Surface ablation of RbTiOPO4 by femtosecond laser

We report here the results obtained in surface ablation of RbTiOPO₄ single crystals by femtosecond laser. We fabricated and characterized one-dimensional (1D) diffraction gratings with different lattice spacings of 15 and 20 μm, and with a sub-modulation of the period introduced in the later. The optical and electronic microscopy characterization and filling factor analysis of these diffraction gratings are reported. We also show that the roughness generated on the grooves by the ablation process can be improved by chemical etching.     

Etching-enhanced growth of indentation crack in barium titanate single crystal

The effect of etching on an unloaded indentation crack in a poled BaTiO₃ single crystal whose poling direction is lying in or normal to the indentation plane, has been investigated. The result showed that for the sample whose poling direction was lying in the indentation plane, the indentation cracks and 90° domain switching zones surrounded by two pairs of indentation cracks grew gradually during etching using HCl + HF aqueous solution, and reached saturation after etching for 30 s, however, the effect of etching on the crack length and the size of the domain switching zone was very small for the sample whose poling direction was normal to the indentation plane. Etching-enhanced domain switching and crack propagating is due to adsorption-decreased surface energy.     

Influence of Electric Poling on Pb0.9Bi0.1Fe0.55Nb0.45O3 Multiferroic

This paper analyzes the influence of electric poling on structure, magnetism, and ferroelectricity by temperature-dependent Raman scattering (180 K–500 K), magnetic susceptibility, and ferroelectric measurements on Pb_0.9Bi_0.1Fe_0.55Nb_0.45O₃ (PBFNO) multiferroic. X-ray diffraction (XRD) has confirmed the monoclinic structure for PBFNO sample before and after poling. Rietveld refined XRD for poled and unpoled sample shows the influence of electric poling on Fe-O1, Fe-O2, Nb–O, and Bi-O modes with small variation in the lattice parameters. The unpoled PBFNO exhibits broad and overlapping 10 active modes at room temperature (100 to 1300 cm^?1) at 147, 212, 255, 431, 479, 561, 700, 795, 835, and 1112 cm^?1. In case of a poled sample, Pb–O and Nb–O-Nb modes become more active compared to the unpoled sample. Changes observed in the temperature-dependent magnetic measurements, i.e., ZFC/FC and M-H loop, evidence the poling effects on Fe–O and Nb–O active modes. By poling the improvement in ferroelectric domain, ordering occurs, and it is confirmed by P-E loops. The consequences of numerous investigations on electric poling of PBFNO will provide the foundation for future device development and design.

     

Submicron-resolved relief formation in poled glasses and glass-metal nanocomposites

The formation of a spatial relief reproducing that of the anode as a result of the thermal poling of glasses and glass-metal nanocomposites in a strong electric field has been studied by atomic force microscopy. The anode surface patterns exhibited either a square grid or a rectangular grating with a depth of 120 nm, a strip width of 0.5 μm, and a period of 1 μm manufactured using electron-beam lithography and ion etching on the surface of an n-type single crystal silicon wafer. The relief depth formed on the surface of poled samples varied within 5–15 nm, depending on the experimental conditions. The mechanism of relief formation in this system is discussed.     

Thinning of CIGS solar cells: Part I: Chemical processing in acidic bromine solutions

CIGSe absorber was etched in HBr/Br₂/H₂O to prepare defined thicknesses of CIGSe between 2.7 and 0.5 μm. We established a reproducible method of reducing the absorber thickness via chemical etching. We determine the dissolution kinetics rate of CIGSe using trace analysis by graphite furnace atomic absorption spectrometry of Ga and Cu. The roughness of the etching surface decreases during the first 500 nm of the etching to a steady state value of the root-mean-square roughness near 50 nm. X-ray photoelectron spectroscopy analyses demonstrate an etching process occurring with a constant chemical composition of the treated surface acidic bromine solutions provide a controlled chemical thinning process resulting in an almost flat surface and a very low superficial Se⁰ enrichment.     

