Si Angle Research Articles

Phase-contrast visualization of human tissues using superimposed wavefront imaging of diffraction-enhanced x-rays.

Phase-contrast computed tomography (CT) using high-brilliance, synchrotron-generated x-rays enable three-dimensional (3D) visualization of microanatomical structures within biological specimens, offering exceptionally high-contrast images of soft tissues. Traditional methods for phase-contrast CT; however, necessitate a gap between the subject and the x-ray camera, compromising spatial resolution due to penumbral blurring. Our newly developed technique, Superimposed Wavefront Imaging of Diffraction-enhanced x-rays (SWIDeX), leverages a Laue-case Si angle analyzer affixed to a scintillator to convert x-rays to visible light, capturing second-order differential phase contrast images and effectively eliminating the distance to the x-ray camera. This innovation achieves superior spatial resolution over conventional methods. In this paper, the imaging principle and CT reconstruction algorithm based on SWIDeX are presented in detail and compared with conventional analyzer-based imaging (ABI). It also shows the physical setup of SWIDeX that provides the resolution preserving second-order differential images for reconstruction. We compare the spatial resolution and the sensitivity of SWIDeX to conventional ABI. To demonstrate high-spatial resolution achievable by SWIDeX, the internal structures of four human tissues-ductal carcinoma in situ, normal stomach, normal pancreas, and intraductal papillary mucinous neoplasm of the pancreas-were visualized using an imaging system configured at the Photon Factory's BL14B beamline under the High Energy Accelerator Research Organization (KEK). Each tissue was thinly sliced after imaging, stained with hematoxylin and eosin (H&E) for conventional microscope-based pathology. A comparison of SWIDeX-CT and pathological images visually demonstrates the effectiveness of SWIDeX-CT for biological tissue imaging. SWIDeX could generate clearer 3D images than existing analyzer-based phase-contrast methods and accurately delineate tissue structures, as validated against histopathological images. SWIDeX can visualize important 3D structures in biological soft tissue with high spatial resolution and can be an important tool for providing information between the disparate scales of clinical and pathological imaging.

Discrete trapping levels of localized states in amorphous silicon nitride

The spectrum of localized hole states (traps) in amorphous silicon nitride, a-Si3N4, is experimentally studied using the method of thermally stimulated depolarization. The experiment is compared with theoretical calculations using three models of the energy spectrum of traps: discrete spectrum (monoenergetic trap), continuous spectrum, and Gaussian trap distribution. The experiment is quantitatively described by a model of a discrete spectrum of traps with an energy of 1.15 eV and a width of no more than 0.01 eV. In the case of a continuous and Gaussian spectrum of traps, the contribution to depolarization is made by the deepest traps. The blurring of the trap energy level in a-Si3N4 due to the absence of long-range order (fluctuations in the Si–N bond length and fluctuations in the N–Si–N and Si–N–Si angles) does not exceed 0.01 eV.

Wide spectral range guided-mode resonant grating designed for the wet etching process

We present wideband guided-mode resonant (GMR) gratings made of Si on a SiO2 substrate. Based on the base angle of the grating as the crystal orientation angle (54.74°) of Si, the design process of reflectors suitable for TM-polarized waves is demonstrated in the near-infrared (NIR) and mid-infrared (MIR) wavelengths. Benefiting from the mutual attraction and interaction of the two GMR modes, the bandwidth of reflectivity above 99% for the reflector under the NIR and MIR bands reaches 297 nm (from 1416 nm to 1713 nm) and 657 nm (from 3154 nm to 3811 nm), respectively. In addition, the effects of the incident light source state and the structural parameters on the performance of the reflector are analyzed in detail. The results show that the reflector will maintain good tolerance and stability during fabrication and use. This work will be compatible with the wet etching process in the microelectromechanical system, and the results can be extended to the design of broadband GMR reflectors in other wavelength bands.

