China
Africa
Explore chapters and articles related to this topic
S
Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
superlattice a stack of ultrathin layers of material. Layer thicknesses are sufficiently thin to produce quantum-confined effects, typically 100- 1000 angstroms; generally, there are two different layer compositions, and the superlattice is built with layer composition in an alternating scheme. supernode a cluster of nodes, interconnected with voltage sources, such that the voltage between any two nodes in the group is known. superparamagnetism a form of magnetism in which the spins in small particles are exchange coupled by may be collectively switched by thermal energy. superpipelined processor a processor where more than one instruction is fetched during a cycle in a staggered manner. That is, in an n-issue superpipelined processor, an instruction is fetched every 1/n of a cycle. For example, in the MIPS R4000, which is two-issue superpipeline, a new instruction is fetched every half cycle. Thus, in effect, the instruction pipeline runs at a frequency double than the system (in the R4000 the pipeline frequency is 100 MHz, while the external frequency
Beryllium Containing II-VI Compounds
Published in Maria C. Tamargo, II-VI Semiconductor Materials and Their Applications, 2018
In order to improve the operation characteristics of ZnSe laser diodes, one should optimize the electronic as well as optical confinement. It recently has been suggested and experimentally demonstrated that the incorporation of alternately strained ZnCdSe-ZnSSe short-period superlattice (SPSL) waveguide layers in the ZnMgSSe-ZnCdSe separate confinement heterostructure (SCH) quantum well (QW) lasers can simultaneously solve both of the above tasks [58,59]. An alternately strained short-period superlattice has been shown to possess higher critical thickness as compared to the bulk layer with the same lattice mismatch and also exceeds the theoretically estimated short-period superlattice critical thickness. Even for compressively strained ZnCdSe-ZnSe QW structures, the experimentally measured critical thickness is almost twice higher than the predicted value [60]. In addition, strained layers are known to reduce defect migration, which also should promote a higher lifetime of the devices. SPSL waveguides have been successfully employed earlier for obtaining the ultra-low threshold current density (Al,Ga)As SCH QW lasers [61].
Thermoelectric Materials, Measurements, and Opportunities for Energy Harvesting
Published in D. M. Rowe, Materials, Preparation, and Characterization in Thermoelectrics, 2017
One fortuitous phenomenon during (111) growth is that PbTe acts to replanarize the surface after the deposition of the nanodot layer, so that a nano-dot-superlattice (NDSL) composed of discrete PbSe0.98Te0.02 nano-dot/wetting layers, separated by flat PbTe matrix layers, is obtained. When the nanodot and planarizing layers are cyclically repeated, a superlattice heterostructure is obtained that can have essentially unlimited thickness. Prepared this way, superlattice materials have an enormous amount of internal dissimilar interface area and that is expected to effect reduction in thermal conductivity well below that from alloying alone.13 To demonstrate the properties in as close to bulk form as possible, we investigated pseudo-bulk NDSL heterostructures having thickness roughly 100 µm, and we used BaF2 substrates because NDSL samples can easily be removed by completely dissolving the BaF2 in aqueous solutions.
A comprehensive review of vapour deposited coatings for cutting tools: properties and recent advances
Published in Transactions of the IMF, 2022
N. Ariharan, C. G. Sriram, N. Radhika, S. Aswin, S. Haridas
Superlattice coatings are made of two different types of layers, which are alternated. The mechanical properties of superlattices are highly dependent on the superlattice period, defined as the bilayer thickness of the two alternating layers. For superlattices, this period is typically less than 10 nm. Nitride superlattices are superhard coatings capable of providing hardness in excess of 3780 HV, depending on the materials and bilayer period used.106 The most accepted reason for this increase in hardness of these coatings is the presence of coherency strains. These alternating stress–strain fields due to changes in shear moduli of the layers, cause the hindrance of dislocation glide between interfaces and also within superlattice layers.107 The superhard behaviour of these coatings is heavily dependent on the superlattice period. As such, the instruments used for the deposition of these coatings must work flawlessly every time. Research has also been done on superlattices with alternating nitride and metal layers which provide lower hardness combined with higher toughness. In high-temperature applications where these superhard coatings are used, the interdiffusion between the layers and oxidation of the coating may reduce their hardness.106
Materials Informatics for Heat Transfer: Recent Progresses and Perspectives
Published in Nanoscale and Microscale Thermophysical Engineering, 2019
Shenghong Ju, Junichiro Shiomi
Based on the knowledge learnt above that layered structures give rise to minimum conductance and do not depend on the size of transverse supercell, we performed further optimization of Si/Ge superlattices as shown in Figure 5: the thickness of the unit layer (UL) is 5.43 Å, and total thickness of interfacial structure ranges from 8 to 16 ULs (from 4.35 to 8.69 nm). Similar to the descriptors used in the alloy structure optimization, 8 binary flags were used to indicate the state of each UL (“1” indicates Ge and “0” indicates Si). By performing BO, all the optimal structures can be obtained for Si–Si and Si–Ge interfacial superlattices with different thickness, equal, or variable fraction of Si/Ge atoms. It was found that as the layer thickness and number of thickness increase, the thermal conductance decreases and eventually asymptotically converges to a constant value, which is consistent with the trends seen in former investigation of Si/Ge structures [65, 70]. When considering a superlattice with a given total thickness, the layer thickness and number of interfaces are two competitive parameters, and this gives rise to the optimal structure with minimum thermal conductance. Another merit of MI lies in possibility to explore new physics in the course of understanding its output. By performing further systematic analyses, it was identified that the small thermal conductance in the aperiodic superlattices originates from their degrees of freedom to mutual-adoptively balance the two competing effects: Fabry–Pérot wave interference [71, 72] and interfacial particle scattering [73–75], which reduces the conductance as thickness of the constituent layers in superlattice increases and decreases, respectively. Consequently, the optimal aperiodic structure was found to restrain the constructive phonon interference, making the phonon transport to approach its incoherent limit.