Post-growth Processing Research Articles

Water assisted atmospheric CVD super growth of vertically aligned CNT forest for supercapacitor application

We report a high growth rate (37 μm/min) synthesis of vertically aligned carbon nanotube (VACNT) forest, achieving remarkable height exceeding a millimetre with good crystallinity. VACNTs with few numbers of walls have been grown over Fe–Co/Al2O3/SiO2 coated Si wafer using the water assisted atmospheric pressure chemical vapour deposition (WACVD) method. The key to this success lies in the synergistic combination of a bimetallic catalyst (Fe-Co) with buffer Al2O3 layer and the WACVD method. Notably, the VACNT forest, synthesised at optimized conditions can be directly used without the need for additional post-growth purification processes, eliminating the risk of potential damage to the CNTs. Finally, the VACNT forest exhibits excellent areal capacitance of 133.33 mF/cm2 at a current density of 1 mA/cm2 with outstanding cyclic stability of 130 % @ 3000 cycles.

(Invited) Bulk Traps in Layered 2D Gate Dielectrics

Ultra-thin ferromagnets, when coupled with magnetoelectric or multiferroic materials, could potentially enable highly energy-efficient electric field control of the magnet for use in nanoelectronic memories. Substitutional doping of magnetic impurities in monolayer transition metal dichalcogenides (TMDs) may be a promising way to create 2D ferromagnets but, according to theoretical calculations, require high doping levels (10-20 %) to achieve above room temperature (RT) Curie temperature. Room-temperature ferromagnetism has been reported for very low doping levels (0.1-1%), in conflict with the theoretical calculations, and always in the presence of high concentrations of defects, making it unclear if the dopants alone are responsible for this ferromagnetism. In this work, we use a combination of molecular beam epitaxy (MBE), plan-view TEM, XRD, XPS, Raman, and magnetometry to study iron and vanadium doping in monolayer WSe2. We show that optimally grown monolayers with up to 35% doping and low defect density show no ferromagnetism. Interestingly, ferromagnetism is observed when these monolayers contain a significant amount of selenium vacancies (Sevac), intentionally created via a post-growth heat treatment process, and magnetism is seen to scale with heating time/vacancy concentration. Moreover, even undoped WSe2 shows similar ferromagnetism for Sevac > 1014 cm-2. This ferromagnetism can later be quenched by filling these vacancies via Se annealing. For films with low Se vacancy concentration, TEM analysis reveals significant clustering of the V and Fe dopants which likely suppresses the ferromagnetism predicted by theory - a problem that has previously plagued III-V based dilute magnetic semiconductors as well. We go so far as to claim that all of the above room-temperature ferromagnetism reports in the literature thus far are due to Se vacancies and not magnetic doping.

Replicating CD Nanogrooves onto PDMS to Guide Nanowire Growth for Monolithic Flexible Photodetectors with High Bending-Stable UV-vis-NIR Photoresponse.

Guided nanowires grown on polymer surfaces facilitate their seamless integration as flexible devices without post-growth processing steps. However, this is challenging due to the inability of polymer films to provide the required lattice-matching effect. In this work, this challenge is addressed by replicating highly aligned nanogrooves from a compact disc (CD) onto a casted flexible polydimethylsiloxane (PDMS) surface. Leveraging the replicated nanogrooves, copper hexadecafluorophthalocyanine (F16CuPc) and various metal phthalocyanines are guided into large-area, self-aligned nanowires. Subsequently, by employing specifically designed shadow masks during electrode deposition, these nanowires are seamlessly integrated as either a monolithic flexible photodetector with a large sensing area or on-chip flexible photodetector arrays. The resulting flexible photodetectors exhibit millisecond and long-term stable response to UV-vis-NIR light. Notably, they demonstrate exceptional bending stability, retaining stable and sensitive photoresponse even at a curvature radius as low as 0.5cm and after enduring 1000 bending cycles. Furthermore, the photodetector array showcases consistent sensitivity and response speed across the entire array. This work not only proves the viability of guided nanowire growth on flexible polymer surfaces by replicating CD nanogrooves but also underscores the potential for large-scale monolithic integration of guided nanowires as flexible devices.

Shadowed versus Etched Superconductor-Semiconductor Junctions in Al/InAs Nanowires.

