ABSTRACT
Diamond as a templating substrate is largely unexplored, and the unique properties of diamond, including its large bandgap, thermal conductance, and lack of cytotoxicity, makes it versatile in emergent technologies in medicine and quantum sensing. Surface termination of an inert diamond substrate and its chemical reactivity are key in generating new bonds for nucleation and growth of an overlayer material. Oxidized high-pressure high temperature (HPHT) nanodiamonds (NDs) are largely terminated by alcohols that act as nucleophiles to initiate covalent bond formation when an electrophilic reactant is available. In this work, we demonstrate a templated synthesis of ultrathin boron on ND surfaces using trigonal boron compounds. Boron trichloride (BCl3), boron tribromide (BBr3), and borane (BH3) were found to react with ND substrates at room temperature in inert conditions. BBr3 and BCl3 were highly reactive with the diamond surface, and sheet-like structures were produced and verified with electron microscopy. Surface-sensitive spectroscopies were used to probe the molecular and atomic structure of the ND constructs' surface, and quantification showed the boron shell was less than 1 nm thick after 1-24 h reactions. Observation of the reaction supports a self-terminating mechanism, similar to atomic layer deposition growth, and is likely due to the quenching of alcohols on the diamond surface. X-ray absorption spectroscopy revealed that boron-termination generated midgap electronic states that were originally predicted by density functional theory (DFT) several years ago. DFT also predicted a negative electron surface, which has yet to be confirmed experimentally here. The boron-diamond nanostructures were found to aggregate in dichloromethane and were dispersed in various solvents and characterized with dynamic light scattering for future cell imaging or cancer therapy applications using boron neutron capture therapy (BNCT). The unique templating mechanism based on nucleophilic alcohols and electrophilic trigonal precursors allows for covalent bond formation and will be of interest to researchers using diamond for quantum sensing, additive manufacturing, BNCT, and potentially as an electron emitter.
ABSTRACT
Many mineral predictive models created based on multicriteria decision making (MCDM) methods use only one conceptually-based MCDM technique for data integration and synthesis of the mineral-related predictors. It is noteworthy that relying on just one mode of the conceptually-based data integration technique is often insufficient, as it fails to address the problems the other mode (in terms of either determining the weights of the predictors or by ranking and prioritising the predictors) deals with before the predictors are synthesised. Herein, a hybrid conceptually-based data integration approach comprising the best-worst method (BWM) and the Technique for Order of Preference by Similarity (TOPSIS) methods have been adopted in mapping viable regions of gold mineralisation occurrences over the Abansuoso Area of Ghana's Ashanti Region. The combined use of these two conceptually-based data integration approaches is rare in the literature, particularly in Ghana and West Africa. Based on the aforementioned approach, weights of nine predictors which were sourced from geological and geophysical datasets comprising magnetics and radiometrics were estimated using the BWM approach to determine their comparative importance towards the gold prospect of the study area. Afterwards, the TOPSIS approach was applied to prioritise and rank the various alternatives that makeup the predictors identified for this study. Subsequently, a predictive model that defines the spatial distribution of the mineral prospects of the study area was developed and was referred to as BWM-TOPSIS based mineral potential map (MPM). The BWM-TOPSIS-based MPM was further classified to characterise zones of low, moderate and high mineral potential, with their resulting areal extents being respectively 237.13 km2, 225.66 km2 and 127.45 km2. An evaluation of the MPM developed based on the BWM-TOPSIS technique was conducted by implementing the prediction-area (P-A) plot. Outputs from the P-A plot indicate that 30 % of the study area has high prospect with 70 % of the existing gold locations observed within it. Additionally, the receiver operating characteristics (ROC) curve was used to evaluate the effectiveness of the MPM developed. The MPM generated based on the BWM-TOPSIS approach yielded an AUC score of 0.81; this AUC score indicates that the performance of the predictive model developed is very good.