Two-layer Research Articles

Noise Spectroscopy of Transport and Ion‐Related Phenomena in Silicon Nanowire Field‐Effect Transistor Biosensors

AbstractHigh‐quality, liquid‐gated two‐layer (TL) nanowire (NW) field‐effect transistor (FET) structures are fabricated and studied in different operation regimes and with different concentrations of MgCl2 solutions. The space‐charge‐limited current (SCLC) effect is sensitive to surface phenomena and is registered at the drain‐source voltage (VDS) above 0.14 V, and analyzed using several methods including noise spectroscopy. Noise spectra reflect the clear transformation from 1/f to 1/ (f in power 1.5) behavior, confirming the SCLC effect, which is sensitive to ion processes at the NW FET surface. Moreover, the dimensionless Hooge parameters, measured at a level of 10−3, reflect the high quality of the fabricated devices and demonstrate the suppression of noise with VDS increasing up to 0.48 V. Such behavior additionally confirms the SCLC effect in the NW channel. The effect of suppression is stronger for small concentrations of MgCl2 solutions. The results should be taken into account for the detection of very small signals in biochemical solutions.

Air–sea exchange of acetone, acetaldehyde, DMS and isoprene at a UK coastal site

Abstract. Volatile organic compounds (VOCs) are ubiquitous in the atmosphere and are important for atmospheric chemistry. Large uncertainties remain in the role of the ocean in the atmospheric VOC budget because of poorly constrained marine sources and sinks. There are very few direct measurements of air–sea VOC fluxes near the coast, where natural marine emissions could influence coastal air quality (i.e. ozone, aerosols) and terrestrial gaseous emissions could be taken up by the coastal seas. To address this, we present air–sea flux measurements of acetone, acetaldehyde and dimethylsulfide (DMS) at the coastal Penlee Point Atmospheric Observatory (PPAO) in the south-west UK during the spring (April–May 2018). Fluxes of these gases were measured simultaneously by eddy covariance (EC) using a proton-transfer-reaction quadrupole mass spectrometer. Comparisons are made between two wind sectors representative of different air–water exchange regimes: the open-water sector facing the North Atlantic Ocean and the terrestrially influenced Plymouth Sound fed by two estuaries. Mean EC (± 1 standard error) fluxes of acetone, acetaldehyde and DMS from the open-water wind sector were −8.0 ± 0.8, −1.6 ± 1.4 and 4.7 ± 0.6 µmol m−2 d−1 respectively (“−” sign indicates net air-to-sea deposition). These measurements are generally comparable (same order of magnitude) to previous measurements in the eastern North Atlantic Ocean at the same latitude. In comparison, the Plymouth Sound wind sector showed respective fluxes of −12.9 ± 1.4, −4.5 ± 1.7 and 1.8 ± 0.8 µmol m−2 d−1. The greater deposition fluxes of acetone and acetaldehyde within the Plymouth Sound were likely to a large degree driven by higher atmospheric concentrations from the terrestrial wind sector. The reduced DMS emission from the Plymouth Sound was caused by a combination of lower wind speed and likely lower dissolved concentrations as a result of the estuarine influence (i.e. dilution). In addition, we measured the near-surface seawater concentrations of acetone, acetaldehyde, DMS and isoprene from a marine station 6 km offshore. Comparisons are made between EC fluxes from the open-water and bulk air–sea VOC fluxes calculated using air and water concentrations with a two-layer (TL) model of gas transfer. The calculated TL fluxes agree with the EC measurements with respect to the directions and magnitudes of fluxes, implying that any recently proposed surface emissions of acetone and acetaldehyde would be within the propagated uncertainty of 2.6 µmol m−2 d−1. The computed transfer velocities of DMS, acetone and acetaldehyde from the EC fluxes and air and water concentrations are largely consistent with previous transfer velocity estimates from the open ocean. This suggests that wind, rather than bottom-driven turbulence and current velocity, is the main driver for gas exchange within the open-water sector at PPAO (depth of ∼ 20 m).

