High-index Si Research Articles

Novel Abietane Type Sugar Triazole Hybrids and Amides against SARS‐CoV‐2 Spike Glycoprotein and Influenza A Virus

AbstractAbietane type diterpenic (dehydroabietic, 2,3‐dihydroquinopimaric and maleopimaric) acids were converted by the acid chloride method into a series of aliphatic and heterocyclic amine spacered conjugates. A number of structurally novel derivatives holding 1,2,3‐triazole moieties were designed and synthesized by treating of the propargylated amides and esters with a sugar azides using the Cu(I)‐catalyzed click chemistry approach. The synthesized N‐containing diterpene derivatives were tested for their potential inhibition of influenza A/PuertoRico/8/34 (H1N1) virus in MDCK cell culture and SARS‐CoV‐2 pseudovirus in BHK‐21‐hACE2 cells. Among tested forty‐five compounds ten derivatives were the most efficacious against influenza virus A with IC50 0.7–63.4 μM together with high selectivity index SI value from 11 from 94. Dihydroquinopimaric acid N‐ethylpiperazine‐amide and dehydroabietic acid 1,2,3‐triazoles spacered with glucose and lactose showed anti‐SARS‐CoV‐2 pseudovirus activity with EC50 values of 1.79–25.46 μM. Molecular docking and dynamics modeling investigated the binding mode of the lead compounds into the binding pocket of influenza A virus M2 protein and the RBD domain of SARS‐CoV‐2 spike glycoprotein.

Antiviral opportunities of Mannich bases derived from triterpenic N-propargylated indoles.

Oleanolic and glycyrrhetic acids alkyne derivatives were synthesized as a result of propargylation of the indole NH-group condensed with the triterpene A-ring, the following aminomethylation led to a series of Mannich bases. The synthesized compounds were tested for their potential inhibition of influenza A/PuertoRico/8/34 (H1N1) virus in Madin-Darby canine kidney (MDCK) cell culture and SARS-CoV-2 pseudovirus in baby hamster kidney-21-human angiotensin-converting enzyme 2 (BHK-21-hACE2) cells. Mannich bases of oleanolic and glycyrrhetic acids N-propargylated indoles 7, 8, and 12 were the most efficacious against influenza virus A with IC50 7-10 μM together with a low toxicity (CC50 > 145 μM) and high selectivity index SI value 20. Indolo-oleanolic acid morpholine amide Mannich base holding N-methylpiperazine moiety 9 showed anti-SARS-CoV-2 pseudovirus activity with EC50 value of 14.8 μM. Molecular docking and dynamics modeling investigated the binding mode of the compounds 7 and 12 into the binding pocket of influenza A virus M2 protein and compound 9 into the RBD domain of SARS-CoV-2 spike glycoprotein.

Study of a High-Index Dielectric Non-Hermitian Metasurface and Its Application in Holograms.

We demonstrate that a high-index dielectric Si metasurface with a designed chiral unit structure possesses an exceptional point (EP) when it is described by a non-Hermitian Hamiltonian associated with the transmission matrix. By encircling any path in the parameter space around the EP, topologically protected 2π-phase accumulation occurs. These typical non-Hermitian properties are ascribed to complex scattering phenomena related to the coupling between electric and magnetic dipolar modes from the high-index dielectric Si metasurface. The topologically guaranteed entire 2π-phase accumulation and chiral distinction around the EP open up many promising possibilities in nanophotonic device designing; for instance, phase-only and polarization multiplexing holograms are realized in this work.

Deep-subwavelength gap modes in all-dielectric metasurfaces for high-efficiency and large-angle wavefront bending.

All-dielectric, phase-gradient metasurfaces manipulate light via a judiciously designed planar distribution of high and low refractive indices. In the established design approaches, the high-index elements play a dominant role, while the electromagnetic field existing between these elements is routinely viewed as either an incidental by-product or detrimental crosstalk. Here we propose an alternative approach that concentrates on exploring the low-index materials for wavefront shaping. In our Si metasurface, the low-index air gap between adjacent Si fins is judiciously tuned, while the high-index Si fins only have a single size across the whole metasurface. These gap modes provide the full 2π phase coverage, as well as high and relatively uniform transmission, at the deep-subwavelength scale. These characteristics are ideal for mapping a steep phase gradient, consequently suitable for high-efficiency and large-angle wavefront bending. This light manipulation capability is exemplified with numerical simulation in PW-SW (freely propagating wave to surface wave) conversion, where the wavefront is deflected by an angle of 90°. In the gap-mode meta-converters, the average unit size can be only 1/60 of free-space wavelength, an order of magnitude smaller than that of conventional all-dielectric metasurfaces. Their conversion efficiency can reach 68%, the highest value reported for any all-dielectric gradient metasurface THz converter.

