飞秒强激光对二氧化钛金红石晶体相变的影响

该文章报道了利用显微激光拉曼光谱仪研究近红外飞秒强激光脉冲诱导二氧化钛金红石单晶所引起的相变.实验辐照时间为60s,当激光辐照平均功率增加时,锐钛矿相的拉曼振动模式强度增强,金红石相的拉曼振动模式强度减弱.通过金红石相和锐钛矿相粉体等拉曼光谱的实验,肯定了随着辐照激光功率的增大,.可以通过拉曼光谱中锐钛矿A1g B1g(515 cm-1)振动模式标志峰和金红石相Eg(445 cm-1)振动标志峰分别对应面积的比判断其相变量.     

Characterization and antibacterial functions of Ag–TiO<Subscript>2</Subscript> and W–TiO<Subscript>2</Subscript> nanostructured thin films prepared by sol-gel/laser-induced technique

A novel sol-gel/laser-induced technique (SGLIT) has been developed to form nanocrystalline titanium dioxide (TiO₂) based thin films with an improved antibacterial performance. TiO₂ precursor films loaded with W⁺⁶ and Ag⁺² ions (W–TiO₂, Ag–TiO₂) were prepared separately by sol-gel method and spin-coated on microscopic glass slides. As-dried films were subjected to KrF excimer laser pulses at optimized parameters to generate mesoporous anatase and rutile phases at room temperature. The anatase phase was obtained after irradiation with 10 laser pulses only at 75–85 mJ/cm² fluence in W–TiO₂ films. However, higher number of laser pulses and higher W⁺⁶ content favored the formation of rutile. Whereas Ag–TiO₂ films exhibited anatase up to 200 laser pulses at the same fluence. The films were characterized by using XRD, FEG-SEM, TEM and UV-Vis spectrophotometer to investigate the crystallographic structure, phase transformation, surface morphology, film thickness and the optical properties. A crystallite size of approximately 20 nm was achieved from the anatase prepared by SGLIT. The films exhibited an enhanced antibacterial function against E-Coli cells under the UV excitation.     

Raman study of phase transformation of TiO2 rutile single crystal irradiated by infrared femtosecond laser

Titanium dioxide (TiO₂) rutile single crystal was irradiated by infrared femtosecond (fs) laser pulses with repetition rate of 250 kHz and phase transformation of rutile TiO₂ was observed. Micro-Raman spectra show that the intensity of E_g Raman vibrating mode of rutile phase increases and that of A_1g Raman vibrating mode decreases apparently within the ablation crater after fs laser irradiation. With increasing of irradiation time, the Raman vibrating modes of anatase phase emerged. Rutile phase of TiO₂ single crystal is partly transformed into anatase phase. The anatase phase content transformed from rutile phase increased to a constant with increasing of fs pulse laser irradiation time. The study indicates the more stable rutile phase is transformed into anatase phase by the high pressure produced by fs pulse laser irradiation.     

Annealing effects on microstructural and optical properties of Nanostructured-TiO2 thin films prepared by sol-gel technique

In this paper we report on the effect of annealing on the microsctructural and optoelectronic properties of titanium dioxide (TiO₂) thin films prepared using sol-gel method onto silicon (Si) (100) and quartz substrates. The annealing temperatures range from 200 to 1000 °C. The Microstructural properties of annealed thin films were investigated by Thermal gravimetric analyses (TGA), X-ray diffraction (XRD) and Raman Spectroscopy. The surface morphology of the film was examined using Atomic Force Microscopy (AFM) method. The optical properties of TiO₂ thin films were characterized using UV-VIS and Spectroscopic ellipsometry. The results have shown that the TiO₂ thin films persist in the anatase phase even after annealing at 800 °C. The phase transformation from anatase to rutile occurred only when the films were annealed at 1000 °C. AFM studies revealed nanocrystalline structure where their shape and density depend strongly on the annealing temperatures. The elaborated nanostructured-TiO₂ thin films present a high transparency in the visible range. Spectroscopic ellipsometry (SE) study was used to determine the effect of annealing temperature on the thickness and on the optical constant of TiO₂ thin films. Spectroscopic ellipsometry and UV-VIS shows that the band gap of TiO₂ thin films was found to decrease when the annealing temperature increases. The Anatase phase was find to show higher photocatalytic activity than the rutile one.     

