Residue-Free Suspended Graphene Transferred by Perforated Template

A residue-free transfer method for graphene is proposed in this study, especially for the fabrication of suspended structures. Using perforated polymer templates, graphene can be precisely transferred onto the specific position in the perforated target SiO2/Si substrates without the need for polymer removal and the subsequent thermal annealing process. The surface of the transferred graphene by the proposed method was analyzed and corroborated via Raman spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy. The results of these analyses suggest that the graphene surface has no polymeric residues resulting from the transfer process. The proposed method provides a powerful approach for the transfer of 2D materials and it enables the exploitation of their suspended structures for device applications as well as the physical characterizations without worry on the effect of contaminants.

Optimization Inspired on Herd Immunity Applied to Non-Hierarchical Grouping of Objects

Characterized as one of the most important operations related to data analysis, one non-hierarchical grouping consists of, even without having any information about the elements to be classified, establish upon a finite collection of objects, the partitioning of the items that constitute it into subsets or groups without intersecting, so that the elements that are part of a certain group are more similar to each other than the items that belong to distinct group. In this context, this study proposes the application of a meta-heuristic inspired by herd immunity to the determination of the non-hierarchical grouping of objects, and compares the results obtained by this method with the answers provided by four other grouping strategies, described in the literature. In particular, the resulting arrangements of the classification of 33 benchmark collections, performed by the suggested algorithm, by the metaheuristic inspired by the particle swarm, by the genetic algorithm, by the K-means algorithm and by the meta-heuristic inspired by the thermal annealing process, were compared under the perspective of 10 different evaluation measures, indicating that the partitions established by the meta-heuristic inspired by the herd immunity may, in certain respects, be more favorable than the classifications obtained by the other clustering methods.

The Effect of Annealing on Additive Manufactured ULTEM™ 9085 Mechanical Properties

Fused filament fabrication (FFF) is increasingly adopted for direct manufacturing of end use parts in an aviation industry. However, the application of FFF technique is still restricted to manufacturing low criticality lightly loaded parts, due to poor mechanical performance. To alleviate the mechanical performance issue, thermal annealing process is frequently utilized. However, problems such as distortion issues and the need for jigs and fixtures limit the effectiveness of the thermal annealing process, especially for low volume complex FFF parts. In this research, a novel low temperature thermal annealing is proposed to address the limitations in conventional annealing. A modified orthogonal array design is applied to investigate the performance of ULTEM™ 9085 FFF coupons. Further, the coupons are annealed with specialized support structures, which are co-printed with the coupons during the manufacturing process. Once the annealing process is completed, multiscale characterizations are performed to identify the mechanical properties of the specimens. Geometrical measurement of post annealed specimens indicates an expansion in the layering direction, which indicates relief of thermal stresses. Moreover, annealed coupons show an improvement in tensile strength and reduction in strain concentration. Mesostructure and fracture surface analysis indicate an increase in ductility and enhanced coalescence. This research shows that the proposed annealing methodology can be applied to enhance the mechanical performance of FFF parts without significant distortion.

Enhanced electrochemical water splitting activity in annealed TiO2 nanoparticles of photoanode

In this paper, we present the electrochemical water splitting characteristics of TiO2/FTO electrodes via spin-coating method. By using thermal annealing approach, the TiO2 nanoparticle (P25) was modified with a more active photocatalyst. The annealed TiO2 nanoparticle-based photoanode in vacuum shows photocurrent density of 0.27 mA/cm2 and photoconversion efficiency of (η = 0.22%) at potential of 0.4 V (vs. RHE), which are higher than those of annealed TiO2 nanoparticle-based electrode in air. The improved photoelectrochemical property is attributed to high oxygen vacancy density with more active sides, while TiO2 nanoparticle was annealed in vacuum (∼10−1 torr) with oxide concentration conditions. From this finding, we propose that a thermal annealing process might serve as an approach for fabricating the photoanodes of TiO2-based materials consisting of much active photocatalyst

