Hydrothermal synthesis and photoluminescent properties of stacked indium sulfide superstructures

Unusual hierarchical stacked superstructures of cubic beta-In2S3 were fabricated via a facile hydrothermal process in the presence of a surfactant cetyltrimethylammonium bromide CTAB; the 3D superstructures were developed by helical propagation of surface steps from microflakes of 10-20 nm thickness.     

Shape evolution of single-crystalline iron oxide nanocrystals

Shape- and size-controlled synthesis of single-crystalline maghemite (gamma-Fe2O3) nanocrystals are performed by utilizing a solution-based one-step thermolysis method. Modulating the growth parameters, such as the type and amount of capping ligands as well as the growth time, is shown to have a significant effect on the overall shape and size of the obtained nanocrystals and on the ripening process itself. The resulting shapes of the novel structures are diverse, including slightly faceted spheres, diamonds, prisms, and hexagons, all of which are in fact truncated dodecahedron structures with different degrees of truncation along the {111}, {110}, or {100} faces. Spherical nanocrystals are easily assembled into the three-dimensional superlattices, demonstrating the uniformity of these nanocrystals. The size-dependent magnetic properties are examined, and large hexagon-shaped gamma-Fe2O3 nanocrystals are shown to be ferrimagnetic at room temperature.     

Three-dimensional Co2V2O7·nH2O superstructures assembled by nanosheets for electrochemical energy storage

Hierarchical superstructures assembled by nanosheets can effectively prevent aggregation of nanosheets and improve performance in energy storage. Therefore, we proposed a facile hydrothermal method to obtain three-dimensional（3D） superstructure assembled by nanosheets. We found that the ratio of Co²⁺/HMTA affected the morphology of the samples, and the 3D hierarchical structures of are obtained while the ratio of Co²⁺/HMTA is 12:25. The hierarchical structures with sufficie...     

Synthesis of NiO Crystals Exposing Stable High-Index Facets

Metal oxides exposing high-index facets are potentially impactful in catalysis and adsorption processes owing to under-coordinated ions and polarities that alter their interfacial properties compared to low-index facets. Here, we report molten-salt syntheses of NiO particles exposing a variety of crystal facets. We show that for a given anion (nitrate or chloride), the alkali cation has a notable impact on the formation of crystals exposing {311}, {611}, {100}, and {111} faces. Based on a parametric analysis of synthesis conditions, we postulate that the crystallization mechanism is governed by the formation of growth units consisting of Ni^II complexes whose coordination numbers are determined by temperature and the selection of anion (associated to the coordination sphere) and alkali cation (associated with the outer coordination sphere). Notably, our findings reveal that high-index facets are particularly favored in chloride media and are stable under prolonged periods of catalysis and steaming.     

Synthetic Semiconductor Diamond Electrodes: Electrochemical Characteristics of Individual Faces of High-Temperature-High-Pressure Single Crystals

Effects of crystal structure on the electrochemistry of boron-doped high-temperature-high-pressure diamond single crystals grown from an Ni–Fe–C–B melt are studied. On the {111}, {100}, and {311} faces, the linear and nonlinear electrochemical impedance spectra and the electrochemical kinetics in the Fe(CN)₆ ^3_/4_ redox system are measured. The acceptor concentration in the diamond interior adjacent to these faces was determined from the Mott–Schottky plots and the amplitude-demodulation measurements. It varies in the 10¹⁸ to 10²¹ cm^–3 range. The difference in the electrochemical behavior of individual crystal faces is primarily attributed to different boron acceptor concentrations in the growth sectors associated with the faces.     

The Effects of Exposed Specific Facets and Sulfation on the Surface Acidity of Cu2O Solids

Cuprous oxide microcrystals with {111}, {111}/{100}, and {100} exposed facets were synthesized. ³¹P MAS NMR using trimethylphosphine as the probe molecule was employed to study the acidic properties of samples. It was found that the total acidic density of samples increases evidently after sulfation compared with the pristine cuprous oxide microcrystals. During sulfation, new {100} facets are formed at the expense of {111} facets and lead to the generation of two Lewis acid sites due to the different binding states of SO₄²⁻ on {111} and {100} facets. Moreover, DFT calculation was used to illustrate the binding models of SO₄²⁻ on {111} and {100} facets. Also, a Pechmann condensation reaction was applied to study the acidic catalytic activity of these samples. It was found that the sulfated {111} facet has better activity due to its higher Lewis acid density compared with the sulfated {100} facet.     