Sn掺杂的纳米TiO_2的拉曼散射

本文主要利用拉曼光谱研究一组在合成过程中掺入了不同浓度锡的纳米二氧化钛样品,确定其从锐钛矿结构到金红石型结构的转变,进而分析其金红石型结构的形成。拉曼光谱测试表明,晶型导向剂SnO2的引入促使金红石型TiO2在较低的反应温度下形成,高温合成条件的免除使我们获得了很好的纳米级的金红石型TiO2晶体。此晶体具有有趣的包覆型结构,金红石型TiO2纳米晶体内包含着同结构的SnO2籽晶。分析其成因,在结晶过程中,掺入的杂质原子Sn4+与O2-结合,先沉积出金红石型结构的SnO2作籽晶,金红石型结构的SnO2和同样结构的TiO2晶格常数十分接近,促使了TiO2在它表面外延生长,形成金红石结构的包覆纳米晶。     

Structural and morphological characterization of TiO2 nanostructured films grown by nanosecond pulsed laser deposition

TiO₂ has attracted a lot of attention due to its photocatalytic properties and its potential applications in environmental purification and self cleaning coatings, as well as for its high optical transmittance in the visible-IR spectral range, high chemical stability and mechanical resistance. In this paper, we report on the growth of TiO₂ nanocrystalline films on Si (1 0 0) substrates by pulsed laser deposition (PLD). Rutile sintered targets were irradiated by KrF excimer laser (λ = 248 nm, pulse duration ∼30 ns) in a controlled oxygen environment and at constant substrate temperature of 650 °C. The structural and morphological properties of the films have been studied for different deposition parameters, such as oxygen partial pressure (0.05-5 Pa) and laser fluence (2- 4 J/cm²). X-ray diffraction (XRD) shows the formation of both rutile and anatase phases; however, it is observed that the anatase phase is suppressed at the highest laser fluences. X-ray photoelectron spectroscopy (XPS) measurements were performed to determine the stoichiometry of the grown films. The surface morphology of the deposits, studied by scanning electron (SEM) and atomic force (AFM) microscopies, has revealed nanostructured films. The dimensions and density of the nanoparticles observed at the surface depend on the partial pressure of oxygen during growth. The smallest particles of about 40 nm diameter were obtained for the highest pressures of inlet gas.     

Formation and Shape Transition of Nanostructures on Si(100) surfaces after MeV Sb Implantation

We have studied the formation of nanostructures on Si(100) surfaces after 1.5 MeV Sb implantation. Scanning Probe Microscopy has been utilized to investigate the ion implanted surfaces. We observe the formation of nanostructures after a fluence of 1×10¹³ ions/cm². These surface structures are elliptical in shape with an eccentricity of 0.86 and their major and minor axes having dimensions of about 11.6 nm and 23.0 nm, respectively. The area of the nanostructure is 210 nm²at this fluence. Although the nanostructures remain of elliptical shape, their area increase with increasing fluence. However, after a fluence of 5×10¹⁴ ions/cm² a transition in shape of nanostructures is observed. Nanostructures become approximately circular with an eccentricity of 0.19 and a diameter of about 30.1 nm. At this fluence we also observe a large increase in the area of the nanostructures to 726 nm². Surface morphology and surface roughness of the ion implanted surfaces has also been discussed.     

Structural modification of poly(methyl methacrylate) by proton irradiation

A general survey is presented on the structural modification of poly(methyl methacrylate) (PMMA) by proton implantation. The implanted PMMA films were characterized by FT-IR attenuated total reflection (FT-IR ATR), Raman, Rutherford backscattering spectroscopy (RBS), gel permeation chromatography (GPC) and surface profiling. The ion fluence of 350 keV protons ranged from 2×10¹⁴ to 1×10¹⁵ ions/cm². The IR and Raman spectra showed the reduction of peaks from the pendant group of PMMA. The change of absorption and composition was observed by UV–VIS and RBS, respectively. These results showed that the pendant group is readily decomposed and eliminated by proton irradiation. The change of molecular weight distribution was also measured by GPC and G-value of scission was estimated to be 0.67.     

