Shuichi Sakata

Gate-Tunable Large Negative Tunnel Magnetoresistance in Ni–C60–Ni Single Molecule Transistors

We have fabricated single C(60) molecule transistors with ferromagnetic Ni leads (FM-SMTs) by using an electrical break junction method and investigated their magnetotransport. The FM-SMTs exhibited clear gate-dependent hysteretic tunnel magnetoresistance (TMR) and the TMR values reached as high as -80%. The polarity of the TMR was found to be always negative over the entire bias range studied here. Density functional theory calculations show that hybridization between the Ni substrate states and the C(60) molecular orbitals generates an antiferromagnetic configuration in the local density of states near the Fermi level, which gives a reasonable explanation for the observed negative TMR.

Proof of Ge-interfacing Concepts for Metal/High-k/Ge CMOS - Ge-intimate Material Selection and Interface Conscious Process Flow

GeO2/Ge and high-k(LaYO3)/Ge interfaces have been significantly improved by suppressing GeO desorption and treating Ge surface with radical nitrogen. With the Ge- intimate material selection and interface conscious process flow, we have achieved that the peak hole mobility of PtGe source/drain p-MOSFET is about 370 cm2/Vsec in FUSI/GeO2/Ge. Furthermore, metal/n-Ge ohmic characteristic has been achieved by inserting ultra-thin GeOx layer between metal and Ge, which enables us to operate metal source/drain Ge n-MOSFETs for the first time.

Highly enantioselective synthesis of β-hydroxy nitriles by the cyanomethylation of aldehydes using DPMPM as a chiral catalysts or ligand

Abstract Optically active β-hydroxy nitriles in up to 93% e.e. were obtained by the enantioselective addition of cyanomethylzinc bromide to aldehydes using DPMPM as a chiral catalyst or ligand.

Low Temperature Phosphorus Activation in Germanium through Nickel Germanidation for Shallow n+/p Junction

To realize scaled germanium (Ge) complementary metal oxide semiconductor (CMOS), ultra shallow junctions, where impurities are sufficiently activated, are strongly required. However, it is not easy for n-type impurities to achieve both high activation and low diffusion in Ge, as long as we adopt a conventional thermal annealing process. In this paper, both activation and segregation of phosphorus at a nickel mono-germanide/Ge interface through a germanidation process at 300 °C are demonstrated. This low temperature activation in Ge-CMOS fabrication is suitable for the self-aligned gate first process without degrading the dielectrics/Ge interface of Ge gate stacks.

Structural Stability of Ni Quantum Point Contacts under Electrical Stresses

We have investigated the structural stability of Ni quantum point contacts (QPCs) under electrical stresses by monitoring the junction conductance as a function of applied voltage. The histogram of the critical junction voltage, VC, at which there occurs one-by-one atom removal due to electromigration is found to have a peak at approximately 0.3 V, which is consistent with the surface diffusion potential of Ni. We have also shown that Ni QPCs are stable and can support extremely high current densities of over 1010 A/cm2, as long as the junction voltage is below the lower edge of the VC-histogram.

Importance of Moisture Control in Formation of Nanogap Electrodes by Electrical Break Junction Method

We have systematically investigated the fabrication of nanogap electrodes of Ni by the electrical break junction (EBJ) method under various environmental conditions. When EBJ was performed in the atmosphere, the anode side of the Ni electrodes was seriously damaged. The damaged region was analyzed by Auger electron spectroscopy and was identified to be Ni oxides formed during EBJ process by anodic oxidation via atmospherically-derived moisture adsorbed on the metal surfaces. When the EBJ process was performed in an evacuated environment, nanogap electrodes with atomic-order spacing were reproducibly fabricated even at room temperature.

Electron transport in endohedral metallofullerene Ce@C82 single-molecule transistors

We have investigated the electron transport in endohedral metallofullerene Ce@C82 single-molecule transistors (SMTs) together with that in reference C84 SMTs. The vibrational modes (bending and stretching) of the encapsulated single Ce atom in the C82 cage appear in Coulomb stability diagrams for the single-electron tunneling through Ce@C82 molecules, demonstrating the single-atom sensitivity of the transport measurements. When a bias voltage larger than 100 mV is applied across the source/drain electrodes, large hysteretic behavior is observed in the current-voltage (I-V) characteristics. At the same time, the pattern in the Coulomb stability diagram is changed. No such hysteretic behavior is observed in the I-V curves of hollow-cage C84 SMTs, even when the bias voltage exceeds 500 mV. This hysteretic change in the I-V characteristics is induced by a nanomechanical change in the configuration of the Ce@C82 molecule in the nanogap electrode due to the electric dipole that exists in Ce@C82.

Critical Voltage for Atom Migration in Ballistic Copper Nanojunctions and Its Implications to Interconnect Technology for Very Large Scale Integrated Circuits

We investigated the critical voltage for electromigration (EM) in atomic-scale Cu nanojunctions by using EM spectroscopy. The critical voltage was determined to be 0.35 V from the peak of the obtained EM spectrum, which is close to the atom diffusion potential for clean Cu surfaces. It was also demonstrated that ballistic Cu nanojunctions can support current densities on the order of 10 GA/cm2, as long as the junctions are biased below the critical voltage. The results suggest that both high current densities and high EM reliabilities can be achieved when the dimension of the metal interconnects is reduced to several tens of atoms.

Elementary process of electromigration at metal nanojunctions in the ballistic regime

We have investigated electromigration process at metal nanojunctions as small as several tens of atoms and found that the elementary process of electromigration in such nanojunctions is the self-diffusion of metal atoms driven by microscopic kinetic energy transfer from single conduction electrons to single metal atoms. We have also shown that metal nanojunctions are stable and can support extremely high current densities of over 1010 A/cm2, as long as the junction voltage is below the critical value.