改善MEMS闪耀光栅衍射效率的研究

研究了在硅材料上利用MEMS (Micro-Electro-Mechanical System)的各向异性腐蚀技术制备 闪耀光栅。采用氧化削尖工艺去除光栅制备过程中掩膜在闪耀面上留下的平台,得到一个连续的闪耀面;同时对闪耀面进行表面抛光,改善闪耀面的粗糙度,减小对入射光的散射。理论分析和实验测试证明,该工艺方法能够将MEMS闪耀光栅的衍射效率提高10%左右。     

Effect of poling field and temperature on dielectric and piezoelectric property of 〈0 0 1〉-oriented 0.70Pb(Mg1/3Nb2/3)O3–0.30PbTiO3 crystals

Effect of poling conditions (different poling fields and temperatures) on dielectric and piezoelectric property of 〈0 0 1〉-oriented 0.70Pb (Mg_1/3Nb_2/3)O₃–0.30PbTiO₃ crystal was investigated. The results show, that it is easy for the crystal to be full poled in high temperature, while it is difficult for the crystal in low temperature. An appropriate poling condition for the crystals is suggested.     

X-ray photoelectron spectroscopy characterization of the interface between Ag electrode and PVDF film treated by electric poling

Interface changes induced by electric poling treatment between an Ag electrode deposited by vacuum thermal evaporation and a polymer thin film have been investigated. The polymer film poly (vinylidene fluoride) (PVDF), a fluoropolymer of repeat unit (–CH₂–CF₂–) was treated under electric poling at high temperature of 90°C. The characterization was accomplished using X-ray photoelectron spectroscopy (XPS) as a primary tool. The results indicate that the piezoelectricity of PVDF thin films and adhesion force between polymer thin film and metallic electrode are improved by electric poling and chemical bond joint.     

Effect of chemical etching on the surface morphology of laser-patterned lines with Er-doped CaF2 nanocrystals in oxyfluoride glass

The chemical etching behavior for the lines consisting of Er³⁺-doped CaF₂ nanocrystals patterned on the surface of an oxyfluoride glass by using a laser-induced crystallization technique (laser: Yb-doped YVO₄; wavelength: 1080 nm; power: 1.7 W; a scanning speed: 2 μm/s) in a nitric acid solution (1N HNO₃) is examined, and the morphology change in the lines due to the etching is characterized from confocal laser microscope observations and photoluminescence (PL) spectrum measurements of Er³⁺ ions. The higher and wider bumps compared with the bump of the original line (no etching) are observed in etched lines, and in particular, the surrounding of lines is etching away preferentially, forming the groove in both sides of line. PL spectra of Er³⁺ ions with strong intensities are observed from etched lines, suggesting that Er³⁺-doped CaF₂ nanocrystals are largely present just at the surface of etched lines. It is found that the chemical etching rate (1.2 × 10⁻² μm/min) of the crystallized bulk sample is smaller than that (5.4 × 10⁻² μm/min) of the precursor bulk glass, suggesting that CaF₂ nanocrystals formed have a high resistance against the chemical attack.     

HFCVD grown graphene like carbon–nickel nanocomposite thin film as effective counter electrode for dye sensitized solar cells

The two step processes of hot filament chemical vapor deposition (HFCVD) and DC sputtering were used to grow graphene like carbon (GLC)–nickel (Ni) nanocomposite thin film on fluorine-doped tin oxide (FTO) glass and applied as counter electrode (CE) for dye sensitized solar cells (DSSCs). The morphological and absorption properties revealed uniform GLC–Ni thin film with reasonable transmittance. The GLC–Ni thin film showed enhanced electrical conductivity as compared to FTO. The good electrocatalytic activity towards iodide ions in redox electrolyte was showed by the prepared GLC–Ni/FTO thin film electrode. The fabricated DSSC with GLC–Ni/FTO counter electrode (CE) presented relatively moderate solar-to-electrical conversion efficiency of ∼3.1% with high short-circuit current density (J_SC) of ∼10.03 mA/cm², open circuit voltage (V_OC) of ∼0.663 V with fill factor (FF) of ∼0.45, which might attribute to enhanced electrical conductivity and the electrocatalytic activity of GLC–Ni/FTO CE.     

Photocatalyst TiO2–Co: the effect of doping depth profile on methylene blue degradation

In this work, we study the effect of doping depth profile on the photocatalytic and surface properties of TiO₂ films. Two thin film layers of TiO₂ (200 nm) and Co (5 nm), respectively, were deposited by physical evaporation on glass substrate. These films were annealed for 1 s at 100 and 400 °C and the Co layer was removed by chemical etching. Atomic force microscopy (AFM) phase images showed changes in the surface in function of thermal treatment. The grazing-incidence X-ray fluorescence (GIXRF) measurements indicated that the thermal treatment caused migration of Co atoms to below the surface, the depths found were between 19 and 29 nm. The contact angle showed distinct values in function of the doped profile or Co surface concentration. The UV–vis spectra presented a red shift with the increasing of thermal treatment. Photocatalytical assays were performed by methylene blue discoloration and the higher activity was found for TiO₂–Co treated at 400 °C, the ESI-MS showed the fragments formed during the methylene blue decomposition.     

