Sulfur Passivation Research Articles

Microscopic and elemental analysis of temperature-induced changes in sulfur/silicon nitride stack-passivated Si surface

Sulfur passivation of different Czochralski Si surfaces along with hydrogenated amorphous silicon nitride capping layer has been reported. The effect of capping layer thickness and deposition temperature on sulfur reacted surface has a strong effect on initial passivation quality and its stability. Sulfur passivation on phosphorus diffused n-type textured Czochralski Si wafers capped with a 100 nm stacked hydrogenated amorphous silicon nitride layer demonstrates improved stability under heat and light with saturation current density <80 fA/cm2. A stack layer of a low temperature (≤300OC) hydrogenated amorphous silicon nitride followed by a high temperature (≈ 450OC) hydrogenated amorphous silicon nitride is adopted to achieve good thermally stable surface passivation. Sulfur-passivation with only a low temperature hydrogenated amorphous silicon nitride capping layer exhibits unstable behavior after thermal treatment due to blister/pinhole formation at ≥300OC and possible oxidation of the S-passivated surface. Photoluminescence imaging shows increased defect recombination loss due to disrupted surface passivation after thermal treatment. Fourier transform infrared spectroscopic studies demonstrate that these blister formations were caused by hydrogen effusion from Si–H and N–H bonds dissociation upon thermal processing. Time of flight secondary ion mass spectroscopy exhibits oxidation of S-reacted surface after thermal treatment that degrades the passivation quality.

Thermoelectric Property Enhancement of Tellurium Nanowires by Surface Passivation.

The pursuit of high-performance thermoelectric materials is of paramount importance in addressing energy sustainability and environmental concerns. Here, we explore the multifaceted impact of sulfur passivation in the matrix of tellurium nanowires (TeNWs), encompassing environmental control, thermoelectric properties, and charge carrier mobility. In this study, we present the facile production of TeNWs using an aqueous solution synthesis approach. The synthesized TeNWs were subsequently subjected to surface modification involving sulfur moieties. Our findings demonstrate that sulfur passivation not only effectively safeguards the nanowires from environmental degradation but also significantly augments their thermoelectric properties. Notably, the highest recorded values were achieved at 560 K for passivated tellurium nanowires, exhibiting a Seebeck coefficient of 246 μV/K, an electrical conductivity of 14.2 S/cm, and power factors of 86.7 μW/m-K2. This strategy presents a promising avenue for the development of advanced thermoelectric materials for applications in energy harvesting, waste heat recovery, and sustainable energy conversion technologies.

Massive Onset Potential Shifting with an Epitaxial GaAs/Si Photocathode for Solar H2 Production

Solar photoelectrochemical (PEC) H2 production has the potential to solve one of the biggest issues confronting humanity nowadays: producing inexpensive, clean and renewable energy. Among various semiconductor materials, GaAs is an excellent candidate for the development of photoelectrodes within PEC cells for unassisted solar water splitting thanks to its appropriate band gap, good transport and optical properties and high quantum yield. However, the main limitations of GaAs photoelectrodes are related to the high substrate cost, their huge overpotentials and the short lifetime under operation. To address these issues, in this work, we report on the photocathode performance of 1 µm-thick GaAs layers grown on a low-cost Si p-doped substrate by MBE (Molecular Beam Epitaxy) and compare them to those of GaAs:p doped wafers . The photocathodes were investigated in 0.2 M H2SO4 (aq) electrolyte under 1 sun (100 mW/cm2) illumination. The onset potential (Vonset) of bare GaAs/Si and bare GaAs:p wafer is quite comparable, at around -0.2 V vs reversible hydrogen electrode (RHE). The significant reduction of surface states density with a sulfur passivation (S-passivation) by immersing samples in (NH4)2S solution is demonstrated but with very limited changes on the Vonset value, for both GaAs:p wafer and GaAs/Si photocathodes. In contrast, the deposition of thin Pt catalyst layers on both photocathodes by electroless deposition technique leads to a large positive shift Vonset. The Vonset of GaAs/Si and GaAs:p wafer photocathodes are increased up to 0.34 and 0.15 V vs RHE respectively. We show that the Vonset of GaAs/Si can be even improved by combining the Pt catalyst and the S-passivation process, reaching 0.4 V vs RHE (Fig. 1), a record value for GaAs-based Schottky-like photocathodes.STEM-EDX analysis was performed to investigate further the difference between Pt/GaAs/Si and Pt/GaAs:p wafer photocathodes. The EDX-line scans show that after the Pt electroless deposition, the Pt layer on GaAs:p wafer is homogeneous and shows an As0-rich Pt surface that can explain the weaker catalytic activity in comparison with GaAs/Si. Indeed, for the latter, Pt is deposited inhomogenously in the form of clusters leaving some bare surface. Here, As0 is expected to be more easily removed from the surface during the electroless deposition, resulting in more efficient catalyst properties of Pt. The morphology differences between the two Pt-coated electrodes are confirmed by XPS measurements. Since the process of electroless deposition strongly depends on the doping concentration of the materials deposited, the difference between GaAs:p wafer and GaAs/Si photocathodes is attributed to variations in their doping concentrations. Furthermore, the inhomogeneity of the Pt coating on GaAs/Si can also benefit to the passivation process by allowing the (NH4)2S solution to reduce more efficiently the surface defects at the oxide/semiconductor interface. Finally, the stability of Pt/GaAs/Si photocathodes was evaluated, and a lifetime larger than 112 h was established. These findings provide guidance for further studies towards the fabrication of scalable, cost-efficient and stable unassisted PEC cells for green hydrogen production. This research is supported by the “France 2030” French National Research Agency NAUTILUS Project (Grant no. ANR-22-PEHY-0013). Figure 1

