Effect Of Compressive Strain Research Articles

Electro-oxidation of methanol on Ru-core Pt-shell type model electrodes

Ru-core Pt-shell nanoparticles show an enhanced electrocatalytic activity for the methanol oxidation reaction (MOR) compared to the respective monometallic or most bimetallic alloy systems. Due to their ill-defined structure, however, a simple interpretation of these findings is challenging. In the present work we present results of a systematic study on the influence of the Pt film thickness of structurally well-defined PtX-ML/Ru(0001) model electrodes with varying Pt film thickness (1.1–5.5 monolayers (ML)) on their MOR performance. The electrodes are prepared and structurally characterized by scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV) conditions. The electrochemical/-catalytic properties of the electrodes are evaluated in an electrochemical flow cell, which is attached to the UHV system and combined with a mass spectrometer in a differential electrochemical mass spectrometry (DEMS) set-up, allowing for online detection of volatile reaction products/intermediates. We demonstrate that the MOR activity of PtX-ML/Ru(0001) increases with increasing Pt film thickness and that thicker Pt films (>2.5 ML) are significantly more active than Pt(111) and thinner Pt films, whereas the selectivity for CO2 formation remains essentially constant. We explain this trend in the activity via the Sabatier principle, where the higher activities of the Pt film electrodes with thicker Pt films compared to both Pt(111) and electrodes with thinner Pt films are due to a lower binding strength of adsorbed species than on Pt(111), due to vertical electronic ligand effects (Ru – Pt interactions) and compressive strain effects in the pseudomorphic films, and due to an increasing binding strength with increasing Pt film thickness, due to decreasing electronic ligand effects. In this picture the Pt5.5-ML/Ru(0001) electrode exhibits the best value of the binding strength and thus the highest rates, while for electrodes with lower/higher binding strength the rates are lower. Consequences of these findings for bimetallic PtRu nanoparticle catalysts are discussed.

Novel insights in growth of intermetallic compounds between Sn–3.0Ag–0.5Cu solder and flexible PCB substrates under strain

The study investigated the effect of tensile and compressive strain on the interfacial reaction of SAC305/Cu system. Experimental results indicated that the thickness of Cu6Sn5 layer on non-strained samples slightly decreased after aging for 120 h and increased with prolonged aging time. The applied tensile strain had an enhanced effect on the growth of Cu6Sn5 phase, while the applied compressive strain inhibited the growth of Cu6Sn5 phase. However, the thickness of Cu3Sn layer at SAC305/Cu solder joints increased gradually with increasing aging time, regardless of whether strain was or not applied on the solder joints. Besides, the mean diameter of Cu6Sn5 grain increased in three systems as the aging time was prolonged to 480 h. The morphology of Cu6Sn5 grain on non-strained samples gradually changed from round-shape into polyhedron-shape with increased aging time. The morphology of Cu6Sn5 grain under tensile or compressive strain was polyhedron-shape. The Kirkendall voids appeared within Cu3Sn layer in three systems after aging for 120 h and the amount of voids increased gradually with prolonged aging time. The applied tensile or compressive strain had an enhanced effect on the formation of voids within Cu3Sn layer and the enhanced effect of applied tensile strain was much remarkable than that of other systems.

Strain Modulated Optoelectronic Properties of CdO Monolayer

We studied the effect of biaxial tensile and compressive strain on the electronic and optical properties using the density function theory. Electronic properties are investigated in terms of the electronic band structure and density of states. CdO monolayer exhibits a direct bandgap ∼ 1.35 eV using a modified Becke–Johnson approximation. The value of bandgap decreases under both biaxial tensile and compressive strains. Moreover, direct to indirect electronic bandgap transition is observed above 8% tensile strain, whereas direct bandgap nature is conserved under compressive strain. The effective mass of an electron is nearly insensitive to strain, whereas hole effective mass shows linear increment with strain and a sudden jump at the electronic transition point of above 8% tensile strain. The noticed low reflectivity in unstrained and compressive strained conditions suggests that the CdO monolayer may be a promising material for transparent conducting oxide applications.