Synthesis of NiO Crystals Exposing Stable High‐Index Facets

Metal oxides exposing high‐index facets are potentially impactful in catalysis and adsorption processes owing to under‐coordinated ions and polarities that alter their interfacial properties compared to low‐index facets. Here, we report molten‐salt syntheses of NiO particles exposing a variety of crystal facets. We show that for a given anion (nitrate or chloride), the alkali cation has a notable impact on the formation of crystals exposing {311}, {611}, {100}, and {111} faces. Based on a parametric analysis of synthesis conditions, we postulate that the crystallization mechanism is governed by the formation of growth units consisting of Ni^II complexes whose coordination numbers are determined by temperature and the selection of anion (associated to the coordination sphere) and alkali cation (associated with the outer coordination sphere). Notably, our findings reveal that high‐index facets are particularly favored in chloride media and are stable under prolonged periods of catalysis and steaming.     

Single-Crystal Superstructures via Hierarchical Assemblies of Giant Rubik's Cubes as Tertiary Building Units

Intricate superstructures possess unusual structural features and promising applications. The preparation of superstructures with single-crystalline nature are conducive to understanding the structure–property relationship, however, remains an intriguing challenge. Herein we put forward a new hierarchical assembly strategy towards rational and precise construction of intricate single-crystal superstructures. Firstly, two unprecedented superclusters in Rubik's cube's form with a size of ≈2×2×2 nm³ are constructed by aggregation of eight {Pr₄Sb₁₂} oxohalide clusters as secondary building units (SBUs). Then, the Rubik's cubes further act as isolable tertiary building units (TBUs) to assemble diversified single-crystal superstructures. Importantly, intermediate assembly states are captured, which helps illustrate the evolution of TBU-based superstructures and thus provides a profound understanding of the assembly process of superstructures at the atomic level.     

Chemical composition and reactivity of water on hexagonal Pt-group metal surfaces

The dissociation behaviour and valence-electronic structure of water adsorbed on clean and oxygen-covered Ru{0001}, Rh{111}, Pd{111}, Ir{111} and Pt{111} surfaces has been studied by high-resolution X-ray photoelectron spectroscopy with the aim of identifying similarities and trends within the Pt-group metals. On average, we find higher reactivity for the 4d metals (Ru, Rh, Pd) as compared to 5d (Ir, Pt), which is correlated with characteristic shifts in the 1b(1) and 3a(1) molecular orbitals of water. Small amounts of oxygen (< 0.2 ML) induce dissociation of water on all five surfaces, for higher coverages (> 0.25 ML) only intact water is observed. Under UHV conditions these higher coverages can only be reached on the 4d metals, the 5d metals are, therefore, not passivated.     

Heterodimers based on CoPt3-Au nanocrystals with tunable domain size

We describe an approach to synthesize colloidal nanocrystal heterodimers composed of CoPt(3) and Au. The growth is based on the nucleation of gold domains on preformed CoPt(3) nanocrystals. It is a highly versatile methodology which allows us to tune independently the size of the two domains in each dimer by varying several reaction parameters. The statistical analysis of the distribution of the domain sizes in the dimers and the compositional mapping achieved by dark field imaging and energy dispersive spectroscopy confirm that the two domains in each dimer are indeed made of CoPt(3) and Au, respectively. Structural characterization by high-resolution transmission electron microscopy shows that the two domains, both having cubic fcc Bravais lattice, can share a common {111}, {100}, or {110} facet, depending on the size of the initial CoPt(3) seeds. The magnetization measurements evidence a ferromagnetic CoPt(3) phase with a relatively low anisotropy as a consequence of their disordered crystalline structure, regardless of the presence of a Au tip. We believe that this prototype of nanocrystal dimer, which can be manipulated under air, can find several applications in nanoscience, as the Au section can be exploited as the preferential anchor point for various molecules, while the CoPt(3) domain can be used for magnetic detection.     