The Me(almIM)<sub>2</sub> structural ZIFs: Synthesis, characterization and application

The Me(almIM)2 structural ZIFs are formed from the metal ions Me2+ and the linker 4-methyl-5-imidazolecarboxaldehyde (HalmIM), with the Me–almIM–Me bond angle similar to the Si–O–Si angle in zeolites (145o). Depending on the type of bond formed, Me(almIM)2 material has RHO or SOD structure with good thermal and chemical stability. With pore diameter of about 3.0-3.7 Å connected to large cavities with sizes from 9.1-17.9 Å and a structural frameworks containing two groups –CH3 and –CHO with hydrophilic properties, when the –CHO groups is modified by amine groups through imine condensation reaction, we can create hydrophobic materials for diverse applications in adsorption, separation, sensing, biomedical and catalysis. This review report collects results from more than 100 research papers related to Me(almIM)2 from 2010 to present and provides some recommendations on their synthesis, characterization and application in the future.

First-principles study on the specific heat jump in the glass transition of silica glass and the Prigogine-Defay ratio

The most important characteristic of glass transition is a jump in the specific heat . Despite its significance, no standard theory exists to describe it. In this study, first-principles molecular-dynamics simulations are used to describe the glass transition of silica glass. The novel view that state variables are extended to include the equilibrium positions of atoms is fully used in analyzing the simulation results. Decomposing the internal energy into three components (structural, phonon, and thermal expansion energies) reveals that the jump of silica glass is entirely determined by the component of structural energy. The reason for the small is its high glass-transition temperature, which makes the fluctuation in the structural energy insensitive to the temperature change. This significantly affects how the Prigogine-Defay ratio Π is interpreted, which was previously unknown. The ratio Π represents the ratio of the total energy change to the contribution of thermal expansion energy at the glass transition. The general property, Π> 1, of glasses indicates that glass transitions occur mainly via the change in the structural energy. Silica glass is an extreme case in that the transition occurs entirely through the change in internal structure, such as the distribution of the bending angle of Si–O–Si bonds.

Robert C. West (1928–2022): A Giant in Organosilicon Chemistry, Cosmopolitan, Mountain Climber and Pilot

Robert C. West (1928–2022): A Giant in Organosilicon Chemistry, Cosmopolitan, Mountain Climber and Pilot

The flexibility of the T–X–T hinges between the coordination tetrahedra in various zeolitic frameworks: an empirical structural study

In recent years, a large number of precisely determined crystal structure determinations of zeolites, that is compounds based on open frameworks of coordination tetrahedra, has accumulated. This gives us the opportunity to evaluate them in terms of the flexibility of their bond angles T–X–T which serve as hinges between the coordination tetrahedra in zeolites containing various SiO4, AlO4, PO4 and similarly sized ions. Out of about 7,000 known crystal structure descriptions of zeolites we have selected 1187 which are based on single crystal diffraction studies and have estimated standard deviations of their T–O bond length of 0.01 Å or less. The mean Si–O–Si angle in zeolitic frameworks with T-sites fully occupied by one type of T atoms is 152.9° and these angles range from 127.0° to 180°, the mean for Al–O–Si is 141.9°, ranging from 124.8° to 179.3°. Straight angles Si–O–Si do occur in some zeolites.

