Search

Artificial visual system empowered by 2D materials-based hardware simulates the functionalities of the human visual system, leading the forefront of artificial intelligence vision. However, retina-mimicked hardware that has not yet fully emulated the neural circuits of visual pathways is restricted from realizing more complex and special functions. In this work, we proposed a human visual pathway-replicated hardware that consists of crossbar arrays with split floating gate 2D tungsten diselenide (WSe2) unit devices that simulate the retina and visual cortex, and related connective peripheral circuits that replicate connectomics between the retina and visual cortex. This hardware experimentally displays advanced multi-functions of red–green color-blindness processing, low-power shape recognition, and self-driven motion tracking, promoting the development of machine vision, driverless technology, brain–computer interfaces, and intelligent robotics. Realizing complex functions in artificial visual systems is challenging. Here, the authors report a human visual pathway-replicated hardware with a split floating gate crossbar arrays and related peripheral circuits, achieving colour-blindness processing, shape recognition, and self-driven motion tracking. [ABSTRACT FROM AUTHOR]

In the devices that integrate phase change memory (PCM) and ovonic threshold switching (OTS), the OTS threshold voltage often surpasses the RESET operation voltage of PCM. The conventional application of square pulses hinders the successful completion of the SET operation in these integrated devices. To address this challenge, a novel pulse called the surge pulse is introduced, which comprises a high amplitude pulse for OTS activation and a low amplitude pulse for PCM operation. By employing COMSOL simulation, the operational effectiveness of both square pulses and surge pulses is validated. Test results reveal that using a square pulse to operate the integrated device accelerates the occurrence of SET-stuck failure (SSF). In contrast, the surge pulse enables the integrated device to operate for at least 1000 cycles while preserving the essential cyclic characteristics. Additionally, an investigation into the overshoot component of the surge pulse is conducted, revealing that an increase in overshoot amplitude and pulse width also accelerates the emergence of SSF. By applying the theory of ion migration induced by the electric field, the root cause of SSF in integrated devices is explained, and the accuracy of the theory is validated through the application of a reverse pulse. In summary, this study elucidates the rationality of replacing the square pulse with a surge pulse, presenting a superior approach for operating PCM and OTS integrated devices. [ABSTRACT FROM AUTHOR]

As the prevailing non-volatile memory (NVM), flash memory offers mass data storage at high integration density and low cost. However, due to the 'speed-retention-endurance' dilemma, their typical speed is limited to ~microseconds to milliseconds for program and erase operations, restricting their application in scenarios with high-speed data throughput. Here, by adopting metallic 1T-LixMoS2 as edge contact, we show that ultrafast (10–100 ns) and robust (endurance>106 cycles, retention>10 years) memory operation can be simultaneously achieved in a two-dimensional van der Waals heterostructure flash memory with 2H-MoS2 as semiconductor channel. We attribute the superior performance to the gate tunable Schottky barrier at the edge contact, which can facilitate hot carrier injection to the semiconductor channel and subsequent tunneling when compared to a conventional top contact with high density of defects at the metal interface. Our results suggest that contact engineering can become a strategy to further improve the performance of 2D flash memory devices and meet the increasing demands of high speed and reliable data storage. The speed-retention-endurance trade-off usually limits the performance of flash memory devices. Here, the authors report the realization of van der Waals flash memory cells based on 2H-MoS2 semiconducting channels with phase-engineered 1T-LixMoS2 edge contacts, showing program/erasing speed of ~10/100 ns, endurance of >106 cycles and expected retention lifetime of >10 years. [ABSTRACT FROM AUTHOR]

