Blue luminescence from porous layers produced by metal-assisted chemical etching on low-doped silicon

Photoluminescent porous layers were formed on highly resistive p-type silicon by a metal-assisted chemical etching method using K₂Cr₂O₇ as an oxidizing agent. A thin layer of Ag is deposited on the (1 0 0) Si surface prior to immersion in a solution of HF and K₂Cr₂O₇. The morphology of the porous silicon (PS) layer formed by this method as a function of etching time was investigated by scanning electron microscopy (SEM). It shows that the surface is formed by macropores filled with microporous silicon. The porous layers were characterized by backscattering spectrometry (BS) as a function of etching time in random and channelling mode. Channelling spectra show that the porous layer remains crystalline after etching. On the other hand, random and channelling spectra show that the deposited silver diffuses into the pore. Luminescence from metal-assisted chemically etched layers was measured. It was found that the PL intensity increases with increasing etching time. This behaviour is attributed to increase of the density of the silicon nanostructure. Finally, the PL spectra show two peaks of emission at 450 and 600 nm.     

Optimisation of the epi-ready semi-insulating GaAs wafer preparation procedure

The surface quality is crucial for growth of epitaxial layers on III-V semiconductor substrates. In this work the procedures of epi-ready semi-insulating (SI) GaAs wafer preparation were developed. The atomic force microscopy (AFM), triple crystal X-ray diffraction (TCD) and X-ray photoelectron spectroscopy (XPS) were used to monitor morphology and composition of substrates with different chemical treatment history. We propose an optimised epi-ready SI GaAs wafer preparation procedure involving NH₄OH:H₂O₂:H₂O/NaOCl:H₂O₂:H₂O etching/polishing.     

Morphology of porous silicon under long anodic etching in electrolyte with internal current source

The results of electron microscopy investigation of morphology of porous silicon (PS) received under long anodic etching by using internal current source in electrolytes such as HF:H₂O₂:H₂C₅OH and HF:H₂O₂ are presented. Mosaic structure of nanoporous silicon is observed as the islands separated by silicon ledges. It was shown that these islands are presented as assemble of oxidized nanocrystallites and silicon ledges. The results of elemental analysis of islands of oxidized nanocrystallites and silicon ledges are presented.     

Attribution of white-light emitting centers with carbonized surface in nano-structured SiO2:C layers

Carbon incorporated silicon oxide layers were fabricated by carbonization of porous silicon layer in acetylene atmosphere followed by oxidation in wet argon. The resulting porous SiO₂:C material exhibited a strong white photoluminescence. Subsequent thermal treatment in oxygen at 600 °C significantly decreased the green-yellow part of photoluminescence band while blue shoulder remained unchanged. Annealing at the same temperature in pure argon did not change light-emission properties indicating that the green-yellow light-emission sites originate from the surface. This study focuses on the interface of silicon oxide matrix and carbon inclusions by high-resolution scanning transmission electron microscopy (STEM) combined with electron energy loss spectroscopy (EELS). It is confirmed by EELS and STEM that the green-yellow emission band is associated with the carbonized interface in the porous layer.     

Liquid etching of metallization layers on GaAs/Al <Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript> as heterostructures with HNO<Subscript>3</Subscript> + HCl + glycerol mixture

A program package is developed for simplex-lattice-design processing of the data on etching of solid systems in multicomponent etchants. The procedure suggested is implemented in studying the processes of etching of metallization layers on GaAs/Al _x Ga_{1 ? x} As semiconductor heterostructures in an HNO₃: HCl: glycerol etching mixture. The etchant compositions are selected to implement controllable removal of Au layers at a rate of 8–10 Å s^?1, with such quality of the surface of the epitaxial structure that allows the subsequent procedures specified by planar technology and the microscopic structural studies of multilayer metallization. The results are applied to the analysis of the characteristics of contacts to the GaAs/Al _x Ga_{1 ? x} As heterostructures in developing photoelectric detectors and can be used in replacing the operation of “dry” etching with the operation of “wet” etching during the technological cycle of formation of GaAs-based device structures.     

Chemical etching of (100) GaAs in a sulphuric acid-hydrogen peroxide-water system

A detailed investigation of the etching of (100) GaAs in H₂SO₄-H₂O₂-H₂O systems has been made. The influence of the concentration of particular etchant components on etching rate and on the shape of the crystal surface was examined. From these results the Gibbs' triangle of etching bath compositions was divided into parts corresponding to the various states of the crystal surfaces and various etching mechanisms. The shape of the crystal surface after etching was closely related to the profiles of the grooves etched in the [110] direction in the same solution.     

