The growth mechanisms of TiO2 film onto PET surfaces by atomic layer deposition

Atomic layer deposition (ALD) was used to coat a polyethylene terephthalate (PET) polymer substrate with TiO _2 film. The TiO _2 was grown onto the surface with better film coverage by using thicker ALD deposition. Further evaluation on the coated substrates indicated that the reactive sites of –C=O that existed on PET surface played a significant contribution to facilitating the initial ALD growth of the TiO _2 thin film. The chemical composition of the coated substrates was characterised using energy dispersive X-ray spectroscopy, which showed that increasing the TiO _2 film thickness increased the Ti element content. Two growth mechanisms, namely, diffusion growth and direct coordination through the precursor coordination with surface reactive sites of –C=O with product release occurred simultaneously in the initial growth of TiO _2 coating onto PET polymer by ALD. The surface alteration of the coated ALD was characterised by Fourier transform infrared spectroscopy, which showed that the hydroxyl –OH groups emerged in the TiO _2 ALD film

Cycling-Induced Capacity Increase of Graphene Aerogel/ZnO Nanomembrane Composite Anode Fabricated by Atomic Layer Deposition

Abstract Zinc oxide (ZnO) nanomembranes/graphene aerogel (GAZ) composites were successfully fabricated via atomic layer deposition (ALD). The composition of GAZ composites can be controlled by changing the number of ALD cycles. Experimental results demonstrated that the anode made from GAZ composite with ZnO nanomembrane of 100 ALD cycles exhibited highest specific capacity and best rate performance. A capacity increase of more than 2 times during the first 500 cycles was observed, and a highest capacity of 1200 mAh g−1 at current density of 1000 mA g−1 was observed after 500 cycles. On the basis of detailed electrochemical investigations, we ascribe the remarkable cycling-induced capacity increase to the alloying process accompanied by the formation of a polymer layer resulting from kinetically activated electrolyte degradation at low voltage regions

Bendable Photodetector on Fibers Wrapped with Flexible Ultrathin Single Crystalline Silicon Nanomembranes

Silicon (Si) nanomembranes (NMs) enable conformal covering on complicated surfaces for novel applications. We adopt classical fibers as flexible/curved substrates and wrap them with freestanding ultrathin Si-NMs with a thickness of ∼20 nm. Intrinsic defects in single-crystalline Si-NMs provide a flow path for hydrofluoric acid (HF) to release the NM with a consecutive area of ∼0.25 cm². Such Si-NMs with ultralow flexural rigidities are transferred onto a single-mode fiber (SMF) and functionalized into bendable photodetectors, which detects the leaked light when the fiber is bent. Our demonstration exemplifies optoelectronic applications in flexible photodetector for Si-NMs in a three-dimensional (3D) geometry

Early Sexual Initiation Is Associated with Suicide Attempts among Chinese Young People

This study aimed to investigate the association between early sexual initiation and suicide attempts (SAs) among Chinese young people. Our analysis included 9131 college students who had sexual experience from a national sample of 31 provincial administrative regions. Self-reported age at first intercourse was categorized as ≤15, 15–18, and ≥18 years, and the experience of SAs was recorded and analyzed. Compared with females whose sexual debut age was ≥18 years, those ≤15 years (defined as early sexual initiation) had higher odds of SAs in both the forced debut group (odds ratio (OR) 17.04, 95% confidence interval (CI) 4.87–59.66) and the voluntary debut group (OR 37.63, 95% CI 14.96–94.66). Early sexual initiators who lived in rural areas were more inclined to have SAs (female: OR 65.76, 95% CI 19.80–218.42; male: OR 15.39, 95% CI 1.64–144.19). Early sexual initiators who never had parent–child communication about sex were more likely to report having SAs (female: OR 37.81, 95% CI 12.28–116.46). Sexual debut during adolescence, particularly early sexual initiation, was a crucial risk factor for SAs among both sexes. Comprehensive sexuality education and smooth parental communication about sex will provide a supportive environment for young people and hence reduce the potential risks of SAs

Extending the search space of Full waveform inversion beyond the single-scattering Born approximation: A tutorial review

International audienceFull Waveform Inversion can be made immune to cycle skipping by matching the recorded data arbitrarily well from inaccurate subsurface models. To achieve this goal, the simulated wavefields can be computed in an extended search space as the solution of an overdetermined problem aiming at jointly satisfying the wave equation and fitting the data in a least-squares sense. This leads to data-assimilated wavefields that are computed by solving the wave equation in the inaccurate background model with a feedback term to the data added to the source term. Then, the subsurface parameters are updated by canceling out these additional source terms, sometime called unwisely wave-equation errors, to push the background model towards the true model in the left-hand side wave-equation operator. Although many studies were devoted to these approaches with promising numerical results, their governing physical principles and their relationships with classical FWI do not seem to be understood well yet. The goal of this tutorial is to review these principles in the framework of inverse scattering theory whose governing forward equation is the Lippmann-Schwinger equation. From this equation, we show how the data-assimilated wavefields embed an approximation of the scattered field generated by the sought model perturbation and how they modify the sensitivity kernel of classical FWI beyond the Born approximation. We also clarify how the approximation with which these wavefields approximate the unknown true wavefields is accounted for in the adjoint source and in the full Newton Hessian of the parameter-estimation problem. The theory is finally illustrated with numerical examples. Understanding the physical principles governing these methods is a necessary prerequisite to assess their potential and limits and design relevant heuristics to manage the latter

