Alkyl-terminated crystalline Ge nanoparticles prepared from NaGe: Synthesis, functionalization and optical properties

High purity NaGe was directly prepared by a low-temperature reaction of NaH and Ge. The product was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy. This material is a useful starting reagent for the preparation of Ge nanoparticles. Hydrogen-terminated germanium (Ge) nanoparticles were prepared by reaction of NaGe with NH₄Br. These Ge nanoparticles could be prepared as amorphous or crystalline nanoparticles in quantitative yields and with a narrow size distribution. The nanoparticles were functionalized via thermally initiated hydrogermylation with 1-eicosyne, CH₃(CH₂)₁₇C≡CH to produce alkyl-terminated Ge nanoparticles. The modified Ge nanoparticles were characterized by powder XRD, transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) and Raman spectroscopy, and photoluminescence (PL) spectroscopy. The alkyl-functionalized Ge nanoparticles can be expected to have promising applications in many technological and biological areas.     

Nitrosonium nitrate: A simple cryogenic preparation and phase transitions

A simple method is suggested for the preparation of pure nitrosonium nitrate (NO⁺ NO ₃ ^– ) thin films, by deposition of nitrogen dioxide from the gas phase onto a cold tip under specified conditions and subsequent warming up of the layer. Fourier-transform infrared spectra were used for its characterization and to determine its purity. The NO⁺ NO ₃ ^– solid thus formed was found to be stable up to 230 K. Raman examination of temperature cycling effects on thev(NO⁺) band and on the phonon region of the thin films indicates one amorphous and two crystalline phases. Amorphous-crystalline and crystalline-crystalline transition temperatures are reported.     

IR laser‐induced synthesis of nanostructured gemanium telluride in the gas phase

The gas‐phase synthesis and chemical vapour deposition of nanostructured germanium telluride has been achieved for the first time. The pulsed IR laser irradiation of gaseous CH₃)₄Ge? (CH₃)₂Te? SF₆ mixtures results in homogeneous decomposition of both organometallics and formation of GeTe_x (x = 1, 2). The amorphous GeTe₂ and crystalline GeTe were identified by Raman and X‐ray photoelectron spectroscopy and by electron diffraction. Their formation is explained by an intermediacy of germanium and tellurium clusters and by reaction between these clusters in a hot laser‐induced zone. Copyright © 2005 John Wiley & Sons, Ltd.     

Preparation and properties of amorphous titania-coated zinc oxide nanoparticles

Amorphous TiO₂-coated ZnO nanoparticles were prepared by the solvothermal synthesis of ZnO nanoparticles in ethanol and the followed by sol-gel coating of TiO₂ nanolayer. The analyses of X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that the resultant ZnO nanoparticles were hexagonal with a wurtzite structure and a mean diameter of about 60 nm. Also, after TiO₂ coating, the TEM images clearly indicated the darker ZnO nanoparticles being surrounded by the lighter amorphous TiO₂ layers. The zeta potential analysis revealed the pH dependence of zeta potentials for ZnO nanoparticles shifted completely to that for TiO₂ nanoparticles after TiO₂ coating, confirming the formation of core-shell structure and suggesting the coating of TiO₂ was achieved via the adhesion of the hydrolyzed species Ti-O⁻ to the positively charged surface of ZnO nanoparticles. Furthermore, the analyses of Fourier transform infrared (FTIR) and Raman spectra were also conducted to confirm that amorphous TiO₂ were indeed coated on the surface of ZnO nanoparticles. In addition, the analyses of ultraviolet-visible (UV-VIS) and photoluminescence (PL) spectra revealed that the absorbance of amorphous TiO₂-coated ZnO nanoparticles at 375 nm gradually decreased with an increase in the Ti/Zn molar ratio and the time for TiO₂ coating, and the emission intensity of ZnO cores could be significantly enhanced by the amorphous TiO₂ shell.     

