Multiple Layer Structures Research Articles

Varifocal augmented reality adopting electrically tunable uniaxial plane-parallel plates.

Vergence-accommodation conflict (VAC) is a major challenge in optical-see through augmented reality (AR) system. To resolve this conflict, many approaches are proposed, for instance, by means of adjustment of the projected virtual image to coincide with the surroundings, called image registration, which is more often referred to as varifocal function. In this paper, a varifocal AR system is demonstrated by adopting electrically tunable liquid crystal (LC) plane-parallel plates to solve VAC problem. The LC plates provide electrically tunable optical paths when the directors of LC molecules are re-orientated with applied voltages, which leads to a corresponding change of light speed for an extraordinary wave. To provide a sufficient tunable optical path, three pieces of multiple-layered LC structures are used with the total thickness of the active LC layers (∼510 μm). In experiments, the projected virtual image can be adjusted from 1.4 m to 2.1 m away from the AR system, while the thickness of LC plane-parallel plates are only less than 3 mm without any mechanical moving part. When light propagates in the uniaxial LC layers, the wave vector and the Poynting vector are different. The longitudinal displacement of the image plane is determined by Poynting vectors rather than wave vectors. As a result, the analysis of the AR system should be based on Poynting vectors during geometrical optical analysis. Surprisingly, the tunable range of the longitudinal displacement of Poynting vectors is 2-fold larger than the tunable range of the wave vectors. Moreover, the virtual image shifts in opposite directions with respect to the Poynting vectors and wave vectors. The proposed AR system is not only simple but also thin, and it exhibits a large clear aperture. The investigation here paves the way to a simple solution of the VAC problem for augmented reality systems.

Facilitating supercritical CO2 assisted exfoliation of graphene nanoplatelets with the polymer matrix

The currently mass-produced graphene materials are typically graphene nanoplatelets (GnPs) with multiple-layer structures the properties of which are not comparable to those of mono-layer or few-layer graphene. In this work, high concentrations of commercial GnPs (15 wt% with potential to be higher) were effectively exfoliated in polypropylene (PP)/GnP nanocomposites using supercritical CO2 (sc-CO2) in a foaming process. It was shown that the exfoliation of GnPs was increased with an increased expansion ratio in the foaming window of PP/GnP (159–163 °C). However, a high degree of GnP exfoliation can be maintained at elevated temperatures (e.g., 200 °C) with minimized expansion ratios (<1.3), indicating gas expansion inside GnPs is the main mechanism for graphene delamination during foaming. The electrical conductivity of the solid PP/15 wt%-GnP was increased by almost 5 orders of magnitude after sc-CO2 treatment. The foaming pressure was shown to have a critical influence on GnP exfoliation, and the pressure threshold to delaminate graphene layers was significantly reduced in the presence of PP matrix, as compared to GnP powder. The results were attributed to PP chain penetration into GnP under sc-CO2, and the prevention of rapid loss of intercalating CO2 by the PP molecules surrounding the GnPs during the pressure release step. This study opens up a new potential avenue for developing highly exfoliated and versatile polymer/graphene solid nanocomposites using supercritical fluid treatment.

Ruggedized Chip-Based Lipid Bilayer Arrays with Permeable multi-MAC Support

Planar lipid bilayers play a central role in nanopore sensing and ion-channel electrophysiology. However, bilayer fragility often limits their application. Previously, we enhanced the mechanical properties of planar lipid bilayers with a single-layered, molecularly thin, minimal actin cortex (MAC). To further increase bilayer robustness, we are developing multiple layered MAC structures (multi-MACs) that can be chemically cross-linked to arbitrary thicknesses, without blocking diffusive access to the outer leaflet of the bilayer. In this work, we describe the multi-MAC formation process in the context of a bilayer array on a fluidic chip, as well as on glass supported bilayers. We report on permeability tests at both the single-molecule and macroscopic levels that show multi-MACs do not significantly block access to the bilayer. We discuss how permeability is achieved by controlling the openness of the F-actin network, which can be tailored using the density of linkage sites, the electrostatic interactions between linkers and filaments, and specific F-actin growth and deposition techniques. We also present results from single-molecule electrical and optical measurements that characterize the multi-MAC structure, permeability, and the approximate pore size of the multi-layered network.