Amyloid-beta peptide detection via aptamer-functionalized nanowire sensors exploiting single-trap phenomena

New highly sensitive direct methods for the early detection of peptides involved in Alzheimer's disease (AD) are required in order to prolong effective and healthy memory and thinking capabilities and also to stop the factors resulting in AD. In this contribution, we report the successful demonstration of a label-free approach for the detection of amyloid-beta (Aβ) peptides by highly selective aptamers immobilized onto the SiO2 surface of the fabricated sensors. A modified single-stranded deoxyribonucleic acid (ssDNA) aptamer was specially designed and synthesized to detect the target amyloid beta-40 sequence (Aβ-40). Electrolyte–insulator–semiconductor (EIS) structures as well as silicon (Si) nanowire (NW) field-effect transistors (FETs) covered with a thin SiO2 dielectric layer have been successfully functionalized with Aβ-40-specific aptamers and used to detect ultra-low concentrations of the target peptide. The binding of amyloid-beta peptides of different concentrations to the surface of the sensors varied in the range from 0.1 pg/ml to 10 μg/ml resulting in a change of the surface potential was registered by the fabricated devices. Moreover, we show that the single-trap phenomena observed in the novel Si two-layer (TL) NW FET structures with advanced characteristic parameters can be effectively used to increase the sensitivity of nanoscale sensors. The obtained experimental data demonstrate a highly sensitive and reliable detection of ultra-low concentrations of the Aβ-40 peptides. This opens up prospects for the development of real-time electrical biosensors for studying and understanding different stages of AD by utilizing Si TL NW FET structures fabricated on the basis of cost-efficient CMOS-compatible technology.

Temperature‐Dependent Noise and Transport in Silicon Two‐Layer Nanowire FETs

Silicon two‐layer (TL) nanowire (NW) field‐effect transistors (FETs) are fabricated by applying a CMOS‐compatible top‐down approach to silicon on insulator (SOI) wafers with additionally epitaxially grown silicon layers. Transport and noise properties of fabricated structures with p‐type conductivity are studied in a wide temperature range (100–300 K). A random telegraph signal (RTS) noise as a special case of trapping‐detrapping processes is registered as a dominant noise component at room temperature. A shift of the characteristic corner (rollover) frequency of the RTS noise to lower frequencies with temperature decreasing is observed. By performing analysis of temperature‐dependent low‐frequency noise, the activation energy and hole capture cross section of a single trap responsible for the RTS noise are estimated to be (0.29 ± 0.02 eV) and (2.22 ± 0.15) ×10−18 cm2, respectively. Obtained values suggest that the trap can be attributed to a vacancy‐boron complex. At the temperature below 200 K fabricated devices demonstrate a clear generation‐recombination noise with power spectral density proportional to 1/f 3/2. Such noise behavior provides the evidence of diffusion‐assisted processes in two‐layer nanowire structures. This confirms the contribution of high‐doped top silicon layer to the transistor transport properties.

Liquid-Gated Two-Layer Silicon Nanowire FETs: Evidence of Controlling Single-Trap Dynamic Processes.

We fabricate two-layer (TL) silicon nanowires (NW) field-effect transistors (FETs) with a liquid gate. The NW devices show advanced characteristics, which reflect reliable single-electron phenomena. A strong modulation effect of channel conductivity with effectively tuned parameters is revealed. The effect opens up prospects for applications in several research fields including bioelectronics and sensing applications. Our results shed light on the nature of single trap dynamics which parameters can be fine-tuned to enhance the sensitivity of liquid-gated TL silicon nanowire FETs.

Forced dried droplet method for MALDI sample preparation

A forced dried droplet method (FDD) is developed to overcome the drawbacks of the conventional dried-droplet (DD) method for matrix assisted laser desorption/ionization (MALDI) sample preparation. The crystals produced by the DD method are heterogeneous and irregularly distributed, and thus many methods have tried to solve the problems. However, most of them spend more time or need additional instruments to generate homogeneous microcrystals. The FDD sample preparation method can produce uniform microcrystals with homogeneous size distribution in few minutes without additional instruments. Stirring the sample spot solution (an agitation process) with a pipette tip can change the crystal size distribution which is observed by the microscope. Mass spectrometric analysis shows that the smaller the crystal size is, the better the ion signal intensity is. The formation of microcrystals can be explained with the effective rate of secondary nucleation. The relative standard deviation (RSD) of the FDD method is ∼16% which is comparable to the two-layer (TL) method and is better than the DD method.

