SiO2 Α-quartz Research Articles

Indirect effect of elevated pressure via the modulations of crystals intrinsic parameters on radiation shielding efficacy: A comparative study between two α-quartz homeotypes SiO2and GeO2

This study investigates the indirect effects of elevated pressure on the radiation shielding competence of two α-quartz homeotypes, SiO2 and GeO2, by examining the modulations of their crystal intrinsic tetrahedral parameters. The study focuses on structural modifications and their correlations with radiation attenuation properties. The results show that both homeotypes exhibit energy-dependent mass attenuation coefficients (MAC) and linear attenuation coefficients (LAC). SiO2 demonstrates higher transparency to incident radiation compared to GeO2, with a relative difference in MAC values of 91% at 0.015 MeV, decreasing to 28% at 15 MeV. However, within the energy range of 0.4 < E < 4 MeV, SiO2 exhibits higher MAC values than GeO2, with the MAC of SiO2 surpassing GeO2 by 17% at 0.4 MeV. The pressure dependence of LAC values indicates that both SiO2 and GeO2 become more effective in attenuating radiation under higher pressure conditions. For instance, at 0.015 MeV, the LAC of GeO2 increased from 274.826 cm−1 at 0.001 GPa to 308.073 cm−1 at 5.57 GPa. GeO2 generally exhibits higher LAC values than SiO2 across the energy and pressure ranges studied. It can be concluded that the structural modifications induced by elevated pressure significantly enhance the radiation shielding capabilities of α-quartz homeotypes, particularly GeO2, making them promising candidates for advanced shielding materials in various high-radiation environments.

Characteristics of coastal sands in Vietnam

The purpose of the presented work is a thorough determination of the characteristics of the coastal sands in Vietnam for the subsequent study of their sorption capacity. The objects of the study are sand samples collected on the banks of the Hong River (near the capital Hanoi), ThuBon (Quang Nam Province), Thachhan (Quangchi Province) and on the sea coast near the city of Hatin. Various industrial and agricultural enterprises are located in these places, in addition, the travel industry is actively developing here. The subject of the study is the granulometric characteristics of sand and its mineralogical composition. To study the mineralogical composition of sand samples the method of X-ray phase analysis is used, which allows to determine the mineralogical composition of the studied samples on the basis of the X-ray images obtained. It has been found that the mineral α-quartz SiO2 prevails in their composition, and there is also a certain amount of α-corundum Al2O3 as well as other impurities. To study the granulometric characteristics of the sands, the standard method of sieve analysis is used. The proportions of various fractions of sand samples, the average grain size, uniformity coefficient, bulk weight, porosity, as well as the specific surface area have been determined.

Metallization-free silver sinter bonding to silicon via in situ decomposition of silver oxalate

Metallization-free Ag sinter bonding to Si and SiO2 substrates was achieved via the thermal decomposition of Ag oxalate. Ag oxalate generated atomic-scale Ag through decomposition at approximately 200 °C and transformed into sintered Ag. Ag derived from Ag oxalate successfully bonded to Si substrates through close contact formation with Si surface oxide. Similarly, amorphous and α-quartz SiO2 substrates were directly bonded with Ag. These results indicate that the atomic-scale Ag generated on SiO2 contributed to interface formation over a large area. Moreover, the joints of the bare Si chip and metal substrate showed a maximum shear strength of 29 MPa at a bonding temperature of 250 °C and a bonding pressure of 5 MPa. The in-situ generation of Ag through the decomposition of Ag precursors can facilitate the direct bonding of electronic materials, making the proposed method a promising one for electronics applications.

Surface energy engineering for LiTaO3 and α-quartz SiO2 for low temperature (&amp;lt;220 °C) wafer bonding