Quartz types, silica sources and their implications for porosity evolution and rock mechanics in the Paleozoic Longmaxi Formation shale, Sichuan Basin

Quartz is a common mineral in mudrocks, displays variable forms and can have multiple origins. Consequently, the form and source of quartz in mudrocks may have a distinct impact on porosity evolution and rock mechanics such as brittleness. In this study, 51 shale samples from both the Lower and Upper parts of the Longmaxi Formation in the Sichuan Basin of China were collected for geochemical, mineralogical and elemental analyses, microscopic observation, porosity characterization, as well as rock mechanics testing, in order to better understand the quartz types, the sources of the silica, and their impacts on porosity evolution and rock mechanical behavior. Optical microscopy and field emission-scanning electron microscopy (FE-SEM) with energy dispersive spectroscopy (EDS) were applied to describe the crystal morphology and investigate the types and silica sources of quartz and their associated pores. Images from both methods reveal several forms of quartz in the Longmaxi Shale, including terrigenous detrital quartz, organism skeletal quartz, quartz overgrowths, authigenic microquartz and quartz veins. Furthermore, the authigenic microquartz has three subcategories, namely clay matrix-dispersed, euhedral and amorphous. The distinguishing criteria include crystalline morphology, luminescence, grain size and forming stage (including the stage of deposition and different periods of the diagenesis progress). Geochemical proxies, such as an Al–Fe–Mn ternary diagram, negative correlations of Zr vs. SiO2, and positive correlations of TOC vs. excess Si, indicate a substantial contribution of biogenic silica to the total silica in the Lower Longmaxi Formation. All possible pores associated with quartz are systematically described and classified into 3 types and 8 subtypes, notably dissolution pores, organism skeletal cavity pores, crystal defect pores, pores between quartz grains, grains contact micro-fractures, shrinkage micro-fractures and quartz filling micro-fractures. This study shows that the origin of the quartz may have implications for porosity evolution and rock mechanics. Positive correlations of surface area vs. excess Si indicate that biogenically derived forms of microquartz (including euhedral microquartz and amorphous microquartz cements) play a constructive role for micro-scale pore development. The correlation between high brittleness index and excess Si in the Lower Longmaxi Formation suggests that biogenic silica is the major cause of the brittleness.

Pentamers with interstitial atoms as the building blocks of the Ge(3 3 1)-5 × 1 surface

High-index Si and Ge surfaces are used for growth of low defect density epitaxial layers and for nanostructure growth. In this work an atomic structure model of the high-index Ge(331)-5 × 1 surface is developed on the basis of the Si(331)-12 × 1 building block, consisting of a pentamer with an interstitial atom. Based on first-principles density functional calculations, it is shown that the proposed surface model leads to very low surface energy and good agreement with scanning tunneling microscopy images of the Ge(331)-5 × 1 surface available in the literature. Thus, we demonstrate that the Ge(331)-5 × 1 belongs to a family of surfaces, whose members are stabilized by pentamers with interstitial atoms, namely Si(331), Si(113), Ge(113), Si(110), Ge(110).

Principal angles and principal azimuths of a high-index transparent thin film on a low-index transparent substrate: Si on glass in the near infrared

Principal angles of incidence and associated principal azimuths, at which incident linearly polarized light becomes circularly polarized upon reflection, are determined for an IR-transparent high-index Si film (of the proper thickness) which is deposited on a low-index SiO2 (glass) substrate at the near-IR wavelength λ = 1.55 μm. The results are substantially different from those reported by the author [Appl. Opt. 57, 9529–9532 (2018)] for the SiO2–Si (film-substrate) system at the same wavelength. The intensity reflectances for incident p- and s-polarized light, and the linear-to-circular polarization conversion efficiency are also calculated as functions of the principal angle.

Au-induced atomic wires on stepped Ge(hhk) surfaces

Au adsorption on high-index Si surfaces is known to form quasi-one-dimensional surface reconstructions with interesting physical properties such as Rashba-split bands and ordered arrays of local magnetic moments. Here we report on a novel family of Au-induced chain systems, hosted on Ge(hhk) substrates. Our study includes Ge(553), Ge(557), and Ge(335) for both bare and Au-adsorbed surfaces, respectively. We employ scanning tunneling microscopy and low-energy electron diffraction to characterize the topography and the occurrence of superstructures. Stable bare surfaces with regularly distributed steps are found for the (553) and (335) orientations. For nominal Ge(557) substrates a refaceting to Ge(223) is observed. Addition of Au tends to promote a change in the surface index which creates Ge(221)-Au, Ge(557)-Au, and Ge(335)-Au surfaces. Their STM images show elements that are reminiscent of the well-understood Si(hhk)-Au surfaces but also reveal important differences.

