Durable diamond-like carbon templates for UV nanoimprint lithography.

The interaction between resist and template during the separation process after nanoimprint lithography (NIL) can cause the formation of defects and damage to the templates and resist patterns. To alleviate these problems, fluorinated self-assembled monolayers (F-SAMs, i.e. tridecafluoro-1,1,2,2,tetrahydrooctyl trichlorosilane or FDTS) have been employed as template release coatings. However, we find that the FDTS coating undergoes irreversible degradation after only 10 cycles of UV nanoimprint processes with SU-8 resist. The degradation includes a 28% reduction in surface F atoms and significant increases in the surface roughness. In this paper, diamond-like carbon (DLC) films were investigated as an alternative material not only for coating but also for direct fabrication of nanoimprint templates. DLC films deposited on quartz templates in a plasma enhanced chemical vapor deposition system are shown to have better chemical and physical stability than FDTS. After the same 10 cycles of UV nanoimprints, the surface composition as well as the roughness of DLC films were found to be unchanged. The adhesion energy between the DLC surface and SU-8 is found to be smaller than that of FDTS despite the slightly higher total surface energy of DLC. DLC templates with 40 nm features were fabricated using e-beam lithography followed by Cr lift-off and reactive ion etching. UV nanoimprinting using the directly patterned DLC templates in SU-8 resist demonstrates good pattern transfer fidelity and easy template-resist separation. These results indicate that DLC is a promising material for fabricating durable templates for UV nanoimprint lithography.

Experimental and theoretical investigation on surfactant segregation in imprint lithography.

The effects of template surface composition on fluorinated surfactant segregation were investigated for imprint lithography with photopolymerizable vinyl ether formulations. Heptadecafluoro-1,1,2,2-tetrahydrodecyl vinyloxy-methyloxy dimethylsilane, containing a vinyl ether group, was employed as the surfactant, and blanket templates were pressed onto the liquid and illuminated with UV radiation from below. The extent of surfactant segregation to the vinyl ether-template interface before polymerization was characterized using contact angle measurements and angle-resolved X-ray photoelectron spectroscopy after removing the template from the cured vinyl ether polymer. Blanket surfaces consisting of bare quartz, high-density polyethylene, and quartz treated with tridecafluoro-1,1,2,2,-tetrahydrooctyltrichlorosilane afforded templates with different surface energy and polarity. The highest degree of surfactant segregation was found with tridecafluoro-1,1,2,2,-tetrahydrooctyltrichlorosilane-treated quartz, whereas little surfactant segregation was found for bare quartz. A thermodynamic model is developed to predict the surface segregation profiles.

Surface hydration and its effect on fluorinated SAM formation on SiO2 surfaces.

Substrate hydration is demonstrated to be crucial to film quality during self-assembled (SA) film deposition of tridecafluoro-1,1,2,2,-tetrahydrooctyltrichlorosilane (FOTS) from the vapor phase. The surface hydration was studied by thermogravimetric analysis, and a model was developed to predict the conditions necessary to desorb all of the water adsorbed on a fused silica surface without significantly altering the concentration of the surface hydroxyl groups. The nature of the SA film was investigated as a function of the degree of rehydration of the dehydrated silica surface. The wettability and microstructure of the SA films were examined by water contact angle, ellipsometry, X-ray photoelectron spectroscopy, and atomic force microscopy. There is an optimum degree of substrate hydration, on the order of 1-1.2 monolayers of adsorbed water, required to produce a dense, durable and uniform FOTS film with high water repellency and a smooth surface.

A new synthetic route to authentic N-substituted aminomaleimides.

A number of compounds reported in the literature as N-aminomaleimides (2) are, instead, isomeric N-aminoisomaleimides (3). The ubiquity of this mischaracterization and its propagation within the literature are discussed. In addition, the first general synthetic route to aliphatic and aromatic N-substituted aminomaleimides is described. As an illustration, the compound reported to be N-(4-bromophenylamino)maleimide (2b) was prepared and determined to be N-(4-bromophenylamino)isomaleimide (3b). The authentic compound was synthesized by the condensation of 4-bromophenylhydrazine (7b) and the exo-furan/maleic anhydride Diels-Alder adduct (8) in acetic acid to produce the furan-protected aminomaleimide 10b, followed by heating to remove furan through the retro Diels-Alder reaction. The structures of 2b, 3b, and 10b were established unequivocally by X-ray crystallography and other spectroscopic techniques.

Peptide sweeteners. 3. Effect of modifying the peptide bond on the sweet taste of L-aspartyl-L-phenylalanine methyl ester and its analogues.

A series of analogues designed to assess the importance of the amide bond in the dipeptide sweetener L-aspartyl-L-phenylalanine methyl ester has been synthesized and tested. The peptide bond was methylated, replaced by an ester bond, or reversed. all of these modifications produced compounds that did not have a sweet taste. We conclude that the steric, electronic, and directional characteristics of the amide bond are essential for biological activity in the dipeptide sweeteners.

Stereochemistry of the porphyrin-protein bond of cytochrome c. Stereochemical comparison of Rhodospirillum rubrum, yeast, and horse heart porphyrins c.

Porphyrins c have been obtained from Rhodospirillum rubrum cytochrome c2, yeast cytochrome c, and horse heart cytochrome c and compared using proton magnetic resonance and circular dichroism. Identity of the spectra establishes that chemically and stereochemically the three porphyrins c are identical. Since the stereochemistry of the porphyrin alpha-thioether linkage is not affected in the conversion to porphyrin c, the stereochemistry at the porphyrin alpha-thioether bonds among the corresponding cytochromes c also must be the same. Differences between the proton magnetic resonance of R. rubrum cytochrome c2 and horse heart cytochrome c which were rationalized by invoking an opposite stereochemistry at these condensation sites (Smith, G. M., and Kamen, M. D. (1974), Proc. Natl. Acad. Sci. U.S.A. 71, 4303) must therefore be attributed to other factors.