Normal compressive strain-induced modulation of electronic and mechanical properties of multilayer MoS2 and Graphene/MoS2 heterostructure: A first-principles study

In this paper the effect of normal compressive strain on the electronic and mechanical properties of multilayer molybdenum disulfide (MoS2) and graphene/MoS2 heterostructure are examine using density functional theory. The effects of layer number and stacking order of layers on the band structure and elastic constants are studied. Two different graphene/MoS2 heterostructure were studied. The first heterostructure consists of 5 × 5 graphene and 4 × 4 MoS2 unitcells in which MoS2 is compressed, whereas the second one is constructed of 4 × 4 graphene and 3 × 3 MoS2 unitcells and MoS2 is stretched in this structure. We find that due to sensitive dependence of the band gap of multilayer MoS2 on the normal compressive strain, a semiconductor-metal transition can be observed. The elastic constant of multilayer MoS2 increases with the rise in the number of layers, while the band gap decreases. Our simulations also illustrate that the AA3 and AB3 stacking orders are the most unstable structures. In the first heterostructure, the Schottky barrier strongly depends on the normal compressive strain. The n-type to p-type Schottky barrier transition occurs at the strain of 13.5%. In addition normal compressive strain changes the charge transfer between graphene and MoS2 in the second heterostructure. Furthermore, the direct and indirect band gap of MoS2 in the heterostructures can be adjusted by normal compressive strain and owning to stretching of MoS2, the band gap of MoS2 is smaller in the second heterostructure.

Thermal conductivity of two-dimensional BC3: a comparative study with two-dimensional C3N.

The thermal conductivities of single-layer BC3 (SLBC) sheets and their responses to environmental temperature, vacancy defects and external strain have been studied and compared with those of single-layer C3N (SLCN) sheets by molecular dynamics (MD) simulations. We found that SLBC and SLCN are isotropic in the basal plane and that their predicted thermal conductivities for infinite length sheets are 488.54 W m-1 K-1 and 799.87 W m-1 K-1, respectively. Despite many similar features in the structures of these materials, SLBC exhibits a lower thermal conductivity than SLCN due to stronger flexural acoustic phonon-defect scattering rates and weaker interatomic bonding stiffnesses. The vibrational density of states (VDOS) are calculated in both structures to elucidate their thermal conductivity differences. SLBC exhibits a more substantial redshift phenomenon in the high- and low-frequency domains than SLCN. In addition, the thermal conductivities of these materials exhibit decreasing trends in response to increases in temperature and defect ratio, and the temperature effect in SLBC is more substantial than that in SLCN, while the defect effect in SLBC is less substantial than that in SLCN. The influences of uniaxial compressive and tensile strains on the thermal conductivities of these materials are analysed separately. These two deformation modes cause different effects on the thermal transport behaviours of SLBC and SLCN: the effect of uniaxial compressive strain is slightly negative, while the effect of uniaxial tensile strain is initially positive and then negative. Moreover, the biaxial strains result in a more severe reduction in thermal conductivity than the uniaxial strains. Remarkably, the impact of uniaxial and biaxial tensile strains on thermal transport was stronger in SLBC than in SLCN. We propose that SLBC nanomembranes are promising candidates for various thermal applications.

First-principles study of the effect of compressive strain on oxygen adsorption in Pd/Ni/Cu-alloy-core@Pd/Ir-alloy-shell catalysts

Through synergism between the ligand effect, the d-band center shift, and the surface alloying effect, the Pd3CuNi@PdIr catalyst exhibits the poorest dioxygen adsorption and, consequently, the best catalytic ORR performance.

The electronic and optical properties of armchair germanene nanoribbons

The electronic and optical properties of armchair germanene nanoribbons (AGeNRs) are studied using the first principles calculations. The band structure, band-gap size, projected density of states (PDOS), and dielectric function of AGeNRs are calculated. Moreover, the variation of these parameters as a function of various ribbon widths is investigated. By increasing the width of ribbons the band-gap size of pristine AGeNRs is decreased according to three different trends. Based on these trends, it is extracted that the AGeNRs can be divided into three categories named as n = 3P, n = 3P+1, n = 3P+2, here n is the number of germanium atoms in the width and P is an integer. Moreover, all these categories are direct band-gap materials and the order of band-gap size is changed as: EG (3P+2) < EG (3P) < EG (3P+1). Due to the direct band-gap size, it can be extracted that all of AGeNR categories are proper for optical applications. Based on the simulation results of this work, it is demonstrated that the AGeNRs are appropriate for optical devices in the range of infrared applications. In addition, the effect of uniaxial tensile and compressive strain on the band-gap size and the dielectric function of AGeNRs is investigated and it is shown that the electronic and optical properties of AGeNRs can be tuned by strain in a wide range.

