The development of advanced materials to improve the efficiency of photoelectrochemical (PEC) water splitting paves the way for widespread renewable energy technologies. Efficient photoanodes with strong absorbance in visible light increases the effectiveness of solar energy conversion systems. MoS2 in a two-dimensional semiconductor that has excellent absorption performance in visible light and high catalytic activity, showing considerable potential as an agent of PEC water splitting. In this study, we successfully modulated the MoS2 morphology on indium tin oxide substrate by using the metalorganic chemical vapor deposition method, and applied the PEC application. The PEC photocurrent of the vertically grown MoS2 nanosheet structure significantly increased relative to that of MoS2 nanoparticles because of the efficient transfer of charge carriers and high-density active sites. The enhanced photocurrent was attributed to the efficient charge separation and improved light absorption of the MoS2 nanosheet structure. Meanwhile, the photocurrent property of thick nanosheets decreased because of the limit imposed by the diffusion lengths of carriers. This study proposes a valuable photoelectrode design with suitable nanosheet morphology for efficient PEC water splitting.

Titanium nitride (TiN) is a material of interest for electrodes owing to its high-temperature stability, robustness, low-cost, and suitable electrical properties. Herein, we studied the surface morphology and electrical properties of TiN thin film deposited onto an Si/SiO2 <100> substrate through direct current (DC) sputtering with a high-purity TiN target in an argon-gas environment. The electrical properties and surface morphology of TiN thin film significantly improved with increased source power and decreased working pressure. The improved electrical properties could be attributed to the suppressed secondary phase (Ti2N) formation and the reduced electron scattering on smoother surface. Consequently, high-quality TiN thin film with the lowest resistivity (ρ = 0.1 mΩ·cm) and the smallest surface roughness (RMS roughness, Rq = 0.3 nm) was obtained under the optimized condition. The TiN film was further used as the bottom electrode for a metal–insulator–metal (MIM) capacitor. Results demonstrated that the electrical properties of TiN film were comparable to those of noble-metal thin films. Therefore, the TiN thin film fabricated by DC sputtering method had excellent electrical properties and good Rq, indicating its potential applications in MIM capacitors and Si technology.

Praseodymium (Pr)and bismuth (Bi)-substituted yttrium (Y) iron (Fe) garnet (PrxY2-xBi1Fe5O12 where x = 0.25, 0.5, 1, and 2) thin films were prepared on glass substrate using a metal-organic decomposition (MOD) method. Their magneto-optical properties were studied as a function of Pr concentration. Praseodymium has two functions in PrxY2-xBi1Fe5O12 thin films, i.e., it (i) improves spin-orbit interaction strength and (ii) increases magnetic properties; both are expected to strongly enhance the Faraday rotation (FR) angle of the thin film. Our study demonstrated that the Pr1Y1Bi1Fe5O12 thin-film displayed the highest FR angle, of –13 °/μm, which is 1.6-times higher than that of the PrxY2-xBi1Fe5O12 thin film without Pr dopant. The Pr1Bi1Y1Fe5O12 thin film fabricated on a glass substrate by the MOD method displayed excellent MO performance and is a potential candidate for application in optical devices.

We report the growth and enhanced photoelectrochemcial (PEC) water-splitting reactivity of few-layer MoS2 nanosheets on TiO2 nanowires. TiO2 nanowires with lengths of ~1.5 ~ 2.0 μm and widths of ~50~300 nm are synthesized on fluorine-doped tin oxide substrates at 180 oC using hydrothermal methods with Ti(C4H9O)4. Few-layer MoS2 nanosheets with heights of ~250 ~ 300 nm are vertically grown on TiO2 nanowires at a moderate growth temperature of 300 oC using metalorganic chemical vapor deposition. The MoS2 nanosheets on TiO2 nanowires exhibit typical Raman and ultraviolet-visible light absorption spectra corresponding to few-layer thick MoS2. The PEC performance of the MoS2 nanosheet/TiO2 nanowire heterostructure is superior to that of bare TiO2 nanowires. MoS2/TiO2 heterostructure shows three times higher photocurrent than that of bare TiO2 nanowires at 0.6 V. The enhanced PEC photocurrent is attributed to improved light absorption of MoS2 nanosheets and efficient charge separation through the heterojunction. The photoelectrode of the MoS2/TiO2 heterostructure is stably sustained during on-off switching PEC cycle.

