Optimal Buffer Layer Thickness Research Articles

Meniscus inspired flexible superhydrophobic coating with remarkable erosion resistance for pipeline gas transmission

Inspired by human meniscus, a superhydrophobic inner pipeline coating with has been developed to mitigate the erosion and corrosion damages to gas transportation pipeline. The erosion-resistant coating, consisting of modified TiO2 nanoparticles (NPs), multi-walled carbon nanotube (CNTs), and epoxy resin (EP), is built on a buffer layer made of polydimethylsiloxane (PDMS). The optimized buffer layer thickness (100 μm) was determined by finite element simulation when mixing ratio between the curing agent and PDMS was 1:30. The erosion resistance of the prepared coating was quantified by an erosion ring experiment. Finally, erosion resistance of materials produced by different filler types (fibrous and spherical) were compared. The erosion resistance of the material is significantly improved by the tensile force of the fiber filler, similar to the steel in reinforced concrete. The result shows that the buffer-structure coating can reduce the magnitude of erosion rate significantly. Compared to the coating with no buffer structure, the maximum reduction of erosion rate is up to 37.55 %. In addition, the water contact angle (CA) of the sample could maintained over 150° after various mechanical shocks, such as 350 times of 90° bending test, 1500 times of sand impact test, and 4H pencil hardness test. Compared with the 316L steel sample, the corrosion potential of the coating in 3.5 wt% NaCl solution increased from −0.18 V to 0.04 V, making it potentially applicable for the corrosive environment of submarine pipelines.

The evaluation on shock absorption performance of buffer layer around the cross section of tunnel lining

The buffer layer around the cross section of lining structure would be the most simple and effective shock absorption measure, which can cut off the transferring paths of adverse effects from surrounding rock to lining structures. Meanwhile, it can reduce the seismic action intensity and minimize the extra pressure from surrounding rock by changing seismic acting patterns. This paper presents outcomes by investigating the interaction between lining structure and surrounding rock during excitation as well as deriving influencing parameters with regard to shock absorption performances of buffer layer. Afterwards, series numerical calculations are systematically carried out with attention given to the seismic-induced deformation responses of rock-layer-lining system. Finally, an elaborated evaluation method for assessing shock absorption performance of buffer layer with an evaluation expression is proposed, which is validated by series shaking table model tests and numerical simulations. This evaluation expression would be able to guide the selection and construction of buffer layer according to the geological conditions and construction circumstances by changing geometric and material parameters. The evaluation result would have uniqueness once all the parameters are confirmed. From this expression and its derivation process, the following findings can be drawn: (1) The cross section of tunnel has the identical particular deformation pattern in each constructing phase during excitation regardless of the existence of lining structure and buffer layer, that is, the two orthogonal diagonal diameters of cross section alternatively expand and contract. (2) The geometric and material parameters simultaneously determine the shock absorption performances of buffer layer, which grows in direct proportion to geometric variables but decreases in inversely proportion to material variables. (3) When the ratio of lining inside radius to buried depth is equal to 0.2 (i.e. r0/H = 0.2), the buried depth of tunnel engineering should be the ideal position for adopting buffer layer. Meanwhile, when the ratio of buffer layer thickness to lining inside radius is equal to 0.2 (i.e. tb/r0 = 0.2), it can be confirmed the optimal thickness of buffer layer. (4) The evaluation expression of shock absorption performance is independent of seismic waveforms but involved in the excitation intensities and the destruction states of lining structure.

Correlating optimal electrode buffer layer thickness with the surface roughness of the active layer in organic phototransistors

Inserting a C60 buffer layer between Au source/drain electrodes and pentacene active layer has been proved to improve the performances of pentacene organic phototransistors (PENT-OPTs) in our previous study. Buffer layer certainly has an optimal thickness with which the modified device can achieve the best performance. Based on the surface morphology analysis of different thickness C60 buffer layer on pentacene film, we further optimized the thickness of C60 buffer layer for best performance of PENT-OPTs and investigated its physical origins. Studies on PENT-OPTs with different pentacene surface morphology realized by different substrate temperatures indicate that the optimal thickness of C60 buffer layer directly related to the surface roughness of pentacene active layer and it is found that the optimized buffer layer thickness increases with the roughness of pentacene layer. Besides, we found that the photogenerated current of OPTs increases with the increasing of gate electric bias and then gradually reach saturation. An approximate analytical expression for gate voltage dependence of the photogenerated current was derived and used to fit the experiment data. An important parameter, saturated photoresponsivity, was introduced for better comparing the performances of OPTs.

Investigating the effect of buffer layer on magnetoresistance in organic spin-valves

According to the magnetoresistance (MR) experiments in the Co/Al2O3/Alq3/LSMO device, we investigate spin injection and MR of this organic device. Taking into account the spin-related resistance and partial voltage of the Al2O3 buffer layer, we obtain an apparent adjustable MR of the organic device. A large MR is predicated with an optimized buffer layer thickness. In addition, the effects of different buffer layer materials on the MR are discussed to give a suggestion on experimental investigations.