Modifications in structural and optical properties of Mn-ion implanted CdS thin films

In this paper, we report on modifications in structural and optical properties of CdS thin films due to 190 keV Mn-ion implantation at 573 K. Mn-ion implantation induces disorder in the lattice, but does not lead to the formation of any secondary phase, either in the form of metallic clusters or impurity complexes. The optical band gap was found to decrease with increasing ion fluence. This is explained on the basis of band tailing due to the creation of localized energy states generated by structural disorder. Enhancement in the Raman scattering intensity has been attributed to the enhancement in the surface roughness due to increasing ion fluence. Mn-doped samples exhibit a new band in their photoluminescence spectra at 2.22 eV, which originates from the d-d (⁴T₁ → ⁶A₁) transition of tetrahedrally coordinated Mn²⁺ ions.     

Polymerization of solid C<Subscript>60</Subscript> under C<Stack><Subscript>60</Subscript><Superscript>+</Superscript></Stack> cluster ion bombardment

The structure transformation occurring in fullerene film under bombardment by 50 keV C₆₀⁺ cluster ions is reported. The Raman spectra of the irradiated C₆₀ films reveal a new peak rising at 1458 cm⁻¹ with an increase in the ion fluence. This feature of the Raman spectra suggests linear polymerization of solid C₆₀ induced by the cluster ion impacts. The aligned C₆₀ polymeric chains composing about 5–10 fullerene molecules have been distinguished on the film surface after the high-fluence irradiation using atomic force microscopy (AFM). The surface profiling analysis of the irradiated films has revealed pronounced sputtering during the treatment. The obtained results indicate that the C₆₀ polymerization occurs in a deep layer situated more than 40 nm below the film surface. The deep location of the C₆₀ polymeric phase indirectly confirms the dominant role of shock waves in the detected C₆₀ phase transformation.     

Raman scattering and electrical studies of the phase stability in the Hg<Subscript>1−x</Subscript>Cd<Subscript>x</Subscript>Te

Raman scattering is performed to access phase stability in the boron-implanted Hg_0.7Cd_0.3Te with fluences ranging from 1 × 10¹² to 1 × 10¹⁵ cm^?2. Threshold fluence for the formation of an amorphous phase is invoked here using Thomas–Fermi statistical model. Asymmetric broadening and red shift of the Raman active HgTe-like LO phonon mode are observed with varying fluencies. Electrical properties such as sheet carrier concentration and mobility are also changed with the fluence and reach their saturated values beyond threshold fluence of 5 × 10¹³ cm^?2. Threshold fluence for the formation of amorphous phase is also validated by the Raman measurements and electrical transport properties in the implanted layers. The excess free energy of 6.8 kJ/mole is found corresponding to the threshold fluence for phase transition.     

Au5+ ion implantation induced structural phase transitions probed through structural,microstructural and phonon properties in BiFeO3 ceramics,using synergistic ion beam energy

Implanted Au⁵⁺-ion-induced modification in structural and phonon properties of phase pure BiFeO₃ (BFO) ceramics prepared by sol–gel method was investigated. These BFO samples were implanted by 15.8?MeV ions of Au⁵⁺ at various ion fluence ranging from 1?×?10¹⁴ to 5?×?10¹⁵?ions/cm². Effect of Au⁵⁺ ions’ implantation is explained in terms of structural phase transition coupled with amorphization/recrystallization due to ion implantation probed through XRD, SEM, EDX and Raman spectroscopy. XRD patterns show broad diffuse contributions due to amorphization in implanted samples. SEM images show grains collapsing and mounds’ formation over the surface due to mass transport. The peaks of the Raman spectra were broadened and also the peak intensities were decreased for the samples irradiated with 15.8?MeV Au⁵⁺ ions at a fluence of 5?×?10¹⁵?ion/cm². The percentage increase/decrease in amorphization and recrystallization has been estimated from Raman and XRD data, which support the synergistic effects being operative due to comparable nuclear and electronic energy losses at 15.8?MeV Au⁵⁺ ion implantation. Effect of thermal treatment on implanted samples is also probed and discussed.     