A controllable approach that combines surface plasmon resonance and two-dimensional (2D) graphene/MoS2 heterojunction has not been implemented despite its potential for efficient photoelectrochemical (PEC) water splitting. In this study, plasmonic Ag-decorated 2D MoS2 nanosheets were vertically grown on graphene substrates in a practical large-scale manner through metalorganic chemical vapor deposition of MoS2 and thermal evaporation of Ag. The plasmonic Ag-decorated MoS2 nanosheets on graphene yielded up to 10 times higher photo-to-dark current ratio than MoS2 nanosheets on indium tin oxide. The significantly enhanced PEC activity could be attributed to the synergetic effects of SPR and favorable graphene/2D MoS2 heterojunction. Plasmonic Ag nanoparticles not only increased visible-light and near-infrared absorption of 2D MoS2, but also induced highly amplified local electric field intensity in 2D MoS2. In addition, the vertically aligned 2D MoS2 on graphene acted as a desirable heterostructure for efficient separation and transportation of photo-generated carriers. This study provides a promising path for exploiting the full potential of 2D MoS2 for practical large-scale and efficient PEC water-splitting applications.

Two-dimensional (2D) SnS2 nanosheets vertically grown on graphene electrodes have still not been demonstrated despite their considerable research interest and potential for photoelectrochemical (PEC) applications. Herein, the controllable growth and enhanced PEC water-splitting performance of vertically aligned 2D SnS2 nanosheets on graphene are reported. The heterojunction quality of the graphene/2D SnS2 nanosheets was ensured by low-temperature growth at 230 degrees C using metalorganic chemical vapor deposition, resulting in significantly improved charge transfer properties. The PEC photocurrent density and photoconversion efficiency significantly increased upon insertion of a graphene layer. In addition, the 2D SnS2 nanosheet microscopic structure dependency of the PEC performance was systematically studied. The best PEC reactivity of the 2D SnS2 nanosheets was achieved at a height of similar to 0.85 mu m, corresponding to nearly the limit of the carrier diffusion length, and a thickness of similar to 70nm to balance the low interfacial contact resistance with an effective photogenerated carrier dynamics. These results, including the low-temperature vertical growth of 2D SnS2 on graphene, can effectively be utilized to exploit the full potential of 2D SnS2 for various PEC applications. (C) 2020 Elsevier Ltd. All rights reserved.

Vertically-standing, few-layer MoS2 flakes were uniformly and conformally grown on closely-packed TiO2 nanowire substrates using metal-organic chemical vapor deposition. The TiO2/MoS2 hetero-structures exhibited remarkably improved photoelectrochemical (PEC) performance and long-term stability owing to enhanced photogenerated electron-hole separation and transfer properties across the heterojunction. Due to the built-in heterojunction potential, the onset potential of TiO2/MoS2 heterostructures was cathodic-shifted to -0.3 V, thereby resulting in maximum PEC reactivity at approximately zero potential. In contrast, MoS2 flakes on fluorine-doped tin oxide substrates exhibited an onset potential of approximately 0.3 V. Furthermore, PEC performance was critically affected by the size of the vertically-standing MoS2 flakes, indicating that controlled conformal growth of MoS2 flakes on appropriate nanostructures is essential to exploit these nanostructures as efficient, non-toxic, inexpensive, and earth-abundant PEC electrodes. (C) 2018 Elsevier B.V. All rights reserved.

