مقاله انگلیسی رایگان در مورد طیف سنجی مادون قرمز میکرو فوتوکوسیت – الزویر 2018

This investigation establishes, for the first time, the viability of micro-photoacoustic infrared spectroscopy (microPAS). A cell that allows photoacoustic (PA) infrared spectroscopy measurements on small samples was constructed and tested in this work. The setup allows visualizing the sample and selecting specific measurement positions. It can be used with conventional Fourier-Transform infrared spectrometers and a variety of light sources, including conventional near- and mid-infrared lamps, synchrotron radiation, and laser sources. The cell was successfully used to discriminate between individual polymer beads based on differences between their PA spectra. The demonstrated spatial resolution is better than 100 µm and, in at least one case, as good as 20 µm.

Introduction

Photoacoustic (PA) spectroscopy has been used to characterize a wide variety of materials during the last four decades. The technique belongs to the extensive group of photothermal and thermophysical methodologies, interrogating both optical and thermal properties of matter. PA spectroscopy generally enables non-destructive, non-preparative analysis of solids and liquids; this capability may be critically important in situations where sample quantities are limited and/or traditional preparation methods must be avoided. Depth profiling of layered or inhomogeneous materials can also be effected in favourable circumstances. These attributes have motivated the development and utilization of PA spectroscopy, at a broad range of wavelengths, for many years [1]. In the infrared (IR) region, PA spectroscopy has particularly benefitted from the availability of commercial Fourier Transform Infrared (FT-IR) spectrometers, microphone-based detectors and, more recently, cantilever acoustic detectors. PA IR studies of solids have in most cases been directed to the analysis of bulk (macro) samples, with quantities on the order of a few milligrams or more being most common [2]. Despite this fact, it is important to recognize that a microsampling accessory has been manufactured by MTEC Photoacoustics for a number of years; this device was first utilized successfully to obtain PA spectra of single beads and fibres in 1999 [3]. Its design relies on the use of gaskets to locate a sample into a pre-centred location at the focal point of a parabolic mirror. The functionality of this accessory confirms that PA detection is, in fact, sufficiently sensitive to allow collection of signals from samples about 100 µm in size. The micro-sampling PA technique does not allow for visual inspection of the sample, or mapping of extended regions by selecting a region of interest across a larger sample area. With the illuminated spot neither diffraction-limited by the focusing optics nor defined by slits, its scientific utility is moderate from an IR microspectroscopy perspective. The present article describes initial work with a novel sample cell for microphotoacoustic spectroscopy (microPAS). This cell, designed and constructed at the Canadian Light Source, facilitates the acquisition of PA spectra of micrometre-sized solid specimens having a two-dimensional structure. In contrast with the microsampling accessory mentioned in the previous paragraph, the microPAS cell can be used together with a standard infrared microscope/FT-IR spectrometer system.