CdS Surface Research Articles

Terpyridine Ni(II) Complex Grafted CdS Nanorods for Cooperative Selective Benzyl Alcohol Oxidation and Hydrogen Production.

Efficient utilization of photogenerated charge carriers to realize photocatalytic solar fuel production and oxidative chemical synthesis is a challenging task. Herein, a conventional amidation reaction route is adopted to successfully construct a novel composite photocatalyst composed of a Ni(II)-terpyridine complex with carboxyl groups grafted on CdS nanorods (labeled as CdS@Ni(terpyC)2). Experimental results have unequivocally revealed that the as-fabricated composite catalyst exhibited a remarkable enhancement in photocatalytic activity for the dehydrogenation of benzyl alcohol under visible light, demonstrating superior hydrogen evolution efficiency and benzaldehyde selectivity, surpassing both pristine CdS and the blend of CdS and Ni(terpyC)2. The carrier dynamics study demonstrated that the Ni(terpyC)2 on the surface of CdS could quickly extract the photogenerated electrons of CdS, which reduced the carrier recombination efficiency, further improving the photocatalytic activity of the catalyst. This work illustrates the effect of surface active site engineering on photocatalysis and is expected to shed substantial inspiration on future surface modulation and design of semiconductor photocatalysts.

Specific Photocatalytic C-C Coupling of Benzyl Alcohol to Deoxybenzoin or Benzoin by Precise Control of Cα-H Bond Activation or O-H Bond Activation by Adjusting the Adsorption Orientation of Hydrobenzoin Intermediates.

Benzyl alcohol (BA) is a major biomass derivative and can be further converted into deoxybenzoin (DOB) and benzoin (BZ) as high-value products for industrial applications through photocatalytic C-C coupling reaction. The photocatalytic process contains two reaction steps, which are (1) the C-C coupling of BA to hydrobenzoin (HB) intermediates and (2) either dehydration of HB to DOB or dehydrogenation of HB to BZ. We found that generation of DOB or BZ is mainly determined by the activation of Cα-H or O-H bonds in HB. In this study, phase junction CdS photocatalysts and Ni/CdS photocatalysts were elaborately designed to precisely control the activation of Cα-H or O-H bonds in HB by adjusting the adsorption orientation of HB on the photocatalyst surfaces. After orienting the Cα-H groups in HB on the CdS surfaces, the Cα-H bond dissociation energy (BDE) at 1.39 eV is lower than the BDE of the O-H bond at 2.69 eV, therefore improving the selectivity of the DOB. Conversely, on Ni/CdS photocatalysts, the O-H groups in HB orient toward the photocatalyst surfaces. The BDE of the O-H bonds is 1.11 eV to form BZ, which is lower than the BDE of the Cα-H bonds to the DOB (1.33 eV), thereby enhancing the selectivity of BZ. As a result, CdS photocatalysts can achieve complete conversion of BA to 80.4% of the DOB after 9 h of visible light irradiation, while 0.3% Ni/CdS photocatalysts promote complete conversion of BA to 81.5% of BZ after only 5 h. This work provides a promising strategy in selective conversion of BA to either DOB or BZ through delicate design of photocatalysts.

Robust photocatalytic hydrogen evolution performance of 0D/1D NiO/CdS S-scheme heterojunction

Constructing heterojunction, especially S-scheme heterojunction, is an effective strategy for achieving effective separation of photogenerated electron-hole pairs and obtaining high electrode potential. In this study, a unique 0D/1D NiO/CdS S-scheme heterojunction was constructed by solvent evaporation induced self-assembly method. The loading of NiO was found to greatly enhance the photogenerated carrier separation efficiency of CdS by photoluminescence (PL) spectroscopy, electrochemical impedance spectroscopy (EIS), Kelvin probe force microscopy (KPFM) and transient photocurrent tests. The best photogenerated carrier separation effect was observed at a NiO loading ratio of 15 wt% and the largest photocatalytic hydrogen evolution rate reached 7.89 mmol h-1g−1 under visible light, which was 24.66 times that of pristine CdS. In addition, the cycling experiments showed that the loading of NiO led to the alleviation of the photocorrosion phenomenon of CdS, and the performance remained at 94.2 % after five cycles. This is due to the fact that the formation of S-type heterojunction combines the photogenerated holes of CdS with the photogenerated electrons of NiO, which hinders the oxidation of S2- on the surface of CdS, thus alleviating the photocorrosion phenomenon of CdS and improving the stability of CdS. This work furnishes a new strategy for the development of stable and high-performance photocatalysts with inexpensive co-catalysts.

