Alexey N. Kirichenko

Currently, nanocomposites based on graphene and transition metal oxides are considered as promising materials for energy accumulation and storage due to their widespread occurrence in nature, low toxicity, and the ability of the metals to change the oxidation state. The rate of surface exchange electrons processes plays an important role in the formation of the electrophysical properties of materials. It is studied an effect of oxygen‐free graphene sheets on the activity of nanostructured ceria and zirconia in oxidation–reduction processes, where the rate of surface exchange electron interactions plays a key role. The reaction of CO oxidation is chosen as a model. It is shown that the introduction of oxygen‐free graphene sheets up to 3 nm thick into ceria or zirconia nanopowders leads to a decrease in the CO oxidation temperature. Apparently, this effect is caused by the formation of highly active centers with elongated terminal MO bonds in the presence of the sp ² ‐electron system of graphene. It is found that graphene increases the ability of metals to reversible oxygen exchange. The introduction of oxygen‐free graphene into the Mn _x O _y /CeO ₂ system leads to acceleration of surface exchange processes due to the facilitation of electron transfer in the system as a whole.

Благодаря особенностям прозрачного алмазного индентора-объектива стало возможным исследование in situ областей упругих деформаций материалов под наконечником как в контакте, так и вне области контакта без использования специальных иммерсионных жидкостей. В связи с этим появилась возможность эффективного точечного сканирования данных областей до 1 мкм с использованием спектроскопии комбинационного рассеяния. В данной работе по сдвигам мод комбинационного рассеяния (LO мод) благодаря концепции тензора фононных мод Грюнайзена в деформированном кремнии были точечно рассчитаны относительные изменения объемов и соответствующие им давления, являющиеся средним значением всех трех составляющих нормальных напряжений. Тем самым был показан переход от картографирования оптических свойств к определению механических свойств исследуемого материала с пространственной привязкой получаемых данных с микронной точностью. Обсуждается возможность изучения типа деформаций в кристаллах (растяжение или сжатие) во время индентирования с применением спектроскопии комбинационного рассеяния в геометрии обратного рассеяния. Также обсуждается возможность определения направления деформаций с применением поляризационных методов, использование которых позволит измерить продольные TO моды. В данной работе исследовался образец кремниевого чипа с ориентацией (100). Индентирование проводилось при нагрузках 250 и 1500 мН. По полученным данным для нагрузки в 250 мН для одного из секторов под индентором была построена карта распределения давлений с шагом 1 мкм области упругой деформации вне отпечатка. По характеру изменения спектров комбинационного рассеяния были сделаны выводы об однородности и неоднородности деформаций в измеренных точках. Картографирование напряжений деформированной области по предложенной методике эффективно на малых нагрузках. Для цитирования: Вотяков С.А., Кудряшов И.А., Будич К., Кириченко А.Н., Усеинов А.С., Султанова Г.Х. Картографирование напряжений in situ при индентировании кремния с использованием спектроскопии комбинационного рассеяния. Изв. вузов. Химия и хим. технология. 2024. Т. 67. Вып. 10. С. 22-28. DOI: 10.6060/ivkkt.20246710.10y.

Tightly focused 515-nm, 0.3-ps laser pulses modify in a laser filamentation regime the crystalline structure of an Ib-type high-pressure, high-temperature (HPHT) synthesized diamond in a thin-plate form. The modified microregions (micromarks) in the yellow and colorless crystal zones, possessing different concentrations of elementary substitutional nitrogen (N) impurity atoms (C-centers), exhibit their strongly diminished local IR absorption (upon correction to the thickness scaling factor). Simultaneously, local visible-range (400–550 nm) absorption coefficients were increased, and photoluminescence (PL) yield was strongly enhanced in the broad range of 450–800 nm. The strong yellow-red PL enhancement saturates with laser exposure, implying the complete conversion of C-centers into nitrogen-vacancy (NV^0,−) ones due to the laser-induced generation of Frenkel “interstitial-vacancy” I–V carbon pairs. The other emerging blue-green (>470 nm) and green-yellow (>500 nm) PL bands were also simultaneously saturated versus the laser exposure. The observed IR/optical absorption and PL spectral changes enlighten the ultrashort pulse laser inscription of NV⁰⁻-based quantum-emitter centers in synthetic diamonds and enable the evaluation of the productivity of their inscription along with the corresponding I–V generation rates.

