Gallium nitride laser diodes are shown to be a viable alternative to the solid- state lasers typically used in Ocean LiDARs. Their ability to operate at various wavelengths enables new excitation schemes for depth resolved water column temperature measurements.

Tailoring the surface chemistry of diamond is critical to a range of applications from quantum science to electronics. It has been recently shown that dosing the diamond surface with pulsed UV light at fluences below the ablation threshold provides a practical method for precision etching of the surface. Here, we track the evolution of the surface chemistry and its electrical properties as a function of dose using x-ray surface analysis, Hall and resistance measurements. It is found that the surface properties evolve rapidly, even for doses that correspond to removal of less than 5% of the top carbon monolayer and fluences less than 1 J/cm2. As well altering XPS-measured surface populations, sub-monolayer etch doses lower the valence band by up to 0.2 eV, and produce a permanent increase in the conductivity of the hydrogen terminated surface by up to 7 times. Similar enhancements in conductivity are obtained for doses that remove up to 1600 ML. The results provide guidance for manipulating diamond surface chemistry by UV laser etching and introduce a promising method for enhancing the performance of diamond devices such as field-effect transistors.

Levitated systems in vacuum have many potential applications ranging from new types of inertial and magnetic sensors through to fundamental issues in quantum science, the generation of massive Schrodinger cats, and the connections between gravity and quantum physics. In this work, we demonstrate the passive, diamagnetic levitation of a centimeter-sized massive oscillator which is fabricated using a novel method that ensures that the material, though highly diamagnetic, is an electrical insulator. By chemically coating a powder of microscopic graphite beads with silica and embedding the coated powder in high-vacuum compatible wax, we form a centimeter-sized thin square plate which magnetically levitates over a checkerboard magnet array. The insulating coating reduces eddy damping by almost an order of magnitude compared to uncoated graphite with the same particle size. These plates exhibit a different equilibrium orientation to pyrolytic graphite due to their isotropic magnetic susceptibility. We measure the motional quality factor to be Q 1.58*10^5 for an approximately centimeter-sized composite resonator with a mean particle size of 12 microns. Further, we apply delayed feedback to cool the vertical motion of frequency 19 Hz from room temperature to 320 millikelvin.

We present a method to simultaneously determine water temperature and salinity, which uses a pulsed excitation laser and a three-channel Raman spectrometer. The method relies on the systematic dependence of the Raman OH stretching band on temperature and salinity, and is compatible with LiDAR techniques. We have measured the variation of the OH stretching band in two seawater samples and a NaCl solution, and constructed a linear mapping between signal ratios derived from the three spectral channels and the temperature and salinity of each sample. For the natural seawater this approach has been determined by cross-validation to have a predictive accuracy of ±1.6 PSU and ±0.5 °C.

Diamond is an exceptional material with stable colour centres, a wide band gap, high thermal conductivity, and a unique surface. Engineering the termination, orientation, and defects of the surface is important for quantum computing and sensing, and electronic applications. Techniques for manipulating the surface include processes based on plasma, chemical, electron and ion beams, and laser treatments. We report the sub-monolayer manipulation of diamond surfaces using deep-UV laser processing. Laser pulses at 266 nm of fluence below the ablation threshold were used to oxidize the surface and remove carbon, through 2-photon-induced photo-chemical ejection, and the effects on the electrical and chemical surface properties were measured. It is found that the resistance of a hydrogen surface increases with the UV dose from 2 to 3 kΩ up to the measurement limit of 100 GΩ for doses corresponding to 0.5 monolayers, behaviour which agrees well with geometric and tunneling percolation arguments for the surface conduction. We also show that dosing before hydrogenation produced up to five times reduction in surface resistance and an increase in carrier concentration, and that these effects enable enhancement of the current density of diamond surface field effect transistors. We use XPS measurements of the surface chemistry as a function of dose to help elucidate the UV-induced mechanism responsible for enhancement.

Manipulation and patterning of diamond surface chemistry is of interest for a wide range of diamond-based technologies. We report the patterned oxidation of hydrogen-terminated diamond surfaces with sub-monolayer (ML) precision by a deep-UV two-photon process performed in air. Using focused laser pulses of photon energy 4.66 eV (266 nm; below the diamond bandgap of 5.47 eV), hydrogen-terminated (001) surfaces were exposed with calibrated doses to remove carbon with a precision of 0.02 ML. The measurement of the electrical properties of the laser-exposed zone between ohmic electrodes enabled monitoring of the transition from a conducting H-terminated surface to insulating O-terminated. The surface resistance increases by more than 7 orders of magnitude for doses corresponding to 0.5 ML, and the I–V characteristics show a transition from linear to nonlinear for doses above 0.30 ML. We show that this behavior agrees well with a surface percolation model for carrier diffusion in which the laser etch rate for the H-terminated top layer is the same as for O-terminated. Hence, this work reveals an ultra-precise method for modifying the sub-monolayer surface chemistry with the practical advantages of a laser-induced mechanism compared to conventional plasma or chemical processing methods.

