Influence of Sulfurization Time on Sb2S3 Synthesis Using a New Graphite Box Design

In recent years, antimony sulfide (Sb2S3) has been investigated as a photovoltaic absorber material due to its suitable absorber coefficient, direct band gap, extinction coefficient, earth-abundant, and environmentally friendly constituents. Therefore, this work proposes Sb2S3 film preparation by an effective two-step process using a new graphite box design and sulfur distribution, which has a high repeatability level and can be scalable. First, an Sb thin film was deposited using the RF-Sputtering technique, and after that, the samples were annealed with elemental sulfur into a graphite box, varying the sulfurization time from 20 to 50 min. The structural, optical, morphological, and chemical characteristics of the resulting thin films were analyzed. Results reveal the method's effectivity and the best properties were obtained for the sample sulfurized during 40 min. This Sb2S3 thin film presents an orthorhombic crystalline structure, elongated grains, a band gap of 1.69 eV, a crystallite size of 15.25 Å, and a nearly stoichiometric composition. In addition, the formation of a p-n junction was achieved by depositing silver back contact on the Glass/FTO/CdS/Sb2S3 structure. Therefore, the graphite box design has been demonstrated to be functional to obtain Sb2S3 by a two-step process.

Unusual Raman Enhancement Effect of Ultrathin Copper Sulfide

In surface-enhanced Raman spectroscopy (SERS), 2D materials are explored as substrates owing to their chemical stability and reproducibility. However, they exhibit lower enhancement factors (EFs) compared to noble metal-based SERS substrates. This study demonstrates the application of ultrathin covellite copper sulfide (CuS) as a cost-effective SERS substrate with a high EF value of 7.2 × 104 . The CuS substrate is readily synthesized by sulfurizing a Cu thin film at room temperature, exhibiting a Raman signal enhancement comparable to that of an Au noble metal substrate of similar thickness. Furthermore, computational simulations using the density functional theory are employed and time-resolved photoluminescence measurements are performed to investigate the enhancement mechanisms. The results indicate that polar covalent bonds (Cu─S) and strong interlayer interactions in the ultrathin CuS substrate increase the probability of charge transfer between the analyte molecules and the CuS surface, thereby producing enhanced SERS signals. The CuS SERS substrate demonstrates the selective detection of various dye molecules, including rhodamine 6G, methylene blue, and safranine O. Furthermore, the simplicity of CuS synthesis facilitates large-scale production of SERS substrates with high spatial uniformity, exhibiting a signal variation of less than 5% on a 4-inch wafer.

Two-Channel Indirect-Gap Photoluminescence and Competition between the Conduction Band Valleys in Few-Layer MoS2

MoS2 is a two-dimensional layered transition metal dichalcogenide with unique electronic and optical properties. The fabrication of ultrathin MoS2 is vitally important, since interlayer interactions in its ultrathin varieties will become thickness-dependent, providing thickness-governed tunability and diverse applications of those properties. Unlike with a number of studies that have reported detailed information on direct bandgap emission from MoS2 monolayers, reliable experimental evidence for thickness-induced evolution or transformation of the indirect bandgap remains scarce. Here, the sulfurization of MoO3 thin films with nominal thicknesses of 30 nm, 5 nm and 3 nm was performed. All sulfurized samples were examined at room temperature with spectroscopic ellipsometry and photoluminescence spectroscopy to obtain information about their dielectric function and edge emission spectra. This investigation unveiled an indirect-to-indirect crossover between the transitions, associated with two different Λ and K valleys of the MoS2 conduction band, by thinning its thickness down to a few layers.

Co4S3 Nanoparticles Confined in an MnS Nanorod-Grafted N, S-Codoped Carbon Polyhedron for Highly Efficient Sodium-Ion Batteries

Sodium-ion batteries (SIBs) suffer from limited ion diffusion and structural expansion, generating the urgent demand for Na+ accommodable materials with promising architectures. In this work, the rational exploration for Co4S3 nanoparticles confined in an MnS nanorod-grafted N, S-codoped carbon polyhedron (Co-Mn-S@N-S-C) is achieved by the in situ growth of MOF on MnO2 nanorod along with the subsequent carbonization and sulfurization. Benefiting from the distinctive nanostructure, the Co-Mn-S@N-S-C anode delivers excellent structural stability, resulting in prolonged cycling stability with a capacity retention of 90.2% after 1000 cycles at 2 A g-1. Moreover, the reaction storage mechanism is clarified by the in situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. The results indicate that properly designed electrode materials have huge potential applications for highly efficient energy storage devices.

Fe- and S-Modified BiOI as Catalysts to Oxygen Evolution and Hydrogen Evolution Reactions in Overall Photoelectrochemical Water Splitting

Developing catalysts with superior activity to hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is equally important to the overall photoelectrochemical water splitting to produce hydrogen. In this work, bismuth oxyiodide (BiOI), iron-modified bismuth iodide Fe/BiOI, and the sulfurized S-Fe/BiOI were prepared using the solvothermal method. The three materials all have good absorption ability for visible light. The photoelectrochemical catalytic activity of BiOI to oxygen evolution reaction (OER) is significantly enhanced after iron modification, while the sulfurized product S-Fe/BiOI exhibits better catalytic activity to hydrogen evolution reaction (HER). Hence, OER and HER can be simultaneously catalyzed by using Fe/BiOI and S-Fe/BiOI as anodic and cathodic catalysts to facilitate the overall photoelectrochemical water splitting process.

Reduction of Friction and Wear for AISI321 Stainless Steel through Surface Modification Using Nanocrystallization

Through surface nanocrystallization and low-temperature ion sulfurization, the nanocrystalline/FeS thin film with excellent friction-reduction and antiwear properties was fabricated on the surface of AISI321 stainless steel. The nanocrystallization treatment formed the high hardness and active nanocrystalline structure on the surface of AISI321, with the harness increased from 4.6 GPa to 7.56 GPa. Furthermore, the significantly refined nanostructure strongly increased the concentration of S element in comparison with the single-sulfurized layer on the substrate. Tribological tests reveal that both the original AISI321 substrate and the single-sulfurizing-treated samples are subject to severe abrasion. Single nanocrystallization treatment can improve the wear resistance of AISI321, while the compound treatment can obviously improve the comprehensive tribological properties. The compound-modified layer presents excellent tribological properties with the lowest coefficient of friction (COF) of 0.33, which is related to the increased hardness of the substrate and increased thickness, density, and homogeneity of the sulfurized layer. Furthermore, a physical model is developed for the vacuum tribological behavior of the samples after different treatments. This model provides a reference for revealing the tribological mechanism of the compound-modified layer treated using surface nanocrystallization-assisted chemical heat treatment.