Low-temperature phase transition and magnetic properties of K3YbSi2O7

The new ambient-temperature hexagonal (space group P63 /mmc) polymorph of tripotassium ytterbium(III) disilicate (β-K3YbSi2O7) has been synthesized by the high-temperature flux method and subsequently structurally characterized. In the course of the temperature-dependent single-crystal diffraction experiments, a phase transformation of β-K3YbSi2O7 to a novel low-temperature orthorhombic phase (β′-K3YbSi2O7, space group Cmcm) has been observed at about 210 K. β-K3YbSi2O7 is isostructural with K3ErSi2O7, whereas β′-K3YbSi2O7 adopts a new type of structure. Both compounds can be built up from a regular alternation of layers of two types, which are parallel to the (001) plane. In the octahedral layer, YbO6 octahedra are isolated and linked by K1O6+3 polyhedra. The second, slightly thicker sorosilicate layer is formed by a combination of Si2O7 dimers and K2O6+3 polyhedra. The boundary between the layers is a pseudo-kagome oxide sheet based on 3.6.3.6 meshes. The phase transition is due to a tilt of the two SiO4 tetrahedra forming a single dimer which induces a decrease of the Si—O—Si angle between bridging Si—O bonds from 180° (dictated by symmetry in space group P63/mmc) to ≃164°. Magnetic characterization indicates that K3YbSi2O7 remains paramagnetic down to 2 K, showing no apparent influence of the phase transformation on its magnetic properties. Analysis of the magnetization data revealed the positions of the three lowest crystal field levels of the Yb3+ cations, as well as the corresponding projections of their angular momentum on the direction of the magnetic field.

Laser-induced structural modification in calcium aluminosilicate glasses using molecular dynamic simulations

Glass structures of multicomponent oxide systems (CaO–Al2O3–SiO2) are studied using a simulated pulsed laser with molecular dynamics. The short- and intermediate-range order structures revealed a direct correlation between the transformation of Al(IV) to Al(V), regions of increased density following laser processing, inherent reduction in the average T–O–T (T = Al, Si) angle, and associated elongation of the T–O bonding distance. Variable laser pulse energies were simulated across calcium aluminosilicate glasses with high silica content (50–80%) to identify densification trends attributed to composition and laser energy. High-intensity pulsed laser effects on fictive temperature and shockwave promotion are discussed in detail for their role in glass densification. Laser-induced structural changes are found to be highly dependent on pulse energy and glass chemistry.

Molecular Dynamics Simulations of the Interface between Porous and Fused Silica

Molecular dynamics simulations are performed to gain insights into the structural and vibrational properties of interface between porous and fused silica. The Si–O bonds formed in the interface exhibit the same lengths as the bulk material, whereas the coordination defects in the interface are at an intermediate level as compared with the dense and porous structures. Clustered bonds are identified from the interface, which are associated with the reorganization of the silica surface. The bond angle distributions show that the O–Si–O bond angles keep the average value of 109°, whereas the Si–O–Si angles of the interface present in a similar manner to those in porous silica. Despite the slight structural differences, similarities in the vibrations are observed, which could further demonstrate the stability of porous silica films coated on the fused silica.

Atomic Structure and Morphology of Fumed Silica

The comparative analysis of atomic structure and morphology of fumed silica nanoparticles prepared under different synthesis conditions are studied using TEM, FTIR, quantum chemistry, and low-temperature nitrogen adsorption methods. It was determined that the structure of amorphous silica nanoparticles is formed by branched chain-like clusters of the length of 0.6-2.4 nm that correspond to proto-particles or nuclei of nanoparticles. A linear part of the smallest clusters is consisted of two tetrahedra SiO4 with common oxygen atom and oppositely directed vertices. The inter-tetrahedral average angle of Si ‒ O ‒ Si bonds is about 180˚. It is shown that textural porosity of fumed silica powder depends on the initial degree of aggregation of nanoparticles. The average mesopores (1 nm < R < 25 nm) volume is in the rage of 0.26-0.60 cm3∙g-1 for materials pretreated at different temperatures. It is found out that the mean mesopores radius decreases from 34 nm to 10 nm with decreasing average size of silica nanoparticles. The micropores (R < 1 nm) contribution to the total pore volumes is small for all materials (0.003-0.029 cm3∙g-1).