Researchers seek methods to levitate matter for a wide variety of purposes, ranging from exploring fundamental problems in science through to developing new sensors and mechanical actuators. Many levitation techniques require active driving and most can only be applied to objects smaller than a few micrometers. Diamagnetic levitation has the strong advantage of being the only form of levitation which is passive, requiring no energy input, while also supporting massive objects. Known diamagnetic materials which are electrical insulators are only weakly diamagnetic and require large magnetic field gradients to levitate. Strong diamagnetic materials which are electrical conductors, such as graphite, exhibit eddy damping, restricting motional freedom and reducing their potential for sensing applications. In this work, we describe a method to engineer the eddy damping while retaining the force characteristics provided by the diamagnetic material. We study, both experimentally and theoretically, the motional damping of a magnetically levitated graphite plate in high vacuum and demonstrate that one can control the eddy damping by patterning the plate with through-slots which interrupt the eddy currents. We find that we can control the motional quality factor over a wide range with excellent agreement between the experiment and numerical simulations.

The synthesis and characterization of carbon black supported rhodium and iridium heterobimetallic hybrid catalysts and their application in the hydrosilylation of alkynes is described.

A series of Rh- and Ir-hybrid catalysts with varying tether lengths has been prepared by immobilization of RhI, RhIII and IrIII complexes on carbon black, and applied in the hydrosilylation of alkynes.

Two-photon etching of diamond surfaces is a novel technique for providing controlled removal of atomic layers and nano-patterning the surface. However, the details of the etching mechanism and pattern development are not well understood so that the full capability of the process is unclear. Here, a comprehensive investigation into the dynamics of nanopattern formation on the (100), (110) and (111) facets is reported as a function of polarization, for CVD and HPHT diamond, and for nanosecond and picosecond laser pulse durations. A diverse array of behaviour is observed including sub-wavelength scale structuring with morphologies characteristic of the facet and the selected polarization. As etching proceeds, the anisotropies in the quantum photon-lattice interaction are imprinted on the emergent patterns on nano and mesoscopic scales. The sum of the results leads to rules for predicting pattern type, roughness and etch rate. We also argue that they support a mechanism for carbon ejection based on the photo-ejection of carbonyl groups from carbonyl-supporting surfaces, defects and atomic-level step edges. The results provide guidance for optically manipulating diamond surfaces and comprise a major step towards a complete model for the process to aid laser direct-write structuring of functional diamond surfaces.

Ultraviolet laser-induced etching is a method of machining and nanostructuring diamond surfaces in which carbon is removed from the surface via a photochemical process involving oxygen. We show here that using a dry source of oxygen at pressures in the range of 0.01–1 Torr leads to a 10-fold increase in the etch rate compared to etching in atmospheric air. The enhanced etch rate is also found to be accompanied by a marked change in the nanopatterned surface morphology. We developed a rate equation model for the etch rate that provides good agreement with measurements for pressures up to approximately 0.1 Torr. For higher pressures, the reduced etch rate and departure from the model are attributed to the contamination of the diamond surface by trace amounts of water vapor, introduced as an impurity from the gas sources. The results provide a method for markedly increasing the etch rate, as well as a better understanding of the role of gas impurities on the etch mechanism and emergent nanopattern formation.

An investigation into UV two-photon etching of diamond surfaces in low pressure conditions is presented. A tenfold increase in etch rate was observed, attributed to the reduced role of water vapour in suppressing carbon ejection.

Low power UV laser radiation has been previously found to etch diamond surfaces via a multiphoton process. Here we show that UV exposure also increases the NV photoluminescence and enhances hydrogen-terminated surface conductivity.

The surface of diamond is reported to undergo nonablative photochemical etching when exposed to ultraviolet (UV) radiation which allows controlled single and partial layer removal of lattice layers. Oxygen termination of surface dangling bonds is known to be crucial for the etching process; however, the exact mechanism of carbon ejection remains unclear. We investigate the interaction of UV laser pulses with oxygen-terminated diamond surfaces using atomic-scale surface characterization combined with first-principles time-dependent density functional theory calculations. We present evidence for laser-induced desorption (LID) from carbonyl functional groups at the diamond {001} surface. The doubly bonded carbonyl group is photoexcited into a triply bonded CO-like state, including scission of the underlying C─C bonds. The carbon removal process in LID is atom by atom; therefore, this mechanism provides a novel "top-down" approach for creating nanostructures on the surface of diamond and other carbon-containing semiconductors.

