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Measurement of zeta potential of Ga and N-face gallium nitride has beencarried out as function of pH. Both the faces show negative zeta potential inthe pH range 5.5-9. The Ga face has an isoelectric point at pH 5.5. The N-faceshows higher negative zeta potential due to larger concentration of adsorbedoxygen. Zeta potential data clearly showed that H-terminated diamond seedsolution at pH 8 will be optimal for the self assembly of a monolayer ofdiamond nanoparticles on the GaN surface. Subsequent growth of thin diamondfilms on GaN seeded with H-terminated diamond seeds produced fully coalescedfilms confirming a seeding density in excess of 10$^{12}$ cm$^{-2}$. Thistechnique removes the requirement for a low thermal conduction seeding layerlike silicon nitride on GaN.

Nanocrystalline diamond (NCD) thin films grown by chemical vapour deposition (CVD) have an intrinsic surface roughness, which hinders the development and per-\ud formance of the films' various applications. Traditional methods of diamond polishing are not effective on NCD thin films. Films either shatter due to the combination\ud of wafer bow and high mechanical pressures or produce uneven surfaces, which has led to the adaptation of the chemical mechanical polishing (CMP) technique for\ud NCD films. This process is poorly understood and in need of optimisation. To compare the effect of slurry composition and pH upon polishing rates, a series of NCD\ud thin films have been polished for three hours using a Logitech Tribo CMP System in conjunction with a polyester/polyurethane polishing cloth and six different slurries. The reduction in surface roughness was measured hourly using an atomic force microscope. The nal surface chemistry was examined using X-ray photoelectron\ud spectroscopy and a scanning electron microscope. It was found that of all the various properties of the slurries, including pH and composition, the particle size was\ud the determining factor for the polishing rate. The smaller particles polishing at a greater rate than the larger ones.

Chemical vapour deposition (CVD) grown nanocrystalline diamond is an attractive material for the fabrication of devices. For some device architectures, optimisation of its growth on silicon nitride is essential. Here, the effects of three pre-growth surface treatments, often employed as cleaning methods, were investigated. Such treatments provide control over the surface charge of the silicon nitride substrate through modification of the surface functionality, allowing for the optimisation of electrostatic diamond seeding densities. Zeta potential measurements and X-ray photoelectron spectroscopy (XPS) were used to analyse the silicon nitride surface following each treatment. Exposing silicon nitride to an oxygen plasma offered optimal surface conditions for the electrostatic self-assembly of a hydrogen-terminated diamond nanoparticle monolayer. The subsequent growth of boron-doped nanocrystalline diamond thin films on modified silicon nitride, under CVD conditions, produced coalesced films for oxygen plasma and solvent treatments, whilst pin-holing of the diamond film was observed following RCA-1 treatment. The sharpest superconducting transition was observed for diamond grown on oxygen plasma treated silicon nitride, demonstrating it to be of the least structural disorder. Modifications to the substrate surface optimise the seeding and growth processes for the fabrication of diamond on silicon nitride devices.

Chemical vapour deposition (CVD) grown nanocrystalline diamond is an attractive material for the fabrication of devices. For some device architectures, optimisation of its growth on silicon nitride is essential. Here, the effects of three pre-growth surface treatments, often employed as cleaning methods of silicon nitride, were investigated. Such treatments provide control over the surface charge of the substrate through modification of the surface functionality, allowing for the optimisation of electrostatic diamond seeding densities. Zeta potential measurements and X-ray photoelectron spectroscopy (XPS) were used to analyse the silicon nitride surface following each treatment. Exposing silicon nitride to an oxygen plasma offered optimal surface conditions for the electrostatic self-assembly of a hydrogen-terminated diamond nanoparticle monolayer. The subsequent growth of boron-doped nanocrystalline diamond thin films on modified silicon nitride substrates under CVD conditions produced coalesced films for oxygen plasma and solvent treatments, whilst pin-holing of the diamond film was observed following RCA-1 treatment. The sharpest superconducting transition was observed for diamond grown on oxygen plasma treated silicon nitride, demonstrating it to be of the least structural disorder. Modifications to the substrate surface optimise the seeding and growth processes for the fabrication of diamond on silicon nitride devices.

