We describe the operation of, and demonstrate logic functionality in, networks of physically coupled, nanometer-scale magnets designed for digital computation in magnetic quantum-dot cellular automata (MQCA) systems. MQCA offer low power dissipation and high integration density of functional elements and operate at room temperature. The basic MQCA logic gate, that is, the three-input majority logic gate, is demonstrated.
Tukey methods [G. M. Jenkins and D. G. Watts, Spectral Analysis and its Applications (Holden-Day, Oakland, CA, 1968)] to the ␦ 18 O anomalies resolves statistically significant (minimum of 80% level) spectral peaks at 12.2-, 8.3-, 5.5-, 3.78-, 2.3-, and 1.7-year periods. The maximum entropy method places these peaks at 11.4, 7.8, 5.5, and 3.5, 2.3, and 1.7 years. 13. We used singular spectrum analysis (SSA) [R. Vautard and M. Ghil, Physica D 35, 395 (1989)] to reconstruct the most energetic modes in the coral record. After the removal of the seasonal cycle and the longterm trend, with a window length of M ϭ 39 years, SSA produces two modes in clean quadrature: modes 1 and 2, with a period of 11.8 years, and modes 3 and 4, with a period of 5.3 years (modes with periods greater than 39 years are unresolved). After the further removal of the decadal and interdecadal modes and with a window length of M ϭ 25 years, two modes emerge in quadrature: modes 1 and 2, with a period of 5.3 years, and modes 3 and 4, with a period of 3.5 years. The quasi-biennial signal emerges in clean quadrature when a 10-year window length is used. Monte Carlo simulations suggest that all of these modes represent statistically significant (at the 95% confidence level) concentrations of variance. More conventional band-pass filtering yields nearly identical patterns.
A functioning logic gate based on quantum-dot cellular automata is presented, where digital data are encoded in the positions of only two electrons. The logic gate consists of a cell, composed of four dots connected in a ring by tunnel junctions, and two single-dot electrometers. The device is operated by applying inputs to the gates of the cell. The logic AND and OR operations are verified using the electrometer outputs. Theoretical simulations of the logic gate output characteristics are in excellent agreement with experiment.
The amine functionality of the linker on the dinuclear complex [trans-Ru(dppm)(2)(Ctbd1;CFc)(NCCH(2)CH(2)NH(2))][PF(6)] reacts with Si-Cl bonds of a chlorinated, highly B doped Si (111) surface to yield Si-N surface-complex bonds. The surface bound complex is constrained to a near vertical orientation by the chain length of the linker as confirmed by variable angle XPS. Oxidation of the dinuclear complex with ferrocenium ion or electrochemically generates a stable, biased Fe(III)-Ru(II) mixed-valence complex on the surface. Characterization of the array of surface bound complexes with spectroscopic as well as electrochemical techniques confirms the presence of strongly bound, chemically robust, mixed-valence complexes. Capping the flat array of complexes with a minimally perturbing mercury electrode permits the equalization of the Fe and Ru energy wells by an applied electric field. The differential capacitance of oxidized and unoxidized bound complexes is compared as a function of voltage applied between the Hg gate and the Si. The results show that electron exchange between the Fe and Ru sites of the array of dinuclear mixed-valence complexes at energy equalization generates a fluctuating dipole that produces a maximum in the capacitance versus voltage curve for each complex-counterion combination present. Passage through the capacitance maximum corresponds to switching of the molecular quantum cellular automata (QCA) cell array by the electric field from the Fe(III)-Ru(II) configuration to the Fe(II)-Ru(III) configuration, thereby confirming that molecules possess an essential property necessary for their use as elements of a QCA device.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.