Study On The Application Of 2D Photonic Crystals In STXM Detection

Scintillators can convert the X-rays into photons ranging from ultraviolet to near-infrared,which are widely used in synchrotron radiation and free electron lasers.The ideal scintillator has the characteristics of high light yield and fast decay time.At present,P43（Gd₂O₂S:Tb）phosphor as detector material is generally used in scanning transmission soft X-ray microscopy（STXM）.Despite P43 phosphors have high light yield,its long decay time（about 1ms）limits the acquisition time of the detector.Due to the long decay time,the P43 phosphors cannot be used in the fast STXM detector.The YAG:Ce scintillator has capability of high radiation resistance and short response time with 70 ns,which is suitable for fast X-ray detector material.Due to the total reflection effect,most of the photons generated by the scintillator cannot be received by the detector.To enhance the light output of scintillator can improve the sensitivity and time resolution of X-ray detector.Two-dimensional photonic crystal（Ph C）is the periodic arrangement of materials with different dielectric constants in two-dimensional space.Similarly to transmission gratings,photonic crystals can extract partical light greater than the critical angle.The total internal reflection is reduced and thus the light output of scintillators is enhanced.The scintillator patterned by two-dimensional Ph C has the characteristics of fast response and high light output.Therefore,the scintillator can be used in STXM imaging and spectral detection in the field of synchrotron radiation and free electron lasers.The main research in this paper is present as follows.1.X-ray excited optical luminescence（XEOL）detection system was built at BL08U1A beamline in the SSRF.It can be used to study the effect of two-dimensional Ph C on the luminescence spectrum of scintillator.Scanning luminescent X-ray microscopy（SLXM）was built to realize high spatial resolution imaging of luminescent samples.The luminescence angular distribution detection platform was built for optimizing the parameters of Ph C structure.2.The YAG:Ce scintillator with Si Nx two-dimensional Ph C was fabricated by X-ray interference lithography.The STXM detector has hundreds of nanoseconds response time when using the scintillator with Ph C.The Ph C pattern has the period of 600nm,air hole diameter of 380nm,air hole depth of 220nm and square arrays.The X-ray energy is 705e V.The image counter is approximately 3.6 times than that of the unpatterned YAG:Ce scintillator and the signal-to-noise ratio was increased from 6.4d B to 10d B.Using two-dimensional Ph C to improve the light output and combining the fast response characteristics,scintillators have the potential application in situ detection of dynamic electrochemical reaction process,formation and agglomeration of nanoparticles,catalytic mechanism,free electron lasers high repetition frequency single pulse detection and other fields.3.GAGG:Ce scintillator has the highest light yield among all known oxide scintillators.The optimized Ph C structures have square arrays of air holes etched into Ti O₂ layer（Period 528nm,Hole diameter 360nm）.Compared with unpatterned GAGG:Ce scintillator,the light output of the Ph C-patterned GAGG:Ce scintillator was enhanced by a factor of about 2.2 with air coupling and 43%with the optical grease coupling.4.Scanning luminescent X-ray microscopy（SLXM）realized nano spatial resolution imaging by scanning luminescent samples point by point.Combined with STXM,spatial distribution information of luminescent samples can be obtained.Photonic crystal structures with the period of 600nm,air hole depth of 480nm and hexagonal arrays were patterned on the surface of Si N_x window.The Si N_x window patterned by two-dimensional Ph C is used to improve the imaging quality of SLXM and obtain more high-frequency information.The luminescence intensity of the perovskite quantum dot film was enhanced to 3.9 times by using two-dimensional Ph C.5.The luminescent substrate material patterned by two-dimensional Ph C can be used for high sensitive transmission mode near edge X-ray absorption fine structure（NEXAFS）detection,reducing signal acquisition time and radiation damage.The simultaneous acquisition of transmission mode NEXAFS spectrum and total electron yield mode NEXAFS spectrum is realized based on the luminescent substrate.The surface and bulk information of the sample were obtained simultaneously.