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Non-equilibrium fractal growth of MoS2 was induced by establishing an extremely Mo rich chemical vapor deposition (CVD) environment using a rapid heating rate in a confined reaction space. In addition, a detailed shape evolution mechanism was suggested based on the results of thermodynamics and kinetics studies. The extremely Mo rich CVD condition allowed various MoS2 flakes to be synthesized with triangular, star-like, and dendrite-like shapes in series, owing to the thermodynamic preference to increase the number of growth directions. Moreover, numerous small triangular crystals led to the formation of MoS2 flakes with jagged edges, probably as a result of the aggressive nucleation triggered by a fast and abundant supply of MoO3−x vapors. Lastly, using the MoS2 flakes with various fractal shapes, a systematic improvement of the hydrogen evolution reaction performance was demonstrated in accordance with the increase in the surrounding edge length. [ABSTRACT FROM AUTHOR]

Bothenhancing the excitons’ lifetime and ingeniously controllingthe spatial charge transfer are the key to the realization of efficientlyphotocatalytic and artificially photosynthetic devices. Nanostructuredmetal/metal-oxide interfaces often exhibit improved energy conversionefficiency. Understanding the surface potential changes of nano-objectsunder light illumination is crucial in photoelectrochemical cells.Under ultraviolet (UV) illumination, here, we directly observed thecharge separation phenomena at the Au-nanoparticle/TiO2-nanotube interfaces by using Kelvin probe force microscopy. Thesurface potential maps of TiO2nanotubes with and withoutAu nanoparticles were compared on the effect of different substrates.We observed that in a steady state, approximately 0.3 electron perAu particle of about 4 nm in diameter is effectively charged and consequentlyscreens the surface potential of the underlying TiO2nanotubes.Our observations should help design improved photoelectrochemicaldevices for energy conversion applications. [ABSTRACT FROM AUTHOR]

Lead zirconate titanate (PZT) thin films were prepared by a sol–gel process on platinized Si substrate. Their microstructure and surface morphology were characterized by XRD and Scanninn Force Microscopy. Phase transformation of the prepared PZT films from pyrochlore to ferroelectric was observed by XRD and PFM (piezoresponse force microscopy), respectively. Self-assembling nano-structured ferroelectric phases are fabricated by solution deposition technique followed by the controlling kinetics of the transformation. Complex structures of ferroelectric domains in the isolated ferroelectric phases were found in the furnace annealed PZT films in the temperature range of 400–500°C. Single ferroelectric domain structure in the isolated ferroelectric phases could be found in thinner PZT films and used to study the size effect of laterally confined ferroelectric domains. [Copyright &y& Elsevier]

We describe a procedure for one-step patterning and transfer of self-assembled organic monolayers (SAMs) on SiO2/Si substrates. This procedure was inspired from an idea of pattern formation at contact area, which realizes high patterning fidelity, and enables a universal approach for the micro/nanometre scale patterning of SAMs. [ABSTRACT FROM AUTHOR]

We report, for the first time, a novel procedure for fabricating multiwall anatase TiO2nanotubes by utilizing templated atomic layer deposition synthesis in conjunction with alternating TiO2/Al2O3nanolaminate structures. [ABSTRACT FROM AUTHOR]

We describe the direct formation of mixed-phase (1T and 2H) MoS2 layers on Si as a photocathode via atomic layer deposition (ALD) for application in the photoelectrochemical (PEC) reduction of water to hydrogen. Without typical series-metal interfaces between Si and MoS2, our p-Si/SiOx/MoS2 photocathode showed efficient and stable operation in hydrogen evolution reactions (HERs). The resulting performance could be explained by spatially genuine device architectures in three dimensions (i.e., laterally homo and vertically heterojunction structures). The ALD-grown MoS2 overlayer with the mixed-phase 1T and 2H homojunction passivates light absorber and surface states and functions as a monolithic structure for effective charge transport within MoS2. It is also beneficial in the operation of p-i-n heterojunctions with inhomogeneous barrier heights due to the presence of mixed-phase cocatalysts. The effective barrier heights reached up to 0.8 eV with optimized MoS2 thicknesses, leading to a 670 mV photovoltage enhancement without employing buried Si p-n junctions. The fast-transient behaviors via light illumination show that the mixed-phase layered chalcogenides can serve as efficient cocatalysts by depinning the Fermi levels at the interfaces. A long-term operation of ~70 h was also demonstrated in a 0.5 M H2SO4 solution. [ABSTRACT FROM AUTHOR]

Rational synthesis of coordinated spherical colloids is reported by site-selective growth of secondary hemispherical patches on primary spherical particles with quasi-defined coordination numbers and positions. We clarify the importance of mass transport phenomena on the site-specific secondary nucleation/growth in nanoparticulate colloidal systems. By comparing ultrasonic and conventional agitation during patch growth, we found that enhanced mass transfer is the key to controlled, homogeneous transport of the molecular precursors in a solvent onto the nanoparticles. With chemically defined nucleation sites, the surfaces of spherical silica particles were modified for use as a new kind of colloid with patches at desired coordination positions. Our observations represent a significant breakthrough in colloidal chemistry and self-assembly. [ABSTRACT FROM AUTHOR]

