The effect of porosity on the laser induced damage threshold of TiO2 and ZrO2 single layer films

Monolayer ZrO₂ and TiO₂ films were prepared on BK7 glass by physical vapor deposition (PVD) and were subsequently annealed for 1 h at 300 °C. By using the transmission spectra of two samples and the envelope method, the refractive index dispersion and extinction coefficients have been calculated. Laser induced damage threshold (LIDT) measurement shows that despite slight differences between the extinction coefficients of the two samples, the LIDT parameter of the ZrO₂ film is greater than that of the TiO₂ film. This fact leads us to consider thermal conductivity as an important parameter for interpreting the LIDT difference. According to our theoretical analysis, as a consequence of increase in the number of thermal barriers along poorer film, its thermal conductivity, and hence LIDT, decreased, which is in agreement with our experimental results. The measured porosity of the two samples shows higher porosity for TiO₂ single layer, which is in agreement with atomic force (AFM) images. The gradual and smooth damage morphology of ZrO₂ observed in optical images implies higher thermal conductivity than TiO₂.     

From anodic TiO2 nanotubes to hexagonally ordered TiO2 nanocolumns

We report on the formation of hexagonally ordered TiO₂ nanocolumnar layers by electrochemical oxidation in a fluoride containing electrolyte, using self-organizing nanotube formation conditions at elevated potentials and low temperatures. The influence of the substrate temperature on the nanocolumn morphology and composition is investigated and characterized by FE-SEM and EDX. The origin of these nanocolumns can be attributed to a thickening of the inner tube wall of the double wall structure of self-organized TiO₂ nanotubes. Furthermore, a transition from nanocolumnar to nanotubular structure can be established by changing the applied voltage or applying a post-immersion treatment.     

Micro-structuring of TiO2 thin films by laser-assisted diffraction processing

Thin films of TiO₂ are deposited by magnetron sputtering on glass substrate and are irradiated by UV radiation using a KrF excimer laser (248 nm). These thin films are patterned with a razor blade placed on the way of the radiation just in front of the TiO₂ thin film. Just near the edge of the razor blade on the thin film, diffraction lines are observed, resulting in the ablation of the film. These patterns are characterized by optical microscopy, mechanical profilometry. Diffraction up to the 35th order is observed. The results are shown to be compatible with a model in which electronic excitation plays the major role.     

Small size TiO2 nanoparticles prepared by laser ablation in water

Titanium dioxide nanoparticles in distilled H₂O solvent were prepared by laser ablation. The experiments were performed irradiating a Ti target with a second harmonic (532 nm) output of a Nd:YAG laser varying the operative fluence between 1 and 10 J cm⁻² and for an ablation time ranging from 10 to 30 min. Electron microscopy measurements have evidenced the predominant presence of nanoparticles with diameter smaller than 10 nm together with agglomerations of 100-200 nm whose content increases with the laser fluence. At low laser fluence the particles’ size distribution shows that more than 85% of the nanoparticles have a size smaller than 5 nm while at mid and high fluences the presence of 5-7 nm nanoparticles is predominant. XPS analysis has revealed the presence of different titanium suboxide phases with the prevalence of Ti-O bonds from TiO₂ species. The optical bandgap values, determined by UV-vis absorption measurements, are compatible with the anatase phase.     

Deposition of Au/TiO2 film by pulsed laser

Au nanoparticles, which were photoreduced by a Nd:YAG laser in HAuCl₄ solution containing TiO₂ colloid and accompanied by the TiO₂ particles, were deposited on the substrate surface. The film consisting of Au/TiO₂ particles was characterized by the absorption spectra, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The adhesion between the film and substrate was evaluated by using adhesive tape test. It was found that the presence of TiO₂ dramatically enhanced the adhesion strength between the film and the substrate, as well as the deposition rate of film. The mechanism for the deposition of Au/TiO₂ film was also discussed.     

Composite SiO2/TiO2 and amine polymer/TiO2 nanoparticles produced using plasma-enhanced chemical vapor deposition

Plasma-enhanced chemical vapor deposition was used to conformally coat commercial TiO₂ nanoparticles to create nanocomposite materials. Hexamethyldisiloxane (HMDSO)/O₂ plasmas were used to deposit SiO₂ or SiO_xC_yH_z films, depending on the oxidant concentration; and hexylamine (HexAm) plasmas were used to deposit amorphous amine-containing polymeric films on the TiO₂ nanoparticles. The composite materials were analyzed using Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). These analyses reveal film composition on the nanoparticles was virtually identical to that deposited on flat substrates and that the films deposit a conformal coating on the nanoparticles. The performance of the nanocomposite materials was evaluated using UV-vis spectroscopy to determine the dispersion characteristics of both SiO_x and HexAm coated TiO₂ materials. Notably, the coated materials stay suspended longer in distilled water than the uncoated materials for all deposited films.     