One-Nanometer-Thick PtNiRh Trimetallic Nanowires with Enhanced Oxygen Reduction Electrocatalysis in Acid Media: Integrating Multiple Advantages into One Catalyst.

Finding an active and durable catalyst for the acidic oxygen reduction reaction (ORR), a key process for fuel cells, remains an open challenge due to the thermodynamically contradictory requirements for activity and durability. Here, we report that an active and durable ORR catalyst can be achieved by integrating multiple structural and compositional advantages into one catalyst. The mass activity and specific activity of as-obtained 1-nm-thick PtNiRh trimetallic nanowires/C catalyst were 15.2 and 9.7 times as high as that of commercial Pt/C catalyst, respectively. The compressive strain and ligand effects arising from the advantageous microstructure and optimal composition of the nanowires were revealed to enhance the activity. Besides, the PtNiRh trimetallic nanowires/C catalyst exhibited substantially improved durability relative to commercial Pt/C catalyst, due to the combination of its one-dimensional structure and incorporated Rh atoms. This work provides a general guidance for the design of an impressive heterogeneous catalyst.

Topological features of the thermal Hall conductivity in a chiral p-wave superconductor under strain

Motivated by experimental studies on the effect of tensile and compressive strain or uniaxial pressure in the superconducting phase of the transition metal oxide Sr2RuO4, the pairing symmetry assuming the chiral p-wave superconducting state and the transport property are investigated theoretically by means of the self-consistent Bogoliubov-de Gennes approach. The uniaxial strain leads to the Fermi surface deformation. The topological properties are sensitive to the Fermi surface geometry induced by the strain and switch around the Lifshitz transition in the γ band. The temperature dependence of the thermal Hall conductivity is connected with the amplitude of the strain. While the topological number is reflected in the temperature linear contribution in the low-temperature limit of the thermal Hall conductivity, the deviation from this behavior depends on the pairing channel. Our result may enable us to provide information on the gap function of the chiral p-wave phase.

Nanoporous (Pt1-xCox)3Al intermetallic compound as a high-performance catalyst for oxygen reduction reaction

Nanocatalysts that boost the sluggish kinetics of oxygen reduction reaction with a long-term durability are crucial for widespread use of low-temperature fuel cells. Here we report a nanoporous intermetallic compound typically composed of platinum–cobalt–aluminum intermetallic core with in-situ grown atomic-layer-thick Pt skin as a novel oxygen-reduction-reaction nanocatalyst with remarkably enhanced performance. Both Pt and Co atoms thermodynamically prefer to locate nearby Al element within face-centered cubic Pt3Al matrix via the formation of strong PtAl and CoAl bonds, which not only enable synergistic ligand and compressive strain effects to moderately weaken the oxygen adsorption energy of Pt skin, but alleviate the evolution of surface Pt atoms to protect against the further dissolution of less-noble Co and Al. As a result, the nanoporous platinum–cobalt–aluminum nanocatalyst exhibits specific activity of 3.40 mA cm−2Pt and mass activity of 2.2 A mg−1Pt for the oxygen reduction reaction at 0.9 V versus reversible hydrogen electrode (∼13- and ∼20-fold enhancement relative to commercially available platinum nanoparticles supported carbon) with an exceptional durability, showing genuine potential as cathode catalyst in next-generation electrochemical energy conversion devices.

One-Pot Synthesis of Icosahedral PdPtNi/C Twin Crystal Catalyst with High Activity toward Oxygen Reduction Reaction

Pt and Pt-based alloys are still the mainstream electrocatalysts for oxygen reduction reaction (ORR) so far, which is an important process for fuel cell. Herein, for the first time ternary icosahedral nanocrystals supported on carbon PdPtNi/C are constructed by a facile one-pot approach and are characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The electrocatalytic performance of the as-prepared catalyst for ORR is evaluated in acid electrolyte and compared with the state-of-the-art commercial Pt/C catalyst at identical condition. The icosahedral structure with 20 exposed {111} facets and twin boundaries are the distinguishing features of the PdPtNi/C nanoparticles, which enable them to be more active. The compressive strain effect and electronic interaction (ligand effect) of Pd, Pt, and Ni elements are also responsible for the excellent performance of the catalyst: the higher onset potential of ORR than that of commercial Pt/C, the outstanding specific activity and mass activity, which is about 9.59 and 5.40 times higher than those of commercial Pt/C at 0.90 VRHE, respectively, while 5.39 and 4.75 times higher at 0.85 VRHE, respectively. These results can promote the practical application of Pt-based catalyst and thus accelerate the widespread commercialization of fuel cell technologies.