We report on the interplay between nanostructuring and defect activation in dense polycrystalline Bi2Te3 thin films in terms of the thermopower engineering. The Bi2Te3 thin films were prepared at relatively low temperatures (100–160 °C) by atomic layer deposition and their grains showed different sizes in the range of 50–200 nm according to the deposition temperatures. We monitored the conductivity, Seebeck coefficient, and power factor of all samples from the temperature of 50–400 K. By increasing the growth temperature, remarkably, we observed the gradual defect activation from the nominal p-type to n-type in our binary end compound, Bi2Te3 without any alloying. The present results give us an insight on the optimization of thermoelectric materials not only by nanostructuring (i.e., phonon engineering) but also by controlled defect activation (i.e., electron engineering). [ABSTRACT FROM AUTHOR]

We report visualization of three-dimensional domain structures in ferroelectric PbTiO3 (PTO) nanotubes (NTs) using piezoresponse force microscopy (PFM). The domain distributions of the x, y, and z-axes in PTO NTs were separately measured out-of and in-planes at angles of 0° and 90° by vertical and lateral PFM. The separately obtained PFM images were combined to reconstruct the complex domain structures based on some basic assumptions and finite element modeling. The cross-sectional domain configurations of the PTO NTs were visualized by the proposed approach. The results can provide insight into complex domain configurations of ferroelectric nanostructures. [ABSTRACT FROM AUTHOR]

Abstract: During a surface treatment using CF4/O2 gas plasma, energetic ions affected the defect structures on the top surface of ITO thin films. C-AFM and local I–V measurements showed the formation of the depleted layer after a plasma treatment with a bias of 20W; XPS showed the creation of new defect structures. Donor concentration in the damaged top surface of the ITO films was found to be decreased. Sn-based neutral defect complexes and reduced oxygen, which could trap the electrons, have been proposed to be formed. This can also explain the increase of the work function of ITO. [Copyright &y& Elsevier]

Hafnium zirconium oxide (HZO) has been studied intensively due to its potential application to memory and logic devices based on its outstanding dielectric and ferroelectric properties. Because many process factors can significantly impact the properties of HZO thin film, an optimized process or post‐treatment is necessary to ensure its performance. Herein, the effect of hydrogen on HZO thin film can make the film degraded. Analysis of the polarization–voltage hysteresis loops and I–V measurements indicate a leaky behavior in the film. To address this issue, post‐oxygen‐plasma treatment is performed on the film, which results in the decrease in hydrogen ions inside the film and consequently reduces the leakage current density. This finding can provide new insight into the effect of hydrogen incorporation for HZO thin films and methodology to remove leaky components inside ferroelectric films using O2 plasma treatment. [ABSTRACT FROM AUTHOR]

In the photoelectrochemical (PEC) water splitting (WS) reactions, a photon is absorbed by a semiconductor, generating electron-hole pairs which are transferred across the semiconductor/electrolyte interface to reduce or oxidize water into oxygen or hydrogen. Catalytic junctions are commonly combined with semiconductor absorbers, providing electrochemically active sites for charge transfer across the interface and increasing the surface band bending to improve the PEC performance. In this review, we focus on transition metal (di)chalcogenide [TM(D)C] catalysts in conjunction with silicon photoelectrode as Earth-abundant materials systems. Surprisingly, there is a limited number of reports in Si/TM(D)C for PEC WS in the literature. We provide almost a complete survey on both layered TMDC and non-layered transition metal dichalcogenides (TMC) co-catalysts on Si photoelectrodes, mainly photocathodes. The mechanisms of the photovoltaic power conversion of silicon devices are summarized with emphasis on the exact role of catalysts. Diverse approaches to the improved PEC performance and the proposed synergetic functions of catalysts on the underlying Si are reviewed. Atomic layer deposition of TM(D)C materials as a new methodology for directly growing them and its implication for low-temperature growth on defect chemistry are featured. The multi-phase TM(D)C overlayers on Si and the operation principles are highlighted. Finally, challenges and directions regarding future research for achieving the theoretical PEC performance of Si-based photoelectrodes are provided. [ABSTRACT FROM AUTHOR]

Nanostructured electrodes and their flexible integrated systems have great potential for many applications, including electrochemical energy storage, electrocatalysis and solid-state memory devices, given their ability to improve faradaic reaction sites by large surface area. Although many processing techniques have been employed to fabricate nanostructured electrodes onto flexible substrates, these present limitations in terms of achieving flexible electrodes with high mechanical stability. In this study, the adhesion, mechanical properties and flexibility of TiN nanotube arrays on a Pt substrate were improved using a Ti interlayer. Highly ordered and well-aligned TiN nanotube arrays were fabricated on a Pt substrate using a template-assisted method with an anodic aluminum oxide (AAO) template and atomic layer deposition (ALD) system. We show that with the use of a Ti interlayer between the TiN nanotube arrays and Pt substrate, the TiN nanotube arrays could perfectly attach to the Pt substrate without delamination and faceted phenomena. Furthermore, the I-V curve measurements confirmed that the electric contact between the TiN nanotube arrays and substrate for use as an electrode was excellent, and its flexibility was also good for use in flexible electronic devices. Future efforts will be directed toward the fabrication of embedded electrodes in flexible plastic substrates by employing the concepts demonstrated in this study. [ABSTRACT FROM AUTHOR]