A room temperature etching route to tungsten oxide hydrate nanoplates with expanded surface area

Tungsten oxide hydrate nanoplates with expanded surface area have been synthesized through the acid treatment of tungstate−aluminum keggin nanocomposite. According to powder X-ray diffraction and W L_III-edge X-ray absorption spectroscopic analyses, X-ray amorphous nanocomposite is changed into crystalline WO₃·2H₂O upon the acidic etching of alumina component. Nitrogen adsorption−desorption isotherm and field emission-scanning electron microscopy measurements clearly demonstrated that the surface area of the nanocomposite is increased by the selective etching of alumina component, a result of the formation of the porous stacking assembly of nanoplates. From optoelectrochemical analysis, the etched derivative is found to be applicable as an electrode material for electrochromic devices. Based on the experimental findings, we are able to conclude that the present selective etching method can provide a soft-chemical synthetic route to nanocrystalline metal oxides with expanded surface area.     

New roots to formation of nanostructures on glass surface through anodic oxidation of sputtered aluminum

New processes for the preparation of nanostructure on glass surfaces have been developed through anodic oxidation of sputtered aluminum. Aluminum thin film sputtered on a tin doped indium oxide (ITO) thin film on a glass surface was converted into alumina by anodic oxidation. The anodic alumina gave nanometer size pore array standing vertically on the glass surface. Kinds of acids used in the anodic oxidation changed the pore size drastically. The employment of phosphoric acid solution gave several tens nanometer size pores. Oxalic acid cases produced a few tens nanometer size pores and sulfuric acid solution provided a few nanometer size pores. The number of pores in a unit area could be changed with varying the applied voltage in the anodization and the pore sizes could be increased by phosphoric acid etching. The specimen consisting of a glass substrate with the alumina nanostructures on the surface could transmit UV and visible light. An etched specimen was dipped in a TiO₂ sol solution, resulting in the impregnation of TiO₂ sol into the pores of alumina layer. The TiO₂ sol was heated at ∼400 °C for 2 h, converting into anatase phase TiO₂. The specimens possessing TiO₂ film on the pore wall were transparent to the light in UV–Visible region. The electro deposition technique was applied to the introduction of Ni metal into pores, giving Ni nanorod array on the glass surface. The removal of the barrier layer alumina at the bottom of the pores was necessary to attain smooth electro deposition of Ni. The photo catalytic function of the specimens possessing TiO₂ nanotube array was investigated in the decomposition of acetaldehyde gas under the irradiation of UV light, showing that the rate of the decomposition was quite large.     

Field-induced effect in the <111>-oriented 0.70Pb(Mg1/3Nb2/3)O3–0.30PbTiO3 single crystals

Temperature-dependent dielectric constant, X-ray diffraction(XRD), thermally stimulated discharging current (TSDC) and polarization hysteresis loops for <111>-oriented 0.70Pb(Mg_1/3Nb_2/3)O₃–0.30PbTiO₃ crystals after poling under different fields were measured. Comparing with unpoled sample during heating, except that there is a transition from the state of normal ferroelectric rhombohedral (macro-domain) to the state of relaxor ferroelectric rhombohedral (micro-domain) for the poled samples, it was found that no other phase transition was induced by poling fields. XRD showed that after poling the piezoelectric elongation of the unit cell occurred along the polar direction. It was suggested that an extra peak in the T–ε curve of poled sample around 105 °C is not only caused by a macro–micro domain transition but also caused by the depolarization process of 180° and 71° domain switching simultaneously.     

