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1.
Highly oriented silicon nanowire (SiNW) layer was fabricated by etching Si substrate in HF/(AgNO3 + Na2S2O8) solution at 50 °C. The morphology and the photoluminescence (PL) of the etched layer as a function of Na2S2O8 concentration were studied. The SiNW layers formed on silicon were investigated by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX). It was demonstrated that the morphology of the etched layers depends on the Na2S2O8 concentration. Room-temperature photoluminescence (PL) from etched layer was observed. It was found that the utilisation of Na2S2O8 decreases PL peak intensity. Finally, a discussion on the formation process of the silicon nanowires is presented.  相似文献   

2.
It was demonstrated that the etching in HF-based aqueous solution containing AgNO3 and Na2S2O8 as oxidizing agents or by Au-assisted electroless etching in HF/H2O2 solution at 50 °C yields films composed of aligned Si nanowire (SiNW). SiNW of diameters ∼10 nm were formed. The morphology and the photoluminescence (PL) of the etched layer as a function of etching solution composition were studied. The SiNW layers formed on silicon were investigated by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and photoluminescence. It was demonstrated that the morphology and the photoluminescence of the etched layers strongly depends on the type of etching solution. Finally, a discussion on the formation process of the silicon nanowires is presented.  相似文献   

3.
In this work, an experimental study on the chemical etching reaction of polycrystalline p-type 6H-SiC was carried out in HF/Na2O2 solutions. The morphology of the etched surface was examined with varying Na2O2 concentration, etching time, agitation speed and temperature. The surfaces of the etched samples were analyzed using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) Fourier transform infrared spectroscopy (FT-IR) and photoluminescence. The surface morphology of samples etched in HF/Na2O2 is shown to depend on the solution composition and bath temperature. The investigation of the HF/Na2O2 solutions on 6H-SiC surface shows that as Na2O2 concentration increases, the etch rate increases to reach a maximum value at about 0.5 M and then decreases. A similar behaviour has been observed when temperature of the solution is increased. The maximum etch rate is found for 80 °C. In addition, a new polishing etching solution of 6H-SiC has been developed. This result is very interesting since to date no chemical polishing solution has been developed on the material.  相似文献   

4.
In this work, we present the formation of porous layers on hydrogenated amorphous SiC (a-SiC: H) by Ag-assisted photochemical etching using HF/K2S2O8 solution under UV illumination at 254 nm wavelength. The amorphous films a-SiC: H were elaborated by d.c. magnetron sputtering using a hot pressed polycrystalline 6H-SiC target. Because of the high resistivity of the SiC layer, around 1.6 MΩ cm and in order to facilitate the chemical etching, a thin metallic film of high purity silver (Ag) has been deposited under vacuum onto the thin a-SiC: H layer. The etched surface was characterized by scanning electron microscopy, secondary ion mass spectroscopy, infrared spectroscopy and photoluminescence. The results show that the morphology of etched a-SiC: H surface evolves with etching time. For an etching time of 20 min the surface presents a hemispherical crater, indicating that the porous SiC layer is perforated. Photoluminescence characterization of etched a-SiC: H samples for 20 min shows a high and an intense blue PL, whereas it has been shown that the PL decreases for higher etching time. Finally, a dissolution mechanism of the silicon carbide in 1HF/1K2S2O8 solution has been proposed.  相似文献   

5.
X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) have been used to investigate the effect of reactive ion etching (RIE) on poly(methylhydrogensiloxane-co-dimethylsiloxane) surface in fluorine-based plasmas. Polysiloxane layers supported on the standard silicon wafers were etched using SF6 + O2 or CF4 + O2 plasmas. SEM studies show that the polysiloxane morphology depends on plasma chemical composition strongly. Presence of a columnar layer likely covered with a fluorine rich compound was found on the elastomer surface after the CF4 + O2 plasma exposure. After the SF6 + O2 or CF4 + O2 plasma treatment the polysiloxane surface enriches with fluorine or with fluorine and aluminum, respectively. Different morphologies and surface chemical compositions of the silicone elastomer etched in both plasmas indicate different etching mechanisms.  相似文献   

6.
In this paper, we present an experimental study on the chemical and electrochemical etching of silicon carbide (SiC) in different HF-based solutions and its application in different fields, such as optoelectronics (photodiode) and environment (gas sensors). The thin SiC films have been grown by pulsed laser deposition method. Different oxidant reagents have been explored. It has been shown that the morphology of the surface evolves with the etching conditions (oxidant, concentration, temperature, etc.). A new chemical polishing solution of polycrystalline 6H-SiC based on HF:Na2O2 solution has been developed. Moreover, an electrochemical etching method has been carried out to form a porous SiC layer on both polycrystalline and thin SiC films. The PL results show that the porous polycrystalline 6H-SiC and porous thin SiC films exhibited an intense blue luminescence and a green-blue luminescence centred at 2.82 eV (430 nm) and 2.20 eV (560 nm), respectively. Different device structures based on both prepared samples have been investigated as photodiode and gas sensors.  相似文献   