Superspherical-shape approximation to describe the morphology of small crystalline particles having near-polyhedral shapes with round edges

Small crystalline particles are often formed comprising near-polyhedral shapes with round edges. When near-polyhedral shapes are analyzed and discussed, it is convenient if these shapes can be expressed by equations with simple parameters. Superspheres are solids expressing various shapes between those of polyhedra and spheres. The superspherical-shape approximation is used in this study to consider the morphology of cubic crystal structure particles. Various near-polyhedral shapes composed of {100}, {111} and {110} planes are described using a simple equation with three shape-related parameters. It is shown that the superspherical-shape approximation is a useful geometrical tool for evaluating the morphology of small crystalline particles.     

Hierarchically structured cobalt oxide (Co3O4): the morphology control and its potential in sensors

A polyol process was developed to synthesize Co3O4 with controllable superstructures. By tuning the reaction conditions, the prepared Co3O4 were readily regulated in its morphologies, which could vary from nanosphere to two-dimensional (2D) nanoplates and 3D hierarchical structures, and finally to microspheres. The growth kinetics of such a process was also studied. The synthesized Co3O4 exhibited good sensitivity, remarkable selectivity, and high stability as an alcohol sensor material.     

Elucidating the effect of additives on the growth and stability of Cu2O surfaces via shape transformation of pre-grown crystals

A new strategy of using pre-grown crystals to study preferential adsorption of various additives is demonstrated for the electrocrystallization of Cu2O. In this method, micron-size Cu2O crystals with well-defined cubic and octahedral shapes were first electrochemically grown, and their crystallization was resumed in a medium containing the additive to be investigated (e.g., Na+, NH4+, SO42-, Cl-, dodecyl sulfate). This method makes it possible to systematically study the interaction of additives with specific planes (e.g., {100} of a cube and {111} of an octahedron) already present. By observing shape transformation over time, the relative stabilities of {100}, {111}, and {110} planes of Cu2O in various growth media could be determined. During this study, a general scheme of forming new crystal shapes containing crystallographic planes that cannot be directly stabilized by preferential adsorption alone was also established (i.e., rhombicuboctahedral shape of Cu2O containing {110} planes). This method can be extended to other crystal systems, which will enable us to classify common features of additives (e.g., charges, type of atoms) and crystallographic planes (e.g., atomic arrangement, surface termination, surface charge) required to allow for strong preferential adsorption.     

Structural relationships and mechanisms for the stoichiometry change from MX3 (YF3-type) through MX2 (fluorite-type) to M2X3 (C-type sesquioxide)

Structures produced by inducing stoichiometry changes in crystalline fluorides and oxide-fluorides of yttrium by pyrohydrolysis have been studied by X-ray powder diffraction and electron microscopy. The structures of YF₃, various fluorite-related intermediates and the ultimate product of hydrolysis, Y₂O₃, are all closely related. The pyrohydrolysis is topotactic; the anion sublattice remains intact and vacancies and oxygen substitute for fluorine on the anion sublattice in an ordered, cooperative way to produce fully ordered product structures. A ‘unit slip’ mechanism, involving the most favourable slip systems for a primitive cubic sublattice, 〈001〉{110} and 〈001〉{110}, is postulated as a possible mechanism for the process.     

Anion-Regulated Hierarchical Self-Assembly and Chiral Induction of Metallo-Tetrahedra

The precise control over hierarchical self-assembly of superstructures relying on the elaboration of multiple noncovalent interactions between basic building blocks is both elusive and highly desirable. We herein report a terpyridine-based metallo-cage T with a tetrahedral motif and utilized it as an efficient building block for the controlled hierarchical self-assembly of superstructures in response to different halide ions. Initially, the hierarchical superstructure of metallo-cage T adopted a hexagonal close-packed structure. By adding Cl⁻/Br⁻ or I⁻, drastically different hierarchical superstructures with highly-tight hexagonal packing or graphite-like packing arrangements, respectively, have been achieved. These unusual halide-ion-triggered hierarchical structural changes resulted in quite distinct intermolecular channels, which provided new insights into the mechanism of three-dimensional supramolecular aggregation and crystal growth based on macromolecular construction. In addition, the chiral induction of the metallo-cage T can be realized with the addition of chiral anions, which stereoselectively generated either PPPP- or MMMM-type enantiomers.     

