Quantum phase transition and Coulomb blockade effect in triangular quantum dots with interdot capacitive and tunnel couplings

The quantum phase transition and the electronic transport in a triangular quantum dot system are investigated using the numerical renormalization group method.We concentrate on the interplay between the interdot capacitive coupling V and the interdot tunnel coupling t.For small t,three dots form a local spin doublet.As t increases,due to the competition between V and t,there exist two first-order transitions with phase sequence spin-doublet-magnetic frustration phase-orbital spin singlet.When t is absent,the evolutions of the total charge on the dots and the linear conductance are of the typical Coulomb-blockade features with increasing gate voltage.While for sufficient t,the antiferromagnetic spin correlation between dots is enhanced,and the conductance is strongly suppressed for the bonding state is almost doubly occupied.

COULOMB BLOCKADE EFFECT IN SELF-ASSEMBLED GOLD QUANTUM DOTS

Nanometer-scale Au quantum dots have been assembled on SiO2 by controlling the reaction of raw materials to form a citrate Au sol and an aminosilane/dithiol-treated patterned Si wafer. The detailed formation mechanism has been studied. Three gold colloidal particles (15 nm), aligned in a chain to form a one-dimensional current path, was bridged across an 80-nm gap between source and drain metal electrodes. The device exhibited a Coulomb blockade effect at 33 K.

Effect of Nano Silver Modification on the Dielectric Properties of Ag@TiO_(2)/PVDF Composites

To get a dielectric material with a high dielectric permittivity and suppressed dielectric loss,nano-Ag with a particle size of 20 nm and Ag@TiO_(2)core-shell particles with diameters of approximately 70-120 nm were embedded in polyvinylidene fluoride(PVDF)to fabricate nano-Ag/Ag@TiO_(2)/PVDF composites.After being modified by nano-Ag with 3 vol%optimal amount,the relative permittivity(ε_r)at 100 Hz of 50 vol%Ag@TiO_(2)/PVDF composites was 61,and the dielectric loss can be suppressed to 0.04,almost 96.4%lower than that of unmodified composites,and a higher frequency stability of bothε_r and loss has also been found.The underlying mechanism of the reduced loss was attributed to Maxwell-Wagner polarization and the Coulomb blockade effect caused by the introduction of a small amount of nano-Ag,which will block the movement of electrons between metal nanoparticles and composites.The space charge polarization and conductance loss are weakened at lower and higher Ag@TiO_(2)filling ratios,respectively,thus leading to a very low loss of the composites.

Preparation of size controllable copper nanocrystals for nonvolatile memory applications

A method of fabricating Cu nanocrystals embedded in SiO2 dielectric film for nonvolatile memory applications by magnetron sputtering is introduced in this paper. The average size and distribution density of Cu nanocrystal grains are controlled by adjusting experimental parameters. The relationship between nanocrystal floating gate micro-structure and its charge storage capability is also discussed theoretically.

Theoretical investigation on tunneling magnetoresistance in ferromagnetic/anti-ferromagnetic core/shell system

Based on Monte Carlo simulations,the effect of structural configuration on the hysteresis behavior and tunneling magnetoresistance(TMR) of composite nanoparticles with ferromagnetic(FM) core/anti-ferromagnetic(AFM) shell is investigated.The simulated results indicate that the coercive field(H c) of composites increases with the decreasing ratio of core-radius(r core) to shell-radius(r shell).When the ratio of r shell to r core is approaching 4:3,H c decreases with increasing AFM thickness.In addition,TMR is found to increase with the decreasing ratio of r core to r shell,resulting from the enhancement of resistance changes in disordered AFM shell.