Hybrid semiconductor-superconductor nanowires have emerged as a cornerstone in modern quantum devices. Integrating such nanowires into hybrid devices typically requires extensive postgrowth processing which may affect device performance unfavorably. Here, we present a technique for in situ shadowing superconductors on nanowires and compare the structural and electronic properties of Al junctions formed by shadowing versus etching. Based on transmission electron microscopy, we find that typical etching procedures lead to atomic-scale surface roughening. This surface perturbation may cause a reduction of the electron mobility as demonstrated in transport measurements. Further, we display advanced shadowing geometries aiding in the pursuit of bringing fabrication of hybrid devices in situ. Finally, we give examples of shadowed junctions exploited in various device geometries that exhibit high-quality quantum transport signatures.

Research on Evolution of Relevant Defects in Heavily Mg-Doped GaN by H Ion Implantation Followed by Thermal Annealing.

This study focuses on the heavily Mg-doped GaN in which the passivation effect of hydrogen and the compensation effect of nitrogen vacancies (VN) impede its further development. To investigate those two factors, H ion implantation followed by thermal annealing was performed on the material. The evolution of relevant defects (H and VN) was revealed, and their distinct behaviors during thermal annealing were compared between different atmospheres (N2/NH3). The concentration of H and its associated yellow luminescence (YL) band intensity decrease as the thermal annealing temperature rises, regardless of the atmosphere being N2 or NH3. However, during thermal annealing in NH3, the decrease in H concentration is notably faster compared to N2. Furthermore, a distinct trend is observed in the behavior of the blue luminescence (BL) band under N2 and NH3. Through a comprehensive analysis of surface properties, we deduce that the decomposition of NH3 during thermal annealing not only promotes the out-diffusion of H ions from the material, but also facilitates the repair of VN on the surface of heavily Mg-doped GaN. This research could provide crucial insights into the post-growth process of heavily Mg-doped GaN.

A route to fabricate low resistance joints between Eu–Ba–Cu–O bulk, single grain superconductors

The fabrication of large (RE)–Ba–Cu–O single grains [(RE)BCO], where RE = Y, Gd, Eu or Sm, with the complex geometries required for many practical applications is currently limited by the time intensive, complex nature of the grain growth process. In addition, the shapes achievable using established melt processing techniques, such as top seeded melt growth, are constrained significantly by the limited number of post-processing techniques readily available. Machining of these materials is also difficult given their ceramic-like mechanical properties, which makes them both brittle and hard. A potential alternative to the slow and inflexible melt growth processes is to join many small, single grains to form one large composite grain, connected by electrically and mechanically high-performance joints. A reliable joining technique would also greatly reduce the need for post-growth machining processes. In this work we extend our previous investigation of the use of single grain YBCO-Ag as an intermediate joining material to achieve effective and reliable superconducting joints between EuBCO-Ag bulk, single grain superconductors. The technique reported in the earlier studies requires limited specialist equipment and does not require tight process parameter control, since there is no need to re-grow the joining material at the intergrain interface. This technique is of particular interest given that the difference between the peritectic temperatures of the bulk superconductor and the intermediate joining material is large. We report the properties of seven joints engineered at different joining temperatures. The trapped field properties of the resulting joined samples were measured and the microstructure at the position of the joint examined. We demonstrate that this simple and the rapid joining technique makes it possible to manufacture composite grains in an industrially important (RE)BCO bulk superconductor with comparable superconducting properties to those of a single grain of similar dimensions.

Spatially correlated stress-photoluminescence evolution in GaN/AlN multi-quantum wells

In the manufacture of semiconductor devices, cracking of heterostructures has been recognized as a major obstacle for their post-growth processing. In this work, we explore cracked GaN/AlN multi-quantum wells (MQWs) to study the influence of pressure on the recombination energy of the photoluminescence (PL) from the polar GaN QWs. We grow GaN/AlN MQWs on a GaN(0001)/sapphire template, which provides 2.4% tensile strain for epitaxial AlN. This strain relaxes through the generation and propagation of cracks, resulting in a final inhomogeneous distribution of stress throughout the film. The crack-induced strain variation investigated by micro-Raman spectroscopy and X-ray diffraction mapping revealed a correlation between the spacing of the cracks and the amount of strain between them. We have developed a 2D model that allows us to calculate the spatial variation of the in-plane strain in the GaN and AlN layers. The measured values of compressive in-plane strain in the GaN QWs vary from -0.4 % away from cracks, to -0.7 % near cracks. PL from the GaN QWs exhibits a clear correlation to the varying strain resulting in an energy shift of ∼ 140 meV. As a result, we can experimentally calculate a pressure coefficient of PL energy of ∼ -60.4 meV/GPa for the ∼ 7 nm thick polar GaN QWs. This agrees well with the previously predicted theoretical results by Kaminska et al. in 2016 [DOI: 10.1063/1.4962282], which were demonstrated to break down for such wide QWs. We will discuss this difference with respect to the reduction in both the expected point defects and extended defects resulting from not doping and growth on a GaN template, respectively. As a result, our work indicates that cracks can be utilized for investigating some fundamental material properties related to strain effects.