A Versatile Sulfur-Assisted Pyrolysis Strategy for High-Atom-Economy Upcycling of Waste Plastics into High-Value Carbon Materials

With the overconsumption of disposable plastics, there is a considerable emphasis on the recycling of waste plastics to relieve the environmental, economic, and health-related consequences. Here, a sulfur-assisted pyrolysis strategy is demonstrated for versatile upcycling of plastics into high-value carbons with an ultrahigh carbon-atom recovery (up to 85%). During the pyrolysis process, the inexpensive elemental sulfur molecules are covalently bonded with polymer chains, and then thermally stable intermediates are produced via dehydrogenation and crosslinking, thereby inhibiting the decomposition of plastics into volatile small hydrocarbons. In this manner, the carbon products obtained from real-world waste plastics exhibit sulfur-rich skeletons with an enlarged interlayer distance, and demonstrate superior sodium storage performance. It is believed that the present results offer a new solution to alleviate plastic pollution and reduce the carbon footprint of plastic industry.

Nucleation and Growth of Monolayer MoS2 at Multisteps of MoO2 Crystals by Sulfurization

Two-dimensional (2D) materials and their heterostructures are promising for next-generation optoelectronics, spintronics, valleytronics, and electronics. Despite recent progress in various growth studies of 2D materials, mechanical exfoliation of flakes is still the most common method to obtain high-quality 2D materials because precisely controlling material growth and synthesizing a single domain during the growth process of 2D materials, for the desired shape and quality, is challenging. Here, we report the nucleation and growth behaviors of monolayer MoS₂ by sulfurizing a faceted monoclinic MoO₂ crystal. The MoS₂ layers nucleated at the thickness steps of the MoO₂ crystal and grew epitaxially with crystalline correlation to the MoO₂ surface. The epitaxially grown MoS₂ layer expands outwardly on the SiO₂ substrate, resulting in a monolayer single-crystal film, despite multiple nucleations of MoS₂ layers on the MoO₂ surface owing to several thickness steps. Although the photoluminescence of MoS₂ is quenched owing to efficient charge transfer between MoS₂ and metallic MoO₂, the MoS₂ stretched out to the SiO₂ substrate shows a high carrier mobility of (15 cm² V^-1 s^-1), indicating that a high-quality monolayer MoS₂ film can be grown using the MoO₂ crystal as a seed and precursor. Our work shows a method to grow high-quality MoS₂ using a faceted MoO₂ crystal and provides a deeper understanding of the nucleation and growth of 2D materials on a step-like surface.

Vapor-Liquid-Solid Growth of Site-Controlled Monolayer MoS2 Films Via Pressure-Induc ed Supercritical Phase Nucleation

In this study, a novel pressure-induced supercritical phase nucleation method is proposed to synthesize monolayer MoS₂ films, which is promoter free and can avoid contamination of films derived from these heterogeneous promoters in most of the existing techniques. The low-crystallinity and size-controlled MoO₂(acac)₂ particles are recrystallized on the substrate via the pressure-sensitive solvent capacity of supercritical CO₂ and these particles are used as growth sites. The size of single-crystal MoS₂ on the substrate is found to be dependent on the wetting area of the pyrolyzed precursor droplets (MoO₂) on the surface, and the formation of continuous films with high coverage is mainly controlled by the coalescence of MoO₂ droplets. It is enhanced by the increase of the nucleation site density, which can be adjusted by the supersaturation of the supercritical fluid solution. Our findings pave a new way for the controllable growth of MoS₂ and other two-dimensional materials and provide sufficient and valuable evidence for vapor-liquid-solid growth.

Comparative Study between Sulfurized MoS2 from Molybdenum and Molybdenum Trioxide Precursors for Thin-Film Device Applications

Two-dimensional (2D) materials have been studied as an emerging class of nanomaterials owing to their attractive properties in nearly every field of science and technology. Molybdenum disulfide (MoS₂) is one of the more promising candidates of these atomically thin 2D materials for its technological potential. The facile synthesis of MoS₂ remains a matter of broad interest. In this study, MoS₂ was synthesized by chemical vapor deposition sulfurization at various temperatures (550 °C, 650 °C, and 750 °C) of either precursor molybdenum metal (Mo) or molybdenum trioxide (MoO₃) deposited on silicon/silicon dioxide (Si/SiO₂) via e-beam evaporation. Monolayer, bilayer, and few layers sulfurized samples have been grown and verified by Raman, photoluminescence spectroscopy, XRD, XPS, and AFM. MoO₃ sulfurization provided monolayer growth in comparison to Mo sulfurization under the same conditions and precursor thicknesses. Optical microscopy showed the homogeneous nature of grown samples. A main finding of this work is that MoO₃ sulfurization produced higher quality MoS₂ as compared to those grown by an Mo precursor. Device characteristics based on monolayer MoO₃ sulfurized MoS_2-x include nonvolatile resistive switching with I_on/I_off ≈ 10⁴ at a relatively low operating bias of ±1 V. In addition, field-effect transistor characteristics revealed p-type material growth with a carrier mobility ∼ 41 cm² V^-1 s^-1, which is in contrast to typically observed n-type characteristics.