Evolution of crystallinity in photodegraded polyethylene films studied by ft-raman spectroscopy

FT-Raman spectroscopic studies of photodegraded polyethylene films have enabled the evolution of the crystallinity process to be measured. Commercial polyethylene films of M_w=90 000 were exposed in a weathering UV-chamber under known conditions of exposure time and radiant energy. The spectral profiles were modelled using Fourier methods. The relative amounts of the orthorrombic crystalline phase, α_c, the amorphous phase, α_a and the interphase, α_b, were calculated using Raman bands at 1416 cm⁻¹ characteristic of the crystalline phase and the bands at 1080, 1305 cm⁻¹, characteristic of the amorphous phase. The interphase content can be calculated from the relationship αb= 1-(α_c+α_a). It was found that the weathering process affects only the relative intensities of the bands attributed to crystalline and amorphous fractions; the crystalline content increases at the expenses of the amorphous fraction. These results are discussed in terms of the changes in the intermolecular forces caused by radiation exposure.     

Raman spectra of crystalline and molten MgCl2

The Raman active phonon frequencies have been assigned in crystalline magnesium chloride and are found consistent with that expected for the D_3d⁵ space group. Residual lattice bands are observed in the melt, just above the melting point of MgCl₂, which strongly suggests it is structurally similar to the solid layer lattice.     

Thermal properties and the structure of amorphous Sb2Se3 thin film

The amorphous Sb₂Se₃ film with a thickness ~0.9 µm was prepared by thermal evaporation and its composition was confirmed using an energy-dispersive X-ray analysis. The amorphous state was checked by an X-ray diffraction analysis. The optical gap E _g ^opt was determined to be 1.32 eV. The glass transition temperature could not be found by either a differential scanning calorimetry or a thermomechanical analysis. The film was crystallized and characterized using the quasi-isothermal method. The temperature dependence of the isobaric heat capacity was raised monotonously and no drop over the course of the crystallization was observed. The temperature-modulated thermomechanical analysis determined a temperature T = 133 °C which can be assumed to be the temperature of the structural reorganization beginning. Raman spectra of amorphous Sb₂Se₃ revealed that the vibrations of both the amorphous and crystalline phase are close to one other. Raman scattering revealed that both the short and the medium-range order of amorphous and crystalline phases are similar.     

The vibrational spectra of hexafluorocyclobutene and 1,2-dichlorotetrafluorocyclobutene

Infra-red spectra of hexafluorocyclobutene and 1,2-dichlorotetrafluorocyclobutene were recorded in the region 4000-50 cm⁻¹ in the vapour phase, in solution and as amorphous and crystalline solids at ca 90 K. Raman spectra of the liquids, including semiquantitative polarization measurements, of the amorphous and crystalline solids at ca 90 K, and of gaseous hexafluorocyclobutene at room temperature were recorded. The fundamental frequencies of both compounds were assigned in terms of C_2υ symmetry, although small deviations from this symmetry cannot be excluded.     

Electrochemical properties of all-solid-state lithium batteries with amorphous titanium sulfide electrodes prepared by mechanical milling

Amorphous titanium trisulfide (TiS₃) active materials were prepared by ball milling of an equimolar mixture of crystalline titanium disulfide (TiS₂) and sulfur. A high-resolution transmission electron microscope image revealed no periodic lattice fringes on the amorphous TiS₃. The all-solid-state lithium secondary batteries using a sulfide solid electrolyte and the amorphous TiS₃ electrode showed high capacity of greater than 300 mAh g^?1 for 10 cycles. The amorphous TiS₃ had a higher capacity than the mixture of crystalline TiS₂ and S, which was used as the starting material of amorphous TiS₃. The X-ray diffraction patterns and the Raman spectra of the amorphous TiS₃ electrode after the first and tenth charge–discharge measurements were similar to those before the measurement. The amorphous structure of TiS₃ did not change greatly during the first few cycles. The all-solid-state cells with the amorphous TiS₃ electrode showed higher initial coulombic efficiency because the amorphous TiS₃ active material retained its structure during the initial electrochemical test.     