Pentagons in theSi(331)−(12×1)surface reconstruction

The microscopic structure of the high-index Si$(331)-(12\times1)$ surface is investigated combining scanning tunneling microscopy with ab initio calculations. We present a structural model of the Si(331) surface, employing a reconstruction element composed of six pentagons integrated to the structure of the adjacent pentamer with an interstitial atom. We demonstrate that appropriately arranged additional pentagons significantly lower the surface energy of the high-index surface. The model predicts the existence of multiple Si(331) buckled configurations with similar energies.

Ten-Micrometer-Thick Si Wafers with Ag Nanoclusters: Substrate Effects on Plasmon-Enhanced Optical Absorption

We present the optical characteristics of 10-μm-thick crystalline Si wafers with an Ag heptamer nanocluster (NC) array, using a finite-difference time-domain method. The anti-reflection properties of the Ag NC array were more pronounced at long wavelengths, with respect to a monomer array, resulting in significantly enhanced optical absorption in the underlying Si wafer. The scattering cross-section spectra of the NC on the Si wafer exhibited one broad peak with a kink, whereas those in air showed two broad peaks and a sharp Fano dip between them. The high refractive index Si wafer weakened the near-field coupling between particles in the NCs, which modified the optical cross-sections of the Ag NC more drastically than those of the Ag monomer. Therefore, the implementation of the NC nanoantennae for Si-based optoelectronic devices requires careful consideration of the substrate effects.

Heteroepitaxial growth of GaN on vertical Si{110} sidewalls formed on trench-etched Si(001) substrates

A maskless Si trench structure was developed to integrate crystallographically non-polar GaN microstructures with semi-polar facets on Si(001). GaN “fins” were preferentially grown by MOCVD on Si{110} trench sidewalls formed by deep reactive ion etching (DRIE) of Si(001) such that GaN(0001)//Si{110} and GaN(10-10)//Si(001), resulting in a non-polar crystal structure with respect to the Si(001) substrate surface. No masking layer was required to prevent GaN growth on the Si(001) top surface of the trenches, instead, it was found that GaN nucleated preferentially on the Si{110} trench sidewalls. GaN was also observed to nucleate at the top corner of the trenches due to Si etching and exposure of high-index Si facets during the pre-growth H2 anneal. This undesired GaN nucleation was successfully suppressed by reducing the H2 anneal time and/or increasing the growth temperature and decreasing the precursor V/III to enhance Ga-adatom diffusion. Cross-sectional TEM studies confirmed that the GaN fins were crystallographically non-polar with respect to the Si(001) substrate surface and were bounded by semi-polar and non-polar facets. The reported Si fabrication and GaN growth process shows promise for the integration of non-polar and semi-polar GaN microstructures on industry standard Si(001) substrates.

Growth of Ag nanostructures on high-index Si (5 5 12) surfaces under UHV conditions: effect of prior surface treatment before deposition

High-index substrates, such as Si (5 5 12), provide self-assembled one-dimensional periodic array of structures upon reconstruction and can be used as templates for growth of aligned nanoscale structures. Crystalline quality of Ag nanostructures grown under UHV conditions using a molecular beam epitaxy system on reconstructed Si (5 5 12) surface is compared with those structures grown on HF-treated and native-oxide-covered Si (5 5 12) surfaces. These have been characterized by using reflection high-energy electron diffraction (RHEED), transmission electron microscopy (TEM) and in situ scanning tunneling microscopy methods. The RHEED and TEM studies confirm the polycrystalline, textured and crystalline nature of the Ag nanostructures grown on Si (5 5 12) with native oxide, HF-treated, and reconstructed surfaces, respectively. The crystalline quality of Ag nanostructures on HF-treated substrate was found to improve at higher substrate temperatures during growth.

