Thicknesses Of Constituent Layers Research Articles

Investigation of Transmission Properties in One-Dimensional Quasi-periodic Superconducting Photonic Crystal

This paper explores the transmission characteristics of superconducting quasi-periodic photonic crystal structure arranged in Thue-Morse and double-period sequences. We mainly focused on the cutoff frequency of transmittance spectra. The study shows that the cutoff frequency can be appreciably tuned by generation number of sequence, thicknesses of constituent layers and operating temperature. Shifting behaviour of cutoff frequency is in contrast with periodic structure on varying superconductor thickness and temperature whereas it shows opposite trend on changing the dielectric layer thickness. It is also observed that different quasi-periodic structures show distinct values of cutoff frequency and different transmission properties. This features allow to tune the cutoff frequency or band gap in the whole infrared frequency region.

Doped Single-Wall Carbon Nanotubes in Propagating Surface Plasmon Resonance-Based Fiber Optic Refractive Index Sensing

We propose a surface plasmon resonance (SPR)-based fiber coupled refractive index sensing probe utilizing single-wall carbon nanotubes (SWCNTs) as the upper most layer. The sensor is designed by considering indium tin oxide (ITO) film on the bare core of a multi-moded step-index fiber, followed by the deposition of silicon, and then by that of the highly doped bundled SWCNTs layers. The film thicknesses of different constituent layers are optimized with respect to the sensitivity and the detection accuracy of the sensor. The theoretical analysis results in high sensitivity of 9.78 μm per refractive index unit (μm/RIU) for the optimized probe in the infra-red (IR) region of the electromagnetic (EM) spectrum.

Optimization of Magneto-Optical Kerr Effect in Cu/Fe/Cu Nano-structure

We use an analytical approach to describe the optical response of a magnetoplasmonic structure upon surface plasmon polariton (SPP) excitation in glass/Cu/Fe/Cu multilayer. The proposed structure is based on Kretschmann prism couplers, Fe layer as magneto-optical (MO) medium, and Cu layer as plasmonic metal layer, to enhance the MO effects thanks to the resonant excitation of surface plasmons. The influence of constituent layer thicknesses and layer order is investigated to obtain the maximum MO Kerr signal and figure of merit (FOM) in polar geometry. In addition, we show a range of parameters to determine the maximum Kerr rotation accompanied by minimum Kerr ellipticity which is desirable for data storage applications. Results demonstrate the important role of film thicknesses and incidence angle distribution on resonant excitation of surface plasmons.

(Invited) Controlling Component Distribution in Electrodeposited Multilayer and Alloy Films