Solar absorber Cu2ZnSnS4 (CZTS) films were uniformly deposited on Si/Mo substrates via a facile, cost-effective chemical bath deposition (CBD) by using ribonucleic acid (RNA) nucleobase uracil as the functional building block. The functional sites of uracil, i.e., C=O and N-H, played a critical role in the complexation of metals via uracil-quartet functional architectures. Stable metal-uracil complexes significantly affected the growth kinetics, enhancing the uniform delivery of multimetal components into films and suppressing the undesirable formation of CuS particles. CZTS films obtained with the addition of 0.05 and 0.5 M uracil exhibited a smooth surface morphology and significantly improved photoconductive performance. The developed RNA-nucleobase-mediated CBD method demonstrates promise as multicomponent compound absorber films, including CZTS and CuInGaSe2, in cost-effective solar cells.

We investigate the characteristics of self-assembled quantum dot infrared photodetectors(QDIPs) based on doping level. Two kinds of MP samples are prepared using molecular beam epitaxy : n(+)-i(QD)-n(+) MP with undoped quantum dot(QD) active region and n(+)-n (QD)-n(+) MP containing Si direct doped QDs. InAs QDIPs were grown on semi-insulating GaAs (100) wafers by molecular-beam epitaxy. Both top and bottom contact GaAs layer are Si doped at 2x 10(18)/cm(3). The QD layers are grown by two-monolayer of InAs deposition and capped by InGaAs layer. For the n(+)-n(-)(QD)-n(+) structure, Si dopant is directly doped in InAs QD at 2x10(17)/cm(3). Undoped and doped QUI's show a photoresponse peak at about 8.3 mu m, ranging from 6-10 mu m at 10 K. The intensity of the doped QDIP photoresponse is higher than that of the undoped MP on same temperature. Undoped QDIP yields a photoresponse of up to 50 K, whereas doped MP has a response of up to 30 K only. This result suggests that the doping level of QDs should be appropriately determined by compromising between photoresponsivity and operating temperature.

We report the properties of infrared photodetectors based on two kinds of quantum dots(QDs): i) 2.0 ML InAs QDs by the Stranski-Krastanov growth mode(SK QDs) and ii) sub-monolayer QDs by 4 x [0.3 ML/1 nm In0.15Ga0.85As] deposition(SML QDs). The QD infrared photodetector(QDIP) structure of n(+)-n(-)(QDs)-n(+) is epitaxially grown on GaAs (100) wafers using molecular-beam epitaxy. Both the bottom and top contact GaAs layers are Si doped at 2 x 10(18)/cm(3). The QD layers are grown with Si doping of 2 x 10(17)/cm(3) and capped by an In0.15Ga0.85As layer at 495 degrees C. The photoluminescence peak(1.24 eV) of the SML QDIP is blue-shifted with respect to that (1.04 eV) of SK QDIPs, suggesting that the electron ground state of SML QDIP is higher than that of the SK QDIP. As a result, the photoresponse regime(similar to 9-14 mu m) of the SML QDIP is longer than that (similar to 6-12 mu m) of the SK QDIP. The dark current of the SML QDIP is two orders of magnitude smaller value than that of the SK QDIP because of the inserted Al0.08Ga0.92As layer.

We present a simple, ultrasonic vibration-assisted lift-off-based patterning approach for graphene and graphene-Ag nanowire (NW) hybrid films. A 20 μm width pattern with uniform and smooth pattern edges was neatly defined on various rigid and flexible substrates. The patterned graphene-Ag NW electrodes showed a low sheet resistance of 19 Ω/sq with a high transmittance of 93% at 550 nm, a robust stability against oxidation, and a high reliability under a bending test. The electrodes also exhibited markedly higher performance than that of commercial fluorine-doped tin oxide electrodes for dye-sensitized solar cells. Given its low-cost, high throughput, and nondamaging effect, this simple and reliable patterning approach stimulates the practical applications of graphene-based flexible transparent electrodes in soft electronic and optoelectronic devices.

