Considering the chemistry of the formation and physics at interfaces, we report on the heterostructure of a promising new energy material, Au–Cu2ZnSnS4 (Au-CZTS), and investigate the impact of coupling on Au on improving both the photostability and the photoresponse behavior. We focus primarily on the fundamental issues involved in bringing together two dissimilar materials having different chemical and physical properties in a single building block where one is a multinary semiconductor nanomaterial and the other is a plasmonic noble metal. The formation of heteroepitaxy at the junction of Au and CZTS was investigated for two different phases of CZTS. Considering epitaxy formation along the {111} planes of Au, it was observed that the wurtzite and tetragonal phases of CZTS exhibit coincident site epitaxy with different periodic intervals. A detailed study of this epitaxy formation with Au in both phases of CZTS has been carried out and reported. Because Au-CZTS is a promising new material, we have further investigated its photocurrent and photoresponse behavior and compared them with the properties and behavior of pure CZTS. We believe that these findings will help the energy-materials community, providing guidelines for investigating new functional materials and their applications.

In nanoscale, with size variation, Au shows different optical behaviors. For the small size clusters (sub-5 nm), it behaves more like semiconductors having sp and d band electronic energy levels splitting and also do not show the characteristic plasmon. However, for larger size particles (>5 nm), it shows the plasmonic absorption. Considering these two structures of Au 0 , we report here their coupling with a low bandgap semiconductor SnS and study the difference in their formation chemistry and materials' properties. Following a common synthetic approach in which a smaller size SnS cube and tetrahedron shapes result in Au cluster decorated Au-SnS heterostructures, larger size SnS cubes form coupled Au-SnS nanostructures. Contrastingly, the nonplasmonic Au 0 cluster-SnS hinders the photocatalytic activity, whereas the plasmonic coupled Au-SnS enhances the catalytic activity toward reduction of organic dye methylene blue. However, both types of heterostructures show enhanced photocurrent as well as photoresponse activities. Details of the chemistry of formation, epitaxy at the junction, and change in the materials' properties are studied and reported here in this article.

As per the classical growth mechanism, tuning the reaction parameters in the growth stage remains pivotal to control the shape, size, dispersity, and size distribution of the colloidal nanocrystals, but what would be the case when the growth is very fast and the nanomaterials are formed instantaneously? Certainly, it needs a different chemical protocol. We investigate here one of such cases: the formation of different shapes of SnS nanostructures. With proper programming of chemical reaction, highly monodisperse α-SnS nanocubes and nanotetrahedrons are obtained within 5 s of the reaction. Furthermore, tuning the density of nucleation, the size of the nanostructures is tuned in a wide window. These two shapes of SnS are also explored for the study of photocatalytic dye degradation, and the facet-dependent rate for this photocatalytic activity has been compared.

How efficient could a superionic conductor catalyst be? Beyond the traditionally used molecular precursors when the solution dispersed solid nanomaterials of variable size, shape and phase are introduced under certain reaction condition; the catalyst is found to digest all these structures in minutes irrespective of their phase and morphology, resulting unique heteronanowires. This has been inspected here by employing different ZnSe nanostructures as precursor for Ag2Se nanocrystal catalyst in its superionic conductor phase to obtain the Ag2Se-ZnSe heteronanowires. This dissolution and formation process of these nanostructures is correlated with the change in the reaction temperature profile, the phase of the catalyst, the shape/phase and surface ligands of the source nanostructures, and the possible mechanism of the unique heteronanowires growth has been investigated.

