| In-situ,fast solid micron sampling technique is an important research area in analytical chemistry.In contrast to solution analysis,the direct solid analysis avoids the risks of tedious sample preparation,introduction of contamination,sample loss,etc.It not only saves time and effort,but also retains the spatial distribution information of sample composition.In the field of elemental analysis,it is of great importance to carry out the research on solid sample ablation/excitation source which is suitable for emission spectrometry.The atmospheric pressure discharge plasma source has the merits of simple structure,low price,simplicity of operation,etc.By combining this solid ablation/excitation source with emission spectrometry,the miniaturization of the analysis system can be realized.On the other hand,laser technology has been widely used in micron sampling analysis of conductors and non-conductors.Although it is mature,the understanding of the laser-matter interaction,particle formation and plasma expansion should be improved.Currently,the sub-microanalysis requirements have promoted the development of laser sampling techniques.The combination of near-field tip-enhanced laser ablation and emission spectrometry is expected to be a new tool for microanalysis.In this paper,the applications of near-field tip-enhanced and pulsed needle discharge emission spectrometry are introduced.The related works are divided into three parts:1.The pulsed needle arc discharge device and the microscope light collection system are set up.This pulsed needle discharge plasma source can realize micron ablation and excitation.The crater diameter is about 180 μm.The emICCD photograpy is used to record the evolution process of discharge plasma.The results show that the variation of luminescence intensity is similar to the trend of discharge current.The electron excitation temperature and electron density of this atmospheric micro-arc plasma are about 6700 K and 1017 cm-3,respectively.The pulsed needle discharge analysis system can quickly analyze the element in aluminum alloy.This system has the merits of low price,convenient operation,fast analysis,etc.2.The near-field tip-enhanced laser ablation emission spectrometric system is set up for submicron elemental analysis.The near-field effect is used to enhance the localized electromagnetic field at the tip apex during laser illumination.When the distance between tip and sample is less than 10 nm,submicron ablation and excitation of the sample under the needle tip can be realized.Compare with none spectral signal collected by far-field,the spectral signal can be obtained after the tip approaches.This result fully verifies the existence of near-field enhancement effect.This system is applied to analyse Si wafer with an Al film.The spectroscopic information from a crater of～650 nm diameter is obtained.Besides,the elemental imaging analysis is performed on the Al lines on SIM card chip,obtaining～830 nm lateral resolution and realizing the atomic emission spectroscopic analysis at sub-micron resolution.3.The related research of ion kinetic energy distribution in laser plasma is systematically introduced.The macroscopic behavior of laser-induced aluminum plasma and the spatial-temporal evolution of component species in plasma are diagnosed by fast emICCD photography.The characteristics of plasma expansion are deeply understood.The results indicate that ions and neutrals are spatially separated under the bipolar diffusion electrostatic acceleration mechanism.Ions are distributed at the front end of the expanded plume.The velocity of vacuum expansion is about 10~4 m/s.Species with higher charge state have higher velocity.Under the influence of the ambient gas,when the pressure is greater than 1 Pa,there is a high luminous intensity region at the front end of the plasma plume,and the plasma plume splitting phenomenon occurs. |
PDF Full Text Request