Raman Scattering Characterization of the Microscopic Structure of Semi-Insulating Polycrystalline Si Thin Films

Raman scattering experiments were carried out to study the microscopic structure of semi-insulating polycrystalline Si (SIPOS) thin films prepared by low-pressure chemical vapor deposition. The samples contain 18, 25, and 30 at. % of oxygen and after growth they were annealed at 900 and 1000°C for 30 min. The Raman spectra show in the vibrational region of the optical frequencies of Si two bands, which arise from scattering in crystalline grains and disordered forms of Si. The behavior of these bands as a function of oxygen content and annealing temperatures was established in detail. The crystallinelike band peaks below the transverse optical frequency of Si at zone center and is broadened with respect to the Raman line of a Si wafer. From the broadenings, estimates of grain sizes are obtained. The band due to the disordered form of Si appears at frequencies above those of an extended network of amorphous Si. A model for the SIPOS microscopic structure is proposed in which the disordered Si corresponds to the surface layers of the crystalline grains. The latter are embedded in an amorphous SiO2 matrix. Quantitative estimates of the contributions of the ordered and disordered phases of Si to the SIPOS structure are attempted. The Raman results provide additional experimental evidence that the crystallization temperature of Si increases under the presence of oxygen

Strains in Si-onSiO\u3csub\u3e2\u3c/sub\u3e Structures Formed By Oxygen Implantation: Raman Scattering Characterization

Low-temperature Raman scattering measurements were carried out to characterize Si-on-SiO2 structures formed by oxygen implantation and subsequent furnace or lamp annealing. The experiments were conducted with 413.1 nm laser light to probe only the thin Si layers at the top of the structures. The Raman spectra of the furnace-annealed samples are red shifted and broadened when compared with a virgin Si surface. The shifts and broadenings decrease with increasing annealing temperatures but they are still present in samples annealed above 1250°C for 3 h. No shifts or broadenings affect the Raman peaks of the layers, which were lamp annealed at 1405°C for half an hour. The red shifts indicate that the recrystallized Si layers are under tensile strains, whose origin is attributed to oxide precipitates. Quantitative estimates of the strains and associated stresses are obtained from the measured Raman shifts

Discovery and Measurement of Sleptons, Binos, and Winos with a Z'

Extensions of the MSSM could significantly alter its phenomenology at the LHC. We study the case in which the MSSM is extended by an additional U(1) gauge symmetry, which is spontaneously broken at a few TeV. The production cross-section of sleptons is enhanced over that of the MSSM by the process $pp\to Z' \to \tilde{\ell} \tilde{\ell}^*$, so the discovery potential for sleptons is greatly increased. The flavor and charge information in the resulting decay, $\tilde{\ell} \to \ell + {LSP}$, provides a useful handle on the identity of the LSP. With the help of the additional kinematical constraint of an on-shell Z', we implement a novel method to measure all of the superpartner masses involved in this channel. For certain final states with two invisible particles, one can construct kinematic observables bounded above by parent particle masses. We demonstrate how output from one such observable, m_T2, can become input to a second, increasing the number of measurements one can make with a single decay chain. The method presented here represents a new class of observables which could have a much wider range of applicability.Comment: 20 pages, 15 figures; v2 references added and minor change

Predictors of outcome for severely emotionally disturbed children in treatment

Despite general agreement that severely emotionally disturbed children and adolescents are an "at risk" group, and that ongoing evaluation and research into the effectiveness of services provided for them is important, very little outcome evaluation actually takes place. The absence of well-conducted and appropriately interpreted studies is particularly notable for day or residential treatment programs, which cater for the most severely emotionally disturbed youths. This thesis outlines the main areas of conceptual, pragmatic and methodological confusion and neglect which impede progress in research in this area. It argues for plurality of data analytic strategies and research designs. It then critically reviews the reported findings about the effectiveness of day and residential treatment in specialist facilities, and the predictors of good outcomes for this treatment type. This review confirms that there is very little to guide practice. Having argued for the legitimacy of its methods and the necessity to address basic questions, the thesis reports the results of a naturalistic study based on data accumulated during a decade-long evaluative research program taking place at Arndell Child and Adolescent Unit, Sydney. The study addresses the question of what child, family and treatment variables predict outcome for 159 children and adolescents treated at this facility from 1990 to 1999. Statistically significant results with large effect size were obtained. Among the most disturbed subgroup of forty three children, (a) psychodynamic milieu-based treatment was shown to be more effective than the “empirically-validated” cognitive-behavioural treatment which superseded it in 1996, and (b) children from step-families showed better outcome than those from other family structures. Furthermore, it was found for the study sample as a whole that severe school-based problem behaviours were associated with a limited trajectory of improvement in home-based problem behaviour. These results are discussed with regard to implications for treatment, research methodology, policy and further studies

