Search

Rolling ceramic thermal insulation balls have advantages of low cost, large output and easy control of particle size, so it is likely to become the main raw material for 3D printing in the future, but there is little research on its thermal insulation. In this study, we used three kinds of rolling aluminum oxide balls as raw materials to obtain single-granularity-level and multi-granularity-level bulk materials. And the effects of temperature, particle size, and thermal fatigue times on the thermal conductivity of the samples were analyzed. Additionally, the experimental results were verified by FloEFD heat conduction simulation software using finite analysis method to analyze their heat conduction characteristics. With the increase of temperature from 400 °C to 1500 °C, the thermal conductivity of single-granularity-level and multi-granularity-level bulk materials increased linearly. The thermal conductivity of single-granularity-level bulk materials have no direct relationship with the particle size, and the thermal conductivity of multi-granularity-level materials with small particle size difference was a bit lower than that of materials with large particle size difference, and a bit higher than that of materials with single-granularity-level. The simulation results showed that the main reason for the above phenomenon was that the point contact between particles played a dominating role in the heat transfer process. When the contact area increased, the thermal conductivity increased obviously, and the thermal conductivity with the increasing of temperature decreased in a quadratic curve. The improved model considering the shrinkage could improve accuracy of simulation results. Heat flux at the surface contact area was 10.19 times higher than that of the point contact and 15.10 times higher than that of the solid-gas contact at 400 °C. Therefore, reducing the surface contact area and increasing the porosity could significantly reduce the thermal conductivity of the materials.

β-SiAlON–ZrO2 composite ceramics were prepared, and their phase composition, microstructure, bulk density, porosity, flexural strength, Young's modulus, and ion release were characterized. Their biological properties were detected by culturing osteoblast MC3T3-E1 cells on the ceramic surfaces. Si4Al2O2N6 formed by reaction of α-Al2O3, Al, and Si with N2 and sintered with ZrO2, resulting in β-SiAlON–ZrO2 composite ceramics. The porosity of the ceramics decreased and the bulk density, flexural strength, and Young's modulus increased with increasing ZrO2 content. MC3T3-E1 cells have a good adhesion and growth state on the surface of composite ceramics; the composite ceramics exhibited good biocompatibility. The cells' wound-healing ability was improved by addition of a small amount of ZrO2 but was adversely affected by the addition of excessive ZrO2. Thus, properties of β-SiAlON–ZrO2 were regulated by addition of ZrO2, and the resulting ceramic composites satisfy the requirements for biomaterials used in diverse applications.

In this study, SiAlON–Si3N4 composite ceramic are prepared by direct nitridation and investigated to overcome the limitations associated with ceramic Si3N4, which includes the difficulty in fabricating ceramic Si3N4 into shaped parts for use in the human body. Phase composition and microstructure of the SiAlON–Si3N4 composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively, and the porosity, bulk density, compressive strength, and ion release were also measured. The biological properties were evaluated by bone cell cultures on the ceramic surfaces. Results show that Si4Al2O2N6 is formed by the reaction of Al, Si, and Al2O3 with nitrogen at high temperature that forms Si3N4, thereby fabricating SiAlON–Si3N4 composite ceramics. Some α-Si3N4 grains underwent a phase transition from α-to β-Si3N4 fiber at high temperature. Porosity of the samples increases with increasing Si3N4 content, while the bulk density of the samples decreases. The compressive strength increases and then slightly decreases with increasing Si3N4 content. Water leaching experiments of the SiAlON–Si3N4 composite ceramics reveal that the composites exhibit outstanding chemical stability. Studies using bone cell culture indicate that the cells present a fusiform and extend two or three thin pseudopodia. The phenomena demonstrate that MC3T3-E1 cells have excellent growth activity and have the potential ability to proliferate to osteocytes on the surfaces of the samples, thus suggesting that SiAlON–Si3N4 based ceramics are biocompatible and could be implemented as a potential bone-repairing material.

