FAST, HIGH RESOLUTION NEGATIVE CHEMICHALLY AMPLIFIED EPOXY PHOTORESIST FOR X-RAY IMAGING OF LIVING BIOLOGICAL SPECIMENS IN THE WATER WINDOW

摘要

Soft X-ray contact microscopy (SXCM), enables the study of the ultrastructure of living hydrated specimens, without the need of dehydration or any other chemical pre-treatment, by using suitable pulsed X-ray sources such as laser plasmas. The interest in using soft X-rays, in the so-called "water window" (2.3-4.4nm), is based on the low attenuation at these wavelengths caused by water, as compared to the attenuation caused by organic matter. Therefore, good contrast masking of the incident radiation is provided. The successful imaging of biological specimen requires the development of sensitive photoresist materials for image recording; these should have capabilities of high-resolution lithography and an extended greyscale. A very sensitive photoresist, used for the first time in SXCM, enabled the biological imaging with the specific source in single pulse experiments in the water window spectral range. This photoresist is an epoxy novolac based chemically amplified photoresist (EPR) which has been proven capable of resolving sub tenth micron features. ). The photoresist response was at least two orders of magnitude "faster" than PMMA (polymethyl methacrylate), the standard resist used so far in soft X-ray contact microscopy (SXCM). Atomic force and scanning electron microscopy of the biological specimen images recorded in the resist, clearly showed the flagella of the motile green alga, Chlamydomonas, suggesting a lateral resolution better than 150nm. The resist was also capable of providing height features, as small as 20nm, in AFM depth profiles and discriminating the flagella intersection areas.