer for improving the corrosion resistance. These MAO/EN composite coatings have been prepared using chromic acid and HF pretreatment process. As the replacement for the chromate-HF pretreatment, SnCl2 and PdCl2 sensitization and activation procedures respectively were adopted over MAO layer for the deposition of Ni-P coating. From the above reported literature, it can be inferred that for the activation of inert MAO layer to deposit electroless nickel coating, the hazardous chromate/HF and highly expensive PdCl2 activation processes were followed. Therefore, there is a need for identifying an alternative simple and cost effective pretreatment process for the deposition of electroless nickel. It is well known that borohydride is a strong reducing agent that has been used for the deposition of Ni-B coatings. In the present study, an attempt has been made to utilize borohydride in the pretreatment process for the reduction of Ni2+ ions over the MAO interlayer, which provides the nucleation sites for the deposition of Ni-P coating. Ni-P and Ni-P/Ni-W-P duplex coatings were deposited from stabilizer free carbonate bath on AZ31B Mg alloy to improve the corrosion resistance of the base substrate. The conventional chromate and HF pretreatment processes were followed for the deposition of electroless nickel coating. In order to improve the corrosion resistance of the duplex coating, post treatments such as heat treatment (4 h at 150°C) and chromate passivation were adopted. EDX analysis of AZ31B Mg alloy showed the presence of 2.8 wt.% of Al and 1.2 wt. % Zn with the balance of Mg for AZ31B Mg alloy. After the chromic acid and HF treatment, the magnesium content was reduced from 90.0 wt % to 54.9 wt%, which could be due to the incorporation of chromium on the surface layer. The surface showed about 17.8 wt. % of F. The alloy exhibited the roughness of about 0.29± 0.01µm after mechanical polishing. The roughness value was significantly changed after the chromic acid treatment processes. The maximum roughness of about 1.28±0.06 µm was obtained after the HF activation. XPS analysis confirmed the existence of chromium in +3 oxidation state after the chromic acid treatment. The Ni-P coating thickness of about 25 microns was obtained in 1 h and 15 min. In the case of duplex coatings, Ni-P plating was done for 45 min. to obtain approx. 17 microns thickness and Ni-W-P plating was done for 1.15 h to obtain a thickness of approx. 10 microns, resulting in a total thickness of 25 ± 5 microns. Ni–P coating exhibited nodular morphology with porosity. The size of these cluster nodules were of about 10 µm in diameter. On the other hand, the duplex coating exhibited a less nodular, dense and smooth appearance. From the compositional analysis it was found that Ni–P coating contained about 6 wt. % P. In the case of duplex coating, the P content was reduced to 3 wt % due to the incorporation of about 2 wt% of tungsten. In corrosion studies, the potentiodynamic polarization data obtained for bare Ni-P coating in 0.15 M NaCl solution exhibited a higher current of about 218 μA/cm2 as compared to the substrate due to the porosity of the coating. However, the Ni-P/Ni-W-P duplex showed 55 times improvement in corrosion resistance, vis-a-vis Ni-P due to the dense nature of the coating. The corrosion resistance of the coatings increased in the following order: Ni-P < bare alloy < duplex < duplex-passivated < duplex-heat treated passivated. In EIS study, the Nyquist plot obtained for the bare substrate and Ni–P coating showed the presence of inductance behavior at the lower frequency region due to the adsorption of electroactive species over the substrate through the porous oxide layer. However, the passivated and duplex passivated coatings exhibited only capacitive behavior due to their compact nature. From the above, it can be concluded that, direct deposition of Ni-P coating over the chosen Mg alloy using chromic acid and HF pretreatment process resulted in porous morphology, which affected the corrosion resistance of the coating. As an alternative strategy, the microarc oxidation conversion coating was developed on Mg alloy and characterized. The MAO coating was developed using silicate electrolyte at three different current densities (0.026, 0.046 and 0.067 A/cm2) for about 15 min. With respect to the MAO coating, an increase in the current density increased the pore diameter and decreased the pore density. The surface of the coating became coarser and rough. The cross-sectional morphology of the coating showed two district layers namely the dense and thin inner layer and a porous thick outer layer. The thickness of the coating increased with increase in current density. MAO coating prepared at an intermediate current density of 0.046 A/cm2 exhibited a higher thickness of about 12 µm and a further increase in current density showed a decrease in thickness, due to the greater rate of dissolution of Mg, relative to the rate of deposition. The surface roughness of