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Growth of ZnSnN2 films on (0001) Al2O3 substrates is performed by plasma-assisted molecular-beam epitaxy by changing the growth temperatures from 350 to 650 °C. Single crystal ZnSnN2 films have been grown by using ZnO buffer while the film grown without the ZnO buffer has shown amorphous-like disordered characteristics addressed by no observation of any diffraction from reflection high-energy electron diffraction. All the grown crystalline ZnSnN2 films with ZnO buffer show a pseudowurtzite structure without the formation of an orthorhombic structure. Epitaxial relationships between Al2O3 substrate, ZnO buffer, and ZnSnN2 film are determined to be [1120] ZnSnN2//[1120] ZnO//[1010] Al2O3 and [0001] ZnSnN2//[0001] ZnO//[0001] Al2O3. The bandgaps of ZnSnN2 films could be tuned from 1.85 to 2.15 eV, simply by increasing the growth temperatures from 350 to 650 °C. The carrier concentrations and carrier mobilities were investigated and compared. Since the growth of single crystal ZnO films has been reported on various kinds of cheap and large size substrates, our results can expand the method to grow single crystal ZnSnN2 films, which is needed to fabricate new ZnSnN2-based devices. [ABSTRACT FROM AUTHOR]

A cobalt containing mixed-anion uranyl oxide-fluoride was synthesized using a mild hydrothermal crystal growth method. The uranyl ions are condensed into a one-dimensional chain motif separated by isolated cobalt hexa-aqua centers. The 1-D uranyl material was characterized by single-crystal and powder X-ray diffraction. The optical, thermal, and magnetic properties were studied and are reported herein. Using the reported composition as a model, a system was derived to predict the dimensionality of hypothetical structures to advance our ability to rationally predict solid-state materials. [ABSTRACT FROM AUTHOR]

A beryllium-free nonlinear optical (NLO) crystal K3Ba3Li2Al4B6O20F (KBLABF) with sizes up to 18 × 13 × 8 mm3 was successfully grown by the top-seeded solution growth method using LiOH-H3BO3–BaF2 flux. The key limiting factors on the crystal morphologies and sizes were carefully analyzed. Meanwhile, by using the minimum deviation technique, the refractive index dispersion was measured and fitted well by the Sellmeier equations. The results suggest that KBLABF is a negative uniaxial crystal with moderate birefringence of 0.06050–0.06834 at a wavelength range from 363 to 852.1 nm. Furthermore, the type-I phase matching range for fundamental (second harmonic) light is down to 486 (243 nm) in theory, which indicates that KBLABF crystal could achieve 532 and 266 nm light generation by direct second-harmonic generation. As compared with the famous NLO crystals β-BaB2O4 and CsLiB6O10, KBLABF crystal exhibits a smaller walk-off angle and larger acceptance angle at the wavelength of 532 nm while having a comparable short absorption edge, sufficient birefringence, and moderate NLO response. Furthermore, in contrast to highly hygroscopic CsLiB6O10, it is nonhygroscopic. These attributes make KBLABF a promising candidate for practical applications in UV light generation. [ABSTRACT FROM AUTHOR]

Sintering is an important issue in creating crystalline metal oxides with high porosity and surface area, especially in the case of high-temperature materials such as metal aluminates. Herein we report a rationally designed synthesis of metal aluminates that diminishes the surface area loss due to sintering. MeAl2O4 (Me = Ni, Co or Cu) supported on γ-Al2O3 with ultralarge mesopores (up to 30 nm) was synthesized through microwave-assisted peptization of boehmite nanoparticles and their self-assembly in the presence of a triblock copolymer (Pluronic P123) and metal nitrates, followed by co-condensation and thermal treatment. The resulting materials showed the surface area up to 330 m2·g-1 , porosity up to 1.6 cm3·g-1 , and very good thermal stability. The observed enhancement in their thermomechanical resistance is associated with the faster formation of the metal aluminate phases. The nanometer scale path diffusion and highly defective interface of γ-alumina facilitate the counter-diffusion of Mex+ and Al3+ species and further formation of the metal aluminate phase. Additionally, it is shown that the type of transition metal affects the pore size of the nanostructured metal oxide by shifting the decomposition temperature of the triblock copolymer. Overall, the synthesis strategy requires easy steps and readily available precursors and promotes the formation of highly porous nanostructured oxides suitable for several applications such as catalysis and adsorption. [ABSTRACT FROM AUTHOR]

Tl6SeI4 is a promising wide-bandgap semiconductor for room-temperature high-energy photon detection. Because of the air-sensitive Tl precursor or Tl-based binary precursors used in the synthesis, this material can contain deleterious Tl oxide impurities. These impurities lead to problems during syntheses and crystal growth including glass attack, tube rupture, and parasitic nucleation, which subsequently deteriorate detector performance. In this work, we present a facile way to chemically reduce Tl oxides and eliminate oxygen impurities in Tl6SeI4 by adding high-purity graphite powder during synthesis. The addition of carbon leads to reduction of the residual Tl oxides and formation of CO2 and CO. The resistivity and hard radiation detection performance for 122 keV γ-rays of Tl6SeI4 single crystals were significantly improved. The improvement in the crystallinity was also confirmed by a narrower near-band-edge emission band in the photoluminescence spectra. We confirmed that the reaction between Tl oxide and graphite occurs, and propose a mechanism which is highly effective in substantially reducing oxide impurities from Tl-containing precursors. First-principles density functional theory calculations reveal that the presence of interstitial oxygen atoms (Oint) leads to the formation of a deep level located near the middle of the gap, which can act as carrier traps detrimental to detector performance. The calculations also indicate that graphite addition is safe for detector performance because all carbon-induced defects have high formation energy and are not likely to appear in lattice. [ABSTRACT FROM AUTHOR]

Single crystals of an environmental friendly material LiInSe2 (LISe) with dimensions up to Φ16 mm × 55 mm were grown successfully through a modified vertical Bridgman technique. The quality of the crystal was measured by a high resolution X-ray diffraction rocking curve, and a full width at half-maximum (fwhm) for a, b, and c faces are 47", 46", 36", respectively. It indicates that the as-grown crystal is high quality. The complete sets of dielectric, elastic, and piezoelectric constants of LISe crystals at room temperature were obtained by the resonant technique and impedance analysis for the first time. The piezoelectric constants d24 and d33 reached -13.6 pC/N and 8.5 pC/N, respectively. The corresponding electromechanical coupling coefficient k33 is 21%. In addition, the structural distortions and dipole moments of LISe were analyzed in detail. Our results show that LISe is a promising candidate as an environmental friendly piezoelectric material. [ABSTRACT FROM AUTHOR]

