Long-range Crystalline Structure Research Articles

Γ-Graphyne: A Promising Electron Acceptor for Organic Photovoltaics

The most significant discovery of recent years is graphene, which consists of a single layer of sp2-hybrid carbon atoms arranged in a two-dimensional (2D) honeycomb lattice nanostructure.Graphynes – a two-dimensional materials similar to graphene, but composed of sp-hybridized carbons periodically integrated into a sp2-hybridized carbon network. Structure of graphynes were first theoretically proposed in 1987 by Baughman et al.[1] More than 20 years later, in 2010, Li et al. developed the first successful methodology for creating γ-graphdiyne films [2]. Despite the significant attention from the scientific community, only recently Hu et al. reported the synthesis of γ -graphyne with unified long-range crystalline structure [3].We demonstrate that γ -graphyne is an efficient electron acceptor due to its low LUMO and its ability to delocalize an excess charge. Moreover, in contrast to other 2D sheets like graphene its electronic properties are not sensitive to vacancy defects. Investigation of photoinduced electron transfer processes in complexes of γ -graphyne with typical electron-accepting and electron-donating partners shows that the lowest excited states with donors are charge separated states formed by the electron transfer from partner to γ -graphyne. This electron transfer is thermodynamically favorable and occurs on nano-to-picosecond time scale. In contrast, electron transfer from γ -graphyne to strong electron acceptors such as fullerenes or arylenediimides is unlikely [4].

Fabrication and Characterization of p-Sb2O3:CuO/n-Si Solar Cell Via Thermal Evaporation Technique

Antimonous oxide (Sb2O3) has intriguing physical and chemical features that make it useful in various device applications, including solar cells. Pure and CuO-doped Sb2O3 nanofilms were prepared on glass and silicon substrates etched by laser using a thermal evaporation process in a vacuum, with doping ratios (0.02 wt.%, 0.04 wt.% and 0.06 wt.%) of CuO with a thickness of about 40 nm. The deposited nanofilms have no distinguishing peaks in X-ray diffraction analysis. Broadening of X-ray peaks shows the absence of long-range symmetry (either translational, rotational or conformational); as a consequence, the nanocrystalline structure is disorganized (disordered solids are nonamorphous materials that have lost their long-range crystalline structure). Scanning electron microscopy analysis of the surface morphology of the formed nanofilms showed that the particles were all about the same size and spread out uniformly. Atomic force microscopy scanning images showed the nanofilms’ homogeneous surface morphology with granular shape. The optical properties showed a minor increase in absorbance spectra with increasing CuO doping. Contrarily, the optical energy gap ([Formula: see text]) was decreased by quantum confinement from 3.51 eV to 3.31 eV. As can be seen from the [Formula: see text]–[Formula: see text] characteristics, the solar cell’s conversion efficiency increases to 7.62% at [Formula: see text] mW/cm2 with a filling factor (FF) of 0.198, an open-circuit voltage of 12 V, and a short-circuit current of 3.2 mA.

Inhibitory effect of chitosan coating on oil absorption in French fries based on starch structure and morphology stability

The effect of chitosan (CS) coating on oil absorption, water migration, starch structure and morphology in French fries was evaluated. The penetrated surface oil, structure oil, total oil content, and a* of coated fries decreased, while the water content, L*, b*, and hardness significantly (P < 0.05) increased compared to uncoated samples. 1 % CS-coated fries had the lowest oil content, which decreased by 43.0 % compared to uncoated samples. CS-coated fries had higher free water, and lower T2 relaxation time, immobile and binding water than the control. CS coating reduced the pores on the fries' surface and the interaction between oil and the component of fries, which was observed by confocal laser scanning microscopy and scanning electron microscopy (SEM). As for starch morphology, the pores and cracks of starch granules in the coated samples reduced. As for the starch structure, the relative crystallinity, R1047/1022 respectively increased by 47.2 % and 2.35 times, and ΔH of CS-coated fries increased from 0 to 2.09 J/g, indicating that the long-range crystalline structure, short-range ordered structure, and hydrogen bonds between the double helices in starch increased. Therefore, CS coating reduced oil penetration into fries by reducing water migration and increasing starch ordered structure and morphological integrity.