Controlling the magnetic properties of layered Cr2Te3 thin films via ex-situ annealing

We present a post-growth ex-situ annealing method to control the Curie temperature and magnetic anisotropy of Cr2Te3 van der Waals ferromagnetic thin films. The as-grown Cr2Te3 films exhibit a Curie temperature ∼ 170 K with an out-of-plane magnetic easy axis. Upon high temperature (300 – 400 °C) ex-situ annealing, the magnetic phase of the film changes: the Curie temperature is significantly increased to ∼ 300 K and the magnetic easy axis is reoriented to the in-plane direction. Electronic, chemical, and structural analyses suggest that the c-axis lattice constant expansion, accompanying the annealing process, is the origin of the ex-situ-annealing-induced modulation of the Cr2Te3 film magnetic properties. These results demonstrate that a practical ex-situ annealing process can be effectively used to control the magnetic properties of van der Waals ferromagnetic thin films. Furthermore, the room temperature ferromagnetic ordering emerging upon annealing, along with its robustness against post-growth thermal processes, suggests that the Cr2Te3 thin film is a promising magnetic material candidate for potential application in van-der-Waals-material-based spintronic devices.

Growth of droplet-free InSbBi on GaAs substrate

Indium antimonide bismide (InSbBi) has emerged as a highly promising material for long-wavelength infrared photodetection devices due to its unique small energy bandgap (<0.17 eV) compared to existing III–V compound semiconductors. Despite its potential, experimental studies on InSbBi are still incomplete and scarce. Furthermore, the challenges associated with incorporating Bi and producing high-quality, defect-free samples are yet to be adequately addressed. To tackle these issues, we systematically investigated the growth of InSbBi on a GaAs substrate in this study. We incorporated up to 3.4% of Bi into InSbBi material. Our research contributes significantly to the field by demonstrating a technique for growing high-quality InSbBi material with Bi content of up to 2.3%, which is free of droplets and features a smooth surface. We achieved this goal by dynamically adjusting the Sb flux, carefully controlling the interplay between the Bi flux and the growth temperature, and implementing a post-growth annealing process. Our work is crucial for developing InSbBi technology as it contributes to the understanding of the growth process and surface morphology of InSbBi. Moreover, our results provide a path toward producing high-quality InSbBi samples.

Hubungan Post Traumatic Growth Dengan Kualitas Hidup Pada Anak Usia Sekolah Yang Sedang Menjalani Palliative Care

Chronic disease in children requires long-term care because of the prognosis and development of the disease. Chronic illness is not an easy thing for children and parents to deal with. Children undergoing medical and nursing care are scary things, these conditions require them to adapt to new routines that are part of their lives every day. This condition can be categorized as a traumatic event, which can affect psychological changes. These psychological changes are called post traumatic growth. Changes in these conditions become one of the factors that affect the quality of life. This study aims to determine the relationship between post traumatic growth and the quality of life of school-age children who are undergoing palliative care. This type of quantitative research with cross sectional approach method. The sampling technique used was purposive sampling with a sample size of 63 respondents. Based on the results of the Sperm- rank statistical test, a p-value of 0.013 was obtained with a positive correlation with a result of 0.312, so that it can be interpreted that there is a relationship between post traumatic growth and the quality of life of school-age children undergoing palliative care. Suggestions to parents or families are expected to always pay attention to physical and psychological conditions, as well as provide motivation and enthusiasm in undergoing palliative care so as to improve the quality of life in patients after experiencing a post traumatic growth process.