When used as implants, Al2O3 is unable of directly achieving good chemical bonding with soft and hard tissues. To overcome this problem, SiAlON–Al2O3 ceramics were prepared in this study by direct nitridation. Phase composition, porosity, bulk density, and compression strengths were examined, and biological properties were evaluated by cell culture on ceramic surface. Major phase of SiAlON–Al2O3 ceramics was identified as Si4Al2O2N6, formed by reaction of Si, Al and Al2O3 under nitrogen atmosphere at high temperature. As Al2O3 content increased, porosity and compressive strength decreased. Therefore, Si4Al2O2N6 phase could improve sintering, leading to formation of composites with better properties. The porosity and compression strength were found suitable for requirement of biomaterials. Cell culture experiments showed that cells could proliferate and survival well on ceramic surface, indicating good biocompatibility of Si4Al2O2N6 phase in SiAlON–Al2O3 ceramics. Overall, these data look promising and might provide novel strategies for development of future SiAlON–Al2O3 bioceramics.

Platinum disulfide (PtS2), a member of the recently developed group 10 transition metal dichalcogenide (TMD) materials, exhibits great potential in optoelectronics applications. Nevertheless, its photoluminescence (PL) behavior still remains obscure. Quantum dots (QDs) are believed having the capability to enhance photoluminescence property compared to the bulky or layered structure owing to their quantum confinement effects. Inspired by remarkable PL enhancement works on other TMD materials QDs, the fabrication of PtS2 QDs suspension via a low-cost liquid exfoliation technique is demonstrated in this work. The PtS2 QDs with an average diameter of 3.9 nm and average thickness of 2.9 nm are observed, respectively. For the first time, the PL spectra of PtS2 QDs suspension are successfully obtained and monitored over time. The PL spectra display an excitation-dependent luminescence. The maximum emission peak is observed at 407.2 nm for the excitation wavelength of 330 nm. This PtS2 QDs also shows a decent long-term stability. These results open up encouraging prospects of luminescence applications of PtS2 QDs.

Functional oxides on silicon have been the subject of in-depth research for more than 20 years. Much of this research has been focused on the quality of the integration of materials due to their intrinsic thermodynamic incompatibility, which has hindered the flourishing of the field of research. Nevertheless, growth of epitaxial transition metal oxides on silicon with a sharp interface has been achieved by elaborated kinetically controlled sequential deposition while the crystalline quality of different functional oxides has been considerably improved. In this Research Update, we focus on three applications in which epitaxial ferroelectric oxides on silicon are at the forefront, and in each of these applications, other aspects of the integration of materials play an important role. These are the fields of piezoelectric microelectromechanical system devices, electro-optical components, and catalysis. The overview is supported by a brief analysis of the synthesis processes that enable epitaxial growth of oxides on silicon. This Research Update concludes with a theoretical description of the interfaces and the possibility of manipulating their electronic structure to achieve the desired coupling between (ferroelectric) oxides and semiconductors, which opens up a remarkable perspective for many advanced applications. © 2021 Author(s).

The high-performance broadband photodetectors have attracted intensive scientific interests due to their potential applications in optoelectronic systems. Despite great achievements in two-dimensional (2D) materials based photodetectors such as graphene and black phosphorus, obvious disadvantages such as low optical absorbance and instability preclude their usage for the broadband photodetectors with the desired performance. An alternative approach is to find promising 2D materials and fabricate heterojunction structures for multifunctional hybrid photodetectors. In this work, 2D WS2/Si heterojunction with a type-II band alignment is formed in situ. This heterojunction device produced a high Ion/Ioff ratio over 10,6 responsivity of 224 mA/W, specific detectivity of 1.5 × 1012 Jones, high polarization sensitivity, and broadband response up to 3043 nm. Furthermore, a 4 × 4 device array of WS2/Si heterojunction device is demonstrated with high stability and reproducibility. These results suggest that the WS2...

In this work, we examined the performance of 2D titanate nanosheets for dye adsorption. Their adsorption capacity for methylene blue (MB) is up to 3937 mg g−1, which is more than 10 times higher than active carbon and occupies the highest place among all the reports.