A wideband triple-layer microperforated panel sound absorber

Microperforated panels are light, clean and tunable sound absorbers, which fundamentals were already established in the previous century. They consist of a distribution of minute holes of diameter d on a panel of thickness t with perforation ratio ϕ in front of an air layer of thickness D. Therefore, the frequency band of absorption of a single-layer microperforated panel depends on (d, t, ϕ, D). In noise control applications, such a simple structure provides absorption in the frequency range of interest if holes are of sub-millimetric diameter. The former single-layer microperforated panels had two main weaknesses: narrow frequency band of absorption and a high manufacturing cost. However, nowadays these deficiencies can be easily surpassed. The absorption frequency band can be drastically increased by means of multiple-layer structures. The manufacturing cost may be reduced with the application of techniques currently used in the advanced circuitry industry. This is illustrated by the design of a triple-layer microperforated panel yielding absorption in almost four and a half octaves. The parameters of the triple-layer microperforated panel are optimised by Simulated Annealing to provide maximum absorption within a prescribed frequency band.

Single-Crystalline Si1−xGex (x = 0.5~1) Thin Films on Si (001) with Low Threading Dislocation Density Prepared by Low Temperature Molecular Beam Epitaxy

Single-crystalline Si1−xGex thin films on Si (100) with low threading dislocation density (TDD) are highly desired for semiconductor industrials. It is challenging to suppress the TDD since there is a large mismatch (4.2%) between Ge and Si—it typically needs 106–107/cm2 TDD for strain relaxation, which could, however, cause device leakage under high voltage. Here, we grew Si1−xGex (x = 0.5–1) films on Si (001) by low temperature molecular beam epitaxy (LT-MBE) at 200 °C, which is much lower than the typical temperature of 450–600 °C. Encouragingly, the Si1−xGex thin films grown by LT-MBE have shown a dramatically reduced TDD down to the 103–104/cm2 level. Using transmission electron microscopy (TEM) with atomic resolution, we discovered a non-typical strain relaxation mechanism for epitaxial films grown by LT-MBE. There are multiple-layered structures being introduced along out-of-plane-direction during film growth, effectively relaxing the large strain through local shearing and subsequently leading to an order of magnitude lower TDD. We presented a model for the non-typical strain relaxation mechanism for Si1−xGex films grown on Si (001) by LT-MBE.

Microstructures and mechanical properties of Ti3Al/Ni-based superalloy joints brazed with AuNi filler metal

For the purpose of high-temperature service and the weight reduction in aviation engineering applications, the dissimilar joining of Ti3Al-based alloy to Ni-based superalloy (GH536) was conducted using Au-17.5Ni (wt%) brazing filler metal. The microstructure and chemical composition at the interfaces were investigated by scanning electron microscope, X-ray diffraction and transmission electron microscope. The diffusion behaviors of elements were analyzed as well. The results indicated that the Ti3Al/GH536 joint microstructure was characterized by multiple layer structures. Element Ni from Au-Ni filler metal reacted with Ti3Al base metal, leading to the formation of AlNi2Ti and NiTi compounds. Element Ni from Ti3Al base metal reacted with Ni and thus Ni3Nb phase was detected in the joint central area. Due to the dissolution of Ni-based superalloy, (Ni,Au) solid solution ((Ni,Au)ss) and Ni-rich phase were visible adjacent to the superalloy side. The average tensile strength of all the joints brazed at 1253 K for 5–20 min was above 356 MPa at room-temperature. In particular, the joints brazed at 1253 K/15 min presented the maximum tensile strength of 434 MPa at room-temperature, and the strength of 314 MPa was maintained at 923 K. AlNi2Ti compound resulted in the highest hardness area and the fracture of the samples subjected to the tensile test mainly occurred in this zone.