Patterning of porous silicon nanostructures and eliminating microcracks on silicon nitride mask using metal assisted chemical etching

A method for selective formation of reproducible, high fidelity and controllable nano and micrometer size porous Si areas over n-type Si wafers is provided. A 400 nm thick Silicon Nitride layer was used as the mask layer while Platinum and Palladium nanoparticles were deposited over the unprotected areas to obtain porous areas through metal assisted chemical etching process. Nanoparticles were deposited by electroless plating solutions containing H₂PtCl₆ and PdCl₂. Good controls over pore size and depth were obtained with well defined and sharp edges of the patterned areas. The results were compared to porous structures obtained via electrochemical etching process, indicating the superiority of metal assisted etching in terms of its simplicity as well as the ability of Silicon Nitride layer acting as the mask layer.     

Growth of ZnO thin films at low temperature by plasma-enhanced atomic layer deposition using H2O and O2 plasma oxidants

Zinc oxide (ZnO) thin films were grown at 70 °C by plasma-enhanced atomic layer deposition using H₂O and O₂ plasmas. Plasma oxidants were used in order to improve the ZnO crystallinity and optoelectronic properties, avoiding high-temperature synthesis. The deposition parameters were optimized to achieve saturation in each reaction step. X-ray photoelectron spectroscopy (XPS) reveals high purity of the obtained ZnO films. X-ray diffraction (XRD) measurements indicate that the grown layers are polycrystalline and that the H₂O plasma synthesis leads to better crystallinity than the O₂ plasma as inferred from the intensity of the (100) and (002) peaks. The films are with high optical transmission, ~90%, as inferred from UV–visible (UV–Vis) transmittance measurements, and optical band gaps of 3.22 and 3.23 eV for H₂O and O₂ plasma, respectively. Atomic force microscopy (AFM) indicates that the films are smooth, with an average roughness of ~?0.22 nm. The growth rate was found to be in the range of 1.2–1.4 Å/cycle. The XPS, XRD, UV–Vis, and AFM results prove the possibility to obtain high-quality ZnO films by O₂ and H₂O plasma processes at 70 °C with chemical, structural, and optical properties promising for flexible electronics. ZnO films were successfully deposited on polyethylene terephthalate substrates using the optimal conditions for H₂O plasma process. No damage of the film surface or substrate was observed.

     

Influence of Treatment Conditions on the Chemical Oxidative Activity of H2SO4/H2O2 Mixtures for Modulating the Topography of Titanium

Host‐tissue integration of medical implants is governed by their surface properties. The capacity to rationally design the surface physico‐chemical cues of implantable materials is thus a fundamental prerequisite to confer enhanced biocompatibility. Our previous work demonstrated that different cellular processes are elicited by the nanotexture generated on titanium (cpTi) and Ti6Al4V alloy by chemical oxidation with a H₂SO₄/H₂O₂ mixture. Here, we illustrate that by varying the etching parameters such as temperature, concentration, and treatment time, we can create a variety of surface features on titanium which are expected to impact its biological response. The modified submicron and nanotextured surfaces were characterized by scanning electron (SEM) and atomic force (AFM) microscopies. Contact angle measurements revealed the higher hydrophilicity of the modified surfaces compared to untreated samples and Fourier transform infrared spectroscopy (FT‐IR) established that the etching generated a TiO₂ layer with a thickness in the 40–60 nm range.     

Structure of hydrogeno bis (dihydrogeno diphosphonate) trithallium: T13H(H2CH2P2O6)2

T1₃H(H₂CH₂P₂O₆)₂ was found to be monoclinic B2/b, a = 10.736 (6) Å, b = 12.382 (7) Å, c = 11.527 (4) Å, γ = 106.11 (5)°, Z = 4. The structure was solved with MULTAN and refined to R(Fo) = 0.063 for 1500 reflections measured with MoKα radiation. This structure can be described as a succession, parallel to the (100) plane, of diphosphonate groups and thallium ions layers.Hydrogen bondings are found between the diphosphonate groups' layers. This bonding conduct to the formation of anionic group (H₂CH₂P₂O₆HH₂CH₂P₂O₆)³⁻ analogous to the (H₂P₂O₇HH₂P₂O₇)³⁻ complex anion.     

