Pure Cu films and Cu alloy films containing insoluble substances(Zr and Cr)were deposited on Si(100)substrates,in the presence of interfacial native suboxide(SiOx),by magnetron sputtering.Samples were vacuum annealed ...Pure Cu films and Cu alloy films containing insoluble substances(Zr and Cr)were deposited on Si(100)substrates,in the presence of interfacial native suboxide(SiOx),by magnetron sputtering.Samples were vacuum annealed between 300℃and 500 ℃to investigate effects of Zr and Cr additions on the thermal performance of Cu films.After annealing,copper silicides were found in the Cu(Zr)films,while no detectable silicides were observed in Cu and Cu(Cr)films.Upon annealing,Zr accelerated the diffusion and reaction between the film and the substrate,and lowered the thermal stability of Cu(Zr)alloy films on Si substrates,which was ascribed to the‘purifying effect’of Zr on the Si substrates.Whereas,Cr prohibited the agglomeration of Cu films at 500℃and decreased the surface roughness.As a result,the diffusion of Cu in Si substrates for Cu(Cr)films was effectively inhibited.In contrast to the high resistivity of Cu(Zr)films,the final resistivity of about 2.76μΩ·cm was achieved for the Cu(Cr)film.These results indicate that Cu(Cr)films have higher thermal stability than Cu(Zr)films on Si substrates and are preferable in the advanced barrierless Cu metallization.展开更多
UV-Vis, fluorescence spectroscopy and time resolved spectroscopic technique on picosecond and femto- second scales have been utilized to investigate the effect of steric hindrance and multiple hydroxyl groups of solve...UV-Vis, fluorescence spectroscopy and time resolved spectroscopic technique on picosecond and femto- second scales have been utilized to investigate the effect of steric hindrance and multiple hydroxyl groups of solvents on the barrierless isomerization in excited state of 3, 3′- di(3-sulfopropyl)thiacyanine triethylaminium salt. The re-sults show that the factors mentioned above may be respon-sible for a different 搒hort-time behavior?of the bleaching signal on the ground state and nonlinear viscosity depend-ence of the excited-state lifetime in isopropanol and glycol. These phenomena are distinguished from the situation re-ported in the long-chained monohydroxyl alcohol solvents. However, the dye molecule still exhibits the analyzing- wavelength dependence of the observed fluorescence lifetime, that is, the fluorescence lifetime increases with the increasing of analyzing-wavelength. The conclusions are in agreement with those drawn from femtosecond upconversion fluores-cence experiments and further exemplify the barrierless isomerization model in the excited state.展开更多
Time-dependent quantum wave packet calculations were carried out for the F ＋ HBr reaction on the latest London-Erying-Polanyi-Sato potential energy surface constructed by Persky et al. The calculated reaction probabi...Time-dependent quantum wave packet calculations were carried out for the F ＋ HBr reaction on the latest London-Erying-Polanyi-Sato potential energy surface constructed by Persky et al. The calculated reaction probabilities dramatically increase near the zero collision energy and then slightly decrease with increasing collision energy, which corresponds well to the behavior of a barrierless reaction. The effects of reagent HBr excitation were examined, it is shown that both the vibrational and the rotational excitations of reagent HBr have a negative effect on the reactivity of F ＋ HBr. The integral cross-section for the ground state of the reagent HBr decreases at a low collision energy and then becomes plat with increasing collision energy, which is reasonable for the feasibility of such an exothermal reaction. The rate constant that was obtained is slightly higher than that obtained in the quasi-classical trajectory calculation.展开更多