Many advanced materials are produced by electrodeposition nowadays which are mostly alloys or multilayers and contain at least two components. The electrodeposition of some elements and element combinations often requires the use of bath formulations different from the traditional aqueous-based solutions. For the investigation of the properties of such novel electrodeposited materials, it is important to be able to control the deposit composition over the sample volume. For alloy films, this requires ensuring a homogeneous composition profile both laterally and along the growth direction since otherwise the changes of a certain sample property upon varying the deposition conditions may be masked by composition inhomogeneities. For multilayers consisting of two alternating layers of different kind, in addition to the requirement of lateral uniformity, the control of a regular change of composition along the thickness is also necessary. Over the last two decades, our group was strongly involved in the research activity on the giant magnetoresistance (GMR) effect in electrodeposited (ED) magnetic/non-magnetic multilayer films [1]. During attempts towards a better understanding of layer formation in such multilayers and improving their GMR characteristics, we have identified some factors decisively influencing lateral composition variations and composition modulation in multilayers. We have also succeeded in suppressing the composition variation along the thickness in ED alloy films. In the present talk, the discussion of progress along these lines will cover the following three topics. A. Controlling lateral composition homogeneity of electrodeposits Lateral variations can occur due to the well-known edge-effects in the case of electrodeposition in a cell with lateral dimensions much larger than the cathode surface area. Also, the commonly used vertical cathode arrangement usually leads to composition and thickness variations along the cathode surface from the bottom to the top due to the buoyancy effect. The particular sensitivity of GMR to individual layer thicknesses was of great help in revealing macroscopic lateral inhomogeneities of ED multilayers due to both above described effects [2]. The use of a cell with a cathode completely filling the cross-section of the cell and the placement of the cathode with an upward-looking position at the bottom of the cell eliminates these drawbacks [3]. This way one can produce ED films which show a large degree of lateral homogeneity. B. Controlling composition modulation in multilayered electrodeposits It turned out from an analysis of possible two-pulse combinations for preparing magnetic/non-magnetic multilayers from a single bath that the best way is the use of a G/P pulse sequence in which a galvanostatic (G) pulse is used for the deposition of the less-noble magnetic metal whereas the more-noble non-magnetic metal is deposited under potentiostatic (P) control. The introduction of a method for establishing the electrochemically optimized potential for the deposition of the non-magnetic spacer layer on the basis of an analysis of current transients during multilayer deposition enabled us to control the composition modulation with a high accuracy. This implies also a proper control of constituent layer thicknesses which was a prerequisite for studying the true dependence of physical properties (e.g., GMR) on layer thicknesses not available beforehand. We have also made attempts to control multilayer formation by a partial anodic dissolution of a thick deposited non-magnetic layer in each period [4] or by intentionally applying a more positive potential for non-magnetic layer deposition than the optimized value and, thus, enabling a partial replacement of the magnetic layer atoms by non-magnetic atoms [5]. C. Controlling composition profile along the thickness in electrodeposited alloys In magnetic alloys such as permalloy (Ni-Fe), there is an inherent initial composition variation along the thickness when produced by d.c. plating. This occurs due to the interplay of the different deposition preference of the two components and the partial depletion of the solution near the cathode. The initial composition variation may lead to a deterioration of the magnetic properties which can be very pronounced at the small layer thicknesses required in applications striving for miniaturization. Based on depth-profile analysis results, a proper pulse-plating technique could be elaborated to ensure a composition homogeneity even in the initial first few hundred nanometer range [6]. 1. I. Bakonyi, L. Péter: Progr. Mater. Sci. 55 (2010) 107 2. I. Bakonyi et al., Phys. Rev. B 70(2004) 054427 3. V. Weihnacht et al., J. Electrochem. Soc. 150(2003) C507 4. N. Rajasekaran et al., J. Electrochem. Soc. 161(2014) D339 5. N. Rajasekaran et al., J. Electrochem. Soc. 162 (2015) D204 6. K. Neuróhr et al., Electrochim. Acta 103 (2013) 179

Possible p-Wave Superconductivity in Epitaxial Bi/Ni Bilayers**Supported by the National Basic Research Program of China under Grant Nos 2015CB921400 and 2011CB921802, the National Natural Science Foundation of China under Grant Nos 11374057, 11434003 and 11421404, the research of Andreev reflection wassupported as part of the SHINES, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of

Superconductivity (SC) is one of the most intriguing physical phenomena in nature. Nucleation of SC has long been considered highly unfavorable if not impossible near ferromagnetism, in low dimensionality and, above all, out of non-superconductor. Here we report observation of SC with TC near 4K in Ni/Bi bilayers that defies all known paradigms of superconductivity, where neither ferromagnetic Ni film nor rhombohedra Bi film is superconducting in isolation. This highly unusual SC is independent of the growth order (Ni/Bi or Bi/Ni), but highly sensitive to the constituent layer thicknesses. Most importantly, the SC, distinctively non-?? pairing, is triggered from, but does not occur at, the Bi/Ni interface. Using point contact Andreev reflection, we show evidences that the unique SC, naturally compatible with magnetism, is triplet p-wave pairing.

