Polyacrylonitrile （PAN） based carbon fibers with different surface morphology were electrochemically treated in 3 wt% NH4HCO3 aqueous solution with current density up to 3.47 A/m 2 at room temperature, and surface s...Polyacrylonitrile （PAN） based carbon fibers with different surface morphology were electrochemically treated in 3 wt% NH4HCO3 aqueous solution with current density up to 3.47 A/m 2 at room temperature, and surface structures, surface morphology and residual mechanical properties were characterized. The crystallite size （La） of carbon fibers would be interrupted due to excessive electrochemical etching, while the crystallite spacing （d（002）） increased as increasing current density. The disordered structures on the surface of carbon fiber with rough surface increased at the initial oxidation stage and then removed by further electrochemical etching, which resulting in continuous increase of the extent of graphitization on the fiber surface. However, the electrochemical etching was beneficial to getting ordered morphology on the surface for carbon fiber with smooth surface, especially when the current density was lower than 1.77 A/m 2 . The tensile strength and tensile modulus could be improved by 17.27% and 5.75%, respectively, and was dependent of surface morphology. The decreasing density of carbon fibers probably resulted from the volume expansion of carbon fibers caused by the abundant oxygen functional groups intercalated between the adjacent graphite layers.展开更多
In this work,we used femtosecond laser double-pulse trains to produce laser-induced periodic surface structures(LIPSS)on 304 stainless steel.Surprisingly,a novel type of periodic structure was discovered,which,to the ...In this work,we used femtosecond laser double-pulse trains to produce laser-induced periodic surface structures(LIPSS)on 304 stainless steel.Surprisingly,a novel type of periodic structure was discovered,which,to the best of our knowledge,is the first in literature.We surmised that the cause for this novel LIPSS was related to the weak energy coupling of subpulses when the intrapulse delay was longer than the thermal relaxation time of stainless steel.Furthermore,we found that the fluence combination and arrival sequence of subpulses in a double-pulse train also influenced LIPSS morphology.展开更多
Single crystal GaN films of hexagonal modification have been fabricated on Al2O3/Si （001） substrates via a low pressure metalorganic chemical deposition （LP-MOCVD） method. The full width at half-maximum of （0002...Single crystal GaN films of hexagonal modification have been fabricated on Al2O3/Si （001） substrates via a low pressure metalorganic chemical deposition （LP-MOCVD） method. The full width at half-maximum of （0002） X-ray diffraction peak for the GaN film 1.1 μm thick was 72 arcmin, and the mosaic structure of the film was the main cause of broadening to the X-ray diffraction peak. At room temperature, the photoluminescence （PL） spectrum of GaN exhibited near band edge emission peaking at 365 nm.展开更多
基金supported by the National Basic Research Program of China (No. 2011CB605602)
文摘Polyacrylonitrile （PAN） based carbon fibers with different surface morphology were electrochemically treated in 3 wt% NH4HCO3 aqueous solution with current density up to 3.47 A/m 2 at room temperature, and surface structures, surface morphology and residual mechanical properties were characterized. The crystallite size （La） of carbon fibers would be interrupted due to excessive electrochemical etching, while the crystallite spacing （d（002）） increased as increasing current density. The disordered structures on the surface of carbon fiber with rough surface increased at the initial oxidation stage and then removed by further electrochemical etching, which resulting in continuous increase of the extent of graphitization on the fiber surface. However, the electrochemical etching was beneficial to getting ordered morphology on the surface for carbon fiber with smooth surface, especially when the current density was lower than 1.77 A/m 2 . The tensile strength and tensile modulus could be improved by 17.27% and 5.75%, respectively, and was dependent of surface morphology. The decreasing density of carbon fibers probably resulted from the volume expansion of carbon fibers caused by the abundant oxygen functional groups intercalated between the adjacent graphite layers.
基金supported by the National Key R&D Program of China(No.2018YFB1107200)the National Natural Science Foundation of China(Nos.51675048 and 11704028)。
文摘In this work,we used femtosecond laser double-pulse trains to produce laser-induced periodic surface structures(LIPSS)on 304 stainless steel.Surprisingly,a novel type of periodic structure was discovered,which,to the best of our knowledge,is the first in literature.We surmised that the cause for this novel LIPSS was related to the weak energy coupling of subpulses when the intrapulse delay was longer than the thermal relaxation time of stainless steel.Furthermore,we found that the fluence combination and arrival sequence of subpulses in a double-pulse train also influenced LIPSS morphology.
文摘Single crystal GaN films of hexagonal modification have been fabricated on Al2O3/Si （001） substrates via a low pressure metalorganic chemical deposition （LP-MOCVD） method. The full width at half-maximum of （0002） X-ray diffraction peak for the GaN film 1.1 μm thick was 72 arcmin, and the mosaic structure of the film was the main cause of broadening to the X-ray diffraction peak. At room temperature, the photoluminescence （PL） spectrum of GaN exhibited near band edge emission peaking at 365 nm.