Enhancement of photoluminescence signal from ultrathin layers with silicon nanocrystals

Using the model of oscillating dipoles, we simulated the photoluminescence intensity of a triple-layered structure where the silicon nanocrystals layer was enclosed by buffer and capping silicon dioxide layers. It was found that a structure with an optimized buffer layer thickness exhibited photoluminescence which was approximately 20 times more intense than that from the structure without a buffer layer. Theoretical simulations were verified by photoluminescence measurements for the corresponding structures with silicon nanocrystals fabricated by plasma enhanced chemical vapour deposition.

A parametric study of TiO2/CuInS2 nanocomposite solar cells: how cell thickness, buffer layer thickness, andTiO2 particle size affect performance

3D CuInS2/TiO2 nanocomposite solar cell performance is strongly influenced by several structuralfactors, including cell thickness, buffer layer thickness, and the morphology of theTiO2 nanoparticulate matrix. To delineate the effect of these structural factors on photovoltaic performance,a series of parametric studies are performed where a single structural parameter is varied(TiO2 nanoparticulatematrix thickness, In2S3 buffer layer thickness, or TiO2 particle size) while all other fabrication conditions are held constant. The bestoverall performance (3.0% efficiency at AM 1.5) is achieved from a device withTiO2 matrixthickness ≈200 nm,In2S3 buffer layerthickness ≈60 nm, and TiO2 nanoparticulate size = 300 nm. Notably, the film thickness in the best-performing cell (200 nm) is less than theTiO2 particle size (300 nm), corresponding to a discontinuous nanoparticulate film. ThickerTiO2 nanoparticulatefilms or smaller TiO2 particles sizes lead to decreased performance due to increased chargetransport resistance. However, the performance from a planar cell (where theTiO2 nanoparticulate layer is not used) is inferior to the performance from thebetter-optimized 3D cells, indicating that some degree of nanostructuringimproves performance. Device performance is also observed to depend strongly onIn2S3 buffer layer thickness, with optimal performance achieved for a buffer layerthickness of approximately 60 nm. The optimal buffer layer thickness is governedby two opposing factors: increasing the buffer layer thickness improves theinterfacial characteristics (as measured by decreasing leakage conductance,G) but also screens the incoming light and causes an increase in thecharge transport resistance (as measured by the cell series resistance,Rs).

Low-resistance graded Al xGa 1−xN buffer layers for vertical conducting devices on n-SiC substrates

We investigated the Al composition and thickness dependence of the resistance of graded Al x Ga 1− x N buffer layers for vertical conducting devices on n-type 6H-SiC substrates. To measure current–voltage characteristics, a Ti/Au ohmic contact was formed on the backside of the SiC substrate. The Al composition of the buffer layer was varied from 2% to 10%. We found that the optimal buffer layer thickness for the lowest resistance decreases with increasing Al composition because the nucleation seeds on SiC substrate coalesce faster. Since the optimal layer thickness depends on the Al composition, the sheet Al concentration, which is calculated from the Al composition and the thickness, should be considered as a critical parameter for low buffer resistance of vertical conducting devices on n-SiC substrates.

Polarity Control of LP-MOVPE GaN using N2 the Carrier Gas

The polarity control of GaN films grown on c-plane sapphire substrates by LP-MOVPE using N2 as carrier and diluent gas was investigated in detail. The polarity type depended on the substrate preparation prior to the high temperature (HT) GaN growth. Device-quality Ga-polar GaN was obtained by using a low temperature (LT) AlN buffer layer followed by a specific annealing process. Optimized buffer layer thickness was 10 nm, with an annealing time of 20 min and a temperature of 1050 °C. By using these conditions for the buffer layer growth, mirror-like Ga-polarity GaN was grown using a V/III ratio of 100. The full width at half maximum (FWHM) of Ga-polar GaN films was 360 arcsec for the symmetric (00.2) reflection and 640 arcsec for the skew-symmetric (30.2) reflection. The surface roughness was measured by AFM to be 0.2 nm RMS and the growth rate was estimated at 2.0 μm/hr. These results indicated that by exclusively using N2 carrier gas, one can achieve films of the same quality as those more commonly grown by using H2 carrier gas.

Buffer-layer-induced barrier reduction: Role of tunneling in organic light-emitting devices

Based on the WKB approximation of the tunneling model, we calculate the J–V characteristics of organic light-emitting devices (OLEDs) having buffer layers of different thickness. The results show how the insertion of a buffer layer with proper thickness lowers the OLED turn-on voltage. Further calculation suggests some parameters, such as the resistivity ratio and the position of the conduction band minimum of the buffer layer relative to the lowest unoccupied molecular orbital of the organic layer, are important in selecting a buffer material. A quantitative estimation of the optimal buffer layer thickness is also presented to serve as a guide to device design. The model is validated by comparison of its predictions to experimental results.

Growth and properties of a multilayer system based on Y1Ba2Cu3Ox and amorphous Y-ZrO2

The growth of c-axis oriented Y1Ba2Cu3Ox thin films on an amorphous buffer layer of Y-ZrO2, deposited on sapphire substrates, was investigated. Both films were grown by a pulsed laser deposition technique. A strong correlation was observed between the properties of Y1Ba2Cu3Ox and the thickness of the buffer layer. A Tc of 89 K was obtained for an optimal buffer layer thickness of 9 nm. A model that adequately describes the film growth process was developed. A multilayer system of Y1Ba2Cu3Ox and amorphous Y-ZrO2 was grown and a Tc of 87 K for the upper c-axis oriented layer was measured.