Formation Of Amorphous Layer Research Articles

Structural and phonon transport analysis of surface-activated bonded SiC-SiC homogenous interfaces

To avoid the interfacial thermal stress problem caused by high temperature, room temperature bonding techniques such as surface-activated bonding (SAB) are currently receiving widespread attention. However, the thermal boundary resistance (TBR) is challenging in reaching the theoretical value because the bombardment of the surface by energetic particle beams causes the formation of amorphous layers. In this paper, we have prepared SiC/SiC interfaces by surface-activated bonding and tried to explain the effect of the interfacial amorphous layer on the thermal properties. The results show that an amorphous layer of about 9 nm was formed at the SiC/SiC interface, mainly composed of carbon atoms. Molecular dynamics simulations derive an effective thermal boundary resistance (TBReff) of 4.78 m2K/GW for this interface, where the TBR of SiC/a-C is only approximately 0.50 m2K/GW. The TBReff with 30 % Fe after modification increased to 6.74 m2K/GW. The lower TBR between SiC/a-C can be attributed to coupling extended modes (EMs) and localized modes (LMs) at the interface and acting as a phonon bridge. In addition, the bulk thermal resistance of the amorphous layer accounts for 79.3 % of the TBReff. Besides, the molecular dynamics results show that the decrease in the thickness of the amorphous layer can significantly reduce the TBReff. As the thickness of the amorphous layer tends to zero, the TBReff is almost close to zero. The above conclusions will be beneficial to understanding the main factors influencing the thermal properties in the SiC/SiC interface, which point out the way for the subsequent improvement of the interfacial thermal conductivity.

Effect of Cr on high-temperature oxidation resistance of Cr–Si–Mn alloyed press-hardened steel during press hardening

It is of great interest to overcome the problem of high-temperature oxidation of press-hardened steels (PHS) in press hardening with a cost-effective Cr alloying strategy. Therefore, since Cr is one of the expensive metals, the effect of Cr (Cr ≤ 3 wt%) content on the oxidation resistance of Cr–Si–Mn alloyed steels was investigated. It was found that Cr–Si–Mn alloyed PHS with a Cr content of about 1.5 wt% or less cannot form a continuous Cr2O3 layer during press hardening. However, when the Cr content reaches around 2.5 wt%, the PHS shows excellent oxidation resistance due to the formation of continuous Cr2O3 and amorphous SiO2 layers, as well as an Mn-rich oxide layer. However, further addition of 0.5 wt% could not significantly improve the oxidation resistance of this PHS. Moreover, the increase in Cr content simultaneously enhances the positive role of Si and Mn in high-temperature oxidation resistance. This work provides new insights into the design of the next generation of PHSs with economical and superior performance.

Polishing performance and material removal mechanism in the solid-phase Fenton reaction based polishing process of SiC wafer using diamond gel disc

The use of SiC wafer is widespread in many fields, especially in aerospace, energy, 5 G communications, and microelectronics. Chemical-mechanical polishing (CMP) is the primary method used for achieving an ultra-smooth surface on SiC wafers. However, CMP suffers from low efficiency, leading to increased processing time and costs. To address this issue, we developed a novel diamond gel polishing disc that incorporates SiO2/Fe3O4 (S/F) powder. The disc enhances polishing efficiency through a solid-phase Fenton reaction between the disc and SiC. The research investigates the reaction mechanism and the material removal model of the polishing process using SEM, TEM, and XPS analysis. Experimental studies are conducted to assess the polishing performance and validate the effectiveness of the theoretical model. The findings indicate that SiC undergo a solid-phase Fenton reaction with polishing disc mixed S/F powder (SG-S/F disc) during polishing. The Fenton reaction generates hydroxyl radicals (·OH), which break the Si-C and Si-Si bonds in the crystal structure, leading to the formation of a softer nanoscale amorphous oxide layer on the SiC surface. The cyclic generation and removal of this oxide layer enable highly efficient polishing of SiC wafers. Compared to a gel disc without S/F (SG disc), SiC polished with the SG-S/F disc exhibits superior surface quality. Additionally, the material removal rate (MRR) of the SG-S/F disc reaches 1.42 μm/h, representing a 51.1 % improvement over that of the SG disc. These results clearly demonstrate that the solid-phase Fenton reaction significantly enhances the polishing performance of the gel polishing disc.