The research of ultraviolet photodetectors (UV PDs) have been attracting extensive attention, due to their important applications in many areas. In this study, PtSe2/GaN heterojunction is in-situ fabricated by synthesis of large-area vertically standing two-dimensional (2D) PtSe2 film on n-GaN substrate. The PtSe2/GaN heterojunction device demonstrates excellent photoresponse properties under illumination by deep UV light of 265 nm at zero bias voltage. Further analysis reveals that a high responsivity of 193 mA·W–1, an ultrahigh specific detectivity of 3.8 × 1014 Jones, linear dynamic range of 155 dB and current on/off ratio of ~ 108, as well as fast response speeds of 45/102 μs were obtained at zero bias voltage. Moreover, this device response quickly to the pulse laser of 266 nm with a rise time of 172 ns. Such high-performance PtSe2/GaN heterojunction UV PD demonstrated in this work is far superior to previously reported results, suggesting that it has great potential for deep UV detection.

Methylammonium lead iodide perovskite (MAPbI 3), as a new type of light absorber for optoelectronic devices, has attracted much interest and served as foundation for new device concepts. However, most studies to date are mainly focusing on the fabrication of MAPbI3 -based solar cells and photodetectors . Here we report a facile method to prepare a large-scale MAPbI 3 photocatalyst through atmospheric pressure physical vapor deposition . The photocurrent density of the MAPbI 3 coated with an Au layer can reach 30.8 and 85.5 μA/cm2 in ethanol and H2SO4 electrolytes, respectively. Meanwhile, the strong interaction between H2O orbitals and the conduction band of MAPbI3 is revealed by density functional theory calculations. Our study opens a new pathway for the development of perovskite-based photo-electrochemical reaction systems.

The development of cost-effective, durable and high-efficient oxygen evolution reaction (OER) electrocatalysts is an extremely critical technology for the large-scale industrial water electrolysis. Here, a new strategy is proposed to significantly enhance the electrocatalytic activity by forming a hybrid electrode of NiSe and Fe4.4Ni17.6Se16 through direct selenization of porous iron-nickel (FeNi) alloy foam via thermal selenization process. The obtained self-supported Fe4.4Ni17.6Se16/NiSe hybrid (FNS/NiSe) foam displays outstanding durability and remarkable catalytic activity in 1.0 M KOH with low overpotentials of 242 and 282 mV to achieve the current densities of 100 and 500 mA cm−2, respectively. To the best of our knowledge, it exceeds most of the reported OER electrocatalysts in alkaline electrolytes.

An equivalent multisector analytical method is proposed for the high-frequency characteristics of the slow-wave structure (SWS) in an integrated three-helix traveling wave tube. The discrete unit in the SWS is divided into multiple regions, and every region is treated equivalently as a sector using the equal area method. The accuracy of the equivalent multisector structure is verified by comparing it with an equivalent circular structure and the original SWS in computer simulation technology (CST). The analytical solution for high-frequency characteristics of the equivalent multisector structure is obtained by using the tape-helix model and the infinite number of vanes model. The calculation result is obtained and compared with the CST simulation result to analyze the accuracy of the method. The maximum error for dispersion characteristics and coupling impedance is 5.3% and 6.1%, respectively, so the feasibility of the analytical method is verified.