Beyond the Platinum Era─Scalable Preparation and Electrochemical Activation of TaS2 Flakes

Among 2D materials, transition-metal dichalcogenides (TMDCs) of group 5 metals recently have attracted substantial interest due to their superior electrocatalytic activity toward hydrogen evolution reaction (HER). However, a straightforward and efficient synthesis of the TMDCs which can be easily scaled up is missing. Herein, we report an innovative, simple, and scalable method for tantalum disulfide (TaS₂) synthesis, involving CS₂ as a sulfurizing agent and Ta₂O₅ as a metal precursor. The structure of the created TaS₂ flakes was analyzed by Raman, XRD, XPS, SEM, and HRTEM techniques. It was demonstrated that a tuning between 1T (metallic) and 3R (semiconductor) TaS₂ phases can be accomplished by varying the reaction conditions. The created materials were tested for HER, and the electrocatalytic activity of both phases was significantly enhanced by electrochemical self-activation, up to that comparable with the Pt one. The final values of the Tafel slopes of activated TaS₂ were found to be 35 and 43 mV/dec for 3R-TaS₂ and 1T-TaS₂, respectively, with the corresponding overpotentials of 63 and 109 mV required to reach a current density of 10 mA/cm². We also investigated the mechanism of flake activation, which can be attributed to the changes in the flake morphology and surface chemistry. Our work provides a scalable and simple synthesis method to produce transition-metal sulfides which could replace the platinum catalyst in water splitting technology.

Novel sulfur isotope analyses constrain sulfurized porewater fluxes as a minor component of marine dissolved organic matter

Marine dissolved organic matter (DOM) is a major reservoir that links global carbon, nitrogen, and phosphorus. DOM is also important for marine sulfur biogeochemistry as the largest water column reservoir of organic sulfur. Dissolved organic sulfur (DOS) can originate from phytoplankton-derived biomolecules in the surface ocean or from abiotically "sulfurized" organic matter diffusing from sulfidic sediments. These sources differ in ³⁴S/³²S isotope ratios (δ³⁴S values), with phytoplankton-produced DOS tracking marine sulfate (21‰) and sulfurized DOS mirroring sedimentary porewater sulfide (∼0 to -10‰). We measured the δ³⁴S values of solid-phase extracted (SPE) DOM from marine water columns and porewater from sulfidic sediments. Marine DOM_SPE δ³⁴S values ranged from 14.9‰ to 19.9‰ and C:S ratios from 153 to 303, with lower δ³⁴S values corresponding to higher C:S ratios. Marine DOM_SPE samples showed consistent trends with depth: δ³⁴S values decreased, C:S ratios increased, and δ¹³C values were constant. Porewater DOM_SPE was ³⁴S-depleted (∼-0.6‰) and sulfur-rich (C:S ∼37) compared with water column samples. We interpret these trends as reflecting at most 20% (and on average ∼8%) contribution of abiotic sulfurized sources to marine DOS_SPE and conclude that sulfurized porewater is not a main component of oceanic DOS and DOM. We hypothesize that heterogeneity in δ³⁴S values and C:S ratios reflects the combination of sulfurized porewater inputs and preferential microbial scavenging of sulfur relative to carbon without isotope fractionation. Our findings strengthen links between oceanic sulfur and carbon cycling, supporting a realization that organic sulfur, not just sulfate, is important to marine biogeochemistry.

Field-Effect Transistor Based on 2D Microcrystalline MoS2 Film Grown by Sulfurization of Atomically Layer Deposited MoO3

Atomically thin molybdenum disulfide (MoS₂) is a promising channel material for next-generation thin-body field-effect transistors (FETs), which makes the development of methods allowing for its controllable synthesis over a large area an essential task. Currently, one of the cost-effective ways of its synthesis is the sulfurization of preliminary grown oxide- or metallic film. However, despite apparent progress in this field, the electronic quality of the obtained MoS₂ is inferior to that of exfoliated samples, making the detailed investigation of the sulfurized films' properties of great interest. In this work, we synthesized continuous MoS₂ films with a thickness of ≈2.2 nm via the sulfurization of an atomic-layer-deposited MoO₃ layer. X-ray photoelectron spectroscopy, transmission electron microscopy, and Raman spectroscopy indicated the appropriate chemical composition and microcrystalline structure of the obtained MoS₂ films. The semiconductor quality of the synthesized films was confirmed by the fabrication of a field-effect transistor (FET) with an I_on/I_off ratio of ≈40, which was limited primarily by the high contact resistance. The Schottky barrier height at the Au/MoS₂ interface was found to be ≈1.2 eV indicating the necessity of careful contact engineering. Due to its simplicity and cost-effectiveness, such a technique of MoS₂ synthesis still appears to be highly attractive for its applications in next-generation microelectronics. Therefore, further research of the electronic properties of films obtained via this technique is required.

Multiscale Investigation of the Structural, Electrical and Photoluminescence Properties of MoS2 Obtained by MoO3 Sulfurization

In this paper, we report a multiscale investigation of the compositional, morphological, structural, electrical, and optical emission properties of 2H-MoS2 obtained by sulfurization at 800 °C of very thin MoO3 films (with thickness ranging from ~2.8 nm to ~4.2 nm) on a SiO2/Si substrate. XPS analyses confirmed that the sulfurization was very effective in the reduction of the oxide to MoS2, with only a small percentage of residual MoO3 present in the final film. High-resolution TEM/STEM analyses revealed the formation of few (i.e., 2-3 layers) of MoS2 nearly aligned with the SiO2 surface in the case of the thinnest (~2.8 nm) MoO3 film, whereas multilayers of MoS2 partially standing up with respect to the substrate were observed for the ~4.2 nm one. Such different configurations indicate the prevalence of different mechanisms (i.e., vapour-solid surface reaction or S diffusion within the film) as a function of the thickness. The uniform thickness distribution of the few-layer and multilayer MoS2 was confirmed by Raman mapping. Furthermore, the correlative plot of the characteristic A1g-E2g Raman modes revealed a compressive strain (ε ≈ -0.78 ± 0.18%) and the coexistence of n- and p-type doped areas in the few-layer MoS2 on SiO2, where the p-type doping is probably due to the presence of residual MoO3. Nanoscale resolution current mapping by C-AFM showed local inhomogeneities in the conductivity of the few-layer MoS2, which are well correlated to the lateral changes in the strain detected by Raman. Finally, characteristic spectroscopic signatures of the defects/disorder in MoS2 films produced by sulfurization were identified by a comparative analysis of Raman and photoluminescence (PL) spectra with CVD grown MoS2 flakes.