Photoresponse and noise characteristics of in-situ fabricated NiPc nanowire photodetectors

The interface between organic nanowires and metal layers plays a key role in determining the photoresponse and noise characteristics of organic nanowires. Herein, nickel phthalocyanine (NiPc) nanowires are self-aligned along parallel nanogrooves on a sapphire surface, and then photodetectors are fabricated in situ without post-growth transfer and alignment steps. This in-situ fabrication eliminates unpredictable factors associated with post-growth processing steps and allows us to focus on studying the influence of different nanowire-metal interfaces. Two different electrodes prepared by thermal evaporation deposition (TED) and etching-assisted transfer printing (ETP) are compared. While both electrodes ensure that NiPc nanowires exhibit a sensitive photoresponse in the 380–800 nm spectrum, the ETP electrodes result in higher sensitivity but an order of magnitude slower response due to the increased nanowire-metal interfacial capacitance. The noise power spectral density (PSD) confirms that for both photodetectors, the frequency-dependent 1/f noise dominates at frequencies below 10 kHz while the frequency-independent white noise increases significantly at higher frequencies. However, while the noise PSD of the photodetectors with TED electrodes remains stable with increasing temperature and bias, the noise PSD of the photodetectors with ETP electrodes increase by four to twelve orders of magnitude due to significantly increased electromigration and structural damage.

Growing sustainable materials from filamentous fungi

The urgent need to transition to a more sustainable way of life is driving the development of natural and sustainable materials. One such example is mycelium materials, which are partially or solely composed of hyphae, the vegetative life form of filamentous fungi. Mycelium materials offer a sustainable and environmentally friendly alternative to synthetic materials like plastics and to animal leather, by minimizing waste, reducing CO2 emissions and promoting a circular economy. In their natural habitat, fungi play a vital role in maintaining balanced forest ecosystems by decomposing and recycling organic matter. From a material application perspective, the mycelium itself is now being considered as a product that can be easily generated by cultivating the fungus on renewable biomass feedstocks. Mycelium-based composites and pure mycelium materials can be produced through different fermentation techniques, including solid-state (SSF), liquid-state submerged (LSF) and liquid-state surface fermentation (LSSF). Interestingly, the properties of mycelium materials are highly tuneable by altering the growth and post-growth process parameters, the choice of fungal species and the used substrate. Although the link between the biology of a living organism and the emergent material characteristics thereof offers great opportunities for fine-tuning material properties, a current lack of understanding of the underlying scientific principles makes industrial scalability and product reproducibility a challenging step. In this article, we discuss the opportunities and challenges of mycelium materials as a novel class of biomaterials.

In situ strain-induced phase transition and defect engineering in CVD-synthesized atomically thin MoS2

Alkali metal halides have recently received great attention as additives in the chemical vapor deposition (CVD) process to promote the growth of transition metal dichalcogenides (TMDs). However, the multi-faceted role of these halide salts in modulating the properties and quality of TMD monolayers remains mechanistically unclear. In this study, by introducing excessive gaseous sodium chloride (NaCl) into the CVD system, we demonstrate that preferential NaCl deposition along the monolayer edges causes large in situ strain that can invoke localized domains of high defect density and 2H to 1T phase transition. High-resolution scanning transmission electron microscopy, Raman mapping and molecular dynamics simulations revealed that higher NaCl concentrations can promote the coalescence of independent local strain domains, further increasing the 1T/2H phase ratio and defect density. Furthermore, excessive NaCl was also proven by density functional theory calculations to convert thermodynamic growth to kinetic growth, accounting for the unique cloud-shaped MoS2 crystals acquired. Compared with post-growth strain processing methods, this one-step approach for phase and defect engineering not only represents a deeper understanding of the role that NaCl plays in the CVD process, but also provides a convenient means to controllably synthesize conductive/defect-rich materials for further electrocatalysis and optoelectronic applications.

Aligned Phthalocyanine Molecular Nanowires by Graphoepitaxial Self‐Assembly and Their In Situ Integration into Photodetector Arrays

AbstractLarge‐scale on‐chip integration of organic nanowire‐based devices requires the deterministic assembly of organic small molecules into highly‐aligned nanowires. In this work, phthalocyanine molecules are self‐assembled into horizontally‐aligned nanowires after generating parallel hydrophobic nanogrooves on a sapphire surface. In contrast to previous self‐oriented inorganic nanowires, these molecular nanowires are separated from their supporting sapphire by an ultrathin amorphous layer, indicating a complete elimination of lattice matching between nanowires and substrates. Therefore, small molecules beyond phthalocyanines hold promise to form aligned nanowires using this graphoepitaxial self‐assembly strategy. The excellent alignment and high crystallinity of these nanowires enable the desired in‐situ integration of nanowire‐based devices without additional postgrowth processing steps. As a proof of concept, self‐oriented CuPc nanowires are integrated into photodetector arrays directly on their growth substrate after electrode arrays are transferred onto the nanowires. Compared to previous CuPc photodetectors constructed using other approaches, these detectors exhibit a faster response to the spectrum in the 488–780 nm range (rise and fall times are 0.05–0.43 s and 0.38–2.34 s, respectively) while offering comparable detectivities (2.49 × 1010 Jones on average). This graphoepitaxial self‐assembly offers new opportunities for the aligned growth of organic crystalline nanowires and their large‐scale in‐situ integration into functional devices.

