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C W Hagen

Publications and source records attributed to C W Hagen.

6 recordsLinked to original sources
PubMed2006

Diffraction patterns of artificial two-dimensional crystals synthesized in situ in an environmental scanning transmission electron microscope.

In this study, we demonstrated the use of electron-beam-induced deposition for synthesis of artificial two-dimensional crystals with an in situ scanning transmission electron microscope. The structures were deposited from W(CO)6 in an environmental scanning transmission electron microscope on a 30-nm-thick Si3N4 substrate. We present clear electron beam diffraction patterns taken from those structures. The distance between the diffraction peaks corresponded to the dot spacing in the self-made surface crystal. We propose using these arrays of dots as anchor points for making artificial crystals for diffraction analysis of weakly scattering or beam-sensitive molecules such as proteins.

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PubMed2002

Low-energy foil aberration corrector.

A spherical and chromatic aberration corrector for electron microscopes is proposed, consisting of a thin foil sandwiched between two apertures. The electrons are retarded at the foil to almost zero energy, so that they can travel ballistically through the foil. It is shown that such a low-voltage corrector has a negative spherical aberration for not too large distances between aperture and foil, as well as a negative chromatic aberration. For various distances the third- and fifth-order spherical aberration coefficients and the first- and second-order chromatic aberration coefficients are calculated using ray tracing. Provided that the foils have sufficient electron transmission the corrector is able to correct the third-order spherical aberration and the first-order chromatic aberration of a typical low-voltage scanning electron microscope. Preliminary results show that the fifth-order spherical aberration and the second-order chromatic aberration can be kept sufficiently low.

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PubMed1968

The Differentiation of Pigmentation in Flower Parts, IV. Flavonoid Elaborating Enzymes From Petals of Impatiens balsamina s.

Extracts of the flower petals of Impatiens balsamina L. contain enzymes which catalyze the glycosylation of phenolic compounds. Enzymes have been extracted which glycosylate hydroquinone to arbutin and at least 3 different flavonols to the 3-monoglucoside. The hydroquinone glucosylating enzyme is similar to enzymes previously described except that it requires an unidentified low molecular weight cofactor. The glucosylation of flavonols follows normal enzyme kinetics; it requires a nucleotide diphosphate glucose donor for activity, and is made more evident by the presence of glucono-1:5-lactone, an inhibitor of endogenous glucosidases. It is suggested that the flavonol glucosylating enzyme acts naturally to glucosylate a precursor of both flavonols and anthocyanins to the 3-monoglucoside. The only elaboration of an anthocyanin observed with petal extracts was an acylation of pelargonidin-3-monoglucoside.

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PubMedDate not supplied

Resolution limit for electron beam-induced deposition on thick substrates.

Recently, the fabrication resolution in electron beam-induced deposition (EBID) has improved significantly. Dots with an average diameter of 1 nm have been made. These results were all obtained in transmission electron microscopes on thin samples. As one may think that such resolution can be achieved on thin samples only, it is the objective of this paper to show that this should also be possible on thick samples. For that purpose we use Monte Carlo simulations of the electron-sample interaction and determine the surface area where secondary electrons are emitted. Assuming that these electrons cause the deposition in EBID, a comparison can be made between deposition on a thin and a thick sample. The Monte Carlo code we developed will be described and applied to the deposition induced by a 200 keV primary electron beam on an ultra-thin (10 nm) and a bulk-like (1,000 nm) Cu sample. Near the point of incidence of the primary beam, the deposit size is independent of the substrate thickness, such that a 1-nm resolution should be possible to achieve on a thick substrate as well. Thicker substrates only affect the tails of the deposit distribution which contain more mass than thin substrate deposit tails.

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