Probing into the Low Efficiency of CdS/SnS-based Solar Cells and Remediation through Surface Treatments

Tin sulfide (SnS) is a highly promising photovoltaic absorption material in thin-film solar cells with abundant reserves, environmental friendliness, low cost and long-term stability. An efficiency of up to 4.8% has been achieved for SnS absorber/CdS heterojunction solar cells where the CdS buffer layer is usually obtained by chemical bath deposition. However, current CdS/SnS devices often suffer from severe interface recombination loss, which deteriorates device performance. This report focuses on the CdS film surface to identify performance-degrading factors for CdS/SnS-based solar cells. XRD and XPS reveal numerous oxides on freshly fabricated CdS films increasing surface roughness and reducing conductivity. Herein, a method based on ammonium sulfide (AS) chemical treatment is proposed, which can effectively reduce the oxide content on the surface of CdS and optimize the band alignment, leading to the facilitation of charge carrier transport and the suppression of interface recombination. Consequently, the PCE of the FTO/CdS/SnS/Ag device is enhanced about three times (from 0.18% to 0.47%) with excellent moisture stability.

Preparation and mechanism study of highly sensitive NH3 gas sensor based on Au-modified CdS nanoparticles

A high-performance ammonia (NH3) gas sensor based on Au nanoparticles (AuNPs) modified CdS (Au/CdS) was synthesized by hydrothermal method, and the sensing mechanism of Au/CdS was studied by first-principles based on density functional theory (DFT). Experimental results show that the addition of AuNPs can effectively enhance CdS-based NH3 gas sensor performance. Au/CdS sensor exhibits high response (16580), short response/recovery time (2.25 s/1.25 s), and low limit detection (500 ppb), good repeatability and stability. Because AuNPs can effectively increase the generation of sulfur vacancies on the surface of CdS, increasing the amount of chemisorbed oxygen and providing more active sites for NH3. Furthermore, the good conductivity of AuNPs promotes the separation and transport of carriers on CdS surface, thereby improving the gas sensing performance. DFT calculations indicate that the ionization energy of Au is less than that of Cd, which causes some Cd atoms to lose their coordination with S atoms and increase sulfur vacancies on the surface of CdS. In Au/CdS sensors, sulfur vacancies accelerate the cleavage of NH3, and resulting electrons participate in charge transport, thereby enhancing the adsorption energy. This study introduces a new method for fabricating high performance NH3 sensor based on CdS rich in sulfur vacancies.

Surface sulphur vacancies of CdS/MIL-68(In)–NH2 for Boosting Visible-Light photocatalytic hydrogen evolution

The incorporation of sulfur vacancies (SVs) during the synthesis of CdS represents an essential approach for enhancing its photocatalytic hydrogen production performance. The CdS/MIL-68(In)–NH2 photocatalytic material with SVs was successfully synthesized via a facile two-step method and employed for visible light photocatalytic hydrogen evolution. Among various loading ratios, the CdS(30)/MIL-68(In)–NH2 composite exhibited remarkable photocatalytic performance, demonstrating hydrogen evolution rates 3.7 times and 7.3 times higher than those of pure CdS and mechanically mixed CdS with MIL-68(In)–NH2, respectively, while maintaining significant photocatalytic stability. The incorporation of MIL-68(In)–NH2 effectively enhanced the dispersion of CdS particles, thereby increasing the availability of active sites for efficient photocatalytic reactions. Moreover, the presence of SVs on the surface of CdS served as electron trapping levels, significantly improving charge separation efficiency. This study not only provides novel insights into fabricating composite photocatalysts but also explores a defect engineering regulation strategy.

Optimizing photocatalytic hydrogen evolution performance by rationally constructing S-scheme heterojunction to modulate the D-band center