Structurally Ordered Nanowire Formation from Co-Assembly of DNA Origami and Collagen-Mimetic Peptides.

We describe the co-assembly of two different building units: collagen-mimetic peptides and DNA origami. Two peptides CP++ and sCP++ are designed with a sequence comprising a central block (Pro-Hyp-Gly) and two positively charged domains (Pro-Arg-Gly) at both N- and C-termini. Co-assembly of peptides and DNA origami two-layer (TL) nanosheets affords the formation of one-dimensional nanowires with repeating periodicity of ∼10 nm. Structural analyses suggest a face-to-face stacking of DNA nanosheets with peptides aligned perpendicularly to the sheet surfaces. We demonstrate the potential of selective peptide-DNA association between face-to-face and edge-to-edge packing by tailoring the size of DNA nanostructures. This study presents an attractive strategy to create hybrid biomolecular assemblies from peptide- and DNA-based building blocks that takes advantage of the intrinsic chemical and physical properties of the respective components to encode structural and, potentially, functional complexity within readily accessible biomimetic materials.

Numerical Benchmark of Nonconventional RANS Turbulence Models for Film and Effusion Cooling

Over the course of the years, several turbulence models specifically developed to improve the predicting capabilities of conventional two-equations Reynolds-averaged Navier–Stokes (RANS) models have been proposed. They have, however, been mainly tested against experiments only comparing with standard isotropic models, in single hole configuration and for very low blowing ratio. A systematic benchmark of the various nonconventional models exploring a wider range of application is hence missing. This paper performs a comparison of three recently proposed models over three different test cases of increasing computational complexity. The chosen test matrix covers a wide range of blowing ratios (0.5–3.0) including both single row and multi-row cases for which experimental data of reference are available. In particular the well-known test by Sinha et al. (1991, “Film-Cooling Effectiveness Downstream of a Single Row of Holes with Variable Density Ratio,” J. Turbomach., 113, pp. 442–449) at BR = 0.5 is used in conjunction with two in-house carried out experiments: a single row film-cooling test at BR = 1.5 and a 15 rows test plate designed to study the interaction between slot and effusion cooling at BR = 3.0. The first two considered models are based on a tensorial definition of the eddy viscosity in which the stream-span position is augmented to overcome the main drawback connected with standard isotropic turbulence models that is the lower lateral spreading of the jet downwards the injection. An anisotropic factor to multiply the off diagonal position is indeed calculated from an algebraic expression of the turbulent Reynolds number developed by Bergeles et al. (1978, “The Turbulent Jet in a Cross Stream at Low Injection Rates: A Three-Dimensional Numerical Treatment,” Numer. Heat Transfer, 1, pp. 217–242) from DNS statistics over a flat plate. This correction could be potentially implemented in the framework of any eddy viscosity model. It was chosen to compare the predictions of such modification applied to two among the most common two-equation turbulence models for film-cooling tests, namely the two-layer (TL) model and the k–ω shear stress transport (SST), firstly proposed and tested in the past respectively by Azzi and Lakeal (2002, “Perspectives in Modeling Film Cooling of Turbine Blades by Transcending Conventional Two-Equation Turbulence Models,” J. Turbomach., 124, pp. 472–484) and Cottin et al. (2011, “Modeling of the Heat Flux For Multi-Hole Cooling Applications,” Proceedings of the ASME Turbo Expo, Paper No. GT2011-46330). The third model, proposed by Holloway et al. (2005, “Computational Study of Jet-in-Crossflow and Film Cooling Using a New Unsteady-Based Turbulence Model,” Proceedings of the ASME Turbo Expo, Paper No. GT2005-68155), involves the unsteady solution of the flow and thermal field to include the short-time response of the stress tensor to rapid strain rates. This model takes advantage of the solution of an additional transport equation for the local effective total stress to trace the strain rate history. The results are presented in terms of adiabatic effectiveness distribution over the plate as well as spanwise averaged profiles.