The newly discovered Group-10 transition metal dichalcogenides (TMDs) like PtSe2 have promising applications in high-performance microelectronic and optoelectronic devices due to their high carrier mobilities, widely tunable bandages and ultrastabilities. However, the optoelectronic performance of broadband PtSe2 photodetectors integrated with silicon remains undiscovered. Here, we report the successful preparation of large-scale, uniform and vertically grown PtSe2 films by simple selenization method for the design of a PtSe2/Si nanowire array heterostructure, which exhibited a very good photoresponsivity of 12.65 A/W, a high specific detectivity of 2.5 × 1013 Jones at −5 V and fast rise/fall times of 10.1/19.5 μs at 10 kHz without degradation while being capable of responding to high frequencies of up to 120 kHz. Our work has demonstrated the compatibility of PtSe2 with the existing silicon technology and ultrabroad band detection ranging from deep ultraviolet to optical telecommunication wavelengths, which can largely cover the limitations of silicon detectors. Further investigation of the device revealed pronounced photovoltaic behavior at 0 V, making it capable of operating as a self-powered photodetector. Overall, this representative PtSe2/Si nanowire array-based photodetector offers great potential for applications in next-generation optoelectronic and electronic devices. Aligning ultra-thin semiconductors with silicon nanowires enables high-speed sensing of an unusually broad range of ultraviolet, visible, and infrared light frequencies. The shapes of silicon nanowires enable quicker and more effective light detection than conventional thin films, but their spectral response still falls outside the parameters needed for various applications, including optical telecommunication. Researchers led by Di Wu from China’s Zhengzhou University and Yuen Hong Tsang at Hong Kong Polytechnic University turned to the broadband absorption of graphene-like platinum selenide (PtSe2) films to extend the light sensitivity. To parallel the geometry of nanowires, the team used precision deposition techniques to grow 2D PtSe2 films into vertically-oriented layers, some tens of nanometers thick. Direct transfer of the PtSe2 film onto a large-scale nanowire array produced a microsecond-fast device sensitive to multiple optical bands. Platinum diselenide (PtSe2) is a newly discovered Group-10 transition metal dichalcogenide (TMD) which has unique electronic properties, in particular a semimetal-to-semiconductor transition. In this work, we have demonstrated the proposed vertically standing layered structure PtSe2 nanofilms based on hybrid heterojunction with high overall performance was realized for broadband light photodetection ranging from 200 nm to 1550 nm. The high-performance broadband photodetector will open up a new pathway for the development of next-generation two dimensional Group-10 materials based optoelectronic devices.

Flexible and sensitive sensors that can detect external stimuli such as pressure, temperature, and strain are essential components for applications in health diagnosis and artificial intelligence. Multifunctional sensors with the capabilities of sensing pressure and temperature simultaneously are highly desirable for health monitoring. Here, we have successfully fabricated a flexible and simply structured bimodal sensor based on metal–organic frameworks (MOFs) derived porous carbon (PC) and polydimethylsiloxane (PDMS) composite. Attributed to the porous structure of PC/PDMS composite, the fabricated sensor exhibits high sensitivity (15.63 kPa–1), fast response time ( 0.11 °C–1) and fast response time (∼100 ms), indicating its p...

Nanosheet Ca2Nb3O10 (CNOns) layers were deposited on ultralow expansion glass substrates by the Langmuir–Blodgett method to obtain preferential (001)-oriented growth of Pb(Zr0.52Ti0.48)O3 (PZT) thin films using pulsed laser deposition (PLD) to enhance the ferroelectric and piezoelectric properties of the films. The PLD deposition temperature and repetition frequency used for the deposition of the PZT films were found to play a key role in the precise control of the microstructure and therefore of the ferroelectric and piezoelectric properties. A film deposited at a high repetition frequency has a columnar grain structure, which helps to increase the longitudinal piezoelectric coefficient (d33f). An enhanced d33f value of 356 pm V–1 was obtained for 2-μm-thick PZT films on CNOns/glass substrates. This high value is ascribed to the preferential alignment of the crystalline [001] axis normal to the substrate surface and the open columnar structure. Large displacement actuators based on such PZT films grown on CNOns/glass substrates should be useful in smart X-ray optics applications.

Methods and mechanisms for improvement of photocatalytic activity, are important and popular research topics for renewable energy production and waste water treatment. Here, we demonstrate a facile laser drilling method for engineering well-aligned pore arrays on magnetron-sputtered WS2 nanofilms with increased active edge sites; the proposed method promotes partial oxidation to fabricate WS2/WO3 heterojunctions that enhance the separation of photogenerated electron-hole pairs. The WS2 film after one, two, and three treatments exhibited photocurrent density of 3.9, 6.2, and 8 μA/cm2, respectively, reaching up to 31 times larger than that of pristine WS2 film along with greatly improved charge recombination kinetics. The unprecedented combinational roles of laser drilling revealed in this study in regards to geometric tailoring, chemical transformation, and heterojunction positioning for WS2-based composite nanomaterials create a foundation for further enhancing the performance of other 2D transition metal dichalcogenides in photocatalysis via laser treatment.