Advances in Electrocatalyst Design and Mechanism for Sulfide Oxidation Reaction in Hydrogen Sulfide Splitting

AbstractSulfide oxidation reaction (SOR) is a semi‐reaction for the electrochemical decomposition of hydrogen sulfide. Combining SOR with the hydrogen evolution reaction (HER) allows for the simultaneous splitting of hydrogen sulfide (H2S) to produce green hydrogen, reducing energy input and environmental pollution. However, the phenomenon of sulfur passivation on the anode leads to catalyst deactivation, posing a bottleneck in developing efficient SOR. Electrocatalysts with decent performance and sulfur‐tolerance play a central role in the application of SOR. Here, recent progress on electrocatalysis mechanisms and catalyst design strategies of SOR are summarized. A summary of recent progress is made in materials such as alloys, metal oxides, metal sulfides, metal selenides, and heterostructures as SOR catalysts. Additionally, some valuable design and modulation strategies are highlighted and included. Finally, this review offers an outlook on the future directions in this emerging field.

Insight into the effective electrocatalytic sulfide removal from aqueous solutions using surface oxidized stainless-steel anode and its desulfurization mechanism

The electrochemical oxidation of hydrogen sulfide (H2S) has shown its potential for the real application of H2S emission control in wastewater treatment. In this study, a surface corrosion treatment of stainless steel (SS) was optimized by regulate Ni content in the oxide film on the SS AISI 304 surface for sulfide removal. The X-ray photoelectron spectroscopy and linear sweeping voltammetry results indicated a higher Ni content in the oxide film of surface-oxidized stainless steel (SOSS) attributed to a higher sulfide removal potential. Sulfide removal experiment results showed that SS-150 (with 150 s anodic pretreatment) anodes achieved the highest Ni content of 69% with the best sulfide removal efficiency, i.e., 97% within 48 h, which increased by 20% compared to the untreated SS. This study also demonstrated a strategy for in situ removal of deposited sulfur on the anodes by cathodic treatment at −0.38 V vs. RHE to alleviate the common issue of sulfur passivation. Density functional theory (DFT) calculation revealed that NiOOH was the major active species in SS-150 oxide film for a faster sulfide removal rate. The study developed a SS surface modification process for Ni content regulation that contributed to better sulfide removal efficiency.