Synthesis of Au–Ag Alloy Nanoparticles with Au/Ag Compositional Control in SiO2 Film Matrix

Au-Ag alloy nanoparticles with tunable atomic ratios have been generated in SiO2 film matrix using a new two layer (TL) approach. Two successive overlapping coating layers of similar thickness were deposited on silica glass substrates using Au- and Ag-incorporated inorganic-organic hybrid silica sols, respectively. The Au and Ag concentrations in the individual layers were varied to obtain the desired Au-Ag alloys of different compositions. Four sets of such TL coating assemblies were prepared from the following pair of sols: (i) 4 equivalent mol.% Au-96% SiO2 and 2 equivalent mol.% Ag-98% SiO2, (ii) 3 equivalent mol.% Au-97% SiO2 and 2 equivalent mol.% Ag-98% SiO2, (iii) 3 equivalent mol.% Au-97% SiO2 and 3 equivalent mol.% Ag-97% SiO2, and (iv) 2 equivalent mol.% Au-98% SiO2 and 3 equivalent mol.% Ag-97% SiO2 and subjected to UV (2.75 J/cm2) and heat-treatments (450-550 degrees C) in air and H2-N2 atmospheres for the generation of Au-Ag alloy nanoparticles of approximate compositions Au.66Ag0.33, Au0.6Ag0.4, Au0.5Ag0.5, and Au0.4Ag0.6, respectively. After UV-treatment, individual Au and Ag nanoparticles were formed in the respective layers. The heat-treatment (450-550 degrees C) induces interlayer diffusion of Au and Ag to each other with the generation of Au-Ag alloy nanoparticles, and as a result, Au-Ag alloy surface plasmon resonance (SPR) absorptions were observed in between the Ag- and Au-SPR absorption positions in the visible spectra. The expected alloy compositions are formed through several intermediate alloy nanoparticles, which can also be arrested by controlling the annealing parameters. The alloy formations were monitored by UV-VIS, FTIR, XRD, EDAX, and TEM studies.

Oriented Au–Cu nanoalloy particle incorporated SiO2films using a new layer by layer deposition technique

Oriented Au–Cu nanoalloys have been generated in SiO2 films using a new two-layer (TL) coating approach. Two successive overlapping coating layers were deposited on silica glass substrate using Au- and Cu-incorporated inorganic–organic hybrid silica sols. The concentrations of the Au and Cu (3 equivalent mol% metal–97% SiO2 in each case) in the respective layers and their individual coating thicknesses were kept similar for the generation of Au–Cu alloys of an approximate atomic ratio 1 : 1. The UV-visible and X-ray diffraction (XRD) spectra of the TL films show the formation of nanoalloys with a gradual increase of Cu content with increasing heat-treatment temperature up to 750 °C in 10% H2–90% Ar. The XRD patterns reveal that the Au and Cu gradually formed Au–Cu nanoalloys of different ratios with a orientation. Estimation shows that the final nanoalloy composition reaches Au0.58Cu0.42. The transmission electron microscope (TEM) image obtained from an Au0.58Cu0.42 nanoalloy containing film shows the presence of mainly oriented plate-like circular nanoalloys of diameter 9–14 nm. XRD and TEM confirm that the alloy formation took place mainly through the diffusion and gradual dissolution of Cu atoms onto the planes of Au and intermediate Au–Cu nanoalloy crystals.