Activating Silent Synapses in Sulfurized Indium Selenide for Neuromorphic Computing

The transformation from silent to functional synapses is accompanied by the evolutionary process of human brain development and is essential to hardware implementation of the evolutionary artificial neural network but remains a challenge for mimicking silent to functional synapse activation. Here, we developed a simple approach to successfully realize activation of silent to functional synapses by controlled sulfurization of chemical vapor deposition-grown indium selenide crystals. The underlying mechanism is attributed to the migration of sulfur anions introduced by sulfurization. One of our most important findings is that the functional synaptic behaviors can be modulated by the degree of sulfurization and temperature. In addition, the essential synaptic behaviors including potentiation/depression, paired-pulse facilitation, and spike-rate-dependent plasticity are successfully implemented in the partially sulfurized functional synaptic device. The developed simple approach of introducing sulfur anions in layered selenide opens an effective new avenue to realize activation of silent synapses for application in evolutionary artificial neural networks.

Fabrication and characterization of well-ordered PbS nanowires in aluminum oxide template by sulfurization and vacuum injection molding processes

Lead (Pb) nanowire arrays were fabricated with anodic aluminum oxide (AAO) templates of 30, 100 and 300 nm in pore diameters. Through vacuum injection molding process, Pb/AAO composite was obtained, and lead sulfide (PbS) could further be synthesized after exposing to sulfur gas. AAO templates with different pore sizes were fabricated by using pure aluminum in a two-step anodization. Three types of solutions, which are 10 vol% sulfuric acid, 3 wt% oxalic acid and 1 vol% phosphoric acid, were adopted to achieve AAO of various pore sizes. Different sulfurization temperatures and time spans were applied for studying on the formation mechanism of PbS. Finally, the morphology, composition, structure and elements distribution of the as-prepared Pb and PbS nanowires were confirmed through the use of scanning electron microscopy, energy dispersive x-ray spectroscopy, element-mapping, x-ray diffraction and transmission electron microscopy analysis. The results indicated that Pb nanowires were successfully obtained after applying vacuum injection molding process with 50 kgf cm^-2hydraulic pressure, and PbS nano arrays can be formed by sulfurization at 500 °C for 5 h. Furthermore, an optical property, ultraviolet-visible (UV-Vis) absorption, was also measured. The measurement of the PbS nanowires showed that a significant quantum confinement effect made the energy gap produce a blue shift from 0.41 eV to 1.65 eV or 1.72 eV.

MOF-Templated Sulfurization of Atomically Dispersed Manganese Catalysts Facilitating Electroreduction of CO2 to CO

To reach a carbon-neutral future, electrochemical CO2 reduction reaction (eCO2RR) has proven to be a strong candidate for the next-generation energy system. Among potential materials, single-atom catalysts (SACs) serve as a model to study the mechanism behind the reduction of CO2 to CO, given their well-defined active metal centers and structural simplicity. Moreover, using metal-organic frameworks (MOFs) as supports to anchor and stabilize central metal atoms, the common concern, metal aggregation, for SACs can be addressed well. Furthermore, with their turnability and designability, MOF-derived SACs can also extend the scope of research on SACs for the eCO2RR. Herein, we synthesize sulfurized MOF-derived Mn SACs to study effects of the S dopant on the eCO2RR. Using complementary characterization techniques, the metal moiety of the sulfurized MOF-derived Mn SACs (MnSA/SNC) is identified as MnN3S1. Compared with its non-sulfur-modified counterpart (MnSA/NC), the MnSA/SNC provides uniformly superior activity to produce CO. Specifically, a nearly 30% enhancement of Faradaic efficiency (F.E.) in CO production is observed, and the highest F.E. of approximately 70% is identified at -0.45 V. Through operando spectroscopic characterization, the probing results reveal that the overall enhancement of CO production on the MnSA/SNC is possibly caused by the S atom in the local MnN3S1 moiety, as the sulfur atom may induce the formation of S-O bonding to stabilize the critical intermediate, *COOH, for CO2-to-CO. Our results provide novel design insights into the field of SACs for the eCO2RR.

Mist chemical vapor deposition of crystalline MoS2atomic layer films using sequential mist supply mode and its application in field-effect transistors

Molybdenum disulfide (MoS₂) mono/bilayer have been systematically investigated using atmospheric-pressure mist chemical vapor deposition (mist CVD) from (NH₄)₂MoS₄dissolved in N-methyl-2-pyrrolidone as a precursor. Film deposition was performed by alternating MoS₂mist storage within a closed chamber and mist exhaust, i.e. sequential mist supply mode at different furnace temperatures, storage times of precursor, and repetition cycles of mist supply on thermally grown SiO₂(th-SiO₂) and mist-CVD grown Al_1-xTi_xO_y(ATO) layers coated on p⁺-Si substrates. The average size of the MoS₂flake and their number of stack layers could be controlled by tuning the deposition parameters combined with substrate pretreatment. Field-effect transistors with MoS₂atomic mono/bilayer as a channel layer exhibited mobility up to 31-40 (43-55) cm²V^-1s^-1with a threshold voltage of -1.6 (-0.5) V, subthreshold slope of 0.8 (0.11) V dec.^-1, and on/off ratio of 3.2 × 10⁴(3.6 × 10⁵) onth-SiO₂(ATO) layers as gate dielectric layers without mechanical exfoliation. These findings imply that mist CVD is available for the synthesis of metal transition metal dichalcogenide and metal oxide layers as channel and gate dielectric layers, respectively.

Fabrication of Iron Pyrite Thin Films and Photovoltaic Devices by Sulfurization in Electrodeposition Method

Iron pyrite is a cheap, stable, non-toxic, and earth-abundant material that has great potential in the field of photovoltaics. Electrochemical deposition is a low-cost method, which is also suitable for large-scale preparation of iron pyrite solar cells. In this work, we prepared iron pyrite films by electrochemical deposition with thiourea and explored the effect of sulfurization on the synthesis of high-quality iron pyrite films. Upon sulfurization, the amorphous precursor film becomes crystallized iron pyrite film. Optical and electrical characterization show that its band gap is 0.89 eV, and it is an n type semiconductor with a carrier concentration of 3.01 × 10¹⁹ cm^-3. The corresponding photovoltaic device shows light response. This work suggests that sulfurization is essential in the electrochemical preparation for fabricating pure iron pyrite films, and therefore for low-cost and large-scale production of iron pyrite solar cells.