Optimizing interface properties of HfO2/Si0.73Ge0.27 gate stacks through sulfur passivation and post-deposition annealing

This paper presents a comprehensive exploration of low interface trap density (Dit) in HfO2/Si0.73Ge0.27 metal-oxide semiconductor (MOS) capacitors achieved through sulfur passivation and post-deposition annealing (PDA). Our investigation revealed that devices subjected to sulfur passivation and PDA exhibit noteworthy reductions in Dit and hysteresis. Specifically, a low Dit value of 1.2 × 1011 eV−1 cm−2 has been achieved at Ei–0.1 eV for the SiGe MOS device. The observed enhancement in interface properties can be attributed to two key factors: the reduction of the GeOx concentration in the interfacial layer (IL) by sulfur passivation on the SiGe surface and the IL densification with stoichiometric oxygen during PDA.

Working mechanism of CTAB as an inhibitor of platinum anode sulfur passivation

Working mechanism of CTAB as an inhibitor of platinum anode sulfur passivation

Low-Cost Passivated Al Front Contacts for III-V/Ge Multijunction Solar Cells

Improving the performances and reducing costs of III-V multijunction solar cells are crucial in aerospatial energy systems and in terrestrial concentrator modules. We attempted to achieve both objectives by implementing non-ohmic metal/semiconductor interface contacts on the front surface of III-V/Ge triple-junction solar cells. We demonstrate the feasibility of this concept for this type of solar cell by a simple evaporation of Al only either on the GaAs contact layer or the AlInP window. The best results were obtained when sulfur passivation by (NH4)2Sx was conducted on the GaAs contact layer. This allowed for a reduction in reverse saturation dark current density by one order of magnitude and a slight increase in Voc of almost 20 mV under 1 sun illumination relative to a reference device with Pd/Ge/Ti/Pd ohmic contacts. However, poor performances were observed at first under concentrated sunlight. Further annealing the solar cells with Al front metallization resulted in the reduction of Voc to the same level as the reference solar cell but allowed for good performances under high illumination. Indeed, an efficiency over 34% was observed at 500 suns light intensity both for Al and Pd/Ge/Ti/Pd contacted solar cells.

Arresting the surface oxidation kinetics of bilayer 1T′-MoTe2 by sulphur passivation

MoTe2 garnered much attention among 2D materials due to stable polymorphs with distinctive structural and electronic properties. Among the polymorphs, 1T′-MoTe2 in bulk form is type—II Weyl semimetal while, in monolayer form is a quantum spin Hall insulator. Thus, it is suitable for a wide variety of applications. Nevertheless, 1T′-MoTe2 degrades within a few hours when exposed to the atmosphere and causes hindrances in device fabrication. Here the degradation kinetics of CVD-synthesized 1T′-MoTe2 was investigated using Raman spectroscopy, XPS, and microscopic characterizations. The degradation rate of as-grown 1T′-MoTe2 obtained was 9.2 × 10−3 min−1. Further, we prevented the degradation of 1T′-MoTe2 by introducing a thin coating of S that encapsulates the flakes. 1T′-MoTe2 flakes showed stability for several days when covered using sulphur, indicating 25 times enhanced structural stability.

Electrocatalytic-mediated in situ heterojunction formation for amplified electrochemical sensing platform based on Mn-doped Cu(OH)2 hexagonal nanoring

Developing distinct sensing strategies and their rational combination for specific detection has been demonstrated as an efficient approach to boost the analytical performance of electrochemical biosensors. In contrast to existing sensing mechanisms, a novel biocatalytic-mediated method via in-situ combining Mn-doped Cu(OH)2 hexagonal nanoring is designed to form a CuxS-based heterojunction on electrode surface for highly selective hydrogen sulfide (H2S) detection, resulting in an obviously electro-current signal change due to the fast electron transfer rate. Meanwhile, the combination of heterojunction strategy and electrochemical detection can address sulfur poisoning-caused electrode passivation. Atomically dispersed nanocomposites active sites on the sensing interface enhance H2S electrocatalytic activity at a low potential to stimulate electrochemical signals on. This H2S-responsive electrochemical sensing platform exhibits excellent sensitivity, selectivity, and stability. Under optimal experimental parameters, the constructed sensing platform shows a wide linear range for H2S in the range of 0.1–260 μM, which will promote us better understand the H2S mechanism in complex living systems.

Real-Time Investigation of Sulfur Vacancy Generation and Passivation in Monolayer Molybdenum Disulfide via in situ X-ray Photoelectron Spectromicroscopy.