Effects of deposition rates on laser damage threshold of TiO2/SiO2 high reflectors

TiO₂ single layers and TiO₂/SiO₂ high reflectors (HR) are prepared by electron beam evaporation at different TiO₂ deposition rates. It is found that the changes of properties of TiO₂ films with the increase of rate, such as the increase of refractive index and extinction coefficient and the decrease of physical thickness, lead to the spectrum shift and reflectivity bandwidth broadening of HR together with the increase of absorption and decrease of laser-induced damage threshold. The damages are found of different morphologies: a shallow pit to a seriously delaminated and deep crater, and the different amorphous-to-anatase-to-rutile phase transition processes detected by Raman study. The frequency shift of Raman vibration mode correlates with the strain in film. Energy dispersive X-ray analysis reveals that impurities and non-stoichiometric defects are two absorption initiations resulting to the laser-induced transformation.     

Interband optical transition strengths in SiO2, GeO2, SnO2 and TiO2

An analysis of interband optical transition strengths for a series of MO₂ oxides is presented which gives clear evidence for a direct proportionality between transition strengths (as measured by the dispersion energy) and nearest-neighbor cation coordination number. It is also found that neither the extent of O2p orbital delocalization nor the d-electron configuration has a strong influence on transition strengths suggestin that these strengths can be viewed, to a good approximation, as intrinsic properties of valence s,p-electrons which are largely independent of band structure details.     

Nanoclusters of TiO2 wetted with gold

We combined scanning tunneling microscopy and density functional theory to establish the structure-functionality relationship for nanometer-sized defects on TiO₂(1 1 0). Three-angstrom high topographically distinct dots are ascribed to stoichiometric TiO₂ nanoclusters with low coordination numbers. The under-coordinated O atoms of the nanocluster, with surface O atoms, provide exceptionally strong binding sites for Au nanoparticles. Our atomistic model elucidates a number of characteristics salient to low temperature CO oxidation by Au nanoparticles.     

TiO2∶Mo体系的光子雪崩上转换

在978nm激光二极管的激发下，Mo掺杂的TiO₂材料表现出很强的宽带上转换发光 ，该发光来源于［MoO₄］^2-基团的激发态³T₁, ³T₂能级到基态¹A₁能级的电子跃迁.通过研究发光强度与抽运功率的关系及上转换发光的上升时间曲线，发现TiO₂∶Mo体系的上转换发光中存在着雪崩机制，应用转 关键词： 上转换 光子雪崩 转移函数理论     

Raman spectroscopic analysis of sulphur-doped TiO2 by co-grinding with TiS2

Doping sulphur into titania has been tried using TiS₂ as a doper based on the mechanically induced solid-state reaction between TiO₂ and TiS₂. The prepared samples have been characterized by X-ray diffraction (XRD), Raman spectroscopy and UV-Vis reflectance spectroscopy. Raman analysis, particularly has been proved to be effective in assessing the sulphur doping by correlating the oxygen deficiency of the doped oxide with the change of active Eg mode of rutile phase.     

Characterization of TiO2/Au/TiO2 films deposited by magnetron sputtering on polycarbonate substrates

Transparent and conducting TiO₂/Au/TiO₂ (TAuT) films were deposited by reactive magnetron sputtering on polycarbonate substrates to investigate the effect of the Au interlayer on the optical, electrical, and structural properties of the films. In TAuT films, the Au interlayer thickness was kept at 5 nm. Although total thickness was maintained at 100 nm, the stack structure was varied as 50/5/45, 70/5/25, and 90/5/5 nm.In XRD pattern, the intermediate Au films were crystallized, while all TAuT films did not show any diffraction peaks for TiO₂ films with regardless of stack structure. The optical and electrical properties were dependent on the stack structure of the films. The lowest sheet resistance of 23 Ω/□ and highest optical transmittance of 76% at 550 nm were obtained from TiO₂ 90 nm/Au 5 nm/TiO₂ 5 nm films. The work function was dependent on the film stack. The highest work function (4.8 eV) was observed with the TiO₂ 90 nm/Au 5 nm/TiO₂ 5 nm film stack. The TAuT film stack of TiO₂ 90 nm/Au 5 nm/TiO₂ 5 nm films is an optimized stack that may be an alternative candidate for transparent electrodes in flat panel displays.     

Preparation and characterization of nitrogen-doped TiO2 nanoparticles by the laser pyrolysis of N2O-containing gas mixtures

Nitrogen-doped TiO₂ nanoparticles have been prepared by the IR laser pyrolysis technique. A sensitized mixture of TiCl₄ (vapors) and N₂O was used as titanium and nitrogen precursors, respectively. The structural properties of the resultant N-doped nanoparticles such as the phase formation and the average particle size and distributions were investigated by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The phase composition varied from almost pure anatase to mixtures of rutile and anatase. A decrease of the mean particle diameters from about 18 nm in case of the almost pure anatase sample to about 13 nm in case of the anatase-rutile mixture is observed. XPS analysis suggests and interstitial character of the doping process.     

