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We report surface charge separation analysis of rutile with a Cr concentration gradient produced by ion implantation with the appropriate annealing process. For comparison, TiO 2 films with uniformly distributed Cr were prepared by pulse laser deposition using Cr/TiO 2 multi-targets. Cr depth profiles were obtained by secondary ion mass spectrometry and X-ray photoelectron spectroscopy was used to determine surface Cr concentration for both films. Photo-induced transient charge separation measurements were applied to demonstrate the inherent property without disturbing spontaneously formed surface band bending. As the results, Cr implanted rutile exhibited remarkable charge separation performance, even in the visible light. The charge separation was superior to that of uniformly Cr distributed rutile and of epitaxial anatase 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.

Titanium dioxide (TiO 2 ) films on glass substrates were prepared by pulsed laser deposition (PLD) technique. The dependence of crystal structure, morphology and photocatalytic activity on oxygen partial pressure were investigated using X-ray diffraction (XRD), atomic force microscope (AFM) and UV–VIS spectrophotometer. By increasing oxygen partial pressure, the surface morphology changed from smooth to rough, and the crystal structure changed from rutile to anatase at fixed substrate temperature of 773 K. The change of the surface morphology and the formation of anatase structure by variation of oxygen partial pressure resulted in an increase of photocatalytic activity.

Epitaxial titanium dioxide thin films with anatase and rutile structures have been deposited by pulsed laser deposition (ArF excimer laser) under a controlled O 2 atmosphere. The anatase TiO 2 (0 0 1) films have been successfully prepared on LaAlO 3 (0 0 1), LSAT (0 0 1), SrTiO 3 (0 0 1) and YSZ (0 0 1) substrates. Also, high-quality epitaxial rutile TiO 2 (1 0 0) films were grown on α -Al 2 O 3 (0 0 0 1) substrates. The substrate temperature during the deposition was in the range from 349°C to 608°C under 6×10 −3 Torr O 2 gas pressure. The quality of films and crystallographic relationships were assessed by X-ray diffraction, X-ray pole figures and Rutherford backscattering spectroscopy (RBS)/channeling. The optical properties were characterized in the ultraviolet-visible region by optical absorption measurement. The optical band gaps for anatase and rutile TiO 2 epitaxial films were evaluated to be 3.22 and 3.11 eV, respectively.

Implantation with 100 keV C + ions in a transmission electron microscope (TEM) was performed in copper at temperatures from 570 to 970 K to reveal the agglomeration process of implanted species immiscible in the substrates. Phase and strain contrast features with diameters of ∼5 nm appeared in Cu TEM samples at a fluence of 1 × 10 17 C/cm 2 , at which carbon concentration and radiation damage were roughly evaluated as 10 at% and four displacements per carbon atom, respectively. The features were determined as carbon onions due to their spherical morphology and concentric graphene shells with the interlayer distance of bulk graphite. The strain contrast around onions indicated that they were embedded in the substrate enhancing isotropic strain. We have further derived evidence on the location of onions, such as the interaction of onions with dislocations and with the sample edge, the latter of which was observed due to irradiation-enhanced evaporation of Cu. On the other hand, carbon nanocapsules (concentric graphitic spheres with cavities), typically observed in implanted polycrystalline Cu substrates, were formed through the graphitization at substrate grain boundaries and following emission of the encapsulated copper particles.

Time- and space-resolved characteristics of laser-ablated carbon particles were studied by x-ray absorption spectroscopy. Absorption peaks from the 1s→2p transition of neutral carbon atom ( C 0), C −, C +, and C 2+ ions were observed, An absorption peak from 1s→π* and a broad absorption maximum from the 1s→σ* transition of small clusters were also observed. Neutral carbon, C −, C +, and small carbon clusters were emitted from the sample long after laser irradiation. Spatial distributions of laser-ablated carbon particles in the localized helium-gas environment were measured. In the helium-gas environment, the ablation plume was depressed by the helium cloud generated on the top of the ablation plume.

We have performed x-ray absorption measurements of laser-ablated Si particles in vacuum and in Hegas environment. It is found that the spatial distributions of laser-ablated particles are very different between the two cases. This suggests that a higher-density region of helium gas is formed at the top of the plume of the ablated particles, and free expansion of particles is restrained by this helium cloud. Moreover, the spectrum obtained at 260 ns indicates that it takes more than 260 ns to form Si clusters. It is also demonstrated that Al particles can be sputtered in vacuum by laser-ablated Si particles if an Al plate is placed in front of the plume.

We have studied dynamical mechanism of laser ablation using combined time- and spatially-resolved measurements of laser plasma soft x-ray absorption spectroscopy and visible light emission imaging/spectroscopy. The obtained results indicate that there are no significant formation of silicon clustres and no growth of silicon nanoclusters till 2.55 ms after laser ablation. We have fabricated nanocluster-based silicon films by laser ablation in ambient gases and investigated photoluminescence at room temperature from the films. It is found that the growth of silicon nanocluster-based films with visible light emission can be well controlled by means of novel laser ablation methods.

In this work, ilmenite structure FeTiO3 thin films on α-Al2O3 (0001) substrates were prepared by Nd:YAG pulsed laser deposition. Different deposition conditions with different temperatures, and different partial gas pressures of different gases were used. It was found that an epitaxial and stoichiometric FeTiO3 single-crystal film can be prepared at 450°C in several different ambients, including pure argon, vacuum and Ar+5%O2 at different partial pressures respectively. However, the best film was ablated using 5% oxygen and argon gas mixed ambient of 0.01 mbar at 450°C. With the temperature lower than 300°C or higher than 500°C, we could not obtain crystalline or even single-phase FeTiO3 film. X-ray diffraction and Rutherford backscattering spectrometry with channeling were used to characterize the films.

Compressed C60 powder, a C60 pellet, has been irradiated by second harmonics of Nd:YAG/glass pulsed laser light. From the x‐ray photoelectron spectroscopic measurement, it was suggested that some reorganization occurred on the surface of the ablated C60 pellet. A periodic structure was discovered on the laser ablated C60 pellet and the spacing of that periodic structure was in good agreement with the prediction based on the surface scattering model.

Time‐resolved X‐ray absorption spectroscopy using laser plasma has been developed to measure the time evolution of the electronic and geometrical structures of laser ablated particles and their spatial distribution. This method is demonstrated to have potential for pulsed‐laser induced, fast‐phase changes like laser annealing and laser ablation. Laser‐ablated particles of silicon and carbon have been investigated by this method to clarify dynamics of ablated particles. We show the obtained results of laser ablation of Si and C, the first experimental determination of Si–L2,3 edges of Si atom and ions, and absorption lines suggesting formation of Si clusters and negative C ions.

We propose a new simple method for characterizing photocatalytic activity by measuring photo-generated transient charge separation at the surface of semiconductor photocatalysts. In this method, the charge separation generated by a pulse dye laser is obtained as a function of the incident laser energy. Using this method, the photocatalytic activity and the type of surface reaction (reduction or oxidation) in titanium dioxide films were rapidly determined.