The research in the field of photocatalysis has progressed, with the development of heterojunctions being recognized as an effective method to improve carrier separation efficiency in light-induced processes. In this particular study, CuCo2S4 particles were attached to a new cubic CdS surface to create an S-scheme heterojunction, thus successfully addressing this issue. Specifically, owing to the higher conduction band and Fermi level of CuCo2S4 compared to CdS, they serve as the foundation and driving force for the formation of an S-scheme heterojunction. Through in-situ X-ray photoelectron spectroscopy and electron paramagnetic resonance analysis, the direction of charge transfer in the composite photocatalyst under light exposure was determined, confirming the charge transfer mechanism of the S-scheme heterojunction. By effectively constructing the S-scheme heterojunction, the d-band center of the composite photocatalyst was adjusted, reducing the energy needed for electron filling in the anti-bonding energy band, promoting the transfer of photogenerated carriers, and ultimately enhancing the photocatalytic hydrogen production. performance. After optimization, the hydrogen evolution activity of the composite photocatalyst CdS-C/CuCo2S4-3 reached 5818.9 μmol g−1h−1, which is 2.6 times higher than that of cubic CdS (2272.3 μmol g−1h−1) and 327.4 times higher than that of CuCo2S4 (17.8 μmol g−1h−1), showcasing exceptional photocatalytic activity. Electron paramagnetic resonance and in situ X-ray photoelectron spectroscopy have established a theoretical basis for designing and constructing S-scheme heterojunctions, offering a viable method for adjusting the D-band center to enhance the performance of photocatalytic hydrogen evolution.

S vacancy in n-n type heterojunction accelerate electron transfer, improve the photocatalytic activity of CO2RR and H2 evolution

The introduction of anionic vacancies is a promising strategy to improve the photocatalytic activity of catalysts, however, the introduction of sulfur vacancy defects at the interface of heterojunction is a challenging task. Therefore, in this work, a secondary hydrothermal method was used to generate sulfur vacancy defects (Vs) at the interface of CdS/MoS2 heterojunction (Vs-CdS/MoS2), which was applied to photocatalytic reduction of CO2 and hydrogen evolution. The CO yield of the prepared CM-7 sample was 3.1 times higher than that of pristine CdS, and the H2 yield was 10.2 times higher. Experimental analysis showed that sulfur vacancies were detected on the (002) crystal surface of CdS in the heterojunction, providing active sites, redistributing the local charge, lowering the charge transport resistance and carrier complexation rate, and increasing the carrier migration rate, which led to the improvement of the photocatalytic activity. This work provides a novel strategy for designing heterojunctions with defect engineering applied to photocatalytic reduction of CO2 and hydrogen evolution.

Photodeposition of NiS thin film enhanced the visible light hydrogen evolution performance of CdS nanoflowers

The use of loaded co-catalysts has been found to be effective in addressing the issue of rapid recombination of photogenerated carriers, which can limit photocatalytic efficiency. Herein, we report on the adsorption of Ni2+ on the surface of CdS by photodeposition to obtain NiS/CdS composites. It improves visible light response while providing abundant active sites for photocatalytic reaction. NiS/CdS exhibits a superior photocatalytic H2 evolution rate of up to 7557 μmol·g−1·h−1, which is approximately 4.9 times higher than that of CdS. The corresponding AQE is 19.6% at 420 nm. XPS and photoelectrochemical testing provide a possible mechanism, indicating that the heterojunction between NiS and CdS promotes the transfer and separation of interfacial charge, thus accelerating the water decomposition reaction. This work demonstrates the effectiveness of loading two-dimensional thin film co-catalysts to design high-performance and low-cost composites for promoting the photocatalytic reaction.

CdS-based Schottky junctions for efficient visible light photocatalytic hydrogen evolution

Heterojunctions photocatalysts play a crucial role in achieving high solar-hydrogen conversion efficiency. In this work, we mainly focus on the charge transfer dynamics and pathways for sulfides-based Schottky junctions in the photocatalytic water splitting process to clarify the mechanism of heterostructures photocatalysis. Sulfides-based Schottky junctions (CdS/CoP and CdS/1T-MoS2) were successfully constructed for photocatalytic water splitting. Because of the higher work function of CdS than that of CoP and 1T-MoS2, the direction of the built-in electric field is from CoP or 1T-MoS2 to semiconductor. Therefore, CoP and 1T-MoS2 can act as electrons acceptors to accelerate the transfer of photo-generated electron on the surface of CdS, thus improving the charge utilization efficiency. Meanwhile, CoP and 1T-MoS2 as active sites can also promote the water dissociation and lower the H+ reduction overpotential, thus contributing to the excellent photocatalytic hydrogen production activity (23.59 mmol·h−1·g−1 and 1195.8 mol·h−1·g−1 for CdS/CoP and CdS/1T-MoS2).

