Spin interference in silicon one-dimensional rings

We present the first findings of the spin transistor effect caused by the Rashba gate-controlled ring embedded in the p-type self-assembled silicon quantum well that is prepared on the Si (100) surface. The coherence and phase sensitivity of the spin-dependent transport of holes are studied by varying the value of the external magnetic field and the gate voltage that are perpendicular to the plane of the double-slit ring. Firstly, the quantum scatterers connected to two one-dimensional leads and the quantum point contact inserted in the one of the arms of the double-slit ring are shown to define the amplitude and the phase of the Aharonov-Bohm and the Aharonov-Casher conductance oscillations. Secondly, the amplitude and phase sensitivity of the 0.7 feature of the hole quantum conductance staircase revealed by the quantum point contact inserted are found to result from the interplay of the spontaneous spin polarization and the Rashba spin-orbit interaction.Comment: 2 pages, 2 figures, presented at the 5th International Conference on Strongly Correlated Electron Systems, SCES'05, Vienna, Austria, 26-30 July, 200

Mg(2)Si(x)Sn(1-x)heterostructures on Si(111) substrate for optoelectronics and thermoelectronics

Thin (50-90 m) non-doped and doped (by Al atoms) Mg2Sn0.6Si0.4 and Mg(2)Sn(0.4)Si(0.6)films with roughness of 1.9-3.7 nm have been grown by multiple deposition and single annealing at 150 degrees C of multilayers formed by repetition deposition of three-layers (Si-Sn-Mg) on Si(111) p-type wafers with 45 cm resistivity. Transmission electron microscopy has shown that the first forming layer is an epitaxial layer of hex-Mg2Sn(300) on Si(111) substrate with thickness not more than 5-7 nm. Epitaxial relationships: hex-Mg2Sn(300)parallel to Si(111), hex-Mg2Sn[001]parallel to Si[-112] and hex-Mg2Sn[030]parallel to Si[110] have been found for the epitaxial layer. But inclusions of cub-Mg2Si were also observed inside hex-Mg2Sn layer. It was found that the remaining part of the film thickness is in amorphous state and has a layered distribution of major elements: Mg, Sn and Mg without exact chemical composition. It was established by optical spectroscopy data that both type films are semiconductor with undispersed region lower 0.18 eV with n(o) = 3.59 +/- 0.01, but only two direct interband transitions with energies 0.75-0.76 eV and 1.2 eV have been determined. The last interband transition has been confirmed by photoreflectance data at room temperature. Fourier transmittance spectroscopy and Raman spectroscopy data have established the formation of stannide, silicide and ternary compositions

Ca silicide films-promising materials for silicon optoelectronics

Single-phase films of semiconductor and semimetallic calcium silicides (Ca2Si, CaSi, and CaSi2), as well as films with a significant contribution of Ca5Si3 and Ca14Si19 silicides, were grown on single-crystal silicon and sapphire substrates. The analysis of the crystal structure of the grown films was carried out and the criterion of their matching with silicon and sapphire substrates was determined. Some lattice-matching models were proposed, and the subsequent deformations of the silicide lattices were estimated. Film's optical functions, including the optical transparency, were calculated from the optical spectroscopy data and an extended comparison was performed with the results of ab initio calculations. The real limits of the optical transparency for the films on sapphire substrates were established. The maximum transparency limit (3.9 eV) was observed for the CaSi film. Based on an analysis of the photoelectric properties of Ca2Si/Si diodes on n- and p-type silicon substrates, a perspective of their applications in silicon optoelectronics was discussed

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Growth, structure, optical and electrical properties of Si/2D Mg2Si/Si(111) double heterostructures and Schottky diodes on their base

Mg2Si layers were grown on silicon by RDE at 150 °C and by SPE at 160 °C, and they were covered by silicon cap grown by MBE at 150-180 °C. The silicide layers and the silicon cap were investigated by in situ and ex situ methods. The 2D Mg2Si layer continuity and electrical properties were conserved during cap growth. The point defects in the structure are dominated by contamination of the substrate and by diffusion of the not reacted Mg into silicon. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

A low temperature growth of Ca silicides on Si(100) and Si(111) substrates: Formation, structure, optical properties and energy band structure parameters

The low-temperature formation of Ca silicides on silicon substrates with (100) and (111) orientations and on the oxidized silicon surface during deposition using solid phase epitaxy (SPE) and molecular beam epitaxy (MBE) was studied by the in situ electron spectroscopy. The temperature ranges for the formation of Ca2Si (273–346 °C) and CaSi (554–663 °C) on the Si(100) 2 × 1 surface were established during isochronous annealing of a thin Ca layer (10 nm). It was shown that an amorphous Ca2Si layer was formed by a SPE process at 330 °C from a Ca–Si mixture on the Si(100)2 × 1 surface, but under the surface the silicon and CaSi nanocrystals (NCs) were formed at the interface with the substrate. According to the optical spectroscopy data, films grown by the SPE method are semiconducting with the first direct interband transition at 1.16 eV, but the intraband absorption below 1 eV was determined by the carrier transitions in the CaSi NCs and transitions to defect levels. Raman active and far IR active peaks in amorphous Ca2Si films were firstly determined. When the MBE method (T = 330 °C) with an additional annealing at 330 °C was used, a Ca2Si layer was formed on the film surface, but the main contribution is made by faceted CaSi crystals (100 × 25 nm2) according to AFM, X-ray and electron diffraction. In the film consisting of the Ca2Si and CaSi phases, there are Raman peaks from both phases, which is associated with their separation according to the positions of the Raman shifts. A decrease in the temperature of the MBE process to 190 °C on the Si(111)7 × 7 surface with additional annealing at T = 300 °C leads to the formation of amorphous calcium silicide with a high density of embedded CaSi NCs (3–7 nm) with a stressed structure. When these CaSi NCs films were studied by the Raman spectroscopy method, 8 Raman phonons in the range of 105–422 cm−1 were detected. It was established that films containing CaSi in the crystalline phase are a semimetal with a constant absorption coefficient ((1–2)∙104 cm−1) at photon energies (0.5–1.1 eV) and a quasi-band gap with an energy from 1.26 eV to 1.36 eV depending on the size of CaSi NCs. MBE growth from a mixture of Ca–Si on an oxidized Si(100) surface led to the formation of shapeless CaSi and Ca2Si grains (weak contribution) with sizes from 50 to 200 nm, creating a structural-continuous film