High-density integration of ferroelectric field-effect transistors (FeFETs) is hindered by factors such as interfacial states, short-channel effects, and ferroelectricity degradation in ultrathin films. Accordingly, the introduction of two-dimensional (2D) materials could effectively solve these problems. However, most current studies focus on the replacement of Si-based channels with 2D channels. Little progress has been made in addressing issues caused by bulk-phase ferroelectric gate layers, such as the unavoidable rough interfaces and the fading of ferroelectricity in ultrathin films. Herein, the 2D ferroelectric material In2Se3 is introduced as the gate dielectric. Combined with 2D insulating h-BN and 2D channel MoS2, an all-van der Waals (vdW) stacking FeFET is fabricated to provide a straight solution for the abovementioned issues. First, the robust ferroelectric phase of In2 Se3 is verified in an ultrathin film case and a high-temperature case, which is outstanding among recently reported 2D ferroelectrics. Second, device-level out-of-plane ferroelectric polarization switching is achieved in the cross-structure device. Based on these results, In2 Se3 is adopted as the ferroelectric gate dielectric to fabricate all-vdW stacking FeFETs. The subsequent transistor performance measurement on the fabricated FeFETs indicates that the ferroelectric polarization of the In2 Se3 layer plays a dominating role in forming a counterclockwise hysteresis loop. Further pulse response measurements manifest the feasibility of nonvolatile channel conductance tuning of these devices with a proper pulse design. Our findings suggest that In2Se3 is a suitable 2D ferroelectric gate material and that all-vdW stacking FeFETs based on 2D ferroelectrics are promising in the application of high-density memory. [ABSTRACT FROM AUTHOR]

In recent years, two-dimensional (2D) materials-based fundamental preparing process such as high-quality wafer-level single crystal thin film synthesis technology and high-performance electrode preparing technology has developed rapidly. In addition, the integrated application prospect of 2D materials has been preliminarily verified, owing to the flat and clean interface between 2D materials and substrates. From the perspective of electronics and optoelectronics based on 2D materials, this paper will summarize the recent studies of integrated circuit hardware, integrated optoelectronic hardware, and hetero-integrated hardware, showing their advantages and potential application. [ABSTRACT FROM AUTHOR]

Arsenic is an essential dopant in conventional silicon-based semiconductors and emerging phase-change memory (PCM), yet the detailed functional mechanism is still lacking in the latter. Here, we fabricate chalcogenide-based ovonic threshold switching (OTS) selectors, which are key units for suppressing sneak currents in 3D PCM arrays, with various As concentrations. We discovered that incorporation of As into GeS brings >100 °C increase in crystallization temperature, remarkably improving the switching repeatability and prolonging the device lifetime. These benefits arise from strengthened As-S bonds and sluggish atomic migration after As incorporation, which reduces the leakage current by more than an order of magnitude and significantly suppresses the operational voltage drift, ultimately enabling a back-end-of-line-compatible OTS selector with >12 MA/cm2 on-current, ~10 ns speed, and a lifetime approaching 1010 cycles after 450 °C annealing. These findings allow the precise performance control of GeSAs-based OTS materials for high-density 3D PCM applications.Spin defects in semiconductors are promising for quantum technologies but understanding of defect formation processes in experiment remains incomplete. Here the authors present a computational protocol to study the formation of spin defects at the atomic scale and apply it to the divacancy defect in SiC. [ABSTRACT FROM AUTHOR]

The exchange bias (EB) effect plays an undisputed role in the development of highly sensitive, robust, and high-density spintronic devices in magnetic data storage. However, the weak EB field, low blocking temperature, as well as the lack of modulation methods, seriously limit the application of EB in van der Waals (vdW) spintronic devices. Here, we utilized pressure engineering to tune the vdW spacing of the two-dimensional (2D) FePSe3/Fe3GeTe2 heterostructures. The EB field (HEB, from 29.2 mT to 111.2 mT) and blocking temperature (Tb, from 20 K to 110 K) are significantly enhanced, and a highly sensitive and robust spin valve is demonstrated. Interestingly, this enhancement of the EB effect was extended to exposed Fe3GeTe2, due to the single-domain nature of Fe3GeTe2. Our findings provide opportunities for the producing, exploring, and tuning of magnetic vdW heterostructures with strong interlayer coupling, thereby enabling customized 2D spintronic devices in the future. When an antiferromagnet is in close proximity to a ferromagnet, the antiferromagnet pins the spins of the ferromagnet, resulting in an exchange bias effect. This effect has been instrumental in the development of a variety of spintronic devices. Here, Haung et al. use pressure to tune the exchange bias effect in all van der Waals heterostructure composed of FePSe3/Fe3GeTe2. [ABSTRACT FROM AUTHOR]