Investigations on ion irradiation induced microstructural changes in Gd2O3 nanorods

Ion irradiation induced phase transformations in Gd2O3 nanorods dispersed on TEM grids, are investigated using synchrotron X-ray diffraction and transmission electron microscopy. Ion irradiation induced cubic (C) to monoclinic (B) phase transformation is observed in Gd2O3 nanorods. Gd2O3 nanorods are partially transformed to monoclinic phase at 0.63 dpa (5 × 1016 ions/cm2) itself. The C→B phase transformation is reconstructive type transformation where the role of O-vacancies and diffusion are very important. During He+ ion irradiation, the displacement cascades produced O-vacancies and during the non-melting thermal spike regime, diffusion was assisted and it resulted in the phase transformation. In addition to phase transformation, TEM investigations shows formation of amorphous carbon layer around the nanorods and welding of the nanorods, upon ion irradiation. These observations are explained based on the mechanisms of GOLF (giant onion like fullerene) formation and the localized surface melting during thermal spike.

Novel nano-thin amorphous Ta-coating on 3D-printed porous TC4 implant: Microstructure and enhanced biological effects

Bone defects caused by tumors, trauma, or other bone diseases are common in clinical practice. Titanium alloy (TC4) and tantalum (Ta) are the primary metallic materials for bone repair. However, TC4 frequently suffers from poor osseointegration and implant loosening, while the high cost of Ta limits its widespread use for reconstructing large bone defects. To address this issue, this research employs magnetron sputtering (MSP) to deposit a nano-thin amorphous Ta-coating on the 3D-printed TC4 implant. SEM examinations of compressed samples show robust interfacial bonding without shedding, while the presence of Ta within the porous structure indicates high coverage. High-resolution TEM analysis first reveals a distinct multilayer amorphous zone consisting of surface TaOx, Ta-coating, and hybrid TaOx and TiOx, along with an impact-refinement nanocrystalline TC4 zone. Insufficient energy leads to the formation of amorphous layers. Meanwhile, interfacial bonding is strengthened through the solid solution of oxygen and interfacial densification of amorphous-crystalline bonding and impact compression. Biological evaluations demonstrate that the Ta-coating exhibits superior cell proliferation and bone ingrowth effects compared to TC4 and pure Ta implants, primarily attributed to the amorphous oxide composition on the surface. This study offers novel, cost-efficient, and excellent biological performance materials for bone defect implants.

Tuning Morphology and Electronic Structure of Cobalt Metaphosphate Via Vanadium‐Doping for Efficient Water and Urea Splitting

AbstractDesigning efficient multifunctional electrocatalysts for water and urea splitting to produce green hydrogen presents a significant yet worthwhile challenge. Herein, the morphology and electronic structure of cobalt metaphosphate (Co2P4O12) by vanadium (V) doping, resulting in improved electrocatalytic activity and stability for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and urea oxidation reaction (UOR) are simultaneously regulated. Theory calculations show that V‐doped Co2P4O12 (V‐Co2P4O12) can boost the kinetics of catalytic reactions by optimizing the d‐band center of Co atoms and the binding strength of intermediates, as well as enhancing the density of states. Moreover, the doping of V into Co2P4O12 crystalline structure benefits the formation of a thicker amorphous layer during the catalytic process, which could enhance its alkaline corrosion resistance and stability. Additionally, the multilevel nanostructures of V‐Co2P4O12 provide rich active sites for catalytic reactions. As a result, a two‐electrode electrolyzer assembled by V‐doped Co2P4O12 delivers low voltages for overall water and urea splitting. The superior performance suggests that the proposed V‐doping strategy is a promising way to regulate electrocatalytic activity for catering to green electrocatalytic applications.

The Multifunctionality of Lanthanum-Strontium Cobaltite Nanopowder: High-Pressure Magnetic Studies and Excellent Electrocatalytic Properties for OER.