Decaying Hidden Dark Matter in Warped Compactification

The recent PAMELA and ATIC/Fermi/HESS experiments have observed an excess of electrons and positrons, but not anti-protons, in the high energy cosmic rays. To explain this result, we construct a decaying hidden dark matter model in string theory compactification that incorporates the following two ingredients, the hidden dark matter scenario in warped compactification and the phenomenological proposal of hidden light particles that decay to the Standard Model. In this model, on higher dimensional warped branes, various warped Kaluza-Klein particles and the zero-mode of gauge field play roles of the hidden dark matter or mediators to the Standard Model.Comment: 15 pages; v4, several clarifications added, update on Fermi/HESS result

Cosmological constraints from galaxy clustering

In this manuscript I review the mathematics and physics that underpins recent work using the clustering of galaxies to derive cosmological model constraints. I start by describing the basic concepts, and gradually move on to some of the complexities involved in analysing galaxy redshift surveys, focusing on the 2dF Galaxy Redshift Survey (2dFGRS) and the Sloan Digital Sky survey (SDSS). Difficulties within such an analysis, particularly dealing with redshift space distortions and galaxy bias are highlighted. I then describe current observations of the CMB fluctuation power spectrum, and consider the importance of measurements of the clustering of galaxies in light of recent experiments. Finally, I provide an example joint analysis of the latest CMB and large-scale structure data, leading to a set of parameter constraints.Comment: 30 pages, 13 figures. Lecture given at Third Aegean Summer School, The invisible universe: Dark matter and Dark energ

Physics Opportunities with the 12 GeV Upgrade at Jefferson Lab

This white paper summarizes the scientific opportunities for utilization of the upgraded 12 GeV Continuous Electron Beam Accelerator Facility (CEBAF) and associated experimental equipment at Jefferson Lab. It is based on the 52 proposals recommended for approval by the Jefferson Lab Program Advisory Committee.The upgraded facility will enable a new experimental program with substantial discovery potential to address important topics in nuclear, hadronic, and electroweak physics.Comment: 64 page

Longitudinal double-spin asymmetry and cross section for inclusive neutral pion production at midrapidity in polarized proton collisions at sqrt(s) = 200 GeV

We report a measurement of the longitudinal double-spin asymmetry A_LL and the differential cross section for inclusive Pi0 production at midrapidity in polarized proton collisions at sqrt(s) = 200 GeV. The cross section was measured over a transverse momentum range of 1 < p_T < 17 GeV/c and found to be in good agreement with a next-to-leading order perturbative QCD calculation. The longitudinal double-spin asymmetry was measured in the range of 3.7 < p_T < 11 GeV/c and excludes a maximal positive gluon polarization in the proton. The mean transverse momentum fraction of Pi0's in their parent jets was found to be around 0.7 for electromagnetically triggered events.Comment: 6 pages, 3 figures, submitted to Phys. Rev. D (RC

Partonic flow and ϕ\phi-meson production in Au+Au collisions at sNN\sqrt{s_{NN}} = 200 GeV

We present first measurements of the $\phi$-meson elliptic flow ($v_{2}(p_{T})$) and high statistics $p_{T}$ distributions for different centralities from $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions at RHIC. In minimum bias collisions the $v_{2}$ of the $\phi$ meson is consistent with the trend observed for mesons. The ratio of the yields of the $\Omega$ to those of the $\phi$ as a function of transverse momentum is consistent with a model based on the recombination of thermal $s$ quarks up to $p_{T}\sim 4$ GeV/$c$, but disagrees at higher momenta. The nuclear modification factor ($R_{CP}$) of $\phi$ follows the trend observed in the $K^{0}_{S}$ mesons rather than in $\Lambda$ baryons, supporting baryon-meson scaling. Since $\phi$-mesons are made via coalescence of seemingly thermalized $s$ quarks in central Au+Au collisions, the observations imply hot and dense matter with partonic collectivity has been formed at RHIC.Comment: 6 pages, 4 figures, submit to PR

Measurement of Transverse Single-Spin Asymmetries for Di-Jet Production in Proton-Proton Collisions at s=200\sqrt{s} = 200 GeV

We report the first measurement of the opening angle distribution between pairs of jets produced in high-energy collisions of transversely polarized protons. The measurement probes (Sivers) correlations between the transverse spin orientation of a proton and the transverse momentum directions of its partons. With both beams polarized, the wide pseudorapidity ($-1 \leq \eta \leq +2$) coverage for jets permits separation of Sivers functions for the valence and sea regions. The resulting asymmetries are all consistent with zero and considerably smaller than Sivers effects observed in semi-inclusive deep inelastic scattering (SIDIS). We discuss theoretical attempts to reconcile the new results with the sizable transverse spin effects seen in SIDIS and forward hadron production in pp collisions.Comment: 6 pages total, 1 Latex file, 3 PS files with figure