Electrochemical crystal growth of hollandite-type CsxTi8O16 was examined employing high-temperature electrolysis of a molten mixture consisting of TiO2 and Cs2MoO4 with constant applied voltages. The resultant needle-like crystals showed obviously distinct appearances, either optical transparency or metallic luster, depending on the applied voltage. While the transparent crystals were electrical insulators, the metallic luster crystals were moderately conductive, with ρ-T curves being fitted with the one-dimensional (1D) VRH model, suggesting that the compound is a 1D metal involving carrier localization. [ABSTRACT FROM AUTHOR]

The last decades have witnessed the discovery of tens of thousands of rare earth (RE) (e.g., Eu2+) and non-RE (e.g., Mn2+) doped photonic materials for near-ultraviolet (NUV) and blue converted white light-emitting diodes (wLEDs), but the future development of wLEDs technology is limited greatly by the intrinsic problems of these traditional dopants, such as the insurmountable visible light reabsorption, the weak absorption strength in NUV or blue region, and so on. Here we report a feasible strategy guided by density functional theory (DFT) calculation to discover novel Bi3+ red luminescent materials, which can solve the above problems eventually. Once the untraditional ion of bismuth is doped into ZnWO4 crystal, multiple defects can be possibly created in different charge states such as BiZn, BiW, interstitial Bi, and even defect complexes of 2 BiZnVW among others, and they, as DFT calculated results illustrate, have the potential to produce emission spanning from visible to near-infrared. As confirmed by experiment, tunable emission can be led to cover from 400 to 800 nm after controls over temperatures, defect site-selective excitation schemes, and the energy transfer between these defects and host. A novel red luminescence was observed peaking at ~665 nm with a broad excitation in the range of 380-420 nm and no visible absorption, which is evidenced by the temperature-dependent excitation spectra and the diffuse reflection spectra. DFT calculation on defect formation energy shows that BiZn3+, the valence state of which is identified by X-ray photoelectron spectroscopy, is the most preferentially formed and stable defect inside a single Bi-doped ZnWO4 crystal, and it produces the anomalous red luminescence as confirmed by the single-particle level calculations. Calculation based on dielectric chemical bond theory reveals that the high covalency of the lattice site which Bi3+ prefers to occupy in ZnWO4 is the reason why the emission appears at longer wavelength than the previously reported compounds. On the basis of this work, we believe that future combination of DFT calculation and dielectric chemical bond theory calculation can guide us to efficiently find new phosphors where Bi3+ can survive and emit red light upon NUV excitation. In addition, the DFT calculation on Bi defects in different charge states will help better understand the longstanding as yet unsolved problem on the mechanism of NIR luminescence in bismuth-doped laser materials. [ABSTRACT FROM AUTHOR]

Potassium (K) post-treatment on CIGSSe has been shown to yield the highest efficiency reported to date. However, very little is known on the effect of K doping in CZTSSe and the mechanism behind the efficiency improvement. Here we reveal the mechanism by which K enhances the charge separation in CZTSSe. We show that K accumulates at the CdS/CZTSSe, passivating the recombination at the front interface and improving carrier collection. K is also found to accumulate at the CZTSSe/Mo interface and facilitates the diffusion of Cd into the absorber which affects the morphology and grain growth of CZTSSe. As revealed by the C-V, external quantum efficiency, and color J-V test, K doping significantly increases the carrier density, improves carrier collection, and passivates the front interface and grain boundaries, leading to the enhancement of V oc and J sc. The average power conversion efficiency has been promoted from 5% to above 7%, and the best 7.78% efficiency has been achieved for the 1.5 mol % K-doped CZTSSe device. This work offers some new insights into the K doping effects on CZTSSe via solution-based approach and demonstrates the potential of facile control of K doping for further improvement of CZTSSe thin film solar cells. [ABSTRACT FROM AUTHOR]

A drawback of nanocrystal-based processing, that leads to the notoriously poor crystallinity of pure-sulfide Cu2ZnSnS4 absorber, was recently reported to be effectively overcome by the annealing of thin films made from the ink of metastable wurtzite Cu2ZnSnS4 nanocrystals in a combined S and SnS atmosphere. However, the formation pathway from nanometer-sized crystals in the wurtzite phase to micrometer-sized grains with the kesterite phase during this process still lacks in-depth study. In this work, the spatial grain growth and composition evolution during the sulfurization of wurtzite nanocrystal coatings are systematically investigated by classifying samples into temperature and time series. In the process of heating up, the reversible migration of Cu and Zn species contributes to a continuous growth of kesterite Cu2ZnSnS4 grains on the surface. At higher temperature, a fast phase-transition growth from wurtzite Cu2ZnSnS4 nanoparticles to kesterite grains is also directly observed in the region away from the surface. After reaching 580°C, the thin film experiences impressive decomposition and reorganization changes as a function of time, which cause the formation of an absorber with good crystallinity and homogeneous compositional distribution. The solar cell device, fabricated by employing this pure-sulfide Cu2ZnSnS4 absorber from wurtzite nanocrystal-based coatings, demonstrated an energy conversion efficiency of 6.0% in the absence of an antireflection coating. [ABSTRACT FROM AUTHOR]

Polycrystalline films were prepared by annealing coatings cast from colloidal dispersions of Cu2ZnSnS4 (CZTS) nanocrystals in sulfur vapor. This nanocrystal dispersion-based route is a promising potential low-cost approach for production of low-cost thin-film solar cells. We studied the effects of nanocrystal size, sulfur pressure, and carbon concentration on the microstructure development and grain growth during annealing. Coatings prepared from dispersions of CZTS nanocrystals with an average diameter of either 5 or 35 nm were annealed for 10-60 min at 600 °C in 50 or 500 Torr of sulfur. The CZTS nanocrystal size influenced both the rate and mechanism of grain growth. When coatings composed of 5 nm nanocrystals are annealed, abnormal grain growth forms micrometer-scale CZTS grains on the surface of the coating. In contrast, when CZTS coatings composed of 35 nm nanocrystals are annealed, grains grow uniformly via normal grain growth. Grain growth rates increased with sulfur pressure regardless of the nanocrystal size. The presence of carbon, originating from ligands used to stabilize nanocrystal dispersions, enhances abnormal grain growth, but too much carbon eventually inhibits all grain growth. On the basis of these observations, we propose a mechanism for microstructure development during annealing of CZTS nanocrystal coatings in sulfur. While much research effort has been expended on the reduction of carbon from nanocrystal coatings prior to sulfidation or selenization by means of ligand exchange or preannealing treatments in the belief that reduced carbon concentration aids CZTS microstructure development and solar cell efficiencies, this work indicates that carbon plays a more complex and significant role in CZTS grain growth than previously assumed: carbon may be beneficial or even required for rapid grain growth during sulfidation. [ABSTRACT FROM AUTHOR]