Design and Fabrication of Bulk Micromachined 4H-SiC Piezoresistive Pressure Chips Based on Femtosecond Laser Technology

Silicon carbide (SiC) has promising potential for pressure sensing in a high temperature and harsh environment due to its outstanding material properties. In this work, a 4H-SiC piezoresistive pressure chip fabricated based on femtosecond laser technology was proposed. A 1030 nm, 200 fs Yb: KGW laser with laser average powers of 1.5, 3 and 5 W was used to drill blind micro holes for achieving circular sensor diaphragms. An accurate per lap feed of 16.2 μm was obtained under laser average power of 1.5 W. After serialized laser processing, the machining depth error of no more than 2% and the surface roughness as low as 153 nm of the blind hole were measured. The homoepitaxial piezoresistors with a doping concentration of 1019 cm−3 were connected by a closed-loop Wheatstone bridge after a rapid thermal annealing process, with a specific contact resistivity of 9.7 × 10−5 Ω cm2. Our research paved the way for the integration of femtosecond laser micromachining and SiC pressure sensor chips manufacturing.

Microtubule-based hierarchical porous carbon for lightweight and strong wideband microwave absorption

A lightweight and strong wideband microwave absorber, microtubule-based porous carbon, is synthesized by a feasible pretreatment and thermal annealing process.

A Facile and Broadly Applicable CdBr2-Passivating Strategy for Halide Migration-Inhibiting Perovskite Films and High-Performance Solar Cells

The defects including halide vacancy and uncoordinated Pb in perovskite films caused by the cracking Pb-I bonds in thermal annealing process are responsible for degradation of the photovoltaic performance and...

Room temperature wideband tunable photoluminescence of pulsed thermally annealed layered black phosphorus

Newly explored two-dimensional (2D) materials have shown promising optical properties, owning to the tunable band gap of the layered material with its thickness. A widely used method to achieve tunable light emission (or photoluminescence) is through thickness modulation, but this can only cover specific wavelengths. This approach limits the development of tunable optical devices with high spectral resolution over a wide range of wavelengths. Here, we report wideband tunable light emission of exfoliated black phosphorus nanosheets via a pulsed thermal annealing process in ambient conditions. Tunable anisotropic emission was observed between wavelengths of 590 and 720 nm with a spectral resolution of 5 nm. This emission can be maintained for at least 11 days when proper passivation coupled with adequate storage is applied. Using hyperspectral imaging X-ray photoelectron spectroscopy (i-XPS), this tunable emission is found to be strongly dependent on the level of oxidation. We finally discuss the underlying mechanism responsible for the observed tunable emission and show that tunable emission is only observed in nanosheets with thicknesses of (70–125 nm) ± 10 nm with the maximum range achieved for nanosheets with thicknesses of 125 ± 10 nm. Our results shed some light on an emerging class of 2D oxides with potential in optoelectronic applications.

Gold Nanoisland Agglomeration upon the Substrate Assisted Chemical Etching Based on Thermal Annealing Process

In this study, we proposed the self-organization process and its localized surface plasmon resonance property (LSPR) to study the effect of chemically treated quartz glass substrates for gold nanoisland array formation. Firstly, we etched a quartz glass substrate using a sputter etching machine. Secondly, n-butanol was treated on the surface of the substrate. Then, we deposited a gold thin film on the substrate with assisted chemical etching. Finally, the self-organization method examined the thermal annealing of gold nanoisland arrays on a substrate. The results showed that the gold nanoisland that was aggregated on an etched quartz glass substrate was large and sparse, while the gold nanoisland aggregated on a chemically treated substrate was small and dense. Further, it was revealed that a substrate’s surface energy reduced chemical treating and increased the gold nanoisland contact angle on the substrate via the thermal annealing process. It was also confirmed that chemical treatment was useful to control the morphology of gold nanoisland arrays on a substrate, particularly when related to tuning their optical property.