Simultaneous study of magnetic and electrocatalytic properties of cobaltites under extreme conditions expands the understanding of physical and chemical processes proceeding in them with the possibility of their further practical application. Therefore, La0.6Sr0.4CoO3 (LSCO) nanopowders were synthesized at different annealing temperatures tann = 850-900 °C, and their multifunctional properties were studied comprehensively. As tann increases, the rhombohedral perovskite structure of the LSCO becomes more single-phase, whereas the average particle size and dispersion grow. Co3+ and Co4+ are the major components. It has been found that LSCO-900 shows two main Curie temperatures, TC1 and TC2, associated with a particle size distribution. As pressure P increases, average ⟨TC1⟩ and ⟨TC2⟩ increase from 253 and 175 K under ambient pressure to 268 and 180 K under P = 0.8 GPa, respectively. The increment of ⟨dTC/dP⟩ for the smaller and bigger particles is sufficiently high and equals 10 and 13 K/GPa, respectively. The magnetocaloric effect in the LSCO-900 nanopowder demonstrates an extremely wide peak δTfwhm > 50 K that can be used as one of the composite components, expanding its working temperature window. Moreover, all LSCO samples showed excellent electrocatalytic performance for the oxygen evolution reaction (OER) process (overpotentials of only 265-285 mV at a current density of 10 mA cm-2) with minimal η10 for LSCO-900. Based on the experimental data, it was concluded that the formation of a dense amorphous layer on the surface of the particles ensures high stability as a catalyst (at least 24 h) during electrolysis in 1 M KOH electrolyte.

Experimental observation and characterization of amorphous carbon generated in graphene on gold nanoparticles.

The interaction of graphene with gold nanoparticles is investigated using transmission electron microscopy. We observe gold-nanoparticle-mediated etching of graphene flakes, often leading to hole formation. Further, using a combination of high-angle annular dark field imaging and electron energy loss spectroscopy, we highlight that the catalytic effects of gold nanoparticles on graphene lead to the formation of amorphous carbon layers. From the extracted diffractograms, we observe regions with diffraction halos as well as some regions with a weak tetrahedral motif. Using independently performed Raman measurements, we confirm the presence of tetrahedral amorphous carbon as well as mixed graphitic-amorphous regions. For the amorphous carbon regions with mixed sp2-sp3 states, the Raman G peak is red-shifted to 1564 cm-1 and an I D/I G ratio of 0.63 indicates less than 20% sp3 content. For the tetrahedral amorphous carbon regions, we observe that the Raman G peak is at 1580 cm-1, close to that of monolayer graphene. However, there is no Raman D peak, i.e., I D/I G = 0, which indicates close to 100% sp3 content. The translation of the Raman G peak location and the I D/I G ratios is on par with the amorphization trajectory analysis of Ferrari and Robertson (Phys. Rev. B: Condens. Matter Mater. Phys., 2000, 61, 14095) and validates the conversion route of graphite to amorphous carbon to tetrahedral amorphous carbon. The presented method provides a promising pathway for creating defect-induced amorphous carbon at room temperature, which has a broader impact on the electronics and semiconductor industries.

Phosphorus doping to promote the reconstruction of NiS nanorods for efficient electrocatalytic water oxidation

Transition metal sulfides have been verified as effective precatalysts for OER in alkaline conditions, and the in-situ reconstructed metal (oxy)hydroxides on their surface were the real active sites. The rational reconstruction can regulate the amount and chemical state of the metal (oxy)hydroxides and thus promote the OER performance efficiently, but also remains a challenge. Herein, we report a unique rationally controllable in-situ anodic electrochemical activation (AEA) strategy to promote the surface reconstruction for the formation of amorphous NiOOH layer onto the P-doped NiS nanorod arrays on nickel foam (P-NiS@NiOOH-aea/NF). The doping of P atom promotes the dissolution of S and accelerates the reconstitution of NiOOH on its surface. The optimized P-NiS@NiOOH-aea/NF through the unique AEA strategy exhibits outstanding OER activity requiring ultra-low overpotentials of 203 and 349 mV to reach 10 and 1000 mA cm−2, respectively, together with robust electrocatalytic stability and satisfactory selectivity (nearly 100% Faraday efficiency) in 1.0 M KOH solution. The density functional theory (DFT) calculations further demonstrate that heteroatomic P-doping reduces the adsorption free energy of intermediate species and enhances the OER intrinsic activity of adjacent nickel active site. This work has a guiding significance for the rational design of introducing anions in the in-situ reconstruction process.