Selectively Tuning the Substrate Adhesion Strength of Aligned Carbon Nanotube Arrays via Thermal Postgrowth Processing.

The excellent intrinsic properties of aligned nanofibers, such as carbon nanotubes (CNTs), and their ability to be easily formed into multifunctional 3D architectures motivate their use for a variety of commercial applications, such as batteries, chemical sensors for environmental monitoring, and energy harvesting devices. While controlling nanofiber adhesion to the growth substrate is essential for bulk-scale manufacturing and device performance, experimental approaches and models to date have not addressed tuning the CNT array-substrate adhesion strength with thermal processing conditions. In this work, facile "one-pot" thermal postgrowth processing (at temperatures Tp = 700-950 °C) is used to study CNT-substrate pull-off strength for millimeter-tall aligned CNT arrays. CNT array pull-off from the flat growth substrate (Fe/Al2O3/SiO2/Si wafers) via tensile testing shows that the array fails progressively, similar to the response of brittle microfiber bundles in tension. The pull-off strength evolves nonmonotonically with Tp in three regimes, first increasing by 10 times through Tp = 800 °C due to graphitization of disordered carbon at the CNT-catalyst interface, and then decreasing back to a weak interface through Tp = 950 °C due to diffusion of the Fe catalyst into the substrate, Al2O3 crystallization, and substrate cracking. Failure is observed to occur at the CNT-catalyst interface below 750 °C, and the CNTs themselves break during pull-off after higher Tp processing, leaving residual CNTs on the substrate. Morphological and chemical analyses indicate that the Fe catalyst remains on the substrate after pull-off in all regimes. This work provides new insights into the interfacial interactions responsible for nanofiber-substrate adhesion and allows tuning to increase or decrease array strength for applications such as advanced sensors, energy devices, and nanoelectromechanical systems (NEMS).

Post-Growth Dynamics and Growth Modeling of Organic Semiconductor Thin Films.

The ability to control the properties of organic thin films is crucial for obtaining highly performant thin-film devices. However, thin films may experience post-growth processes, even when the most sophisticated and controlled growth techniques such as organic molecular beam epitaxy (OMBE) are used. Such processes can modify the film structure and morphology and, thus, the film properties ultimately affecting device performances. For this reason, probing the occurrence of post-growth evolution is essential. Equally importantly, the processes responsible for this evolution should be addressed in view of finding a strategy to control and, possibly, leverage them for driving film properties. Here, nickel-tetraphenylporphyrin (NiTPP) thin films grown by OMBE on highly oriented pyrolytic graphite (HOPG) are selected as an exemplary system exhibiting a remarkable post-growth morphology evolution consistent with Ostwald-like ripening. To quantitatively describe the growth, the height-height correlation function (HHCF) analysis of the atomic force microscopy (AFM) images is carried out, clarifying the role of the post-growth evolution as an integral part of the whole growth process. The set of scaling exponents obtained confirms that the growth is mainly driven by diffusion combined with the presence of step-edge barriers, in agreement with the observed ripening phenomenon. Finally, the results together with the overall approach adopted demonstrate the reliability of the HHCF analysis in systems displaying post-growth evolution.

Formation of a-type dislocations near the InGaN/GaN interface during post-growth processing of epitaxial structures

Cross-sectional transmission electron microscopy studies often reveal a-type dislocations located either below or above the interfaces in InGaN/GaN structures deposited along the [0001] direction. We show that these dislocations do not emerge during growth but rather are a consequence of the stress state on lateral surfaces and mechanical processing, making them a post-growth effect. In cathodoluminescence mapping, these defects are visible in the vicinity of the edges of InGaN/GaN structures exposed by cleaving or polishing. Finite element calculations show the residual stress distribution in the vicinity of the InGaN/GaN interface at the free edge. The stress distribution is discussed in terms of dislocation formation and propagation. The presence of such defects at free edges of processed devices based on InGaN layers may have a significant negative impact on the device performance.

