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Lensless imaging of red blood cells using coherent soft x-ray scattering Nazerzadeh-Yazdi, Arvin

Abstract

I am reporting on lensless imaging of human red blood cell using coherent x-ray scattering (CXS) technique. The successful microfabrication of a sample-mask structure using focused ion beam (FIB) milling was the key element in this imaging technique. The sample-mask structure is 600 - 800 nm gold films deposited using sputtering or electron beam evaporation on Si₃N₄ membrane windows. We used commercially available 100 nm thick Si₃N₄ membranes held by 3 mm diameter silicon frames that are designed for use in transmission electron microscopy. The red blood cell (RBC) sample was mounted in front of a 3 μm hole milled through both gold and Si₃N₄ layers on the opposite side. Three smaller reference apertures with diameters 300, 250 and 200 nm on the gold side were milled all the way through both layers at a distance of 9 am center-to center from the sample aperture. These holes are used for holographic lensless x-ray imaging. It was found that a gold surface roughens during ion milling due to a sputter instability and which produces cup-like features with a characteristic length up to few hundred nm. We found apertures milled through gold films deposited by sputtering show good circularity and sidewall roughness of 20 nm. We present result on CXS measurements in transmission geometry near Fe L₃₋ and C K-absorption edges on a single RBC. We captured high resolution images of the sample by simple Fourier inversion of the recorded far-field scattered intensity. We found 8.5 % reduction in the transmission intensity near Fe L₃₋edge due to presence of Fe in the form of hemoglobin molecules inside RBC. This absorption agrees with estimated agrees well with the estimated value of 9 % within experimental uncertainty. From limited data measured below C K-edge we measured a presence of at least 300 nm thick carbon inside RBC which lies in the range of the estimated value of 1.8 μm. The resolution of our lensless imaging technique is about 55 nm near Fe L₃₋edge and 78 nm near C K-edge.

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