Klaus Krambrock

Bio: Klaus Krambrock is an academic researcher from Universidade Federal de Minas Gerais. The author has contributed to research in topics: Electron paramagnetic resonance & Catalysis. The author has an hindex of 23, co-authored 133 publications receiving 1959 citations. Previous affiliations of Klaus Krambrock include University of Paderborn.

Initialization and read-out of intrinsic spin defects in a van der Waals crystal at room temperature

Abstract: Optically addressable spins in wide-bandgap semiconductors are a promising platform for exploring quantum phenomena. While colour centres in three-dimensional crystals such as diamond and silicon carbide were studied in detail, they were not observed experimentally in two-dimensional (2D) materials. Here, we report spin-dependent processes in the 2D material hexagonal boron nitride (hBN). We identify fluorescence lines associated with a particular defect, the negatively charged boron vacancy ($${\mathrm{V}}_{\mathrm{B}}^ -$$), showing a triplet (S = 1) ground state and zero-field splitting of ~3.5 GHz. We establish that this centre exhibits optically detected magnetic resonance at room temperature and demonstrate its spin polarization under optical pumping, which leads to optically induced population inversion of the spin ground state—a prerequisite for coherent spin-manipulation schemes. Our results constitute a step forward in establishing 2D hBN as a prime platform for scalable quantum technologies, with potential for spin-based quantum information and sensing applications. An ensemble of spins associated with an intrinsic defect of two-dimensional hexagonal boron nitride is shown to be optically addressable, allowing spin polarization of its triplet ground state and providing evidence of spin coherence.

A new appraisal of sri lankan bb zircon as a reference material for LA-ICP-MS U-Pb geochronology and Lu-Hf isotope tracing.

Abstract: A potential zircon reference material (BB zircon) for laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb geochronology and Hf isotope geochemistry is described. A batch of twenty zircon megacrysts (0.5–1.5 cm3) from Sri Lanka was studied. Within-grain rare earth element (REE) compositions are largely homogeneous, albeit with some variation seen between fractured and homogeneous domains. Excluding fractured cathodoluminescence bright domains, the variation in U content for all analysed crystals ranged from 227 to 368 μg g−1 and the average Th/U ratios were between 0.20 and 0.47. The Hf isotope composition (0.56–0.84 g/100 g Hf) is homogeneous within and between the grains – mean 176Hf/177Hf of 0.281674 ± 0.000018 (2s). The calculated alpha dose of 0.59 × 1018 g−1 for a number of BB grains falls within the trend of previously studied, untreated zircon samples from Sri Lanka. Aliquots of the same crystal (analysed by ID-TIMS in four different laboratories) gave consistent U-Pb ages with excellent measurement reproducibility (0.1–0.4% RSD). Interlaboratory assessment (by LA-ICP-MS) from individual crystals returned results that are within uncertainty equivalent to the TIMS ages. Finally, we report on within- and between-grain homogeneity of the oxygen isotope systematic of four BB crystals (13.16‰ VSMOW).

Nanostructured δ-FeOOH: An efficient Fenton-like catalyst for the oxidation of organics in water

Abstract: δ-FeOOH nanoparticles were prepared by the precipitation of Fe(OH)2 followed by rapid oxidation with H2O2. Samples with different surface areas and particle sizes were obtained by controlling the final pH of the reaction medium. The samples were characterized by X-ray powder diffractometry, 57Fe Mossbauer spectroscopy, saturation magnetization measurements, total Fe chemical analyses and BET surface area measurements. The catalytic activities of these samples for H2O2 decomposition were strongly influenced by the δ-FeOOH surface area. EPR was used to monitor catalytic H2O2 decomposition in the presence of methanol, indicating that the mechanism of decomposition involves radicals in accord with the Haber–Weiss mechanism. Methylene blue and indigo carmine were used to simulate the degradation of contaminants. Monitoring these experiments with ESI-MS revealed that δ-FeOOH can activate H2O2 to produce reactive radicals, which can further promote the oxidation of the dyes. The dye degradation rates depended on the amount of Fe2+ generated in situ on the δ-FeOOH surface.

Room Temperature Initialisation and Readout of Intrinsic Spin Defects in a Van der Waals Crystal

Abstract: Optically addressable spins in widebandgap semiconductors have become one of the most prominent platforms for exploring fundamental quantum phenomena. While several candidates in 3D crystals including diamond and silicon carbide have been extensively studied, the identification of spindependent processes in atomically thin 2D materials has remained elusive. Although optically accessible spin states in hBN are theoretically predicted, they have not yet been observed experimentally. Here, employing rigorous electron paramagnetic resonance techniques and photoluminescence spectroscopy, we identify fluorescence lines in hexagonal boron nitride associated with a particular defect, the negatively charged boron vacancy and determine the parameters of its spin Hamiltonian. We show that the defect has a triplet ground state with a zero field splitting of 3.5 GHz and establish that the centre exhibits optically detected magnetic resonance at room temperature. We also demonstrate the spin polarization of this centre under optical pumping, which leads to optically induced population inversion of the spin ground state a prerequisite for coherent spin manipulation schemes. Our results constitute a leap forward in establishing two dimensional hBN as a prime platform for scalable quantum technologies, with extended potential for spin based quantum information and sensing applications, as our ODMR studies on hBN NV diamonds hybrid structures show.

Principles Of Fluorescence Spectroscopy

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Quantum emission from hexagonal boron nitride monolayers

Abstract: We demonstrate first room temperature, and ultrabright single photon emission from a color center in two-dimensional multilayer hexagonal boron nitride. Density Functional Theory calculations indicate that vacancy-related centers are a likely source of the emission.

A review on Fenton-like processes for organic wastewater treatment

Abstract: Fenton-like processes have been studied widely in recent years and are considered promising for organic wastewater treatment. Due to the demand for high efficiency wastewater treatment, a summary of the study status of Fenton-like processes is necessary to develop a novel and high efficiency organic wastewater treatment method. In this review, some important effect parameters (pH, H2O2 dosage, catalyst dosage, temperature) in hetero-/homo-geneous Fenton-like processes are discussed, and then the physical field/phenomenon-assisted hetero-/homo-geneous Fenton-like processes are presented. After that, catalyst types and the evaluation of wastewater treatment costs for various Fenton-like processes are summarized and discussed. Finally, possible future research directions and some guidelines for Fenton-like processes are given.