Synthesis and structural study of new potassium uranyl selenates K2(H5O2)(H3O)[(UO2)2(SeO4)4(H2O)2](H2O)4 and K3(H3O)[(UO2)2(SeO4)4(H2O)2](H2O)5

Single crystals of new uranyl selenates K₂(H₅O₂)(H₃O)[(UO₂)₂(SeO₄)₄(H₂O)₂](H₂O)₄ (1) and K₃(H₃O)[(UO₂)₂(SeO₄)₄(H₂O)₂](H₂O)₅ (2) were prepared by isothermal evaporation at room temperature. The crystal structure of 1 was solved by the direct method [C2/c, a = 17.879(5), b = 8.152(5), c = 17.872(5) Å, β = 96.943(5)°, V = 2585.7(19) ų, Z = 4] and refined to R ₁ = 0.0449 (wR ₂ = 0.0952) for 2600 reflections with |F _o| ≥ 4σ _F . The structure of 2 was solved by the direct method [P2₁/c, a = 17.8377(5), b = 8.1478(5), c = 23.696(1) Å, β = 131.622(2)°, V = 2574.5(2) ų, Z = 4] and refined to R ₁ = 0.0516 (wR ₂ = 0.1233) for 4075 reflections with |F _o| ≥ 4σ _F . The structures of 1 and 2 are based on [(UO₂)₂(SeO₄)₄(H₂O)₂]^4? layers. The charge of the inorganic layer is compensated by potassium and oxonium ions arranged in the interlayer space. Each K ion is surrounded by seven O atoms belonging to uranyl selenate layers and water molecules, so that it binds with each other the adjacent uranyl selenate structural elements.     

Thermal quenching of 3.0-eV photoluminescence in α-Al2O3 single crystals

The thermal quenching of 3.0-eV photoluminescence (PL) in oxygen-deficient α-Al₂O₃ single crystals upon preliminary UV irradiation has been studied. It is established that the parameters of the PL quenching kinetics vary within broad limits depending on the duration of UV pretreatment. The compensation effect related to a change in the energy state of the thermodynamic system “F-centers-electron traps” has been observed.     

Reactive ion etching of ZnS films for thin-film electroluminescent devices

Reactive ion etching (RIE), employing CH₄/H₂/Ar plasmas, of ZnS films grown by metalorganic chemical vapor deposition (MOCVD) is reported. The etching rates are investigated as functions of the plasma parameters: pressure, RF power and relative composition of reactive gases. It is found that the amount of CH₄ in a CH₄/H₂/Ar gas discharge will decide whether the polymer will be produced. The optimum composition of the mixed gas is 1CH₄/7H₂/4Ar, when the pressure, RF power and total flow rate are 30 mTorr, 245 W and 30 sccm, respectively. The etching mechanism is also proposed. The quality of the etched surfaces under these conditions is examined by X-ray photoelectron spectroscopy. It is found that the amount of overt damage is small under these etching conditions. A dot-matrix thin-film electroluminescent device employing a ZnS:Mn phosphor layer is also fabricated by this etching process.     

Reactive ion etching of diamond in CF4, O2, O2 and Ar-based mixtures

The reactive ion etching of diamond in O₂, CF₄/O₂, CHF₃/O₂, O₂/Ar discharges has been examined as a function of bias voltage, flow rate and composition of the gas mixtures. Etching in O₂ and O₂/Ar plasmas (with flow ratio of O₂/Ar 25%) was characterised by a high etch rate (35 nm/min) and an increase in surface roughness with rising bias voltage. The CF₄/O₂ plasmas also produced a high etch rate (50 nm/min) but with only minor dependence of roughness on bias voltage. In comparison, the O₂/Ar (with O₂/Ar flow ratio <25%) and CHF₃/O₂ plasmas resulted in a low etch rate (7–10 nm/min). The high and low rate regimes were identified as ionenhanced chemical etching and physical sputtering respectively. Etching in the O₂/Ar plasmas has been attributed to a combination of the two processes dependent on the O₂ content.     

Chemical etching of (100) GaAs in the (NH4)2Cr2O7-H2SO4-N H4Cl-H2O system

The etching solution containing ammonium dichromate, sulphuric acid and ammonium chloride in water solution allows for the investigation of the influence of individual active components and their concentration on the etching reaction with GaAs. The influence of these agents on etching as well as the temperature and stirring were examined. The etching rate increases with increasing Cl^– ion concentration, increases and subsequently decreases with the increasing of H⁺ ion concentration and remains constant in the wide range of oxidant anion concentration. The effect of stirring on etching rate allows us to estimate regions dominated by diffusion kinetics. The activation energy in the wide range of parameters is constant and equal to 60 kJ mol^–1. Microscopic observations reveal surfaces of various morphologies: smooth; covered with round hills; or with a network of veins. Various profiles of grooves arranged in various directions are revealed due to the preferential characteristic of etching; these profiles are also influenced by the mask material.     