Facile Sulfurization under Ambient Condition with Na2S to Fabricate Nanostructured Copper Sulfide

The sulfurization reaction was investigated as a promising fabrication method for preparing metal sulfide nanomaterials. Traditional sulfurization processes generally require high vacuum systems, high reaction temperatures, and toxic chemicals, utilizing complicated procedures with poor composition and morphology controllability. Herein, a facile method is reported for synthesizing nanostructured copper sulfide using a sulfurization reaction with Na₂S at room temperature under non-vacuum conditions. Moreover, we demonstrate that the morphology, composition, and optical properties of nanostructured copper sulfides could be controlled by the Na₂S solution concentration and the reaction time. Nanostructured copper sulfides were synthesized in nanospheres, nanoplates, and nanoplate-based complex morphologies with various oxidation states. Furthermore, by comparing the optical properties of nanostructured copper sulfides with different oxidation states, we determined that reflectivity in the near infrared (NIR) region decreases with increasing oxidation states. These results reveal that the Na₂S solution concentration and reaction time are key factors for designing nanostructured copper sulfides, providing new insights for synthesis methods of metal sulfide nanomaterials.

Interface-engineered Co3S4/CoMo2S4nanosheets as efficient bifunctional electrocatalysts for alkaline overall water splitting

Exploring bifunctional electrocatalysts with high efficiency, inexpensive, and easy integration is still the daunt challenge for the production of hydrogen on a large scale by means of water electrolysis. In this work, a novel free-standing Co₃S₄/CoMo₂S₄heterostructure on nickel foam by a facial hydrothermal method is demonstrated to be an effective bifunctional electrocatalyst for overall water splitting (OWS). The synthesized Co₃S₄/CoMo₂S₄electrocatalyst achieves ultralow overpotentials of 143 mV@10 mA cm^-2for hydrogen evolution reaction (HER) and 221 mV@25 mA cm^-2for oxygen evolution reaction (OER), respectively, in 1 M KOH. Moreover, it presents a greatly improved durability and stability under operando electrochemical conditions. When used as catalysts for OWS, the Co₃S₄/CoMo₂S₄-3//Co₃S₄/CoMo₂S₄-3 electrodes just need 1.514 V to make it to the current density of 10 mA cm^-2. It is supposed that the introduction of heterogeneous interface between Co₃S₄and CoMo₂S₄could give rise to plentiful active sites and enhanced conductivity, and thus boost excellent catalytic performances. Moreover, the porous feature of free-standing nanosheets on nickel foam could benefits catalytic performances by accelerating charge transport and releasing bubbles rapidly. This work proposes a bifunctional catalyst system with the heterogeneous interface, which could be used in a sustainable green energy system.

Synthesis and Reactivity of 3H-1,2-dithiole-3-thiones

3H-1,2-Dithiole-3-thiones are among the best studied classes of polysulfur-containing heterocycles due to the almost explosive recent interest in these compounds as sources of hydrogen sulfide as an endogenously produced gaseous signaling molecule. This review covers the recent developments in the synthesis of these heterocycles, including both well-known procedures and important novel transformations for building the 1,2-dithiole-3-thione ring. Diverse ring transformations of 3H-1,2-dithiole-3-thiones into various heterocyclic systems through 1,3-dipolar cycloaddition, replacement of one or two sulfur atoms to form carbon- and carbon-nitrogen containing moieties, and other unexpected reactions are considered.

Arsenic Removal and Recovery of Germanium and Tungsten in Toxic Coal Fly Ash from Lignite by Vacuum Distillation with a Sulfurizing Reagent

Every year, billions of tons of lignite are burnt to generate electricity, meanwhile generating large amounts of coal fly ash (CFA) that is regarded as an industrial waste. During lignite combustion, arsenic and scarce metals are simultaneously volatilized in the form of oxide into CFA. This study proposed an effective vacuum distillation method to remove As and recover Ge and W from CFA. The feasibility of separating As and recycling Ge and W from CFA was verified by the theoretical analysis. The experimental result indicated that the removal ratio of As was 96 ± 1% and the contents of Ge and W reached 0.75 ± 0.023 and 0.24 ± 0.016 wt % in the residue, which were enriched 17.2 and 1.2 times, respectively, at a temperature of 550 °C, with 50 wt % sulfurizing agent added under pressure of 1 Pa and 240 min of heating. For the condensed product, chemical species As₂S₃ and As₄S₄ were detected by X-ray photoelectron spectroscopy analysis. For Ge and W in the residue, GeO_x (x < 2), GeS, WO_x (x < 3), and WS₂ were the main chemical species. The potential mechanism involved in the release of arsenic from CFA, vacuum sulfurization, evaporation, and condensation was proposed. The kinetic analysis indicated that the apparent activation energy (E_α) was 31.24 kJ mol^-1. Those results encourage further exploration of vacuum separation technology to environmentally friendly recycle CFA.

Influence of Sulfur Evaporation during or after KF-Post Deposition Treatment On Cu(In,Ga)Se2/CdS Interface Formation

This work investigates the impact of the elemental sulfur evaporation during or after KF-post deposition treatment (KF-PDT) on the resulting Cu(In,Ga)Se₂/chemical bath deposited(CBD)-CdS interface. Chemical composition of the various interfaces were determined through Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger spectroscopy (XAES). Cu(In,Ga)Se₂ absorber which experienced KF-PDT in selenium atmosphere (KSe sample) exhibits the formation of the well-reported In-Se based topping layer. Additional exposure to elemental sulfur, resulting in KSe+S sample, induces the partial sulfurization of this overlayer and/or of the absorber. After short immersion into the CdS bath, the resulting In-rich surfaces of KSe and KSe+S are likely to turn into few atomic layers of Cd-In-(Se/S)-O whose [S]/[Se]+[S] ratio and O content depend on their respective post deposition treatment. In contrast, KF-PDT performed in S atmosphere does not show an In-rich surface, making the early stage of CdS growth similar to that observed on untreated CIGSe.