Growth kinetics of indium metal atoms on Si(1 1 2) surface

The growth kinetics and desorption behavior of indium (In) atoms grown on high index Si(112) surface at different substrate temperatures has been studied. Auger electron spectroscopy analysis revealed that In growth at room temperature (RT) and high substrate temperature (HT) ∼250°C follows Frank–van der Merve growth mode whereas at temperatures ≥450°C, In growth evolves through Volmer–Weber growth mode. Thermal desorption studies of RT and 250°C grown In/Si(112) systems show temperature induced rearrangement of In atoms over Si(112) surface leading to clusters to layer transformation. The monolayer and bilayer desorption energies for RT grown In/Si(112) system are calculated to be 2.5eV and 1.52eV, while for HT-250°C the values are found to be 1.6eV and 1.3eV, respectively. This study demonstrates the effect of temperature on growth kinetics as well as on the multilayer/monolayer desorption pathway of In on Si(112) surface.

Reduction in the interface-states density of metal-oxide-semiconductor field-effect transistors fabricated on high-index Si (114) surfaces by using an external magnetic field

After fabrication of Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) devices on high-index silicon (114) surfaces, their threshold voltage (Vth) and interface-states density (Dit) characteristics were measured under the influence of an externally applied magnetic field of B = 6 μT at room temperature. The electron flow of the MOSFET's channel presents high anisotropy on Si (114), and this effect is enhanced by using an external magnetic field B, applied parallel to the Si (114) surface but perpendicular to the electron flow direction. This special configuration results in the channel electrons experiencing a Lorentzian force which pushes the electrons closer to the Si (114)-SiO2 interface and therefore to the special morphology of the Si (114) surface. Interestingly, Dit evaluation of n-type MOSFETs fabricated on Si (114) surfaces shows that the Si (114)-SiO2 interface is of high quality so that Dit as low as ∼1010 cm−2·eV−1 are obtained for MOSFETs with channels aligned at specific orientations. Additionally, using both a small positive Vds ≤ 100 mV and B = 6 μT, the former Dit is reduced by 35% in MOSFETs whose channels are aligned parallel to row-like nanostructures formed atop Si (114) surfaces (channels having a 90° rotation), whereas Dit is increased by 25% in MOSFETs whose channels are aligned perpendicular to these nanostructures (channels having a 0° rotation). From these results, the special morphology of a high-index Si (114) plane having nanochannels on its surface opens the possibility to reduce the electron-trapping characteristics of MOSFET devices having deep-submicron features and operating at very high frequencies.

Kinetically Controlled Growth and Thermal Stability of Potassium on Reconstructed High Index Si(5512) 2 x 1 Surface

Kinetically Controlled Growth and Thermal Stability of Potassium on Reconstructed High Index Si(5512) 2 x 1 Surface

Evolution of kinetically controlled In-induced surface structure on Si(5 5 7) surface

• Evolution of In induced superstructures on Si(5 5 7) surface during RT and HT adsorption/desorption process. • Kinetics is governed by substrate temperature which exhibits various growth modes (FM, SK, VB) under different conditions. • Strain relaxation play significant role in the commencement of desorption/rearrangement of atoms. • A consolidated phase diagram of In/Si(5 5 7) interface has been reported with new √3 × √3-R30̊ and 4 × 1 phases. This paper introduces issue of kinetically controlled and temperature driven superstructural phase transition of Indium (In) on atomically clean high index Si(5 5 7)-7 × 1 surface. Auger electron spectroscopy analysis reveals that at room-temperature (RT) with a controlled incident flux of 0.002 ML/s; In overlayers evolve through the Frank-van der Merwe growth mode and yield a (1 × 1) diffraction pattern for coverage ≥1 ML. For substrate temperature <500 °C, growth of In follows Stranski–Krastanov growth mode while for temperature >500 °C island growth is observed. On annealing the In/Si(5 5 7) interface in the temperature range 250–340 °C, clusters to two dimensional (2D) layer transformation on top of a stable monolayer is predominated. In-situ RT and HT adsorption and thermal desorption phenomena revealed the formation of coverage and temperature dependent thermally stable In induced superstructural phases such as (4 × 1) at 0.5 ML (520 °C), (√3 × √3-R30°) at 0.3 ML (560 °C) and (7 × 7) at 0.1 ML (580 °C). These indium induced superstructures could be utilized as potential substrate for the growth of various exotic 1D/2D structures.

