H2S Plasma Research Articles

Biosynthesis of H2S is impaired in non‐obese diabetic (NOD) mice

Hydrogen sulphide (H2S) has been involved in cardiovascular homoeostasis but data about its role in animal models of diabetic pathology are still lacking. Here, we have analysed H2S signalling in a genetic model of diabetes, the non-obese diabetic (NOD) mice. NOD mice exhibit a progressive endothelial dysfunction characterized by a reduced reactivity of blood vessels as diabetes develops. NOD mice were divided into three groups according to different glycosuria values: NOD I, NOD II and NOD III. Age-matched non-obese resistant (NOR) mice were used as controls. H(2)S levels in plasma and aortic tissue were measured. Functional studies in aorta were carried out in isolated organ baths using both an exogenous source of H2S (NaHS) and the metabolic precursor (L-cysteine). Real time PCR and western blot analysis were also carried out on aortic tissues. NOD mice exhibited a progressive reduction of H2S plasma levels, which paralleled disease severity. L-cysteine-induced H2S production by aortic tissues was also progressively reduced. L-cysteine-induced vasorelaxation was significantly reduced in NOD mice while NaHS-induced relaxation was unaffected. ODQ (guanylate cyclase inhibitor), L-NAME (NO synthase inhibitor) or PAG, an inhibitor of cystathionine-gamma-lyase (CSE) inhibited H2S production induced by L-cysteine. In NOD mice, endogenous H2S production is significantly impaired. Also, the ability of isolated aorta to respond to exogenous H2S is enhanced and endothelium-derived NO appears to be involved in the enzymatic conversion of L-cysteine into H2S.

硫化氢等离子体钝化790 nm 激光器腔面的研究

In order to improve the optical properties of the III-V laser diodes (LDs) by means of H2S plasma passivation technology, H2S plasma passivation treatment is performed on the GaAs(110) surface. The optimum passivation conditions obtained are 60-W radio frequency (RF) power and 20-min duration. So the laser cavity surfaces are treated under the optimum passivation conditions. Consequently, compared with unpassivated lasers with only AR/HR-coatings, the catastrophic optical damage (COD) threshold value of the passivated lasers by H2S plasma treatment is increased by 33%, which is almost the same as that of (NH4)2Sx treatment. And the life-test experiment has demonstrated that this passivation method is more stable than (NH4)2Sx solution wet-passivated treatment.

Optical properties of ZnS1−xSex alloys fabricated by plasma-induced isoelectronic substitution

Nonequilibrium growth of thin-film ternary ZnS1−xSex semiconductor alloys was accomplished using physical vapor deposition with simultaneous electron cyclotron resonance H2S plasma activation. Substrate temperature, gas flow, and plasma power determine the ZnS1−xSex alloy composition and structure. Integrated optical transmission spectra for the ZnS1−xSex semiconductor alloys as a function of H2S plasma power are presented. Using the α2 vs hν plots for the various ZnS1−xSex films, the optical band gap Eg is extrapolated from each curve. This methodology yields the values of the band gap as a function of stoichiometry. We observe that the plasma induced isoelectronic substitution of S into the ZnSe lattice increases the band gap. This study shows that plasma-induced isoelectronic substitution is technologically feasible and useful for fabricating ternary II–VI alloys under nonequilibrium conditions.

Photoreflectance study of H2S plasma-passivated GaAs surface

Photoreflectance is used to study the effect of H2S plasma passivation on the GaAs surface. GaAs samples are treated with a H2S plasma in an electron cyclotron resonance chemical vapor deposition system and in-situ encapsulated with a SiNx film. The surface Fermi level moves towards the conduction band after H2S plasma passivation and a surface state density of 6×1010 cm−2 is achieved under optimal passivation conditions. The surface state density is highly dependent on the sample temperature during passivation. The movement of the surface Fermi level is due to the reduction of the surface state density and not due to a shift of midgap surface states, suggesting that S–Ga bonds play the major role in H2S plasma passivated GaAs surfaces. This work demonstrates the need to measure both the surface Fermi level and the density of surface states.

Novel method for growing CdS on CdTe surfaces for passivation of surface states and heterojunction formation

Large-grain polycrystalline CdTe was subjected to in situ H2S plasma processing for <30 min at 100 and 200 °C. High-resolution x-ray photoemission measurements on the Cd 4d, Te 4d, and S 2p core levels, and the valence band were used to determine the resultant chemical environment of S and the electronic structure at the CdTe surface following plasma processing. Auger electron spectroscopy compositional depth profiling was also used to determine the distribution of S in the near surface region. Furthermore, time-resolved photoluminescence was used to measure carrier lifetimes and, thus, determine the degree of passivation of CdTe surface states. These results provide evidence for a CdS/CdS1−xTex/CdTe heterojunction device structure, as a result of the H2S plasma processing, and a reduction in the surface recombination velocity through passivation of surface states. This is a novel method of fabricating CdS/CdTe heterojunction devices.