Conclusion: The comprehensive studies aimed at the interplay between the quantum confinement effect and device statistical variability among process design of experiments for sub-5 nm NSTs have been presented and analyzed through strictly calibrated TCAD simulation platform for the first time. The impact of quantum confinement variation on the key performance parameters of NSTs with different channel geometry structures also have been studied. It is found that the NSTs with the optimized nanosheet thickness of approximate 4 nm have the best key figures of merit. After considering the interplay between the quantum confinement and statistical variability, MGG as the dominant statistical variability source brings the largest threshold voltage fluctuation and the MGG-induced variability can be suppressed with the average grain size reduction, but SER can also cause the comparable threshold voltage variation for 3 nm thick NSTs mainly due to the strong quantum confinement variation. Meanwhile the SER-induced variability can also be suppressed by the uniform smooth nanosheet edges. [ABSTRACT FROM AUTHOR]

As the main topic in modern scientific computing and machine learning tasks, matrix equation solving is suffering high computational latency and tremendous power consumption due to the frequent data movement in traditional von Neumann computers. Although the in-memory computing paradigms have shown the potential to accelerate the execution of solving matrix equations, the existing memristive matrix equation solvers are still limited by the low system versatility and low computation precision of the memristor arrays. In this work, we demonstrate a hybrid architecture for accurate, as well as efficient, matrix equation solving problems, where the memristive crossbar arrays are used for the parallel vector-matrix multiplication and the digital computer for accuracy. The linear neural-network solving (NNS) method is adopted here and its versatility for various types of matrix equations is proved. The weight-slice computation method is developed to perform the analog matrix multiplication with high efficiency and high robustness in the array. The solution results confirmed that typical matrix equations can be solved by this memristive matrix equation solver with high accuracy. Further performance benchmarking demonstrates that the generalized memristive matrix equation solver has low solving time-complexity while outperforming the state-of-the-art CMOS and in-memory processors. [ABSTRACT FROM AUTHOR]

In order to further reduce the energy required for SET/RESET operations of interfacial phase change memory, Bi2Te3/GeTe, a novel chalcogenide superlattice interfacial phase change material (iPCM), was proposed by introducing greater stress at the superlattice interface. Based on the Ge-atom flip-flop model, ab initio simulation was employed to design and optimize the Ge atom movement path at the interface. Compared with the conventional Sb2Te3/GeTe iPCM, Bi2Te3/GeTe iPCM needs to overcome a lower energy barrier to complete the phase change process, presenting a lower SET/RESET power consumption advantage for interfacial phase change memory applications. [ABSTRACT FROM AUTHOR]

Hafnia-based ferroelectrics have greatly revived the field of ferroelectric memory (FeRAM), but certain reliability issues must be satisfactorily resolved before they can be widely applied in commercial memories. In particular, the imprint phenomenon severely jeopardizes the read-out reliability in hafnia-based ferroelectric capacitors, but its origin remains unclear, which hinders the development of its recovery schemes. In this work, we have systematically investigated the imprint mechanism in TiN/Hf0.5Zr0.5O2 (HZO)/TiN ferroelectric capacitors using experiments and first-principles calculations. It is shown that carrier injection-induced charged oxygen vacancies are at the heart of imprint in HZO, where other mechanisms such as domain pinning and dead layer are less important. An imprint model based on electron de-trapping from oxygen vacancy sites has been proposed that can satisfactorily explain several experimental facts such as the strong asymmetric imprint, leakage current variation, and so forth. Based on this model, an effective imprint recovery method has been proposed, which utilizes unipolar rather than bipolar voltage inputs. The remarkable recovery performances demonstrate the prospect of improved device reliability in hafnia-based FeRAM devices. [ABSTRACT FROM AUTHOR]