the MAO coatings also increased with increase in current density. The Ra value increased from 1.39±0.06 to 3.52±0.17 µm with increase in current density. XRD peaks obtained for the Mg substrates corresponded predominately to magnesium. However, the coated specimens showed the presence of peaks corresponding to Mg2SiO4 along with Mg and MgO. The corrosion measurements for the bare substrate and MAO coatings were carried out in 3.5% NaCl medium (0.6 M). Based on potentiodynamic polarization studies, the MAO coating prepared at 0.046 A/cm2 exhibited a lower corrosion current density with a higher Rp value, which was about five orders of magnitude higher than the bare substrate, due to the dense nature of the coating. In EIS study, MAO coatings were fitted with the two time constants equivalent circuit containing outer porous layer and inner barrier layer. The barrier layer resistance values were higher than that of porous layer resistance, which indicated that the resistance offered by barrier layer was higher than the porous layer. The total resistance value obtained for the coating prepared at 0.046 A/cm2 were higher compared to the other coatings, which attested to its better corrosion resistance. The electrochemical noise measurement was carried out for longer immersion durations upto 336 h in 3.5% NaCl solution. The noise resistance value obtained for the base Mg alloy was about 100 Ω at 1h immersion, whereas for the MAO coating prepared at 0.04 A/cm2 a maximum value of about 34.8 MΩ was achieved and it was retained even after 96 h of immersion. Mott–Schottky analysis showed that the oxide layer on magnesium substrate acted as a n-type semiconductor, whereas the MAO coatings exhibited p-type semiconductor behavior. The MAO coating obtained at an intermediate current density showed a higher acceptor density and the flat band potential, which resulted in the better performance of the coating in corrosive environment. In another set of investigations, the Ni-P and Ni-P/Ni-W-P coatings were deposited on AZ31B Mg alloy with MAO coating as an interlayer. The MAO layer was activated by a simple borohydride pretreatment process. During the pretreatment process, the MAO coating was subjected to mild alkali treatment, immersion in the Ni-P plating solution and finally immersion in borohydride solution. During each pretreatment step, the sample was characterized for their surface morphology and composition. The surface morphology showed the distribution of spherical particles over the surface of MAO coating after immersion in the Ni-P plating solution. EDX analysis showed the presence of 2.4 wt. % of Ni, which confirmed that Ni ions were adsorbed over the surface of the MAO coating during the pretreatment process. XPS analysis carried out after immersion in the Ni-P plating solution indicated that Ni existed in +2 oxidation state. The surface became smooth and uniform with flake- like morphology after the borohydride treatment, which indicated that the surface was etched by the borohydride solution. EDX analysis showed the presence of 1.8 wt.% of Ni after borohydride reduction. XPS analysis confirmed the reduction of nickel to the zero oxidation state. Additionally, MAO/Ni-P and MAO/Ni-P/Ni-W-P duplex coatings were developed on MAO coating after a simple borohydride pretreatment. Ni-P and duplex coatings showed uniform and dense nodular morphology without any defects, which clearly indicated that the borohydride treatment provided a uniform and homogeneous active surface for the deposition of electroless nickel based coatings. Borohydride pretreatment process resulted in excellent bonding between MAO/Ni-P layers in the cross section. Based on potentiodynamic polarization studies, the corrosion current values obtained for MAO/ Ni-P and MAO/Ni-P/Ni-W-P duplex coatings were about 1.44 and 1.42 µA/cm2, respectively. The coating showed about 97 times improvement in corrosion resistance compared to the bare substrate, attesting to the dense nature of the coating. In EIS study, the single time constant equivalent circuit was used for fitting the spectra, which pertained to the coating /electrolyte interface. The single time constant could be attributed to the pore-free dense, uniform coatings developed over the MAO interlayer. For the MAO/Ni-P and MAO/Ni-P-Ni-W-P duplex coatings, the charge transfer resistance of about 15 and 11 kΩcm2 were obtained for duplex and Ni-P coatings, which reinforce the better corrosion protective ability of the coating. The above investigation confirms that MAO coatings have good corrosion resistance in the aggressive chloride medium. Consequently, they can serve as an ideal interlayer for the deposition of the electroless nickel coating. Even if the electroless nickel coating is found to fail in harsh environments, the MAO interlayer can protect the base substrate due to its higher corrosion resistance. It is also noteworthy that the borohydride treatment provides better adhesion between the MAO/Ni-P interlayer.