Graphene, a two-dimensional sp-bonded carbon system, has been extensively studied during the last several years to understand the synthesis, physics, and potential device applications (Geim & Novoselov, 2007). Various synthesis methods have been developed, including mechanical exfoliation of highly ordered pyrolytic graphite (Geim & Novoselov, 2007), chemical reduction of exfoliated graphene oxide (Becerril et al., 2008), thermal decomposition of SiC (de Heer et al., 2007), and chemical vapor deposition (CVD) growth (Bae et al., 2010; Li et al., 2009a; Nang & Kim, 2012; Reina et al., 2009). Of the many synthesis methods available, CVD is potentially the most attractive technique for direct synthesis of graphene on various large-area substrates for the practical transparent electrodes and electronic device applications (Bae et al., 2010). In particular, plasma-enhanced CVD (PECVD) is a useful approach for controllable highquality graphene synthesis. Compared with thermal CVD, PECVD possesses the unique advantage of additional highdensity reactive gas atoms and radicals, which facilitate lowtemperature, rapid, and controllable synthesis of carbon nanostructures (Gopichand et al., 2010; Küttel et al., 1998; Li et al., 2004; Wang et al., 2004; Zhu et al., 2007). Recently, there have been considerable research reports on graphene synthesis on metal and oxide substrates using PECVD (Dato et al., 2008; Kim et al., 2011a, 2011b; Lee et al., 2011; Nandamuri et al., 2010; Nang & Kim, 2012, 2013). However, direct CVD synthesis of high-quality graphene on insulators or oxides at a moderate growth temperature remains a challenge. Moreover, little information is available on the fundamental aspects of PECVD, i.e., the effect of plasma on graphene synthesis which results in a synthesis behavior that is different from that of thermal CVD. In this study, we study the unique CVD growth kinetics of graphene on metal (Cu) and oxide (Fe2O3) substrates under inductively-coupled plasma (ICP). ICPCVD has several advantages for high-quality film growth because it provides a high-density plasma via a simple and low-cost plasma-generating setup. pISSN 2287-5123·eISSN 2287-4445 https://doi.org/10.9729/AM.2017.47.1.13

In this study, we present the device performance of dual color infrared light emitting diode (IR-LED) based on InGaAsSb/AlGaAsSb quantum well structure.The LED sample was grown on n-type GaSb substrate using the molecular beam (MBE) with As 2 and Sb 2 cracker cells.The active layer of device structure consists of three different quantum well widths (5, 10 and 15 nm) of InGaAsSb and a 200 nm thick Al 0.35 Ga 0.65 As 0.03 Sb 0.97 barrier.The structural and electrical characterization of LED sample was measured by high-resolution X-ray diffractometer (HR-XRD) and current-voltages (I-V).The LED sample was processed by the conventional photolithographic technique.By using the e-beam evaporation system, ohmic contact was formed on the p-and n-type of the layer.The electroluminescence (EL) of the device was observed 1.94 and 2.1 ㎛ at room temperature.

Vertically aligned MoS2 flakes were grown on indium tin oxide (ITO) and ITO/ZnO substrates using metalorganic chemical vapor deposition. The thickness of MoS2 flakes was manipulated at the few-layer level (5-10), which is desirable for energy-storage and energy-conversion applications. For photoelectrochemical (PEC) cells, a few-layer flake photoelectrode yielded a considerably higher photocurrent density (930 mu A/cm(2) at 0.2 V) than a MoS2 thin-film photoelectrode (360 mu A/cm(2) at 0.2 V) due to the former's high density of active sites, slow intraband relaxation rate from excitonic states, and low defect density. Furthermore, the heterostructure of ZnO/MoS2 flakes exhibited a remarkably high photocurrent density of 1.6 mA/cm(2) at 0.2 V and a long-term stability under the PEC operating conditions because of its enhanced photogenerated carrier separation and transfer. Thus, such a heterostructure is promising as an efficient, nontoxic, inexpensive, and earth-abundant PEC electrode. (c) 2017 Elsevier Ltd. All rights reserved.