Effect of oil modification on the multiscale structure and gelatinization properties of crosslinked starch and their relationship with the texture and microstructure of surimi/starch composite gels

This work investigated the multiscale structure and gelatinization properties of different oil-modified crosslinked starches and their relationship with the texture and microstructure of surimi/starch composite gels. The results showed clusters were formed by the agglomeration of starch, with oil on the surface of granules. Oil modification did not damage the long-range crystalline structure but impaired the short-range ordered structure. A high oil modification degree was shown to weaken starch structure, in contrast to an adverse effect for a high crosslinking level. Furthermore, compared with crosslinked starches, Oil-CTS had lower pasting temperature and gelatinization enthalpy, a higher viscosity, and better gel-reinforcing effect. Correlation analysis revealed the texture of surimi/starch composite gels was negatively correlated with the helical structure and pasting temperature of starch, and positively correlated with final and setback viscosity of starch and the swollen size of starch granules in surimi gel.

Ultrasmall Blueshift of Near-Infrared Fluorescence in Phase-Stable Cs2SnI6 Thin Films

Cubic ${\mathrm{Cs}}_{2}{\mathrm{Sn}\mathrm{I}}_{6}$ perovskite is considered to be an ideal lead-free and air-stable alternative to traditional $A\mathrm{Pb}{X}_{3}$ [A = $\mathrm{Cs}$, $\mathrm{K}$, ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}$, $\mathrm{CH}({\mathrm{NH}}_{2}{)}_{2}$] perovskites for optoelectronic applications, such as solar cells and photodetectors. Herein, both experiments and theoretical calculations are carried out to study the lattice dynamics and temperature dependences of band gaps. Using Raman spectroscopy, we show that the obtained ${\mathrm{Cs}}_{2}{\mathrm{Sn}\mathrm{I}}_{6}$ film maintains a long-range crystalline structure of the cubic phase within 77--300 K, which is further confirmed via lattice dynamics calculations based on density functional theory (DFT). An ultrasmall net blueshift of 0.035 eV deduced from its temperature-dependent photoluminescence (PL) spectrum is observed as the temperature increases from 103 to 300 K, making it an ideal material for optoelectronic devices. Notably, this blueshift of the ${\mathrm{Cs}}_{2}{\mathrm{Sn}\mathrm{I}}_{6}$ film is significantly smaller than that of the DFT-calculated band-gap shift (\ensuremath{\sim}0.085 eV) based on thermal expansion theory. This deviation is attributed to the strong phonon-electron (ph-e) interaction inherently occurring in ${\mathrm{Cs}}_{2}{\mathrm{Sn}\mathrm{I}}_{6}$ material, which counterbalances the thermal expansion effects. We further evaluate the magnitude of the ph-e interaction by fitting the full width at half maximum (FWHM) of the PL spectrum. The fitted Huang-Rhys factor (S) of 4.9 is consistent with reduced electronic dimensionality and increased vibrational degree of freedom, indicating stronger ph-e coupling strength in the ${\mathrm{Cs}}_{2}{\mathrm{Sn}\mathrm{I}}_{6}$ film compared with regular ${A\mathrm{Pb}X}_{3}$-type perovskites (S 3.3). Adopting both thermal expansion and ph-e coupling effects, the ultrasmall band-gap shift is theoretically calculated and is in good agreement with the experimental blueshift of the band gap. In summary, our work illustrates the solid structural stability of ${\mathrm{Cs}}_{2}{\mathrm{Sn}\mathrm{I}}_{6}$ in both lattice and electronic structures, paving the way for the next generation of optoelectronic devices.

Effect of pullulan on oil absorption and structural organization of native maize starch during frying

The oil-absorption behavior of native maize starch (NMS) during frying was investigated in the presence or absence of pullulan (PUL) using a LF-NMR method. The morphology, long-range order, short-range order, and thermal properties of fried NMS-PUL mixtures were further evaluated using SEM, XRD, ATR-FTIR, and DSC, respectively. Pullulan addition significantly reduced the oil content of the fried starch samples: 0.395, 0.310, 0.274, and 0.257 g/g in NMS with addition of 0, 1, 3, and 5% PUL, respectively (p < 0.05). SEM analysis showed that the intact granular morphology of the starch granules was preserved upon addition of pullulan. The XRD, FTIR, and DSC results showed that pullulan protected both the short-range double helices and long-range crystalline structure of the granules during frying. As a result, fried NMS-PUL mixtures were denser than fried NMS, thus inhibiting oil absorption during frying. These results may have important implications for creating healthier reduced-fat fried food products.