The master thesis focuses on the preparation of nickel coating on ceramic (Al2O3) substrate. The deposition of nickel was carried out by the electroless plating method in bath at various kinetic conditions. An impact of varied size, shape and roughness on the quality of the coated surface was investigated. The main goal was to find optimized conditions of the plating process of the thin metal coatings. Prepared nickel coatings were analysed by SEM, EDX analysis, mechanical profilometry and the plating bath was analysed by UV-VIS spectrophotometry. The continuous nickel coatings were achieved by modifying the deposition process, and the kinetic mechanism of experimental conditions was described.

The beginning of this thesis is dedicated to polymeric materials, which include plastics an composites. Plastics are shortly divided into two groups, thermoplastics and thermosets. The following part is the use of plastics and composites in traffic industry and briefly this work focuses on techniques of recycling of this materials. This work also focuses on the techniques of thin film deposition, electroless plating, electrodeposition as well and plating in the vacuum environment. special techniques of thin film deposition are also mentioned shortly. The coatings of polymer including cleaning and surface activation is introduced using various techniques including plasma treatment. The surface treatment of polyetheretherketone (PEEK) is included too. The final part describes performed experiments and discussion of results.

No description available.

The goal of this project is to study novel nanoscale excitation volumes, sensitive enoughto study individual chromophores and go on to study new and exciting self assemblyapproaches to this problem. Small excitation volumes may be engineered using light con-finement inside apertures in metal films. These apertures enhance fluorescence emissionrates, quantum yields, decrease fluorescence quenching, enable higher signal-to-noiseratios and allow higher concentration single chromophore fluorescence, to be studied byrestricting this excitation volume. Excitation volumes are reported on using the chro-mophore's fluorescence by utilising fluorescence correlation spectroscopy, which monitorsfluctuations in fluorescence intensity. From the correlation in time, we can find the res-idence time, the number of chromophores, the volume in which they are diffusing andtherefore the fluorescence emission efficiency. Fluorescence properties are a probe ofthe local environment, a particularly powerful tool due to the high brightness (quantumyield) fluorescent dyes and sensitive photo-detection equipment both of which are readilyavailable, (such as avalanche photodiodes and photomultiplier tubes). Novel materialscombining the properties of conducting and non-conducting materials at scales muchsmaller than the incident wavelength are known as meta-materials. These allow combi-nations of properties not usually possible in natural materials at optical frequencies. Theproperties reported so far include; negative refraction, negative phase velocity, fluorescenceemission enhancement, lensing and therefore light confinement has also been proposed tobe possible. Instead of expensive and slow lithography methods many of these materialsmay be fabricated with self assembly techniques, which are truly nanoscopic and otherwiseinaccessible with even the most sophisticated equipment. It was found that nanoscaled volumes from ZMW and HMMs based on NW arrays wereall inefficient at enhancing fluorescence. The primary cause was the reduced fluorescencelifetime reducing the fluorescence efficiency, which runs contrary to some commentatorsin the literature. NW based lensing was found to possible in the blue region of the opticalspectrum in a HMM, without the background fluorescence normally associated with a PAAtemplate. This was achieved using a pseudo-ordered array of relatively large nanowireswith a period just smaller than lambda / 2 which minimised losses. Nanowires in the traditionalregime lambda / 10 produced significant scattering and lead to diffraction, such that they werewholly unsuitable for an optical lensing application.

<p>Micro- and nanoparticles (MNP) attract much attention owing to their unique properties, structural tunability, and wide range of practical applications. To deposit these important materials on surfaces for generating functional coatings, a variety of special delivery systems and coating/printing techniques have been explored. Herein, spray coating technique is a promising candidate to advance the field of nanotechnology due to its low-cost, high-deposition rate, manufacturing flexibility, and compatibility with roll-to-roll processing. Despite great advances, direct scalable spray writing of functional materials at high-spatial resolution through fine patterning without a need of vacuum and mask equipment still remains challenging. Addressing these limitations requires the development of efficient spray deposition techniques and novel manufacturing approaches to effectively fabricate functional coatings. To this end, this dissertation employs three different spray coating methods of (1) cold spray; (2) atomization-assisted supersonic spray, and (3) dual velocity regime spray to address the aforementioned limitations. A comprehensive set of coating materials, design principles, and operational settings for each spray system are tailored for rapid, direct, and sustainable deposition of MNP on various substrates. Besides, through the two-phase flow modeling, droplets dispersion and deposition characteristics were investigated under both subsonic and supersonic flow conditions to uncover the process-structure-property relationships of the established spray systems. Moreover, novel spray-based manufacturing approaches are developed to fabricate functional coatings in various applications, including (i) functional polymer metallization, (ii) printed flexible electronics, (iii) advanced thin-film nanocoating, (iv) laser direct writing, and (v) electronic textiles.</p>