Hot injection synthesis of CuS decorated CdS and ZnS nanomaterials from metal thiosemicarbazone complexes as single source precursors: Application in the photocatalytic degradation of methylene blue

CdS and ZnS are considered excellent semiconductors for photocatalysis, but photocorrosion and low photocatalytic activity limit their practical application. In order to improve on their photocatalytic activities, Copper sulfide-decorated CdS and ZnS (CuS@CdS and CuS@ZnS) nanocomposites were synthesized from Cu(II), Zn(II) and Cd(II) complexes of 2–(phenyl(pyridin–2–yl)methylene)hydrazine–1–carbothioamide, as single source precursors using a facile hot injection method at 250 °C, employing olive oil as capping agent. The structure, morphology, and optical properties of the as-prepared nanocomposites were determined using various analytical techniques. The results of powder X-ray diffraction (p-XRD), energy dispersive X-ray spectroscopy (EDX) and elemental mapping showed the presence of CuS, CdS and ZnS in CuS@CdS and CuS@ZnS, confirming the formation of nanocomposites. Transmission Electron Microscopy (TEM) images show agglomeration of CuS nanoparticles on the surface of CdS and ZnS nanoparticles. Scanning electron microscopy (SEM) images of CuS@CdS and CuS@ZnS nanocomposites revealed an agglomerated flower-like structure with porous surface. The band gap energies of 2.84 eV and 3.12 eV for CuS@CdS and CuS@ZnS, respectively, obtained from Tauc plots, demonstrate that combining CuS with single CdS and ZnS has an effect on their optical properties which probably account for the improved photocatalytic responses. The photocatalytic performance of the as-prepared materials was evaluated using the photodegradation of methylene blue (MB) dye under UV light irradiation. Results show that the degradation efficiencies for CuS@CdS (57 %) and CuS@ZnS (65 %) nanocomposites exhibited higher photocatalytic activity compared to those of pure CuS (42.0 %), CdS (35.1 %) and ZnS (57 %), suggesting that thiosemicarbazone complexes can be used as precursors for the development of metal sulphide nanocomposites as useful photocatalysts for the degradation of organic pollutants.

The effect of surface orientation on band alignment and carrier transfer at WS2/CdS interface: Insight from first-principles calculations

Loading of WS2 can greatly improve water splitting H2 generation efficiency of CdS in experiments. Here, we constructed WS2/CdS(100) and WS2/CdS(110) heterostructures with smaller mismatches and explored their interaction energy and band offset by first-principles calculations. Our calculation suggests that the WS2/CdS(100) interface with a stronger binding energy is more active in experiments, while the WS2/CdS(110) interface is metastable. The band alignment between CdS and WS2 is highly dependent on the orientation of the interfaces, and WS2/CdS(100) and WS2/CdS(110) belong to type-I and type-II band alignments, respectively. Therefore, a metal electrode and hole scavenger may be essential in experiments to help WS2/CdS(100) efficiently trap electrons, and a suitable substrate and an appropriate growth temperature are also needed to composite the CdS(110) surface to achieve a higher photocatalytic efficiency. In addition, we performed a detailed analysis of the macroscopic average potential and found that the calculated accuracy of potential difference across the heterostructures due to slab thickness is less than 80 meV at WS2/CdS interfaces. In total, our calculations not only explain the physical reasons for the increased efficiency of WS2/CdS, but also provide a detailed guideline for the design of a more efficient synergistic catalyst.

Hydrogen‐Bond‐Mediated Formation of C−N or C=N Bond during Photocatalytic Reductive Coupling Reaction over CdS Nanosheets

AbstractReductive amination of carbonyl compounds and nitro compounds represents a straightforward way to attain imines or secondary amines, but it is difficult to control the product selectivity. Herein, we report the selective formation of C−N or C=N bond readily manipulated through a solvent‐induced hydrogen bond bridge, facilitating the swift photocatalytic reductive coupling process. The reductive‐coupling of nitro compounds with carbonyl compounds using formic acid and sodium formate as the hydrogen donors over CdS nanosheets selectively generates imines with C=N bonds in acetonitrile solvent; while taking methanol as solvent, the C=N bonds are readily hydrogenated to the C−N bonds via hydrogen‐bonding activation. Experimental and theoretical study reveals that the building of the hydrogen‐bond bridge between the hydroxyl groups in methanol and the N atoms of the C=N motifs in imines facilitates the transfer of hydrogen atoms from CdS surface to the N atoms in imines upon illumination, resulting in the rapid hydrogenation of the C=N bonds to give rise to the secondary amines with C−N bonds. Our method provides a simple way to control product selectivity by altering the solvents in photocatalytic organic transformations.

