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Nanoscale materials have been intensely studied since the discovery that the optical properties of semiconductor nanoparticles are size dependent. [1][2][3] This and subsequent research has demonstrated that a given physical property of a particle exhibits a size dependence when the size becomes comparable to its characteristic length scale. Examples of relevant length scales include the de Broglie wavelength and/or the mean free path of electrons, phonons, and elementary excitations, all of which typically range from one to a few hundred nanometers. The ability to tune a wide variety of properties by controlling the particle size has spurred the development of novel chemistries for preparing nanostructured elements and compounds with goals of precisely controlling size, shape, and ligand shell. [4][5][6][7][8] As the size of a nanocrystal decreases, the ratio of bulk to surface atoms decreases. This progression increases the relative contribution of the surface free-energy relative to the volume free-energy of the bulk structure, such that distortions from bulk equilibrium structures might be expected as the nanoparticle size decreases. Unfortunately, while researchers have demonstrated the ability to prepare ordered lattices of nanoparticles, [9][10][11][12][13][14] the isolation of lattices of nanoparticles with long-range atomic periodicity is rare. [11,13,15] Hence detailed atomic structures and, in turn, the size-structure-property relationships of most nanoparticle systems cannot readily be determined. [15][16][17] Recently we reported that the intergrown compounds [(MSe) 1+y ] m (TSe 2 ) n , with M = {Pb, Bi, Ce} and T = {W, Nb, Ta} self-assemble from designed precursors. [18,19] The values of m and n represent, respectively, the number of MSe and TSe 2 structural units of the unit cell of the superstructure and y describes the misfit between these structural units. As reported herein, the long-range structural order along the modulation direction permits us to determine the atomic structure of these precisely defined one-dimensional (1D) nanolaminate structures as a function of m and n using a combination of scanning transmission electron microscopy (STEM) high-angle annular dark-field (HAADF) imaging and X-ray diffraction (XRD) with Rietveld refinement.STEM-HAADF images of the first five [(PbSe) 1.00 ] m -(MoSe 2 ) n compounds in the family where m = n are shown in Figure 1 along with aggregate intensity plots used to quantify the PbSe intra-and inter-pair distances. All have a regular periodic structure along the modulated axis with well-defined layers of PbSe and MoSe 2 . The STEM images show ordered domains of PbSe with characteristic dimensions of a single structural unit along the layering direction and tens of nanometers perpendicular to the layering direction, with random in-plane rotational variants both within a layer and between layers. The orientations of the MoSe 2 domains are more difficult to discern from the STEM images, but rotational variants have been observed between individual MoSe 2...

The materials Cu 3 PQ 4 (Q ¼ S, Se) of the enargite structure are studied as photovoltaic (PV) absorbers.Optical band gaps in the series Cu 3 PS 4Àx Se x (0 # x # 4) are found to range from 2.36 eV (x ¼ 0) to 1.35 eV (x ¼ 4). Seebeck measurements on powder samples at room temperature yield large positive values (>100 mV K À1 ) indicating p-type behavior. Hole carrier concentrations are found in the range of 10 16 -10 17 cm À3 . Crystal structures of Cu 3 PS 1.89 Se 2.11 and Cu 3 PS 0.71 Se 3.29 are refined in the orthorhombic space group Pmn2 1 with the unit-cell parameters -Cu 3

Emergence of a terawatt scalable photovoltaic (PV) thin film technology is currently impeded by the limited supply of relatively rare elements like In or Te, which has spurred active research in recent years on earth-abundant PV materials. Instead of searching for alternative PV materials, we approach the problem here by structural modification through alloying of a known PV material, namely, tin sulfide. Although SnS is a strong visible light absorber that is naturally p-doped, its indirect band gap reduces the open circuit voltage of SnS-based solar cells. The anisotropic crystal structure results in undesirable anisotropic transport properties. Based on the observation that the isoelectronic sulfides MgS, CaS, and SrS assume the rock-salt structure, we use ab initio calculations to explore the structure and electronic properties of metastable Sn 1Àx (II) x S (II ¼ Mg, Ca, Sr) alloys, finding that the isotropic rock-salt phase is stabilized above x ¼ 0.2-0.3, and predicting direct band gaps in the range of interest for PV applications, i.e., 0.6-1.5 eV for Ca and Sr alloying. We subsequently synthesized such Sn 1Àx (Ca) x S films by pulsed laser deposition, confirmed the cubic rock-salt structure, and observed optical band gaps between 1.1 and 1.3 eV. These results highlight the potential of structural modification by alloying as a route to widen the otherwise limited materials base for promising earth-abundant materials. V

Atomic solid state energy scale: Universality and periodic Trends in oxidation state, Journal of Solid State Chemistry, http://dx. ABSTRACTThe atomic solid state energy (SSE) scale originates from a plot of the electron affinity (EA) and ionization potential (IP) versus band gap (E G ). SSE is estimated for a given atom by assessing an average EA (for a cation) or an average IP (for an anion) for binary inorganic compounds having that specific atom as a constituent. Physically, SSE is an experimentally-derived average frontier orbital energy referenced to the vacuum level. In its original formulation, 69 binary closed-shell inorganic semiconductors and insulators were employed as a database, providing SSE estimates for 40 elements.In this contribution, EA and IP versus E G are plotted for an additional 92 compounds, thus yielding SSE estimates for a total of 64 elements from the s-, p-, d-, and f-blocks of the periodic table. Additionally, SSE is refined to account for its dependence on oxidation state. Although most cations within the SSE database are found to occur in a single oxidation state, data are available for nine d-block transition metals and one p-block main group metal in more than one oxidation state. SSE is deeper in energy for a higher cation oxidation state. Two p-block main group non-metals within the SSE database are found to exist in both positive and negative oxidation states so that they can function as a cation or anion.SSEs for most cations are positioned above -4.5 eV with respect to the vacuum level, and SSEs for all anions are positioned below. Hence, the energy -4.5 eV, equal to the hydrogen donor/acceptor ionization 2 energy ε(+/-) or equivalently the standard hydrogen electrode energy, is considered to be an absolute energy reference for chemical bonding in the solid state.

A strategy is demonstrated to evaluate the carrier mobility in-plane and out-of-plane using contactless time resolved microwave conductivity.

Anorganische Nanokristalle: Die Strukturen der Verbindungen [(PbSe)1.00]m(MoSe2)n und [(PbSe)0.99]m(WSe2)n (m≥1 und n≤5) wurden mit Röntgenbeugung und Raster‐Transmissionselektronenmikroskopie untersucht. Sie weisen eine Paarungsverzerrung der PbSe‐Komponente auf, die abhängig ist von der Dicke der PbSe‐Schicht (m), aber unabhängig von Dicke des Dichalkogenids (n).