The two-dimensional electron liquid which forms between the band insulators LaAlO3 (LAO) and SrTiO3 (STO) is a promising component for oxide electronics, but the requirement of using single crystal SrTiO3 substrates for the growth limits its applications in terms of device fabrication. It is therefore important to find ways to deposit these materials on other substrates, preferably Si, or Si-based, in order to facilitate integration with existing technology. Interesting candidates are micron-sized nanosheets of Ca2Nb3O10 which can be used as seed layers for perovskite materials on any substrate. We have used low-energy electron microscopy (LEEM) with in-situ pulsed laser deposition to study the subsequent growth of STO and LAO on such flakes which were deposited on Si. We can follow the morphology and crystallinity of the layers during growth, as well as fingerprint their electronic properties with angle resolved reflected electron spectroscopy. We find that STO layers, deposited on the nanosheets, can be made crystalline and flat; that LAO can be grown in a layer-by-layer fashion; and that the full heterostructure shows the signature of the formation of a conducting interface., 11 pages, 7 figures

Group‐10 transition metal dichalcogenides (TMDs) with distinct optical and tunable electrical properties have exhibited great potential for various optoelectronic applications. Herein, a self‐powered photodetector is developed with broadband response ranging from deep ultraviolet to near‐infrared by combining FA1−xCsxPbI3 perovskite with PdSe2 layer, a newly discovered TMDs material. Optoelectronic characterization reveals that the as‐assembled PdSe2/perovskite Schottky junction is sensitive to light illumination ranging from 200 to 1550 nm, with the highest sensitivity centered at ≈800 nm. The device also shows a large on/off ratio of ≈104, a high responsivity (R) of 313 mA W−1, a decent specific detectivity (D*) of ≈1013 Jones, and a rapid response speed of 3.5/4 µs. These figures of merit are comparable with or much better than most of the previously reported perovskite detectors. In addition, the PdSe2/perovskite device exhibits obvious sensitivity to polarized light, with a polarization sensitivity of 6.04. Finally, the PdSe2/perovskite detector can readily record five “P,” “O,” “L,” “Y,” and “U” images sequentially produced by 808 nm. These results suggest that the present PdSe2/perovskite Schottky junction photodetectors may be useful for assembly of optoelectronic system applications in near future.

The oxide nanosheet concentration at the liquid–air interface (LAI) is a key parameter in the formation of Langmuir–Blodgett (LB) deposited nanosheet films. Knowledge of the oxide nanosheet concentration at the LAI as a function of process conditions is needed to understand the relevant processes and achieve better control over the LB fabrication process. In this study, the concentration of Ti0.87O2δ− titanate nanosheets at the LAI was investigated by considering the trend in the lift-up point (LUP) in the surface pressure–surface area isotherm of an LB compression process as a function of time and exfoliation agent. The oxide nanosheet concentrations in the bulk solutions were studied using UV–vis spectroscopy. The results show that the restacking process in the bulk solution does not significantly retard the occurrence of nanosheets at the LAI. The nanosheet concentration changes in the bulk and at the LAI occur on different time scales. Short exfoliation times yield higher nanosheet concentrations at the LAI than longer exfoliation times, in contrast to the bulk where the nanosheet concentration increases in the course of time. We found the same behavior for other metal oxide nanosheet solutions, i.e., iron-doped titanate (Ti0.6Fe0.4O20.4–) and calcium niobate (Ca2Nb3O10–) nanosheets. The reason behind this phenomenon is likely related to the high degree of adsorption of surfactant molecules on the nanosheet surface after short exfoliation times.

