Integrated three-dimensional optical multilayer using free-space optics

An integrated three-dimensional optical multilayer system for optical data communications is presented. It is based on the use of free-space optical light propagation and combines two integration principles, namely, planar and stacked integration. The combination of both integration schemes aims at a maximal design flexibility for complex geometric layouts. On the other hand, packaging issues that stem from assembly and tolerance have to be considered. Here we describe the basic concept and demonstrate the implementation of an optical interface module in a processor-memory bus.     

Single and multilayer metamaterials fabricated by nanoimprint lithography

We demonstrate for the first time a fast and easy nanoimprint lithography (NIL) based stacking process of negative index structures like fishnet and Swiss-cross metamaterials. The process takes a few seconds, is cheap and produces three-dimensional (3D) negative index materials (NIMs) on a large area which is suitable for mass production. It can be performed on all common substrates even on flexible plastic foils. This work is therefore an important step toward novel and breakthrough applications of NIMs such as cloaking devices, perfect lenses and magnification of objects using NIM prisms. The optical properties of the fabricated samples were measured by means of transmission and reflection spectroscopy. From the measured data we retrieved the effective refractive index which is shown to be negative for a wavelength around 1.8 μm for the fishnet metamaterial while the Swiss-cross metamaterial samples show a distinct resonance at wavelength around 1.4 μm.     

Keystroke dynamics enabled authentication and identification using triboelectric nanogenerator array

Cyber security has become a serious concern as the internet penetrates every corner of our life over the last two decades. The rapidly developing human–machine interfacing calls for an effective and continuous authentication solution. Herein, we developed a two-factor, pressure-enhanced keystroke-dynamics-based security system that is capable of authenticating and even identifying users through their unique typing behavior. The system consists of a rationally designed triboelectric keystroke device that converts typing motions into analog electrical signals, and a support vector machine (SVM) algorithm-based software platform for user classification. This unconventional keystroke device is self-powered, stretchable and water/dust proof, which makes it highly mobile and applicable to versatile working environments. The promising application of this novel system in the financial and computing industry can push cyber security to the next level, where leaked passwords would possibly be of no concern.     

Layer by layer composite film of dimyristoyl-phosphatidylcoline and bacteriorhodopsin fabricated by multilayer molecular thin film method using fatty acid and lipid

A composite film of dimyristoyl-phosphatidylcoline (DMPC) and bacteriorhodopsin (BR) was fabricated by multilayer molecular thin film method using fatty acid and lipid on a quartz substrate or a hydrogenated amorphous silicon thin film. FTIR reflection absorption spectrums and UV absorption spectrums of the films were characterized on the detail of surface structure of the films. The spectroscopic data exhibited a specific layer by layer interaction of BR and environmental molecule DMPC above fatty acid. Especially, 4 layer composite LB films DMPC and BR exhibited an entirely different feature of IR reflection absorption spectrum depend on fatty acid species.     

Microwave based nanogenerator using the ratchet effect in Si/SiGe heterostructures

Ratchet based microwave current generators and detectors were developed in Si/SiGe heterostructures for wireless communication with the possibility of extending the detection limit to the terahertz range. A microwave induced ratchet current was generated in the two-dimensional electron gas by patterning an array of semicircular antidots in hexagonal geometry. The spatial asymmetry created by the semicircular antidots forces the electrons under the influence of the microwave electric field to move preferentially towards the direction of the semidisc axis. A photovoltage of the order of few millivolts was observed. Such a photovoltage was completely absent in a symmetric system consisting of circular antidots. The induced photovoltage increased monotonically with microwave power and was found to be independent of the microwave polarization. This device opens the possibility of employing silicon based heterostructures for nanogenerators and other wireless communication devices using microwaves.     