Relativistic effects in low-lying electronic states of iron

Excited electronic states of Fe I have been calculated using the MRCI Douglas?CKroll?CHess method. Average spin-free excitation energies of the eight lowest even electronic terms ( $\hbox{a}^5\hbox{D}, \hbox{a}^5\hbox{F}, \hbox{a}^3\hbox{F}, \hbox{a}^5\hbox{P}, \hbox{a}^3\hbox{P2}, \hbox{a}^3\hbox{H}, \hbox{b}^3\hbox{F2}, \hbox{and a}^3\hbox{G}$ ) are reported. The RASSI method was employed for calculation of individual J levels of the four lowest terms. All reported values are in good agreement with experiment. Our study pointed out significant relativistic effects even in relatively light element like iron.     

Shape Control of VO2 (B) Hierarchical Nanostructures

A green route is designed to gain a clear idea of growth mechanism of complex VO₂ (B) hierarchical microstructures, since this kind of metal oxide has various metastable phases due to their diverse valence states. Three‐dimensional (3D) uniform flower‐like VO₂ (B) hierarchical microstructure has thus been assembled with the interleaving nanoplates, which are about 25 nm in thickness and well‐crystallized in structure with {114} planes as the dominant surfaces. Results of the systemic control experiments revealed that formation of the flower‐like VO₂ (B) results from a fast nucleation‐growth process, where ethylene glycol (EG) not only acts as a green solvent and reductive agent, but also plays a key role in self‐assembly of the resulted VO₂ (B) hierarchical microstructures. Hydroxyl amount on the solvent molecule is crucial in formation and shape control of VO₂ (B) hierarchical microstructures. Result of this work would be helpful to understand the growth mechanism of complex three‐dimensional hierarchical superstructures of different metal oxides, which is very important to material science and inorganic synthetic chemistry.     

1-Adamantanethiolate monolayer displacement kinetics follow a universal form

Alkanethiol molecules in solution displace 1-adamantanethiolate self-assembled monolayers on Au{111}, ultimately leading to complete molecular exchange. Specifically, here, fast insertion of n-dodecanethiolate at defects in the original 1-adamantanethiolate monolayer nucleates an island growth phase, which is followed by slow ordering of the n-dodecanethiolate domains into a denser and more crystalline form. Langmuir-based kinetics, which describe alkanethiolate adsorption on bare Au{111}, fail to model this displacement reaction. Instead, a Johnson-Mehl-Avrami-Kolmogorov model of perimeter-dependent island growth yields good agreement with kinetic data obtained by Fourier transform infrared spectrometry over 100-fold variation in n-dodecanethiol concentration. Rescaling the growth rate at each concentration collapses all the data onto a single universal curve, suggesting that displacement is a scale-free process. The rate of displacement varies as the square-root of the n-dodecanethiol concentration across the 0.01-1.0 mM range studied.     

Silicon Wafers with Facet‐Dependent Electrical Conductivity Properties

By breaking intrinsic Si (100) and (111) wafers to expose sharp {111} and {112} facets, electrical conductivity measurements on single and different silicon crystal faces were performed through contacts with two tungsten probes. While Si {100} and {110} faces are barely conductive at low applied voltages, as expected, the Si {112} surface is highly conductive and Si {111} surface also shows good conductivity. Asymmetrical I –V curves have been recorded for the {111}/{112}, {111}/{110}, and {112}/{110} facet combinations because of different degrees of conduction band bending at these crystal surfaces presenting different barrier heights to current flow. In particular, the {111}/{110} and {112}/{110} facet combinations give I –V curves resembling those of p–n junctions, suggesting a novel field effect transistor design is possible capitalizing on the pronounced facet‐dependent electrical conductivity properties of silicon.     

Coverage‐Controlled Superstructures of C3‐Symmetric Molecules: Honeycomb versus Hexagonal Tiling

The competition between honeycomb and hexagonal tiling of molecular units can lead to large honeycomb superstructures on surfaces. Such superstructures exhibit pores that may be used as 2D templates for functional guest molecules. Honeycomb superstructures of molecules that comprise a C₃ symmetric platform on Au(111) and Ag(111) surfaces are presented. The superstructures cover nearly mesoscopic areas with unit cells containing up to 3000 molecules, more than an order of magnitude larger than previously reported. The unit cell size may be controlled by the coverage. A fairly general model was developed to describe the energetics of honeycomb superstructures built from C₃ symmetric units. Based on three parameters that characterize two competing bonding arrangements, the model is consistent with the present experimental data and also reproduces various published results. The model identifies the relevant driving force, mostly related to geometric aspects, of the pattern formation.