In this study, the impact of radial deviation of the electron beam on backward wave oscillation (BWO) in a helix travelling wave tube (TWT) is explored. By using CST simulation, the output power of a helix TWT with the electron beam deviation of 0.01 mm is obtained and compared with that of a normal TWT. We found that the output power of the helix TWT changes by 40 W. By analysing the backward wave signal when the TWT works at 11 GHz for different values of the radial deviation of the electron beam, we found that the backward wave amplitude increases as the radial deviation of the electron beam increases. When the radial deviation reaches 0.04 mm (9.5% relative to the electron beam), the backward wave starts to oscillate. When the radial deviation reaches 0.06 mm (14.3% relative to the electron beam), the BWO becomes more severe. It has been proved that the radial deviation of the electron beam is one of the contributing factors for BWO in the helix TWT.

The compounds of KCa2Nan−3NbnO3n+1 (n = 3–6) are a series of layered niobates, consisting of the interlayer ions K+ and the layer stacks with different layer thickness. Synthesis of these compounds is critical for their applications. In literature, there are two synthetic ways reported, i.e., step-by-step synthesis and direct synthesis. Among them, the direct synthesis method is an emerging technique. In this work, synthesis parameters such as temperature, additives for both of methods were carefully studied for controllable synthesis. Our results show that all the compounds of KCa2Nan−3NbnO3n+1 (n = 3–6) can be synthesized by the direct synthesis. High purity synthesis for KCa2Na2Nb5O16 and KCa2Na3Nb6O19 phases requires an excess of 20 mol% K2CO3 and 5 mol% Na2CO3, and 20% K2CO3 and 10% Na2CO3 respectively at temperature of 1300℃ for 15 h. In comparison, the highest order homologue by the step-by-step synthesis is KCa2NaNb4O13 in this study.

First CCD photometry for the contact binary MT Cas is performed in 2013 in December. The spectral type of F8V is determined from the low-precision spectrum observed on 2018 Oct 22. With Wilson-Devinney code, the photometric solutions are deduced from VRc light curves (LCs) and AAVSO’s and ASAS-SN’s data, respectively. The results imply that MT Cas is a W-type weak-contact binary with a mass ratio of q=2.365(±0.005) and a fill-out factor of f=16.6(±1.2)%, respectively. The asymmetric LCs in 2013 are modeled by a dark spot on the more massive component. By analyzing the (O-C) curve, it is discovered that the orbital period may be undergoing a secular increase at a rate of dP/dt=1.12(±0.09)×10-8d yr-1, which may result from mass transfer from the less massive component to the more massive one. With mass transferring, MT Cas may evolve into a broken-contact configuration as predicted by TRO theory.

The comprehensive photometry and spectroscopy for the neglected eclipsing binary EU Pegasi are presented. We determine its spectral type to be A3V. With the W-D program, the photometric solution was deduced from the four-color light curves. The results imply that EU Peg is a detached binary with a mass ratio of q = 0.3105(+/- 0.0011), whose components nearly fill their Roche lobes. The low-amplitude pulsation occurs around the secondary eclipse, which may be attributed to the more massive component. Three frequencies are preliminarily explored by the Fourier analysis. The pulsating frequency at f(1) = 34.1 c d(-1) is a p-mode pulsation. The orbital period may be undergoing a secular decrease, superimposed by a cyclic variation. The period decreases at a rate of dP/dt = -7.34 +/- 1.06 d yr(-1), which may be attributed to mass loss from the system due to stellar wind. The cyclic oscillation, with P-mod = 31.0 +/- 1.4 yr and A = 0.0054 +/- 0.0010 d, may be caused by the light-time effect due to the assumed third body. With its evolution, the pulsating binary EU Peg will evolve from the detached configuration to the semi-detached case.