Phosphopeptide enrichment using MALDI plates modified with high-capacity polymer brushes

Matrix-assisted laser desorption/ionization plates coated with poly(2-hydroxyethyl methacrylate) (PHEMA) brushes that are derivatized with Fe(III)-nitrilotriacetate (NTA) complexes allow selective, efficient phosphopeptide enrichment prior to analysis by mass spectrometry (MS). Fe(III)-NTA-PHEMA brushes (60 nm thick) have a phosphopeptide binding capacity of 0.6 microg/cm(2) and exhibit phosphopeptide recoveries of over 70%, whereas much thinner polymer films containing Fe(III)-NTA afford a recovery of only 20%, and a monolayer of Fe(III)-NTA shows a recovery of just 10%. Recoveries are determined by comparing signals from enriched unlabeled phosphopeptides with those of their deuterium-labeled analogues that were added to the plate just prior to addition of matrix. Mass spectra of phosphopeptide-containing samples enriched using Fe(III)-NTA-PHEMA-modified plates also demonstrate higher recoveries or fewer interfering peaks than corresponding spectra obtained with enrichment using several commercially available Fe(III)-containing films and resins or metal oxide materials. When analyzing tryptic digests of beta-casein, the Fe(III)-NTA-PHEMA brushes allow detection of as little as 15 fmol of phosphopeptide. Moreover, with both ovalbumin and beta-casein digests, phosphopeptide signals dominate the mass spectra obtained using these modified plates.     

Enhancement of charge-transport characteristics in polymeric films using polymer brushes

We show that charge-transporting polymer chains in the brush conformation can be synthesized from a variety of substrates of interest, displaying a high degree of stretching and showing up to a 3 orders of magnitude increase in current density normal to the substrate as compared with a spin-coated film. These nanostructured polymeric films may prove to be suitable for electronic devices based on molecular semiconductors as current fabrication techniques often provide little control over film structure.     

Improving efficiency of organic light-emitting diodes fabricated utilizing AZO/Ag/AZO multilayer electrode

Multilayer transparent electrode based on Al-doped zinc oxide (AZO)/Ag/Al-doped zinc oxide (AZO) was fabricated by sputtering, and a green organic light-emitting diode (OLED) device utilizing AZO/Ag/AZO as anode was fabricated. The AZO/Ag/AZO multilayer film exhibited superior square resistance and optical transmittance to those of commercial indium tin oxide (ITO). In comparison with the green OLEDs based on ITO and pure AZO anode, the green OLED based on AZO/Ag/AZO showed the highest light-emitting efficiency. The results indicate that AZO/Ag/AZO multilayer electrodes are a promising low-cost, low-toxic and low-temperature processing electrode scheme for OLED application.     

Longitudinal-bending mode micromotor using multilayer piezoelectric actuator

Longitudinal-bending mode ultrasonic motors with a diameter of 3 mm were fabricated using stacked multilayer piezoelectric actuators, which were self-developed from hard lead zirconate titanate (PZT) ceramic. A bending vibration was converted from a longitudinal vibration with a longitudinal-bending coupler. The motors could be bidirectionally operated by changing driving frequency. Their starting and braking torque were analyzed based on the transient velocity response. With a load of moment of inertia 2.5 x 10(-7) kgm2, the motor showed a maximum starting torque of 127.5 microNm. The braking torque proved to be a constant independent on the motor's driving conditions and was roughly equivalent to the maximum starting torque achievable with our micromotors.     

Synthesis of Ga-doped ZnO nanorods using an aqueous solution method for a piezoelectric nanogenerator

Mechanical energy is a potential energy source for self-powered electronic devices. Due to their unique semiconducting and piezoelectric properties, wurtzite-structured nanomaterials have been considered as potential candidates for piezoelectric nanogenerators that convert mechanical energy into electricity. In the present work, we report on the growth of Ga-doped ZnO (GZO) nanorods and investigate the performance of nanogenerators fabricated from undoped ZnO (UZO) nanorods, low Ga-doped ZnO (LGZO) nanorods, and high Ga-doped ZnO (HGZO) nanorods. A nanogenerator integrated with LGZO nanorods exhibited a current density of 1.2 microA/cm2, an enhancement over the 0.4 microA/cm2 and 0.7 microA/cm2 current densities of nanogenerators integrated with UZO and HGZO nanorods, respectively.     

