We report that the Kondo effect exerted by a magnetic ion depends on its chemical environment. A cobalt phthalocyanine molecule adsorbed on an Au111 surface exhibited no Kondo effect. Cutting away eight hydrogen atoms from the molecule with voltage pulses from a scanning tunneling microscope tip allowed the four orbitals of this molecule to chemically bond to the gold substrate. The localized spin was recovered in this artificial molecular structure, and a clear Kondo resonance was observed near the Fermi surface. We attribute the high Kondo temperature (more than 200 kelvin) to the small on-site Coulomb repulsion and the large half-width of the hybridized d-level.

We demonstrate in this joint experimental and theoretical study how one can alter electron transport behavior of a single melamine molecule adsorbed on a Cu (100) surface by performing a sequence of elegantly devised and well-controlled single molecular chemical processes. It is found that with a dehydrogenation reaction, the melamine molecule becomes firmly bonded onto the Cu surface and acts as a normal conductor controlled by elastic electron tunneling. A current-induced hydrogen tautomerization process results in an asymmetric melamine tautomer, which in turn leads to a significant rectifying effect. Furthermore, by switching on inelastic multielectron scattering processes, mechanical oscillations of an N-H bond between two configurations of the asymmetric tautomer can be triggered with tuneable frequency. Collectively, this designed molecule exhibits rectifying and switching functions simultaneously over a wide range of external voltage.hydrogen tautomerization ͉ melamine molecules ͉ rectifying effect ͉ switching property E lectron transport is a fundamental process that controls physical properties and chemical activities of molecular and biological systems. Over the years, different electron transport behaviors of a variety of molecules have been observed, and much effort has been made to elucidate the underlying mechanisms (1-12). Despite of these recent advances, it remains a great challenge to actively control the electron transport in a molecule and to systematically change its behavior from one type to another since this requires not only precise control of molecular structure, but also accurate activation of different electron tunneling processes. Controlling electron transport at the molecular level has important consequences for many applications, such as molecular electronics (13-26), biosensors (27), and solar cells (28,29). For certain molecules, change of electron transport properties could take place due to their specific response to the change of molecular conformation or orientation (19-25), chemical reactions (26), and tautomerization (18). The latter experiment (18) has attracted considerable attention owning to the facts that the switching process involved does not result in drastic molecular conformation changes as often occurring in mechanical molecular switches induced by cis-trans isomerization of azobenzene (23-25), making the process potentially more relevant to applications in memory devices.Although many studies have been conducted over the years, only a limited number of special molecules can be chosen for such experiments. In this joint experimental and theoretical study, we demonstrate the possibility of changing the electron transport behavior of an ordinary molecule, melamine, with the help of surface chemistry and scanning tunneling microscope (STM) in a controllable manner. It is shown that the involvement of a dehydrogenation process can make the molecule standing on a Cu (100) surface and behaving like a conducting molecule. By applying a high-voltage pulse, the energeti...

This paper describes a simple solution route to ZnS nanotubes assisted by CNTs and to ZnS hollow nanospheres by templating with in situ generated bubbles at low temperature. Two types of nanotube exist. One has two open ends with a very thin wall; the other has a sealed end with a thicker wall. The hollow nanospheres have uniform thickness of  nm and they formed dynamically controlled by the quantity of water. HREM results reveal that the nanotubes and hollow nanospheres are both composed of ZnS nanoparticles. The UV–vis absorption spectra exhibit large blue shifts because of quantum size effects. These hollow structures may have potential applications in some areas.

Magnetic ordering and Kondo behavior coexist in three (Ce,Al)-based compounds: CeAl2, Ce3Al, and Ce3Al11. A common feature apparently independent of crystal structures also prevails in terms of the size-induced transition between these two magnetic phenomena. As the particle size is reduced to nanoscale, the specific heat anomaly associated with the magnetic ordering diminishes. Although the Kondo temperature also decreases, the entropy associated with Kondo anomaly exhibits a large increase. This results in an enhancement of the Kondo behavior and an increased coefficient gamma of the linear term in specific heat. For example, in 80 A CeAl2 the extrapolated r(0) reaches 9000 mJ mol Ce-1 K-2.

Atomic manipulation has been rarely used in the studies of complex structures and a low temperature requirement usually limits its application. Herein we have demonstrated a vertical manipulation technique to reproducibly and reversibly manipulating Ag atoms on an Si(111)-(7×7) surface by a scanning tunneling microscope tip at room temperature. Simple and complex Ag nanoclusters were assembled and disassembled with a precise control of single Ag atoms, which provided critical information on the size of these nanoclusters. The manipulation showed the growth processes of these Ag clusters and even partly unveiled their atomic structures. This technique can form a fundamental basis for further studies of the Ag/Si(111)-(7×7) system and for fabricating functional nanodevices in various metal-semiconductor systems.

Since molecular electronics has been rapidly growing as a promising alternative to conventional electronics towards the ultimate miniaturization of electronic devices through the bottom-up strategy, it has become a long-term desire to understand and control the transport properties at the level of single molecules. In this Research News article it is shown that one may modify the electronic states of single molecules and thus control their transport properties through designing and fabrication of functional molecules or manipulating molecules with scanning tunneling microscopy. The rectifying effect of single molecules can be realized by designing a donor-barrier-acceptor architecture of Pyridine-sigma-C(60) molecules to achieve the Aviram-Ratner rectifier and by modifying electronic states through azafullerene C(59)N molecules. The effect of the negative differential resistances can be realized by appropriately matching the molecular orbital symmetries between a cobalt phthalocyanine (CoPc) molecule and a Ni electrode. The electronic states and transport properties of single molecules, such as CoPc and melamine molecules, can be altered through manipulation or modifying molecular structures, leading to functionalized molecular devices.

Using scanning tunneling spectroscopy, we have studied the interface effect on quantum well states of Pb thin films grown on various metal-terminated (Pb, Ag, and Au) n-type Si(111) surfaces and on two different p-type Si(111) surfaces. The dispersion relation E(k) of the electrons of the Pb film and the phase shift at the substrate interface were determined by applying the quantization rule to the measured energy positions of the quantum well states. Characteristic features in the phase shift versus energy curves were identified and were correlated to the directional conduction band of the silicon substrate and to the Schottky barrier formed between the metal film and the semiconductor. A model involving the band structure of the substrate, the Schottky barrier, and the effective thickness of the interface was introduced to qualitatively but comprehensively explain all the observed features of the phase shift at the substrate interface. Our physical understanding of the phase shift is critically important for using interface modification to control the quantum well states.

Silicon nitride (Si 3 N 4 ) nanowires and nanobelts have been successfully prepared via direct crystallization of amorphous Si 3 N 4 nanoparticles under high temperature in a N 2 flow. The products were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution electron microscopy, and electron diffraction. They are pure a-phase hexagonal single-crystal structures. The nanowires are long and smooth; nanobelts are long and twisted. In our samples, there exist some special nanostructures, such as wire-inserted hexagonal nanosheet and hollow-chain-shaped structure. The different growth modes were understood upon the observations and characterization of those microstructures. The solid-liquid-solid growth mechanism is also discussed.J ournal