Effect of p-NiO and n-ZnSe interlayers on the efficiency of p-GaN/n-ZnO light-emitting diode structures

We report on a numerical study of the characteristics of p-GaN/n-ZnO light-emitting diodes (LEDs) with p-NiO and n-ZnSe interlayers, and on LED design optimization which includes bandgap engineering, thickness and doping of constituent layers. The current-voltage dependences of investigated LEDs show a threshold voltage of 3.1 V, 5.4 V and 5.6 V for LED devices without and with the presence of p-NiO and n-ZnSe interlayers, respectively. It is found that p-NiO, n-ZnSe and n-ZnO interlayers act as an electron blocking layer, active media layer, and electron transport layer, respectively. It is established that the insertion of both p-NiO and n-ZnSe interlayers leads to the enhancement of charge carrier-confinement in the active region and to the significant increase of internal quantum efficiency (IQE) of the LED device up to 82%, which is comparable with IQE values in order to obtain better AlGaN- and InGaN-based LEDs. It is found that the efficiency of LED devices at 100 A cm−2 is equal to 0.024, 0.09 and 16.4% of external quantum efficiency (EQE), 1.3 × 10−4, 1.6 × 10−4, and 6.4 lm W−1 of PE, and 1.3 × 10−4, 2.9 × 10−4, and 12 cd A−1 of CE for p-GaN/n-ZnO, p-GaN/p-NiO/n-ZnO, and p-GaN/p-NiO/n-ZnSe/n-ZnO LED devices, respectively.

Tunable Fano Resonance in One-Dimensional Superconducting Photonic Crystal

The transmission properties of one-dimensional photonic crystal consisting superconducting and dielectric material has been investigated theoretically by transfer matrix method (TMM). The transmission spectra obtained by simulation of superconductor photonic crystal shows Fano resonance line profile. The Fano resonance observed in transmission spectra is the function of the thickness of constituent layers, number of periods, and temperature of superconductor. The maxima and minima of Fano resonance can be changed by varying thickness of superconductor and dielectric layers. Increase in thickness of superconductor layer increases the maxima of Fano resonance towards 100 % transmittance, while minima of Fano resonance tends towards zero transmittance. The gradient between maxima and minima of the Fano resonance decreases with increasing the thickness of the superconductor layer while the gradient of Fano resonance increases with increase in thickness of dielectric layer. Increasing the thickness of dielectric layer decreases the maxima of Fano resonance. The position of Fano resonance can be tuned over a definite frequency range by varying temperature of the superconductor layer.

Near-infrared longitudinal plasmon polariton photonic gaps in a semiconductor metamaterial photonic crystal

We perform a theoretical investigation on the near-infrared longitudinal plasmon polariton gaps in a one-dimensional semiconductor metamaterial photonic crystal. The considered structure is (AB)N where N is the number of periods, layer A is a dielectric, and layer B is a semiconductor metamaterial composed of Al-doped ZnO (AZO) and ZnO. For oblique incidence under transverse magnetic mode, it is found that, due to the anisotropic permittivity of semiconductor metamaterial, there exist multiple longitudinal plasmon polariton gaps which are ascribed to the coupling between photon mode and metamaterial bulk electric plasmon. The photonic band and gap structures are investigated as functions of incident angle, filling factor of semiconductor metamaterial, thicknesses of constituent layers, and number of periods as well.

Giant Magnetoresistance and Structure of Electrodeposited Co/Cu Multilayers: The Influence of Layer Thicknesses and Cu Deposition Potential

The giant magnetoresistance (GMR) and structure was investigated for electrodeposited Co/Cu multilayers prepared by a conventional galvanostatic/potentiostatic pulse combination from a pure sulfate electrolyte with various layer thicknesses, total multilayer thickness and Cu deposition potential. X-ray diffraction (XRD) measurements revealed superlattice satellite reflections for many of the multilayers having sufficiently large thickness (at least 2 nm) of both constituent layers. The bilayer repeats derived from the positions of the visible superlattice reflections were typically 10 – 20% higher than the nominal values. The observed GMR was found to be dominated by the multilayer-like ferromagnetic (FM) contribution even for multilayers without visible superlattice satellites. There was always also a modest superparamagnetic (SPM) contribution to the GMR and this term was the largest for multilayers with very thin (0.5 nm) magnetic layers containing apparently a small amount of magnetically decoupled SPM regions. No oscillatory GMR behavior with spacer thickness was observed at any magnetic layer thickness. The saturation of the coercivity as measured by the peak position of the MR(H) curves indicated a complete decoupling of magnetic layers for large spacer thicknesses. The GMR increased with total multilayer thickness which could be ascribed to an increasing SPM contribution to the GMR due to an increasing surface roughness, also indicated by the increasing coercivity. For multilayers with Cu layers deposited at more and more positive potentials, the GMRFM term increased and the GMRSPM term decreased. At the same time, a corresponding reduction of surface roughness measured with atomic force microscopy indicated an improvement of the multilayer structural quality which was, however, not accompanied by an increase of the superlattice reflection intensities. The present results underline that whereas the structural quality as characterized by the surface roughness generally correlates fairly well with the magnitude of the GMR, the microstructural features determining the amplitude of superlattice reflections apparently do not have a direct influence on the GMR.