Modelling of multilayer films using spectroscopic ellipsometry

A systematic investigation of the ellipsometric parameters of MBE-grown heterostructures of ln_xGa_1–x As on GaAs substrate has been completed. The index of refraction n, and extinction coefficient, k, values of the above heterostructure in the wavelength range 500–800 nm, are presented, a region of interest in many applications. A model has been proposed for the multilayered structures, through which the thickness of the oxide layer can be determined and the observed optical characteristics of these heterostructures explained. The validity of the model was established by the excellent agreement between the measured and calculated values of the ellipsometric parameters and .     

Biological characteristic effects of human dental pulp stem cells on poly-ε-caprolactone-biphasic calcium phosphate fabricated scaffolds using modified melt stretching and multilayer deposition

Craniofacial bone defects such as alveolar cleft affect the esthetics and functions that need bone reconstruction. The advanced techniques of biomaterials combined with stem cells have been a challenging role for maxillofacial surgeons and scientists. PCL-coated biphasic calcium phosphate (PCL-BCP) scaffolds were created with the modified melt stretching and multilayer deposition (mMSMD) technique and merged with human dental pulp stem cells (hDPSCs) to fulfill the component of tissue engineering for bone substitution. In the present study, the objective was to test the biocompatibility and biofunctionalities that included cell proliferation, cell viability, alkaline phosphatase activity, osteocalcin, alizarin red staining for mineralization, and histological analysis. The results showed that mMSMD PCL-BCP scaffolds were suitable for hDPSCs viability since the cells attached and spread onto the scaffold. Furthermore, the constructs of induced hDPSCs and scaffolds performed ALP activity and produced osteocalcin and mineralized nodules. The results indicated that mMSMD PCL-BCP scaffolds with hDPSCs showed promise in bone regeneration for treatment of osseous defects.     

a-Si:H/SiO2 multilayer films fabricated by radio-frequency magnetron sputtering for optical filters

We examined the optical properties of a-Si:H/SiO2 multilayer films fabricated by radio-frequency magnetron sputtering for optical bandpass filters (BPFs). Because of the high refractive-index contrast between a-Si:H and SiO2, the total number of layers of an a-Si:H/SiO2 multilayer can be relatively small. We obtained an a-Si:H refractive index of 3.6 at lambda = 1550 nm and its extinction coefficient k < 1 x 10(-4) and confirmed by Fourier-transform infrared spectroscopy that such small k is influenced by the Si-H bonding in the film. We fabricated a-Si:H/SiO2 BPFs by using in situ optical monitoring. Thermal tuning of a-Si:H/SiO2 BPF upon a silica substrate was also performed, and a thermal tunability coefficient of 0.07 nm/degree C was obtained.     

Probing the responsive behavior of polyelectrolyte brushes using electrochemical impedance spectroscopy

Cyclic voltammetry and impedance spectroscopy were employed to probe the responsive properties of polyelectrolyte brushes. Poly[(dimethylamino)ethyl methacrylate] (PDMAEMA) brushes over 100 nm thick on gold substrates were synthesized via surface-initiated atom-transfer radical polymerization and quaternized with methane iodide to obtain cationic brushes (Q-PDMAEMA). Q-PDMAEMA brushes respond to electrolytes by exhibiting swollen and collapsed states. Swollen brushes allow good permeability of electroactive probes, while collapsed states block electron transport. Electrolytes have different impacts on the electrochemical properties of Q-PDMAEMA. Some salts (NaNO3) cause brush collapse due to charge screening, while others such as those with more hydrophobic anions (ClO4-, PF6-, and Tf2N-) induce brush collapse because of solubility changes. The collapsed brushes exhibit intrinsically different resistance as probed with impedance. Charged screened brushes retain good permeability to electroactive probes. Strongly coordinating hydrophobic anions lead to insoluble brushes, resulting in a high resistance. These results show that electrochemical impedance spectroscopy is a powerful technique to probe the properties and structure of polyelectrolyte brushes.     