薄膜沉积过程中TiO_2的金红石相向锐钛矿相转变

用ＲＦ磁控放电方法以纯金属钛做靶材在氩氧混合气体中制备了ＴｉＯ２薄膜,Ｒａｍａｎ光谱测量表明,在２Ｐａ工作气压下制备的ＴｉＯ２薄膜为锐钛矿结构,而在０２Ｐａ工作气压下制备的是金红石结构。工作气压的改变引起了ＴｉＯ２薄膜沉积中的相转变。     

Effect of the excimer laser irradiation on sol–gel derived tungsten–titanium dioxide thin films

A novel technique based on the excimer laser induced crystallization and modification of TiO₂ thin films is being reported. W⁺⁶ ions loaded TiO₂ (WTO) precursor films were prepared by a modified sol–gel method and spin-coated onto microscopic glass slides. Pulsed KrF (248 nm, 13 ns) excimer laser was used to irradiate the WTO amorphous films at various laser parameters. Mesoporous and nanostructured films consisting of anatase and rutile were obtained after laser irradiation at room temperature. The effect of varying W⁺⁶ ions concentrations on structural and optical properties the WTO films was analyzed by X-ray diffraction, field-emission scanning electron microscope, UV-Vis spectrophotometer and transmission electron microscope before and after laser treatment. Films irradiated for 10 pulses at 65–75 mJ/cm² laser fluence, exhibited anatase whereas higher parameters promoted the formation of rutile. XPS results revealed WO₃ along with minor proportion of WO₂ compounds after laser irradiation. Photo-absorbance of the WTO films was increased with increase in W⁺⁶ ions concentration in the film. TEM results exhibited a crystallite size of 15 nm which was confirmed from SEM results as well.     

Analyses of surface coloration on TiO2 film irradiated with excimer laser

TiO₂ film of around 850 nm in thickness was deposited on a soda-lime glass by PVD sputtering and irradiated using one pulse of krypton-fluorine (KrF) excimer laser (wavelength of 248 nm and pulse duration of 25 ns) with varying fluence. The color of the irradiated area became darker with increasing laser fluence. Irradiated surfaces were characterized using optical microscopy, scanning electron microscopy, Raman spectroscopy and atomic force microscopy. Surface undergoes thermal annealing at low laser fluence of 400 and 590 mJ/cm². Microcracks at medium laser fluence of 1000 mJ/cm² are attributed to surface melting and solidification. Hydrodynamic ablation is proposed to explain the formation of micropores and networks at higher laser fluence of 1100 and 1200 mJ/cm². The darkening effect is explained in terms of trapping of light in the surface defects formed rather than anatase to rutile phase transformation as reported by others. Controlled darkening of TiO₂ film might be used for adjustable filters.     

Defects mediated diffusion in Pt/Co/Pt multilayers induced by dense electronic excitations

Present study compares the effects of 200 MeV Ag¹⁵⁺ and 100 MeV O⁷⁺ ion irradiations on the structural, interfacial mixing and magnetic properties of annealed Pt/Co/Pt layers fabricated by DC magnetron sputtering. X-ray diffraction analysis shows that ion irradiations coupled with post annealing results in the formation of the face centred tetragonal L1₀ CoPt phase. Irradiation using 200 MeV Ag¹⁵⁺ ions having higher ionizing energy transfer to the film was found to be more efficient in causing structural phase transition as compared with that using 100 MeV energy O⁷⁺ ions having lower ionizing energy transfer at similar fluence. Rutherford back scattering analysis reveals the role of defect mediated inter-atomic diffusion in tailoring the alloy composition of the film irradiated by different energetic ions. A broad magnetic switching field distribution for O⁷⁺ ion irradiated films compared to Ag¹⁵⁺ ion irradiation was evident from the magnetic measurements. The contribution of alloy composition to switching field distribution has been discussed in details. Above results showed that the electronic energy loss and fluence dependent defects, generated by irradiation, played an important role in tuning the structural, atomic diffusion and magnetic reversal properties of Pt/Co/Pt.     