We report a quantitative analysis of the symmetry reduction phenomenon involved in the seed-mediated growth of Pd nanocrystals under dropwise addition of a precursor solution. In addition to the elimination of self-nucleation, the dropwise approach allows for the formation of a steady state for the number of precursor ions in the growth solution, which only fluctuates in a narrow range defined by experimental parameters such as the initial concentration of precursor solution and the injection rate. We can deterministically control the growth mode (symmetric vs asymmetric) of a seed by tuning these parameters to quantitatively manipulate the reaction kinetics and thus the lower and upper limits that define the steady state. We demonstrate that there exists a correlation between the growth mode and the lower limit of precursor ions in the steady state of a seed-mediated growth process. For the first few drops of precursor solution, the resultant atoms will only be deposited on a limited number of available sites on the seed if the lower limit of the steady state is below a critical value. Afterward, the deposition of atoms will be largely confined to these initially activated sites to induce symmetry reduction if atom deposition is kept at a faster rate than surface diffusion by controlling the lower limit of precursor ions in the steady state. Otherwise, the migration of atoms to other regions through surface diffusion can access other sites on the surface of a seed and thus lead to the switch of growth mode from asymmetric to symmetric. Our study suggests that symmetry reduction can only be initiated and retained by keeping the atom deposition at a rate slow enough to limit the number of initial nucleation sites on a seed but fast enough to beat the surface diffusion process. [ABSTRACT FROM AUTHOR]

Anisotropic(nonspherical) metal nanoparticles are of widespreadresearch interest because changing the shape of metals at the nanoscalecan provide access to materials with unique optical, electronic, andcatalytic properties. The development of seeded growth syntheses hasprovided researchers unprecedented access to anisotropic metal nanocrystals(particularly, gold, silver, platinum, and palladium nanocrystals)with precisely controlled dimensions and crystallographic features.The mechanisms by which the various reagents present in seeded growthsyntheses accomplish shape control, however, have yet to be fullyelucidated. Recently, the role halide ions play in controlling metalnanocrystal shape has become a subject of particular interest. Thereare many ways in which the halide ions may direct the anisotropicgrowth of metal nanocrystals, including modulating the redox potentialsof the metal ions, acting as face-specific capping agents, and/orcontrolling the extent of silver underpotential deposition at thenanocrystal surface. In this Perspective, we examine recent progressin elucidating and articulating the role halide ions play in seededgrowth with particular emphasis on gold nanoparticles. [ABSTRACT FROM AUTHOR]

The highly visible and infrared (upto 6 μm) transparentSr3Al2O6polycrystalline ceramicwas obtained by full crystallization of the corresponding glass composition.The glass synthesis and the direct congruent crystallization processesare described, and the material transparency is discussed in lightof its microstructure. This new transparent ceramic exhibits a highdensity (i.e., complete absence of porosity) and micrometer-scalecrystallites with very thin grain boundaries. These microstructuralcharacteristics, inherent to the preparation method, minimize lightscattering and demonstrate the advantages of this synthesis routecompared to the high-pressure process used for the few reported transparentpolycrystalline materials. This Sr3Al2O6ceramic shows a H= 10.5 GPa hardness, a Er= 150 GPa reduced elasticity modulus, anda 9.6 × 10–6K–1thermalexpansion coefficient. Such a transparent strontium aluminate ceramicopens the way to a wide range of applications, especially photonicswhen doped by various doping agents. As examples, the luminescenceof Sr3Al2O6:Eu3+and Sr3Al2O6:Er3+, which show strongemissions in the visible and infrared ranges, respectively, is presented.Moreover, the Sr3Al2O6:Ce3+material was found to exhibit scintillation properties under X-rayexcitation. Interestingly, the analogous Sr3Ga2O6transparent polycrystalline ceramic material couldequally be prepared using the same elaboration method, although itshygroscopicity prevents the preservation of its high transparencyunder normal conditions. The establishment of the key factors forthe transparency of this economical and innovative synthesis methodshould enable the prediction of new classes of technologically relevanttransparent ceramics. [ABSTRACT FROM AUTHOR]

Single crystals of the previously unknown thallium silicate T14Si5O12 Have been prepared from hydrothermal crystallization of a glassy starting material at 500 °C and lkbar. Structure analysis resulted in the following basic crystallographic data: monoclinic symmetry, space group C2/c, a = 9.2059(5) Å, b = 11.5796(6) Å, c = 13.0963(7) Å, β = 94.534(5)°. From a structural point of view the compound can be classified as an interrupted framework silicate with Q3- and Q4-units in the ratio 2:1. Within the framework 4-, 6-, and 12-membered rings can be distinguished. The framework density of 14.4 T-atoms/1000 Å3 is comparable with the values observed in zeolitic materials like Linde type A, for example. The thallium cations show a pronounced one-sided coordination each occupying the apex of a distorted trigonal T1O3 pyramid. Obviously, this reflects the presence of a stereochemically active 6s2 lone pair electron. The porous structure contains channels running along [110] and [–1 1 0], respectively, where the T1+ cations are located for charge compensation. Structural investigations have been completed by Raman spectroscopy. The interpretation of the spectroscopic data and the allocation of the bands to certain vibrational species have been aided by DFT calculations, which were also employed to study the electronic structure of the compound. [ABSTRACT FROM AUTHOR]

Two noncentrosymmetric isostructural compounds Pb4Ga4GeQ12 (Q = S, Se) with their own structure type have been synthesized by solid-state reactions at high temperature. They crystallize in the tetragonal space group P421c (No. 114) with a = 12.673(2) Å and c = 6.128(2) Å, and a = 13.064(7) Å and c = 6.310(5) Å, respectively, and Z = 2. The major structure motif features a three-dimensional framework constructed by chains of GaQ4 tetrahedra that are interconnected by separated GeQ4 tetrahedra at regular intervals. Interestingly, such a [Ga4GeQ12]8- framework is flexible to allow the addition of Ag+ or Li+ to occupy the embedded A- or B-type of vacancies to generate the previously reported [AgGa5Q12]7- or [LiGa5Q12]7- interstitial compounds without symmetry breaking. The title compounds (Q = S, Se) have optical band gaps of 2.35 and 1.91 eV, respectively, and wide IR transparent regions of 0.80-22.5 and 0.75-22.5 µm, respectively. Significantly, the powder Pb4Ga4GeSe12 sample exhibits a strong second-harmonic-generation (SHG) response that is ˜2 times that of the benchmark AgGaS2 at a laser radiation of 2.05 µm with a non phase-matchable behavior. The calculated d36 coefficient agrees well with the experimental observation. The density functional theory (DFT) calculations suggest that the SHG response originates from the electronic transitions from Se 4p states to Pb 6p, Ga 4p, and Ge 4p states. [ABSTRACT FROM AUTHOR]