Optimization of Sulfurization Process of Cobalt Sulfide and Nitrogen Doped Carbon Material for Boosting the Oxygen Reduction Reaction Catalytic Activity in Alkaline Medium

In order to reduce fuel cell material cost and promote its application, it is urgent to develop non-noble metal materials to replace platinum as the cathode catalysts in fuel cells. The cobalt sulfide and nitrogen co-doped carbon (S-Co-N/C) materials with metal-organic frameworks as precursors have shown good oxygen reduction reaction (ORR) catalytic activity. Benefiting from the protection of catalytic active sites by sulfur atoms, the stability and alcohol-tolerance of the S-Co-N/C catalyst can be significantly improved. In order to fully understand the effect of the sulfurization process on the properties of the material, zeolite imidazole frameworks (ZIF)-8, and ZIF-67 are used as precursors to prepare a novel material of S-Co-N/C by using a sulfurization-pyrolysis method. Another S-Co-N/C material by using a pyrolysis- sulfurization method is prepared for comparison. The effects of the sulfurization process in the preparation on the morphology, chemical structure, specific surface area, and ORR catalytic activity of the final material are investigated. The experimental results show that the surface of the S-Co-N/C material tends to be rough due to the sulfurization reaction of the metal elements. The porosity of the material is reduced to some extent due to the remaining Zn elements in the final product. Interestingly, some carbon nanotubes are found to be generated on the surface of the S-Co-N/C material because of the synergistic effect of Zn and Co on the carbon material during the pyrolysis process, which is beneficial to accelerate the adsorption of oxygen on the S-Co-N/C surface and the electron transportation during the oxygen reduction reaction. In addition, the generated CoS during the sulfurization process can further protect the Co elements from agglomeration, which can effectively increase the ORR catalytic active sites in the final material. The S-Co-N/C material prepared by the sulfurization-pyrolysis method performs a superior ORR catalytic activity to the one synthesized by the pyrolysis-sulfurization method.

Exceptionally Uniform and Scalable Multilayer MoS2 Phototransistor Array Based on Large-Scale MoS2 Grown by RF Sputtering, Electron Beam Irradiation, and Sulfurization

Two-dimensional molybdenum disulfide (MoS₂) has emerged as a promising material for optoelectronic applications because of its superior electrical and optical properties. However, the difficulty in synthesizing large-scale MoS₂ films has been recognized as a bottleneck in uniform and reproducible device fabrication and performance. Here, we proposed a radio-frequency magnetron sputter system, and post-treatments of electron beam irradiation and sulfurization to obtain large-scale continuous and high-quality multilayer MoS₂ films. Large-area uniformity was confirmed by no deviation of electrical performance in fabricated MoS₂ thin-film transistors (TFTs) with an average on/off ratio of 10³ and a transconductance of 0.67 nS. Especially, the photoresponsivity of our MoS₂ TFT reached 3.7 A W^-1, which is a dramatic improvement over that of a previously reported multilayer MoS₂ TFT (0.1 A W^-1) because of the photogating effect induced by the formation of trap states in the band gap. Finally, we organized a 4 × 4 MoS₂ phototransistor array with high photosensitivity, linearity, and uniformity for light detection, which demonstrates the great potential of 2D MoS₂ for future-oriented optoelectronic devices.

Highly Efficient Nanocarbon Coating Layer on the Nanostructured Copper Sulfide-Metal Organic Framework Derived Carbon for Advanced Sodium-Ion Battery Anode

High theoretical capacity and low-cost copper sulfide (Cu_xS)-based anodes have gained great attention for advanced sodium-ion batteries (SIBs). However, their practical application may be hindered due to their unstable cycling performance and problems with the dissolution of sodium sulfides (Na_xS) into electrolyte. Here, we employed metal organic framework (MOF-199) as a sacrificial template to fabricate nanoporous Cu_xS with a large surface area embedded in the MOF-derived carbon network (Cu_xS-C) through a two-step process of sulfurization and carbonization via H₂S gas-assisted plasma-enhanced chemical vapor deposition (PECVD) processing. Subsequently, we uniformly coated a nanocarbon layer on the Cu_1.8S-C through hydrothermal and subsequent annealing processes. The physico-chemical properties of the nanocarbon layer were revealed by the analytical techniques of high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM). We acquired a higher SIB performance (capacity retention (~93%) with a specific capacity of 372 mAh/g over 110 cycles) of the nanoporous Cu_1.8S-C/C core/shell anode materials than that of pure Cu_1.8S-C. This encouraging SIB performance is attributed to the key roles of a nanocarbon layer coated on the Cu_1.8S-C to accommodate the volume variation of the Cu_1.8S-C anode structure during cycling, enhance electrical conductivity and prevent the dissolution of Na_xS into the electrolyte. With these physico-chemical and electrochemical properties, we ensure that the Cu_1.8S-C/C structure will be a promising anode material for large-scale and advanced SIBs.

Lithium Sulfide-Carbon Composites via Aerosol Spray Pyrolysis as Cathode Materials for Lithium-Sulfur Batteries

We demonstrate a new technique to produce lithium sulfide-carbon composite (Li₂S-C) cathodes for lithium-sulfur batteries via aerosol spray pyrolysis (ASP) followed by sulfurization. Specifically, lithium carbonate-carbon (Li₂CO₃-C) composite nanoparticles are first synthesized via ASP from aqueous solutions of sucrose and lithium salts including nitrate (LiNO₃), acetate (CH₃COOLi), and Li₂CO₃, respectively. The obtained Li₂CO₃-C composites are subsequently converted to Li₂S-C through sulfurization by reaction to H₂S. Electrochemical characterizations show excellent overall capacity and cycle stability of the Li₂S-C composites with relatively high areal loading of Li₂S and low electrolyte/Li₂S ratio. The Li₂S-C nanocomposites also demonstrate clear structure-property relationships.