Tailoring atomic structures of noblemetal nanomaterials with size close to single-unit cell range is essential in both fundamental researchand applications,including their development into high catalytic performance m...Tailoring atomic structures of noblemetal nanomaterials with size close to single-unit cell range is essential in both fundamental researchand applications,including their development into high catalytic performance materials in renewable,green energy conversions,devices for energy storage,and as biosensors for environmental pollutants.However,several strategies used in fabricating these materials still impose enormous challenges,arising from lack of even size distribution,shape uniformity,and controlled composition,which are critical in determining their specific activities and efficiencies.Herein,we report a facile approach for preparing sub-nano-thick palladium nanobelt-based(PdNB)materials.Then we rationalized the formation mechanism of such highly anisotropic structures by morphology-related thermodynamic and kinetic analysis.Moreover,we investigated if electrocatalysis performance of these NB-basedmaterialswere enhanced.Thepalladium(Pd)NBs featured a thickness of∼0.9-1.2 nm and width of 5-18nmwith length extending to severalmicrometers[denoted as Pd(0.9)],or a thickness of∼0.7-0.9 nm and width of 2.5-6 nmwith length of several hundreds of nanometers[denoted as Pd(0.7)].According to our theoretical analysis,one-dimensional(1D)growth encountered almost no energy barrier at optimal reaction conditions,whereas the growth of Pd nanostructures with other dimensions confronted high barriers,indicating that it was plausible to prepare 1D structures with sizes close to single-unit cells.Also,platinum(Pt)could be successfully doped into the Pd(0.9)NBs through a galvanic epitaxial growth,forming edge-Pt-enriched Pd NBs(eePtPd NBs).Further,electron transfer from Pd to Pt imparted the eePtPd NBs with high hydrogen evolution reaction(HER)activity.The eePtPd NBs showed a 3.5 and 1.8 times higher in exchange current density and mass activity(at−0.1 V),respectively,compared to those of Pt catalysts in perchloric acid(HClO_(4))solutions.Finally,the NBs all showed high activity toward ethanol and formic acid oxidation reactions.Our current work aids in gaining insights into tailoring Pd nanostructures at an atomic level and provides Pd sub-nanometric 1D structures for further research.Moreover,our morphology-related thermodynamic and kinetic analysis extend our understanding of the control of nanostructure morphology and might shed light on the precision of designing specific morphologies of noble metal nanocrystal structures.展开更多
基金Project(08520740200)supported by the Applied Materials Research and Development Fund of Shanghai,China
文摘Pure Cu films and Cu alloy films containing insoluble substances(Zr and Cr)were deposited on Si(100)substrates,in the presence of interfacial native suboxide(SiOx),by magnetron sputtering.Samples were vacuum annealed between 300℃and 500 ℃to investigate effects of Zr and Cr additions on the thermal performance of Cu films.After annealing,copper silicides were found in the Cu(Zr)films,while no detectable silicides were observed in Cu and Cu(Cr)films.Upon annealing,Zr accelerated the diffusion and reaction between the film and the substrate,and lowered the thermal stability of Cu(Zr)alloy films on Si substrates,which was ascribed to the‘purifying effect’of Zr on the Si substrates.Whereas,Cr prohibited the agglomeration of Cu films at 500℃and decreased the surface roughness.As a result,the diffusion of Cu in Si substrates for Cu(Cr)films was effectively inhibited.In contrast to the high resistivity of Cu(Zr)films,the final resistivity of about 2.76μΩ·cm was achieved for the Cu(Cr)film.These results indicate that Cu(Cr)films have higher thermal stability than Cu(Zr)films on Si substrates and are preferable in the advanced barrierless Cu metallization.
基金supported by the State Key Basis Research and Development Plans(Grant No.G1998010100)the National Natural Science Foundation of China(Grant Nos.3989039 and 90101010).