Wafer bonding can be substituted for heteroepitaxy when manufacturing specific heterojunction-based devices. Devices manufactured using wafer bonding include multijunction solar cells, integrated sensors, heterogeneously integrated photonic devices on Si (such as high-performance laser diodes), Mach-Zehnder modulators, photodetectors, optical filters, and surface acoustic wave devices. In these devices, creating heterointerfaces between different semiconductors with heavily mismatched lattice constants and/or significant thermal expansion mismatch presents significant challenges for heteroepitaxial growth. High costs and poor yields in heavily mismatched heteroepitaxy can be addressed by wafer bonding in these optoelectronic devices and sensors, including the LiTaO3/Si and LiTaO3/SiO2 heterostructures. In the present work, heterostructure formation between piezoelectric LiTaO3 (100) and Si (100) and α-quartz SiO2 (100) is investigated via wafer bonding. Direct bonding is selected instead of heteroepitaxy due to a significant thermal expansion mismatch between LiTaO3 and Si-based materials. The coefficient of thermal expansion (CTE) of LiTaO3 is 18.3 × 10−6/K. This is 1 order of magnitude larger than the CTE for Si, 2.6–2.77 × 10−6/K and 25–30 times larger than the CTE for fused SiO2 and quartz (which ranges 0.54–0.76 × 10−6/K). Thus, even at 200 °C, a 4 in. LiTaO3/Si bonded pair would delaminate with LiTaO3 expanding 300 μm in length while Si would expand only by 40 μm. Therefore, direct wafer bonding of LiTaO3/Si and LiTaO3/SiO2 is investigated with low temperature (T &amp;lt; 500 K) Nano-Bonding™, which uses surface energy engineering (SEE). SEE is guided by fast, high statistics surface energy measurements using three liquid contact angle analysis, the van Oss/van Oss–Chaudhury–Good theory, and a new, fast Drop Reflection Operative Program analysis algorithm. Bonding hydrophobic LiTaO3 to hydrophilic Si or SiO2 is found to be more effective than hydrophilic LiTaO3 to hydrophobic Si or SiO2 temperatures for processing LiTaO3 are limited by thermal decomposition LiTaO3 into Ta2O5 at T ≥ 180 °C due to Li out-diffusion as much as by LiTaO3 fractures due to thermal mismatch.

H2S adsorption process on (0001) α-quartz SiO2 surfaces

We theoretically study the H2S adsorption process on (0001) α-quartz SiO2 surfaces, which is the preconditioning process for the atomic layer deposition growth of metal sulfide materials. The surface structures of dense and fully hydroxylated (0001) α-quartz SiO2 are energetically stable, but their reaction with a H2S molecule is not so active, whereas the cleaved SiO2 surface is chemically reactive to the dissociative adsorption of a H2S molecule with an adsorption energy of –3.08 eV/molecule. On the cleaved surface, we confirm that adsorbed H2S is dissociated into H and H-S fragments, and the energy barrier in this reaction process is computed as 0.042 eV.

The deposition characteristics of PAN/PPY on SiO2 substrate by density functional theory (DFT) calculations

The oxides with abundant functional groups on the surface (such as SiO2), have been specifically applied for synthesis of polymer composites like polyaniline (PAN) and polypyrrole (PPY) to improve the adsorption capacity. In this work, we investigated how α-quartz SiO2 surface influences the deposition characteristics of PAN/PPY through density functional theory (DFT) calculations. The PAN/PPY polymer chain has stable adsorption performance on the unoccupied SiO2 substrate due to the hydrogen bond interactions. When two overlapped polymer chains are packing on SiO2 surface, PAN and PPY exhibits different performances. For PAN, the physisorption between the two packed chains is fairly weak (0.07 eV/cell), so PAN prefers to adsorb on the unoccupied SiO2 surface and cannot pack on the as-deposited chain until the surface is fully covered. Differently, the PPY polymer won’t exhibit uniform deposition on SiO2 surface as PAN does, attributing to its more flexible chain configuration. The following calculations reveal that there is significant charge transfer between polymer chain and the silica substrate, which helps to understand the origin of different adsorption performances for PAN and PPY. This investigation provides theoretical insight into the experimental observation of PAN on SiO2 substrate, and helps to understand the microscopic mechanism in polymer-oxide composites.

Adhesion properties of Cu(111)/α-quartz (0001) interfaces: A molecular dynamics study

The fundamental properties of Cu/SiO2 interface are worth studying because they impact the quality and performance of silicon-based microelectronics and related devices. Using the charge-optimized many-body (COMB) potential in this study, we present a molecular dynamics simulation study of the structural, adhesive and electronic properties of Cu(111)/α-quartz SiO2 (0001) interfaces with two different crystalline orientations and various terminations by double-oxygens (OO), single-oxygen(O) and silicon(Si). For the equilibrated interfaces, the largest adhesion energies correspond to the oxygen richest OO-terminated interface in which the oxidation level of Cu is highest due to the largest charge transfer across the interface. In particular, we also investigate the properties of a series of nonequilibrated OO-, O- and Si-terminated interfaces that are created from their equilibrated counterparts by introducing vacancies of different numbers and different types. It is found that the adhesion energies of interfaces mostly decrease upon vacancy introductions only except for Si vacancies added in the Si-terminated interface. For all nonequilibrated interfaces of different terminations, we found a linear correlation between adhesive energy and area average excess charge transfer in Cu.

Variable-cell double-ended surface walking method for fast transition state location of solid phase transitions.