Structural and magnetic transitions accompanied by large responses in epitaxial Sr0.5Ba0.5MnO3 films

The effect of epitaxial compressive and tensile strains on the physical properties of multiferroic ${\mathrm{Sr}}_{0.5}{\mathrm{Ba}}_{0.5}{\mathrm{MnO}}_{3}$ films is investigated via the use of ab initio calculations. Striking phenomena are predicted. Examples include (1) the existence of a previously overlooked strain-induced low-symmetry phase bridging the tetragonal (compressively strained) and orthorhombic (tensile-strained) ferroelectric structures, which exhibits a very large piezoelectric response; (2) a first-order magnetic transition within the tetragonal polar state, which is accompanied by remarkable changes in polarization and out-of-plane lattice constant; (3) the existence of a state that is both ferromagnetic and ferroelectric with a large polarization and axial ratio at large enough compressive strain; and (4) the possibility to induce a structural phase transition between states of different symmetries (e.g., between tetragonal and monoclinic, or between orthorhombic and monoclinic) by applying a magnetic field, which constitutes an original magnetoelectric effect. Experiments are called for to confirm such predictions.

Tunable Thermoelectric Performance in Porous Armchair Graphene Nanoribbons as a Function of Strain, Pore Morphology and Temperature

In this paper, the thermoelectric performance of porous armchair graphene nanoribbons under tensile and compressive strain is investigated as a function of pore morphology and temperature. For all the porous structures irrespective of their pore size, the performance improves at a compressive strain of 10%, while for tensile nature, the minimum cut-off strain required for improved thermoelectric figure of merit (ZT) shows an inverse relation with the pore size. In addition, optimal pore shape geometry can yield better performance, even at lower values of strain. Further analysis reveals that tensile strain is not able to improve the performance at low and intermediate temperatures of around 300 K, whereas tensile/compressive strain is effective in enhancing the performance of porous armchair graphene nanoribbons at higher temperatures. Furthermore, the structures are found to be more sensitive to compressive strain than the tensile one since the effect of compressive strain is found to improve ZT more significantly. Our analysis based on Non-Equilibrium Green’s function calculations suggests a possible route for tailoring the functionality of nanomaterials so as to achieve great potentials for thermoelectric applications at various temperatures.

Influence of Compressive, Tensile and Fatigue Stresses on Asphalt and Concrete Cement Road Pavements in Nigeria - Using Linear Elastic Theory

The high brittle nature of pavement structures have been carefully examined based on compressive, tensile strain and the harsh effects of fatigue cycle with reference to the base layer thicknesses and elastic strains during and after construction were examined. Subjection of asphalt and concrete-cement pavements to traffic loading and tyre pressure also influences the vertical stress and strain values for the asphalt and concrete materials under the same axial loading conditions. Using various fundamental equations under linear elastic conditions for the analysis of Asphalt and Concrete Cement structure revealed that both materials do respond differently to compressive and tensile stresses under similar mechanical conditions. Effect of compressive stresses and strains on concrete pavement is larger compare to asphalt pavement due to large thickness sub-base layer of its pavement structure. Both pavement layer thicknesses are independent of fatigue cycle under harsh traffic loading. Thus, concrete pavement has shown better fatigue resistance and less tensile strain values than asphalt pavements due to high pavement layer thickness regardless of the load distribution.

