Niobium diselenide superconducting photodetectors

We report the photoresponse of niobium diselenide (NbSe2), a transition metal dichalcogenide which exhibits superconducting properties down to a single layer. Devices are built by using micromechanically cleaved 2–10 layers and tested under current bias using nano-optical mapping in the 350 mK–5K range, where they are found to be superconducting. The superconducting state can be perturbed by absorption of light, resulting in a voltage signal when the devices are current biased. The response is found to be energy dependent, making the devices useful for applications requiring energy resolution, such as bolometry, spectroscopy, and infrared imaging

Coalification by Clay-Catalyzed Oligomerization of Plant Monomers. [Eugenols]

During this reporting period, we have continued with our study of the chemistry of C{sub 6}-C{sub 3} plant monomers with montmorillonite clay (K-10). We have examined the reaction of K-10 with methyleugenol. Indane dimers (2 and 3) were observed. These same two dimers are formed in the reaction of K-10 with methylisoeugenol. Consequently, it seems likely that 1 is isomerized to 4 in the acidic environment of the K-10. Of particular interest in this reaction are the two new dimers 5 and 6. The structure of the anthracene dimer 6 has been confirmed by comparison of its ultraviolet spectrum with that of the dimethyl analog 7. Finally, while no presently known, naturally occurring lignans or lignins have structures related to 5 and 6, the formation of at least the anthracene ring system from 1 may be of significance, since anthracene units are known to occur in coal. We have also examined the photochemistry of 4. The original question that lead us into this area of lignan chemistry was whether 4 might be induced to undergo Diels-Alder dimerizations to form the natural products galbulin or isogalbulin

Coalification by Clay-Catalyzed Oligomerization of Plant Monomers. [Methyleugenol]

During this report period, we have obtained a model of montmorillonite clay, and this model has been of great assistance in visualizing how the chemistry of substrate molecules might be altered as it occurs on the surface of the clay. A stereochemical representation of this montmorillonite model is shown. Of particular significance, this model indicates that hydroxyl groups are located in the center of each siloxane ring on the surface of the montmorillonite clay. These hydroxyl groups might serve to bond substrate molecules to the surface of the clay. The next step in our systematic examination of the radical cation-initiated dimerization of plant monomers from the C{sub 6}-C{sub 3} pool of shikimic acid metabolites was to study the dimerization of cinnamic acid and its derivatives. In the next block of research, we examined the reaction of montmorillonite clay (K-10) with methyleugenol. 2 refs

Coalification by Clay-Catalyzed Oligomerization of Plant Monomers

The next step in our systematic examination of the radical cationinitiated dimerization of plant monomers from the D{sub 6}-C{sub 3} pool of shikimic acid metabolites was to study the dimerization of cinnamic acid and its derivatives. In order to do this we needed a radical cation initiator that has a reduction potential greater than that of BAHA (E{sub red} = 1.30 volts), since the electron-withdrawing carboxylate functional group of cinnamates renders them inert to oxidation with BAHA. This problem was solved with the observation that DBAHA tris-(2,4-dibromophenyl)aminium hexachloroantimonate, E{sub red} = 1.74 volts, intiated the radical cation dimerization of methyl 3,4-dimethoxycinnamate

Coalification by Clay-Catalyzed Oligomerization of Plant Monomers

One of the main objectives is to explore the possibility that radical cation Diels-Alder reactions are involved in the biosynthesis of lignans in plants. Two of the most highly sought after classes of lignans are the dibenzocyclooctadienes represented by stegnol and the aryltetralins represented by podophyllotoxin. Both are powerful anticancer agents and have structures that might be assembled from C{sub 6}-C{sub 3} units via radical cation processes. A common feature of both of these molecules is the benzyllic hydroxyl group. The hydroxyl group is cis to the lactone carbonyl carbon. The hypothetical mechanism by which this hydroxyl group might be introduced into the aryltetralins is outlined. We have also begun to study the radical cation Diels-Alder chemistry of cinnamate salts. The preliminary results are described. In an extension of our previous work with tethered cinnamates, we have returned to the tethered molecule and are in the process of reexamining its radical cation Diels-Alder chemistry in the presence of Na{sub 2}CO{sub 3}. We have begun to investigate the radical cation chemistry of polycyclic aromatic hydrocarbons in an effort to find chemistry that will produce the coupling of these aromatic molecules. Our first effort has been to look at naphthalene treated with DBAHA. 2 refs