We report the preparation of single-layer layered double hydroxide (LDH) two-dimensional (2D) nanosheets by exfoliation of highly crystalline NiAl-NO3 LDH. Next, these unilamellar moieties have been incorporated layer-by-layer (LbL) into a poly(sodium 4-styrenesulfonate)/LDH nanosheet multilayer ultrathin film (UTF). Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible light (UV-vis), and X-ray diffraction (XRD) profiles have been used to follow the uniform growth of the UTF. The use of a magnetic LDH as the cationic component of the multilayered architecture enables study of the resulting magnetic properties of the UTFs. Our magnetic data show the appearance of spontaneous magnetization at ~5 K, thus confirming the effective transfer of the magnetic properties of the bulk LDH to the self-assembled film that displays glassy-like ferromagnetic behavior. The high number of bilayers accessible-more than 80-opens the door for the preparation of more-complex hybrid multifunctional materials that combine magnetism with the physical properties provided by other exfoliable layered inorganic hosts. [ABSTRACT FROM AUTHOR]

The widely applied metal-catalyzed growth mechanism ofZnO nanowires(NWs) is investigated by advanced methods of transmission electronmicroscopy and is discussed with respect to thermodynamic growth conditions.Au catalyst particles do not contain a substantial amount of Zn provinga solid Au catalyst at 1173 K growth temperature. This result is owedto the high equilibrium Zn partial pressure over Au–Zn alloyswhich in turn leads to a very low sticking coefficient of Zn fromvapor and prevents alloying. Growth rates of ZnO NWs were measuredbetween 5.5 nm s–1and 36 nm s–1as a function of oxygen partial pressure. The enhanced growth rateat higher oxygen partial pressures is explained by an increased stickingcoefficient of Zn atoms at the Au catalyst. A growth mechanism isproposed which is quite different from the classic vapor–liquid–solid(VLS) mechanism: Zn alloys only in a thin surface layer at the catalystand diffuses to the vapor–catalyst–NW triple phase line.There, together with oxygen, ZnO ledges nucleate which grow laterallyto inner regions of the ZnO–Au heterointerface where Zn andoxygen can diffuse and finally promote NW growth in a rather kineticallycontrolled process. The geometry of the ZnO–Au interface planar or stepped  and the associated diffusional transportproperties are shown to be determined by the orientation relationshipbetween Au and ZnO and hence by the atomic structure of the interface. [ABSTRACT FROM AUTHOR]

The structure and magnetic properties of epitaxial (CexSr1-x)(Ti0.6Fe0.4)O3-δ (x = 0, 0.1, 0.2 and 0.3) and (LaxSr1-x)-(Ti0.6Fe0.4)O3-δ (x = 0, 0.1, 0.2, 0.3 and 0.4) perovsklte -structure thin films deposited by pulsed laser deposition on (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) substrates are reported. Both La and Ce ions showed a dominant 3+ valence state and acted as donors on the Sr2+ site (A site) in the perovskite lattice. The optical band gap widened, and the Fermi level moved toward the vacuum level with increased Ce or La content; meanwhile the Ti and particularly the Fe ions were driven to a lower valence state, resulting in a higher Fe2+ concentration. The materials were magnetic at room temperature with up to 0.8 μB/Fe and a magnetoelastic out-of-plane anisotropy. Ce and La lowered the coercivity while raising both the Faraday rotation at 1550 nm and the optical absorption at near-infrared wavelengths. [ABSTRACT FROM AUTHOR]

In any given matrix control over the final particle size distribution requires a constitutive understanding of the mechanisms and kinetics of the particle evolution. In this contribution we report on the formation mechanism of silver nanoparticles embedded in a soda-lime silicate glass matrix. For the silver ion-exchanged glass it is shown that at temperatures below 410 °C only molecular clusters (diameter <1 nm) are forming which are most likely silver dimers. These clusters grow to nanoparticles (diameter >1 nm) by annealing above this threshold temperature of 410 °C. It is evidenced that the growth and thus the final silver nanoparticle size are determined by matrix-assisted reduction mechanisms. As a consequence, particle growth proceeds after the initial formation of stable clusters by addition of silver monomers which diffuse from the glass matrix. This is in contrast to the widely accepted concept of particle growth in metal-glass systems, in which it is assumed that the nanoparticle formation is predominantly governed by Ostwald ripening processes. [ABSTRACT FROM AUTHOR]

Single crystals of Ln2Fe4Sb5 (Ln = La--Nd and Sm) were grown from an inert Bi flux. Measurements of the single crystal X-ray diffraction revealed that these compounds crystallize in the tetragonal space group I4/mmm with lattice parameters of a≈4Ȧ, c≈26Ȧ,V≈500 Ȧ³, and Z = 2. This crystal structure consists of alternating LnSb8 square antiprisms and Fe-sublattices composed of nearly equilateral triangles of bonded Fe atoms. These compounds are metallic and display spin glass behavior, which originates from the magnetic interactions within the Fe-sublattice. Specific heat measurements are void of any sharp features that can be interpreted as contributions from phase transitions as is typical for spin glass systems. A large, approximately linear in temperature, contribution to the specific heat of La2Fe4Sb5 is observed at low temperatures that we interpret as having a magnetic origin. Herein, we report the synthesis, structure, and physical properties of Ln2Fe4Sb5 (Ln = La--Nd and Sm). [ABSTRACT FROM AUTHOR]

A unique approach has been developed to deposit ZnO withtunablemorphology and physical properties by introducing methanol in an electrochemicalprocess. As the methanol increases in the aqueous electrolyte, thegrowth mode of ZnO transforms from thin films to nanostructures, correspondingto a crystalline orientation change from (002) to (102) and then to(101). These structural changes are accompanied by significant variationsof optical and electrical properties, including a widening of theband gap from 3.31 to 3.53 eV, increase of resistivity, and decreasein charge carrier concentration. Compositional analysis indicatesthat the samples grown at higher methanol concentrations contain Zn(OH)2, which is likely responsible for the band gap change. Thegrowth mechanism is discussed in terms of the impact of methanol onthe chemical reaction, i.e., the changing growth mode results fromthe adsorption of nitrate ions on the polar surface of ZnO. This findinghelps to grow specific ZnO nanostructures with desired morphologiesand properties for device applications. [ABSTRACT FROM AUTHOR]

