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Single substitutional nitrogen atoms N0s are the prerequisite to create nitrogen-vacancy (NV) centers in diamonds. They not only serve as the electron donors to create the desired NV- center and provide charge stability against photo-ionisation but also are the main source of decoherence. Therefore, precise and quick determination of N0s concentration is a key advantage to a multitude of NV-related research in terms of material improvement as well as applications. Here, we present a method to determine the N0s concentration based on absorption spectroscopy in the UV-Visible range and fitting the 270 nm absorption band. UV-Visible spectroscopy has experimental simplicity and widespread availability that bear advantages over established methods. It allows a rapid determination of N0s densities, even for large numbers of samples. Our method shows further advantages in determining low concentrations as well as the ability to measure locally, which is highly relevant for diamonds with largely varying N0s concentrations in a single crystal. A cross-check with electron paramagnetic resonance shows high reliability of our method and yields the absorption cross section of the 270 nm absorption band σ=1.96±0.15 cm−1 ppm−1 (in common logarithm) or σe=4.51±0.35 cm−1 ppm−1 (in natural logarithm), which serves as a reference to determine N0s concentrations and makes our method applicable for others without the need for a known N0s-reference sample and calibration. We provide a rapid, practical, and replicable pathway that is independent of the machine used and can be widely implemented as a standard characterization method for the determination of N0s concentrations.

Herein, the in situ generation of nitrogen-vacancy (NV) centers in diamond during chemical vapor deposition (CVD) is investigated depending on the electric-field strength at the sample position. The alteration of the electric-field strength is induced by changing the resonance conditions within the resonator cavity while keeping the growth input variables constant. The electric-field strength distribution is obtained by simulation results. During the growth experiments, optical-emission spectroscopy data is collected, which shows the impact of the electric-field strength on the radical concentrations within the plasma and the gas temperature. Through the reduction of the electric-field strength, the synthesis of thick, high-quality, nitrogen-doped diamond without the formation of a polycrystalline rim around the sample edges and the twinning-induced growth of polycrystalline grains was accomplished. Therefore, a reduced internal and more homogeneous stress distribution is achieved. Furthermore, significant influences on the in situ NV doping are discovered. In addition to a considerable gain of the in situ NV generation, also a major enhancement of the in situ incorporation efficiency of NV centers in comparison to N0s centers up to almost 3% is observed. Depending on the application, this makes posttreatment processes for additional NV generation dispensable.

Silicon carbide is a material with a multistable crystallographic structure, i.e., a polytypic material. Different polytypes exhibit different band gaps and electronic properties with nearly identical basal plane lattice constants, making them interesting for heterostructures without concentration gradients. The controlled formation of this heterostructure is still a challenge. The ability to adjust a defined temperature&ndash, time profile using rapid thermal processing was used to imprint the polytype transitions by controlling the nucleation and structural evolution during the temperature ramp-up and the steady state. The influence of the linear heating-up rate velocity during ramp-up and steady-state temperature on the crystal structure of amorphized ion-implanted silicon carbide layers was studied and used to form heteropolytype structures. Integrating the structural selection properties of the non-isothermal annealing stage of the ion-implanted layers into an epitaxial growth process allows the imprinting of polytype patterns in epitaxial layers due to the structural replication of the polytype pattern during epitaxial growth. The developed methodology paves the way for structural selection and vertical and lateral polytype patterning. In rapid thermal chemical vapor deposition, the adjustment of the process parameters or the buffer layer allowed the nucleation and growth of wurtzite silicon carbide.

Silicon carbide is a material with a multistable crystallographic structure, i.e., a polytypic material. Different polytypes exhibit different band gaps and electronic properties with nearly identical basal plane lattice constants, making them interesting for heterostructures without concentration gradients. The controlled formation of this heterostructure is still a challenge. The ability to adjust a defined temperature-time profile using rapid thermal processing was used to imprint the polytype transitions by controlling the nucleation and structural evolution during the temperature ramp-upand the steady state. The influence of the linear heating-up rate velocity during ramp-up and steady-state temperature on the crystal structure of amorphized ion-implanted silicon carbide layers was studied and used to form heteropolytype structures. Integrating the structural selection properties of the non-isothermal annealing stage of the ion-implanted layers into an epitaxial growth process allows the imprinting of polytype patterns in epitaxial layers due to the structural replication of the polytype pattern during epitaxial growth. The developed methodology paves the way for structural selection and vertical and lateral polytype patterning. In rapid thermal chemical vapor deposition, the adjustment of the process parameters or the buffer layer allowed the nucleation and growth of wurtzite silicon carbide.

We present the epitaxial growth of ferroelectric potassium tantalate-niobate (KTN) thin films by pulsed laser deposition. As a result of the optimization of the deposition and the surface finishing processes, a c-axis oriented KTa0.5Nb0.5O3 thin film with homogeneous polarization phase grown on KTaO3 and an efficient KTa0.5Nb0.5O3 waveguiding thin film grown on MgO are demonstrated. The highly improved crystalline and optical quality of KTN layers grown in this work reveal the great potential of such films for integrated nonlinear optics.

This work presents an adsorption model based on the Sips isotherm for sensing different concentrations of DNA with open gate AlGaN/GaN high electron mobility field effect transistors (HEMTs). Probe-DNA was immobilized on the transistor gate before the application of target-DNA. Concentrations of 10-15 to 10-6 mol/L were tested. The sensor has a detection limit of 10-12 mol/L and saturates after the addition of 10-8 mol/L target-DNA.

The effects of low-energy irradiation by light ions (H and He) on the properties of In-rich InxGa1−xN alloys are investigated by optical and structural techniques. H-irradiation gives rise to a remarkable blue-shift of light emission and absorption edge energies. X-ray absorption measurements and first-principle calculations address the microscopic origin of these effects.