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Low band gap

The present paper reports the synthesis of xanthan gum/titanium dioxide (TiO2 ) nanocomposite for efficient visible light-induced degradation of highly toxic methyl orange dye. Synthesized xanthan gum/titanium dioxide nanocomposite showed good photocatalytic activity due to its high surface area, high light absorption ability and low energy potential between valence and conduction band. Tauc plot studies revealed the band gap of 2.8 eV for fabricated xanthan gum/titanium dioxide nanocomposite denoting its semiconductor nature...
October 15, 2018: International Journal of Biological Macromolecules
Shuo Wang, Liang Chen, Yang Wu, Qiuju Zhang
The identification of HER catalysts with high conductivity and high activity is the top priority in developing the renewable energy. O-terminated Ti2C (Ti2CO2), as one of the typical MXenes, shows good HER free energy at low hydrogen coverage, while the large band gap of approximately 1.0 eV limits its conductivity in HER performance. By doping P/S to partially substitute the surficial O, the average free energy at various hydrogen coverages has been dragged to approach zero, and the conductivity is significantly improved by narrowing the band gap to < 0...
October 18, 2018: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
Dong Yang, Ruixia Yang, Shashank Priya, Shengzhong Liu
Flexible perovskite solar cells have attracted widespread research effort because of their promising potential in light-weight wearable, portable, flyable and deployable for ultralight-weight space and near-space applications. During just the past few years, the efficiency has exceeded 18% due to the high quality perovskite film achieved by various low-temperature fabrication methods and the great achievements in developing matched interface and electrode materials. This review focuses on the recent progress of flexible perovskite solar cells concerning: Low-temperature fabrication methods to improve the properties of perovskite films, such as full coverage, uniform morphology and good crystallinity; The demonstrated interface layers used in flexible perovskite solar cells, considering key figure-of-merit such as high transmittance, high carrier mobility, suitable band gap and easy fabrication via low-temperature methods; The flexible transparent electrode materials developed to enhance the mechanical stability of the devices; Mechanical and long-term environmental stability of flexible perovskite device; Outlook of flexible perovskite solar cell in portable electronic device and its cost; Prospective of commercialization feasibility of the flexible perovskite solar cells...
October 17, 2018: Angewandte Chemie
Maxim Varenik, Xiao-Dong Zhang, Gregory Leitus, Nimrod Yavo, Raanan Carmieli, Ellen Wachtel, Xin Guo, Igor Lubomirsky
The magnetic properties of undoped, bulk CeO2 are not fully understood. In contrast to nanocrystalline ceria that exhibits paramagnetism attributed to Ce3+ at grain surfaces, bulk ceria is weakly paramagnetic, despite the absence of magnetic ions. In the present work, the magnetic susceptibility of bulk ceria ceramics doped with Lu3+, which has neither spin nor orbital angular momentum, was measured in order to assess the relative contributions of the crystal lattice, residual Ce3+ and oxygen vacancies to the overall bulk magnetization...
October 17, 2018: Physical Chemistry Chemical Physics: PCCP
Stephen G Dale, Axel D Becke, Erin R Johnson
Alkalides are crystalline salts in which the anion is a negatively charged alkali metal. A systematic investigation of the electronic structure of thirteen alkalides, with known crystal structures, is conducted using density-functional theory. For each alkalide, a high-lying valence state is identified that is localised on the alkali anions and is consistent with the low band gap and strong reducing power characteristic of these materials. This 'alkalide state' is compared to a similar state in the related class of electride materials, where the alkali anions are replaced by crystal voids occupied by localised, interstitial electrons...
October 16, 2018: Physical Chemistry Chemical Physics: PCCP
Julian Gaberle, Alexander L Shluger
The electronic and geometric structures of a range of intrinsic and extrinsic defects in black phosphorus (BP) are calculated using Density Functional Theory (DFT) and a hybrid density functional. The results demonstrate that energy barriers to form intrinsic defects, such as Frenkel pairs and Stone-Wales type defects, exceed 3.0 eV and their equilibrium concentrations are likely to be low. Therefore, growth conditions and sample preparation play a crucial role in defect chemistry of black phosphorus. Mono-vacancies (MV) are shown to introduce a shallow acceptor state in the bandgap of BP, but exhibit fast hopping rates at room temperature...
October 15, 2018: Nanoscale
Chunyang Sheng, Sungwook Hong, Aravind Krishnamoorthy, Rajiv K Kalia, Aiichiro Nakano, Fuyuki Shimojo, Priya Vashishta
Layered transition metal dichalcogenide (TMDC) materials have received great attention because of their remarkable electronic, optical, and chemical properties. Among typical TMDC family members, monolayer MoS2 has been considered a next-generation semiconducting material, primarily due to higher carrier mobility and larger band gap. The key enabler to bring such a promising MoS2 layer into mass production is chemical vapor deposition (CVD). During CVD synthesis, gas-phase sulfidation of MoO3 is a key elementary reaction, forming MoS2 layers on a target substrate...