In this study, we demonstrated that by using annealedAu thin films as catalysts, high-density, defect-free, and taper-restrainedepitaxial GaAs nanowires were grown on GaAs (111)B substrates. Theas-grown nanowires were compared with low-density Au colloidal nanoparticlecatalyzed GaAs nanowires grown under identical conditions in the samemetal–organic chemical vapor deposition reactor. Throughdetailed morphological and structural characterizations using advancedelectron microscopy, we discovered that GaAs epitaxial nanowire taperingcan be efficiently restrained by increasing the density of Au catalysts.By increasing the density of the Au catalysts, the axial growth rateof nanowires is reduced, which, in turn, limits the formation of latticedefects. Furthermore, the comprehensive investigation of GaAs nanowirescatalyzed by Au thin film of different thicknesses (1 nm, 2 nm, 3nm, and 5 nm) and Au colloidal particles of different densities indicatesthat the density of the Au catalysts play an important role in GaAsnanowire growth. This comprehensive study provides an opportunityto explore the effects of the catalysts and the growth mechanismsof III–V epitaxial semiconductor nanowires. [ABSTRACT FROM AUTHOR]

Given the diverse scientific and technological applicationsofgold nanoparticles (Au NPs), understanding the impact of macromolecularadditives on the distribution of size, shape, and composition is crucialto ensure reproducibility and lower production cost. In situ measurementof the evolution of these distributions challenges current techniques;however, it is critical for in-line manufacturing controls. Usingmild Au(I) reduction by tert-butylamine-borane intoluene, the utility and limitations of SAXS, UV/Vis spectroscopy,and TEM are considered by comparing the mean nanoparticle size, sizedistribution, and relative number density. Individually, these techniquesare insufficient to follow these parameters through the initial processof nucleation and growth; either providing insufficient informationon the number of particles (UV/Vis), introducing artifacts (TEM),or not providing a unique solution for the shape of the distribution(SAXS). However, when used in conjunction, especially SAXS calibratedwith TEM of reaction aliquots, the time evolution of these parameterscan be quantified. For the single-phase Au NP synthesis withAu(I) and mild reductants, four distinct experimental regions arerevealed that entail two growth mechanisms, which complement previousdiscussions of single-mode growth kinetics. The kinetics of Au(I):boranereactions are dependent on the Au precursor/reductant ratio and thethiol capping agent length, when reductant concentration is low. Thefinal reaction products exhibit an LSW size distribution. [ABSTRACT FROM AUTHOR]

In this article, we introduce fully digital selective ZnO nanowire array growth on inkjet-printed seed patterning. Through proper natural convection suppression during hydrothermal growth, successful ZnO nanowire local growth can be achieved. Without any need for photolithographic processing or stamp preparation, the nanowire growth location can be easily modified when the inkjet printing process is integrated with a CAD (computer-aided design) system to allow a high degree of freedom when the design needs to be changed. The current proposed process is very fast, low-cost, environmentally benign, and low-temperature. Therefore, it can be applied to a flexible plastic substrate and scaled up for larger substrates for mass production or roll-to-roll processing. [ABSTRACT FROM AUTHOR]

Four tetrazole-based three-dimensional (3D) metal-organic frameworks (MOFs), {[CuII(btz)]∙0.5H2O}n (1), [CuII(btz)]n (1'), {[CuII(btz)]∙0.5I2}n (1'∙0.5I2), and [CuIICuI2(btz)2]n (2) [H2btz = 1,5-bis(5-tetrazolo)-3-oxapentane)], have been successfully obtained and characterized by crystallography. Compound 1 features a chiral porous framework. The bulk crystallization of 1 is composed of enantiomers 1a (P41) and 1b (P43), which has been demonstrated by the crystal structure analyses of nine crystals of 1 randomly selected. The Cotton effect displayed in the solid-state circular dichroism spectrum of 1 is therefore attributed to enantiomeric excess rather than enantiopurity. The completely dehydrated phase of 1, that is, 1', can adsorb 0.5 I2 molecule per formula unit to yield compound 1'∙0.5I2, which has been supported by single-crystal X-ray diffraction, elemental analysis, and thermogravimetric analysis. The locations of I2 in the pores were unambiguously determined, and the interactions between I2 molecules and the pore structures were investigated. Compound 2 crystallizes in an achiral C2/c space group. Interestingly, the formations of chiral 1 and achiral 2 significantly depend on the reaction temperature. Between 80 and 140 °C, we got compound 1 as the only product. At 150 °C, both 1 and 2 were in coexistence in the final product. From 160 to 180 °C, only compound 2 was obtained. More interestingly, treatment of the crystals of 1 or the mixture of 1 and 2 obtained at 150 °C in their mother liquor at 170 °C yielded the crystals of 2 in a single phase. [ABSTRACT FROM AUTHOR]

We report the formation of ZnO structures with a bimodaldistributionof aspect ratios in a one-batch reaction. In this synthesis, low aspectratio (∼10) ZnO microrods were formed in the bulk solution,whereas high aspect ratio (∼1000) ZnO nanostructures formedon a ZnO thin film-coated substrate immersed in the bulk solution.The two types of structures were easily separated because the highaspect ratio ZnO nanostructures remained immobilized on the substrate.The distinct aspect ratios suggested that two types of ZnO structuresformed by different growth mechanisms in the one-batch reaction. Asystematic investigation led to the proposal of a formation mechanism.In the early stages of the reaction, Zn(OH)2formed andwas converted to ZnO in the bulk solution. The ZnO grew to form lowaspect ratio ZnO mircorods via layer-by-layer growth. As the reactionproceeded, precursors were consumed, which decreased the degree ofsupersaturation. The high aspect ratio 1D ZnO nanostructures grewfrom defects in the ZnO film on the substrate via axial screw dislocationgrowth at a low degree of supersaturation. [ABSTRACT FROM AUTHOR]

Ceria (CeO2) nanocrystals have unique andhighly attractiveproperties that depend on the morphology and structure. In this paper,we demonstrate that by controlling the addition of copper to growingceria nanocrystals it is possible to modulate the resulting structureproperties. We show also by means of X-ray diffraction, high-resolutiontransmission electron microscopy, Fourier transform infrared spectroscopy,X-ray fluorescence spectrometry, and X-ray absorption spectroscopythat copper configuration affects both the morphology and the electronicstructure of cerium oxide nanocrystals. Indeed, external and internalcopper doping on ceria nanocrystals leads to structural transitions,including a morphological transition from cubic to truncated octahedron,along with cerium valence changes. The results of this study, optimizingthe structural properties of such nanocrystals, may certainly triggernew opportunities and, ultimately, new applications. [ABSTRACT FROM AUTHOR]

Understanding of the nanoparticle (NP)-mediated crystal growth mechanism is essential for the syntheses of nanostructures with desired physical and chemical properties. A facile protocol is developed to study the size effect of primary NPs on the silver NP-mediated crystal growth process. Experimental observation shows that the primary NPs size performs a key role for the crystal final shape and structure. Theory study discloses that water solution will promote an amorphous structure of small primary NPs which thus perform a different assembly process for NP-mediated crystal formation compared with larger crystalline primary NPs. [ABSTRACT FROM AUTHOR]