Soft Surface Activated Bonding of Hydrophobic Silicon Substrates

Surface Activated Bonding (SAB) is interesting for strong silicon to silicon bonding at room temperature without any annealing needed, afterwards (1). Although it is a well-known technique, the activation step, in particular, is scarcely documented. This paper offers insights about the impact of soft activation parameters on the amorphous region at the bonding interface. In addition, the adherence energy of hydrophobic silicon bonding with SAB is quantified to better understand bonding mechanisms.With very low dose and acceleration activation parameters, the surface preparation prior to bonding becomes of paramount importance. Indeed, the silicon native oxide is typically removed during the activation step. The thin amorphous silicon region is a side effect of this singular surface preparation(2).In order to work around this potential roadblock, we used instead hydrophobic surface preparation to remove the native oxide, before entering into the activation step. Two types of preparation were evaluated in this study. First, a standard “HF-Last” chemical treatment was used on standard silicon wafers. This treatment removed the silicon native oxide and passivated the surface with Si-H and, to a lesser extent, Si-F bonds (3). We otherwise used epitaxy-reconstructed silicon wafers with fully hydrophobic surfaces (4). Silicon native oxide was removed thanks to an ultra-pure H2 bake at 1100°C, 20 Torr for 2 minutes in an epitaxy chamber. Then, several tens of nm of Silicon were deposited at 950°C to obtain, after another H2 bake, a silicon surface fully passivated by hydrogen atoms with atomically smooth terraces and mono-atomic step edges.Our EVG®ComBond® bonding tool, operating under ultra-high vacuum (UHV), is equipped with an accelerated argon ion beam to perform the activation step. The softest functional settings, on our set up, are 50V (acceleration) and 26 mA (dose). After beam initialization, the two sets of substrates pass through the activation chamber. Activated substrates are then transferred to the bonding chamber within 5 minutes of handling.The exposure time in the activation chamber was evaluated, the aim being to remove adsorbed hydrogen atoms on the silicon surface without any amorphous silicon generation. Different characterization techniques such as transmission electron microscopy or FTIR-MIR were used to quantify the amorphous layer formation and the potential Si-H bonds remaining (after activation). The adherence energy of the bonded pair was measured by a double cantilever beam method under prescribed displacement control in anhydrous atmosphere (5).Figure 1 shows the adherence energy (Gc=2γc) in mJ/m² as a function of activation exposure time with soft activation parameters for both wafer preparations. The 0s reference bonding was conducted without passing through the activation module. We then had very low adherence energies, around 50 mJ/m², as expected for standard hydrophobic silicon wafer bonding under UHV (6). Upon Ar+ exposure, behaviors were very different depending on surface preparation. The adherence energy barely increased with the Ar+ exposure time for “HF-Last” surfaces. Meanwhile, even 1s of exposure to Ar+ had a definite impact on the adherence energy of epi-reconstructed, atomically smooth silicon surfaces, which was definitely higher. The maximum difference between both wafer preparations occurred for 30 up to 60 seconds exposure times. This indicate a change in the bonding mechanism as the comparatively high roughness of the “HF-Last” silicon wafer started to be counter-balanced by activation.The experimental set up, the manufacturing process, as well as further characterizations will be presented. Cross-sectional TEM imaging of the bonding interface, FTIR-MIR and AFM measurements after surface preparation will help us better understand the specificities of such soft activation process on the SAB of hydrophobic surfaces. The impact of the amorphous silicon layer on bonding will be discussed. Suga T et al. STRUCTURE OF A1-A1 A N D A1-Si3N4 INTERFACES BONDED AT ROOM TEMPERATURE BY MEANS OF THE SURFACE ACTIVATION METHOD. Acta Metallurgica et Materialia 1992.Takagi H et al. Surface activated bonding of silicon wafers at room temperature. Appl Phys Lett. 1996.Abbadie A et al. Low thermal budget surface preparation of Si and SiGe. Appl Surf Sci. 2004.Sordes D et al. Nanopackaging of Si(100)H Wafer for Atomic-Scale Investigations. 2017.Maszara WP et al. Bonding of silicon wafers for silicon‐on‐insulator. J Appl Phys. 15 nov 1988;64(10):4943-50.Tong QY et al. The Role of Surface Chemistry in Bonding of Standard Silicon Wafers. J Electrochem Soc. 1997. Figure 1

