现代仪器分析SFG.ppt
Application of Sum frequency generation vibrational spectroscopy in charactering polymer surface聚合物表面和界面的表征和频振动光谱,Reporter：Tan Jiaojun2012-12-10,Contents,Page,Lack of surface selectivity!,Background,Quasi-surface!,Principle,Principal and phenomenon of SFG,Sum frequency spectrum system(5 main units),Principle,Principle,Appearance,Functions,Mono-layerNo damage,Interface specic,Structure Orientation,Crystallize(Stress-induced),Environmental response,Blends behavior,SFG in polymer character,Advantage,Functions,Sample preparation,Attention:1.Spin coating、injection;2.Clean surface（sample&substrate）by piranha solution.,Analysis,Analysis,1.Character composition and structure of surface,.,Indicating that surface is dominated by OCH3 rather than polyethylene,though the amount of additives added is so small that they cannot be detected by IR and Raman spectroscopies.,2926？,OCH3,Jie Wang,Zoltan Paszti.J.Am.Chem.Soc.,2002,124(24),pp 70167023,1.Character composition and structure of surface,Analysis,DISCUSSION,Analysis,2.Glass transition of the PP surfaces,Fig.The ratio of the strengths of the CH2symmetric stretch to the CH3symmetric stretch for APP and IPP as a function of temperature.,Semicrystalline polymer,Amorphous polymer,Analysis,2.Glass transition of the PP surfaces,Blends,Yi Liu,Marie C.messer.J.Phys.Chem.B,2003,107(36):97749779,Blends:(A)fMMA=0.03;(B)fMMA=0.06;(C)fMMA=0.09;(D)fMMA=0.11.,Analysis,3.Structures and Segregation of PS/PMMA Blends,Figure Water contact-angle of blends before(o)and after()annealing.,Figure SFG of blends.Samples were annealed in a vacuum at 150 for 20 h,Yi Liu,Marie C.messer.J.Phys.Chem.B,2003,107(36):97749779,Analysis,3.Structures and Segregation of PS/PMMA Blends,Analysis,4.Environmental response,Prospect,SFG have been used successfully to probe buried interfac in various fields of research.But there are many prolems to be solved:1.IRIRvisible spectroscopy2.doubly resonant SFG spectroscopy molecular chirality3.development of high-power tuneable laser sources,Thank you！-TJJ,原理,IR-visible sum frequency generation spectroscopy uses two laser beams that overlap at a surface of a material or the interface between two materials.An output beam is generated at a frequency of the sum of the two input beams.The two input beams have to be able to access the surface,and the output beam needs to be able to leave the surface to be picked up by a detector.2One of the beams is a visible wavelength laser held at a constant frequency and the other is a tunable infrared laser.By tuning the IR laser,the system can scan over resonances and obtain the vibrational spectrum of the interfacial region.1As a nonlinear optical process,the polarization which generates the output depends on the electric fields of the two input beams.As a second-order nonlinear process,SFG is dependent on the 2nd order susceptibility(2).The fact that the 2nd order susceptibility,a third rank tensor,becomes zero incentrosymmetricmedia,limits what samples are accessible for SFG.Centrosymmetric media include the bulk of gases,liquids,and most solids under the assumption of the electric-dipole approximation,which neglects the signal generated by multipoles and magnetic moments.2At an interface between two different materials or two centrosymmetric media,the inversion symmetry is broken and an SFG signal can be generated.This suggests that the resulting spectra represent a thin layer of molecules.A signal is found when there is a net polar orientation.23,Sum frequency generation spectroscopy(SFG)is a technique used to analyze surfaces and interfaces.This nonlinear laser spectroscopy method was developed in 1987 and rapidly applied to deduce the composition,orientation distributions,and some structural information of molecules at gassolid,gasliquid and liquidsolid interfaces.In a typical SFG setup,two laser beams mix at a surface and generate an output beam with a frequency equal to the sum of the two input frequencies.SFG has advantages in its ability to be monolayer surface sensitive,ability to be performed in situ(for example aqueous surfaces and in gases),and not causing much damage to the sample surface.SFG is comparable tosecond harmonic generation(SFG is a more general form)andInfraredandRaman spectroscopy.,
