Damage formation in Ge during Ar and He implantation at 15 K

Ar⁺ and He⁺ ions were implanted into Ge samples with (1 0 0), (1 1 0), (1 1 1) and (1 1 2) orientations at 15 K with fluences ranging from 1×10¹¹ to 1×10¹⁴ cm⁻² for the Ar⁺ ions and fluences ranging from 1×10¹² to 6×10¹⁵ cm⁻² for the He⁺ ions. The Rutherford backscattering (RBS) technique in the channelling orientation was used to study the damage built-up in situ. Implantation and RBS measurements were performed without changing the target temperature. The samples were mounted on a four axis goniometer cooled by a close cycle He cryostat. The implantations were performed with the surface being tilt 7° off the ion beam direction to prevent channelling effects. After each 300 keV Ar⁺ and 40 keV He⁺ implantation, RBS analysis was performed with 1.4 MeV He⁺ ions.For both the implantation ions, there is about no difference between the values found for the damage efficiency per ion for the four different orientations. This together with the high value (around 5 times higher than that found in Si), gives rise to the assumption of amorphous pocket formation per incident ion, i.e. direct impact amorphization, already at low implantation fluences. At higher fluences, when collision cascades overlap, there is a growth of the already amorphized regions.     

Geometrical symmetry of atoms with applications to semiclassical calculation of energetic values

In previous papers we proved that, for stationary systems, the geometric elements of the wave described by the Schrödinger equation, namely the characteristic surfaces and their normals, are periodic solutions of the Hamilton-Jacobi equation. In this paper we prove that the Hamilton-Jacobi equation admits periodic solutions with the same geometrical symmetries as the wave function of the system in the case of the beryllium, boron, carbon and oxygen atoms. The above property is a reflection of the fact that for a multielectron atomic system the energetically most favorable geometric configuration minimizes the electron electron repulsion, and it leads to a general semiclassical calculation method, which is in principle valid for more complex systems. We show that this property can be used to compute the energetic atomic values, with the help of the central field method which we developed in previous publications. The relative error of our method is of the order 3×10^-3, compared with experimental data for the atoms mentioned above. The accuracy of our method is revealed by a comparison between our theoretical data and values resulting from Hartree-Fock methods.     

Finite-time information consensus for multi-agent systems with fixed and switching topologies

In this paper, we study the consensus problems for a group of interacting agents. First, we analytically establish the explicit expression of the consensus state for the entire group. Second, we prove that the agents of the group under a particular type of nonlinear interaction can reach the consensus state in finite time in the scenarios with fixed and switching undirected topologies. The results are also extended to the case where the topology of the group is directed and satisfies a detailed balance condition on coupling weights. Third, some numerical examples are provided to analyze the influencing factors of the convergence time, that is, the parameter of the particular interaction function and the algebraic connectivity of graphs. Finally, an application of the theoretical results in sensor networks is given, namely, computing the maximum-likelihood estimate of unknown parameters.     

Information and maximum power in a feedback controlled Brownian ratchet

Closed-loop or feedback controlled ratchets are Brownian motors that operate using information about the state of the system. For these ratchets, we compute the power output and we investigate its relation with the information used in the feedback control. We get analytical expressions for one-particle and few-particle flashing ratchets, and we find that the maximum power output has an upper bound proportional to the information. In addition, we show that the increase of the power output that results from changing the optimal open-loop ratchet to a closed-loop ratchet also has an upper bound that is linear in the information.     

Controllability of multiple qubit systems

This paper explores the problem of manipulating multiple-qubit systems when only single-qubit operations or two-qubit-interactive operations are permitted. It is demonstrated that if there exist 2 directional control Hamiltonian for each individual qubit, and one interactive Hamiltonian for each pair of qubits, then multiple qubit systems are open-loop controllable. An important observation of physical interest is emphasized: when only single-qubit operations or two-qubit-interactive operations are permitted, only n(n+3)/2 control Hamilton may guarantee open-loop controllability of n qubit systems, and n(n+3) is, in the restricted sense, also the lower limit on the number of operators needed for controllability. At last, we demonstrate that an n-quantum-dot system is open-loop controllable even when only single-qubit operations or two-qubit-interactive operations are permitted.     

Molecular dynamics simulation of deposition and etching of Si bombarding by energetic SiF

In this study, SiF interaction with amorphous Si surface at normal incidence was investigated using molecular dynamics simulation at 300 and 600 K. The incident energies of 50, 100 and 200 eV were used. The results show that the deposition rate is not sensitive to the incident energy, while with increasing the surface temperature, the deposition rate decreases. The etch yield is sensitive to the incident energy and the surface temperature. The etch yield increases with increasing incident energy and temperature. After bombarding, a Si_xF_y interfacial layer is formed. The interfacial layer thickness increases with increasing incident energy mainly through enhanced penetration of the silicon lattice. In the interfacial layer, for SiF_x (x = 1-3) species, SiF is dominant and only little SiF₃ is present. At the outmost and innermost of the interfacial layer, SiF species is dominant. Most of SiF₃ species is concentrated above the initial surface.     

Nanodomain shock wave in near-field laser–material interaction

In this work, molecular dynamics simulation is conducted to explore the shock wave phenomena in a nanodomain in near-field laser–material interaction. A large system consisting of over 800,000 atoms is studied. The work focuses on the kinetic and physical properties of the disturbed gas compression driven by the high speed movement of the molten particulates ejected from the solid target in a nanodomain. The quick interaction between solid and gas atoms compresses the gas and forms a steep shock wave front, which moves at a supersonic speed. The fast compression of gas also induces a steep interface of density, temperature and pressure distribution, which is viewed as typical characteristics of nanoscale shock waves. Evolutions of shock wave front position, velocity and Mach number are also explored and show quick decay during wave propagation.     

Field-Free Molecular Orientation Generated from Cyclic Rotational States by Using Two Trains of Half-Cycle Pulses

We show that two trains of half-cycle pulses （HCPs） with different amplitudes irradiating alternately on polar molecules can achieve a remarkable enhancement of field-free orientation compared with the case of an equal amplitude HCPs train for the same pulse separation. optimal adjustment of the population distribution on This kind of orientation enhancements is mainly due to an every field-free angular momentum eigenstate, in which the populations on the undesired states of high angular momenta are effectively suppressed, and the populations on the desired states of low angular momenta are correspondingly promoted.     

Anti-synchronization of chaotic systems with uncertain parameters via adaptive control

In this Letter, an adaptive control scheme is developed to study the anti-synchronization behavior between two identical and different chaotic systems with unknown parameters. This adaptive anti-synchronization controller is designed based on Lyapunov stability theory and an analytic expression of the controller with its adaptive laws of parameters is shown. The adaptive anti-synchronization between two identical systems (Chen system) and different systems (Genesio and Lü systems) are taken as two illustrative examples to show the effectiveness of the proposed method. Theoretical analysis and numerical simulations are shown to verify the results.     

Cyclic State Orientation of Polar Molecules Produced by a Train of Half-Cycle Pulse Clusters of a Long Repetition Period

Using a variational method, we derive the optimal population distribution of angular momentum eigenstates for any given population range in a rotational wavepacket within the field-free cyclic state orientation framework. Correspondingly, we devise a train of half-cycle pulse clusters to purposively make the structure of the computed wavepacket approach the optimal population distribution, so that we can now utilize much more powerful means to realize an ideal orientation goal.