Role of sheath dynamics in multiple double layer formations in expanding RF plasma

Potential double layers are observed to form as nested cylindrical sheaths that energize charge particles in the absence of any externally applied magnetic field. These visibly glowing nested cylindrical sheaths are named as “Fire Tube” in the present work. Sheaths, in unmagnetized collisionless plasmas, have been observed to be functional in generating energetic charge particles. Two characteristically different plasma sources are compared in terms of the dependence of potential and density profiles on the plasma sheath formations near the source boundary. The sheath structures, complex fire tube formation, and space charge formations demarcate the two sources in terms of complex structure formations and motion of the charge particles. We present here the characteristic study of high pressure collisional boundary sheath formations through systematic experiments carried out during the transition from unmagnetized to magnetized charge particles, in the case of two different plasma sources designed. The cylindrical ambient plasma sheaths are observed to energize the charge particles, in the absence of any external magnetic field. The fire tube formations essentially represent a non-neutral region located radially away from the plasma source boundary, connecting the ion sheath with the electron sheath. The probe diagnostic results suggest a significant role of energetic electrons in the formation of multiple double layer structures in the present operational regime. Generation of nonthermal electrons during the formation of MDL in radio frequency capacitive discharges is subjected to interactions of the plasma with the electrodes as well as the confining wall material.

A Hybrid Non-destructive Measuring Method of Three-dimensional Profile of Through Silicon Vias for Realization of Smart Devices

Smart devices have been fabricated based on design concept of multiple layer structures which require through silicon vias to transfer electric signals between stacked layers. Because even a single defect leads to fail of the packaged devices, the dimensions of the through silicon vias are needed to be measured through whole sampling inspection process. For that, a novel hybrid optical probe working based on optical interferometry, confocal microscopy and optical microscopy was proposed and realized for enhancing inspection efficiency in this report. The optical microscope was utilized for coarsely monitoring the specimen in a large field of view, and the other methods of interferometry and confocal microscopy were used to measure dimensions of small features with high speed by eliminating time-consuming process of the vertical scanning. Owing to the importance of the reliability, the uncertainty evaluation of the proposed method was fulfilled, which offers a practical example for estimating the performance of inspection machines operating with numerous principles at semiconductor manufacturing sites. According to the measurement results, the mean values of the diameter and depth were 40.420 µm and 5.954 µm with the expanded uncertainty of 0.050 µm (k = 2) and 0.208 µm (k = 2), respectively.

Spray Pyrolysis Technique; High-K Dielectric Films and Luminescent Materials: A Review.

The spray pyrolysis technique has been extensively used to synthesize materials for a wide variety of applications such as micro and sub-micrometer dimension MOSFET´s for integrated circuits technology, light emitting devices for displays, and solid-state lighting, planar waveguides and other multilayer structure devices for photonics. This technique is an atmospheric pressure chemical synthesis of materials, in which a precursor solution of chemical compounds in the proper solvent is sprayed and converted into powders or films through a pyrolysis process. The most common ways to generate the aerosol for the spraying process are by pneumatic and ultrasonic systems. The synthesis parameters are usually optimized for the materials optical, structural, electric and mechanical characteristics required. There are several reviews of the research efforts in which spray pyrolysis and the processes involved have been described in detail. This review is intended to focus on research work developed with this technique in relation to high-K dielectric and luminescent materials in the form of coatings and powders as well as multiple layered structures.

Preparation and Characterization of Sugar-Assisted Cross-Linked Enzyme Aggregates (CLEAs) of Recombinant Cellobiose 2-epimerase from Caldicellulosiruptor saccharolyticus ( CsCE).

High-efficiency lactulose-producing enzyme of Caldicellulosiruptor saccharolyticus cellobiose 2-epimerase (WT- CsCE) was immobilized in the form of cross-linked enzyme aggregates (CLEAs). Conditions for enzyme aggregation and cross-linking were optimized, and a sugar-assisted strategy with less damage to enzyme secondary structures was developed to improve the activity yield of CLEAs up to approximately 65%. The resulting CLEAs with multiple-layer network structures exhibited an enlarged optimal temperature range (70-80 °C) and maintained higher activity at 50-90 °C. Besides, CLEAs retained more than 95% of their initial activity after 10 successive batches at 60 °C, demonstrating superior reusability. Moreover, CLEAs displayed an equivalent or higher catalytic ability to free WT- CsCE in lactulose biosynthesis, and the final sugar ratios were similar, lactulose 58.8-61.7%, epilactose 9.3-10.2%, and lactose 27.8-30%, with a constant isomerization selectivity of 0.84-0.87 regardless of enzymes used and temperature applied. The proposed strategy is the first trial for enzymatic synthesis of lactulose catalyzed by CLEAs of WT- CsCE.