October 8, 2018: Journal of Physical Chemistry Letters
Ana Rovisco, Rita Branquinho, Jorge Martins, Maria João Oliveira, Daniela Nunes, Elvira Fortunato, Rodrigo Martins, Pedro Barquinha
Semiconductor nanowires are mostly processed by complex, expensive, and high temperature methods. In this work, with the intent of developing zinc tin oxide nanowires (ZTO NWs) by low-cost and low-complexity processes, we show a detailed study on the influence of chemical parameters in the hydrothermal synthesis of ZTO nanostructures at temperatures of only 200 °C. Two different zinc precursors, the ratio between zinc and tin precursors, and the concentration of the surfactant agent and of the mineralizer were studied...
August 24, 2018: ACS applied nano materials
Dheeraj Mondal, Biplab Kumar Paul, Santanu Das, Debopriya Bhattacharya, Debopriyo Ghoshal, Papiya Nandy, Kaustuv Das, Sukhen Das
Because of the superior optical and electrical properties, copper impregnated size tuneable high-temperature stable manganese dioxide semiconductor quantum dots (SQDs) have been successfully synthesized by a modified chemical synthesis technique. Their size-dependent dielectric properties, semiconducting properties, and current-voltage (I-V) characteristics have been investigated. X-ray diffraction pattern and Raman spectra (RS) confirmed that the required phase is present. Due to the different sintering temperature tuneable size of SQDs has been found and confirmed by high resolution transmission electron microscopy (HRTEM)...
October 5, 2018: Langmuir: the ACS Journal of Surfaces and Colloids
Shakeel Ahmad Khan, Sadia Kanwal, Komal Rizwan, Sammia Shahid
A novel approach was employed for the synthesis of un-doped tinoxide and Cobalt-doped tinoxide (Co-doped SnO2 ) nanoparticles (NAPs) by using aqueous extract of Clerodendrum inerme with the help of eco-friendly superficial solution combustion method. Synthesized NAPs were characterized by different spectroscopic techniques and results from XRD, TEM, SEM, EDX and UV-Vis examines confirmed the successful synthesis, crystalline nature and spherical structure of un-doped SnO2 and Co-doped SnO2 NAPs with the average grain size of 30 and 40 nm; and band gap energy of 3...
October 2, 2018: Microbial Pathogenesis
Sukanya Ramaraj, Mani Sakthivel, Shen-Ming Chen, Kuo-Chuan Ho
Metal chalcogenides with large active sites have been received great attention as an excellent catalyst due to their hierarchical structural properties. Here, we have demonstrated the synthesis of ytterbium-doped molybdenum selenide (YbMoSe2 ) in the form of two-dimensional nanosheets by using a simple ultrasonic method. The formation of the crystal phase of prepared YbMoSe2 nanosheets was studied by using the selective characterization techniques. The reported HRTEM confirmed that the introduction of heterogeneous spin of Yb with MoSe2 creates the lattice distortion...
September 21, 2018: Ultrasonics Sonochemistry
Bhuvanesh Srinivasan, Bruno Fontaine, Francesco Gucci, Vincent Dorcet, Theo Graves Saunders, Min Yu, François Cheviré, Catherine Boussard-Pledel, Jean-François Halet, Régis Gautier, Michael J Reece, Bruno Bureau
The quaternary AgPb18 SbTe20 compound (abbreviated as LAST) is a prominent thermoelectric material with good performance. Endotaxially embedded nanoscale Ag-rich precipitates contribute significantly to decreased lattice thermal conductivity (κlatt ) in LAST alloys. In this work, Ag in LAST alloys was completely replaced by the more economically available Cu. Herein, we conscientiously investigated the different routes of synthesizing CuPb18 SbTe20 after vacuum-sealed-tube melt processing, including (i) slow cooling of the melt, (ii) quenching and annealing, and consolidation by (iii) spark plasma sintering (SPS) and also (iv) by the state-of-the-art flash SPS...
October 4, 2018: Inorganic Chemistry
G Kumaravel Dinesh, Sankar Chakma
The present study reports the synthesis of metal-free polymeric catalyst, graphitic carbon nitride (g-C3 N4 ), through sonochemical method followed by thermal treatment. The synthesized g-C3 N4 was characterized using XRD, DRS, FESEM, TGA, EDX, etc. and the characterization results revealed that it possesses medium band-gap energy, high thermal and chemical stability. The photo-activity of the catalyst was also evaluated using degradation of 5-Fluorouracil under different experimental conditions. The results revealed that the addition of H2 O2 during sonolysis process did not show any significant synergy...
