Picosecond flash spectroscopy of titania colloids with adsorbed dyes

Abstract

con-containing reactive intermediate present in the gas phase in CVD systems with SiH,Cl2 as a source gas, formed in our experiments by heterogeneous decomposition of SiH2CI2 over the decomposition film, while SiHCl is present as a minor species. Since identical results were obtained with quartz and graphite pyrolyzers and results were independent of deposition time, we are confident that similar results would be obtained from silicon surfaces.It is interesting to note from the mass spectra in Figures 4 and 5 that, at temperatures where the precursor chlorosilane is completely decomposed, the relative concentrations of HCI and SiCl, are nearly the same for dichlorosilane and trichlorosilane. The ratio of SiCl,/HCI is higher in the trichlorosilane case, presumably because there is more chlorine carried to the surface by this feed gas. This is in agreement with previous optical and mass spectrometric studies which showed that the gas-phase species present in CVD systems were independent of the chlorosilane source gas! Gilbert and Ban,4 using mass spectrometry, showed that the gas-phase species found in CVD reactions were independent of the feed gas and that their relative concentrations depended only on the temperature and CI/H ratio of the feed gas. The IR multiphoton dissociation results of Sausa and Ronn showed that only H2 and SiCI,, and not HCI, are produced by the homogeneous gas-phase decomposition of dichlorosilane.' The results in this study show that the HCI observed in previous studies of CVD systems using chlorosilanes as source gases is probably generated by heterogeneous surface decomposition of the chlorosilanes, followed by surface reactions. Speculation Regarding Heterogeneous Decomposition Pathways of ChlorosilanesThe results presented in this study show that SiCI, and HCI desorb from silicon surfaces deposited on both quartz and graphite by the heterogeneous decomposition of SiH2C12 and SiHCI, above 600 and 800 "C, respectively. These species are likely to be important in the removal of excess chlorine and hydrogen from the growing polycrystalline thin silicon film. Under conditions, where the dichlorosilane decomposes on the surface and not above it, species 1 and I1 in Scheme I would be likely to form by dis-Spectra for electrons trapped in TiO, have been reported. In this study, kinetic analysis of processes taking place when TiO, colloids are flashed in the presence of three dyes leads to assignment of the spectrum of a trapped hole. Within the duration of a 20-ps pulse at 350 nm, a transient is formed in Ti02 which decays with a second-order rate constant of 2.4 X IO-'' ne s-I, where n, is the number of electrons. The absorbance is probably attributable to electrons in the "conduction band" (a term that must be used cautiously for these very amorphous systems), and the rate constant measures the rate of hole-electron recombination. Upon addition of a dye that may scavenge carriers, a new transient grows with a rate constant of 5 X IO* s-'. This feature, with an absorption maximum at 630 nm...

Nitrite Reduction to Nitrous Oxide and Ammonia by TiO2 Electrons in a Colloid Solution via Consecutive One-Electron Transfer Reactions

“…The application of TiO 2 nanoparticles for decontamination of wastewater from organic and inorganic hazardous metal ions has become a mature research field. − Most photocatalytic works focus on oxidation reactions in aerated media. Much less is known about the reductive processes, although the reduction of nitrogen compounds, particularly nitrate, has attracted considerable attention. − The reduction of nitrate in aqueous solutions involves the formation of nitrite and several nitrogen intermediates with known physical and chemical properties, including NO, NH 2 OH, N 2 , and N 2 O. Previously, we have shown that TiO 2 electrons (e TiO 2 – ) are unable to reduce N 2 and N 2 O, and the NO reduction under anoxic conditions yields mainly NH 3 and N 2 O via consecutive one-electron transfer reactions.…”

“…Ammonia was assayed using a modification of the Berthelot reaction based on indophenol formation via the reaction of phenol with alkaline hypochlorite. 18 Briefly, phenol (6 g) and sodium nitroprusside (20 mg) were dissolved in 100 mL of phosphate-citrate buffer at pH 12 (3…”

Dynamics of efficient electron–hole separation in TiO2nanoparticles revealed by femtosecond transient absorption spectroscopy under the weak-excitation condition

“…Absorption spectra of electrons and holes in TiO 2 are very broad, extending from the UV to the IR region. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] Most of the early research on electron-hole dynamics in TiO 2 by transient absorption spectroscopy was performed with colloidal TiO 2 nanoparticle samples. 1,4,14,33,34 Assignments of electrons and holes were made by measuring transient absorption spectra in the presence of electron or hole scavengers in the colloidal solution.…”

Nanoplasmon–Semiconductor Hybrid for Interface Catalysis

“…Direct evidence of electron transfer from Au NPs to TiO 2 can be obtained. Furube and coworkers revealed the internal mechanism of ultrafast plasmon-induced electron transfer from 10 nm Au NPs to TiO 2 NPs with femtosecond transient absorption spectroscopy [15,85,86], and revealed that the hot electron generation and injection were completed within 50 fs [42,45,[87][88][89][90][91][92][93][94][95][96][97]. When the plasmons of gold NPs are excited, the electrons with a non-Fermi distribution undergo relaxation through the re-emission of photons or carrier multiplication within 100 fs due to the electron-electron interaction [52,98,99], electron-phonon interaction at the timescale of 1-10 ps, and phonon-phonon interactions around 100 ps [100,101].…”