Understanding the chemical and electronic properties of point defects in two-dimensional materials, as well as their generation and passivation, is essential for the development of functional systems, spanning from next-generation optoelectronic devices to advanced catalysis. Here, we use synchrotron-based X-ray photoelectron spectroscopy (XPS) with submicron spatial resolution to create sulfur vacancies (SVs) in monolayer MoS2 and monitor their chemical and electronic properties in situ during the defect creation process. X-ray irradiation leads to the emergence of a distinct Mo 3d spectral feature associated with undercoordinated Mo atoms. Real-time analysis of the evolution of this feature, along with the decrease of S content, reveals predominant monosulfur vacancy generation at low doses and preferential disulfur vacancy generation at high doses. Formation of these defects leads to a shift of the Fermi level toward the valence band (VB) edge, introduction of electronic states within the VB, and formation of lateral pn junctions. These findings are consistent with theoretical predictions that SVs serve as deep acceptors and are not responsible for the ubiquitous n-type conductivity of MoS2. In addition, we find that these defects are metastable upon short-term exposure to ambient air. By contrast, in situ oxygen exposure during XPS measurements enables passivation of SVs, resulting in partial elimination of undercoordinated Mo sites and reduction of SV-related states near the VB edge. Correlative Raman spectroscopy and photoluminescence measurements confirm our findings of localized SV generation and passivation, thereby demonstrating the connection between chemical, structural, and optoelectronic properties of SVs in MoS2.

Bifunctional Co3S4 Nanowires for Robust Sulfion Oxidation and Hydrogen Generation with Low Power Consumption

AbstractSulfion oxidation reaction holds great potential for replacing kinetically sluggish water oxidation to save power consumption and simultaneously purifying environmental sulfion‐rich sewage. However, it is still challenged by the insufficient mechanism understanding and questionable stability caused by sulfur passivation. Here, it is demonstrated that bifunctional Co3S4 nanowires for assembling hybrid seawater electrolyzer that combines anodic sulfion oxidation and cathodic seawater reduction with an ultra‐low power consumption of 1.185 kWh m−3 H2 under 100 mA cm−2, saving energy consumption over 70% compared to the traditional water splitting system. Unlike water is oxidized into O2 at high potentials under alkaline water splitting system, experiments combined with in situ characterizations uncover the stepwise oxidation of S2− to short‐chain polysulfides and then to value‐added product of S8. Density functional theory calculations prove that Co3S4 possesses reduced energy barriers in the rate‐determining S32− to S4− oxidation step and S8 desorption step, promoting conversion of short‐chain polysulfides and efficient desorption of S8. These findings reveal the catalytic mechanism of sulfion oxidation and inspire an economic approach toward the fabrication of bifunctional Co3S4 for achieving energy‐saving hydrogen production from seawater while rapidly disposing sulfion‐rich sewage with boosted activity and stability.

Highly Stable and Selective Sensing of Hydrogen Sulfide in Living Mouse Brain with NiN4 Single-Atom Catalyst-Based Galvanic Redox Potentiometry

Hydrogen sulfide (H2S) is recognized as a gasotransmitter and multifunctional signaling molecule in the central nervous system. Despite its essential neurofunctions, the chemical dynamics of H2S during physiological and pathological processes remains poorly understood, emphasizing the significance of H2S sensor development. However, the broadly utilized electrochemical H2S sensors suffer from low stability and sensitivity loss in vivo due to sulfur poisoning-caused electrode passivation. Herein, we report a high-performance H2S sensor that combines single-atom catalyst strategy and galvanic redox potentiometry to overcome the issue. Atomically dispersed NiN4 active sites on the sensing interface promote electrochemical H2S oxidation at an extremely low potential to drive spontaneous bipolarization of a single carbon fiber. Bias-free potentiometric sensing at open-circuit condition minimizes sulfur accumulation on the electrode surface, thus significantly enhancing the stability and sensitivity. The resulting sensor displays high selectivity to H2S against physiological interferents and enables real-time accurate quantification of H2S-releasing behavior in the living mouse brain.