September 24, 2018: Ultrasonics Sonochemistry
Heng Liu, Shao-Yong Huo, Lu-Yang Feng, Hong-Bo Huang, Jiu-Jiu Chen
The remarkable properties of topological insulators have inspired numerous studies on topological transport for bulk waves, but the demonstrations of topological edge states with tunable frequency are few attempts. Here, we report on the active frequency tunability of topologically protected edge states for in-plane bulk waves by applying a thermal field. We find that the center frequency of topological band gap is shifted down and the band width is enlarged as the temperature increases. Meanwhile, the frequency range of topologically protected edge states is also shifted to low frequency region with the higher temperature...
September 14, 2018: Ultrasonics
Sergey Milikisiyants, Alexander A Nevzorov, Alex I Smirnov
High-field EPR provides significant advantages for studying structure and dynamics of molecular systems possessing an unpaired electronic spin. However, routine use of high-field EPR in biophysical research, especially for aqueous biological samples, is still facing substantial technical difficulties stemming from high dielectric millimeter wave (mmW) losses associated with non-resonant absorption by water and other polar molecules. The strong absorbance of mmW's by water also limits the penetration depth to just fractions of mm or even less, thus making fabrication of suitable sample containers rather challenging...
September 20, 2018: Journal of Magnetic Resonance
Esteban Rucavado, Miglė Graužinytė, José A Flores-Livas, Quentin Jeangros, Federica Landucci, Yeonbae Lee, Takashi Koida, Stefan Goedecker, Aïcha Hessler-Wyser, Christophe Ballif, Monica Morales-Masis
Transparent conductive oxides (TCOs) are essential in technologies coupling light and electricity. For Sn-based TCOs, oxygen deficiencies and undercoordinated Sn atoms result in an extended density of states below the conduction band edge. Although shallow states provide free carriers necessary for electrical conductivity, deeper states inside the band gap are detrimental to transparency. In zinc tin oxide (ZTO), the overall optoelectronic properties can be improved by defect passivation via annealing at high temperatures...
August 9, 2018: Journal of Physical Chemistry. C, Nanomaterials and Interfaces
Quinn D Gibson, Matthew S Dyer, Craig Robertson, Charlene Delacotte, Troy D Manning, Michael J Pitcher, Luke M Daniels, Marco Zanella, Jonathan Alaria, John B Claridge, Matthew J Rosseinsky
Both layered multiple-anion compounds and homologous series are of interest for their electronic properties, including the ability to tune the properties by changing the nature or number of the layers. Here we expand, using both computational and experimental techniques, a recently reported three-anion material, Bi4 O4 Cu1.7 Se2.7 Cl0.3 , to the homologous series Bi2+2 n O2+2 n Cu2-δ Se2+ n-δ Xδ (X = Cl, Br), composed of parent blocks that are well-studied thermoelectric materials. All of the materials show exceptionally low thermal conductivity (0...
September 26, 2018: Inorganic Chemistry
Anna Hoffman, Michael G Stanford, Cheng Zhang, Ilia N Ivanov, Akinola D Oyedele, Maria Sales, Stephen McDonnell, Michael Koehler, David Mandrus, Liangbo Liang, Bobby G Sumpter, Kai Xiao, Philip D Rack
Atmospheric and long-term aging effects on electrical properties of WSe2 transistors with various thicknesses are examined. While countless published studies report electrical properties of transition metal dichalcogenide materials, many are not attentive to testing environment or to age of samples, which we have found significantly impacts results. Our as-fabricated exfoliated WSe2 pristine devices are predominantly n-type which is attributed to selenium vacancies. Transfer characteristics of as-fabricated devices measured in air then vacuum reveal physisorbed atmospheric molecules significantly reduced n-type conduction in air...
September 26, 2018: ACS Applied Materials & Interfaces
Soumyo Chatterjee, Amlan J Pal
The prevailing issue of wide optical gap in defect-ordered hybrid iodide perovskites has been addressed in this effort by heterovalent substitution at the metal site. With the introduction of Sn4+ in the (CH3 NH3 )3 Sb2 I9 structure, we have successfully lowered the pristine optical gap (2 eV) of the perovskite to a close-to optimum one (1.55 eV). Upon such heterovalent substitution, a gradual shift in the type of electronic conduction of the perovskites was observed. As evidenced from scanning tunneling spectroscopy and correspondingly density-of-state spectra, a significant shift of Fermi energy toward the conduction band edge occurred with an increase in the tin content in the host perovskite...
October 4, 2018: ACS Applied Materials & Interfaces
Yaqing Wei, Zhaohui Zhou, Wei-Hai Fang, Run Long
TiO2 is an excellent photocatalytic and photovoltaic material but suffers low efficiency because of deep trap states giving rise to fast charge and energy losses. Using a combination of time-domain density functional theory and nonadiabatic molecular dynamics, we demonstrate that grain boundaries (GBs), which are common in polycrystalline TiO2 , accelerate nonradiative electron-hole recombination by a factor of 3. Despite GBs increase the band gap without creating deep trap states, and accelerate coherence loss, they enhance nonadiabatic electron-phonon coupling, and facilitate the relaxation...
October 4, 2018: Journal of Physical Chemistry Letters
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