基于SVR的脉冲激光沉积TiN/AlN多层薄膜的工艺优化

根据脉冲激光沉积(PLD)法在单晶Si试样表面沉积制备多层TiN/AlN硬质膜实验数据,应用基于粒子群算法(PSO)寻优的支持向量回归(SVR)方法,建立不同工艺参数下沉积的TiN/AlN多层膜的AlN膜厚及TiN薄膜硬度的SVR预测模型。在相同的训练与测试样本集下,将SVR所得的AlN膜厚预测值与免疫径向基函数(IRBF)神经网络的计算结果进行比较。结果表明,SVR模型训练和预测结果的平均绝对百分误差要比IRBFNN模型的小,其预测精度更高,预测效果更好。应用SVR的TiN薄膜硬度模型对PLD法沉积TiN薄膜的工艺参数进行了优化,分析了多因素对PLD法沉积TiN薄膜硬度的交互作用和影响。该方法可为人们利用PLD法沉积TiN/AlN多层功能薄膜提供科学的理论指导,具有重要的理论意义和实用价值。     

Characterization of FGM monomorph actuators fabricated using EPD

Piezoelectric FGM monomorph actuators fabricated using electrophoretic deposition (EPD) were investigated. Both the physical and electromechanical properties were examined. The high voltage performance of the actuator in both static and dynamic state was focused. It was found that the monomorph exhibits tetragonal phase perovskite structure and the gradient variation of microstructure was observed over the cross section. The displacement keeps a wide range of linearity in the static state. In the dynamic state, the vibration displacement is both frequency and voltage dependent. The resonant frequency shifts to lower frequency range due to the higher vibration loss at higher voltages. This results in the frequency dependence of the vibration limitations. The vibration limitation is also voltage dependent. Above a cutoff voltage, the displacement may not increase. To obtain a higher resonant displacement or velocity, the frequency and voltage should match well. Temperature rise or heat generation is caused by vibration loss. The maximum temperature happens at the clamped end of the monomorph.     

Nanoporous silica membranes fabricated using multiwalled carbon nanotubes

Nanoporous silica membranes were fabricated using 3-aminopropyltriethoxysilane (APS) and acyl chloride-functionalized multiwalled carbon nanotubes (MWCNTs). The amine groups of silane reacted with the functional groups (e.g., acid chloride) that were attached to the sidewall of the MWCNTs. The APS that was grafted to the sidewall of the MWCNTs was polymerized in order to coat the MWCNTs wall through heating. The thickness of the silica layer on the surface of the MWCNTs was controlled by adjusting the growth time of the SiO2 layer. Approximately 20 nm-sized pores were formed through the removal of the MWCNTs using a simple thermal process, but some traces of the MWCNTs still remained. The porous properties of the nanoporous silica membrane were analyzed from the nitrogen adsorption-desorption isotherms that were obtained using a surface area and porosimetry analyzer. The structure and composition of the silane-modified MWCNTs were characterized using scanning electron microscopy, energy dispersive spectroscopy and transmission electron microscopy.     

Modeling of piezoelectric multilayer ceramics using finite elementanalysis

For medical ultrasound imaging, 2-D array transducers have greater versatility than linear arrays. Unfortunately, the tiny array elements in a 2-D array have poor signal-to-noise ratio (SNR). We have previously shown that SNR is increased in 2-D array transducers made from piezoelectric multilayer ceramics. Conventional one-dimensional models provide accurate results when comparing multilayer ceramic performance relative to single layer transducers. However, these models are not accurate when comparing simulations directly to measurements. Because multilayer ceramics have a complex structure, a 3-D model, such as finite element analysis, is needed for accurate simulations. We modeled four arrays that were previously fabricated: a single layer and multilayer 1 MHz, 2-D array element, and a single layer and multilayer 2.25 MHz, 1.5-D array element that can focus and steer in azimuth but only steer in the elevation dimension. We compared the simulated and measured impedance plots for each transducer. The finite element analysis plots accurately predicted the impedance for each vibration mode. On the other hand, the one dimensional KLM transmission line model could simulate only the thickness mode vibrations and the results were inaccurate compared to measurements. We also simulated the transmit output pressure for the 2.25 MHz arrays and compared the results to measurements. The simulated pressure vs. time plots and their spectra were accurate when compared to measurements. Finally, we obtained a series of images that show the impulse response vibrations for the 2.25 MHz, arrays. These animations show the vibration modes in the complex multilayer ceramic structure. Measurements were not available to confirm the animations. Our results show that finite element analysis in three dimensions is a valuable tool to predict the performance of multi-layer transducers