Growth of ZnO nanostructures on Si by means of plasma immersion ion implantation and deposition

Crystalline zinc oxide (ZnO) nanostructures have been grown on Si substrates by means of Plasma Based Ion Implantation and Deposition (PIII&D) at temperature of about 300 0C and in the presence of an argon glow discharge. In the process a crucible filled with small pieces of metallic zinc plays the role of the anode of the discharge itself, being polarized by positive DC voltage of about 400V. Electrons produced by thermionic emission by an oxide cathode (Ba, Sr, Ca)O impact this crucible, causing its heating and vaporization of Zn. Partial ionization of Zn atoms takes place due to collisions with plasma particles. High negative voltage pulses (7 kv/40μs/250Hz) applied to the sample holder cause the implantation of metallic zinc into Si surface, while Zn deposition happens between pulses. After annealing at 700 0C, strong UV and various visible photoluminescence bands are observed at room temperature, as well as the presence of ZnO nanoparticles. The coated surface was characterized in detail using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and photoluminescence (PL) spectroscopy. XRD indicated the presence of only ZnO peaks after annealing. The composition analysis by EDS revealed distinct Zn/O stoichiometry relation depending on the conditions of the process. AFM images showed the formation of columns in the nanoscale range. Topography viewed by SEM showed the formation of structures similar to cactus with nanothorns. Depth analysis performed by XPS indicated an increase of concentration of metallic Zn with increasing depth and the exclusive presence of ZnO for outer regions. PIII&D allowed to growing nanostructures of ZnO on Si without the need of a buffer layer

Hermitian conjugate measurement

We propose a new class of probabilistic reversing operations on the state of a system that was disturbed by a weak measurement. It can approximately recover the original state from the disturbed state especially with an additional information gain using the Hermitian conjugate of the measurement operator. We illustrate the general scheme by considering a quantum measurement consisting of spin systems with an experimentally feasible interaction and show that the reversing operation simultaneously increases both the fidelity to the original state and the information gain with such a high probability of success that their average values increase simultaneously.Comment: 26 pages, 4 figures; a paragraph is added in the introductio

Weakly coupled s=1/2s = 1/2 quantum spin singlets in Ba3_{3}Cr2_{2}O8_{8}

Using single crystal inelastic neutron scattering with and without application of an external magnetic field and powder neutron diffraction, we have characterized magnetic interactions in Ba$_3$Cr$_2$O$_8$. Even without field, we found that there exist three singlet-to-triplet excitation modes in $(h,h,l)$ scattering plane. Our complete analysis shows that the three modes are due to spatially anisotropic interdimer interactions that are induced by local distortions of the tetrahedron of oxygens surrounding the Jahn-Teller active Cr$^{5+} (3d^1)$. The strong intradimer coupling of $J_0 = 2.38(2)$ meV and weak interdimer interactions ($|J_{\rm inter}| \leq 0.52(2)$ meV) makes Ba$_3$Cr$_2$O$_8$ a good model system for weakly-coupled $s = 1/2$ quantum spin dimers

Evaluation of Effective Astrophysical S factor for Non-Resonant Reactions

We derived analytic formulas of the effective S astrophysical S factor,S^eff for a non-resonant reaction of charged particles using a Taylor expension of the astrophysical S factor and a uniform approximation.The formulas will be able to generate generate more accurate approximation to S^eff than previous ones

Orbital and spin chains in ZnV2O4

Our powder inelastic neutron scattering data indicate that \zvo is a system of spin chains that are three dimensionally tangled in the cubic phase above 50 K due to randomly occupied $t_{2g}$ orbitals of V$^{3+}$ ($3d^2$) ions. Below 50 K in the tetragonal phase, the chains become straight due to antiferro-orbital ordering. This is evidenced by the characteristic wave vector dependence of the magnetic structure factor that changes from symmetric to asymmetric at the cubic-to-tetragonal transition

Addendum: Attenuation of the intensity within a superdeformed band

We investigate a random matrix model [Phys. Rev. C {\bf 65} 024302 (2002] for the decay-out of a superdeformed band as a function of the parameters: $\Gamma^\downarrow/\Gamma_S$, $\Gamma_N/D$, $\Gamma_S/D$ and $\Delta/D$. Here $\Gamma^\downarrow$ is the spreading width for the mixing of an SD state $|0>$ with a normally deformed (ND) doorway state $|d>$, $\Gamma_S$ and $\Gamma_N$ are the electromagnetic widths of the the SD and ND states respectively, $D$ is the mean level spacing of the compound ND states and $\Delta$ is the energy difference between $|0>$ and $|d>$. The maximum possible effect of an order-chaos transition is inferred from analytical and numerical calculations of the decay intensity in the limiting cases for which the ND states obey Poisson and GOE statistics. Our results show that the sharp attenuation of the decay intensity cannot be explained solely by an order-chaos transition.Comment: 4 pages, 4 figures, submitted to Physical Review

Energy averages over regular and chaotic states in the decay out of superdeformed bands

We describe the decay out of a superdeformed band using the methods of reaction theory. Assuming that decay-out occurs due to equal coupling (on average) to a sea of equivalent chaotic normally deformed (ND) states, we calculate the average intraband decay intensity and show that it can be written as an ``optical'' background term plus a fluctuation term, in total analogy with average nuclear cross sections. We also calculate the variance in closed form. We investigate how these objects are modified when the decay to the ND states occurs via an ND doorway and the ND states' statistical properties are changed from chaotic to regular. We show that the average decay intensity depends on two dimensionless variables in the first case while in the second case, four variables enter the picture.Comment: 8 pages, 1 figure, presented at FUSION03, Matsushima, Miyagi, Japan, Nov 12-15, 2003, to appear in Progress of Theoretical Physics; corrected typo