Phase Stability of Hexagonal/cubic Boron Nitride Nanocomposites

Boron nitride (BN) is an exceptional material and among its polymorphs, two-dimensional (2D) hexagonal and three-dimensional (3D) cubic BN (h-BN and c-BN) phases are most common. The phase stability regimes of these BN phases are still under debate and phase transformations of h-BN/c-BN remain a topic of interest. Here, we investigate the phase stability of 2D/3D h-BN/c-BN nanocomposites and show that the co-existence of two phases can lead to strong non-linear optical properties and low thermal conductivity at room temperature. Furthermore, spark-plasma sintering of the nanocomposite shows complete phase transformation to 2D h-BN with improved crystalline quality, where 3D c-BN grain sizes governs the nucleation and growth kinetics. Our demonstration might be insightful in phase engineering of BN polymorphs based nanocomposites with desirable properties for optoelectronics and thermal energy management applications.Comment: 29 pages, 5 figure

Benchmarking diamond surface preparation and fluorination via inductively coupled plasma-reactive ion etching

Diamond, renowned for its exceptional semiconducting properties, stands out as a promising material for high-performance power electronics, optics, quantum, and biosensing technologies. This study methodically investigates the optimization of polycrystalline diamond (PCD) substrate surfaces through Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE). Various parameters, including gaseous species, flow rate, coil power, and bias power were tuned to understand their impact on surface morphology and chemistry. A thorough characterization, encompassing chemical, spectroscopic, and microscopic methods, shed light on the effects of different ICP-RIE conditions on surface properties. CF4/O2 plasma emerged as a viable treatment for achieving smooth PCD surfaces with minimal etch pit formation. Most notably, surface fluorination, a critical aspect of increasing chemical and thermal stability, was successfully accomplished using CF4, SF6, and other F-containing plasmas. The fluorine concentration and surface chemistry variations were studied, with high resolution X-ray Photoelectron Spectroscopy unveiling differences amongst the sp2 C phase, sp3 C phase, C–O, C[dbnd]O, and C–F bonds. Time-of-flight secondary Ion Mass Spectrometry (ToF-SIMS) and depth-profile analysis unveiled a consistent surface fluorination pattern with CF4/O2 treatment. Furthermore, contact angle measurements showcased heightened hydrophobicity. This study provides valuable insights into precise diamond surface engineering, important for the development of future diamond-based semiconductor technologies.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)National Science FoundationArmy Research OfficeDepartment of Materials Science and Nanoengineering Rice UniversitySIMS Laboratory Shared Equipment Authority Rice UniversityDepartment of Physics and Meteorology School of Sciences São Paulo State University (Unesp), SPApplied Physics Graduate Program Smalley-Curl Institute Rice UniversityDEVCOM Army Research Laboratory RF Devices and CircuitsChemistry Division U.S. Naval Research LaboratoryDepartment of Physics and Meteorology School of Sciences São Paulo State University (Unesp), SPFAPESP: 2023/08122–0National Science Foundation: 2236422CNPq: 304957/2023–2National Science Foundation: CBET-1626418Army Research Office: W911NF-19-2-026

Heteroatom Functionalization of H‑Terminated Diamond Surfaces

Diamond surface functionalization has received significant research interest recently. Specifically, H-termination has been widely adopted because it endows the diamond surface with negative electron affinity and the hole carrier is injected in the presence of surface transfer dopants. Exploring different functional groups’ attachment on diamond surfaces and their impact on the electronic structure, using wet and dry chemical approaches, would hence be of interest in engineering diamond as a semiconductor. Here, we report the functionalization of the H-terminated diamond surface with nitrogen and sulfur heteroatoms. Surface characterization of functionalized diamond surfaces shows that these groups are well-distributed and covalently bonded to diamonds. Four chemical functional groups (−SH, −S–S–, −S–O, and −S=O) were found on the sulfurized diamond surface, and two groups (−NH2 and =NH) upon amination. We also report co-functionalization of surface with N and S (N–S), where sulfurization promotes sequential amination efficiency with reduced exposure time. Electrical measurement shows that heteroatom-modified diamond surfaces possess higher conductivity than H-terminated diamonds. Density functional theory (DFT) shows that upon functionalization with various N/S ratios, the conduction band minimum and valence band maximum downshift, which lowers the bandgap in comparison to an H-terminated diamond. These observations suggest the possibility of heteroatom functionalizations with enhanced surface electrical conductivity on the diamond that are useful for various electronic applications

Phase Stability of Hexagonal/Cubic Boron Nitride Nanocomposites

Boron nitride (BN) is an exceptional material, and among its polymorphs, two-dimensional (2D) hexagonal and three-dimensional (3D) cubic BN (h-BN and c-BN) phases are most common. The phase stability regimes of these BN phases are still under debate, and phase transformations of h-BN/c-BN remain a topic of interest. Here, we investigate the phase stability of 2D/3D h-BN/c-BN nanocomposites and show that the coexistence of two phases can lead to strong nonlinear optical properties and low thermal conductivity at room temperature. Furthermore, spark-plasma sintering of the nanocomposite shows complete phase transformation to 2D h-BN with improved crystalline quality, where 3D c-BN possibly governs the nucleation and growth kinetics. Our demonstration might be insightful in phase engineering of BN polymorph-based nanocomposites with desirable properties for optoelectronics and thermal energy management applications