Partners

Abstract:
The microscopic fate of dopants introduced under nonequilibrium conditions remains largely unresolved in wide-band gap oxides. Using temperature-dependent N K-edge X-ray absorption spectroscopy, we directly resolve the local bonding configuration of implanted nitrogen in (100) β-Ga2O3. The spectra are dominated by a sharp π* resonance characteristic of N≡N bonding that systematically intensifies upon annealing, providing a direct spectroscopic fingerprint of molecular nitrogen formation. First-principles calculations and multiple-scattering simulations reproduce these spectral features and identify molecular N2 as the dominant dopant state. Rather than forming substitutional acceptors, implanted nitrogen evolves toward N2-like configurations stabilized in defect-rich environments associated with local β→γ-like structural motifs. This behavior reflects a thermally driven reconfiguration of nitrogen within the damaged layer. These results demonstrate that dopant incorporation can proceed via molecularization pathways that bypass conventional substitutional doping, providing a general mechanism for dopant deactivation under nonequilibrium incorporation conditions in oxides.

Abstract:
Doping of β-Ga2O3 (100) with Si by ion implantation onto heated substrates is investigated. The study reveals complex ion beam-induced defect processes in β-Ga2O3, characterized by the formation of various defect types and their temperature-dependent transformation. By employing X-Ray Diffraction, Rutherford Backscattering Spectrometry, Particle-Induced X-Ray Emission, X-ray Absorption Near Edge Structure Spectroscopy, Transmission Electron Microscopy, and Density Functional Theory analyses, we examine lattice deformation, identify the local environment of dopants, assess electronic structure modifications, and verify the presence of extended defects induced by ion implantation. Our findings highlight the predominant contribution of substitutional and interstitial Si ions incorporated into complexes that act as donors manifesting n-type conductivity, while some fraction of the defects form complexes that act as traps for charge carriers. Notably, no monoclinic phase transformations were observed during implantation despite substrate temperature variations from 300 to 800 °C.

Keywords:
β-Ga2O3, WBG, Implantation, XRD, RBS/PIXE/c, XANES, TEM, DFT, FMS

Keywords:
self-reinforced composites, fatigue, self-heating effect, fracture mechanisms, unconventional injection molding

Abstract:
This paper shows the graphene and graphene oxide nanoflakes as the 0.1, 0.5, 1, 2, and 4 wt.% reinforcement of epoxy-resin matrix to enhance the thermal and mechanical characteristics of the composite. Experimental measurement of the glass transition temperature and thermal expansion coefficient indicated that the addition of nanostructural filler improving the glass transition temperature about ~12 oC for nanocomposite filled carbon-based nanoparticles for both heating and cooling cycles compared to the bare epoxy resin. Young's modulus measured by nanoindentation and the stress versus strain curves for different weight fractions of graphene nanoflakes additives during uniaxial compression and tension considered were obtained from the experiments. The distributions of strain field for the transverse, axial and shear components on the nanocomposites, during the uniaxial tension process for quasi-static strain rates, were analyzed. The tensile strengths show improvement for nanocomposites with less than 1 % weight fraction of carbon-based nanoparticles. The compressive yield stress increased to a maximal value (at the recorded peak on the curve) for an epoxy nanocomposite having 2 wt.% oxidized graphene flakes, where both parameters were enhanced with the oxidized form of graphene for the more effective dispersion in the epoxy resin matrix over the bare graphene filler.

Keywords:
epoxy resin, nanocomposite, carbon nanoparticles, tensile strength, compression strength, thermal stability