Key Engineering Materials Vol. 1034

Abstract: The VN thin films were deposited on glass and Al₂O₃ substrates using reactive magnetron sputtering with a vanadium target in an Ar/N₂ mixed atmosphere. The deposition process was carried out at a substrate temperature of 25 °C and a sputtering power of 250 W. VN thin films were systematically prepared on glass substrates by varying the N₂/(Ar+N₂) ratio to 25%, 33%, 42%, and 56%. The results demonstrated that all as-deposited films consistently exhibited a face-centered cubic (FCC) NaCl-type crystal structure, regardless of the N₂/(Ar+N₂) ratio. Notably, the crystallization phase remained stable even when annealed at temperatures ranging from room temperature to 400 °C. As the nitrogen content increased, the resistivity of the films decreased, and the temperature coefficient of resistance (TCR) shifted toward smaller values. At a nitrogen content of 56%, the film exhibited the lowest resistivity of 63 μΩ-cm, along with a TCR of-460 ppm/°C. Furthermore, the resistivity demonstrated good stability, with only a 3% variation observed over one month.

Abstract: Nitrogen-vacancy (NV) color centers in diamond serve as promising atomic spin systems for measurement applications requiring high accuracy and sensitivity. A key challenge in NV-based quantum sensing is minimizing spin readout noise to approach the standard quantum limit (SQL). Based on a six-level model, this work analyze the dependence of NV-based quantum sensing performance, including spin state readout noise and signal-to-noise ratio (SNR), on controllable parameters such as the Purcell factor and excitation laser pulse characteristics. This study demonstrates that a shorter excitation pulse duration results in a higher saturation value of ground-state spin polarization, while the total time required for the polarization process remains constant. Additionally, the spin readout noise does not improve monotonically with decreasing excitation pulse duration; instead, it initially decreases and subsequently increases as the pulse duration varies. The spin readout noise reaches its optimal level when the pulse duration is 3 ns. Furthermore, no positive correlation exists between the signal-to-noise ratio (SNR) and the Purcell factor, and there is also an optimal value for SNR. When the pulse duration ranges from 1 ns to 40 ns, the variation in SNR is relatively insignificant. This research offers a novel perspective for enhancing the performance of quantum sensing based on diamond defects, such as nitrogen-vacancy (NV) centers.

Abstract: This article deals with the application of surface structure replication technique in the monitoring of steels used in VVER 440 and VVER 1000 type NPPs. Experimental samples were extracted from the primary circulation pipe made of austenitic steel 08Ch18N12T. In total, four sets were evaluated. The first of them was a segment from storage. The second of them was specimens cut off the main circulation pipeline after 28 years of operation at the Jaslovské Bohunice V1 NPP. The third and fourth were samples after artificial thermal aging at 450 °C in an atmospheric furnace. RepliSet F5 resin was used to replicate the microstructure of extracted specimens. Light and scanning electron microscopy techniques were used for replica and specimen evaluation. These analyses were supplemented by hardness measurement and EDS chemical composition analysis. The results showed a slight difference in the hardness and grain size for the AR and MCP segments. The carbide particle inclusions' size and shape were similar for all specimen sets.

Abstract: Research and development of materials in the nuclear industry, including the assessment of irradiated components in nuclear power plants, rely heavily on research infrastructures that facilitate the preparation and analysis of radioactive samples. The metallographic preparation of samples must be carried out in shielded, hermetically sealed boxes and hot cells, as a large amount of dusty radioactive particles is released during the sample preparation process. Small samples, thin films for scanning and transmission electron microscopy (SEM, TEM), and powdered samples from biological shielding concretes are prepared in glove boxes, where a constant negative pressure is maintained. The enclosures of the boxes are constructed of thick-walled steel plates to shield against the ionizing radiation emitted by radioactive samples, protecting personnel. Subsequent microscopic analyses allow for the assessment of material degradation in operational nuclear power plant components caused by radiation-induced microstructure damage. These analyses focus both on existing materials, with the aim of extending the lifespan of nuclear power plants, and on newly tested materials irradiated as part of domestic and international programs, including those conducted at research reactors like LVR-15, operated by the Řež Research Center (CVŘ). Different analytical requirements call for the preparation of various types of samples. At CVŘ, X-ray diffraction analysis of powdered samples is primarily used to evaluate structural and phase changes in the cement and aggregate of concrete structures caused by radiation aging, which can impact the overall integrity of the structure. Monitoring these changes and predicting material behavior are essential for evaluating the safety, stability and durability of concrete used in biological shielding, containment structures, spent nuclear fuel storage pools and future deep radioactive waste repositories. Thin films for electron microscopy are prepared specifically to assess detailed changes, such as radiation-induced microstructure damage in reactor internals or fuel cladding, which result in dimensional changes and the degradation of mechanical properties due to neutron radiation.

Abstract: The preparation of metallographic samples remains a crucial aspect of microstructural analysis, especially with the continuous development of advanced materials and imaging techniques. Despite its significance, sample preparation is often underestimated, yet achieving a surface with minimal structural distortion is essential for accurate microstructure evaluation and data interpretation. This study aimed to optimize steel sample preparation methods to obtain surfaces suitable for correlative imaging using multiple microscopic techniques, including modern scanning electron microscopy (SEM) with sample bias and electron backscatter diffraction (EBSD). The results demonstrate that specific contrast features observed in SEM can, in some cases, be qualitatively verified using EBSD. Furthermore, variations in SEM settings, such as lower landing energy, influence information depth, which in turn affects the accuracy of phase quantification, particularly when utilizing artificial intelligence-based methods.