With the rapid growth of computer science and big data, the traditional von Neumann architecture suffers the aggravating data communication costs due to the separated structure of the processing units and memories. Memristive in-memory computing paradigm is considered as a prominent candidate to address these issues, and plentiful applications have been demonstrated and verified. These applications can be broadly categorized into two major types: soft computing that can tolerant uncertain and imprecise results, and hard computing that emphasizes explicit and precise numerical results for each task, leading to different requirements on the computational accuracies and the corresponding hardware solutions. In this review, we conduct a thorough survey of the recent advances of memristive in-memory computing applications, both on the soft computing type that focuses on artificial neural networks and other machine learning algorithms, and the hard computing type that includes scientific computing and digital image processing. At the end of the review, we discuss the remaining challenges and future opportunities of memristive in-memory computing in the incoming Artificial Intelligence of Things era. [ABSTRACT FROM AUTHOR]

Document clustering has been commonly accepted in the field of data analysis. Nevertheless, the challenging issues for the clustering are the massive similarity measurement operations in the von Neumann architecture which result in huge time consumption. Memristive in-memory computing provides a brand-new path to solve this problem. In this article, utilizing the memristive dot product engine, we demonstrate a cosine similarity accelerated document clustering method for the first time. The memristor-based clustering method lowers the time complexity from O(N · d) of the conventional algorithm to O(N) by executing similarity measurement in one step. Focused on the unit-length vectors, an in-situ normalization scheme for the stored vectors in the crossbar array is proposed to provide an efficient hardware training scheme and reduce the normalization steps during the clustering. Utilizing the BBCSport dataset as a benchmark, we further discussed the impact of the non-ideal factors in the memristors, including the available quantized states, the inevitable programming noise, and the device failure. Simulation results indicate that the 6-bit quantized states and 5% programming noise are acceptable for the document clustering tasks. Besides, high resistance states of the failure cells are recommended for higher performance clustering results. [ABSTRACT FROM AUTHOR]

The resistive switching effect in memristors typically stems from the formation and rupture of localized conductive filament paths, and HfO2 has been accepted as one of the most promising resistive switching materials. However, the dynamic changes in the resistive switching process, including the composition and structure of conductive filaments, and especially the evolution of conductive filament surroundings, remain controversial in HfO2-based memristors. Here, the conductive filament system in the amorphous HfO2-based memristors with various top electrodes is revealed to be with a quasi-core-shell structure consisting of metallic hexagonal-Hf6O and its crystalline surroundings (monoclinic or tetragonal HfOx). The phase of the HfOx shell varies with the oxygen reservation capability of the top electrode. According to extensive high-resolution transmission electron microscopy observations and ab initio calculations, the phase transition of the conductive filament shell between monoclinic and tetragonal HfO2 is proposed to depend on the comprehensive effects of Joule heat from the conductive filament current and the concentration of oxygen vacancies. The quasi-core-shell conductive filament system with an intrinsic barrier, which prohibits conductive filament oxidation, ensures the extreme scalability of resistive switching memristors. This study renovates the understanding of the conductive filament evolution in HfO2-based memristors and provides potential inspirations to improve oxide memristors for nonvolatile storage-class memory applications. Understanding the mechanism of the formation and rupture of conductive filaments in HfO2-based memristors is essential to solve the problem of scalability of the devices. Here, Zhang et al. visualize this process by tracking atomic-scale evolution of conductive filaments during resistive switching cycles. [ABSTRACT FROM AUTHOR]