Correlation of the electronic and atomic structure at passivated n-InP(100) surfaces

Photoluminescence, Raman spectroscopy and X-ray photoelectron spectroscopy are used to study electronic and atomic structure of n-InP(100) surfaces treated with different sulfide solutions. It is shown that the sulfide treatment causes removal of the native oxide layer from the semiconductor surface and formation of the passivating layer consisting of In-S chemical bonds with the structure dependent on the solution composition and atomic arrangement at the initial surface of the semiconductor. This is accompanied by an increase in photoluminescence intensity and narrowing of the surface depletion layer. Atomic structure of the passivating layer determines the total dipole that modifies the depth distribution of the bands potentials and thus the surface electronic structure. Keywords: surface modification, sulfur passivation, Raman spectroscopy, photoluminescence, X-ray photoelectron spectroscopy.

Efficient passivation of n-type and p-type silicon surface defects by hydrogen sulfide gas reaction

An efficient surface defect passivation is observed by reacting clean Si in a dilute hydrogen sulfide–argon gas mixture (<5% H2S in Ar) for both n-type and p-type Si wafers with planar and textured surfaces. Surface recombination velocities of 1.5 and 8 cm s−1 are achieved on n-type and p-type Si wafers, respectively, at an optimum reaction temperature of 550 °C that are comparable to the best surface passivation quality used in high efficiency Si solar cells. Surface chemical analysis using x-ray photoelectron spectroscopy shows that sulfur is primarily bonded in a sulfide environment, and synchrotron-based soft x-ray emission spectroscopy of the adsorbed sulfur atoms suggests the formation of S–Si bonds. The sulfur surface passivation layer is unstable in air, attributed to surface oxide formation and a simultaneous decrease of sulfide bonds. However, the passivation can be stabilized by a low-temperature (300 °C) deposited amorphous silicon nitride (a-Si:N X :H) capping layer.

Enhanced Band Edge Luminescence in GaAs with Sulfur Passivation

In this work, we perform a sulfur chemical passivation on GaAs substrate, which leads to a change in the photoluminescence (PL) owing to a reduction of surface states. By varying the reaction time of passivation, we can modify the chemical bonds of the GaAs surface and reduce the surface depletion region thickness, which strongly affects the emission efficiency of the GaAs band edge. Based on systematic PL measurements and energy band model with surface states, the sulfur passivation also enhances the number of free and bound excitons. Therefore, sulfur passivation is important to improve the performance of GaAs-based optoelectronics devices.

Sulfophobic and Vacancy Design Enables Self‐Cleaning Electrodes for Efficient Desulfurization and Concurrent Hydrogen Evolution with Low Energy Consumption

AbstractSulfide oxidation reaction (SOR) is one central step of electrochemical desulfurization and sulfur‐based batteries. However, the electrochemical performance of desulfurization and sulfur batteries has been severely hindered by sulfur passivation. Here, a discovery of sulfophobic phenomenon of electrocatalysts having weak interaction to sulfur species is reported. A self‐cleaning NiS2 electrode is developed to avoid the long‐perplexing passivation issue of solid sulfur during the SOR. Furthermore, sulfur‐vacancies are engineered into NiS2 lattice to synthesize v‐NiS2 for the hydrogen evolution reaction (HER). The resultant lattice expansion and electron redistribution can adjust the adsorbed hydrogen to reach a nearly thermos‐neutral state, enabling high catalytic activity for the HER. By coupling the HER and SOR, efficient desulfurization and simultaneous hydrogen production is demonstrated. Bifunctional NiS2 enables such a one‐stone‐kills‐two‐birds strategy to realize continuous electrochemical desulfurization with superior energy efficiency (1.05 gsulfur Wh−1). As a general design principle, sulfophobic electrocatalysts can improve the properties of lithium–sulfur batteries by minimizing the passivation of S8 during charge. In brief, interfacial interaction between electrocatalysts and sulfur species are systematically investigated and a sulfophobic strategy to significantly enhance the electrochemical performance of the SOR is offered.