Effect of tensile and compressive strain on the magnetic ordering of the ( $$\hbox {LaMnO}_{3})_{1}/\hbox {(SrTiO}_{3})_{1}$$ LaMnO 3 ) 1 / (SrTiO 3 ) 1 superlattice

We study the effects of tensile and compressive strain on the $$(\hbox {LaMnO}_{3})_{1}/(\hbox {SrTiO}_{3})_{1}$$ superlattice from density functional theory using Quantum-Espresso open source code. In the unstrained superlattice, electron interactions in out-of-plane Mn–O–Ti chains are dominated by superexchange interactions, giving rise to ferromagnetic and half-metallic conducting characters. We found that the most stable magnetic configuration is G-type antiferromagnetic configuration for strong compressive strain and for strong tensile strain it is A-type antiferromagnetic configuration. The results are in accordance with the experimental observations which show that the superlattices can be grown on different substrates, and due to the difference in lattice parameters of the substrate and the main layer, there are also changes in the amount of strain applied to the superlattice.

Effects of compressive strain on the evolution of interfacial strength of steel/nickel solid-state bonding at low temperature

ABSTRACTSolid-state bonding between ultralow-carbon steel and pure nickel was conducted by hot pressing with various compressive strain ranging from 5 to 15% and subsequent isothermal holding at 923 K. It was found that the interfacial strength of contact area is accounted for by the evolution of the intrinsic strength of the interface and the amount of plastic energy dissipation at the crack tip during interface fracture. The compression induces severe deformation around the interface and consequently inhibits the plastic energy dissipation during interface fracture. In the first stage of isothermal holding, the residual strain around the interface on the steel side is reduced by recovery process, which concurrently decreases in the yield stress of the area adjacent to the interface. This promotes plastic energy dissipation of the area, leading to a significant increase in interfacial strength in the first stage.

(Keynote) Theoretical Inspirations from Radoslav Adzic’s Electrocatalysis Work

When combined with controlled synthesis of well-defined facets and shapes, density functional theory (DFT) could give especially accurate descriptions of electrocatalytic reactions on surfaces. Dr. Adzic’s group has pioneered the controlled and uniform deposition of a monolayer (or overlayers) of Pt on a single crystal or nanoparticles of another transition metal or transition metal alloys.1-6 Not only does this morphology achieve better utilization of the overlying Pt atoms, but the resulting structures also possess remarkable stability as electrocatalysts. Here, we review our long-standing collaboration with Dr. Adzic on the oxygen reduction reaction (ORR) over Pt monolayer or overlayers atop a variety of transition metals5,7-12, as well as the electrooxidation of formic acid on Pt monolayers on single-crystals of transition metals. A logical extension of this methodology is to support Pt overlayers atop shape-selected nanoparticles, which selectively expose well-defined facets. Time-permitting, we will also be discussing insights from studying ORR of Pt overlayers on Pd icosahedra13, octahedra14, and nanocubes15. In several cases, the induced compressive strain and ligand effects that the Pt monolayer or overlayers experience on various substrates weaken the adsorption of oxygenated species (e.g.: OH) compared to pure Pt, thereby enhancing the ORR activity. Zhang J, Mo Y, Vukmirovic MB, Klie R, Sasaki K, Adzic RR. Platinum monolayer electrocatalysts for O-2 reduction: Pt monolayer on Pd(111) and on carbon-supported Pd nanoparticles. J. Phys. Chem. B. Jul 29 2004;108(30):10955-10964. Sasaki K, Naohara H, Cai Y, et al. Core-Protected Platinum Monolayer Shell High-Stability Electrocatalysts for Fuel-Cell Cathodes. Angew. Chem. Int. Ed. 2010;49(46):8602-8607. Adzic R. Platinum Monolayer Electrocatalysts: Tunable Activity, Stability, and Self-Healing Properties. Electrocatalysis. Dec 2012;3(3-4):163-169. Bliznakov ST, Vukmirovic MB, Yang L, Sutter EA, Adzic RR. Pt Monolayer on Electrodeposited Pd Nanostructures: Advanced Cathode Catalysts for PEM Fuel Cells. Journal of the Electrochemical Society. 2012;159(9):F501-F506. Knupp SL, Vukmirovic MB, Haldar P, Herron JA, Mavrikakis M, Adzic RR. Platinum Monolayer Electrocatalysts for O-2 Reduction: Pt Monolayer on Carbon-Supported PdIr Nanoparticles. Electrocatalysis. Dec 2010;1(4):213-223. Sasaki K, Wang JX, Naohara H, et al. Recent advances in platinum monolayer electrocatalysts for oxygen reduction reaction: Scale-up synthesis, structure and activity of Pt shells on Pd cores. Electrochimica Acta. Mar 2010;55(8):2645-2652. Yang L, Vukmirovic MB, Su D, et al. Tuning the Catalytic Activity of Ru@Pt Core-Shell Nanoparticles for the Oxygen Reduction Reaction by Varying the Shell Thickness. J. Phys. Chem. C. Jan 31 2013;117(4):1748-1753. Herron JA, Jiao J, Hahn K, Peng G, Adzic RR, Mavrikakis M. Oxygen Reduction Reaction on Platinum-Terminated "Onion-structured" Alloy Catalysts. Electrocatal. Dec 2012;3(3-4):192-202. Zhou W-P, Yang X, Vukmirovic MB, et al. Improving Electrocatalysts for O-2 Reduction by Fine-Tuning the Pt-Support Interaction: Pt Monolayer on the Surfaces of a Pd3Fe(111) Single-Crystal Alloy. J. Am. Chem. Soc. Sep 9 2009;131(35):12755-12762. Vukmirovic MB, Zhang J, Sasaki K, et al. Platinum monolayer electrocatalysts for oxygen reduction. Electrochim. Acta. Jan 20 2007;52(6):2257-2263. Adzic RR, Zhang J, Sasaki K, et al. Platinum monolayer fuel cell electrocatalysts. Topics in Catalysis. Dec 2007;46(3-4):249-262. Zhang JL, Vukmirovic MB, Xu Y, Mavrikakis M, Adzic RR. Controlling the catalytic activity of platinum-monolayer electrocatalysts for oxygen reduction with different substrates. Angewandte Chemie-International Edition. 2005;44(14):2132-2135. Wang X, Choi S-I, Roling LT, et al. Palladium-platinum core-shell icosahedra with substantially enhanced activity and durability towards oxygen reduction. Nature Commun. Jul 2015;6. Park J, Zhang L, Choi S-I, et al. Atomic Layer-by-Layer Deposition of Platinum on Palladium Octahedra for Enhanced Catalysts toward the Oxygen Reduction Reaction. Acs Nano. Mar 2015;9(3):2635-2647. Xie S, Choi S-I, Lu N, et al. Atomic Layer-by-Layer Deposition of Pt on Pd Nanocubes for Catalysts with Enhanced Activity and Durability toward Oxygen Reduction. Nano Lett. Jun 2014;14(6):3570-3576.