The synthesis of hybrid 0D-2D dot−disk Au-CIS heterostructures is enabled through nucleating wurtzite ternary I−III−VI CuInS 2 (CIS) semiconductor nanostructures on cubic Au particles via thiol-activated interface reactions. Chemistry of formation of these unique hybrid metal− semiconductor nanostructures is established by correlating successive X-ray diffraction patterns and microscopic images. Furthermore, these nanostructures are explored as an efficient photocathode material for photoelectrochemical (PEC) production of hydrogen from water. Although CIS nanostructures are extensively used as PEC active materials for solar-tohydrogen conversion, the coupled structures with Au for their exciton−plasmon coupling is observed in producing a higher photocurrent with efficient evolution of hydrogen. In the comparison of materials properties, it is observed that the cathodic photocurrent, onset potential, and the half-cell solar-to-hydrogen efficiency (HC-STH) are recorded to be superior to all CISbased photocathodes reported up to the current time. These results suggest that designing proper heterostructured functional materials can enhance the hydrogen production in the PEC cell and would be helpful for the ongoing technological needs for a greener way of generating and storing hydrogen energy. ■ INTRODUCTIONHydrogen evolution from solar water splitting, a possible alternative way of generating green energy, is on the forefront of current research. 1−6 In this aspect, photoelectrochemical (PEC) solar-to-hydrogen conversion remains as a promising approach and has been studied extensively. 1,7−14 The performance of the PEC cell and the efficiency of hydrogen evolution typically depend on the effectiveness of the involved photoactive electrode material. Among these, semiconducting nanomaterials having absorption in the solar spectrum, high excitonic coefficient, and high charge carrier mobility are more focused. 15−17 Moreover, electrodes are also designed following proper band engineering with other materials for feasible transfer of the photoexcited electron to water. 15,17−20 In recent developments, even success has been obtained to a large extent for improving the PEC cell performance using different nanomaterials, but finding more efficient and stable materials for boosting the cathodic current and enhancing the efficiency of hydrogen evolution in a single building block are still in demand.Among the different developed functional photoactive materials, noble metal−semiconductor heterostructures have recently emerged as ideal photocatalytic materials where the semiconductor generates the charge carriers and metal acts as a sink for trapping the electron. 21−32 For the case of metal Au, the electron transfer is even more facilitated as the surface plasmon of Au couples with semiconductor exciton and enhances the excited state lifetime of the photoelectron. 33−38 Among the semiconductor counter parts, for high carrier mobility and high extinction coefficient, multinary materials are recently more focused. 22,23,35,3...

Photo-oxidation of semiconductor quantum dots is the prime concern during their processability, as it often induces nonradiative states and quenches the band edge excitonic emission. Nevertheless, similar effects have been observed for light emitting doped semiconductor nanocrystals, and the dopant emissions are also quenched due to the surface oxidation. This is more pronounced for selenide-based host semiconductors. To overcome this, we study the interface chemistry of Cu-doped and Mn-doped ZnSe nanocrystals and report here the retrieving and brightening of the emission from completely quenched months old doped nanocrystals. This has been obtained by treating the doped nanocrystals with appropriate organic thiol ligands which remove the surface oxidative states as well as resist further oxidation of the nanocrystals. Here, we investigate details of the redox chemistry at the interface and study related photophysics in retrieving the dopant emission.

The use of colloidal self-assembly to form the complex multiscale patterns in many optoelectronic devices has been a long-standing dream of the nanoscience community. While great progress has been made using charged colloids in polar solvents, controlled assembly from nonpolar solvents is much more challenging. The major challenge is colloidal clustering caused by strong van der Waals (vdW) attraction between long-chain surface capping ligands passivating the surface of nanocrystals. Such clustering degrades ordering in packing during the self-assembly process. While ligand exchange to provide colloidal stability in polar phases is often an option, this is not the case for the exciting new class of halide perovskites due to the material’s solubility in essentially all polar solvents. Here, we report surface-functionalized self-assembly of luminescent CsPbBr 3 perovskite nanocubes by partially replacing long-chain oleyl groups (18 carbon chain) with short-chain thiocyanate (SCN – ). This enables the fabrication of ultrasmooth monolayer thin films of nanocubes with a root-mean-square (RMS) roughness of around 4 Å. This ultrasmooth large area self-assembled layer could act as high-efficiency optoelectronic devices like solar cells, light-emitting diodes (LEDs), transistors, etc. We correlate our experimental results with simulations, providing detailed predictions for lattice constants with chain conformations showing reduced free energy for cubes grafted with short-chain thiocyanate compared to long-chain oleyl groups, thus facilitating better self-assembly.

Doping foreign impurities in host nanomaterials can induce new materials properties. In addition, doping can also influence the crystallization process and change the shape and/or phase of the host material. While dopant-induced changes in the properties of materials have been well studied, the concept of doping and its chemistry in the design of different nanostructures has rarely been investigated. In order to further understand the doping chemistry, this study investigated the dopant-controlled enhancement of the rate of the chemical reaction during the transformation from one doped material to another and the consequent effect on the shape evolution of the nanostructures. These are performed during the selenization of metal Pd(0), using Ag dopant. While the controlled process produced cuboidal Pd17Se15 from the quasi-spherical nanocrystals of Pd(0), on doping, the shape of Pd17Se15 transformed into hollow cubes. The rate was also enhanced by more than 30 times for the doped case in comparison to undoped Pd(0). Importantly, while for the undoped nanocrystals, the selenization approached in one direction, where for the doped particles, it occurred all around the nanocrystals and triggered the Kirkendall effect. Detailed investigations were conducted to elucidate the influence of the dopant on both the rate and directional approach of selenization in Pd(0), initiation of the fast diffusion of Pd, change in shape, and formation of the hollow structures. To our understanding, the role of dopants in controlling chemical processes is of fundamental importance, and this will undoubtedly broaden the scope of research on the chemistry of doping and crystal growth in solution.