Hydrogen-Bond-Mediated Formation of C-N or C=N Bond during Photocatalytic Reductive Coupling Reaction over CdS Nanosheets.

Reductive amination of carbonyl compounds and nitro compounds represents a straightforward way to attain imines or secondary amines, but it is difficult to control the product selectivity. Herein, we report the selective formation of C-N or C=N bond readily manipulated through a solvent-induced hydrogen bond bridge, facilitating the swift photocatalytic reductive coupling process. The reductive-coupling of nitro compounds with carbonyl compounds using formic acid and sodium formate as the hydrogen donors over CdS nanosheets selectively generates imines with C=N bonds in acetonitrile solvent; while taking methanol as solvent, the C=N bonds are readily hydrogenated to the C-N bonds via hydrogen-bonding activation. Experimental and theoretical study reveals that the building of the hydrogen-bond bridge between the hydroxyl groups in methanol and the N atoms of the C=N motifs in imines facilitates the transfer of hydrogen atoms from CdS surface to the N atoms in imines upon illumination, resulting in the rapid hydrogenation of the C=N bonds to give rise to the secondary amines with C-N bonds. Our method provides a simple way to control product selectivity by altering the solvents in photocatalytic organic transformations.

Introduction and Quantification of Sulfide Ion Defects in Highly Crystalline CdS for Photocatalysis Applications

To evaluate and diversify, control methods for surface defects in photocatalysts have surged because of their significant effect on carrier dynamics and reactivity. Sulfide photocatalysts, wherein anion defects act as electron traps, are not as extensively researched as oxide photocatalysts, and therefore, the knowledge of defects remains incomplete. Herein, simple treatments such as grinding, alkali immersion, and annealing are used to introduce surface defects into CdS, which is a representative sulfide photocatalyst. Moreover, Pt‐loaded CdS is prepared by reducing Pt ions using electrons trapped in the defects. The amount of defects on the CdS surface is successfully estimated by quantifying the amount of unreacted Pt ions through the absorbance of the reaction solution. The results indicate that the defect density can be increased using any of these employed methods. The surface state varies with the introduction method, leading to significant changes in photocatalytic activity. Grinding induces particle refinement and amorphization, alkali immersion induces oxidation and hydroxylation, and annealing enables the formation of a sulfurized surface. These surface conditions degrade the photocatalytic activity, and therefore, introduction of defects under relatively mild conditions is preferred. Herein, the sample calcined at 473 K shows the highest photocatalytic activity.

Investigation of Optical Characteristics and Synthesis of Cobalt-Doped Cds (Cds: Co) Using Simple and Rapid Microwave Activated Method

Cobalt-doped cadmium sulphide semiconductor nanoparticles (CdS: Co NPs) were made using a microwave-assisted method with different cobalt concentrations. Chemicals like sodium sulphide, cobalt chloride, and cadmium acetate were used. The Debye-Scherer equation helped find the nanoparticles' size, revealing a 2 to 4 nm range. X-ray diffraction showed a zinc-blend structure. The optical bandgap energies were found to be undoped and doped are 2.44eV and 2.58eV, respectively. For pure CdS, the XRD spectra display three main peaks at 2θ = 26.68°, 44.16°, and 52.32°. Modest alterations have been noted in 2θ for Co doping levels of 3% in CdS NPs. The peaks point to the samples' cubic structure and correlate to the (1 1 1), (2 2 0), and (3 1 1) planes. The sizes of the nanoparticles, which are 2.29 nm, 3.64 nm, for pure and Co (3%) doped CdS, were determined using the FWHM and Debye Scherer equation. The substitution of Co2+ion for Cd2+ion may be the cause of the decrease in nanoparticle size observed in the Co-doped CdS sample as concentration rises. The difference in the ionic radii of Cd2+ (0.98 Å) and Co2+ (0.72 Å) shows that when the concentration of Co-doped CdS increases, the lattice constant falls. The peak at 3646 cm-1 in the higher energy area of the 400–4000 cm–1 FTIR spectra is attributed to the O–H stretching of absorbed water on the surface of CdS. Its bending vibration confirms the existence of water. Using HRTEM, the size of the produced nanoparticles was examined. Additionally, it confirms the sample's nanocrystalline structure. For 3% Co-doped CdS, the average size of randomly chosen nanoparticles is determined.

Tailoring Advanced CdS Anisotropy-Driven Charge Spatial Vectorial Separation and Migration via In Situ Dual Co-Catalyst Synergistic Layout.

