Contact Microscopy using a Compact Laser Produced Plasma Soft X-Ray Source

Soft X-ray contact microscopy potentially allows imaging of wet living biological specimens at a spatial resolution higher than optical microscopy and without many of the constraints of scanning electron microscopy. In this paper, we present the development of a laboratory scale contact microscope that uses a laser produced plasma soft X-ray source. The source is based on a double-stream gas-puff target approach and it operates in the "water window" spectral range which enables to capture images of biological samples with a natural contrast. In the preliminary experiments the contact microscope system has been used for imaging of fixed and dried non-malignant HCV29 human bladder cell lines cultured on polymethyl methacrylate photoresists. The samples were exposed with 150 pulses of soft X-rays as an initial test to demonstrate the possibility of image formation. The soft X-ray contact images registered in the photoresists exhibit high resolution in the atomic force microscopy topography which indicates the potential application of soft X-ray contact microscopy in life science to examine small features as small as few tens of nm. The technique could also be used for living cell imaging with further optimization of the microscope system and development of a special specimen holder. The details of the soft X-ray contact microscopy technique and the experimental results are presented and discussed.