Исследование характеристик сверхрешетки InGaAs/InAlGaAs для вертикально-излучающих лазеров спектрального диапазона 1300 nm

X-ray structural analysis and photoluminescence spectroscopy techniques were used to study heterostructures based on InGaAs/InAlGaAs superlattice for active regions of 1300 nm range lasers grown by molecular beam epitaxy. It is shown that the grown heterostructures have a high crystal quality. The perpendicular lattice mismatch of the average crystal lattice constant of the InGaAs/InAlGaAs superlattice with respect to the crystal lattice constant of the InP substrate is estimated at ~ +0.01%. An analysis of the photoluminescence spectra made it possible to conclude that the contribution of Auger recombination is insignificant in the studied range of excitation power density. Studies of vertical-cavity surface-emitting lasers with an active region based on the InGaAs/InAlGaAs superlattice made it possible to estimate the gain coefficient at a level of 650 cm-1 for the standard logarithmic approximation of the dependence of the gain on the current density. The transparency current density of the laser was ~150 А/cm2, which is comparable to the record low values for the case of highly strained InGaAs-GaAs and InGaAsN-GaAs quantum wells in the spectral ranges of 1200 nm and 1300 nm, respectively.

The Rise of (Chiral) 3D Mechanical Metamaterials

On the occasion of this special issue, we start by briefly outlining some of the history and future perspectives of the field of 3D metamaterials in general and 3D mechanical metamaterials in particular. Next, in the spirit of a specific example, we present our original numerical as well as experimental results on the phenomenon of acoustical activity, the mechanical counterpart of optical activity. We consider a three-dimensional chiral cubic mechanical metamaterial architecture that is different from the one that we have investigated in recent early experiments. We find even larger linear-polarization rotation angles per metamaterial crystal lattice constant than previously and a slower decrease of the effects towards the bulk limit.

Ultrafast acoustics for modulating matter / Bayer M.

Illumination of matter by intense ultrashort light pulses can lead to launching of coherent phonon pulses through the ultrafast thermal expansion. The duration of these pulses may be as short as a ps and their amplitude may reach one thousandth of a crystal lattice constant. This dynamic change of the lattice can vary the band gap of a semiconductor on corresponding time scales, which can be exploited to modulate light emitters on sub-THz frequencies. Further, in magnetic materials the acoustic pulses can be used to vary the magnetic anisotropy, by which a precession of the magnetization can be triggered. In suitably tailored structures, this precessing magnetization can serve as ultacompact source of microwave radiation with frequencies up to 100 GHz and more, by which high resolution magnetic resonance spectroscopy may be achieved. In this contribution we will discuss the basic principles of ultrafast acoustics of matter and gives examples of applications. The author acknowledges, among others, the long-lasting collaboration with Andrey Akimov (Nottingham), Alexey Scherbakov (St. Petersburg & Dortmund), and Dmitri Yakovlev (Dortmund & St. Pertersburg), without which the work would not have been possible

Characterization of The Volcanic Rocks of Mount Sinabung, Simacem Village, Karo Regency, Conducted With XRD, SEM-EDX

The study of volcanic rocks characterization of Sinabung Volcano erupted on September 15, 2017. The volcanic rocks crystal system was performed with XRD, elemental analysis and microstructure with SEM-EDX. Volcanic rocks contain: Anorthite phase 87,11 (wt%), Triclinic crystal, lattice constant, a = 8.1742 Å, b = 12,844 Å, c = 14,204 Å; Quartz phase 2.26%, Hexagonal crystals, lattice constants, a = 4,799 Å, b = 4,799 Å, c = 5,379 Å; Cristobalite phase 7.72 (wt%), Tetragonal crystals, lattice constants a = 4,970 Å, b = 6,990 Å, c = 6,998 Å; Alunite phase 2.91 (wt%), Hexagonal crystals, lattice constants, a = 6,990 Å, b = 6,990 Å, c = 17,282 Å.

Calculation of Dynamic Hardness by Molecular Dynamics

Based on the molecular-dynamic simulation of the impact of a solid ball on the surface of polycrystalline copper, a method for calculating the dynamic hardness of nanocrystalline materials is proposed. It is proposed to carry out the calculation of hardness by dividing the impact work by the squeezed volume. It is shown that this expression of dynamic hardness is consistent with Meyer hardness in the case of quasistatic indentation. As a result of this simulation, it is shown that under conditions when the diameter of the impactor decreases and approaches the crystal lattice constant of the target, the dynamic hardness increases. Also, in the calculations, the impactor density varied approximately twice, which was equal to the density of steel and the density of tungsten carbide. For a striker diameter of 5 nm, dynamic hardness increases with the speed of the striker and does not depend on its density.

Density and Mechanical Strength of Ferrite for Inertial Gyroscope

The effects of NiO on density and mechanic strength of Mn-Zn ferrite used for inertial gyroscope were investigated by measurements of crystal lattice constant, Vickers hardness, bending strength. To investigate this further, powder of Mn-Zn ferrite was characterized by x-ray diffraction (XRD) and the fracture surface of Mn-Zn ferrite was checked by scanning electronic microscope (SEM). The investigation revealed that the substitution of Ni2+ modified crystal lattice constant and crystal grain size so that it caused crystal lattice constant of Mn-Zn ferrite to decline and crystal grain size to decrease, therefore it was useful to improve density and mechanic strength of Mn-Zn ferrite by this way. The results show that proper addition of NiO can bring higher density and more perfect mechanic strength of Mn-Zn ferrite used for inertial gyroscope.