The Role of Carbon in Metal-Organic Chemical Vapor Deposition-Grown MoS2 Films.

Acquiring homogeneous and reproducible wafer-scale transition metal dichalcogenide (TMDC) films is crucial for modern electronics. Metal-organic chemical vapor deposition (MOCVD) offers a promising approach for scalable production and large-area integration. However, during MOCVD synthesis, extraneous carbon incorporation due to organosulfur precursor pyrolysis is a persistent concern, and the role of unintentional carbon incorporation remains elusive. Here, we report the large-scale synthesis of molybdenum disulfide (MoS2) thin films, accompanied by the formation of amorphous carbon layers. Using Raman, photoluminescence (PL) spectroscopy, and transmission electron microscopy (TEM), we confirm how polycrystalline MoS2 combines with extraneous amorphous carbon layers. Furthermore, by fabricating field-effect transistors (FETs) using the carbon-incorporated MoS2 films, we find that traditional n-type MoS2 can transform into p-type semiconductors owing to the incorporation of carbon, a rare occurrence among TMDC materials. This unexpected behavior expands our understanding of TMDC properties and opens up new avenues for exploring novel device applications.

Effects of fluorine on dynamic reaction interfaces in hydrothermal feldspar alteration

Fluid-induced mineral reactions exert an important control on the physico-chemical properties of the crust and hydrothermal plumbing systems. Feldspars are the most abundant minerals in the Earth's crust and a major host of the main cations found in geofluids (Na, K, Ca). In previous work, we discovered that K-feldspar-albite-sanidine zonation textures developed dynamically when sanidine ((K,Na)AlSi3O8) was reacted with NaCl or NaF in H216O- and H218O-enriched solutions at 600 °C and 2 kbar in a closed system. Based on a detailed SEM and TEM characterisation, the present study aims to constrain the reaction mechanism and the effect of fluorine on reaction kinetics and overall reaction textures in alkali feldspar replacement reaction interfaces. Replacement of high-sanidine (Sa) by albite (Ab) and/or K-feldspar (Kfs) proceeded via an interface-coupled dissolution-reprecipitation reaction, with the products preserving the crystallographic orientation of the parent Sa in both NaCl- and NaF-bearing solutions. Mineral interfaces with different micro-textures were observed depending on the nature of the interface (Ab-Sa, Kfs-Ab, Kfs-Sa) and whether the reaction occurred in NaCl-only or NaF-bearing solutions. Abundant amorphous domains (25–50 nm thick) occur both within Ab and at Ab-Sa and Kfs-Ab interfaces formed in NaF-bearing solutions. At the Kfs-Sa interface formed in NaCl-only solutions, a complex interfacial zone characterised by a high density of defects may represent sealed fluid pathways. These results reveal that the nature of the reaction interface depends on both mineral properties, in particular microtextures (i.e. polysynthetic twinning in Ab); and solution chemistry; this directly affects porosity development, the chemical environment at the interface, and chemical exchanges between the reaction front and the bulk solution. Fluorine aids the formation of amorphous layers that modify nucleation mechanisms; and facilitates element transport by forming Na-Si-Al-fluoride complexes, resulting in accelerated reaction rates relative to chloride-solutions. These nm- to μm-level processes contribute to efficient coupling between fluid-flow and mass transfer, explaining why sodic and potassic alteration associated with metal and fluid transport in some of the world's largest ore deposits can develop extensively, and subsequently access metals locked within silicate mineral assemblages.