A New Approach for the Synthesis of Au−Ag Alloy Nanoparticle Incorporated SiO2 Films

A new synthesis procedure has been developed to prepare Au−Ag alloy nanoparticles inside glassy SiO2 film matrix. Two successive overlapping coating layers were prepared on glass substrate using Au- and Ag-incorporated inorganic−organic hybrid silica sols, respectively. The concentrations of the Au and Ag (3 equivalent mol % metal − 97% silica in each case) in the respective layers and their individual coating thicknesses were kept similar for the generation of 1:1 Au−Ag (Au0.5Ag0.5) alloy. The dried two-layer (TL) coating assembly after UV (2.75 J/cm2) and followed by thermal treatments (450−550 °C) yielded Au−Ag alloy nanoparticles of controllable molar ratios in a glassy SiO2 matrix. Thus, the UV-treated TL film when heated at 450 °C yielded spherical Au−Ag alloy nanoparticles (Au mol fraction ≈ 0.8) of average diameter (〈D〉) 2.5 nm whereas the 550 °C heated film sample showed relatively larger alloy nanoparticles of 〈D〉 4.5 nm having Au mol fraction of ≈0.5. The alloy nanoparticles were formed through...

INCREASING OF ACCURACY FOR ENGINEERING CALCULATION OF HEAT TRANSFER PROBLEMS IN TWO LAYER MEDIA

In this paper we study the simple algorithms for modelling the heat transfer problem in two layer media. The initial model which is based on a partial differential equation is reduced to ordinary differential equations (ODEs). The increase of accuracy is shown if instead of first order ODE initial value problem ([4, 5]) the second order differential equations is taken. Such a procedure allows us to obtain a simple engineering algorithm for solving heat transfer equations in two layered domain of Cartesian, cylindrical (with axial symmetry) and spherical coordinates (with radial symmetry). In a stationary case the exact finite difference scheme is obtained. Šiame straipsnyje yra nagrinejami paprasti dvisluoksnes srities šilumos laidumo problemos modeliavimo algoritmai, keičiant diferencialines lygtis dalinemis išvestinemis i paprastas diferencialines lygtis. Parodoma, kad didesnio tikslumo pasiekimui, vietoje pirmos eiles paprastu diferencialiniu lygčiu pradinio uždavinio nagrinejamos antros eiles diferencialines lygtys. Ši proced ura leidžia gauti paprasta inžinerini dvisluoksies srities šilumos laidumo lygties sprendini stačiakampeje, cilindrineje (su ašiu simetrija) ir sferineje (su spinduline simetrija) koordinačiu sistemoje. Tiksli baigtiniu skirtumu schema buvo sudaryta stacionariam atvejui.

Oblique bending of a bimetallic bar with a cross section bounded by circular arcs

The p re sen t paper concerns the bending of a twol ayer p r i s m a t i c ba r whose c ross sect ion is bounded by c i r c u l a r a r c s . The solution to the problem is cons t ruc ted with the aid of funct ions s i m i l a r to the bending s t r e s s function proposed by Timoshenko [1] with r e f e r ence to the bending of homogeneous rods . w Let us cons ider the e las t i c bending of the twol aye r p r i s m a t i c bar whose c ross sect ion is shown in the f igure . The side sur faces 71 and 7z as well as the boundary 3 0 between the two layers are all cy l ind r i ca l su r faces , The or igin of the r ec t angu la r coordinate sy s t em is placed in the fixed end of the ba r in such a way that the y axis coincides with the axis of symmet ry , while the x axis coincides with the c r o s s s e c t i o n chord. The force is applied to the f ree end of the bar and passes through the bend center , so that there is no to r s ion . Let the l aye r s be isot ropie , the e las t ic moduIi E~ and E 2 of the m a t e r i a l s dis t inct , and the Po isson coeff ic ients #j and P2 equal . Then, as in the bending of homogeneous rods, only three components of the s t r e s s ) t e n s o r a r e d i f ferent f rom zero, namely 0"~1), T(zlx ) , T~ly ) for layer I and the analogous components for l ayer II. Henceforth the analogous exp r e s s ions for both reg ions will contain the index i which has the value i =1 in region I and i = 2 in region II. The indices of p wil l be omit ted . The n o r m a l s t r e s s atzL)" is given by the fo rmula