Spintronics: Fundamentals and applications

Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes from the published versio

Fiber-shaped electronic devices

Textile electronics embedded in clothing represent an exciting new frontier for modern healthcare and communication systems. Fundamental to the development of these textile electronics is the development of the fibers forming the cloths into electronic devices. An electronic fiber must undergo diverse scrutiny for its selection for a multifunctional textile, viz., from the material selection to the device architecture, from the wearability to mechanical stresses, and from the environmental compatibility to the end-use management. Herein, the performance requirements of fiber-shaped electronics are reviewed considering the characteristics of single electronic fibers and their assemblies in smart clothing. Broadly, this article includes i) processing strategies of electronic fibers with required properties from precursor to material, ii) the state-of-art of current fiber-shaped electronics emphasizing light-emitting devices, solar cells, sensors, nanogenerators, supercapacitors storage, and chromatic devices, iii) mechanisms involved in the operation of the above devices, iv) limitations of the current materials and device manufacturing techniques to achieve the target performance, and v) the knowledge gap that must be minimized prior to their deployment. Lessons learned from this review with regard to the challenges and prospects for developing fiber-shaped electronic components are presented as directions for future research on wearable electronics

Studies of a xenon chloride laser

A compact, transverse discharge XeCl laser has been constructed. The laser employs an LC double inversion circuit, and is operated, at an optimum gas mix containing 1.12% Xe, 0.56% HCl, and 98.32% He, at a maximum filling pressure of 80 Psi. The electrical efficiency of the laser is typically 0.3%, with an output energy of ≈ 95 mj and an output laser pulse FWHM of 13.5 nsec, resulting in an output power of ≈ 7 MW. The discharge current reaches a peak value of 7.75 KA, with a rise time of 24 nsec, whereas the voltage reaches a maximum value of 29.1 KV, with a rise time of 111 nsec. By using a CO₂ Mach-Zehnder interferometer, the electron density was measured for the optimum mix (4.01±x10¹⁵cm⁻³). Several studies at different Xe : HCl ratios showed that the dissociative attachment of HCl molecules is responsible for the electron loss during the discharge. The electron temperature was calculated using the measured values of discharge resistance and the drift velocity. The results show that electrons cool by inelastic collisions with HCl molecules.Science, Faculty ofPhysics and Astronomy, Department ofGraduat

Ultrafast switching of CO₂ laser pulses by optically-induced plasma reflection in semiconductors

Ultrafast mid-infrared laser pulse generation using optical semiconductor switching is investigated experimentally for application to subpicosecond CO₂ laser pulse generation at 10.6 μm. Time-resolved infrared measurements, which are based on cross-correlation and reflection-reflection correlation techniques, are used to determine the duration of the reflected infrared pulses from a GaAs infrared reflection switch. These time-resolved measurements together with time-integrated measurements are used to derive a model describing the behaviour of the GaAs infrared reflection switch. it is found that diffusion and two-body recombination whose rate is taken to be density-dependent, can accurately describe the ultrafast infrared reflectivity switching process in GaAs. We have also in vestigated some novel semiconductor materials with ultrafast recombination lifetimes for ultrafast semiconductor switching application. A molecular beam epitaxy low tempera ture grown GaAs (LT-GaAs) and radiation damaged GaAs (RD-GaAs) are successfully used to switch out ultrashort CO₂ laser pulses. Application of the time-resolved crosscorrelation technique to nonequilibrium carrier lifetime measurements in highly excited LT-GaAs, RD-GaAs, and In₀.₈₅Ga₀.₁₅As/GaAs relaxed superlattice structure are found to be in good agreement with other reported techniques. As an application to semicon ductor probing, ultrafast infrared transmission experiments are conducted to determine the absorption of infrared pulses in Si of various dopings after free carriers have been generated by absorption of a subpicosecond laser pulse of above band gap photon en ergy. By fitting the experimental data to a theoretical model, the free-carrier absorption cross-sections and the momentum relaxation times are calculated.Science, Faculty ofPhysics and Astronomy, Department ofGraduat

Fluorescence and brightfield image of a post-laser manipulated embryo at 8-cell stage

(a, b) Embryo was porated for exogenous delivery using an average laser power of 45 mW with a beam dwell time set to 20 ms and a galvo pulse rate of three. Three pores were made in each of 2 blastomere cells, yielding a total of six pores for the entire embryo. Scale bars for (a, b) represent 200 μm.<p><b>Copyright information:</b></p><p>Taken from "Laser surgery of zebrafish () embryos using femtosecond laser pulses: Optimal parameters for exogenous material delivery, and the laser's effect on short- and long-term development"</p><p>http://www.biomedcentral.com/1472-6750/8/7</p><p>BMC Biotechnology 2008;8():7-7.</p><p>Published online 29 Jan 2008</p><p>PMCID:PMC2270268.</p><p></p

Magnified top and lateral SEM images of key developmental features in larvae reared to 7 dpf

(a, b, c) Depict the olfactory pit, ear, posterior forebrain and dorsal midbrain in laser-manipulated larvae. (d, e, f) Depict the olfactory pit, ear, posterior forebrain and dorsal midbrain in control larvae. (g, h) Illustrated comparison of dorso-lateral views of the posterior forebrain and dorsal midbrain in (g) a laser-manipulated and (h) a control larva at 7 dpf. Location of the eye (E), diencephalon (D) and optic tectum (OT) are shown respectively. Scale bars for (a, d) represent 20 μm and for (b, c, e, f, g, h) 50 μm. Orientation: anterior (left); posterior (right).<p><b>Copyright information:</b></p><p>Taken from "Laser surgery of zebrafish () embryos using femtosecond laser pulses: Optimal parameters for exogenous material delivery, and the laser's effect on short- and long-term development"</p><p>http://www.biomedcentral.com/1472-6750/8/7</p><p>BMC Biotechnology 2008;8():7-7.</p><p>Published online 29 Jan 2008</p><p>PMCID:PMC2270268.</p><p></p