Understanding surface chemistry during MAPbI3 spray deposition and its effect on photovoltaic performance

Sprayed MAPbI3 films exhibit changing surface chemistry that affects electronic band alignment and PV performance. Results highlight the potential for a low costing spray deposition technique.</p

One-step synthesis of strongly confined, defect-free and hydroxy-terminated ZnO quantum dots

This paper reports the production of strongly confined ligand-free, defect-free, hydroxy-terminated ZnO quantum dots with a mean diameter of 1.9 nm, by radio frequency atmospheric pressure microplasma. Systematic characterization is performed to understand the surface chemistry of ZnO quantum dots. Photoluminescence studies show strong confinement effect on emission with only ultraviolet (UV) emission without any defect-related visible emission. Emission is again tested after eighteen months and confirms the QDs long-term emission stability. The mechanism responsible for this UV emission is also discussed and originates from OH-related surface terminations

Controlling the Energy-Level Alignment of Silicon Carbide Nanocrystals by Combining Surface Chemistry with Quantum Confinement

This work was supported by the Marie Curie Initial Training Network (RAPID-ITN, Grant 606889) and by EPSRC (Grants EP/K022237/1 and EP/M024938/1). A.U.H. and S.A. are thankful for the financial support from RAPID-ITN and Ulster University’s Vice Chancellor scholarships, respectively.The knowledge of band edges in nanocrystals (NCs) and quantum-confined systems is important for band alignment in technologically significant applications such as water purification, decomposition of organic compounds, water splitting, and solar cells. While the band energy diagram of bulk silicon carbides (SiCs) has been studied extensively for decades, very little is known about its evolution in SiC NCs. Moreover, the interplay between quantum confinement and surface chemistry gives rise to unusual electronic properties and remains barely understood. Here, we report for the first time the complete band energy diagram of SiC NCs synthesized such that they span the regime from strong to intermediate to weak quantum confinement. The absolute positions of the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals show clear size dependence. While the HOMO level follows the expected behavior for quantum-confined electronic states, the LUMO energy shifts below the bulk conduction band minimum, which cannot be explained by a simple quantum confinement caused by the size effect. We show that this effect is a result of the interplay between quantum confinement and the formation of surface states due to partial and site-selective oxygen passivation.Publisher PDFPeer reviewe

Evolution of Anodic Product from Molybdenum Metal in Absolute Ethanol and Humidity Sensing under Ambient Conditions

Authors would like to thank the support from National Natural Science Foundation of China (NSFC) (Nos. 51702264 and 41371275), Fundamental Research Funds for the Central Universities (No. XDJK2017B033), and Research Funding of Southwest University (No. SWU117019). The funding from the Engineering and Physical Sciences Research Council (EPSRC) (under Grant Nos. EP/K022237/1, EP/K036769/1, and EP/M024938/1) is also acknowledged. We also appreciate the funding from the EU COST Action (No. TD1208) for useful exchanges and discussions.Room-temperature nonaqueous synthetic routes turn out to be particularly competitive among all the available liquid-phase synthetic methods for nanometer-sized metal oxides for multiple applications. Microplasma-assisted anodization is employed to prepare soluble and crystalline Mo species in a water-deficient and extraneous ionic-salt-free ethanol electrolyte. The anodization of Mo in absolute ethanol is found to produce Mo oxyethoxide in the liquid ethanol phase, along with a small montage of mixed hexagonal and orthorhombic MoO3 crystals. The evolution of Mo species in solid and liquid phases is characterized to study the crystallization of MoO3 crystal and the formation of blue spherical Mo polyoxometalates (POMs) after extended aging. The addition of water in the suspension delayed the formation of molybdenum blue while hydrogen peroxide induced the precipitation of a dendritic framework of hexagonal MoO3. A thin MoO3 film was produced from the solution and can be used for humidity sensing by the facile conductivity measurement.PostprintPostprintPeer reviewe