Inverse Capacity Growth and Pocket Effect in SnS2 Semifilled Carbon Nanotube Anode

SnS₂ with high theoretical capacity has been impeded from practical applications as the anode of lithium-ion (Li-ion) batteries due to its large volume expansion and fast capacity decay. A nanostructure of the SnS₂ semifilled carbon nanotube (SnS₂@CNT) has been realized by plasma-assisted fabrication of Sn semifilled CNT (Sn@CNT) followed by post-sulfurization. When serving as the anode of a Li-ion battery, SnS₂@CNT delivers an initial discharge capacity of 1258 mAh g^-1 at 0.3 A g^-1. Instead of capacity fading, SnS₂@CNT shows inverse capacity growth to 2733 mAh g^-1 after 470 cycles. The high-resolution transmission electron microscopy images show that the void in CNTs, after cycling, is fully filled with pulverized SnS₂ grains which have a shortened Li-ion diffusion path and enhanced surface area for interfacial redox reactions. In addition, the CNTs, like a pocket, confine the pulverized SnS₂, maintain the electric contact and structural integrity, and thus allow the electrodes to work safely under long cyclic loadings and extreme temperature conditions.

Sloughing a Precursor Layer to Expose Active Stainless Steel Catalyst for Water Oxidation

Hydrogen production by water electrolysis has been regarded as a promising approach to wean away from sourcing energy through fossil fuels, as the produced hydrogen gas can be converted to electrical or thermal energy without any harmful byproducts. However, an efficient hydrogen production is restricted by the sluggish oxygen evolution reaction (OER) at the counter anode. Therefore, the development of new OER catalysts with high catalytic activities is crucial for high performance water splitting. Here, we report a novel sloughing method for the fabrication of an efficient OER catalyst on a stainless steel (SS) surface. A chalcogenide (Fe-S) overlayer generated by sulfurization on the SS surface is found to play a critical role as a precursor layer in the formation of an active surface during water oxidation. Interestingly, a newly exposed catalytic layer after sloughing off the Fe-S overlayer has a nanoporous structure with changed elemental composition, resulting in a significant improvement in OER performance with an overpotential value of 267 mV at a current density of 10 mA cm^-2 (in 1 M KOH). Our novel method for the preparation of OER catalyst provides an important insight into designing an efficient and stable electrocatalyst for the water splitting community.

Toward the use of CVD-grown MoS2 nanosheets as field-emission source

Densely populated edge-terminated vertically aligned two-dimensional MoS₂ nanosheets (NSs) with thicknesses ranging from 5 to 20 nm were directly synthesized on Mo films deposited on SiO₂ by sulfurization. The quality of the obtained NSs was analyzed by scanning electron and transmission electron microscopy, and Raman and X-ray photoelectron spectroscopy. The as-grown NSs were then successfully transferred to the substrates using a wet chemical etching method. The transferred NSs sample showed excellent field-emission properties. A low turn-on field of 3.1 V/μm at a current density of 10 µA/cm² was measured. The low turn-on field is attributed to the morphology of the NSs exhibiting vertically aligned sheets of MoS₂ with sharp and exposed edges. Our findings show that the fabricated MoS₂ NSs could have a great potential as robust high-performance electron-emitter material for various applications such as microelectronics and nanoelectronics, flat-panel displays and electron-microscopy emitter tips.

Investigation of Surface Sulfurization in CuIn1-x Gax S2-y Sey Thin Films by Using Kelvin Probe Force Microscopy

CuIn_1-x Ga_x S_2-y Se_y (CIGSSe) thin films have attracted a great deal of attention as promising absorbing materials for solar cell applications, owing to their favorable optical properties (e.g. a direct band gap and high absorption coefficients) and stable structure. Many studies have sought to improve the efficiency of solar cells using these films, and it has been found that surface modification through post-heat treatment can lead to surface passivation of surface defects and a subsequent increase in efficiency. The surface properties of solution-processed CIGSSe films are considered to be particularly important in this respect, owing to the fact that they are more prone to defects. In this work, CIGSSe thin films with differing S/Se ratios at their surface were synthesized by using a precursor solution and post-sulfurization heat treatment. These CIGSSe thin films were investigated with current-voltage and Kelvin probe force microscope (KPFM) analyses. Surface photovoltage (SPV), which is the difference in the work function in the dark and under illumination, was measured by using KPFM, which can examine the screening and the modification of surface charge through carrier trapping. As the concentration of S increases on the CIGSSe film surface, higher work functions and more positive SPV values were observed. Based on these measurements, we inferred the band-bending behavior of CIGSSe absorber films and proposed reasons for the improvement in solar cell performance.

Efficiency enhancement of Cu2ZnSnS4 solar cells via surface treatment engineering

Pure-sulphide Cu₂ZnSnS₄ (CZTS) thin film solar cells were prepared by a low-cost, non-toxic and high-throughput method based on the thermal decomposition and reaction of sol-gel precursor solution, followed by a high temperature sulfurization process in sulphur atmosphere, which usually gave rise to the unexpected Cu-poor and Zn-rich phase after sulfurization. In order to remove the formation of detrimental secondary phases, e.g. ZnS, a novel method with hydrochloric acid solution treatment to the CZTS absorber layer surface was employed. By using this method, a competitive power conversion efficiency as high as 4.73% was obtained, which is a factor of 4.8 of that of the control CZTS solar cell without surface treatment. This presents a customized process for CZTS photovoltaic technologies that is more environmentally friendly and considerably less toxic than the widely used KCN etching approach.

Janus Monolayer Transition-Metal Dichalcogenides

The crystal configuration of sandwiched S-Mo-Se structure (Janus SMoSe) at the monolayer limit has been synthesized and carefully characterized in this work. By controlled sulfurization of monolayer MoSe₂, the top layer of selenium atoms is substituted by sulfur atoms, while the bottom selenium layer remains intact. The structure of this material is systematically investigated by Raman, photoluminescence, transmission electron microscopy, and X-ray photoelectron spectroscopy and confirmed by time-of-flight secondary ion mass spectrometry. Density functional theory (DFT) calculations are performed to better understand the Raman vibration modes and electronic structures of the Janus SMoSe monolayer, which are found to correlate well with corresponding experimental results. Finally, high basal plane hydrogen evolution reaction activity is discovered for the Janus monolayer, and DFT calculation implies that the activity originates from the synergistic effect of the intrinsic defects and structural strain inherent in the Janus structure.