STEM employability is a non-homogenous phenomenon with mixed outcomes for graduates from different disciplines. A myriad of factors may contribute to the diverse employability. Here we examine the heterogeneity of career and employability development focuses among different STEM student cohorts in the curricular context. We utilised a structured framework of Career Information Literacy (CIL) to map career and employability focuses of STEM students and employers. This paper presents findings from the Mathematics, Statistics, Physics and Astronomy cohort. Data was collected from final year capstone unit students at a STEM faculty in an Australian university (N=517, response rate 44%). Of which, Maths, Stats, Physics and Astronomy (MSPA) students were analysed as a cohort (N=80, response rate 73%). Concurrent data collection took place with STEM employers and industry stakeholders who engaged this faculty in recruitment and employability activities (N=62, response rate 78%). Upon comparing student cohorts’ focuses on career and employability development with their peers and employers, we found MSPA students differ from both their STEM peers and employers. Most other STEM student cohorts differ from employers, but not their peers. The implications point to a different career development need of this cohort to fully realise the benefits of their STEM education.

A number of quantum technologies require macroscopic mechanical oscillators possessing ultra-high motional Q-factors. These can be used to explore the macroscopic limits of quantum mechanics, to develop quantum sensors and to test the quantum nature of gravity. One approach is to trap nanometer to micron-sized particles in 3D; however, the use of ion or optical traps suffers from a number of difficulties including electrodynamic noise due to patch fields, damage to the particles due to unwanted laser heating, or difficulty in reaching low pressures due to particle loss. In this work, we report a completely passive, magnetic trap which confines a micro-diamond in 3D and which requires no active power—optical or electrical. We design, model, fabricate, and test the operation of our magneto-mechanical trap and experimentally demonstrate trapping down to ∼0.1 Torr. We measure the position fluctuation of the trapped micro-diamond as a function of pressure and find good agreement with Brownian theory.

Using a sample consisting of a thin gold film on lithium niobate, the plasmonic second-harmonic response of gold is measured simultaneously with the optical second-harmonic response of lithium niobate. The non-phase-matched, bulk optical second-harmonic response of the lithium niobate is used to calibrate the plasmonic signal, and these are found to be of comparable intensity over the short propagation distances that arise in this system.

A graphene-gold photo-detector produced enhanced photocurrent due to absorbed surface plasmons with p-polarized near IR excitation light, when compared with s-polarized light. Charge doping was characterized by Raman spectroscopy at different positions on the graphene.

We demonstrate that surface plasmon resonances excited by photon tunneling through an adjacent dielectric medium enhance the photocurrent detected by a graphene photodetector. The device is created by overlaying a graphene sheet over an etched gap in a gold film deposited on glass. The detected photocurrents are compared for five different excitation wavelengths, ranging from gimel(0) = 570 nm to gimel(0) = 730 nm. Although the device is not optimized, the photocurrent excited with incident p-polarized light (which excites resonant surface plasmons) is significantly amplified in comparison with that for s-polarized light (without surface plasmon resonances). We observe that the photocurrent is greater for shorter wavelengths (for both s-and p-polarizations) with increased photothermal current. Position-dependent Raman spectroscopic analysis of the optically-excited graphene photodetector indicates the presence of charge carriers in the graphene near the metallic edge. In addition, we show that the polarity of the photocurrent reverses across the gap as the incident light spot moves across the gap. Graphene-based photodetectors offer a simple architecture which can be fabricated on dielectric waveguides to exploit the plasmonic photocurrent enhancement of the evanescent field. Applications for these devices include photodetection, optical sensing and direct plasmonic detection.

Reconfigurability is an important requirement for implementing quantum photonic processing using waveguide circuits in which both high fidelity and the ability to change the optical transformation dynamically are necessary. This work aims to address the issue of scalability in reconfigurable waveguide circuits fabricated using the femtosecond laser direct-write (FLDW) technique. A set of reconfigurable waveguide Mach-Zehnder interferometers were designed and fabricated using a combination of femtosecond laser waveguide inscription and picosecond laser ablation. Thermal cross-talk between adjacent phase-shifters was managed by machining microchannels into the chip surface to isolate individual waveguides from the rest of the substrate. The tuning efficiency as defined by the dissipated power per unit of induced phase shift was improved by a factor of two in this way while maintaining a smaller device footprint than previous demonstrations of phase tuning in laser-written waveguides. The phase response of the waveguide interferometers to the heaters was thoroughly characterised and was well predicted by simulation. A characterization of the time-dependent response of the reconfigurable interferometers was also performed. A rise time measurement revealed that the circuit can be reconfigured within seconds. No long-term phase drifts away from a set point were observed over a period of more than 12 hours, and the short term phase stability was better than 6 mrad.