Hyperspectral unmixing via deep matrix factorization

Hyperspectral unmixing is one of the most important techniques in hyperspectral remote sensing image analysis. During the past decades, many models have been widely used in hyperspectral unmixing, such as nonnegative matrix factorization (NMF) model, sparse regression model, etc. Most recently, a new matrix factorization model, deep matrix, is proposed and shows good performance in face recognition area. In this paper, we introduce the deep matrix factorization (DMF) for hyperspectral unmixing. In this method, the DMF method is applied for hyperspectral unmixing. Compared with the traditional NMF-based unmixing methods, DMF could extract more information with multiple-layer structures. An optimization algorithm is also proposed for DMF with two designed processes. Results on both synthetic and real data have validated the effectiveness of this method, and shown that it has outperformed several state-of-the-art unmixing approaches.

Optical Hall effect-model description: tutorial.

The optical Hall effect is a physical phenomenon that describes the occurrence of magnetic-field-induced dielectric displacement at optical wavelengths, transverse and longitudinal to the incident electric field, and analogous to the static electrical Hall effect. The electrical Hall effect and certain cases of the optical Hall effect observations can be explained by extensions of the classic Drude model for the transport of electrons in metals. The optical Hall effect is most useful for characterization of electrical properties in semiconductors. Among many advantages, while the optical Hall effect dispenses with the need of electrical contacts, electrical material properties such as effective mass and mobility parameters, including their anisotropy as well as carrier type and density, can be determined from the optical Hall effect. Measurement of the optical Hall effect can be performed within the concept of generalized ellipsometry at an oblique angle of incidence. In this paper, we review and discuss physical model equations, which can be used to calculate the optical Hall effect in single- and multiple-layered structures of semiconductor materials. We define the optical Hall effect dielectric function tensor, demonstrate diagonalization approaches, and show requirements for the optical Hall effect tensor from energy conservation. We discuss both continuum and quantum approaches, and we provide a brief description of the generalized ellipsometry concept, the Mueller matrix calculus, and a 4×4 matrix algebra to calculate data accessible by experiment. In a follow-up paper, we will discuss strategies and approaches for experimental data acquisition and analysis.

Multilayer supercapacitor threads for woven flexible circuits

Purpose – Wearable electronic devices have emerged which require compact, flexible power storage devices such as batteries and supercapacitors. Recently, energy storage devices have been developed based on supercapacitor threads. However, current supercapacitor energy storage threads which use electrolytes based on aqueous gels have a 1 V potential window. This is much lower than the voltage required by most electronic devices. This current contribution presents an approach for fabricating a multilayer supercapacitor working as a circuit unit, in which series combinations of the multiple layer structures can achieve a higher potential window, which can better meet the needs of wearable electronic devices. Design/methodology/approach – Two-capacitive layer thread supercapacitors were fabricated using a semi-automatic dip coating method by coating two capacitive layers sequentially on a 50 μm stainless steel core wire, each capacitive layer includes ink, aqueous-based gel electrolyte and silver conductive paint layers. Findings – Two capacitive layers of the single thread supercapacitor can work independently, or as combination circuits – parallel and series. Cyclic voltammograms showed that all flexible circuits have high electrochemical stability. For the case of series circuit configuration, with H3PO-polyvinyl alcohol (PVA) gel electrolyte, a working potential window of 2 V was achieved. Originality/value – A flexible single thread supercapacitor of multilayer structure, with working voltage above 1 V in H3PO4-PVA gel electrolyte, has not been reported before. A semi-automatic dip coating setup used to process the thread supercapacitor has high potential for transfer to an industrial environment for mass production.