Strain tuning of electronic properties of various dimension elemental tellurium with broken screw symmetry

We present a systematical study of atomic structures and electronic properties of various dimension tellurium (Te) with broken intrinsical screw symmetry by applying reasonable strain. It is demonstrated that (i) bulk trigonal Te has degenerate Weyl nodes around the H point near the Fermi energy, and this degeneracy will be broken by introducing the selenium (Se) atom through creating the inner unsymmetrical strain, instead of external shear strain. (ii) 2D structures of tetragonal Te (t-Te) and 1T-MoS2-like Te (1T-Te) show direct and indirect band gap, respectively. Under the uniform biaxial compressive (BC) strain, monolayer of t-Te shows the direct-to-indirect band gap transition, while 1T-Te monolayer has a band gap transition firstly from indirect to direct and then from direct to indirect. Their effective masses of hole and electron can be effectively tuned by BC strain. (iii) One-dimensional (1D) structures of single helix, triangular Te and hexagonal Te nanowires display the obvious quantum confinement effect on the band structure and different sensitivity to the effect of uniaxial compressive strain.

Numerical Analysis of Effects of Compressive Strain on the Evolution of Interfacial Strength of Steel/Nickel Solid-State Bonding

Numerical Analysis of Effects of Compressive Strain on the Evolution of Interfacial Strength of Steel/Nickel Solid-State Bonding

Stress and strain effects on the electronic structure and optical properties of ScN monolayer

Based on the density functional theory, electronic and optical properties of a monolayer scandium nitride structure have been studied under different strain conditions. Our results indicate that both biaxial compressive and tensile strain effects lead to change the band gap of this structure with different rates. Also, optical absorption spectrum peaks experience an obvious red and blue shifts with the exerting of tensile and compressive strains, respectively. Our results express that ScN monolayer can be the promising candidate for the future nano-base electrical and optical devices.