Failure and deformation mechanisms during indentation in nanostructured Cr/CrN multilayer coatings

The aim of the present work was to investigate the microstructure evolution of the nanostructured Cr/CrN multilayer coatings on titanium Ti6Al4V alloy during indentation. Five types of multilayer (Cr/CrN)×8 coatings were deposited on Ti6Al4V titanium alloy by the PVD vacuum arc method. The coatings had the same total thickness and number of constituent layers, but differed in the thickness ratio of the Cr and CrN constituent layers (QCr/CrN parameter). The indentation measurements were performed with a Berkovich indenter at loads of 100mN, 500mN, and 1N. The SEM and STEM observations were focused on the cracking behaviour in the CrN layers as well as on the microstructure changes in the ductile Cr layers.The investigations demonstrate that the applied surface treatment significantly improves the hardness of the titanium alloy. The hardness of the coatings varied in the range 10 to 35GPa, depending on the thickness ratio of the layers. Observations performed on cross-sections through the indentation zones revealed small radial cracks, which were observed only in the CrN layers. They initiated at the interface and propagated across a given layer, to be arrested at the next interface. The STEM observations also showed microstructure changes in the Cr layers due to the accommodation of plastic deformation. The two main mechanisms of permanent deformation were observed.

Enhanced second-harmonic generation in Pr0.5Ca0.5MnO3/La0.5Sr0.5MnO3 superlattices

We investigated second harmonic generation for manganite superlattices composed of Pr0.5Ca0.5MnO3 and La0.5Sr0.5MnO3. While the second harmonic intensity shows a strong variation as a function of the constituent layer thickness, it is dramatically enhanced when each layer has a same thickness of about 1.4 nm and endows its own ground state nature, i.e., a charge-orbital ordered antiferromagnetic insulator for Pr0.5Ca0.5MnO3 and a ferromagnetic metal for La0.5Sr0.5MnO3. From the detailed symmetry analysis, we discuss a possible role of the coexisting phases and their boundaries in the enhancement of the polar character in this manganese oxide superlattice.

Understanding the role of thickness and morphology of the constituent layers on the performance of inverted organic solar cells

Inverted bulk heterojunction organic solar cells have generated significant interest in organic photovoltaic research due to much improved life times. Efficiency maximization for a given polymer–acceptor blend requires control of thickness and morphology of various constituent layers. In this manuscript, we present our results on the thickness variation of various constituent layers, viz. ZnO (electron transport layer), blend layer of poly(3-hexyl thiophene) and [6,6]-phenyl-C61 butyric acid methyl ester (active layer) and MoO3 (hole extraction layer) vis-à-vis effect of morphology of layers and optical field distribution on the electrical performance of inverted organic solar cells. The peak performance of the devices occurs for 30nm thick ZnO films, 100nm thick active layer and 10nm of MoO3 layers with an average power conversion efficiency of approximately 3.2% and a fill factor of 61%. The maximization of the device performance upon thickness variation of device constituents appears to result from the combined effects of morphology and the optical electric field distribution in the active layer.