Annealing effect on the barrier characteristics and interface properties of Au/Pt/Ti/n-InAlAs Schottky contacts

A comprehensive study of the annealing effect (300–400 °С) on the electrical properties, morphology and chemical composition of the Au/Pt/Ti/n-InAlAs interface (Schottky contact) is carried out. It is shown that the Schottky contact pre-annealing during the formation or primary short (∼1 min) annealing significantly increases the barrier height to the standard 0.68–0.7 eV with an ideality factor close to 1.1 due to the formation of a homogeneous amorphous TiAs layer with a small metallic (elemental) indium content. A further annealing at temperatures 300–350 °С for up to 20 min does not lead to significant changes in the morphology and electrical parameters of the Schottky contact. The annealing at the temperature of 400 °С (∼10 min) leads to an increase in the barrier height and the ideality factor to the values of 0.73 and 1.3, respectively. In this case, the formation of an about 20 nm thick TiAs layer and indium clusters shaped as a pyramids at the Ti/InAlAs interface is also observed. Analysis of the temperature dependences of Schottky barrier parameters within the Tung model showed that only structural changes at the interface after the 400 °С annealing lead to a significant increase in the Ti/InAlAs Schottky contact homogeneity, reducing the density of local regions with a lowered barrier height.

Effects of soft sparking on micro/nano structure and bioactive components of microarc oxidation coatings on selective laser melted Ti6Al4V alloy

We used the soft sparking mode to fabricate microarc oxidation coatings containing micro/nano-scale pores and bioactive Ca/P components on Ti6Al4V alloy samples formed by selective laser melting. The effect of soft sparking on the microstructure and corrosion resistance of the coatings and the codeposition mechanism of the electrolyte anions in the soft sparking layer were investigated using different negative/positive charge ratios. The results showed that the negative charge significantly decreased the intensity of microarc discharge, resuling in the soft sparking phenomenon, which promotes the formation of a thin amorphous TiO2 layer at the barrier layer/substrate interface. In turn, this interface facilitated the electron tunneling and aggregation of the electrolyte anions, which leads to soft sparking at voltages significantly lower than the breakdown voltage of the anodic oxide film on the selective laser melted Ti alloys. Soft sparking promoted the codeposition of the electrolyte anions, including PO43− and Ca2+ ions, in the form of bulk amorphous phases in the coating formed by soft sparking. The soft sparking layer contained amorphous phases, which were corroded more readily than that the outer ceramic layer. However, the submicro/nano-scale pores in the soft sparking layer improved its corrosion resistance. With an increase in negative/positive charge ratio, the effect of soft sparking on the surface morphology of the MAO coating weakened, and the amounts of Ca and P codeposited in the soft sparking layer increased. Finally, the corrosion resistance of the coating was found to first increase and then decrease, reaching the maximum at the 1.1 ratio.

Electrochemical Preparation of Crystalline Hydrous Iridium Oxide and Its Use in Oxygen Evolution Catalysis.

Even the most stable Ir-based oxides inevitably encounter a severe degradation problem during the oxygen evolution reaction (OER) in acid, resulting in quick formation of amorphous IrOx layers on the catalyst surface. Unfortunately, there is still a lack of fundamental understanding of such hydrous IrOx layers, including the atomic arrangement, key active structure, compositions, chemical stability, and so on. In this work, we demonstrate an electrochemical strategy to prepare two types of protonated iridium oxides with well-defined crystalline structures: one possesses a 2D layered structure (denoted as α-HxIrO3) and the other consists of 3D interconnected polymorphs (denoted as β-HxIrO3). Both protonated iridium oxides demonstrate superior electrochemical stabilities with 6 times suppressed Ir dissolution comparing to the initial Li2IrO3 and rutile IrO2. It is hypothesized that the enriched protons and fast diffusions in these two protonated HxIrO3 crystal oxides may promote surface structural stability by suppressing the formation of high-valence Ir species at the solid-liquid interfaces during OER. Overall, the results of this work shed light on the role of proton dynamics toward the OER processes on the catalyst surface in acid media.