7.
The paper presents an approach to enhance a magnetoresistance (MR) effect in CrO2 powder compact by an oxidization reaction process. An aqueous potassium permanganate (KMnO4) was used to react with the CrO2 particles coated naturally with Cr2O3 layer. The experiment indicates that the strong oxidant can effectively adjust thickness of the natural Cr2O3 layer, and thereby change the surface state of the CrO2 particles. Structural and magnetic properties for the improved CrO2 particles have been characterized by X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS) and SQUID magnetometer. The results exhibit that the magnetotransport behavior of CrO2 particles depends sensitively on the chemical reaction time. An optimal reaction process yields an obvious increase up to −33% in magnetoresistance at a temperature of 5 K for the chemical treated CrO2 powder, compared to MR=-27% for the original CrO2 powder. The mechanism of magnetotransport is assumed to originate from the spin-dependent tunneling in the granular system, which is consistent with our experimental results. The simple chemical approach has a potential to achieve an enhanced magnetoresistance in a metallic particle system by adjusting the surface state of the magnetic nanoparticle.  相似文献   

8.
This very paper is focusing on the preparation of porous nanostructures in n-type silicon (1 1 1) wafer by chemical etching technique in alkaline aqueous solutions of 5 M NaOH, 5 M K2CO3 and 5 M K3PO4, and particularly, on its ultraviolet-blue photoluminescence emission. The anodic chemical etched silicon wafer has been characterized by means of optical microscopy, scanning electron microscopy, fluorescence spectroscopy, atomic force microscopy and Fourier transform infrared spectroscopy. This very surface morphology characterization has been clearly shown - the effect of anodic-chemical-etching procedure processed in K2CO3 or K3PO4 was much vigorous than that processed in NaOH. The FTIR spectra indicate that the silicon oxide was formed on the surface of electrochemical etched n-Si (1 1 1) wafers, yet not on that of the pure chemical etched ones anyhow. And an intense ultraviolet-blue photoluminescence emission is observed, which then differs well from the silicon specimen etched in alkaline solution with no anodic potential applied. The proper photoluminescence mechanism is discussed, and hence there may be a belief that the intense ultraviolet-blue photoluminescence emission would be attributed to the silicon oxide coating formed on silicon wafer in anodic-chemical-etching process.  相似文献   

9.
Multicrystalline silicon wafers are used for approximately half of all solar cells produced at present. These wafers typically have dislocation densities of up to ∼106 cm−2. Dislocations and associated impurities act as strong recombination centres for electron–hole pairs and are one of the major limiting factors in multicrystalline silicon substrate performance. In this work we have explored the possibility of using chemical methods to etch out the cores of dislocations from mc-Si wafers. We aim to maximise the aspect ratio of the depth of the etched structure to its diameter. We first investigate the Secco etch (1K2Cr2O7 (0.15 M): 2HF (49%)) as a function of time and temperature. This etch removes material from dislocation cores much faster than grain boundaries or the bulk, and produces tubular holes at dislocations. Aspect ratios of up to ∼7:1 are achieved for ∼15 μm deep tubes. The aspect ratio decreases with tube depth and for ∼40 μm deep tubes is just ∼2:1, which is not suitable for use in bulk multicrystalline silicon photovoltaics. We have also investigated a range of etches based on weaker oxidising agents. An etch comprising 1I2 (0.01 M): 2HF (49%) attacked dislocation cores, but its etching behaviour was extremely slow (<0.1 μm/h) and the pits produced had a low aspect ratio (<2:1).  相似文献   

10.
Surface chemistry of a commercial activated carbon (AC) and of products oxidized in liquid phase using aqueous solutions of a series of oxidizing agents (H2SO4, HNO3, HClO4, H2O2, O3, ClO2, KlO4 and KMnO4) has been studied by FT-IR. Oxidation led to surface groups and structures which, and also the extend of formation, depended on the oxidizing agent and the pH and concentration of the solution used. Most oxidizing agents proved to be effective for the formation of surface C[dbnd]O groups. Variations in pH of solutions of H2O2, KlO4 and KMnO4 unequally affected the oxidation of AC. This was unfavourable with the increase in concentration of the solutions of HNO3 and KMnO4. The reverse was noted with KlO4.  相似文献   