We report the synthesis of uniform and smooth Cu2ZnSnS4 (CZTS) thin films on glass and Mo/Si substrates by a simple single-step chemical bath deposition (CBD) method with an appropriate combination of complexing agents. Effects of triethanolamine (TEA) and ammonium hydroxide (NH4OH), used as complexing agents and P-H stabilizers, on CZTS deposition were systematically investigated. Higher concentration (7 M) and moderate volume (1 ml) of TEA showed uniform and smooth film with a relatively fast growth rate. With increased concentration of NH3 from 2 M to 14 M, film thickness continuously increased because of enhanced heterogeneous growth rate rather than homogeneous precipitation. Based on the results, an appropriate CBD growth mechanism of CZTS film was suggested. The resulting CZTS films were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, photoluminescence and UV-Visible spectroscopy analyses. CZTS thin film, sulfurized at 500 degrees C, showed a Kesterite crystal structure with an optimum bandgap energy of similar to 1.4 eV.

Two types of InAs/GaAs quantum dots (QDs), namely, relatively large/steep QDs and small/shallow QDs, are comprehensively studied for QD infrared photodetector (QDIP) applications. The QDIP with small QDs shows a broad photoresponse over a relatively wide range (similar to 5 mu m to 7 mu m), whereas its QDIP counterpart with large QDs yields a sharp photoresponse peak at similar to 7.2 mu m with a full width at half maximum of 32 meV. The systematic interband and intraband studies suggest that the excited states involved in intraband transitions in QDIPs with small and large QDs have continuum and QD-bound states, respectively. The QDIP with large QDs shows higher photocurrent-to-dark current ratio than the QDIP with small QDs.

The direct synthesis of Cu2ZnSnS4 (CZTS) on substrates by wet-chemistry methods is of great interest for the fabrication photovoltaic thin-film solar cells. We report a simple chemical bath deposition approach to form CZTS thin films on SLG glass substrates. CZTS films were directly deposited onto glass substrate at 60 degrees C using copper sulfate, zinc sulfate heptahydrate, tin sulfate dihydrate, and sodium thiosulfate as precipitating agents. Deposition of individual metal sulfide (Cu2S, ZnS, and SnS2) showed homogeneous-reaction dominant nanostructures rather than continuous thin film. By contrast, the combination of two or three metal precursors formed continuous thin films. As-grown CZTS films deposited with both NH3 and TEA showed a kesterite CZTS crystal structure. However, the absence of either NH3 or TEA caused no crystallized CZTS film formation. The as-grown CZTS films showed a kesterite crystal structure. Optical absorption study indicated that the as-grown CZTS films had the optimum bang gap energy of 1.6 eV. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Graphene oxide has been synthesized by microwave-assisted exfoliation of graphite oxide prepared by modified Hummers method. Graphite was oxidized in a solution of H2SO4 and KMnO4 at 65 similar to 80 degrees C, followed by 10% H2O2 solution treatment at 80 similar to 90 degrees C. The graphite oxide was exfoliated under microwave irradiation of 1 kW and was reduced to graphene effectively by hydrazine hydrate (H4N2 center dot H2O) treatment. The exfoliation of graphene oxide was significantly affected by the microwave irradiation on (heating)/off (cooling) period. An on/off period of 10 s/20 s resulted in much more effective exfoliation than that of 5 s/10 s with the same total treatment time of 10 min. This can be explained by the higher exfoliation temperature of 10 s/20 s. Repetition of the graphite oxidation and exfoliation processes also enhanced the exfoliation of graphene oxide. The thickness of the final graphene products was estimated to be several layers. The D band peaks of the Raman spectra of the final graphene products were quite low, suggesting a high crystal quality.