W.J.M. Naber

The Formation of Large-Area Conducting Graphene-Like Platelets

The treatment of a suspension of graphite oxide (GO) with sodium azide leads to a material that, after reduction, features amino groups at the top and bottom of the sheets. These groups react through microcontact printing with an isothiocyanate monolayer on a silicon oxide substrate to form covalent bonds that strongly attach to the particles on the surface. With ultrasonication it is possible to obtain exfoliation of the sheets that are not covalently bound to the surface leaving single-layer platelets attached to the substrate. The azido derivative can be also used to functionalize the graphene oxide with long alkylic chains through a click chemistry approach. This functionalization results in the exfoliation of this material in dimethylformamide. The novel materials were fully characterized by different techniques including IR spectroscopy, thermogravimetric analysis (TGA), scanning and transmission electron microscopy (SEM and TEM), X-Ray photoelectron spectroscopy (XPS), and solid state NMR spectroscopy. The material with amino groups, after the reduction step, is conductive with a resistivity only approximately seven times larger than that of unprocessed graphite. This implies that after reduction of the GO, the conjugated sp2 network is largely restored. We consider this to be an important step towards a chemical approach for forming conducting large-area platelet films of single-layer graphene.

Local doping of silicon using nanoimprint lithography and molecular monolayers.

Micrometer-scale monolayer patterns of a phosphorus-containing molecular precursor are fabricated on nearly intrinsic Si(100) using nanoimprint lithography. The patterned sample is protected by a SiO2capping layer applied by electron beam evaporation and subjected to rapid thermal annealing (RTA) to diffuse the phosphorus dopant atoms into the bulk silicon locally.

Surface-acoustic-wave-induced transport in a double quantum dot

We report on nonadiabatic transport through a double quantum dot under irradiation of surface acoustic waves generated on chip. At low excitation powers, absorption and emission of single and multiple phonons are observed. At higher power, sequential phonon assisted tunneling processes excite the double dot in a highly nonequilibrium state. The present system is attractive for studying electron-phonon interaction with piezoelectric coupling.

Low-temperature solution synthesis of chemically functional ferromagnetic FePtAu nanoparticles.

Magnetic nanoparticles are of great scientific and technological interest. The application of ferromagnetic nanoparticles for high-density data storage has great potential, but energy efficient synthesis of uniform, isolated, and patternable nanoparticles that remain ferromagnetic at room temperature is not trivial. Here, we present a low-temperature solution synthesis method for FePtAu nanoparticles that addresses all those issues and therefore can be regarded as an important step toward applications. We show that the onset of the chemically ordered face-centered tetragonal (L1(0)) phase is obtained for thermal annealing temperatures as low as 150 degrees C. Large uniaxial magnetic anisotropy (10(7) erg/cm(3)) and a high long-range order parameter have been obtained. Our low-temperature solution annealing leaves the organic ligands intact, so that the possibility for postanneal monolayer formation and chemically assisted patterning on a surface is maintained.

Interaction of a 2‐level system with 2D phonons

We report on the non‐adiabatic interaction between 2D acoustic phonons and an artificial 2‐level system in a GaAs/AlGaAs heterostructure. The 2‐level system is formed by two discrete energy levels inside a double quantum dot, and monochromatic surface acoustic waves (∼2 GHz) are generated by an on‐chip interdigital transducer (IDT). An IDT for better performance is proposed.