11.
Arsenic trisulphide (As2S3) thin films have been deposited onto stainless steel and fluorine doped tin oxide (FTO) coated glass substrates by electrodeposition technique using arsenic trioxide (As2O3) and sodium thiosulphate (Na2S2O3) as precursors and ethylene diamine tetracetic acid (EDTA) as a complexing agent. Double exposure holographic interferometry (DEHI) technique was used to determine the thickness and stress of As2S3 thin films. It was observed that the thickness of the thin film increases whereas film stress to the substrate decreases with an increase in the deposition time. X-ray diffraction and water contact angle measurements showed polycrystalline and hydrophilic surface respectively. The bandgap energy increases from 1.82 to 2.45 eV with decrease in the film thickness from 2.2148 to 0.9492 μm.  相似文献   

12.
Li2O-CaF2-P2O5 glasses mixed with different concentrations of Cr2O3 (ranging from 0 to 1.0 mol%) were crystallized. The samples were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy (EDS), differential thermal analysis and conventional spectroscopic techniques. The X-ray diffraction and scanning electron microscopic studies reveal the presence of lithium phosphate, calcium phosphate and chromium phosphate (complexes of Cr3+, Cr5+ and Cr6+ ions) crystal phases. The study on DTA suggests that the crystallization is predominantly due to the surface crystallization when the concentration of nucleating agent Cr2O3 is around 0.8 mol%. The IR and Raman spectral studies of these samples indicate that the sample crystallized with 0.8 mol% Cr2O3 is more compact and possesses high rigidity due to the presence of chromium ions largely in tetrahedral positions.  相似文献   

13.
Nanoleaf-like Bi2S3 thin films were deposited on indium tin oxide (ITO) glass using Bi(NO3)3 and Na2S2O3 as precursors by a cathodic electrodeposition process. The as-deposited thin films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and photoluminescence spectrum (PL). The influence of precursor solution mole concentration ratios [Bi(NO3)3]/[Na2S2O3] on the phase compositions, morphologies and photoluminescence properties of the obtained thin films were investigated. Results show that a uniform Bi2S3 thin film with nanoleaf structure can be obtained with the precursor solution concentration ratio [Bi(NO3)3]/[Na2S2O3] = 1:7. The as-prepared thin films exhibit blue-green photoluminescence properties under ultraviolet light excitation. With the increase of concentration ratios [Bi(NO3)3]/[Na2S2O3] in the deposition solution, the crystallizations and PL properties of Bi2S3 thin films are obviously improved.  相似文献   

14.
A novel electroless method of producing porous silicon carbide (PSiC) is presented. Unlike anodic methods of producing PSiC, the electroless process does not require electrical contact during etching. Rather, platinum metal deposited on the wafer before etching serves as a catalyst for the reduction of a chemical oxidant, which combined with UV illumination injects holes into the valence band, the holes subsequently participating in the oxidation and dissolution of the substrate. The etchant is composed of HF and K2S2O8 in water. Various porous morphologies are presented as a function of etchant concentration, time of etching, and SiC polytype. Wafer quality is of the utmost concern when utilizing the electroless wet etchant, since defects such as stacking faults, dislocations, and micropipes have a large impact on the resulting porous structure. Results of imaging and spectroscopic characterization indicate that the porous morphologies produced in this manner should be useful in producing sensors and porous substrates for overgrowth of low dislocation density epitaxial material.  相似文献   

15.
The Au-assisted electroless etching of p-type silicon substrate in HF/H2O2 solution at 50 °C was investigated. The dependence of the crystallographic orientation, the concentration of etching solution and the silicon resistivity on morphology of etched layer was studied. The layers formed on silicon were investigated by scanning electron microscopy (SEM). It was demonstrated that although the deposited Au on silicon is a continuous film, it can produce a layer of silicon nanowires or macropores depending on the used solution concentration.  相似文献   

16.
The enthalpies of solution of pure silver halides AgCl and AgI and a composite material with molar composition 0.5 AgCl-0.5 AgI were measured at 298 K in a mixture of Na2S2O3 (1 M) and NH4OH (1 M). X-ray diffraction patterns showed that the composite material contained the metastable γ-AgI phase; different mechanisms for its stabilization were discussed. The phase transition enthalpies of AgI modifications and the enthalpy of formation of the composite material were deduced from the measurements. The latter could be related to a change of interfacial enthalpies.  相似文献   