Tailoring advanced anisotropy-driven efficient separation and migration of photogenerated carriers is a pivotal stride toward enhancing photocatalytic activity. Here, CdS-MoS2 binary photocatalysts are tailored into a dumbbell shape by leveraging the rod-shaped morphology of CdS and employing an in situ tip-induction strategy. To further enhance the photocatalytic activity, an in situ photo-deposition strategy is incorporated to cultivate MnOx particles on the dumbbell-shaped CdS-MoS2. The in situ deposition of MnOx effectively isolated the oxidatively active sites on the CdS surface, emphasizing the reductively active crystalline face of CdS, specifically the (002) face. Benefiting from its robust activity as a reduction active site, MoS2 adeptly captures photogenerated electrons, facilitating the reduction of H+ to produce hydrogen. The anisotropically driven separation of CdS photogenerated carriers markedly mitigates the Coulomb force or binding force of the photogenerated electrons, thus promoting a smoother migration toward the active site for photocatalytic hydrogen evolution. The hydrogen evolution rate of 35MnOx-CdS-MoS2-3 surpasses that of CdS by nearly an order of magnitude, achieving a quantum efficiency of 22.30% at 450nm. Under simulated solar irradiation, it attains a rate of 42.86mmol g-1 h-1. This work imparts valuable insights for the design of dual co-catalysts, anisotropy-driven spatial vectorial charge separation and migration, and the analysis of migration pathways of photogenerated carriers.

Simultaneously Regulating charge separation and proton supply-demand in polyphenol amine for hydrogen peroxide photosynthesis

In the H2O2 photosynthesis, apart from the charge separation, the balance of proton supply and demand was also required between the kinetically faster oxygen reduction reaction (ORR) (μs ∼ ms) and the sluggish kinetics of water oxidation reaction (WOR) (s). Faced by this challenge, the article designed the heterojunction photocatalyst formed by in-situ polymerization of polyphenol amine on the surface of CdS under alkaline conditions. As a result, the synthesized CdS-Poly(catechol-hexamethylenediamine) (PCHA) produced 6.1 mM H2O2 after 8 h of visible light irradiation, which is 29 times that of CdS. The experimental results evidenced that the coating of PCHA increased the charge separation and mobility, inhibited the photocorrosion of CdS, and thus enhanced the stability and photoactivity. Moreover, the catechol units of PCHA could function as a proton supplier and regulate local protons concentrations around the catalytic active sites to balance the proton supply–demand in the ORR and WOR at different reaction time scales.

Preparation and performance study of humidity sensor based on defect-controlled TiO2/CdS heterostructure

In this paper, a high-performance impedance humidity sensor based on defect control TiO2/CdS heterostructure was synthesized by hydrothermal method, and the influence of surface vacancy defects on sensing performance was analyzed by first principles based on density functional theory (DFT). Calculation results show that a large number of surface oxygen and sulfur vacancies appear on the surface of TiO2 and CdS, resulting in a great enhancement of the physical/chemical adsorption energy of TiO2 and CdS on water molecules, which is conducive to TiO2/CdS to capture more water molecules and improving the humidity sensitivity performance of the sensor. Experiments show that the regulation of surface vacancy defects of composite materials can effectively improves responsivity, linearity and hysteresis of TiO2/CdS humidity sensor. Compared with TiO2 and CdS, the TiO2/CdS humidity sensor exhibits high sensitivity (63459), fast response/recovery time (7/5 s), low hysteresis (∼3.5 %), good repeatability and long-term stability in a range of 11–95 % RH. This study not only provides an idea for designing defective TiO2/CdS high-performance humidity sensors, but proposes a new understanding for exploring the underlying mechanism of sensor performance.

Growth of CdS heterojunctions on Cd0.9Zn0.1Te single crystals with H2S

Polished Cd0.9Zn0.1Te (CZT) single crystals have been exposed to dilute H2S in nitrogen at temperatures from 200 to 280 °C in order to produce a sulfide layer on the surface. The composition of the CZT surfaces before and after H2S exposure has been investigated by photoemission, x-ray absorption, cross-sectional SEM, and spectroscopic ellipsometry. At the highest temperature, H2S exposure removes surface oxides and depletes Te, leaving a CdS surface layer. CdS layers 60 nm thick have been grown with a 2 h exposure to H2S at 280 °C. Surfaces that are initially oxidized through ozone exposure are much more reactive with H2S than unintentionally oxidized surfaces.