光刻胶灰化用于全息离子束刻蚀光栅制作

针对全息离子束刻蚀衍射光栅制作中,光刻胶光栅浮雕图形的制作是至关重要和困难的,引入O2反应离子刻蚀对光刻胶光栅进行灰化处理,给出光刻胶灰化技术在全息离子束刻蚀衍射光栅制作闪耀光栅、浅槽矩形位相光栅、自支撑透射光栅中的具体应用。实验结果表明,这一新工艺的突出优点是降低了苛刻的全息曝光、显影要求,使得光栅线条光滑、线空比和槽深可控。     

Pt nanoparticles on graphene – polyelectrolyte nanocomposite: Investigation of H2O2 and methanol electrocatalysis

Poly (diallyldimethylammonium chloride) (PDDA) functionalized graphene oxide (GO) decorated with Pt nanoparticles (PtNPs) was obtained and investigated. This hybrid nanocomposite material was morphologically characterized by several instrumental techniques like high-resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED) and X-ray diffraction (XRD). Good coverage of crystalline Pt nanoparticles was achieved, the average diameter being 2 nm, meanwhile in the absence of polyelectrolyte the average diameter increased up to 4 nm. The electrocatalytic properties of this hybrid nanocomposite against H₂O₂ and methanol were ascertained by cyclic voltammetry. A modified glassy carbon electrode (GC) was able to reduce H₂O₂ at positive potentials (starting from ∼150 mV vs. Ag/AgCl) meanwhile for methanol the ratio of the forward anodic peak current (I_f) to the reverse anodic peak current (I_b) was 1.42, indicating good tolerance of the catalyst towards the intermediate carbonaceous species accumulated on the electrode surface.     

A low-temperature pyroelectric study of PVDF thick films

Pyroelectric coefficient measurements were made at various temperatures for poled and unpoled samples of PVDF films. Samples were produced using the spin-coating technique onto glass substrates. Experiments were made using the quasi-static technique. PVDF samples were poled at various electric field strengths and the relation between poling field strength and the pyroelectric coefficient was investigated. The effect of the poling temperature was also studied. The maximum pyroelectric coefficient was obtained for a poling temperature of 340 K and for a poling field strength of . Dielectric permitivity and dielectric loss measurements were also performed in the 125–375 K temperature range.     

Influence of annealing temperature on domain shape of periodically poled LiNbO3 for Ti:LN waveguides

Periodically poled LiNbO₃ (PPLN) has been fabricated with a 16.6 μm domain-inverted period, a 3.0 μm thick photoresist grating, and a 3.3 μm pattern open width through the electric field poling process using the liquid electrode technique. The average duty cycle for the fabricated PPLN was measured to be 49.9 ± 3.3%. The effect of annealing temperatures on the domain shape of PPLN was investigated in the range of 300 to 800 °C. At 300 °C, residual stress was not relieved completely. As the annealing temperature increases above 800 °C, the domain shape changes. However, no domain damage was observed for annealing temperatures from 400 to 700 °C. The best annealing temperature for the suppression of domain damage and the improvement in the crystalline quality was found to be 400 °C.     

Analysis of Far-field Diffraction Characteristics of Wavelength-sized Surface Relief Gratings

The rigorous boundary matching technique was used to analyse the far-field diffraction from wavelength-sized surface relief gratings for TE polarization. Diffraction characteristics of such surface relief gratings were studied as functions of complex refractive index, groove depth and the angle of incidence. The surface field at the bottom of the grooves is more severely influenced by the edges and walls for metallic material than dielectric ones. The reflectivities of gold gratings show significant fluctuation for different incident wavelengths. This can be clearly seen from the fact that the zeroth-order diffraction efficiency DE ₀ of gold is lower than that of aluminium at u = 0·4 wm but higher at u = 1·0 wm. It is also shown that the depth of the grooves has significant influences on the diffraction efficiencies, an optimum depth can be chosen to minimize the specular component. However, this optimum depth value is found to be different for the gratings of different materials, e.g. aluminium and gold, although the gratings have exactly the same size and shape. The effect of the incident angle, particularly at critical angles when certain diffracted waves are just about to be cut off was discussed. The zeroth-order diffraction efficiencies are found to change noticeably at the critical angles.     

Influence of reemission of neutrals on the shape of etched grooves

The plasmochemical etching of silicon in CF₄+O₂ plasma is considered. The chemical composition of plasma and values of reaction rate constants, determined in previous works, were used to calculate the etched groove profiles at real dimensions. The profiles of etched grooves are calculated as a function of mask dimensions, fluxes of chemically active components and reemission of chemically active components from the surface of groove. The etching anisotropy is reduced when the reemission of F and O atoms from the surface takes place. The increase of etching anisotropy at high O₂ content in the feed (>60%) is explained by the complete sidewall oxidation and decreased concentration of F atoms in the plasma. The influence of reemission of F and O atoms on the shape of etched grooves becomes pronounced for mask width >1 μm.