SnO2/TiO2 mixed oxide particles synthesized in doped premixed H2/O2/Ar flames

SnO₂/TiO₂ mixed oxides with primary particle size ranging between 5 nm d_p 12 nm were synthesized by doping a H₂/O₂/Ar flame with Sn(CH₃)₄ and Ti(OC₃H₇)₄ co-currently. The effects of “flow coordinate,” concentration and flame configurations were investigated with respect to particle size and morphology of the generated mixed oxides. In situ characterization of the mixed oxides was performed using the particle mass spectrometer (PMS), while XRD, TEM, BET and UV–Vis were performed ex situ. Results obtained showed that primary particle size of mixed oxides can be controlled by varying experimental parameters. The mixed oxides have interesting properties compared to those of the pure oxides of TiO₂ and SnO₂, which were also synthesized in flames earlier. Band gap tuning opportunities are possible using mixed oxides.     

Raman spectra of TiO2-II,TiO2-III,SnO2, and GeO2 at high pressure

Raman spectra of the orthorhombic (II) and high pressure (III) phases of titanium dioxide at pressures to 372 kbar and effects of temperature and hydrostatic pressure on Raman spectra of the tetagonal cassiterite-like phases of TiO₂, GeO₂ and SnO₂ are described. At room temperature, the TiO₂ II–III transition is sluggish, and metastable coexistence was observed from 200 to 300 kbar. The Raman spectra of TiO₂-III imply that its primitive cell contains at least four formula units; however, the structure could not be established from the Raman spectra and available powder X-ray diffraction patterns.The temperature and pressure dependences of the spectrum of the tetragonal MO₂ phases together with bulk moduli and thermal expansion data were used to evaluate the pure-volume and pure-temperature contributions to the isobaric temperature dependence of the Raman frequencies. Large anharmonicities in TiO₂ are attributed to hybridization of the oxygen p states with the d states of the Ti ion. GeO₂, where p-electron bonding is involved, is much less Enharmonic.     

等离激元钼掺杂二氧化钛半导体的光催化固氮反应机理研究

近年来光催化固氮引起了广泛的关注,其代表了将N₂有效转化为NH₃的“绿色工业”的可持续发展路线,如何有效合理地设计这方面的光催化剂仍然是本领域地一个挑战. 本文提出了一种策略,即在高浓度掺杂的TiOsub>2中利用等离激元热电子来激活惰性Nsub>2分子. 成功合成的Mo掺杂TiOsub>2催化剂在常温常压条件下显示出高达134 μmol·g^-1·h^-1的NH₃催化效率,这与传统的等离激元贵金属所实现的催化效率相当. 通过超快光谱技术,发现该体系中的等离激元热电子激活了N₂分子,从而提高了TiO₂的催化活性. 本文为基于等离激元半导体的光催化固氮反应开辟了一条新的途径.     

Photo-induced surface charge separation of highly oriented TiO2 anatase and rutile thin films

Surface charge separation behavior of photo-generated carriers in highly oriented TiO₂ anatase and rutile films was investigated using a technique in which the transient surface charge is observed by laser pulse irradiation without metal contacts and an externally applied field. According to the measurements, the quantum efficiency of photo-generated holes transported toward the surface was determined as a function of incident laser energy. The photo-generated holes in anatase can be transported toward the surface for irradiation at the photon energy of its bandgap. The holes transported toward the rutile surface, however, were generated close to the surface for irradiation at the photon energy much higher than its bandgap.     

Visible-light-activated Ce-Si co-doped TiO2 photocatalyst

To enhance the visible photocatalytic activity and thermal stability of TiO₂, Ce-Si co-doped TiO₂ materials were synthesized through a nonaqueous method of which the purpose was to reduce the aggregation between TiO₂ particles. The obtained materials maintained anatase phase and large surface area of 103.3 m² g⁻¹ even after calcined at 800 °C. The XPS results also indicated that Si was weaved into the lattice of TiO₂, and Ce mainly existed as oxides on the surface of TiO₂ particles. The doped Si might enhance surface area and suppress transformation from anatase to rutile, while the doped Ce might cause visible absorption and inhibit crystallite growth during heat treatment. Evaluated by decomposing dye Rhodamine B, visible photocatalytic activity of Ce-Si co-doped TiO₂ was obviously higher than that of pure TiO₂ and reached the maximum at Ce and Si contents of 0.5 mol% and 10 mol%.     

Synthesis of anatase TiO2 nanowires by modifying TiO2 nanoparticles using the microwave heating method

Anatase TiO₂ nanowires with a diameter of 5-10 nm and length of 500 nm to 2 μm have been successfully synthesized by modifying TiO₂ nanoparticles (P25) using the microwave heating method. The microwave power, reaction pressure, and reaction time for the synthesis of TiO₂ nanowires were 500 W, 0.5-3.0 MPa (corresponding to a temperature range of 175-260), and 40-70 min, respectively. X-ray diffraction (XRD), field-emission scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and the BET techniques were used to investigate the phase structures, morphologies, and specific surface areas of the TiO₂ nanowires. The effects of reaction time, pressure, and different post-treatment processes on the microstructures of TiO₂ nanowires were discussed. It has been shown that the microwave heating method is efficient in transforming TiO₂ nanoparticles to anatase TiO₂ nanowires.