Bismuth ferrite bilayered thin films of different constituent layer thicknesses

Bilayered thin films consisting of (Bi 0.90La 0.10)(Fe 0.85Zn 0.15)O 3 and (Bi 0.90La 0.10)(Fe 0.90Zn 0.10)O 3 layers have been fabricated by radio frequency sputtering. Both multiferroic layers are well retained in these bilayers. Their leakage current, multiferroic properties, and fatigue behavior are largely dependent on the thicknesses of (Bi 0.90La 0.10)(Fe 0.85Zn 0.15)O 3. With an increase of the thickness in the (Bi 0.90La 0.10)(Fe 0.85Zn 0.15)O 3 layer, the leakage current density of bilayers is degraded due to different grain growth modes and an increase in oxygen vacancies, the dielectric constant ( ɛ r) becomes larger due to the introduction of (Bi 0.90La 0.10)(Fe 0.85Zn 0.15)O 3 with a high ɛ r value, and their magnetic properties are deteriorated with increasing the thickness ratios of (Bi 0.90La 0.10)(Fe 0.85Zn 0.15)O 3 with a weaker magnetization. All bilayers exhibit a good ferroelectric behavior regardless of varying thicknesses of the (Bi 0.90La 0.10)(Fe 0.85Zn 0.15)O 3 layer, while their coercive field decreases with increasing the thickness of the (Bi 0.90La 0.10)(Fe 0.85Zn 0.15)O 3 layer. An anomalous enhancement in switchable polarization is demonstrated by these bilayers, owing to the involvement of space charges accumulated at the interfaces between two constituent layers.

LOCALIZED WANNIER EXCITON IN DEFECT LAYER EMBEDDED BETWEEN TWO SEMI-INFINITE SUPERLATTICES

The characteristics of the localized Wannier exciton in defect layer (GaAs) embedded between two semi-infinite superlattices (GaAs/Al x Ga 1-x As ) are investigated theoretically using a variational approach. It can be clearly seen the exciton changes in character between three- and quasi-two-dimensional states from the variation of exciton binding energy, in-plane radius, and probability in the superlattices (SLs) growth direction. We find that the extensions of exciton in directions both parallel and perpendicular to the interface of SLs almost approach their minimums as the exciton binding energy reaches peak value at a certain defect width. Our results show that the binding energy of the ground exciton state is sensitive to Al concentration x in Al x Ga 1-x As and thicknesses of the constituent layers. The comparison between excitonic behavior in structural defect SLs and single quantum well is made.

Multiferroic behavior and impedance spectroscopy of bilayered BiFeO3/CoFe2O4 thin films

Lead-free bilayered multiferroic thin films consisting of BiFeO3 (BFO) and CoFe2O4 (CFO) layers with different thicknesses were grown on SrRuO3-coated Pt/TiO2/SiO2/Si substrates by radio frequency sputtering. The effects of constituent layer thicknesses on the ferroelectric and magnetic behavior have been studied. The physical behaviors are shown to strongly depend on the thicknesses of the constituent layers. BFO (220 nm)/CFO (30 nm) bilayered thin film demonstrated much improved ferroelectric and ferromagnetic behavior (2Pr=144.2 μC/cm2, 2Ec=778.0 kV/cm, Ms=61.2 emu/cm3, and Hc=200.8 Oe) as compared to those of the single layer BFO thin film. The dielectric behavior and conductivity of BFO (220 nm)/CFO (30 nm) bilayered thin film were investigated as a function of both temperature (in the range of 294–534 K) and frequency (in the range of 10−1–106 Hz), where an activation energy of ∼1.11 eV for dielectric relaxation was demonstrated. From the conductivity behavior, an activation energies of ∼0.98 eV was derived for dc conductivity are, implying that oxygen vacancies are involved in the conduction of the BFO (220 nm)/CFO (30 nm) bilayered film.

Exchange bias of NiFe/FeMn nanocaps

NiFe/FeMn bilayers are fabricated on two-dimensional closely packed arrays of monodisperse polystyrene spheres. Although the exchange field is inversely proportional to the NiFe layer thickness in both NiFe/FeMn nanocaps and continuous films, the former series have a smaller exchange field than the latter ones. The exchange field and the coercivity both have different evolution trends with the FeMn layer thickness for the two series of samples. More remarkably, the asymmetry of hysteresis loops is more pronounced for the NiFe/FeMn nanocaps. These phenomena are ascribed to the spatial distributions of the constituent layer thickness and the local normal direction along the curved surface.