Case study on complex sporadic E layers observed by GPS radio occultations

Abstract. The occurrence of sporadic E (Es) layers has been a hot scientific topic for a long time. The GNSS (global navigation satellite system)-based radio occultation (RO) has proven to be a powerful technique for detecting the global Es layers. In this paper, we focus on some cases of complex Es layers based on the RO data from multiple missions processed in UCAR/CDAAC (University Corporation for Atmospheric Research (UCAR) the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) Data Analysis and Archive Center (CDAAC)). We first show some examples of multiple Es layers occurred in one RO event. Based on the evaluations between colocated simultaneous RO events and between RO and lidar observations, it could be concluded that some of these do manifest the multiple Es layer structures. We then show a case of the occurrence of Es in a broad region during a certain time interval. The result is then validated by independent ionosondes observations. It is possible to explain these complex Es structures using the popular wind shear theory. We could map the global Es occurrence routinely in the near future, given that more RO data will be available. Further statistical studies will enhance our understanding of the Es mechanism. The understanding of Es should benefit both Es-based long-distance communication and accurate neutral RO retrievals.

Ultrasonic imaging of seismic physical models using a phase-shifted fiber Bragg grating.

We report what is to our knowledge the first ultrasonic imaging of seismic physical models by using a phase-shifted fiber Bragg grating (PS-FBG). Seismic models, which consist of multiple layer structures, were immersed in water. Piezoelectric (PZT) transducer was used to generate ultrasonic waves and a PS-FBG as a receiver. Two-dimensional (2D) ultrasonic images were reconstructed by scanning the PS-FBG with a high-precision position scanning device. In order to suppress the low-frequency drift of the Bragg wavelength during scanning, a tight wavelength tracking method was employed to lock the laser to the PS-FBG resonance in its reflection bandgap. The ultrasonic images captured by the PS-FBG have been compared with the images obtained by the geophysical imaging system, Sinopec, demonstrating the feasibility of our PS-FBG based imaging system in seismic modeling studies.

Electrical and Thermoelectric Performance of 2D Layered Materials: Atomic Simulation Study

The demand for alternative and renewable energy has been increasing globally over the years as the world faces fuel shortage crisis. To solve this crucial challenge to the society, thermoelectric materials have received growing attention as they can generate electricity from waste heat and conversely create a temperature difference when voltage gradient is applied. The thermoelectric power generation, cooling and heating applications are based on solid-state devices with no moving parts which leave the material characteristics as the measurement of the efficiency, which is the dimensionless thermoelectric figure of merit, ZT = S2σT/κ, where S, σ, T and κ are the Seebeck coefficient, electrical conductivity, absolute temperature and thermal conductivity, respectively. The difficulty of optimization of ZT lies in the fact the above parameters are generally interdependent. For example, σ is proportional to n/m*, where n and m* are the carrier concentration and effective mass respectively, while S is proportional to m*/n2/3and κ is proportional to σ; hence traditional materials with larger σ normally have smaller S and larger κ. Therefore, it is a challenge to develop advanced thermoelectric materials with optimization of these conflicting properties to increase ZT.One way to increase ZT is using low-dimensional materials systems, such as quantum wells, quantum wires and quantum dots. [1] All these structures lead the thermoelectric ZT to be significantly improved because of the quantum confinement effects to enhance power factor S2σ, and concurrently remain the thermal conductivity low. For an example, experiments have been conducted by two groups of researchers that prove silicon nanowires are efficient thermoelectric materials due to the suppression of phonon conductivity by surface roughness. [2,3] Among these many materials studied, two-dimensional material, such as graphene related materials, MoS2, etc., have been extensively studied and generated considerable interesting due to their unique electronic, optoelectronic, and phononic properties. For example, cutting the different edge and shape of graphene to form various nanoribbons can significantly change their electron and phonon transport behaviors indicating the capability of controlling the thermoelectric performance. [4] In this work, therefore, I shall firstly give the introduction to fundamental understanding of electron and phonon transport in the nanoscale materials using quantum transport and ballistic transport theories. Next, I will discuss the fundamentals of material properties of these advanced 2D materials including graphene and beyond graphene, such as transition metal dichalcogenides (TMDs) with single layered and multiple layered structures. Interestingly, the results show that two layered WSe2 has the best ZT compared to the different layered WSe2 and MoS2due to its unique electronic bandstructure. [5,6] However, for practical applications, defect and structure engineering may be needed to improve ZT significantly. [4,7]AcknowledgementI will like to thank my collaborators, Wen Huang, Xin Luo, Chee Kwan Gan, Su Ying Quek, Xiaoxi Ni, Baowen Li, and Jian-Sheng Wang, for their contributions in this work.Reference[1] G. Chen, M. S. Dresselhaus, G. Dresselhaus, J. P. Fleurial, and T. Caillat, Int. Mater. Rev. 48, 45 (2003).[2] A. I. Boukai, Y. Bunimovich, J. T. Kheli, J. K. Yu, W. A. Goddard, and J. R. Heath, Nature 451, 168 (2008).[3] A. I. Hochbaum, R. K. Chen, R. D. Delgado, W. J. Liang, E. C. Garnett, M. Najarian, A. Majumdar, and P. D. Yang, Nature 451, 163 (2008).[4] W. Huang, J. Wang, and G. Liang, “Phys. Rev. B 84, 045410 (2011).[5] W. Huang, H. Da, and G. Liang, Journal of Applied Physics 113, 104304, (2013).[6] W. Huang, X. Luo, C. Gan, S. Quek, and G. Liang, submitted for publsication.[7] X. Ni, G. Liang, J. Wang, and B. Li, Appl. Phys. Lett. 95, 192114, (2009).