Surface Functionalization of Grown-on-Tip ZnO Nanopyramids: From Fabrication to Light-Triggered Applications

We report on a combined chemical vapor deposition (CVD)/radio frequency (RF) sputtering synthetic strategy for the controlled surface modification of ZnO nanostructures by Ti-containing species. Specifically, the proposed approach consists in the CVD of grown-on-tip ZnO nanopyramids, followed by titanium RF sputtering under mild conditions. The results obtained by a thorough characterization demonstrate the successful ZnO surface functionalization with dispersed Ti-containing species in low amounts. This phenomenon, in turn, yields a remarkable enhancement of photoactivated superhydrophilic behavior, self-cleaning ability, and photocatalytic performances in comparison to bare ZnO. The reasons accounting for such an improvement are unravelled by a multitechnique analysis, elucidating the interplay between material chemico-physical properties and the corresponding functional behavior. Overall, the proposed strategy stands as an amenable tool for the mastering of semiconductor-based functional nanoarchitectures through <i>ad hoc</i> engineering of the system surface

Microplasma-assisted electrochemical synthesis of Co3O4 nanoparticles in absolute ethanol for energy applications

The authors thank the Engineering and Physical Sciences Research Council (EPSRC) for funding (EP/K036769/1, EP/K022237/1, EP/M024938/1). The authors would also like to acknowledge the EU COST Action TD1208 for useful exchanges and discussions. CN would like to thank the support from Fundamental Research Funds for the Central Universities (XDJK2017B033) and Research Funding of Southwest University (SWU117019) and Natural Science Foundation of China (NSFC, 51702264; 41371275).Plasma at the gas/liquid interface can promote a complex mixture of reactions in solution and microplasma-assisted direct-current anodic oxidation is an efficient and green process in synthesising nanoscale materials for various applications. In this study, we demonstrated the direct synthesis of crystalline Co3O4 quantum dots, ca. 2-5 nm in size, by direct anodization of Co foil with charge balanced by the microplasma at the flowing-helium/pure-ethanol interface under ambient condition. The anodic oxidation of cobalt in ethanol was analysed after characterising the solution using nuclear magnetic resonance (NMR), light absorption, photoluminescence (PL), and the solid product using X-ray photoemission spectroscopy (XPS), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Using the microplasma with high voltage under ambient condition, ethanol was oxidised to acetate as the charge carrier and the size of Co3O4 quantum dots can be controlled by the limiting current. The quantum dots from this method are well dispersed in ethanol and a dense coating for light absorption and a rectified diode can be processed directly from the suspension. These results reveals that microplasma-assisted anodisation in ethanol is an efficient and green route capable of manufacturing quantum dots at low-temperature and avoiding the use of extraneous ionic salts in electrolyte.PostprintPeer reviewe

Impact of silicon nanocrystal oxidation on the nonmetallic growth of carbon nanotubes

Carbon nanotube (CNT) growth has been demonstrated recently using a number of nonmetallic semiconducting and metal oxide nanoparticles, opening up pathways for direct CNT synthesis from a number of more desirable templates without the need for metallic catalysts. However, CNT growth mechanisms using these nonconventional catalysts has been shown to largely differ and reamins a challenging synthesis route. In this contribution we show CNT growth from partially oxidized silicon nanocrystals (Si NCs) that exhibit quantum confinement effects using a microwave plasma enhanced chemical vapor deposition (PECVD) method. On the basis of solvent and a postsynthesis frgamentation process, we show that oxidation of our Si NCs can be easily controlled. We determine experimentally and explain with theoretical simulations that the Si NCs morphology together with a necessary shell oxide of ∼1 nm is vital to allow for the nonmetallic growth of CNTs. On the basis of chemical analysis post-CNT-growth, we give insight into possible mechanisms for CNT nucleation and growth from our partially oxidized Si NCs. This contribution is of significant importance to the improvement of nonmetallic catalysts for CNT growth and the development of Si NC/CNT interfaces