17.
Cr-doped mullites were prepared from single-phase precursors containing up to 9.60 wt% Cr2O3 using a sol-gel technique followed by thermal treatment. Particle induced X-ray emission spectroscopy and X-ray powder diffraction were used to characterize the samples. Mullites were orthorhombic, space group Pbam. Cr doping caused the increase of unit-cell parameters. Strongest expansion was noticed along c-axis followed by a and bc/c=0.089, Δa/a=0.061, Δb/b=0.045% per mole Cr2O3). A second phase, namely θ-(Al,Cr)2O3, was revealed by XRD in the sample containing 9.60 wt% Cr2O3. The structure of mullites was refined by the Rietveld method, location of Cr3+ was performed by the EPR spectroscopy. At low chromium doping level (Cr2O3 content less than ∼5 wt%) Cr3+ ions were substituted for Al3+ in the AlO6 octahedra of the mullite structure (M1 site). For higher doping level, Cr3+ ions were additionally substituted for Al3+ in the AlO6 octahedra of the second phase [θ-(Al,Cr)2O3 at 1400 °C, or α-(Al,Cr)2O3 at 1600 °C] which segregated in the system. Substitution of Cr3+ for Al3+ on M1 site in the mullite structure resulted in increase of average distances in (M1)O6 octahedron and decrease of average distances in T*O4 tetrahedron, while average distances in TO4 tetrahedron stayed almost constant.  相似文献   

18.
Porous silicon is the most studied Si-based light-emitting material. The potential for the application of porous silicon in optoelectronics and also for chemical or biochemical sensing is high. Therefore, the successful patterning of porous silicon on Si wafers is of great interest. HF-based aqueous solutions containing H2O2 as oxidizing agent, in combination with appropriate metal deposition, can supply the necessary current in order to sustain the electrochemical etching of single crystalline Si under no external anodic bias. The H2O2 concentration can tune the etching rate of the Si wafers as well as the observed photoluminescence intensity and photon energy. We demonstrate that porous silicon growth can be preferentially initiated at sites where metal (Pt) has been deposited and effectively be confined there, in order to form a well-defined pattern of desired geometry. Conventional DC sputtering using stainless-steel masks was applied in order to test various patterning geometries and lengthscales. Photoluminescence spectroscopy, atomic force and optical microscopy were used in order to characterize the produced porous silicon patterns. This method could be a simple, cost-effective way for the production of porous silicon patterns on Si wafers, which could be used in various fields of application.  相似文献   

19.
In this study, we investigated the surface properties of diamond-like carbon (DLC) films for biomedical applications through plasma etching treatment using oxygen (O2) and hydrogen (H2) gas. The synthesis and post-plasma etching treatment of DLC films were carried out by 13.56 MHz RF plasma enhanced chemical vapor deposition (PECVD) system. In order to characterize the surface of DLC films, they were etched to a thickness of approximately 100 nm and were compared with an as-deposited DLC film. We obtained the optimum condition through power variation, at which the etching rate by H2 and O2 was 30 and 80 nm/min, respectively. The structural and chemical properties of these thin films after the plasma etching treatment were evaluated by Raman and Fourier transform infrared (FT-IR) spectroscopy. In the case of as-deposited and H2 plasma etching-treated DLC film, the contact angle was 86.4° and 83.7°, respectively, whereas it was reduced to 35.5° in the etching-treated DLC film in O2 plasma. The surface roughness of plasma etching-treated DLC with H2 or O2 was maintained smooth at 0.1 nm. These results indicated that the surface of the etching-treated DLC film in O2 plasma was hydrophilic as well as smooth.  相似文献   

20.
We report a novel method of growing red luminescent (635 nm) Mn-doped CdS (CdS:Mn) nanoparticles capped by an inorganic shell of Mn(OH)2. CdSO4, Na2S2O3 and Mn(NO3)2 were used as the precursors, and thioglycerol (C3H8O2S) was employed as the capping agent and also the catalyst of the reaction. Using these materials resulted in very slow rate of the reaction and particles growth. The self-assembled one-pot process was performed at pH of 8 and Mn:Cd ratio of 10, and took about 10 days for completion. CdS:Mn nanoparticles are slowly formed in the first day of the process; however, the luminescence is weak. After 7 days, the solution turns white turbid through the formation of additional particles, which precipitate on the walls on the next day. At this stage, a relatively strong red luminescence at 635 nm appears from transparent solution of the CdS:Mn nanoparticles. The white deposit on the walls turns to dark-brown color and luminescence increases on the 9th day. Finally, the CdS:Mn nanoparticles agglomerate and precipitate out of the solution on 10th day. X-ray diffraction and optical spectroscopy showed crystalline phase CdS nanoparticles with an average size of 3.6 nm. We explain the luminescence enhancement based on the formation of a Mn(OH)2 shell on the surface of the CdS:Mn nanoparticles during the precipitation stage. This can passivate the S dangling bonds located on the particles surface. As the surface Cd sites are previously capped with thioglycerol molecules, a complete surface passivation is achieved and results in emergence of high-intensity luminescence.  相似文献   

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