Spherically bent mica analyzers as universal dispersing elements for X‐ray spectroscopy

Spherically‐bent crystal analyzers (SBCAs) see considerable use in very high‐resolution hard X‐ray wavelength dispersive X‐ray fluorescence spectroscopy, often called X‐ray emission spectroscopy (XES). While Si and Ge are the most frequently used diffractive components of SBCAs, we consider here the somewhat classical choice of muscovite mica as the dispersing element. We find that the various harmonics of a highest‐quality mica‐based SBCA show ~5–~40% of the integral reflectivity per unit solid angle of a typical Si or Ge SBCA in the hard X‐ray range, and that the mica SBCA have comparable energy resolution to the traditional SBCAs. Interestingly, the choice of mica comes with a practical benefit: the primary (0,0,2) reflection has sufficiently strong harmonics that are fairly tightly spaced in energy so that they span the complete energy range from ~4 to ~11 keV when used at convenient Bragg angles in a Rowland circle spectrometer. Hence, a single mica SBCA can be used for every K‐shell emission line of three dimensional transition metals and every L‐shell emission line of the lanthanide elements simply by selecting the correct mica (0,0,2) harmonic with a final energy‐dispersive solid state detector. The loss in efficiency is counteracted by an operational efficiency, i.e., the “universal” application of a single analyzer over a very large range of elements. This performance suggests future application of mica SBCAs in both laboratory‐based XES and synchrotron‐based photon‐in, photon‐out spectroscopies in the hard X‐ray range.

Modulation of spin-charge conversion in silicon

Silicon (Si) is an important material for the application of spintronics because its spin lifetime is relatively long compared to those of metals, and it is the well-studied semiconductor in term of its electronic properties. However, as a potential spintronic material, the complete knowledge about the spintronic properties of Si is still not established yet. In this work, the technique of ferromagnetic resonance driven spin pumping is adopted to accurately determine several critical parameters, including the spin lifetime (τs), the spin diffusion length (λs), and the spin Hall angle (θISHE) of Si. By changing the type (n- and p-type) of carrier and the carrier concentration (1 × 1013 to 1.7 × 1019 cm−3), a correlation between λs and θISHE is found, suggesting an effective route to tune the efficiency of spin-charge conversion in Si.

Siloxide Podand Ligand as a Scaffold for Molybdenum-Catalyzed Alkyne Metathesis and Isolation of a Dynamic Metallatetrahedrane Intermediate

Triphenylsiloxide is one of the most successful ancillary ligands for Mo(VI)-alkyne metathesis catalysts. It was proposed that flexible siloxide ligands allow Mo–O–Si bond angles to modulate the electrophilicity of Mo≡C and thereby promote the catalysis. Introduction of a siloxide podand ligand allowed elucidation of the effect of ligand flexibility and Mo–O–Si angles on the electrophilicity of Mo≡C. It also allowed for the isolation of a rare metallatetrahedrane of Mo(VI) which was found to be dynamic in solution.

Determination of correct sign in primary angle calibrations

This paper discusses the critical issue of correct sign determination of angle deviations during primary calibration of angle standards and practical realisation of SI angle unit radian. The cases referring to reading direction of angle measuring devices and standards are presented and correct sign determination process is illustrated for primary method, cross calibration. The information should be of use to the laboratories contemplating the establishment of primary angle measurements or high precision angle metrology applications.

Comparisons of the Functional and Basis Set Combinations for Silicon Oxide Clusters: A Density Functional Theory Study

In this study, we evaluate three functionals (B3LYP, PBE, and M06) and 29 basis sets to find a suitable model to calculate silicon oxide clusters using density functional theory. The experimental values of electron affinities and vertical detachment energies of SiO2 and Si2O4 clusters were compared with the calculated ones using combinations of the three functionals and 29 basis sets. The calculated SiO bond lengths and SiOSi angles of Si2O7 cluster were also compared with the experimental values. Our conclusion is that the PBE/DGDZVP model is the best for calculating the structural and electronic properties of silicon oxide clusters.