Zintl Clusters as Wet‐Chemical Precursors for Germanium Nanomorphologies with Tunable Composition

[Ge₉]^4? Zintl clusters are used as soluble germanium source for a bottom–up fabrication of Ge nanomorphologies such as inverse opal structures with tunable composition. The method is based on the assembly and oxidation of [Ge₉]^4? clusters in a template mold using SiCl₄, GeCl₄, and PCl₃ leading to Si and P‐containing Ge phases as shown by X‐ray diffraction, Raman spectroscopy, and energy‐dispersive X‐ray analysis. [Ge₉]^4? clusters are retained using ethylenediamine (en) as a transfer medium to a mold after removal of the solvent if water is thoroughly excluded, but are oxidized to amorphous Ge in presence of water traces. ¹H NMR spectroscopy reveals the oxidative deprotonation of en by [Ge₉]^4?. Subsequent annealing leads to crystalline Ge. As an example for wet‐chemical synthesis of complex Ge nanomorphologies, we describe the fabrication of undoped and P‐doped inverse opal‐structured Ge films with a rather low oxygen contents. The morphology of the films with regular volume porosity is characterized by SEM, TEM, and grazing incidence small‐angle X‐ray scattering.     

Tuning Phonon Energies in Lanthanide-doped Potassium Lead Halide Nanocrystals for Enhanced Nonlinearity and Upconversion

Optical applications of lanthanide-doped nanoparticles require materials with low phonon energies to minimize nonradiative relaxation and promote nonlinear processes like upconversion. Heavy halide hosts offer low phonon energies but are challenging to synthesize as nanocrystals. Here, we demonstrate the size-controlled synthesis of low-phonon-energy KPb₂X₅ (X=Cl, Br) nanoparticles and the ability to tune nanocrystal phonon energies as low as 128 cm⁻¹. KPb₂Cl₅ nanoparticles are moisture resistant and can be efficiently doped with lighter lanthanides. The low phonon energies of KPb₂X₅ nanoparticles promote upconversion luminescence from higher lanthanide excited states and enable highly nonlinear, avalanche-like emission from KPb₂Cl₅ : Nd³⁺ nanoparticles. The realization of nanoparticles with tunable, ultra-low phonon energies facilitates the discovery of nanomaterials with phonon-dependent properties, precisely engineered for applications in nanoscale imaging, sensing, luminescence thermometry and energy conversion.     

Determination of crystallinity of swollen poly(vinyl alcohol) by laser Raman spectroscopy

Laser Raman spectra of atactic poly(vinyl alcohol) (PVA) after heat treatment and/or swelling in water have been obtained. An amorphous Raman band is observed at 1124 cm^?1, while a crystalline Raman band is found at 1147 cm^?1. A new method for crystallinity determination is proposed, in which the amorphous band is used instead of the crystalline band. The method is superior to others for water-swollen PVA samples. Laser Raman spectra of swollen PVA revealed that swelling causes destruction of a major fraction of the crystalline regions and the remaining intact crystalline part increases with increasing temperature of heat treatment.     

Size dependent electron-phonon coupling in Li0.5Co0.1Fe2.4O4 nanoparticles investigated by Raman spectroscopy

The Raman spectra of Li_0.5Co_0.1Fe_2.4O₄ nanoparticles have been recorded in the spectral range, 400-800 cm⁻¹ at four different particle sizes. X-ray and TEM measurements were done to determine crystal structure and size of the nanoparticles. X-ray diffraction (XRD) shows that the Li_0.5Co_0.1Fe_2.4O₄ nanoparticles have an order phase spinel structure without any impurity. The size of the nanocrystal was calculated through XRD patterns and TEM micrographs and it turns out to be 34-42 nm. The Raman spectra of each size nanoparticles show five Raman bands. The most intense Raman band shows a noticeable asymmetrical feature towards lower wavenumber side. A line shape analysis was performed to get the exact spectral parameters of the Raman bands. The intensity of asymmetrical feature keeps on increasing with decreasing the particle size from 42 nm to 34 nm and finally evolved as a new Raman band. The appearance of new band and its intensity response relative to the intensity of the main Raman band as a function of particle size has been explained in terms of electron-phonon coupling. It was observed that the strength of electron-phonon coupling goes on increasing with reducing the particle size. The red shifting of the Raman bands upon reducing the crystalline size is explained in terms of the lattice expansion, which is well supported by the XRD data.     