Surface type conversion of CuInSe2 with H2S plasma exposure: A photoemission investigation

Surface type conversion of CuInSe2 by H2S plasma exposure was studied by synchrotron radiation soft x‐ray photoemission spectroscopy. The low power H2S plasma was generated with a commercial electron cyclotron resonance plasma source using pure H2S with the plasma exposure being performed at 400 °C. In situ photoemission measurements were acquired after each plasma exposure in order to observe changes in the valence band electronic structure as well as changes in the In 4d and Se 3d core lines. The results were correlated in order to relate changes in surface chemistry to the electronic structure. These measurements indicate that the H2S plasma exposure type converts the n‐type CuInSe2 surface to a p‐type surface at this elevated temperature and that the magnitude of the band bending is 0.5 eV, resulting in a homojunction interface.

Investigation on the effect of isoelectronic substitution in ZnS1−xSex alloys

The composition, structure, and optical properties of thin-film ZnS1−xSex semiconductor alloys were studied by x-ray photoemission spectroscopy, x-ray diffraction, and optical transmission. Nonequilibrium growth of the ternary II–VI semiconductor alloys was accomplished using molecular beam epitaxy with simultaneous electron cyclotron resonance H2S plasma activation to form the ZnS1−xSex alloys. Photoemission measurements were used to identify changes in bulk composition and valence band electronic structure as well as changes in the Zn 3d, Se 3d, and S 2p core lines. X-ray diffraction measurements revealed that these films contain the cubic phase and that the lattice constant decreases with sulfur content. Correlation of these results with growth parameters indicates that substrate temperature, gas flow, and plasma power determine the ZnS1−xSex alloy composition and structure. In addition, optical transmission measurements showed that substitution of S into the ZnSe lattice shifted the cutoff from 460 to 380 nm.

Surface type conversion of InP by H2S plasma exposure: A photoemission investigation

The surface chemistry and the electronic structure of InP(100) before and after exposure to a H2S plasma was investigated by synchrotron radiation soft x-ray photoemission spectroscopy. The low power H2S plasma was generated with a commercial electron cyclotron resonance plasma source using H2S with the plasma exposure being performed as a function of incident angle and temperature. Plasma species were identified with optical emission spectroscopy. In situ photoemission measurements were acquired after each plasma exposure in order to observe changes in the valence band electronic structure as well as changes in the In 4d, P 2p, and S 2p core lines. The results were correlated in order to relate the plasma species and characteristics to changes in surface chemistry and electronic properties. These measurements indicate that the H2S plasma exposure type converts the p-type InP(100) surface to an n-type surface resulting in a shallow homojunction interface.

Hydrogen sulfide plasma passivation of indium phosphide

The electrical properties of the SiO2-InP interface are improved using in-situ H2S plasma pretreatments as a reliable method of sulfidizing the InP surface prior to film deposition. High frequency (1 MHz) and quasi-static capitance-voltage measurements on metal-insulator-semiconductor structures show reduced interface trap densities. X-ray photoemission spectroscopy analysis indicates that prior to film deposition, sulfur is bonded to phosphorus at the surface; but after film deposition, very little sulfur remains. Spectroscopic ellipsometry measurements confirm that the interface does remain modified even after film deposition, and photoluminescence data show increased signal intensity for thin SiO2 film on InP with H2S pretreatments as compared to untreated samples.

Photoemission Investigation on The Effect of H2S Plasma Exposure of InP

Synchrotron radiation soft x-ray photoemission spectroscopy was used to characterize the surface chemistry and the electronic structure of InP(100) before and after exposure to an H 2 S plasma. The low power plasma was generated with an electron cyclotron resonance (ECR) plasma source, using H 2 S, with the plasma exposure being performed at two temperatures. In-situ photoemission measurements were acquired after each plasma exposure in order to observe changes in the valence band electronic structure and in the In4d, P2 p and S2 p core lines. The results revealed changes in surface chemistry and electronic properties and indicate that the H 2 S plasma exposure type converts the ptype InP(100) surface to an n-type surface. The magnitude of the band bending is dependent on the substrate temperature, resulting in a homojunction interface.