To identify the low energy pathway for solid-to-solid phase transition has been a great challenge in physics and material science. This work develops a new theoretical method, namely, variable-cell double-ended surface walking (VC-DESW) to locate the transition state (TS) and deduce the pathway in solid phase transition. Inherited from the DESW method ( J. Chem. Theory Comput. 2013 , 9 , 5745 ) for molecular systems, the VC-DESW method implements an efficient mechanism to couple the lattice and atom degrees of freedom. The method features with fast pseudopathway building and accurate TS location for solid phase transition systems without requiring expensive Hessian computation and iterative pathway optimization. A generalized coordinate, consisting of the lattice vectors and the scaled atomic coordinates, is designed for describing the crystal potential energy surface (PES), which is able to capture the anisotropic behavior in phase transition. By comparing with the existing method for solid phase transition in different systems, we show that the VC-DESW method can be much more efficient for finding the TS in crystal phase transition. With the combination of the recently developed unbiased stochastic surface walking pathway sampling method, the VC-DESW is further utilized to resolve the lowest energy pathway of SiO2 α-quartz to quartz-II phase transition from many likely reaction pathways. These new methods provide a powerful platform for understanding and predicting the solid phase transition mechanism and kinetics.

Mechanically tunable magnetism on graphene nanoribbon adsorbed SiO2 surface

Our first-principle calculations reveal that the O-terminated surface of zigzag graphene nanoribbon adsorbed (100) α-quartz SiO2 exhibits antiferromagnetic ground state. This is due to unpaired electrons of dangling O atoms forming on the SiO2 surface, which are caused by the edge C atoms of the adsorbed nanoribbon. The resulting magnetism and spin-resolved states on the SiO2 surface can be effectively tuned by mechanical strain applied on the substrate, with the antiferromagnetic state transforming into ferromagnetic state as well as the total magnetic moment varying from negative to positive when the strain turns from tensile to compressive. We elucidate the mechanism for the modification of the surface magnetism by orbital hybridization between C and O atoms and part of dangling O atoms bonding with the nanoribbon under strain.

General Purpose Electrostatic Embedding Potential

We present a method and a computer code for accurate calculation of electrostatic potential in an arbitrary crystalline lattice modeled using a finite system. The method is based on complementing a lattice unit cell with a set of point charges in order to annihilate simultaneously all components of any number of the lowest multipole moments. The positions and the values of the complementary charges are determined analytically. The electrostatic potential produced by each modified cell is short range, and the corresponding lattice series converges absolutely, which makes it convenient to use in embedded cluster calculations of solids, surfaces, and low-dimensional structures. The method is illustrated by application to the rutile TiO2 and α-quartz SiO2 lattices and to those of several complex minerals.

Thorite versus huttonite: stability, electronic properties and X-ray emission spectra from first-principle calculations

The structural, electronic properties and stability of thorium orthosilicate ThSiO4 polymorphs: thorite and huttonite are investigated by means of the full-potential linearized augmented-plane-wave method with the generalized gradient approximation for the exchange-correlation potential (FLAPW-GGA). The forbidden gaps of thorite and huttonite are estimated at about 7.8 and 7.6 eV, respectively. It is found that Th5f states in ThSiO4 partially overlap with occupied O2p bands. The data obtained showed that thorite is more stable than huttonite; in turn both ThSiO4 polymorphs are unstable with respect to their constituent binary oxides (thorianite ThO2 and α-quartz SiO2) in agreement with the experiments. The theoretical shapes of X-ray emission (XES) (Si,O)Kα,β spectra for thorite, huttonite as well as for SiO2 and ThO2 are calculated and discussed. We show that the XES spectroscopy near the (Si,O)K edge may be very useful technique not only for detailed investigation of the bulk-electronic structure of Th silicates but also for the phase analysis of complex mineral samples containing these species.

X-ray Raman scattering at the Si LII,III-edge of bulk amorphous SiO

X-ray Raman spectra of bulk amorphous SiO have been measured at energy losses around the Si LII,III-edges for different momentum transfers at beamline ID16 of ESRF. The spectra are compared with measurements of the LII,III-edges of Si powder and with results of first-principles calculations for Si and α-quartz SiO2. Indications of sub-oxidic contributions to the LII,III-edges are found in the experiment and discussed with respect to the model of interface clusters mixture in bulk amorphous SiO.

Mechanisms of Energy Transfer in Solids Irradiated with Swift Heavy Ions

ABSTRACTThe damage cross section velocity effect is studied in LiNbO3, Y3Fe5O12 and SiO2 α-quartz. The application of our thermal spike model reveals that the efficiency of track formation varies by a factor of two in the range of 2–4 MeV/nucleon. The effect is explained by the varying fraction of energy deposition to the lattice involving lattice ions.

