Kwon-Ha Yoon

Compact soft x-ray transmission microscopy with sub-50 nm spatial resolution

In this paper, the development of compact transmission soft x-ray microscopy (XM) with sub-50 nm spatial resolution for biomedical applications is described. The compact transmission soft x-ray microscope operates at lambda = 2.88 nm (430 eV) and is based on a tabletop regenerative x-ray source in combination with a tandem ellipsoidal condenser mirror for sample illumination, an objective micro zone plate and a thinned back-illuminated charge coupled device to record an x-ray image. The new, compact x-ray microscope system requires the fabrication of proper x-ray optical devices in order to obtain high-quality images. For an application-oriented microscope, the alignment procedure is fully automated via computer control through a graphic user interface. In imaging studies using our compact XM system, a gold mesh image was obtained with 45 nm resolution at x580 magnification and 1 min exposure. Images of a biological sample (Coscinodiscus oculoides) were recorded.

Conceptual Design of Soft X-ray Microscopy for Live Biological Samples

This study describes the conceptual design of a soft x-ray microscope system based on a laserbased source for biomedical application with high resolution (

Wolter type I x-ray focusing mirror using multilayer coatings

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Alignment of laboratory-scale soft X-ray microscope using laser plasma

50nm). The laboratory scale soft x-ray microscope consists of high power laser plasma x-ray source and grazing incidence mirrors with high reflectivity. The laser plasma source used for developing this system employs Q-switched Nd-YAG pulsed laser. The laser beam is focused on a tantalum (Ta) target. The Wolter type I mirror was used as condenser optics for sample illumination and as objective mirror for focusing on a detector. The fabrication of the Wolter type I mirror was direct internal cutting using ultraprecision DTM. A hydrated biological specimen was put between the two silicon wafers, the center of which was

Figure tolerance of a Wolter type I mirror for a soft-x-ray microscope

Si_3N_4

Development of laser plasma-based soft x-ray microscopy

windows of 100㎚ thickness. The main issues in the future development work are to make a stable, reliable and reproducible x-ray microscope system.

Visfatin promotes angiogenesis by activation of extracellular signal-regulated kinase 1/2.

A multilayer coating is a useful addition to a mirror in the x-ray region and has been applied to normal incidence mirrors used with soft x rays. When a multilayer coating is used on grazing incidence optics, higher performance can be achieved than without it. Cr/Sc multilayers coated on a Wolter type I mirror substrate for a soft x-ray microscope are considered. The reflectivity and effective solid angle are calculated for Wolter type I mirrors with uniform and laterally graded multilayer coatings. The laterally graded multilayer mirror showed superior x-ray performance, and the multilayer tolerances were relaxed. This multilayer mirror could be especially useful in the soft x-ray microscope intended for biological applications.

Precision Machining of Electroless Nickel Mandrel and Fabrication of Replicated Mirrors for a Soft X-Ray Microscope

We demonstrate an alignment method for a laboratory-scale soft X-ray microscope, which utilizes a liquid-jet laser-produced plasma source in combination with a tandem ellipsoidal condenser mirror and a diffractive micro zone plate. Because the intensity of the laser-produced plasma source is relatively low, we developed the tandem ellipsoidal condenser mirror to increase the photon density in the objective plane and to obtain a high-resolution image within a short exposure time. But, aligning the tandem ellipsoidal condenser mirror is a difficult task because it has 5 degrees of freedom (DOF) alignment tolerances and there is a connection among these tolerances. We performed its tolerance analysis and developed a new fully automated alignment algorithm via computer control. As a result, a 12.5-µm-pitch gold mesh image was measured using 700× magnification and a 5 min exposure and the resultant edge detection resolution was about 70 nm.

Optimization of a Wolter type I mirror for a soft X-ray microscope

The demand for an x-ray microscope has received much attention because of the desire to study living cells at a high resolution and in a hydrated environment. A Wolter type I mirror used for soft-x-ray microscope optics has many advantages. From the mirror fabrication point of view, it is necessary to perform tolerance analysis, particularly with respect to figure errors that considerably degrade the image quality. The figure tolerance of a Wolter type I mirror for a biological application in terms of the image quality and the state-of-the-art fabrication technology is discussed. The figure errors rapidly destroyed the image quality, and the required slope error depended on the detector used in the soft-x-ray microscope.

Cellular uptake of folate-conjugated lipophilic superparamagnetic iron oxide nanoparticles

A compact soft X-ray microscope system has been developed for biological applications with nano-scale resolution. Soft X-ray used to the system is emitted from a solid target by using Nd-YAG pulsed laser. Boron nitride (BN) is used as the target materials in the system. The optics of the microscope system is adopted with wolter type-I mirrors, which is consisted of a condenser mirror with demagnification of 1/4× and an object mirror with magnification of 32×. The surface roughness of the machined wolter mirrors is about 0.8 nm (Ra) after polishing. In this paper, the X-ray characteristics, i.e., spectrum and intensity emitted from laser plasma-based x-ray source was measured. Imaging test using the system was performed with gold 2000 mesh. The spatial resolution of the soft x-ray microscope system was obtained about 900 nm.