Di(arylcarbazole) Substituted Oxetanes as Efficient Hole Transporting Materials with High Thermal and Morphological Stability for OLEDs

A group of di(arylcarbazole)-substituted oxetanes has been prepared in Suzuki reactions by using the key starting material 3,3-di[3-iodocarbazol-9-yl]methyloxetane and various boronic acids (fluorophenylboronic acid, phenylboronic acid or naphthalene-1-boronic acid). Full characterization of their structure has been presented. The low molar mass compounds represent materials having high thermal stability with 5% mass loss thermal degradation temperatures in the range of 371-391 °C. Glass transition temperatures of the materials are also very high and range from 107 °C to 142 °C, which is a big advantage for formation of stable amorphous layers for optoelectronic devices, i.e., organic light emitting diodes. Hole transporting properties of the prepared materials were confirmed in formed organic light emitting diodes with tris(quinolin-8-olato)aluminium (Alq3) as a green emitter, which also served as an electron transporting layer. In the device's materials, 3,3-di[3-phenylcarbazol-9-yl]methyloxetane (5) and 3,3-di[3-(1-naphthyl)carbazol-9-yl]methyloxetane (6) demonstrated superior hole transporting properties than that of material 3,3-di[3-(4-flourophenyl)carbazol-9-yl]methyloxetane (4) based device. When material 5 was used in the device structure, the OLED demonstrated rather low turn-on voltage of 3.7 V, luminous efficiency of 4.2 cd/A, power efficiency of 2.6 lm/W and maximal brightness exceeding 11670 cd/m2. HTL of 6 based device also showed exclusive OLED characteristics. The device was characterized by turn-on voltage of 3.4 V, maximum brightness of 13193 cd/m2, luminous efficiency of 3.8 cd/A and power efficiency of 2.6 lm/W. An additional hole injecting-transporting layer (HI-TL) of PEDOT considerably improved functions of the device with HTL of compound 4. The modified OLED with a layer of the derivative 4 demonstrated exclusive characteristics with turn-on voltage of 3.9 V, high luminous efficiency of 4.7 cd/A, power efficiency of 2.6 lm/W and maximal brightness exceeding 21,000 cd/m2. These observations confirmed that the prepared materials have a big potential in the field of optoelectronics.

Synthesis of Sb2S3 nanosphere layer by chemical bath deposition for the photocatalytic degradation of methylene blue dye.

An antimony tri-sulfide Sb2S3 nanosphere photocatalyst was effectively deposited utilizing sodium thiosulfate and antimony chloride as the starting precursors in a chemical bath deposition process. This approach is appropriate for the large-area depositions of Sb2S3 at low deposition temperatures without the sulfurization process since it is based on the hydrolytic decomposition of starting compounds in aqueous solution. X-ray diffraction patterns and Raman spectroscopy analysis revealed the formation of amorphous Sb2S3 layers. The scanning electron microscopy images revealed that the deposited Sb2S3 has integrated small nanospheres into sub-microspheres with a significant surface area, resulting in increased photocatalytic activity. The optical direct bandgap of the Sb2S3 layer was estimated to be about 2.53 eV, making amorphous Sb2S3 appropriate for the photodegradation of organic pollutants in the presence of solar light. The possibility of using the prepared Sb2S3 layer in the photodegradation of methylene blue aqueous solutions was investigated. The degradation of methylene blue dye was performed to evaluate the photocatalytic property of Sb2S3 under visible light. The amorphous Sb2S3 exhibited photocatalytic activity for the decolorization of methylene blue solution under visible light. The mechanism for the photocatalytic degradation of methylene blue has been proposed. Our results suggest that the amorphous Sb2S3 nanospheres are valuable material for addressing environmental remediation issues.