The conformation and vibrational spectra of trans-1,4-dihalocyclohexanes: Part II. trans-1,4-Chlorobromocyclohexane and trans-1,4-chloroiodocyclohexane

The IR spectra of trans-1,4-chlorobromo- and trans-1,4-chloroiodocyclohexane were recorded in the region 4000–30 cm^?1 as solutes in various solvents, as KI and polyethylene pellets and as solids under high pressure (1–50 kbar at ambient temperature). Additional spectra of the melts, amorphous and annealed crystalline solids at 90 K and dichroism of oriented polycrystalline films were obtained above 200 cm^?1. Raman spectra of the compounds were recorded in the amorphous and crystalline states at 90 K, and polarization measurements were made in CCl₄ CS₂ and C₆H₆ solution.The title compounds existed as an equilibrium mixture of ee and aa conformers in solution, in the melts and in the amorphous solids at 90 K. When heated to temperatures in the region 165–195 K the amorphous solids apparently crystallized into a metastable form containing the aa conformer, while above 200 K the solids were converted to a stable crystal containing the ee conformer. Under high pressure the concentration of the aa conformer increased and this form was almost exclusively present at ca. 50 kbar nominal pressure.The fundamental frequencies for both conformers were assigned in terms of C_smolecular symmetry. An extensive normal coordinate analysis on six trans-1,4-dihalocyclohexanes was carried out using the overlay technique.     

Polarized Raman studies of crystalline and amorphous orientation in polyethylene

Polarized Raman intensities have been obtained from thin films of oriented low-density polyethylene (PE) immersed in silicone oil to minimize surface scattering. Studies were made using the 1170 cm^?1 crystalline band and the 1081 cm^?1 amorphous band, and from these the orientation averages 〈cos² θ〉 and 〈cos⁴ θ〉 were calculated. These were found to compare favorably with the values of 〈cos² θ〉 for the polymer chain in the crystalline and amorphous phases obtained from measurements of infrared dichroism. Both orientation averages could be theoretically fitted by using reasonable parameters.     

Raman spectroscopic study on boron-doped silicon nanoparticles

Raman analyses were performed on thin films prepared from B-doped Si nanoparticles with an average diameter of 15 nm using the spin-coating method. The resulting spectrum exhibited a broad band with a peak near 520 cm⁻¹. The band was decomposed into three bands corresponding to the crystalline, grain boundary (GB), and amorphous regions by the least-squares band-fitting method based on the three Voigt bands. The fractions of the crystalline, GB, and amorphous regions were 37%, 35%, and 28%, respectively. A spherical particle exhibited an ordered crystalline core surrounded by a disordered shell in a transmission electron microscope (TEM) image. The crystalline fraction of the 15-nm B-doped Si nanoparticle film was much lower than that of the 19-nm P-doped Si nanoparticle film. This result suggested that the B-doping mechanism was different from that of P-doping. The temperature of the sample was estimated from the ratio of the peak intensities of anti-Stokes to Stokes Raman bands (I^AS/I^S) observed near 520 cm⁻¹. The temperature of the B-doped Si nanoparticle film upon irradiation at a power density of 4.6 kW/cm² was 298 °C, whereas the temperature of the P-doped Si nanoparticle film was 92 °C. The B-doped Si nanoparticle films were capable of producing light-induced heat.     

Characterization of crystalline and amorphous content in pharmaceutical solids by dielectric thermal analysis

Morphological and thermodynamic transitions in drugs as well as their amorphous and crystalline content in the solid state have been distinguished by thermal analytical techniques, which include dielectric analysis (DEA), differential scanning calorimetry (DSC), and macro-photomicrography. These techniques were used successfully to establish a structure versus property relationship with the United States Pharmacopeia standard set of active pharmaceutical ingredient (API) drugs. A distinguishing method is the DSC determination of the amorphous and crystalline content which is based on the fusion properties of the specific drug and its recrystallization. The DSC technique to determine the crystalline and amorphous content is based on a series of heat and cool cycles to evaluate the drugs ability to recrystallize. To enhance the amorphous portion, the API is heated above its melting temperature and cooled with liquid nitrogen to ?120 °C (153 K). Alternatively a sample is program heated and cooled by DSC at a rate of 10 °C min^?1. DEA measures the crystalline solid and amorphous liquid API electrical ionic conductivity. The DEA ionic conductivity is repeatable and differentiates the solid crystalline drug with a low conductivity level (10^?2 pS cm^?1) and a high conductivity level associated with the amorphous liquid (10⁶ pS cm^?1). The DSC sets the analytical transition temperature range from melting to recrystallization. However, analysis of the DEA ionic conductivity cycle establishes the quantitative amorphous and crystalline content in the solid state at frequencies of 0.10–1.00 Hz and to greater than 30 °C below the melting transition as the peak melting temperature. This describes the “activation energy method.” An Arrhenius plot, log ionic conductivity versus reciprocal temperature (K^?1), of the pre-melt DEA transition yields frequency dependent activation energy (E _a, J mol^?1) for the complex charging in the solid state. The amorphous content is inversely proportional to the E _a where the E _a for the crystalline form is higher and lower for the amorphous form with a standard deviation of ±2%. There was a good agreement between the DSC crystalline melting, recrystallization, and the solid state DEA conductivity method with relevant microscopic evaluation. An alternate technique to determine amorphous and crystalline content has been established for the drugs of interest based on an obvious amorphous and crystalline state identified by macro-photomicrography and compared to the conductivity variations. This second “empirical method” correlates well with the “activation energy” method.     