Copper indium sulfide (CIS) quantum dots (QDs) are attractive as potential optoelectronic devices, since they have large absorption coefficients across a broad spectral range, size- and composition-tunable photoluminescence from the visible to the near-infrared, and low toxicity. However, CIS QDs should be hydrophilic in certain applications. In this present work, hydrophilic CIS and CIS/ZnS colloidal QDs were synthesized by a one-pot environmentally-friendly route employing N,N-dimethylformamide (DMF) as the solvent and in situ generated H2S as the sulphur precursor. The effect of stoichiometry was investigated by varying the feeding molar ratios of Cu/In, which did not affect the crystalline structure of the CIS colloidal QDs, while the optical property was influenced significantly. With the decrease of the feeding molar ratios of Cu/In, the band gap of the resulting CIS colloidal QDs had blue-shifts and relative photoluminescence quantum yield of the corresponding CIS/ZnS colloidal QDs increased monotonically. [ABSTRACT FROM AUTHOR]

The perpendicular magnetization of CoFeAl (CFA) full-Heusler alloy films was achieved by intentional insertion of metal layer Pt into CoFeAl thin film to induce the interfacial perpendicular magnetic anisotropy (PMA). Experimental results indicate that 0.8 nm Pt insertion can greatly improve the ratio of H(out-of-plane)/H(in-plane), indicating the generation of PMA in the Pt inserted CoFeAl thin film. At the same time, the effective damping constant of the CoFeAl film with 0.8 nm Pt insertion layer is 0.0007, which is low enough for spintronic application. Theoretically, based on the first-principles, total energy calculations also prove that the 0.8 nm Pt insertion into CoFeAl film can generate the PMA and agrees with the experimental results very well. This work reveals that 0.8 nm Pt layer insertion in CoFeAl film might pave a way towards possessing both strong PMA and 100% theoretical spin polarization in Heusler alloy films. [ABSTRACT FROM AUTHOR]

MnGa films are the promising magnetic recording materials and spintronic materials owing to their intrinsic properties, such as large magnetic anisotropy, high coercivity, moderate magnetization, and high spin polarization. In this paper, MnGa films with high coercivity and low surface roughness have been successfully fabricated onto MgO substrates by magnetron sputtering and post-annealing. Moreover, the effects of post-annealing temperature ( T) on crystalline structure, surface morphology, and magnetic performances of MnGa films have also been investigated. It is found that the crystallization temperature for MnGa films is 400 C. With increasing T, the crystallization degree enhances and an in-plane texture is formed. The grain size and surface roughness of MnGa films increase slowly when T is below 500 C, but they exhibit a rapid rise when T is above 500 C. As T increases, the coercivity ( H) and remanence squareness ratio ( S) for MnGa films improve monotonically, whereas saturation magnetization ( M) increases firstly and then drops. The increases in H, S, and M with T are attributed to the grains' growth and the improvement of crystallinity, and the decrease of M at higher T possibly is due to the partial oxidation of Mn. [ABSTRACT FROM AUTHOR]

In this paper, the thickness dependences of microstructural, magnetic and electrical properties of Mn-doped GeTe phase change magnetic thin films were studied. The X-ray diffraction patterns demonstrate that the as-deposited films with difference thickness are amorphous while the annealed films are polycrystalline. The crystallographic structure investigation shows that the dominant orientation is enhanced with increasing thickness. The lattice parameters of Mn-doped GeTe thin films as function of the thickness were calculated. The grain sizes increase with the films thickness while the full width at half maximum, plane distance and the lattice strain decrease. The temperature dependences of magnetizations of all the films show that the maximum magnetization values occur at the lowest temperature. The data analysis results of the field cooling magnetization showed that Mn-doped GeTe films have the ferromagnetic ordering at T = 48, 97 and 110 K for film with thickness 60, 120 and 200 nm respectively. It was found that the resistivity decreases from 12.6 to 0.863 mΩ cm as the film thickness increases from 60 to 200 nm. [ABSTRACT FROM AUTHOR]