The processes of aggregation and subsequent grain growth of highly twinned, surfactant stabilized gold nanoparticles have been followed in real time using synchrotron X-ray diffraction (XRD) and small-angle X-ray scattering (SAXS). This gives insight into the overall coalescence mechanism of metal nanocrystals. First, the capping ligands melt or desorb, which enables the nanocrystals to aggregate and join together. At longer times, grain growth is observed, and the stacking fault densities decrease. The time scale of the grain growth process is significantly longer than that of the particle aggregation. We contrast the behavior we observe to that of other nanoparticles and discuss the implications of our results on device fabrication. [ABSTRACT FROM AUTHOR]

Using photoemission electron microscopy in combination with X-ray magnetic linear dichroism, we report reconfiguration upon nanostructuring of the antiferromagnetic domain structure in epitaxial LaFeO3thin films. Antiferromagnetic (AFM) nanoislands were synthesized using a dedicated process, devised to define nanostructures with magnetic order embedded in a paramagnetic matrix. Significant impact on the AFM domain configuration was observed. Extended domains were found to form along edges parallel to the in-plane ⟨100⟩ crystalline axes of the cubic substrate, with their AFM spin axis parallel to the edge. No such edge-imposed domain configuration was found for nanoislands defined with the edges at 45° with the in-plane crystalline axes. Epitaxial constraints on the film crystalline structure appear to play an important role in the formation of the edge-bound extended AFM domains. The data indicate a magnetostatic origin of this domain reconfiguration. [ABSTRACT FROM AUTHOR]

We exploited the oxide shell structure to explore the structure confinement effect on the nickel silicide growth in one-dimensional nanowire template. The oxide confinement structure is similar to the contact structure (via hole) in the thin film system or nanodevices passivated by oxide or nitride film. Silicon nanowires in direct contact with nickel pads transform into two phases of nickel silicides, Ni31Si12and NiSi2, after one-step annealing at 550 °C. In a bare Si nanowire during the annealing process, NiSi2grows initially through the nanowire, followed by the transformation of NiSi2into the nickel-rich phase, Ni31Si12starting from near the nickel pad. Ni31Si12is also observed under the nickel pads. Although the same phase transformations of Si to nickel silicides are observed in nanowires with oxide confinement structure, the growth rate of nickel silicides, Ni31Si12and NiSi2,is retarded dramatically. With increasing oxide thickness from 5 to 50 nm, the retarding effect of the Ni31Si12growth and the annihilation of Ni2Si into the oxide confined-Si is clearly observed. Ni31Si12and Ni2Si phases are limited to grow into the Si/SiOx core−shell nanowire as the shell thickness reaches ∼50 nm. It is experimental evidence that phase transformation is influenced by the stressed structure at nanoscale. [ABSTRACT FROM AUTHOR]

Laterally epitaxial single crystalline Ag2Te nanowires (NWs) are synthesized on sapphire substrates by the vapor transport method. We observed the phase transitions of these Ag2Te NWs via in situ transmission electron microscopy (TEM) after covering them with Pt layers. The constrained NW shows phase transition from monoclinic to a body-centered cubic (bcc) structure near the interfaces, which is ascribed to the thermal stress caused by differences in the thermal expansion coefficients. Furthermore, we observed the nucleation and growth of bcc phase penetrating into the face-centered cubic matrix at 200 °C by high-resolution TEM in real time. Our results would provide valuable insight into how compressive stresses imposed by overlayers affect behaviors of nanodevices. [ABSTRACT FROM AUTHOR]

Two new quaternary thioborate compounds with strongly one-dimensional growth, BaSb(BS3)S and BaBi(BS3)S, have been synthesized using the conventional solid state reaction method in closed tubes at 1100 K. The single crystal X-ray diffraction analysis has shown that compound BaSb(BS3)S crystalizes in space group Pnma of the orthorhombic system with unit cell parameters of a = 9.6898(15) Å, b= 6.2293(13) Å, c= 11.670(2) Å, V= 704.4(2) Å3, and Z= 4, while compound BaBi(BS3)S crystallizes in space group C2/m with unit cell parameters of a = 14.9890(17) Å, b = 6.2457(6) Å, c= 7.5591(9) Å, β = 101 .604(5)°, V= 693.19(13) Å3, and Z= 4. The two compounds both crystallize in the structure of infinite one-dimensional chains with [BS3]3- trigonal plane coordination alternately bridged by [MS3]3- (M = Sb, Bi) trigonal pyramids through sharing two sulfur atoms along the crystallographic b axis. First-principles electronic structure calculations performed with the density functional theory (DFT) method show that the calculated band gaps of BaSb(BS3)S and BaBi(BS3)S are 2.29 and 2.16 eV, respectively, which are in good agreement with the experimental values estimated from UV-vis absorption spectra using the Kubelka-Munk equation, and the observed absorption peak is assigned as charge transfers from S-3p states to Sb-5p (Bi6p) states. [ABSTRACT FROM AUTHOR]

A strategy for the preparation of bimetallic mesoflowers (MFs) has been demonstrated by a simple overgrowth reaction. We make hybrid MFs containing Au core and shells of different metals, such as Ag and Pt, by tuning the experimental conditions so as to study region-specific overgrowth. This selective growth is attributed to the specific binding affinity of cetyltrimethylammonium bromide (CTAB) at different crystal planes of Au MF surfaces. We also studied the region-specific, composition dependent surface-enhanced Raman scattering (SERS) activity of single bimetallic MFs to understand their chemical environment. Substrate effects on the SERS activity at single particle level were evaluated by a comparative study of the Raman images of Au, Au/Ag, and Au/Pt MFs. Region-specific SERS activity exhibited by single Au/Ag MF provides an insight into the SERS activity of bimetallic MFs over their monometallic analogues. [ABSTRACT FROM AUTHOR]

A mechanism for grain growth and formation in the interstellar medium is proposed. In this mechanism, hydrogen molecules act as moderators. The process begins when they physisorb to the surface of the grain. Then, when a collision with a heavy atom occurs, the bonding energy is carried away by the evaporation of hydrogen molecules. Estimates are made of the number of hydrogen molecules bound to the surface of a grain that would be sufficient to facilitate this mechanism at 13 K for amorphous carbon and 8 K for a silicate grain. [ABSTRACT FROM AUTHOR]

An interesting shape evolution of Cu2O crystals, that is, from cubes, truncated octahedra, octahedra, and finally to nanospheres was first realized in high yield by reducing the copper−citrate complex solution with glucose. X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM) techniques were employed to characterize the samples. We elucidate the important parameters (including poly (vinyl pyrrolidone) (PVP) concentration, reaction time, and reaction temperature) responsible for the shape-controlled synthesis of Cu2O crystals. The possible formation mechanism for the products with various architectures is presented, which is mainly based on the variation of the ratio (R) of the growth rates along the ⟨100⟩ and ⟨111⟩ direction. In addition, the effect of the low supersaturation on the formation of star-shaped samples with six symmetric branches is also taken into account. This polymer-mediated method should be readily extended to the controlled synthesis of other metal oxides and the proposed growth model could also be used to explain and direct the growth of crystals with a cubic structure. [ABSTRACT FROM AUTHOR]