文摘UV-Vis, fluorescence spectroscopy and time resolved spectroscopic technique on picosecond and femto- second scales have been utilized to investigate the effect of steric hindrance and multiple hydroxyl groups of solvents on the barrierless isomerization in excited state of 3, 3′- di(3-sulfopropyl)thiacyanine triethylaminium salt. The re-sults show that the factors mentioned above may be respon-sible for a different 搒hort-time behavior?of the bleaching signal on the ground state and nonlinear viscosity depend-ence of the excited-state lifetime in isopropanol and glycol. These phenomena are distinguished from the situation re-ported in the long-chained monohydroxyl alcohol solvents. However, the dye molecule still exhibits the analyzing- wavelength dependence of the observed fluorescence lifetime, that is, the fluorescence lifetime increases with the increasing of analyzing-wavelength. The conclusions are in agreement with those drawn from femtosecond upconversion fluores-cence experiments and further exemplify the barrierless isomerization model in the excited state.
基金Supported by the Open Project Program of Key Laboratory of Advanced Materials &Rheological Properties, Ministry of Educa-tion, China(No KF0504)
文摘Time-dependent quantum wave packet calculations were carried out for the F ＋ HBr reaction on the latest London-Erying-Polanyi-Sato potential energy surface constructed by Persky et al. The calculated reaction probabilities dramatically increase near the zero collision energy and then slightly decrease with increasing collision energy, which corresponds well to the behavior of a barrierless reaction. The effects of reagent HBr excitation were examined, it is shown that both the vibrational and the rotational excitations of reagent HBr have a negative effect on the reactivity of F ＋ HBr. The integral cross-section for the ground state of the reagent HBr decreases at a low collision energy and then becomes plat with increasing collision energy, which is reasonable for the feasibility of such an exothermal reaction. The rate constant that was obtained is slightly higher than that obtained in the quasi-classical trajectory calculation.
基金This work was supported by the National Key R&D Program of China(2017YFA0700101 and 2016YFA0202801)NSFC(21431003 and 21521091).
文摘Tailoring atomic structures of noblemetal nanomaterials with size close to single-unit cell range is essential in both fundamental researchand applications,including their development into high catalytic performance materials in renewable,green energy conversions,devices for energy storage,and as biosensors for environmental pollutants.However,several strategies used in fabricating these materials still impose enormous challenges,arising from lack of even size distribution,shape uniformity,and controlled composition,which are critical in determining their specific activities and efficiencies.Herein,we report a facile approach for preparing sub-nano-thick palladium nanobelt-based(PdNB)materials.Then we rationalized the formation mechanism of such highly anisotropic structures by morphology-related thermodynamic and kinetic analysis.Moreover,we investigated if electrocatalysis performance of these NB-basedmaterialswere enhanced.Thepalladium(Pd)NBs featured a thickness of∼0.9-1.2 nm and width of 5-18nmwith length extending to severalmicrometers[denoted as Pd(0.9)],or a thickness of∼0.7-0.9 nm and width of 2.5-6 nmwith length of several hundreds of nanometers[denoted as Pd(0.7)].According to our theoretical analysis,one-dimensional(1D)growth encountered almost no energy barrier at optimal reaction conditions,whereas the growth of Pd nanostructures with other dimensions confronted high barriers,indicating that it was plausible to prepare 1D structures with sizes close to single-unit cells.Also,platinum(Pt)could be successfully doped into the Pd(0.9)NBs through a galvanic epitaxial growth,forming edge-Pt-enriched Pd NBs(eePtPd NBs).Further,electron transfer from Pd to Pt imparted the eePtPd NBs with high hydrogen evolution reaction(HER)activity.The eePtPd NBs showed a 3.5 and 1.8 times higher in exchange current density and mass activity(at−0.1 V),respectively,compared to those of Pt catalysts in perchloric acid(HClO_(4))solutions.Finally,the NBs all showed high activity toward ethanol and formic acid oxidation reactions.Our current work aids in gaining insights into tailoring Pd nanostructures at an atomic level and provides Pd sub-nanometric 1D structures for further research.Moreover,our morphology-related thermodynamic and kinetic analysis extend our understanding of the control of nanostructure morphology and might shed light on the precision of designing specific morphologies of noble metal nanocrystal structures.