Reflection and Absorption of the Medium with Gradient Change of Impedance

The medium with gradient change of acoustic impedance is a new acoustic structure which developed from multiple layer structures. In this paper, the inclusion is introduced and a new set of equations is developed. It can obtain better acoustic properties based on the medium with gradient change of acoustic impedance. Theoretical formulation has been systematically addressed which demonstrates how the idea of utilizing this method. The sound reflection and absorption coefficients were obtained. At last, the validity and the correctness of this method are assessed by simulations. The results show that appropriate design of parameters of the medium can improve underwater acoustic properties.

Self-consistent surface charges and electric field in p-i-n tunneling transit-time diodes based on single- and multiple-layer graphene structures

We develop a device model for p-i-n tunneling transit-time diodes based on graphene single- and multiple-layer structures operating at the reverse bias voltages. The model of the graphene tunneling transit-time diode (GTUNNETT) accounts for the features of the interband tunneling generation of electrons and holes and their ballistic transport in the device i-section, as well as the effect of the self-consistent electric field associated with the self-consistent charges of propagating electrons and holes. Using the developed model, we calculate the dc current-voltage characteristics and the ac frequency-dependent admittance as functions of the GTUNNETT structural parameters, in particular, the number of graphene layers.

Mechanical Behaviors of Wire-woven Metals Composed of Two Different Thickness of Wires

Wire-weaving is virtually only a practical method to fabricate multi-layered truss type cellular metals, except for stacking multiple single layered structures. To date, the wire-woven metals have been fabricated of wires of a uniform thickness. In this work, variations of wire-woven metals fabricated of two different thickness wires in out-of-plane and in-plane directions are introduced. The mechanical properties subjected to compressive or shear loading are investigated.

Mold Pattern Fabrication by Nanoscratching

MEMS technologies for various nano/micro-devices often requires special facilities and complicated,multistage processes. The fabrication cost is thus extremely high. Consequently, alternative solutions have been sought, and NanoImprint Lithography (NIL) is one of the potential solutions. To date, the nano/micromolds for NIL are mainly fabricated using photolithography or focused ion beams. However, such beam methods generally make use of special instruments and require a long time to draw precise patterns. Thus, this study aims to fabricate nanoscale structures on monocrystalline silicon substrates using nanoscratching, which can potentially be used to fabricate nano/micro-molds for NIL. This paper discusses how various nano/micro-scale structures such as lineand-space, single-layer, and multiple-layer structures were fabricated on a silicon substrate using nanoscratching by an atomic force microscope equipped with a sharp probe made of monocrystalline diamond. Subsequent chemical etching was also conducted on the fabricated groove patterns to enlarge the depth of the fabricated groove patterns. The results confirmed that the groove was deepened several times, with only a slight increase in its width. A nanoimprint experiment was also carried out, and the line-and-space patterns were duplicated successfully on a polycarbonate resin film.