The nature of the external crystal facets is critical to control the (photo)catalytic properties. Two-dimensional materials can expose only one type of crystal facet among zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D) materials. Controllable tuning of the nature of the external crystal facets of 2D materials is highly desirable but very challenging. Here, we show that 2D particles with the desirable crystal facet for high-performance photocatalytic H2 generation can be obtained by using 2D metal oxide materials (i.e., nanosheets of Ca2Nb3O10 and Ti0.87O2) as templates taking consideration of the crystal configuration of 2D oxide and target compounds. We demonstrate that anatase TiO2 crystals grown on different nanosheet templates exhibit variations in photocatalytic hydrogen production rates from aqueous phase methanol solutions (6.7%), which can be attributed to the nature of the main crystal facet exposed. In view of the large number of 2D materials that have already been synthesized, this work offers a key to design and synthesize nanoparticles with the desirable specific external crystal facet for (photo)catalysis application.

The temperature distribution and thermal deformation along the slow-wave structure of a travelling wave tube (TWT) under operation have been analyzed. Considering a series of thermal losses, including electron collision on the helix, eddy current loss on the surfaces of the helix and barrel, and the electromagnetic field loss in the attenuators, we analyze the full thermal status for the slow-wave structure of TWT by using CST MPhysics Studio. The simulation results show high-temperature region is concentrated on the last 15-20 turns of the helix on which the highly geometric deformation is produced, and same deformation is also generated on inner conductor of output window with the peak deformation value of 0.0157 mm.

Indium selenide (In2Se3) has attracted tremendous attention due to its favorable electronic features, broad tunable bandgap, high stability and other attractive properties. However, its further applications for nonlinear optics have not yet been fully explored. In this work, we demonstrate that few-layer ?-In2Se3 nanosheets exhibit strong saturable absorption properties over a wide wavelength range covering 800 nm, 1064 nm and 1550 nm. The few-layer ?-In2Se3 nanosheets used for this experiment are fabricated via a simple ultrasonic exfoliation in liquid. Stable ultrafast mode-locking laser pulses are obtained from both ytterbium-doped and erbium-doped fiber laser systems operating at 1064 and 1550 nm, respectively. A pulse duration as short as 215 fs was achieved in the Er-doped fiber laser system. Stable output pulses over 6 hours of operation were obtained in both laser systems. The pulse energy and peak power of the laser output pulses were increased by reducing the In2Se3 thickness. These results indicate that ?-In2Se3 nanosheets with low layer numbers are promising candidates for broad ultrafast photonics devices, such as optical switchers, Q-switchers and mode lockers.

Ca2Nb3O10 (CNOns) and Ti0.87O2 (TiOns) metal oxide nanosheets (ns) are used as a buffer layer for epitaxial growth of piezoelectric capacitor stacks on Si and Pt/Ti/SiO2/Si (Pt/Si) substrates. Highly (001)- and (110)-oriented Pb(Zr0.52Ti0.48)O3 (PZT) films are achieved by utilizing CNOns and TiOns, respectively. The piezoelectric capacitors are characterized by polarization and piezoelectric hysteresis loops and by fatigue measurements. The devices fabricated with SrRuO3 top and bottom electrodes directly on nanosheets/Si have ferroelectric and piezoelectric properties well comparable with devices that use more conventional oxide buffer layers (stacks) such as YSZ, CeO2/YSZ, or SrTiO3 on Si. The devices grown on nanosheets/Pt/Si with Pt top electrodes show significantly improved polarization fatigue properties over those of similar devices grown directly on Pt/Si. The differences in properties are ascribed to differences in the crystalline structures and the density of the films. These results show a route toward the fabrication of single crystal piezoelectric thin films and devices with high quality, long-lifetime piezoelectric capacitor structures on nonperovskite and even noncrystalline substrates such as glass or polished metal surfaces.

