We have developed a cryo scanning transmission X-ray microscope which uses soft X-rays from the National Synchrotron Light Source. The system is capable of imaging frozen hydrated specimens with a thickness of up to 10 microm at temperatures of around 100 K. We show images and spectra from frozen hydrated eukaryotic cells, and a demonstration that biological specimens do not suffer mass loss or morphological changes at radiation doses up to about 1010 Gray. This makes possible studies where multiple images of the same specimen area are needed, such as tomography (Wang et al. (2000) Soft X-ray microscopy with a cryo scanning transmission X-ray microscope: II. Tomography. J. Microsc. 197, 80-93) or spectroscopic analysis.
Using micro-fabrication techniques, we have manufactured a single element kinoform lens in single-crystal silicon with an elliptical profile for 12.398 keV (1A) x-rays. By fabricating a lens that is optimized at fixed wavelengths, absorption in the lens material can be significantly reduced by removing 2_ phase-shifting regions. This permits short focal length devices to be fabricated with small radii of curvatures at the lens apex. This feature allows one to obtain a high demagnification of a finite synchrotron electron source size. The reduced absorption loss also enables optics with a larger aperture, and hence improved resolution for focusing and imaging applications. Our first trial of these lenses has resulted in a one micron line focus (fwhm) at the National Synchrotron Light Source X13B beamline.
X-ray multilevel zone plate fabrication by means of electron-beam lithography: Toward high-efficiency performances J.We report here the optimization of processes for producing sub-20 nm soft x-ray zone plates, using a general purpose electron beam lithography system and commercial resist technologies. We have critically evaluated the failure point of the various process steps and where possible chosen alternate methods, materials, or otherwise modified the process. Advances have been made in most steps of the process, including the imaging resist, pattern conversion for electron beam exposure, and pattern transfer. Two phase shifting absorber materials, germanium and nickel, were compared. Zone plates with 30 nm outer zones have been fabricated in both germanium and nickel with excellent quality using polymethyl methyl accrylate and zones as small as 20 nm have been fabricated in nickel using the calixarene resist. The total efficiency as well as the efficiency of different regions of the zone plates were measured. All zone plates have demonstrated good efficiencies, with nickel zone plates performing better than germanium zone plates.
We have measured the distribution in current for the onset of voltage in small-area Josephson junctions for temperatures down to ~1.6 K. The lifetime of the (V) = 0 state for our highest current density junctions becomes temperature independent for k B T %H(j)i/20 t SLT much less than the WKB prediction (co 0 is the junction resonant frequency). This is consistent with the Caldeira-Leggett theory, which includes damping effects on the quantum tunneling rate. PACS numbers: 74.50.+r, 05.04,+j, 72.70.+m Many experiments have studied the ramifications of the classical Langevin equation, but few have probed the low-temperature, high-frequency regime where quantum corrections to the picture must be expected. High-current-density Josephson tunnel junctions 1 at temperatures of a few kelvins make possible experimental studies 2 in this regime. Biased in the {V) = 0 state at currents near the critical current, the junctions are sensitive to fluctuations in the terahertz range, centered about their natural frequency, a> 0 . Fluctuation effects may be observed by sweeping the junction current through the critical current and noting the distribution, P{i), of current values at which voltage sets in. 3 P(i) should depend on whether k B T»Hu 0 /2 (classical regime) or k B T «h(x) Q /2 (quantum regime). 4 " 6 We have measured the width, a, of P(i) for junctions in the quantum regime and found that quantum effects do not appear until k B T l the potential wells vanish and the phase increases at a speed determined by the damping and the overall steepness of the potential. This corresponds to the finite voltage state of the junction. We are interested in x slightly less than 1, in the presence of fluctuations. The phase is now restrained by a low barrier (inset, Fig. 1) which, in the absence of fluctuations, would hold ( V) = 0 until i exceeds i c . Fluctuations, however, cause p...
Organic thiols have received extensive attention recently because of their relative stability and ease of examination compared to other potential molecular electronic materials. In this work, scanning probe microscopy (SPM) is used to study (i) the structural properties of self-assembled monolayers (SAMs) containing conjugated dithiols and (ii) the formation of the upper molecule-metal interface on dithiol SAMs. The top gold film is deposited either by thermal evaporation or by nano-transfer printing (nTP). Generally, the utility of thermal evaporation is limited because of Au diffusion through the SAMs. However, several dithiol SAMs are identified in this work that bond well to Au overlayers and act as satisfactory diffusion barriers. Coassembly of conjugated dithiols and alkanemonothiols is suggested as a route to obtain dithiols that are denser packed and more vertical (than is obtained from pure dithiol routes). High-yield nTP is demonstrated on coassembled SAMs. Advantages and limitations of different Au deposition and transfer techniques are compared on a variety of length scales.
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