Catalytic conversion of HMF to valuable chemicals was achieved over a Cu-doped porous metal oxide in supercritical methanol. The hydrotalcite catalyst precursor is prepared following simple synthetic procedures, using inexpensive and earth-abundant starting materials in aqueous solutions. The hydrogen equivalents needed for the reductive deoxygenation of HMF originate from the solvent itself upon its reforming. Dimethylfuran, dimethyltetrahydrofuran and 2-hexanol were obtained in good yields. At milder reaction temperatures, a combined yield (DMF + DMTHF) of 58% was achieved. Notably, the formation of higher boiling side products and undesired char from HMF is not detected under these reaction conditions.

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For in-situ measurements of the local electrical conductivity of well-defined crystal surfaces in ultrahigh vacuum, we have developed two kinds of microscopic four-point probe methods. One involves a "four-tip STM prober," in which four independently driven tips of a scanning tunneling microscope (STM) are used for measurements of four-point probe conductivity. The probe spacing can be changed from 500 nm to 1 mm. The other method involves monolithic micro-four-point probes, fabricated on silicon chips, whose probe spacing is fixed around several µm. These probes are installed in scanningelectron-microscopy/electron-diffraction chambers, in which the structures of sample surfaces and probe positions are observed in situ. The probes can be positioned precisely on aimed areas on the sample with the aid of piezoactuators. By the use of these machines, the surface sensitivity in conductivity measurements has been greatly enhanced compared with the macroscopic four-point probe method. Then the conduction through the topmost atomic layers (surface-state conductivity) and the influence of atomic steps on conductivity can be directly measured.

By combining conventional silicon microfabrication and direct three-dimensional growth using electron-beam induced carbon contamination, we have developed a scheme for fabricating nanotweezers with a gap of 25 nm. Four silicon oxide cantilevers with a spacing of 1.5 µm extending over an edge of a silicon support chip, were covered with a thin layer of metal. By focusing an electron beam at the ends of the cantilevers, narrow supertips grew from the substrate. Careful alignment of the substrate made the supertips converge to form a nanoscale gap. We demonstrate customization of the shape and size of the tweezer arms, using a simple scheme that allows conveniently fine-tuning of the tip features and the gap to within 5 nm. The supertips can be metallized subsequently, to be made conducting, without significantly affecting the shape of the tweezers. By applying a voltage on the outer electrodes with respect to the inner two electrodes, the gap can be opened and closed. This enables the device to grab and manipulate small particles, with the option of direct electrical measurement on the particle. The advantage of our approach is that no voltage difference is applied between the tweezer arms, making the device ideal for application with such fragile structures as organic objects.

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A novel approach for extracting genuine surface conductivities is presented and illustrated using the unresolved example of Si(111)-(7 x 7). Its temperature-dependent conductivity was measured with a microscopic four point probe between room temperature and 100 K. At room temperature the measured conductance corresponds to that expected from the bulk doping level. However, as the temperatures is lowered below approximately 200 K, the conductance decreases by several orders of magnitude in a small temperature range and it saturates at a low temperature value of approximately 4 x 10(-8) Omega(-1), irrespective of bulk doping. This abrupt transition is interpreted as the switching from bulk to surface conduction, an interpretation which is supported by a numerical model for the measured four point probe conductance. The value of the surface conductance is considerably lower than that of a good metal.