Tailor-made surface-modified metal oxide nanocrystals enable various applications including medical, electronic, magnetic, and photovoltaic devices. Both the synthesis and application of surface-modified metal oxide nanocrystals rely on the interaction between organic molecules and the surface of metal oxides. From this viewpoint, we have focused on the synthesis of metal oxide nanocrystals using supercritical water in the presence of organic molecules as a surface modifier. Here, we describe the use of dicarboxylic acids with various chain lengths as the modifiers of CeO2nanocrystals. The morphology and displayed crystallite plane of CeO2nanocrystals could be controlled by the length of dicarboxylic acids. Long dicarboxylic acids produced cuboctahedral or cubic CeO2nanocrystals, possibly because of the decreased growth rate of the {200} plane. The growth mechanism of the CeO2nanocrystals is discussed in detail. Furthermore, dicarboxylic acids on the surface of the CeO2nanocrystals changed the isoelectric point of the nanocrystals by displaying carboxyl groups. As a result, we have succeeded in synthesizing water-soluble CeO2nanocrystals with various morphologies using dicarboxylic acids. [ABSTRACT FROM AUTHOR]

Self-assembled arrangement of monodisperse nanoparticles (NPs) forms one-dimensional (1D) to three-dimensional (3D) superlattice (SL) with many useful applications. A simple seed growth (S-G) method is presented to achieve monodisperse gold (Au) NPs and simultaneously arrange them into SL formation. It can simply be done by controlling the hydrophobicity of a capping surfactant and can very well be extended to semiconductor NPs such as PbS as well. It is demonstrated by step-by-step evaluation of a three-step S-G method in the presence of a series of strongly hydrophobic Gemini surfactants. NPs of each step are analyzed by transmission electron microscopy (TEM) and UV−visible measurements to evaluate the mode of aggregation in dried and colloidal bulk phases, respectively. Both studies show complementary results. Crystal growth of NPs is followed through different steps by measuring the X-ray diffraction (XRD) patterns. It allows one to identify different reaction conditions such as the number of nucleating centers (seeds) and concentration of the surfactant to achieve monodisperse morphologies of NPs. All studies pertaining to different steps of the S-G method under different reaction conditions collectively lead to a single conclusion that better capping ability of strongly hydrophobic surfactants allows NPs to achieve both monodisperse morphologies as well as SL formation simultaneously. [ABSTRACT FROM AUTHOR]

YPO4nano/microcrystals with multiform crystal phases and morphologies, such as hexagonal nano/submicroprisms, spherical-like nanoparticles, and nanorods with different length/diameter ratios as well as tetragonal nanospindles, have been synthesized via a facile hydrothermal route. A series of controlled experiments indicate that the pH values in the initial solution, phosphorus sources, and the organic additive trisodium citrate (Cit3−) are responsible for crystal phase and shape determination of final products. It is found that Cit3−as a ligand and shape modifier has the dynamic effect by adjusting the growth rate of different facets under different experimental conditions, resulting in the formation of various geometries of the final products. The possible formation mechanisms for products with diverse architectures have been presented. More importantly, a systematic study on the photoluminescence of Ln3+(Ln = Tb, Eu, Dy) and V5+ion-doped samples annealed at 500 °C has been explored in order to obtain the multicolor emission in a single host lattice. The ability to generate YPO4nano/microstructures with diverse shapes and tunable emission colors provides a great opportunity for systematically evaluating their luminescence properties, as well as fully exploring their application in many types of color display fields. [ABSTRACT FROM AUTHOR]

We have performed real-time atomic force microscopy (AFM) imaging of bismuth crystals that were grown under electrochemical control at low overpotentials to ensure a slow growth rate and allow in situ observation of the growth. A two step chronoamperometric potential was applied to a boron-doped diamond (BDD) working electrode with a short high overpotential, −0.4 V (2 s), to nucleate the bismuth, and then a long low overpotential for slow growth, −0.32 V (4.4 h). Growth rates of individual crystals and detailed growth mechanisms could be followed in real time because of the slow crystal growth. The close proximity of the AFM tip and tip holder to the working electrode appears to hinder the diffusion of bismuth to the BDD surface, as evidenced by the significantly lower density of crystals under the cantilever as compared to the rest of the electrode, therefore slowing down the growth process. [ABSTRACT FROM AUTHOR]

By utilizing a fluidic device, a gold nanoparticle dispersion is cast onto a nanostructured polymer template using solution subjected to hydrodynamic flow. With in situ grazing incidence small-angle X-ray scattering (GISAXS), the progressive gold deposition from a stream of gold solution onto the polymer template of a diblock copolymer with parallel cylinder morphology arranged into powder-like domains is investigated. The continuously flowing solution causes a systematic increase in the X-ray contrast between both of the microphase-separated blocks of the block copolymer film, indicating flow-induced selective gold immobilization on one block. Both in situ GISAXS data and atomic force microscopy of the metal-deposited polymer film prove the 1D coalescence of nanoparticles into continuous nanowires. With additional gold nanoparticle upload by the continuous flow-stream method, the selectivity of the nanoparticle deposition diminishes as a result of the formation of a pseudo uniform gold layer. Consequently, this flow-stream deposition technique introduces an easy alternative method to the vapor deposition technique for surface gold nanopatterning. [ABSTRACT FROM AUTHOR]

A new type of bimetallic Au−Ag heterostructured material was prepared by a selective growing strategy of a Ag nanodewdrop on the petal tip of a Au flower using an electrochemical method. The whole process was strictly controlled by forming the reactive tip of the flower petal and passivating the facet along the body of the metal petal using poly(vinyl pyrrolidone) (PVP) coating film. The formed Au−Ag heterostructured flowers (HSFs) were observed to be about 2 μm in diameter and have the Ag particles of about 50 nm settled on the tips of Au petals. The Au−Ag HSFs were found to display the superior properties on the surface-enhanced Raman scattering (SERS). The presence of Ag nanodewdrops could also facilitate the oxidation of Ru(bpy)32+complex in electrogenerated chemiluminescence (ECL) measurements and dramatically enhance the emission intensity. The features of Au−Ag HSFs can promise a new type of heterogeneous bimetallic alloy material for the potential applications in chemical and biological sensors. [ABSTRACT FROM AUTHOR]