Micromarks were formed in bulk natural IaAB-type diamond laser-inscribed by 515 nm 0.3 ps femtosecond laser pulses focused by a 0.25 NA micro-objective at variable pulse energies in sub-picosecond visible-range laser regimes. These micromarks were characterized at room temperature (25 °C) by stationary 3D confocal photoluminescence (PL) microspectroscopy at 405 nm and 532 nm excitation wavelengths. The acquired PL spectra exhibit the increasing pulse-energy-dependent yield in the range of 550–750 nm (NV⁰, NV⁻ centers) at the expense of the simultaneous reciprocal reduction in the blue–green (490–570 nm, H-band centers) PL yield. The detailed analysis indicates low-energy intensity rise for H-band centers as an intermediate product of vacancy-mediated dissociation of B1 and B2 centers, with H4 centers converting to H3 and NV centers at higher pulse energies, while the laser exposure effect demonstrates the same trend. These results will help solve the problem of direct laser writing technology, which is associated with the writing of micromarks in bulk natural diamond, and promising three-dimensional micro-electrooptical and photonic devices in physics and electronics.

Natural IaA+B diamonds were exposed in their bulk by multiple 0.3 ps, 515 nm laser pulses focused by a 0.25 NA micro-objective, producing in the prefocal region (depth of 20–50 μm) a bulk array of photoluminescent nanostructured microtracks at variable laser exposures and pulse energies. These micromarks were characterized at room (25°) and liquid nitrogen cooling (−120 °C) temperatures through stationary 3D scanning confocal photoluminescence (PL) microspectroscopy at 405 and 532 nm excitation wavelengths. The acquired PL spectra exhibit a linearly increasing pulse-energy-dependent yield in the range of 575 to 750 nm (NV⁰, NV⁻ centers) at the expense of the simultaneous reductions in the blue–green (450–570 nm; N3a, H4, and H3 centers) and near-IR (741 nm; V⁰ center) PL yield. A detailed analysis indicates a low-energy rise in PL intensity for B2-related N3a, H4, and H3 centers, while at higher, above-threshold pulse energies it decreases for the H4, H3, and N3a centers, converting into NV centers, with the laser exposure effect demonstrating the same trend. The intrinsic and (especially) photo-generated vacancies were considered to drive their attachment as separate species to nitrogen centers at lower vacancy concentrations, while at high vacancy concentrations the concerted splitting of highly aggregated nitrogen centers by the surrounding vacancies could take place in favor of resulting NV centers.

Elongated photoluminescent micromarks were inscribed inside a IaAB-type natural diamond in laser filamentation regime by multiple 515 nm, 0.3 ps laser pulses tightly focused by a 0.25 NA micro-objective. The micromark length, diameter and photoluminescence contrast scaled as a function of laser pulse energy and exposure, coming to a saturation. Our Raman/photoluminescence confocal microscopy studies indicate no structural diamond damage in the micromarks, shown as the absent Raman intensity variation versus laser energy and exposition along the distance from the surface to the deep mark edge. In contrast, sTable 3NV (N3)-centers demonstrate the pronounced increase (up to 40%) in their 415 nm zero-phonon line photoluminescence yield within the micromarks, and an even higher—ten-fold—increase in NV⁰-center photoluminescence yield. Photogeneration of carbon Frenkel “interstitial–vacancy” (I–V) pairs and partial photolytic dissociation of the predominating 2N (A)-centers were suggested to explain the enhanced appearance of 3NV- and NV-centers, apparently via vacancy aggregation with the resulting N (C)-centers or, consequently, with 2N- and N-centers.