Uniaxial and tensile strained germanium nanomembranes in rolled-up geometry by polarized Raman scattering spectroscopy

We present a rolled-up approach to form Ge microtubes and their array by rolling-up hybrid Ge/Cr nanomembranes, which is driven by the built-in stress in the deposited Cr layer. The study of Raman intensity as a function of the angle between the crystal-axis and the polarization-direction of the scattered light, i.e., polarized Raman measurement reveals that the strain state in Ge tube is uniaxial and tensile, and can reach a maximal value 1.0%. Both experimental observations and theoretical calculations suggest that the uniaxial-tensile strain residual in the rolled-up Ge tubes correlates with their tube diameters, which can be tuned by the thicknesses of the Cr layers deposited. Using the polarized Raman scattering spectroscopy, our study provides a comprehensive analysis of the strain state and evolution in self-rolled-up nano/micro-tubes

Multifunctional Nanocracks in Silicon Nanomembranes by Notch-Assisted Transfer Printing

Manipulating nanocracks to produce various nanodevices has attracted increasing interest. Here, based on the mature transfer printing technique, a novel notch-assisted transfer printing technique was engaged to produce nanocracks by simply introducing notch structures into the transferred nanomembranes. Both experiments and finite element simulations were used to elucidate the probability of nanocrack formation during the transfer process, and the results demonstrated that the geometry of nanomembranes played a key role in concentrating stress and producing nanocracks. We further demonstrated that the obtained nanocrack can be used as a surface-enhanced Raman scattering substrate because of the significant enhancement of electric fields. In addition, the capillary condensation of water molecules in the nanocrack led to an obvious change of resistance, thus providing an opportunity for the crack-based structure to be used as an ultrasensitive humidity sensor. The current approach can be applied to producing nanocracks from multiple materials and will have important applications in the field of nanodevices

Does 3D frequency-domain FWI of full-azimuth/long-offset OBN data feasible? The Gorgon case study

Frequency-domain Full Waveform Inversion (FWI) is potentially amenable to efficient processing of full-azimuth long-offset stationary-recording seabed acquisition carried out with sparse layout of ocean bottom nodes (OBNs) and broadband sources because the inversion can be performed with a few discrete frequencies. However, computing efficiently the solution of the forward (boundary-value) problem in the frequency domain with linear algebra solvers remains a challenge for large computational domains involving tens to hundreds of millions of parameters. We illustrate the feasibility of 3D frequency-domain FWI with the 2015/16 Gorgon OBN case study in the NorthWestern shelf, Australia. We solve the forward problem with the massively-parallel multifrontal direct solver MUMPS, which includes four key features to reach high computational efficiency: An efficient parallelism combining message-passing interface and multithreading, block low-rank compression, mixed precision arithmetic and efficient processing of sparse sources. The Gorgon subdataset involves 650 OBNs that are processed as reciprocal sources and 400,000 sources. Mono-parameter FWI for vertical wavespeed is performed in the visco-acoustic VTI approximation with a classical frequency continuation approach proceeding from a starting frequency of 1.7 Hz to a final frequency of 13 Hz. The target covers an area ranging from 260 km2 (frequency > 8.5 Hz) to 705 km2 (frequency < 8.5 Hz) for a maximum depth of 8 km. Compared to the starting model, FWI dramatically improves the reconstruction of the bounding faults of the Gorgon horst at reservoir depths as well as several intra-horst faults and several horizons of the Mungaroo formation down to a depth of 7 km

UV/O₃ Generated Graphene Nanomesh: Formation Mechanism, Properties, and FET Studies

The bandgap engineering of graphene is a challenging task for its potential application. Forming unique structures such as nanoribbons or nanomeshes is an effective way to open up a bandgap in graphene. In this work, a graphene nanomesh (GNM) was prepared through UV-mediated oxidation of a graphene oxide (GO) film at atmosphere. Atomic force microscopy (AFM) was used to track the evolution of the surface morphology of GO during the irradiation. It was observed that a nanoporous network structure was progressively produced in the basal plane, which can be attributed to the fact that highly reactive oxygen species preferentially attack sp³ carbon-rich regions of the GO. In particular, the as-prepared GNM shows interesting semiconducting characteristics and photoluminescence (PL) phenomenon, which make it become a promising candidate for the use of electronics, optoelectronics, and biomedical engineering. Finally, the field-effect transistors (FETs) were fabricated using the as-prepared GNM as the active channel. The measured electrical characteristics indicate that the use of UV/O₃ is an available choice to open the bandgap of graphene and tune its properties for optoelectronics or biomedical applications