ＨＩＰ法によるＳｉＯ２系非晶質‐結晶質複合材料の作製

The composites consisting of α-quartz crystallites and amorphous SiO2 were prepared by HIP technique, imitating the structure of natural agate which is practically strong and is widely used in the industry, α-quartz and SiO2 glass powders with 5μm in average grain size were used as starting materials. These powders were mixed with the composition of 0, 5, 10, 25, 50 in wt% of α -quartz. This mixture was pressed into a compact with φ12mm×20mm in size. The Pyrex glass capsule containing the compact was hipped at 800-1200°C for 30-240 minutes under the pressure of 50-200MPa. The specimens with the appearance of agate were obtained at 1200°C under 100 and 200MPa. The polarization microphotograph showed that the crystallites were in the amorphous SiO2 matrix. α-quartz was confirmed as the crystalline phase by x-ray powder diffraction method. The composition of α-quartz increased slightly after hipping. Therefore, chemical bonds may be formed between crystallites of α-quartz and amorphous SiO2. Using the starting mixture with 25wt% of α-quartz, the maximum density of 2.50g/cm3 was obtained at 1200°C for 120 minutes under 200MPa. In the case, the maximum bending strength was obtained to be 9.2Kg/mm2, corresponding to 70% of that in the natural agate.

Acido-basic properties of simple oxide surfaces III. Systematics of H+ and OH− adsorption

Thanks to a self-consistent tight binding approach, applied to clusters embedded in a Madelung field created by an infinite array of charges at the lattice sites, we have modeled the acido-basic properties of various simple oxide surfaces: BaO(001), SrO(001), CaO(001), MgO(001), rutile-TiO(in2)(110), α-quartz SiO2(0001). We have studied H+, OH− and dissociated H2O adsorption characteristics: adsorption energy, charge transfer and density of states. We have proved that the decreasing basic character of the oxygen sites along the series comes from the larger covalency of the compounds, which opposes the proton adsorption, while the increasing acid character of the surface cations comes from their lower and lower electropositivity and from their smaller and smaller ionic radii. This detailed study completes the model that we had elaborated previously [Surf. Sci. 262 (1992) 245 and 259], and confirms the dominant role of covalent effects, as opposed to electrostatic effects, in the acido-basic properties of these insulating oxides.

Studies on the Leaching and Weathering Processes of Coal Ashes

Within the Swedish project Coal-Health-Environment (Kol-Hälsa-Mi1jö) leaching studies were made on several types of coal ashes, fly ashes, bottom ashes and scrubber sludges. Studies were made on the effects of pH, pCl, pCO3. pEDTA and pSO4, in the leaching solution on the leaching of metals from coal ashes. As a model for the leaching system, we studied the leaching of Cr, Co, Ni, tu, Zn, Mo, Se, As, Cd and Pb. The leaching of the metals was found to increase with pH for pH less than 2 and pH greater than 9, and to decrease for 2 &amp;gt; pH &amp;gt; 6. The metal leaching behaviour may in part be explained by the mass-action law. We have also made long-term leaching tests of several coal ashes from Danish and Finnish Power Plants using leaching water of different pH. The dominating crystalline phases in the different coal ashes have been identified by X-ray diffraction technique. The major species in the different coal ashes were found to be mullite (3A12.2SiO2), α-quartz (Sio2) and the iron oxides magnetite and hematite. Leaching and X-ray studies were also made on the magnetic fraction of the fly ashes. Equilibrium analysis were made on the system Me-OH-Cl-CO32− - SO42−, where Me = Cr, Co, Ni, Cu, Zn, Mo, Se, As, Cd and Pb, partly using the computer program HALTAFALL. A model for the metal leaching from a coal ash deposit will be discussed.

Electron states in α-quartz (SiO2)

Valence electron states of α-quartz SiO2 are calculated self-consistently using the pseudopotential method. Excellent agreement is found with photoemission and UV-absorption data. X-ray emission spectra are calculated in an OPW scheme and compared to experiments. While the Si- and O - K spectra agree well with experiment, the Si L2,3 spectrum shows substantial differences. An explanation is offered base on the formation of amorphous Si in SiO2 during electron irradiation.

Inversion layers in abrupt p-n junctions : F. van de Wiele and E. Demoulin, Solid-State Electron.13 (1970), p. 717

Valence electron states of α-quartz SiO2 are calculated self-consistently using the pseudopotential method. Excellent agreement is found with photoemission and UV-absorption data. X-ray emission spectra are calculated in an OPW scheme and compared to experiments. While the Si- and O - K spectra agree well with experiment, the Si L2,3 spectrum shows substantial differences. An explanation is offered base on the formation of amorphous Si in SiO2 during electron irradiation.