Low photogenerated charge density and fast surface charge recombination of TiO2 are two critical factors hampering its solar-to-hydrogen conversion for photoelectrochemical water splitting. Herein, we demonstrate an efficient and facile flame reduction method to produce rich oxygen vacancies in single-crystal rutile TiO2 nanorod arrays without destroying the catalyst and conductive substrate at ambient conditions. The oxygen vacancies improve the conductivity of TiO2 and act as the role that intermediate electron donor increases the charge density. We further construct a Schottky junction by depositing Ag nanoparticles on the flame reduced TiO2 to enhance surface charge separation efficiency. The optimal TiO2 photoelectrodes exhibit an astonishing surface charge separation efficiency of 91% as well as photocurrent density as high as 1.52 mA cm–2 (at 1.23 V, vs reversible hydrogen electrode), which is ∼7.2 times that of the pristine rutile TiO2 (0.21 mA cm–2). This work demonstrates that the facile flame reduction method combined with Schottky junction construction exhibits significant application prospects for the enhanced solar conversion efficiency of metal oxide photoelectrodes.

A highly active Pd supported on TiO2 coating on a SiO2 nanosphere (Pd/SiO2–TiO2(C)) catalyst has been developed for the selective catalytic reduction of NO x by H2 (H2–SCR). The coating structure of TiO2 on the SiO2 nanosphere exerts an important effect on the catalytic performance of the catalyst. This Pd/SiO2–TiO2(C) catalyst shows superior activity with 93.2% NO x conversion at 150 °C, and high tolerance to CO and H2O, which is significantly outperformed Pd supported on TiO2 particle (Pd/TiO2) catalyst. Compared with Pd/TiO2, Pd/SiO2–TiO2(C) has higher Pd dispersion and smaller Pd particle size, more surface chemisorbed oxygen, and metallic Pd species, all of which contributed to the improved performance. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) reveals that more reactive NO x , NH3, and NH4 + species formed on Pd/SiO2–TiO2(C), and the CO poisoning is mainly due to the slight inhibition of the formation of these reactive species. This research provides a promising strategy to design a superior H2–SCR catalyst for the removal of NO x .

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Self-assembled InAs/AlAs quantum dots embedded in a resonant tunneling diode device structure are grown by molecular beam epitaxy. Through the selective etching in a C 6 H 8 O 7 · H 2 O-K 3 C 6 H 5 O 7 · H 2 O-H 2 O 2 buffer solution, 310 nm GaAs capping layers are removed and the InAs/AlAs quantum dots are observed by field-emission scanning electron microscopy. It is shown that as-fabricated quantum dots have a diameter of several tens of nanometers and a density of 1010 cm-2 order. The images taken by this means are comparable or slightly better than those of transmission electron microscopy. The undercut of the InAs/AlAs layer near the edges of mesas is detected and that verifies the reliability of the quantum dot images. The inhomogeneous oxidation of the upper AlAs barrier in H 2 O 2 is also observed. By comparing the morphologies of the mesa edge adjacent regions and the rest areas of the sample, it is concluded that the physicochemical reaction introduced in this letter is diffusion limited.

Molecular beam epitaxy is employed to manufacture self-assembled InAs/AlAs quantum-dot resonant tunneling diodes. The resonant tunneling current is superimposed on the thermal current, and together they make up the total electron transport in devices. Steps in current-voltage characteristics and peaks in capacitance-voltage characteristics are explained as electron resonant tunneling via quantum dots at 77 or 300 K, and thus resonant tunneling is observed at room temperature in III-V quantum-dot materials. Hysteresis loops in the curves are attributed to hot electron injection/emission process of quantum dots, which indicates the concomitant charging/discharging effect.Self-assembled quantum dots ͑QDs͒ grown in the StranskiKrastanow ͑S-K͒ mode have attracted much interest due to their potential applications in novel nanoscale devices. 1 However, with their optical properties having been well clarified, relatively less research has been done on transport through QDs, such as the fabrication of QD resonant tunneling diodes ͑RTDs͒. RTDs have the advantage over conventional circuits 2 in terms of reduced circuit complexity for implementing a given function. Since the quantum dots confine electrons in all three dimensions, resonant tunneling into the quantized states will give rise to additional peaks in currentvoltage ͑I-V͒ characteristics 3 compared with quantum well RTDs. Furthermore, QD RTDs will operate with low power at high speed on account of the small size of these devices. Therefore, QD RTDs should have a more promising future than quantum well RTDs. To date, however, all commercial RTDs are made of quantum wells while much more effort is needed to make the quantum-dot RTDs practical. Room temperature observations of electron resonant tunneling via Si/SiO 2 QDs 4 or InGaN/GaN QDs 5 have been successfully achieved by virtue of the very large barrier height of matrix materials. However, a clear current bump due to resonant tunneling through III-V QDs, e.g., InAs QDs can only be detected at extremely low temperatures, 6-9 typically 1.6-130 K. Furthermore, nearly all this kind of experiment is focused on current-voltage ͑I-V͒ characteristics of the samples, whereas little attention is paid to capacitance-voltage ͑C-V͒ characteristics. In the present letter, clear step structures in the I-V curves of QD RTDs were observed at room temperature, and we explain these in terms of resonant tunneling via an ensemble of InAs/AlAs QDs. Also studied by C-V measurements here is the concomitant resonant charging effect. Hysteresis loops in I-V and C-V curves provide clues of hot electron charging and discharging procedure, thus further convincing us that as-grown samples show quantum-dot behavior. This finding represents a great step forward toward the applications of QD RTDs.Our RTD samples, shown schematically in Fig. 1a, were grown by a Riber 32P solid-source molecular beam epitaxy ͑MBE͒ machine on a GaAs͑100͒ substrate ͑n + = 2 ϫ 10 18 cm −3 ͒. The growth was started at substrate temperature T s of 600°C by depositing 30...