The intercalation of different primary n-alkylamines in the structure of a layered titanate of the lepidocrocite type (H1.07Ti1.73O4) for application in high-temperature solid lubrication is reported. The intercalation process of the amines was explored by means of in situ small-angle X-ray scattering (SAXS), with variations in alkyl chain length (3–12 carbon atoms) and the amine/titanate ratio. The intercalation process was found to be completed within 5 min after mixing of the precursors in water at 80 °C. The topotactic transformation of the layered titanate is driven by an acid–base reaction. The thermal degradation of the modified titanates was investigated by thermogravimetric analysis (TGA), and the chemical changes were investigated by temperature-dependent infrared spectroscopy (DRIFTS). The coefficient of friction of the lubricants was assessed by means of high-temperature pin-on-disc experiments up to 580 °C. The intercalation of amine rendered a deformable layered ceramic upon heating. It was found that the hydrocarbon chain length exerts an influence on the mechanical properties of the titanates, resulting in lower friction forces for lubricants with longer intercalated amine molecules. Films of solid lubricants with longer amine chain lengths showed coefficients of friction as low as 0.01, lower than that of the state-of-the-art material graphite.

In complex chemical syntheses (e.g., coprecipitation reactions), nucleation, growth, and coarsening often occur concurrently, obscuring the individual processes. Improved knowledge of these processes will help to better understand and optimize the reaction protocol. Here, a form-free and model independent approach, based on a combination of time-resolved small/wide-angle X-ray scattering, is employed to elucidate the effect of reaction parameters (such as precursor concentration, reactant stoichiometry, and temperature) on the nucleation, crystallization, and growth phenomena during the formation of nanocrystalline barium titanate. The strength of this approach is that it relies solely on the total scattered intensity (i.e., scattering invariant) of the investigated system, and no prior knowledge is required. As such, it can be widely applied to other synthesis protocols and material's systems. Through the scattering invariant, it is found that the amorphous-to-crystalline transformation of barium titanate is predominantly determined by the total amount of water released from the gel-like barium hydroxide octahydrate precursor, and three rate-limiting regimes are established. As a result of this improved understanding of the effect of varying reaction conditions, elementary boundary conditions can be set up for a better control of the barium titanate nanocrystal synthesis.

Numerous studies have been conducted to explore the performance of two-dimensional (2D) layered nano-materials based saturable absorber (SA) for pulsed laser applications. However, fabricating materials in nanoscale requires complicated preparation processes, high energy consumption, and high expertise. Hence, the study of pulsed laser performance based on the saturable absorber prepared by layered materials with bulk-micro size have gained a great attention. Platinum disulfide (PtS2), which is newly developed group 10 2D layered materials, offers great potential for the laser photonic applications owing to its high carrier mobility, broadly tunable natural bandgap energy, and stability. In this work, the first passively Q-switched Erbium (Er) doped fiber laser is demonstrated with an operational wavelength of 1568.8 nm by using PtS2 microflakes saturable absorber, fabricated by a simple liquid exfoliation in N-Methyl-2-pyrrolidone (NMP) and then incorporated into polyvinyl alcohol (PVA) polymer thin film. A stable Q-switched laser operation is achieved by using this PtS2-SA within a fiber laser ring cavity. The maximum average output power is obtained as 1.1 mW, corresponding to the repetition rate of 24.6 kHz, the pulse duration of 4.2 μs, and single pulse energy of 45.6 nJ. These results open up new applications of this novel PtS2 layered material.

The developments and state of the art in the research on two-dimensional nanosheets derived from layered metal oxides and layered metal hydroxides are reviewed in this paper, with emphasis on their promising applications in various new energy technologies, i.e., as supercapacitor electrodes, lithium ion battery electrodes, solar cell components, photocatalysts, and as functional elements in fuel cells and piezoelectric energy harvesters. Nanosheets are defined by their molecular thickness and large lateral dimensions, which typically differ by 2–5 orders of magnitude. They exhibit a wide range of interesting properties, e.g., flexibility, transparency, semiconductivity, photosensitivity, photocatalytic activity, redox properties, a large specific surface area and a high chemical stability. A large and growing library of metal oxide and hydroxide nanosheet compositions is available from the literature. Moreover, the easy control over nanosheet composition via modification of the layered parent compound provides many opportunities for introducing and optimizing their functional properties. This review focuses on the synthesis of oxide and hydroxide nanosheet colloids, their controlled assembly into nanocomposites, thin films, multilayers, superlattices and spheres, and the utilization of these structures in energy applications.