Phase change random access memory (PCRAM) affords many advantages over conventional solid-state memories due to its nonvolatility, high speed, and scalability. However, high programming current to amorphize the crystalline phase through the melt-quench process of PCRAM, known as the RESET current, poses a critical challenge and has become the most significant obstacle for its widespread commercialization. In this work, an excellent negative tone resist for high resolution electron beam lithography, hydrogen silsesquioxane (HSQ), has been investigated as the insulating material which locally blocks the contact between the bottom electrode and the phase change material in PCRAM devices. Fabrications of the highly scaled HSQ nanopore arrays (as small as 16 nm) are presented. The insulating properties of the HSQ material are studied, especially under e-beam exposure plus thermal curing. Some other critical issues about the thickness adjustment of HSQ films and the influence of the PCRAM electrode on electron scattering in e-beam lithography are discussed. In addition, the HSQ material was successfully integrated into the PCRAM devices, achieving ultra-low RESET current (sub-100 μA), outstanding on/off ratios (~50), and improved endurance at tens of nanometers. [ABSTRACT FROM AUTHOR]

In this work, an effective method to modulate the ferromagnetic properties of Mn-doped GeTe chalcogenide-based phase change materials is presented. The microstructure of the phase change magnetic material GeMnTe thin films was studied. The X-ray diffraction results demonstrate that the as-deposited films are amorphous, and the crystalline films are formed after annealing at 350 °C for 10 min. Crystallographic structure investigation shows the existence of some secondary magnetic phases. The lattice parameters of GeMnTe ( x = 0.04, 0.12 and 0.15) thin films are found to be slightly different with changes of Mn compositions. The structural analysis clearly indicates that all the films have a stable rhombohedral face-centered cubic polycrystalline structure. The magnetic properties of the amorphous and crystalline GeMnTe were investigated. The measurements of magnetization ( M) as a function of the magnetic field ( H) show that both amorphous and crystalline phases of GeMnTe thin film are ferromagnetic and there is drastic variation between amorphous and crystalline states. The temperature ( T) dependence of magnetizations at zero field cooling (ZFC) and field cooling (FC) conditions of the crystalline GeMnTe thin film under different applied magnetic fields were performed. The measured data at 100 and 300 Oe applied magnetic fields show large bifurcations in the ZFC and FC curves while on the 5,000 Oe magnetic field there is no deviation. [ABSTRACT FROM AUTHOR]

A sputter-deposited strontium ferrite film with perpendicular anisotropy has been developed. The film, composed of LaSrCoFeO, has been fabricated directly on quartz glass substrates by radio frequency magnetron sputtering with various heat treatments. The structural and magnetic property dependence of those films on heat treatments has also been studied. The optimized condition is the heat treatment of in situ heating at 400°C and post-annealing at 850°C-900°C. When post-annealing temperature exceeds 900°C, parasitic phases of γ-FeO and LaFeO appear and gradually increase; meanwhile, the magneto plumbite phase gradually decreases. High c-axis perpendicularly oriented films with the coercivity (4148 Oe), remanence squareness ratio (0.89) and perpendicular magnetic anisotropy energy density (1.65 × 10erg/cm) are achieved, which is attributed to the single magneto plumbite phase with compact platelet grains and almost complete (0 0 l) texture of the c-axis normal to the film plane. [ABSTRACT FROM AUTHOR]

Cu(InGa)Se (CIGS) thin films were deposited by a one-step radio frequency (RF) magnetron sputtering process using a quaternary CIGS target. The influence of substrate temperature on the composition, structure, and optical properties of the CIGS films was investigated. All the CIGS films exhibited the chalcopyrite structure with a preferential orientation along the (112) direction. The CIGS film deposited at 623 K showed significant improvement in film crystallinity and surface morphology compared to films deposited at 523 and 573 K. To simplify the manufacturing procedure of solar cells and avoid the use of the toxic element Cd, the properties of ZnS films prepared by RF sputtering were also investigated. The results revealed that the sputtered ZnS film exhibits good lattice matching with the sputtered CIGS film with significantly lower optical absorption loss. Finally, all-sputtered Cd-free CIGS-based heterojunction solar cells with the structure SLG/Mo/CIGS/ZnS/AZO/Al grids were fabricated without post-selenization. Furthermore, the results demonstrated the feasibility of using a full sputtering process for the fabrication of Cd-free CIGS-based solar cell. [ABSTRACT FROM AUTHOR]