Controllable synthesis approaches for organic nanowires that permit the in situ fabrication of devices will enable future applications in nano-electronics and nano-optoelectronics. Here, the first synthesis of single-crystal silver-tetrafluorotetracyano-p-quinodimethane (Ag-TCNQF4) nanowires is reported. Ag-TCNQF4is a good charge-transfer complex and nanowires of this organic semiconductor material were deterministically synthesized in a facile vapor-solid process on selected regions through the reaction of TCNQF4vapor with patterned silver. Use of a growth barrier is shown to control the growth of Ag-TCNQF4nanowires to horizontal alignment, permitting the reproducible in situ growth of single Ag-TCNQF4nanowire devices and device arrays between prefabricated electrodes. The single-crystal nanowires are predominantly monoclinic in structure with efficient π-stacking of the TCNQF4units, leading to a high conductivity along the nanowire. However, the electron-withdrawing fluorine groups on the π-delocalized ring in the TCNQF4results in a distinctly different structure compared to that previously reported for Ag-TCNQ nanowires. The temperature- and bias-voltage-dependent electrical transport properties of in situ fabricated Ag-TCNQF4organic nanowire devices were investigated and exhibit a power-law behavior characteristic of one-dimensional systems. [ABSTRACT FROM AUTHOR]

We demonstrate the overgrowth of Au on CdSe nanowires with control over Au crystal morphology upon increasing addition of Au precursor. Extending this overgrowth technique to catalytically active metals and binary metal systems (Pt, PtCo, and PtNi) exemplifies the broader range of these metal−semiconductor hybrid nanomaterials. Structural and compositional characterization was carried out by low- and high-resolution TEM, EDS analysis, and XRD. Magnetic characterization of the PtCo binary metal hybrid systems was conducted using SQUID magnetometry. Changes in the optical properties of the decorated materials compared to the as-made CdSe nanowires confirm the presence of electronic coupling at the metal−semiconductor interface, an important material property for photocatalytic applications. [ABSTRACT FROM AUTHOR]

Uniform rare earth phosphate (REPO4, RE = La−Tb) nanocrystals were successfully synthesized in a properly designed TBP/[Omim]Cl/H2O (tributylphosphate/1-octyl-3-methyl-imidazolium chloride/water) microemulsion system. The phosphoryl groups anchored the TBP molecules on the surfaces of the nanocrystals, and this made the nanocrystals easily dispersed in some imidazolium-based ILs. LaPO4:Eu3+and CePO4:Tb3+nanocrystals capped with TBP showed bright red and green emission under UV excitation, with enhanced emission intensity and lifetimes compared with the uncapped ones. [Omim]Cl and TBP were found to play the key roles in the nucleation and growth of the nanocrystals. The designed strategy provided a facile way for the fabrication of TBP capped REPO4nanocrystals, which may also be applicable for the synthesis of other inorganic nanocrystals. [ABSTRACT FROM AUTHOR]

In this work, the precipitation of barium sulfate (BaSO4) in a continuous stirred tank reactor (CSTR) is modeled. The flow field is obtained through solving the single-phase Reynolds averaged Navier−Stokes equations with a standard single-phase k−ε turbulence model. The population balance equation is solved through the standard method of moments (SMM) and the quadrature method of moments (QMOM) both with and without aggregation and breakage terms. In the cases of precipitation simulation without aggregation and breakage, the results predicted from 2-node QMOM, 3-node QMOM, and SMM are very close. Thus, 2-node QMOM could replace SMM and be well-incorporated into an in-house CFD code to simulate the precipitation in CSTR with acceptable accuracy. The predicted area-averaged crystal size d32decreases almost linearly with increasing feed concentration, and the deviation from experimental data becomes significant at high feed concentration. Numerical simulation using 2-node QMOM with the Brownian motion and shear-induced aggregation kernels as well as a power-law breakage kernel indicates that the predicted d32shows good qualitative agreement with experimental results, and the quantitative agreement is achieved when the appropriate breakage rate equation is adopted. [ABSTRACT FROM AUTHOR]

ZnO materials with a range of different morphologies have been synthesized via a simple solvothermal method with different solvents. Zinc acetylacetonate was used as the zinc source in such solvothermal syntheses for the first time. XRD data showed that single-phase ZnO with the wurtzite crystal structure was obtained for all the solvents used. FE-SEM imaging showed that ZnO with cauliflower-like, truncated hexagonal conical, tubular and rodlike, hourglass-like, nanorods, and spherical shapes were produced when THF, decane, water, toluene, ethanol, and acetone were used as the solvent, respectively. The TEM data showed that the crystalline ZnO had different growth habits in the different solvents. The optical properties of the as-prepared ZnO materials were investigated by UV−vis absorption and room temperature photoluminescence. Photodegradation of phenol was used as a model reaction to test the photocatalytic activity of the ZnO samples. ZnO samples with different morphologies and crystal growth habits exhibited different activities to phenol degradation. The ZnO material prepared using THF as the solvent showed a nine-times enhancement of the kinetic rate constants over commercial ZnO (0.1496 min−1vs 0.0182 min−1). The influence of the solvents on the morphology of ZnO samples and the effect of the morphologies on the photocatalytic activity are discussed. [ABSTRACT FROM AUTHOR]

Binary metal-semiconductor Zn/ZnO core−shell nanorods have been synthesized through an ethylenediamine-assisted low-temperature hydrothermal process. Well-crystalline wurtzite phase ZnO was epitaxially grown along the [0100] direction, perpendicular to the single-crystalline Zn nanorod cores grown along the [0002] direction. The structure and optical properties of the binary metal-semiconductor nanostructures were studied by SEM, HRTEM, absorption, and emission spectroscopy techniques. The mechanisms for the growth of such binary structures in solution based synthesis are discussed. The growth technique can be extended for the preparation of other hybrid nanostructures. [ABSTRACT FROM AUTHOR]

Nearly monodisperse MnO nanocrystals were synthesized by the thermal decomposition of manganese oleate using the hot-injection method. The growth dynamics of the nanocrystals was studied by the time-sampling method, which revealed an interesting growing-to-shrinking behavior accompanied by a broadening−narrowing−broadening size distribution. The size evolution of nanocrystals is attributed to the kinetics of the monomer concentration in the solution as a result of the competition between crystal growth and Ostwald ripening, which favors the growth of another ensemble of MnO nanocrystals that coexisted in the products with much larger sizes. The two ensembles of MnO nanocrystals with rather different characteristic sizes could be easily separated by their different dispersibilities in hexane, allowing an independent determination of their growth modes in the reaction process. The correlation between the growth of small MnO nanoparticles and that of the large ones indicates that the existence of large MnO nanocrystals help improve the monodispersity of the small ones by reducing the nucleation time and suppressing size coarsening in the Ostwald ripening process. The characteristic size evolution of the nanocrystals in a two-size distribution system suggests an interesting method to control the growth (or dissolution) of nanocrystals with high monodispersity. [ABSTRACT FROM AUTHOR]