Structural transition and magnetic properties of evaporated Fe/Gd multilayers

Fe/Gd multilayers were prepared by alternate vapor deposition of pure Fe and Gd at a rate of 0.01–0.03 nm/s in an ultra-high-vacuum electron-gun evaporation system. The effects of the constituent metal layer thickness on the microstructures and magnetic properties of the films were investigated by low angle X-ray diffraction, transmission electron microscopy, and vibrating sample magnetometer. The experimental results show that a transition from the polycrystalline to amorphous state in the Fe layers occurs with the decrease of Fe layer thickness in the Fe/Gd multilayers. The saturation magnetization of the multilayers reduces significantly with decreasing Fe layer thickness and increasing Gd layer thickness. A superparamagnetic behavior at room temperature is observed for the [Fe(0.6 nm)/Gd(4.0 nm)] 15 multilayer due to the formation of discontinuous Fe layers.

Thickness and coupling effects in bilayered multiferroic CoFe2O4/Pb(Zr0.52Ti0.48)O3 thin films

Four CoFe2O4/Pb(Zr0.52Ti0.48)O3 (CFO/PZT) bilayered thin films with increasing PZT constituent layer thicknesses have been fabricated in order to investigate the optimized PZT layer thickness and the thickness effect on the magnetic and ferroelectric behaviors of the heterolayered multiferroic thin films. These heterostructured thin films were fabricated via a combined route of spin coating and rf sputtering. Both magnetic CFO and ferroelectric PZT phases were successfully retained in the heterostructured thin film. The improved saturation magnetization (Ms) of the CFO/PZT thin films has been observed and the enhancement increases with increasing PZT layer thickness. Both ferroelectric and dielectric measurements suggest the presence of interfacial space charge polarization arising from the ferroelectric/magnetic interface. Among the multiferroic thin films containing different PZT layer thicknesses fabricated, the thin film that consisted of six PZT constituent layers demonstrated the highest Ms value of 397 emu/cm3 and the best ferroelectric property with Pr and Ec of 29.91 μC/cm2 and 138.67 kV/cm, respectively, at 500 kV/cm, together with εr and tan δ values of 116.420 and 0.717, respectively, at 100 kHz. Investigation into its magnetoelectric effect demonstrated an αE,33 of 238 mV/cm Oe, which was measured by superimposing an ac magnetic field of 5 Oe at 5 kHz onto a dc magnetic field of 4.4 kOe.

The hard magnetic properties and microstructure evolution of the multilayer [NdFeBNbCu∕FeBSi]⋅n thin films

The influence of the thickness of constituent layers and annealing conditions for multilayer [NdFeBNbCu∕FeBSi]⋅n thin films on the magnetic properties and microstructure is reported. The Nb–Cu combination inhibits the grain growth and promotes the formation of nucleation sites. The FeSiB layer insertion leads to a slight increase in the Curie temperature and to a rectangular hysteresis loop. As compared to Ta∕NdFeBNbCu (540nm)∕Ta single layer, the Ta∕[NdFeBNbCu(180nm)∕FeBSi(15nm)]⋅3∕Ta multilayer nanocomposite films exhibit very good magnetic properties such as squareness Mr∕Ms of about 0.92, maximum energy product of about 397kJ∕m3, and an increase in the Curie temperature of about 17°C due to stratification by using FeBSi film as space layer.

Hysteretic behavior of angular dependence of exchange bias in FeNi∕FeMn bilayers: A new signature

As a new signature, the hysteretic behavior of angular dependence of exchange bias in FeNi∕FeMn bilayers is studied as function of the constituent layer thickness. When the FeMn layer is thin enough, there is no hysteretic behavior. When the FeMn layer thickness is increased, the hysteretic effect reaches a maximum sharply and then decreases slowly as the FeMn layer thickness is further increased. It is independent of the ferromagnet layer thickness. This new phenomenon implies a thermally driven evolution of the magnetic state in the antiferromagnet layer.