In this paper the design of a simple, space constrained chemical vapour deposition reactor for diamond growth is detailed. Based on the design by NIRIM, the reactor is composed of a quartz discharge tube placed within a 2.45 GHz waveguide to create the conditions required for\ud metastable growth of diamond. Utilising largely off-the-shelf components and a modular design, the reactor allows for easy modification, repair, and cleaning between growth runs. The elements of the reactor design are laid out with the CAD files, parts list, and control files made easily available to enable replication. Finally, the quality of nanocrystalline diamond films produced are studied with SEM and Raman spectroscopy, with the observation of clear\ud faceting and a large diamond fraction suggesting the design offers deposition of diamond with minimal complexity.

Broadband microwave complex permittivity measurements of nanodiamond powders are presented. Previous studies show that measurements of dielectric loss strongly correlate with the presence of nondiamond surface impurities. In this study, the frequency dependence of these losses is investigated using the microwave cavity perturbation (MCP) and broadband coaxial probe (BCP) methods. This allowed further understanding as to what mechanisms contribute to the microwave absorption (free electron conduction or dielectric loss from the disordered surfaces). A multimode MCP system is used which utilizes ${rm TM}_{0np}$ modes to provide partial spectral characterization. The MCP results revealed minimal frequency dependence, unlike any static conduction-related mechanism. The BCP measurements corroborate the MCP results with much higher spectral resolution, and further demonstrate that disorder related loss may dominate over free electron conduction from 1–10 GHz. From 0.1–1 GHz, free electron conduction has a greater influence with a characteristic $1/f$ dependence implying that conduction may dominate at lower frequencies. However, the BCP method, while repeatable, lacks in precision compared to the cavity method. Nonetheless, the major conclusion in this paper is that through simple microwave permittivity measurements, nondiamond carbon impurities in nanodiamond powders are measurable most likely because of disorder related losses as opposed to free electron conduction.

Diamond is one of the hardest and most difficult to polish materials. In this paper, the polishing of {111} and {100} single crystal diamond surfaces by standard Chemical Mechanical Polishing, as used in the silicon industry, is demonstrated. A Logitech Tribo Chemical Mechanical Polishing system with Logitech SF1 Syton and a polyurethane/polyester polishing pad was used. A reduction in roughness from 0.92 to 0.23 nm root mean square (RMS) and 0.31 to 0.09 nm RMS for {100} and {111} samples respectively was observed., Comment: 13 pages 3 figures, ELHT and SM have contributed equally to the work

Micro and Nano-Electro-Mechanical Systems (MEMS/NEMS) incorporating micro- and\ud nano-scale mechanical elements into electronic circuits are of increasing interest in both\ud fundamental physics and technological applications, with uses ranging from atomic resolution\ud mass spectrometers to low cost gravimeters and RF filtering. For applications\ud reliant on the perturbation of mechanical elements, a high resonant frequency (f)\ud with minimal dissipation (Q−1) is desired to increase device response, while for filtering\ud within the RF high Q enables the selection of individual channels. With the resonant\ud frequency of devices proportional to the acoustic value of the material, diamond’s unrivalled\ud value of 18 000ms−1 makes it ideal for high frequency devices with minimal\ud dissipation from scaling induced loss.\ud However, the use of Nanocrystalline Diamond (NCD) for smaller scale NEMS is\ud inhibited by the quality of the resulting films, in particular the non-diamond carbon\ud content, and the considerable surface roughness resulting from the competitive growth\ud of randomly orientated crystallites. Within Chapter 4 spectroscopy ellipsometry, a\ud powerful technique capable of probing the variation in the optical properties with depth,\ud and hence microstructure, of thin films is therefore applied to the characterisation of 25–\ud 75 nm thick NCD films. The model developed is able to discern the point of coalescence\ud of the film, with the indicated surface roughness and composition verified by AFM and\ud Raman spectroscopy.\ud Chapter 5 then details the adaption of chemical mechanical polishing, a technique\ud routinely used within the IC fabrication industry, to the polishing of diamond. Using\ud a soft polymer polishing pad and an alkaline colloidal silica polishing fluid a reduction\ud in roughness is observed for NCD films from 18.3 to 1.7 nm RMS over 25 μm2 after\ud 4 hours. Finally, the polishing technique is used to aid in the construction of NEMS\ud devices within Chapter 6 with the aim of improving the Q factor.