Vibrational and conformational analysis of chloromethylacetate and some deuterated derivatives

The i.r. spectra of gaseous, amorphous and crystalline solid and the Raman spectra of liquid and amorphous solid chloromethylacetate, CH₃COOCH₂Cl, and three deuterated derivatives, CH₃COOCD₂Cl, CD₃COOCH₂Cl and CD₃COOCD₂Cl, were obtained and an assignment proposed. Only one conformer of CMA was found to be present in all phases. Band contour simulation of the i.r. vapour phase bands showed this to be the s-cis gauche conformer. This was confirmed by a study of the partially deuterated compound CD₃COOCDHCl, of which the separate transitions originating from the antiperiplanar and synclinal isolated CH stretches were observed in the i.r. spectra of the vapour and crystalline solid and in the Raman spectrum of the vapour.     

Plasmonic rhenium trioxide self-assembled microtubes for highly sensitive,stable and reproducible surface-enhanced raman spectroscopy detection

Compared with noble metals, improving the sensitivity of semiconducting surface-enhanced Raman scattering (SERS) substrates is of great significance to their fundamental research and practical application of Raman spectroscopy. Herein, a simple chemical method is developed to synthesize a rhenium trioxide (ReO₃) microtubes assembled with highly crystalline nanoparticles. The ReO₃ microtubes show a strong and well-defined surface plasmon resonance (SPR) behavior in visible region, which is rare for non-noble metals. As a low-cost SERS substrate, the plasmonic ReO₃ microtubes exhibit a Raman enhancement factor of 8.9 × 10⁵ and a lowest detection limit of 1.0 × 10^?9 mol/L for phenolic pollutants. Moreover, these ReO₃ microtubule SERS substrates show excellent chemical stability and can resist the corrosion of strong acids and bases.     

In situ Raman spectroscopy reveals the structure evolution and lattice oxygen reaction pathway induced by the crystalline–amorphous heterojunction for water oxidation

One of the most successful approaches for balancing the high stability and activity of water oxidation in alkaline solutions is to use amorphous and crystalline heterostructures. However, due to the lack of direct evidence at the molecular level, the nano/micro processes of amorphous and crystalline heterostructure electrocatalysts, including self-reconstruction and reaction pathways, remain unknown. Herein, the Leidenfrost effect assisted electrospray approach combined with phase separation was used for the first time to create amorphous NiO_x/crystalline α-Fe₂O₃ (a-NiO_x/α-Fe₂O₃) nanowire arrays. The results of in situ Raman spectroscopy demonstrate that with the increase of the potential at the a-NiO_x/α-Fe₂O₃ interface, a significant accumulation of OH can be observed. Combining with XAS spectra and DFT calculations, we believe that more OH adsorption on the Ni centers can facilitate Ni²⁺ deprotonation to achieve the high-valence oxidation of Ni⁴⁺ according to HSAB theory (Fe³⁺ serves as a strong Lewis acid). This result promotes the electrocatalysts to follow the lattice oxygen activation mechanism. This work, for the first time, offers direct spectroscopic evidence for deepening the fundamental understanding of the Lewis acid effect of Fe³⁺, and reveals the synergistic effect on water oxidation via the unique amorphous and crystalline heterostructures.

The amorphous NiO_x/crystalline α-Fe₂O₃ heterojunctions were constructed and exhibited outstanding OER activities. Through the collaboration of multiple characterization techniques, the Lewis acid effect of Fe³⁺ was revealed at molecular level.