The adaptation mechanisms of Acidithiobacillus caldus CCTCC M 2018054 to extreme acid stress: Bioleaching performance, physiology, and transcriptomics

To understand the acid-resistant mechanism of bioleaching microorganism Acidithiobacillus caldus CCTCC M 2018054, its physiology and metabolic changes at the transcriptional level under extreme acid stress were systemically studied. Scanning electron microscopy (SEM), Fourier transform infrared reflection (FTIR) and X-ray diffraction (XRD) showed that with an increase in acidity, the absorption peak of sulfur oxidation-related functional groups such as S–O decreased significantly, and a dense sulfur passivation film appeared on the surface of the ore. Confocal laser scanning microscopy (CLSM) revealed that coverage scale of extracellular polymeric substance (EPS) and biofilm fluctuated accordingly along with the increasing acid stress (pH-stat 1.5, 1.2 0.9 and 0.6) during the bioleaching process. In response to acid stress, the increased levels of intracellular glutamic acid, alanine, cysteine, and proline contributed to the maintenance of intracellular pH homeostasis via decarboxylation and alkaline neutralization. Higher unsaturated fatty acid content was closely related to membrane fluidity. Up to 490 and 447 differentially expressed genes (DEGs) were identified at pH 1.5 vs pH 1.2 and pH 1.2 vs pH 0.9, respectively, and 177 common DEGs were associated with two-component system (TCS) regulation, transporter regulation, energy metabolism, and stress response. The upregulation of kdpB helped cells defend against proton invasion, whereas the downregulation of cysB and cbl implied stronger oxidation of sulfur compounds. The transcriptional level of sqr, sor, and soxA was significantly increased and consolidated the energy supply needed for resisting acid stress. Furthermore, eight of the identified DEGs (sor, cbl, ompA, atpF, nuoH, nuoC, sqr, grxB) were verified as being related to the acid stress response process. This study contributes toward expanding the application of these acidophiles in industrial bioleaching.

Surface Passivation of Crystalline Silicon Wafer Using H2S Gas

We report the effects of H2S passivation on the effective minority carrier lifetime of crystalline silicon (c-Si) wafers. c-Si wafers were thermally annealed under an H2S atmosphere at various temperatures. The initial minority carrier lifetime (6.97 μs) of a c-Si wafer without any passivation treatments was also measured for comparison. The highest minority carrier lifetime gain of 2030% was observed at an annealing temperature of 600 °C. The X-ray photoelectron spectroscopy analysis revealed that S atoms were bonded to Si atoms after H2S annealing treatment. This indicates that the increase in minority carrier lifetime originating from the effect of sulfur passivation on the silicon wafer surface involves dangling bonds.

Dissolution mechanism of the oxidation process of covellite by ferric and ferrous ions

This study explores the influences of external iron ions on the dissolution behavior of covellite minerals at different temperatures. External iron ions can significantly accelerate covellite dissolution. The copper extraction of acid covellite leaching was less than 5%, while the addition of external iron ions (ferric or ferrous ions, Fe3+/Fe2+) effectively enhanced covellite dissolution. Covellite copper extraction with 0.1 mol/L Fe2+ was 25% at 303 K and 40% at 318 K after 18 days, and for leaching systems with 0.1 mol/L Fe3+, it was approximately 40% at 303 K and 60% at 318 K. The dissolution process of covellite with external iron ions can be divided into two stages. The dissolution kinetics at the first stage are controlled by the chemical reaction between iron ions and covellite, as the generated elemental sulfur has not yet blocked the covellite surface. Compared with ferrous ions, ferric ions further increase the dissolution rate of covellite, which is also suggested by the scanning electron microscopy analysis results. Additionally, Fe3+ accelerates the release of copper ions by effectively reducing the particle size of covellite. In the second stage (copper extraction >40%), the reaction kinetics shift to the mixed control of the surface chemical reaction with iron ions and diffusion due to the accumulation of an elemental sulfur layer on the surface. Although Fe2+ cannot directly oxidize covellite, the electron exchange between Fe2+ and oxygen is improved through the covellite mineral, which is attributed to its metallic properties. Then, the ferric ions generated in the above process gradually corrode covellite. In addition, the temperature rise can significantly accelerate the oxidation reaction process of iron ions with covellite by forming a more porous corrosive structure. Finally, leaching bacteria (Acidithiobacillus caldus and Leptospirillum ferriphilum) are proved to boost copper extraction from covellite by transforming Fe2+ into Fe3+ and eliminating surface elemental sulfur passivation. However, dense passivation layers inevitably form on the covellite surface at the end of bioleaching, which passivates the subsequent dissolution process.