Microzone Plates Research Articles

Two new ideas of X-ray holographic tomography with micro-zone plates

Two new ideas about X-ray holographic tomography to develop X-ray three-dimensional microscopic imaging techniques are proposed in this paper. One is called X-ray in-line holographic tomography using one micro-zone plate and the other is X-ray image holographic tomography using two micro-zone plates. For the former, a micro zone plate is used to amplify spacing of interference fringes on in-line holograms. For the latter, a micro. zone plate amplifies the image of a test sample and forms object wave, the other one produces reference wave. The two methods can realize real-time X-ray three-dimensional microscopic imaging for biological specimens with high resolution.

Electron Beam Lithography And Nanometer Structures: Fabrication Of Microzone Plates

Microzone plates have been fabricated with the aid of a 100- keV electron beam lithography system. The system has been designed for generating structures with lateral dimensions of less than 100 nm. The particular demands on high resolution, high efficiency imaging Fresnel zone plates and the resultant problems concerning lithography and pattern transfer are discussed. We show a step-by-step improvement of fabricated microzone plates with an outermost zone width of 50 nm. A thin titanium intermediate layer is used as a stable mask to generate ion-milled gold absorber rings with very steep walls. The zone plates have been tested by imaging one another in an x-ray microscope and ave been compared to the image obtained with the holographically fabricated MZP3 microzone plate from Gottingen.

Imaging zone plates for x-ray microscopy fabricated by electron-beam lithography

Fresnel zone plates have been fabricated by electron‐beam lithography using a modified scanning transmission electron microscope. These microzone plates are designed to work as imaging elements in an x‐ray microscope. To achieve zone plates that are free of distortions, the deflection field of the lithography system has been calibrated by the aid of externally generated reference marks. Microzone plates with a minimum linewidth of 20 nm have been written into polymethylmethacrylate and etched into a 15‐nm‐thick titanium layer. Two methods of transfer into a gold absorber layer have been used, namely sputter etching of the gold layer with a reactively ion etched titanium mask, and electroplating of gold using a suitable trilevel resist system. By these techniques, Fresnel zone plates with 100 zones, a width of the outermost zones of 50 nm, and a thickness of the gold absorber layer of 80 nm have been fabricated. Imaging experiments have been performed at the electron storage ring BESSY in Berlin, and the results have been compared with images obtained by holographically fabricated zone plates.

X-ray picture of the Sun taken with Fresnel zone plates

It is well known that Fresnel zone plates act as a lens with a focal length inversely proportional to the wavelength. At Professor Moellenstedt's Institute of Applied Physics in Tübingen, a technique has been developed to manufacture micro-zone plates electronoptically from Buckbee-Mears zone plates. These micro-zone plates have a diameter of 0·5 mm approximately, 38 zones and a focal length of 30 cm for X-rays of nearly 50 Å. Their resolving power is of the order of a few seconds of arc (Einighammer et al., 1966). One finds, however, experimentally as well as theoretically that the sharply defined image is surrounded by a halo having a diameter of a few minutes of arc for the above-mentioned zone plates. Whereas for a point source the intensity of a halo is poor and therefore unimportant, for extended sources it becomes large as a result of the superposition of the contributions from the individual points of the source. This has been demonstrated by the photometer curves of the images of circular sources by Einighammer (1966) (Figure 1). The halo is not noticeable in case of very narrow sources (curves a and b). With increasing diameter of the source the intensity of the halo rapidly increases (curves c and d). For the same source the brightness distribution of the halo agrees practically with the one obtained by a pinhole camera, provided the diameter of the hole and that of the zone plate are equal; these brightness distributions are represented by the dashed lines c′ d′ in Figure 1.