In-depth modifications of implanted amorphous carbon films

Amorphous carbon films (a-C:H) and nitrogen incorporated carbon films [a-C:H(N)] deposited by a self-bias glow discharge have been implanted with 70 keV nitrogen ions at fluences of 0.6, 1 and 2×10¹⁷ N/cm². The in-depth modifications caused by ion implantation were determined by means of nuclear techniques, such as Rutherford Backscattering Spectrometry (RBS), Nuclear Reaction Analysis (NRA) and Elastic Recoil Detection Analysis (ERDA), as well as by Auger Electron Spectroscopy (AES) and Raman scattering. ERDA profiles show that nitrogen implantation causes hydrogen depletion, the amount of which depends on the film composition and on the ion fluence. In a-C:H(N) films nitrogen loss was also measured. The induced structural modifications in both a-C:H and a-C:H(N) films were followed by both AES, using factor analysis, and microprobe Raman spectroscopy. They turn out to be related to the energy deposited by the incident ions. Our results indicate that the ion-beam bombardment causes in both a-C:H and a-C:H(N) films an increase of either the degree of disorder or the ratio between sp²/sp³ bonds across the hydrogen-depleted layer, which depends on the ion fluence.     

Formation of single-crystalline TiO2 nanomaterials with controlled phase composition and morphology and the application in dye-sensitized solar cell

Single-crystalline TiO₂ nanomaterials with controlled phase composition and morphology were synthesized by hydrothermal transformation of H-titanate nanotubes under different pH. Rutile rectangle nanorods with two four-side tapered tips were produced at pH of 0, whereas anatase nanoparticles with mainly of rhombic shape were obtained at pH from 2 to 7 and their average particle size increased with pH. The transformation mechanisms at different pH were discussed. The single-crystalline anatase nanoparticles obtained at pH of 2 had ca. 12 nm in average particle size, and the powder possessed as large as 112 m²/g specific surface areas; the conversion efficiency of the dye-sensitized solar cell based on the nanoparticles was increased by over 40% as compared with that of the cell based on P25.     

First order Raman scattering analysis of transition metal ions implanted GaN

Transition Metal (TM) ions V, Cr, Mn and Co were implanted into GaN/sapphire films at fluences 5×10¹⁴, 5×10¹⁵ and 5×10¹⁶ cm⁻². First order Raman Scattering (RS) measurements were carried out to study the effects of ion implantation on the microstructure of the materials, which revealed the appearance of disorder and new phonon modes in the lattice. The variations in characteristic modes 1GaN i.e. E₂(high) and A₁(LO), observed for different implanted samples is discussed in detail. The intensity of nitrogen vacancy related vibrational modes appearing at 363 and 665 cm⁻¹ was observed for samples having different fluences. A gallium vacancy related mode observed at 277/281 cm⁻¹ for TM ions implanted at 5×10¹⁴ cm⁻² disappeared for all samples implanted with rest of fluences. The fluence dependent production of implantation induced disorder and substitution of TM ions on cationic sites is discussed, which is expected to provide necessary information for the potential use of these materials as diluted magnetic semiconductors in future spintronic devices.     

Evolution of structural and optical properties of rutile TiO2 thin films synthesized at room temperature by chemical bath deposition method

Nanocrystalline thin films of TiO₂ were prepared on glass substrates from an aqueous solution of TiCl₃ and NH₄OH at room temperature using the simple and cost-effective chemical bath deposition (CBD) method. The influence of deposition time on structural, morphological and optical properties was systematically investigated. TiO₂ transition from a mixed anatase–rutile phase to a pure rutile phase was revealed by low-angle XRD and Raman spectroscopy. Rutile phase formation was confirmed by FTIR spectroscopy. Scanning electron micrographs revealed that the multigrain structure of as-deposited TiO₂ thin films was completely converted into semi-spherical nanoparticles. Optical studies showed that rutile thin films had a high absorption coefficient and a direct bandgap. The optical bandgap decreased slightly (3.29–3.07 eV) with increasing deposition time. The ease of deposition of rutile thin films at low temperature is useful for the fabrication of extremely thin absorber (ETA) solar cells, dye-sensitized solar cells, and gas sensors.