Starch nanoparticles resulting from combination of dry heating under mildly acidic conditions and homogenization

To modify starch granular structure, normal maize starch was subjected to dry heating with various amounts of 1.0M HCl (1.2, 1.4 or 1.6mL) and different treatment times (2, 4 or 8h). For all reaction conditions, at least 80% of the starch substance was recovered, and amylose and amylopectin B1 chains were preferentially cleaved. As acidic condition and/or treatment time increased, the treated granules were readily fragmented by homogenization. The treatment appeared to alter short-range crystalline structure (FT-IR), but long-range crystalline structure (XRD) remained intact. Homogenization for 60min fragmented the treated starch granules (subjected to reaction condition of 1.4mL/4h, 1.6mL/2h, and 1.6mL/4h) into nanoparticles consisting of individual platelet-like and spherical particles with diameters less than 100nm. However, the fragmentation caused obvious damage in the long-range crystalline structure of starch nanoparticles, while the short-range chain associations remained relatively intact.

Production of starch nanoparticles using normal maize starch via heat-moisture treatment under mildly acidic conditions and homogenization

Normal maize starch was subjected to heat-moisture treatment (HMT) under mildly acidic conditions (0.000, 0.050, or 0.075M H2SO4) for various treatment times (3, 5, or 8h) followed by homogenization up to 60min to prepare nanoparticles. The combination of HMT (0.075M, for 8h) and homogenization (60min) produced nanoparticles with diameters of less than 50nm at a yield higher than 80%. X-ray diffractometry and size-exclusion chromatography revealed that HMT under mildly acidic conditions selectively hydrolyzed the starch chains (especially amylose and/or long chains of amylopectin) in the amorphous region of the granules without significant damage to the crystalline structure, however, modification of the molecular structure in the amorphous region increased fragility of the granules during homogenization. Homogenization for 60min caused obvious damage in the long-range crystalline structure of the HMT starch (0.15N, for 8h), while the short-range chain associations (FT-IR) remained intact.

One-phase crystal disorder in pharmaceutical solids and its implication for solid-state stability

Solid-state disorders of active pharmaceutical ingredients have been characterized by means of X-ray diffraction techniques and solid-state nuclear magnetic resonance spectroscopy. The results determined that the pleuromutilin-derivative, I, displays a unique continuous conformational disorder while retaining its long-range crystalline structure. The propionic acid (PA) version of this compound displayed partial crystalline order and site disorder of PA, depending on the quantity of PA incorporated in the structure. Thus, I is a unique example of one-phase crystalline–amorphous model. Physical and chemical stability data was acquired on these disordered systems and discussed in relation with the characterized disorder present in the crystal systems. Analysis of the results showed that in contrast to phase-separated amorphous, restrained disorders do not influence the stability.

Characterization of nitride coatings by XPS

Nitride coatings have been used in numerous applications to increase the hardness and improve the wear and corrosion resistance of structural materials, as well as in various high-tech areas, where their functional rather than mechanical properties are of prime importance. Performance of these coatings is equally dependent on their chemical composition and long-range crystalline structure, as well as on the nature and amount of impurities and intergranular interactions. Significant improvement in the mechanical properties has recently been achieved with multi-component superlattice and nanocomposite nitride coatings. In the case of such multi-component systems, not only is close control of the elemental composition (stoichiometry) necessary to optimize the properties of the coatings, but the influence of chemical bond formation between the components is also of prime importance. Special care needs to be taken when non-equilibrium preparation conditions, activation of CVD and PVD by plasmas or energetic particle beams are applied, occasionally leading to unpredicted deviations, both in composition and structure. As is highlighted in this paper, nitride coatings or nitrided surfaces can be analyzed in detail by X-ray photoelectron spectroscopy (XPS) due to its excellent element selectivity, quantitative character and high surface sensitivity. More importantly, XPS reflects the atomic scale chemical interactions, i.e. the bonds between neighboring atoms, and thus it also provides reliable structural characteristics for amorphous or nano-crystalline coatings of complex composition, for which application of diffraction techniques is not straightforward. A number of examples of the application of XPS are given for various types of nitride coatings, including interstitial compounds, such as TiN, CrN x , etc., as well as compounds with predominantly covalent bonding, such as AlN, GaN, Si 3N 4 and CN x . Special emphasis is placed on ion beam-induced compositional and structural changes and to the formation of ‘superstoichiometric’ TiN 1+ x , ZrN 1+ x compounds.

A Synthesis, MAS NMR, Synchrotron X-ray Powder Diffraction, and Computational Study of Zeolite SSZ-23

The zeolite SSZ-23 (STT) is the first zeolite found to contain channels bounded by seven and nine tetrahedral atom windows. A survey of the synthetic conditions needed to prepare SSZ-23 has been carried out, and the resulting materials characterized by synchrotron X-ray powder diffraction and magic-angle spinning NMR spectroscopy to obtain details of the long-range crystalline structure and short-range connectivity defects. The lattice energy minimized structure is in excellent agreement with the experimental results, and a comparison with other zeolites that have been simulated in this way is made.