Hypoxia causes preservation of labile organic matter and changes seafloor microbial community composition (Black Sea)

Bottom-water oxygen supply is a key factor governing the biogeochemistry and community composition of marine sediments. Whether it also determines carbon burial rates remains controversial. We investigated the effect of varying oxygen concentrations (170 to 0 μM O₂) on microbial remineralization of organic matter in seafloor sediments and on community diversity of the northwestern Crimean shelf break. This study shows that 50% more organic matter is preserved in surface sediments exposed to hypoxia compared to oxic bottom waters. Hypoxic conditions inhibit bioturbation and decreased remineralization rates even within short periods of a few days. These conditions led to the accumulation of threefold more phytodetritus pigments within 40 years compared to the oxic zone. Bacterial community structure also differed between oxic, hypoxic, and anoxic zones. Functional groups relevant in the degradation of particulate organic matter, such as Flavobacteriia, Gammaproteobacteria, and Deltaproteobacteria, changed with decreasing oxygenation, and the microbial community of the hypoxic zone took longer to degrade similar amounts of deposited reactive matter. We conclude that hypoxic bottom-water conditions-even on short time scales-substantially increase the preservation potential of organic matter because of the negative effects on benthic fauna and particle mixing and by favoring anaerobic processes, including sulfurization of matter.

Fossilization of melanosomes via sulfurization

Fossil melanin granules (melanosomes) are an important resource for inferring the evolutionary history of colour and its functions in animals. The taphonomy of melanin and melanosomes, however, is incompletely understood. In particular, the chemical processes responsible for melanosome preservation have not been investigated. As a result, the origins of sulfur-bearing compounds in fossil melanosomes are difficult to resolve. This has implications for interpretations of original colour in fossils based on potential sulfur-rich phaeomelanosomes. Here we use pyrolysis gas chromatography mass spectrometry (Py-GCMS), fourier transform infrared spectroscopy (FTIR) and time of flight secondary ion mass spectrometry (ToF-SIMS) to assess the mode of preservation of fossil microstructures, confirmed as melanosomes based on the presence of melanin, preserved in frogs from the Late Miocene Libros biota (NE Spain). Our results reveal a high abundance of organosulfur compounds and non-sulfurized fatty acid methyl esters in both the fossil tissues and host sediment; chemical signatures in the fossil tissues are inconsistent with preservation of phaeomelanin. Our results reflect preservation via the diagenetic incorporation of sulfur, i.e. sulfurization (natural vulcanization), and other polymerization processes. Organosulfur compounds and/or elevated concentrations of sulfur have been reported from melanosomes preserved in various invertebrate and vertebrate fossils and depositional settings, suggesting that preservation through sulfurization is likely to be widespread. Future studies of sulfur-rich fossil melanosomes require that the geochemistry of the host sediment is tested for evidence of sulfurization in order to constrain interpretations of potential phaeomelanosomes and thus of original integumentary colour in fossils.

Nucleic acids through condensation of nucleosides and phosphorous acid in the presence of sulfur

Short phosphorothioate oligonucleotides have been prepared by refluxing an equimolar mixture of thymidine and triethylammonium phosphite in toluene in the presence of elemental sulfur. Desulfurization and subsequent digestion of the products by P1 nuclease revealed that nearly 80% of the internucleosidic linkages thus formed were of the canonical 3´,5´-type.

NiS1.97: A New Efficient Water Oxidation Catalyst for Photoelectrochemical Hydrogen Generation

NiS1.97, a sulfur-deficient dichalcogenide, in nanoscale form, is shown to be a unique and efficient photoelectrochemical (PEC) catalyst for H2 generation by water splitting. Phase pure NiS1.97 nanomaterial is obtained by converting nickel oxide into sulfide by controlled sulfurization method, which is otherwise difficult to establish. The defect states (sulfur vacancies) in this material increase the carrier density and in turn lead to favorable band line-up with respect to redox potential of water, rendering it to be an effective photoelectrochemical catalyst. The material exhibits a remarkable PEC performance of 1.25 mA/cm(2) vs NHE at 0.68 V in neutral pH, which is almost 1000 times superior as compared with that of the stoichiometric phase of NiS2. The latter is well-known to be a cocatalyst but not as a primary PEC catalyst.

High responsivity photoconductors based on iron pyrite nanowires using sulfurization of anodized iron oxide nanotubes

Iron pyrite (FeS2) nanostructures are of considerable interest for photovoltaic applications due to improved material quality compared to their bulk counterpart. As an abundant and nontoxic semiconductor, FeS2 nanomaterials offer great opportunities for low-cost and green photovoltaic technology. This paper describes the fabrication of FeS2 nanowire arrays via sulfurization of iron oxide nanotubes at relatively low temperatures. A facile synthesis of ordered iron oxide nanotubes was achieved through anodization of iron foils. Characterization of the iron sulfide nanowires indicates that pyrite structures were formed. A prototype FeS2 nanowire photoconductor demonstrates very high responsivity (>3.0 A/W). The presented method can be further explored to fabricate various FeS2 nanostructures, such as nanoparticles, nanoflowers, and nanoplates.

Edge-selectively sulfurized graphene nanoplatelets as efficient metal-free electrocatalysts for oxygen reduction reaction: the electron spin effect

To replace precious platinum (Pt)-based electrocatalysts for cathodic oxygen reduction reaction (ORR), edge-selectively sulfurized graphene nanoplatelets (SGnP) are synthesized as efficient metal-free electrocatalysts simply by ball-milling pristine graphite in the presence of sulfur (S8 ). The resultant SGnPs exhibit remarkable electrocatalytic activity toward ORR with better tolerance to methanol crossover/CO poisoning effects and longer-term stability than those of pristine graphite and commercial Pt/C electrocatalysts. Edge-Selectively Sulfurized Graphene Nanoplatelets as Efficient Metal-Free Electrocatalysts for Oxygen Reduction Reaction: The Electron Spin Effect.