Formation of Potassium Nanostructures on Reconstructed High Index Si (5512)2x1 Surface for Night Vision Devices (NVD)

In the present study potassium nanostructure was grown on the high index reconstructed Si (5512) 2x1 surface due to their potential application in the night vision devices (NVD). The formation of potassium atoms (K) on high index Si semiconductor under controlled kinetic and thermodynamic growth conditions having desired shape and size with low work function were studied. The studies have been performed on a reconstructed high index silicon surface at room temperature as well as on high substrate temperatures such as (375, 550 and 680 oC). The structural properties of the high index trenched template have been exploited for the development of desired nanostructures of different size and shape. It is constructed to a planner surface having a single domain with 1-D symmetry and relatively largest unit cell (5.35 nm). In the present study, growth of potassium nanostructures on the high index reconstructed Si (5 5 12) surface occur, which can be potentially utilized in night vision devices. The experiments were performed in-situ in a Ultra high vacuum (UHV) system in-housed with various surface sensitive techniques such as Auger Electron Spectroscopy (AES), Electron Energy Loss Spectroscopy (EELS), and Low Energy Electron Diffraction (LEED).

Ultra-long-range symmetric plasmonic waveguide for high-density and compact photonic devices

This study reports a symmetric hybrid plasmonic waveguide consisting of a cylindrical metal nanowire surrounded by low-index SiO₂ and high-index Si covered with SiO₂. The symmetric circumambience relative to the metal nanowire significantly facilitates the present design to minimize the energy attenuation resulting from Ohmic losses while retaining highly confined modes guided in the low-index nanoscale gaps between the metal nanowire and the high-index Si. The geometric dependence of the mode characteristics on the proposed structure is analyzed in detail, showing long propagation lengths beyond 10 mm with normalized mode areas on the order of 10⁻². In addition to enabling the building of long-range plasmonic circuit interconnects, the compactness and high-density integration of the proposed structure are examined by analyzing crosstalk in a directional coupler composed of two such waveguides and bending losses for a 90° bend. A relatively short coupling length of 1.16 μm is obtained at a center-to-center separation of 0.26 μm between adjacent waveguides. Increasing the separation to 1.65 μm could completely prevent coupling between waveguides. Power transmission exceeds 80% in the case of a 90° bend with small radius of curvature of 0.5 μm. Moreover, the dependence of spectral response on coupling length and the transmission of a 90° bend, ranging from telecom wavelengths of 1.40 to 1.65 μm, are investigated. Over a wide wavelength range, a strong coupling length dependence on wavelength and a high transmission for a 90° bend also make the proposed plasmonic waveguide promising for the realization of wavelength-selective components.

Residual thermal desorption studies of Ga adatoms on trenched Si(5 5 12) surface

We present here the thermal stability studies of the room temperature adsorbed Ga/Si(5512) interfaces in the monolayer coverage regime, using AES and LEED as in-situ UHV characterization probes. Ga grows in Stranski–Krastanov growth mode at RT on the 2×1 reconstructed Si(5512) surface where islands form on top of 2ML of flat pseudomorphic Ga, yielding a (1×1) LEED pattern for coverages of 1.2ML and above. When this RT adsorbed Ga/Si(5512) interface is annealed at different temperatures, initially the strained Ga adlayers relax by agglomerating into 3D islands on top of a single Ga monolayer with an activation energy of 0.19eV in the temperature range of 200–300°C. The remnant Ga monolayer with a sharp (1×1) LEED pattern desorbs at temperature >400°C, yielding the (112)–6×1 and 2×(337) sub-monolayer superstructural. Finally at 720°CGa completely desorbs from the surface and leaves the clean 2×1 reconstructed Si(5512) surface. The studies demonstrate the richness of the atomically trenched high index Si(5512) surface, in obtaining several anisotropic features that can be used as templates to grow self-assembled nanostructures.

In situ observation of Cu segregation and phase nucleation at a solid–liquid interface in an Al alloy

This paper presents a systematic study comparing experimental in situ transmission electron microscopy observation of microstructural and compositional evolution with complementary thermodynamic calculations, to better understand the redistribution of solute elements and the nucleation behavior of different phases in a commercial Al-alloy powder (AA390). The results show that Cu segregation to the solid Si–liquid Al interface, as well as the significant undercooling achieved in the liquid under non-equilibrium conditions because the Al phase cannot nucleate homogeneously, play a important roles in nucleating Al2Cu at the interface prior to the Mg2Si phase in the alloy. Although Cu segregation can occur at various locations along the interface, the Al2Cu phase appears to preferentially nucleate at a high-index Si–liquid interface as opposed to a low-index one. The Cu concentration during segregation remains essentially constant with time, indicating that the observed segregation behavior is a thermodynamic and not a kinetic phenomenon. These in situ observations and complementary thermodynamic calculations substantially enhance our understanding of potential crystal nucleation and growth processes.