Colloids of Holey Gd2O3 Nanosheets Converted from Exfoliated Gadolinium Hydroxide Layers

This paper proposes a confined solid‐state conversion approach using layered metal‐hydroxides for the production of a colloidal suspension of porous 2D crystalline metal oxide layers with superior electrochemical H₂O₂ sensing performance. This study investigates the conversion chemistry of delaminated layers of gadolinium hydroxide (LGdH), [Gd₂(OH)₅]⁺, encapsulated in a silica nanoshell that provides an antistacking and antisintering environment during the phase‐transition at high temperature. Thermal treatment of the LGdH layers within the protected environment results in a dimensionally confined phase‐transition into crystalline Gd₂O₃ nanosheets with an isomorphic 2D structure. Furthermore, annealing at higher temperatures leads to the evolution of in‐plane mesoporous structure on the Gd₂O₃ nanosheet. Based on insight acquired from in‐depth investigation, the evolution of in‐plane porosity proceeds through the in‐plane dominant silicate‐formation reaction at the interface with the surrounding silica shell. Their 2D‐anisotropic and mesoporous morphological features are preserved, producing a colloidal suspension of holey nanosheets that can be used to fabricate a thin and porous film through wet‐coating deposition. This study also demonstrates the superior electrochemical H₂O₂ sensing ability of the resultant porous Gd₂O₃ film, which represents a ≈1000‐ and 10‐fold enhancement of the detection limit and sensitivity, respectively, in comparison to previously reported Gd₂O₃ films.     

Nature of intrinsic and impure luminescence of MAlP2O7 crystals

The results of the photoluminescence (PL) investigation of pure and chromium-doped MAlP₂O₇ (M = Na, K, Cs) compounds are presented. The spectra of the intrinsic luminescence of MAlP₂O₇ crystals consist of a separated UV band at a peak position near 330 nm and a complex wide band which covers the region of visible light up to 750 nm at excitation by VUV synchrotron radiation. The “red” band in 600–1000 nm diapason appears in the PL spectra of crystals doped with chromium ions. The effect of the temperature on the structure, the peak positions and intensities of the luminescence bands was studied. An assumption about the nature of the intrinsic PL was made. The “red” luminescence was considered as a result of the ⁴Т₂ → ⁴А₂ radiation transitions in the impurity Cr³⁺ ions located in the intermediate crystal field.     

Surface etching effects of amorphous C:H and CNx:H films formed by supermagnetron plasma for field emission use

Supermagnetron plasma was used to deposit amorphous hydrogenated carbon (a-C:H) and hydrogenated carbon nitride (a-CN_x:H) films for field-emission devices using i-C₄H₁₀/(H₂ or N₂). It was also used to improve the field-emission characteristics by surface etching using N₂/H₂ plasma. The best emission threshold electric field (E_TH) was 13 and 12 V/μm for devices using as-deposited a-C:H and as-deposited a-CN_x:H films, respectively, while they were remarkably improved to 11 and 8 V/μm by surface etching using N₂/H₂ (120/40 sccm) gas, though surface roughness was slightly increased by the surface etching. The hardness of as-deposited films was higher than 22 GPa.     

The nature of white luminescence in SiO2:C layers

Silicon oxide layers containing incorporated carbon (SiO₂:C) have been obtained by sequential thermal carbonization/oxidation of porous silicon. The as-synthesized SiO₂:C layers exhibit intense white photoluminescence (PL). The characteristics of excitation, emission, and relaxation of the white luminescence in the SiO₂:C layers have been studied. It is established that the observed broad PL band in fact consists of at least two subbands with the maxima of intensity in the green and blue spectral regions. Based on the experimental data, a model of the PL excitation and radiative recombination in SiO₂:C layers is proposed and justified.     

Evaporation chimique du GaAs sous flux d'hydrogene et d'acide chlorhydrique

Studies of the etching behavior of GaAs with HCl as a function of temperature and etchant concentration indicate that temperature is the most significant parameter affecting the smoothness of the “B” face of the III-V compound. Similars results has been obtained with H₂ as etching gas only. Etching rates in mg.min^?1 and in microns.min^?1 are drawn.