Geochemical bio-signatures in Martian analogue basaltic environments using laboratory experiments and thermochemical modelling

The identification of geochemical bio-signatures is important for assessing whether life existed on early Mars. In this paper, experimental microbiology and thermochemical modelling were combined to identify potential inorganic bio-signatures for life detection on early Mars. An analogue mixed microbial community from an analogue terrestrial fluvio-lacustrine environment similar to an ancient lacustrine system at Gale Crater was used to study microbial dissolution of a basalt regolith simulant and the formation of bio-signatures over a short time frame (1°month) at 14°C, 2 bar. Microbial growth influenced element dissolution (Mg, Fe, Mn, Ca and K) and the formation of morphologies and Fe-Si amorphous layers on mineral surfaces. Thermochemical models were performed at 14°C, 2 bar; the results were compared with experimental data to predict bio-signatures that would occur over geological timescales. The pH was varied to simulate abiotic and biotic experimental conditions. Model results suggest that, at water to rock ratios of 100 to 38, a less complex secondary mineral assemblage forms during biotic dissolution compared to abiotic weathering. Carbonates, quartz, pyrite and hydroxyapatite form under biotic conditions, whereas in the abiotic system magnetite and phyllosilicates would also precipitate. These results could be used to distinguish between abiotic and biotic basalt weathering processes, aiding the interpretation of data from Mars exploration missions.

Nanometer-sized etching of lithium niobate domain wall devices

Ferroelectric LiNbO3 single crystals have piezoelectric, pyroelectric and electro-optic properties and are widely used in nonvolatile memories, sensors, and electro-optic modulators. The material is hard and relatively inert for dying etching using thick Cr/Ni mask layers which are incompatible with the CMOS manufacturing technologies. Moreover, the etching angles are generally below 80° that could result in poor polarization retention and a large imprint effect. Here we developed an etching technique on the basis of the solid-state reaction and wet solution corrosion together that used CMOS-compatible SiO2 masks to fabricate large arrays of LiNbO3 nanodevices in high precision. The LiNbO3 nanopatterns at the regions beyond the SiO2 masks can react with the deposited Al metal below 500 °C in formation of amorphous layers in targeted thicknesses that vary with the annealing temperature and time at a reduced atmosphere. The amorphous layers can be dissolved in mixed solutions of H2O, NH4OH, and H2O2 at 85 °C, and the etching angles of memory cells in lateral sizes of 20–220 nm can approach 90° after the passivation of the LiNbO3 surface layer. The transmission electron microscope study shows the oxygen deficiency at the surface. After the connection of the cell to two side electrodes, domain switching occurs under an applied horizontal electrode field along the polar Z-axis accompanying the formation of conducting domain walls against the peripheral unswitched domain at the substrate. The read current can highly reach the level of 2–20 μA in high reliability. This etching technique promotes the large-scale fabrication of LiNbO3 nanodevices on the Si platform.

Surface microstructures of lunar soil returned by Chang’e-5 mission reveal an intermediate stage in space weathering process

The lunar soils evolution over time is mainly caused by space weathering that includes the impacts of varying-sized meteoroids and charged particles implantation of solar/cosmic winds as well. It has long been established that space weathering leads to the formation of outmost amorphous layers (50–200 nm in thickness) embedded nanophase iron (npFe0) around the mineral fragments, albeit the origin of the npFe0 remains controversial . The Chang’e-5 (CE-5) mission returned samples feature the youngest mare basalt and the highest latitude sampling site , providing an opportunity to seek the critical clues for understanding the evolution of soils under space weathering. Here, we report the surface microstructures of the major minerals including olivine, pyroxene, anorthite, and glassy beads in the lunar soil of CE-5. Unlike the previous observations, only olivine in all crystals is surrounded by a thinner outmost amorphous SiO2 layer (∼10 nm thick) and embedded wüstite nanoparticles FeO (np-FeO, 3–12 nm in size) instead of npFe0. No foreign volatile elements deposition layer and solar flare tracks can be found on the surface or inside the olivine and other minerals. This unique rim structure has not been reported for any other lunar, terrestrial, Martian, or meteorite samples so far. The observation of wüstite FeO and the microstructures support the existence of an intermediate stage in space weathering for lunar minerals by thermal decomposition.