Eco-Friendly Synthesis of Aluminosilicate Bromo Sodalite from Waste Coal Fly Ash for the Removal of Copper and Methylene Blue Dye

The synthesis of sodalite from fly ash seems to be one of the most promising alternatives as it has emphasis on value addition to the waste material. In view of this problem, this study investigated a working procedure for determining the degree of reaction of fly ash subjected to alkali activation at mild temperature, during the synthesis of bromo sodalite, \(\hbox {Na}_{8}[\hbox {AlSiO}_{4}]_{6}\hbox {Br}_{2}\). Obtained sodalite product was analyzed for their composition and physicochemical properties by X-ray diffraction, Fourier transform infrared spectroscopic analysis, inductively coupled plasma, Brunauer–Emmett–Teller surface area analysis, thermogravimetric analysis and scanning electron microscope. The crystal structures show cubic symmetry in a space group \(\hbox {P}{\overline{4}} 3\hbox {n}\). The unit cell parameter \(a = 8.930\) A, and the corresponding Al–O–Si angle is found to be \(140.5624^{\circ }\). The adsorption behavior of synthesized bromo sodalite has been studied in order to determine its applicability for the adsorption of the copper ion and methylene blue dye from their aqueous solutions. Factors influencing the adsorption process including contact time, sodalite concentration variation, copper ion and dye concentration variation were studied for adsorption of copper and methylene blue dye. Copper is removed due to two processes, viz adsorption and ion exchange, whereas methylene blue is removed due to only adsorption. The maximum adsorption capacity of synthesized sodalite was found to be 52.63 mg/g for copper ion removal and 45.46 mg/g for methylene blue dye removal. Thermodynamic parameters like Gibbs free energy (\(\Delta G^{\circ })\), entropy change (\(\Delta S\)) and enthalpy change (\(\Delta H\)) were calculated. Present adsorbent showed much better adsorption capacity for both copper ion and methylene blue as compare to reported low-cost adsorbents.

Microstructural evolution of ion-irradiated sol–gel-derived thin films

The effects of ion irradiation on the microstructural evolution of sol–gel-derived silica-based thin films were examined by combining the results from Fourier transform infrared, Raman, and X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, and elastic recoil detection. Variations in the chemical composition, density, and structure of the constituent phases and interfaces were studied, and the results were used to propose a microstructural model for the irradiated films. It was discovered that the microstructure of the films after ion irradiation and decomposition of the starting organic materials consisted of isolated hydrogenated amorphous carbon clusters within an amorphous and carbon-incorporated silica network. A decrease in the bond angle of Si–O–Si bonds in amorphous silica network along with an increase in the concentration of carbon-rich SiO x C y tetrahedra were the major structural changes caused by ion irradiation. In addition, hydrogen release from free carbon clusters was observed with increasing ion energy and fluence.

Bond length-bond angle correlation in densified silica—Results from 17O NMR spectroscopy

Pressure induced correlated evolution of the distributions of the Si–O distance and Si–O–Si inter-tetrahedral bond angle in vitreous silica quenched from pressures of up to ∼14 GPa at ambient temperature is measured in unprecedented detail using two-dimensional dynamic-angle-spinning 17O nuclear magnetic resonance spectroscopy. The results demonstrate that, in contrast to the conventional wisdom, vitreous silica undergoes irreversible structural changes even at pressures as low as ∼8 GPa. These structural changes at the short range involve a progressive reduction in the mean Si–O–Si angle and a broadening of the corresponding distribution, with increasing pressure. This bond angle reduction is accompanied by a concomitant monotonic increase in the mean Si–O distance. The mean values of the Si–O–Si angle and Si–O distance at various pressures closely follow the minimum in the corresponding potential energy surface calculated for the H6Si2O7 dimer molecule.

Bimodal distribution of Si–O–Si angles in sodo-silicate glasses

Polarized Raman scattering is performed in a series of sodo-silicate glasses. The Si–O–Si inter-tetrahedral angle and its distribution are extracted using a model developed previously for densified silica, and the result are compared to ab initio atomistic calculations. The two techniques reveal a reduction of the most probable angle of about 0.30°/mol% of Na2O, but the shape of the angular distributions are different. The results suggest that Raman scattering enhances a specific angular distribution of Si–O–Si bridges, likely those close to sodium atoms, highlighting local angular heterogeneities.