SmCo film with perpendicular magnetic anisotropy is a promising candidate ultrahigh-density magnetic recording medium due to its huge magnetocrystalline anisotropy. This paper investigates the effect of Cu substitution for Co on the magnetic properties and microstructure of SmCo film by simulations and experiments. The simulation results based on first-principles theory show that Cu substitution for Co in SmCo can reduce the total exchange- correlation constant and increase the coercivity of SmCo film. Sm(Co,Cu)/Cu/TiW film samples with different Cu doping were fabricated on quartz glass substrates by radiofrequency (RF) magnetron sputtering, and the dependence of the coercivity of the Sm(Co,Cu) film on the Cu doping and annealing conditions was studied. The experimental results demonstrate that Cu doping can decrease the grain size and increase the coercivity of SmCo film. By optimizing the sputtering and annealing conditions, perpendicular coercivity of 3796 Oe was obtained in Sm(CoCu) film. [ABSTRACT FROM AUTHOR]

SmCo is an emerging perpendicular magnetic material for super-high density magnetic recording, due to its large magnetic anisotropy energy. In this paper, the magnetic moments of SmCoCu have been studied using first principles calculation based on density-functional theory (DFT). Calculations are performed using the pseudopotential plane wave DFT code Vienna ab initio simulation package (VASP) with the projector augmented wave (PAW) method. The local density approximation LDA+ U method is used for the calculation of the exchange correlation energy of Sm. The calculation results show that the average Co magnetic moment of SmCoCu decreases with the increase of Cu doping concentrations, and the influence of the Cu doping on the spin state of Co is greater than that of Sm. The magnetic anisotropy energy of SmCo is analyzed. The electronic density of states and the differential in spin densities of atoms show that the spatial distribution of 4 f electron and the 4 f-3 d coupling are the controlling factors of the magnetic anisotropy energy of SmCo. [ABSTRACT FROM AUTHOR]

ZnO nanopolycrystalline thin films were deposited by the sol-gel technique on glass and silicon, and compared systematically via atomic force microscopy, scanning electron microscopy, x-ray diffraction, UV-Vis spectrophotometry, and fluorescence spectrophotometry. The thickness of the ZnO films was measured by ellipsometric microscopy. A higher preheating temperature was needed to obtain films with a strong preferential orientation. The optimal annealing temperatures for c-axis films on glass and silicon substrates were 525°C and 750°C, respectively. The relative intensity of the blue-green emission peak tends to increase with the annealing temperature. When the film is annealed in N, the transmittance of the film reduces while the intensity of the blue-green emission increases. [ABSTRACT FROM AUTHOR]

Atomically thin hexagonal boron nitride (h-BN) is often regarded as an elastic film that is impermeable to gases. The high stabilities in thermal and chemical properties allow h-BN to serve as a gas barrier under extreme conditions. Here, we demonstrate the isolation of hydrogen in bubbles of h-BN via plasma treatment. Detailed characterizations reveal that the substrates do not show chemical change after treatment. The bubbles are found to withstand thermal treatment in air, even at 800 °C. Scanning transmission electron microscopy investigation shows that the h-BN multilayer has a unique aligned porous stacking nature, which is essential for the character of being transparent to atomic hydrogen but impermeable to hydrogen molecules. In addition, we successfully demonstrated the extraction of hydrogen gases from gaseous compounds or mixtures containing hydrogen element. The successful production of hydrogen bubbles on h-BN flakes has potential for further application in nano/micro-electromechanical systems and hydrogen storage. Hexagonal boron nitride (hBN) is a two-dimensional material with wide band gap and high thermal and chemical stability. Here the authors demonstrate the formation and trapping of hydrogen gas bubbles in hBN interlayers upon plasma treatment, promising for extracting and storing hydrogen. [ABSTRACT FROM AUTHOR]