Characterizing the structures of zeolites and their catalytic performance with high-spatial-resolution is vital to developing new solid catalysts. We demonstrate the application of photoinduced force microscopy (PiFM), with nanometer scale resolution across the infrared spectral range, for the study of zeolite ZSM-5 thin-films with various Si/Al ratios after the methanol-to-hydrocarbons reaction. This first-of-its kind nanometer scale infrared imaging of zeolite materials demonstrates the possibility of PiFM for the study of functional porous materials.
When excited at 440nm, the emission spectra of riboflavin exhibited maxima at 515nm (delayed fluorescence) and 620nm (phosphorescence). Deconvolution of the spectra to two individual bands characterized by asymmetric lognormal functions (I(n)=I0*exp{-ln(2)(ln[1þ2b(n-np)/D2]/b)}) facilitated the extraction of parameters and the analysis of their temperature dependence. Time resolved intensity decays were fitted using stretch, multi-exponential and distribution (by MEM) models. Riboflavin exhibited a lifetime of 184ms at 77K in glycerol-water. The lifetime decreased slowly below the solvent mixture's Tg (170K) and abruptly above Tg; e.g., an increase of 20K above Tg reduced the lifetime from 100ms to 10ms. This reduction was associated with molecular motions in the matrix. Molecular mobility was also modulated by changing the composition of the matrix, by using components of different molecular sizes or by adding plasticizers. Riboflavin phosphorescence also exhibited good sensitivity towards molecular mobility changes driven by composition. This suggests its use as a GRAS optical probe for molecular mobility and its potential application to optimize matrix composition in food and pharmaceutical products to enhance stability of micro and bioactive components. Continuous monitoring of riboflavin phosphorescence during heating and cooling cycles revealed differences in the delayed luminescence emission spectra, likely due to a higher rate of irreversible photodegradation of riboflavin at high temperatures. If properly characterized, the thermal dependence of riboflavin photodegradation can potentially be operationalized in sensors for temperature abuse.
Carrier mobility enhancement through local strain in silicon is a means of improving transistor performance. Among the scanning probe microscopy based techniques, tip-enhanced Raman spectroscopy (TERS) has shown some promising results in measuring strain. However, TERS is known to depend critically on the quality of the plasmonic tip, which is difficult to control. In this study, a test structure is used to demonstrate the capability of photo-induced force microscopy with infrared excitation (IR PiFM) in direct measurement of strain with approximately 10 nm spatial resolution. For SiGe pitch less than about 800 nm, the region between the SiGe lines should maintain residual strain. For a region with SiGe pitch of 1000 nm, it is verified that the strain between the SiGe lines is fully relaxed. PiFM promises to be a powerful tool for studying nanoscale strain in diverse material.
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