Physical and Electrical Characterization of Synthesized Millimeter Size Single Crystal Graphene, Using Controlled Bubbling Transfer

In this work, we have investigated the influence of the transfer process on the monocrystalline graphene in terms of quality, morphology and electrical properties by analyzing the data obtained from optical microscopy, scanning electron microscopy, Raman spectroscopy and electrical characterizations. The influence of Cu oxidation on graphene prior to the transfer is also discussed. Our results show that the controlled bubbling electrochemical delamination transfer is an easy and fast transfer technique suitable for transferring large single crystals graphene without degrading the graphene quality. Moreover, Raman spectroscopy investigation reveals that the Cu surface oxidation modifies the strain of the graphene film. We have observed that graphene laying on unoxidized Cu is subject to a biaxial strain in compression, while graphene on Cu oxide is subject to a biaxial strain in tension. However, after graphene was transferred to a host substrate, these strain effects were strongly reduced, leaving a homogeneous graphene on the substrate. The transferred single crystal graphene on silicon oxide substrate was used to fabricate transmission line method (TLM) devices. Electrical measurements show low contact resistance ~150 Ω·µm, which confirms the homogeneity and high quality of transferred graphene.

Effects of Anodic Aluminum Oxide Substrate Pore Geometry on the Gas-Phase Photocatalytic Activity of ZnO/Al2O3 Composites Prepared by Atomic Layer Deposition

We report on the photocatalytic activity of ZnO layers deposited by atomic layer deposition on a porous anodic aluminum oxide substrate with hexagonal pore symmetry and varied pore dimensions. ZnO/Al2O3 composites were prepared with pore diameters in the range 93–134 nm and interpore distance in the range 185–286 nm, and their photocatalytic activity was measured for gas-phase photocatalytic oxidation of acetaldehyde at varying UV illumination intensities (0.08–3.94 mW cm−2). The results show that substrates with narrower pore diameters (<115 nm, in the case of this study) have a detrimental effect on the photocatalyst performance, despite their higher effective surface. The results are explained on the basis of limited mass transfer inside the porous structure and can be used as a guideline in the purposeful design of photocatalysts with a nanoporous or nanotubular structure.

NiFeOx decorated Ge-hematite/perovskite for an efficient water splitting system

To boost the photoelectrochemical water oxidation performance of hematite photoanodes, high temperature annealing has been widely applied to enhance crystallinity, to improve the interface between the hematite-substrate interface, and to introduce tin-dopants from the substrate. However, when using additional dopants, the interaction between the unintentional tin and intentional dopant is poorly understood. Here, using germanium, we investigate how tin diffusion affects overall photoelectrochemical performance in germanium:tin co-doped systems. After revealing that germanium is a better dopant than tin, we develop a facile germanium-doping method which suppresses tin diffusion from the fluorine doped tin oxide substrate, significantly improving hematite performance. The NiFeOx@Ge-PH photoanode shows a photocurrent density of 4.6 mA cm−2 at 1.23 VRHE with a low turn-on voltage. After combining with a perovskite solar cell, our tandem system achieves 4.8% solar-to-hydrogen conversion efficiency (3.9 mA cm−2 in NiFeOx@Ge-PH/perovskite solar water splitting system). Our work provides important insights on a promising diagnostic tool for future co-doping system design.

Photocatalytic Activity of Cu2S/WO3 and Cu2S/SnO2 Heterostructures for Indoor Air Treatment

Volatile organic compounds (VOCs) are commonly found in indoor spaces (e.g., homes or offices) and are often related to various illnesses, some of them with carcinogenic potential. The origins of VOC release in the indoor environment are in office products, building materials, electronics, cleaning products, furniture, and maintenance products. VOC removal can be done based on two types of technologies: adsorption in specific materials and decomposition via oxidative processes. The present article reports the development and photocatalytic activity of two heterostructures (Cu2S/WO3 and Cu2S/SnO2) used for indoor air decontamination. The acetaldehyde removal rate is discussed in correlation with the S-scheme mechanisms established between the heterostructure components but also comparatively with the bare catalysts’ activity. Acetaldehyde was considered as a VOC reference because it was found by the International Agency for Research on Cancer to be one of the most frequent air toxins with potential carcinogenic effects. The samples contained monoclinic WO3, tetragonal SnO2, and orthorhombic Cu2S crystalline structures. The Cu2S crystallite size in the heterostructure varied from 75.9 to 82.4 Å, depending on the metal oxide substrate. The highest photocatalytic efficiency (75.7%) corresponded to Cu2S/SnO2, with a constant rate of 0.106 s−1 (which was three times faster than WO3 or SnO2 and seven and a half times faster than Cu2S).

The Effect of Al on the Formation of a CrTaO4 Layer in Refractory High Entropy Alloys Ta-Mo-Cr-Ti-xAl

In this study, the effect of Al on the high temperature oxidation of Al-containing refractory high entropy alloys (RHEAs) Ta-Mo-Cr-Ti-xAl (x = 5; 10; 15; 20 at%) was examined. Oxidation experiments were performed in air for 24 h at 1200 °C. The oxidation kinetics of the alloy with 5 at% Al is notably affected by the formation of gaseous MoO3 and CrO3, while continuous mass gain was detected for alloys with the higher Al concentrations. The alloys with 15 and 20 at% Al form relatively thin oxide scales and a zone of internal corrosion due to the formation of dense CrTaO4 scales at the interface oxide/substrate. The alloys with 5 and 10 at% Al exhibit, on the contrary, thick and porous oxide scales because of fast growing Ta2O5. The positive influence of Al on the formation of Cr2O3 followed by the growth of CrTaO4 to yield a compact scale is explained by getter and nucleation effects.

Facet controlled growth mechanism of SnO2 (101) nanosheet assembled film via cold crystallization

Cold crystallization of SnO2 was realized in aqueous solutions, where crystal growth was controlled to form SnO2 (101) nanosheet assembled films for devices such as chemical sensors. The nanosheets grew directly on a fluorine-doped tin oxide substrate without a seed layer or a buffer layer. The nanosheets had a thickness of 5–10 nm and an in-plane size of 100–1600 nm. Moreover, the large flat surface of the (101) facet was metastable. The thickness of the SnO2 (101) nanosheet assembled film was approximately 800 nm, and the film had a gradient structure that contained many connected nanosheets. TEM results revealed that the predominate branch angles between any two connected nanosheets were 90° and 46.48°, corresponding to type I and type II connections, respectively. These connections were consistent with the calculations based on crystallography. Crystallographic analysis clarified the characteristic crystal growth of the SnO2 (101) nanosheet assembled film in the aqueous solution. Furthermore, we demonstrate that the metastable (101) facet can be exploited to control the rate of crystal growth by adjusting the etching condition.