THIN FILMS OF COPPER OXIDE NANOSTRUCTURED VIA RAPID THERMAL PROCESSING

Nanostructured copper oxide films were obtained by the method of chemical synthesis from solutions (SCS) and exposed to post-growth rapid thermal processing (RTP) in air at different temperatures to study the influence of annealing temperature on morphological, chemical, structural and sensing properties. Controlled modification of surface morphology, in the particular size of nanostructures, crystallinity and phase can be achieved by RTP, which is preferred due to saving of energy budget nowadays. Detailed physico-chemical analysis of the films was performed using the scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman and energy dispersive X-ray (EDX) techniques. Sensors based on the copper oxide nanostructured films after RTP for 30 s only were tested with 100 ppm hydrogen gas at an operating temperature range from 250 ºC to 350 ºC. The difference in the response to 100 ppm hydrogen gas of the sensors based on thermally processed films at different temperatures was determined. We also noted that the change in the response of the sensing structure is correlated with its surface morphology controlled by RTP regime with a short duration. A detection mechanism to hydrogen gas has been proposed as well.

ІНДУКОВАНА ПЕРЕБУДОВА КРИСТАЛІЧНОЇ СТРУКТУРИ ТА АКУСТИЧНИЙ ВІДГУК В НАПІВПРОВІДНИКАХ НА ОСНОВІ ТЕЛУРИДУ КАДМІЮ ДЛЯ ЗАСТОСУВАННЯ В ОПТОЕЛЕКТРОНІЦІ ТА АКТУАЛЬНИХ НАПРЯМАХ НАПІВПРОВІДНИКОВОЇ ТЕХНІКИ (ОГЛЯД)

The reliability and competitiveness of modern semiconductor electronic technology are determined by the level of existing technologies. These requirements set the task of increasing the efficiency of methods for obtaining and post-growth processing of semiconductor materials and structures, research and control of their properties at all stages of manufacturing and operation of products. The question of the quality and maximum reliability of a wide range of various structures and devices for multipurpose purposes, in particular, opto, photoelectronics, sensors, etc., and sometimes the need to use it at the most achievable physical and technical parameters, or in extreme conditions, is becoming increasingly important. The solution to these problems is based on a comprehensive study of the processes of defect formation, failure and destruction of semiconductor structures and devices based on them. In modern conditions, for this purpose, in particular, the method of acoustic emission (AE) is used, based on the registration, theoretical processing of acoustic pulses that arise as a result of the formation, local changes and destruction of the structure of the material under external load. The most widespread practical application in various branches of semiconductor electronics have found materials based on CdTe, given, in particular, basic data on methods and sources of acoustic response induced by external influences. This method makes it possible to obtain information about the state of a solid in the process of deformation, in particular, to detect in a non-destructive way the presence or appearance of dislocations and microcracks. The AE process allows you to determine the mechanical stresses and deformations at which there is a transition from elastic to plastic deformation (yield strength) of the crystal and subsequent destruction. AE, which occurs during the deformation of a solid in local areas, in particular, under mechanical loads, ultrasound, laser irradiation, radiation exposure and in other cases, may have a thermomechanical nature and occur as a result of heterogeneous heating, for example, during the flow of electric current through a heterogeneous medium. Mechanical, thermomechanical or thermobaric stresses appear in crystals under appropriate phase transformations, in particular, during melting during laser irradiation. Thus, AE is an effective non-destructive method for identifying the initial stages of degradation and subsequent destruction of semiconductor materials, structures and devices under various external influences. The main purpose of this review is to distribute AE from macro objects (in technical diagnostics and control of industrial and domestic structures) to micro-objects for materials and structures of low-dimensional electronics, to expand the scientifically conscious application of AE in experimental and practical work in various semiconductor materials and structures on the example of CdTe-based semiconductors (wide- and narrow-band).

Modulation of the NiOx bandgap by controlling oxygen stoichiometry

Transition metal oxides are a class of functional materials widely used in optoelectronics, spintronics, and memory technology. The oxygen stoichiometry of these oxides plays a vital role in determining their electronic, optical, and thermal properties. Post-growth annealing in ozone has shown to be effective in modifying these properties. Here, we choose NiO, an antiferromagnetic Mott insulator in perfect stoichiometry, as an example to show that its stoichiometry can be tuned continuously in a broad range by the control of the oxidation power during growth or a post-growth topotactic reduction process. The bandgap of the as-processed NiOx films was modulated in accordance with their resistivity, lattice constant, and Ni chemical valence. This method can be readily applied to other transition metal oxides for the optimization of their properties.