Built-in Defect Research Articles

Piezoelectric field and defect engineering synergistically improved photocatalytic performance of K0.5Na0.5BixNb1-xO3 for degradation of organic pollutants

Semiconductor photocatalysts have been widely researched in wastewater treatment and photocatalysis predominantly depends on the redox reaction of photoinduced charge carriers on semiconductor surface. Afterwards, photoinduced carrier concentration and the effective separation of electrons and holes have been proved to be pivotal in promoting photocatalytic efficiency. Further, the internal electric field established by polarization of piezoelectric materials is considered an efficient means of separating electrons and holes. Hence, as a typical representative of piezoelectric materials, (K0.5Na0.5)Nb1-xBixO3 was designed and prepared by introducing Bi2O3 in (K0.5Na0.5)NbO3 to construct defects intentionally, and thus reduce the band gap and increase carrier concentration by the hybrid energy levels, for another promote efficient separation of electrons and holes by virtue of the built-in field created by piezoelectric polarization and pinning holes by defects. Thereinto, the K of Rh B degradation by (K0.5Na0.5)Nb0.98Bi0.02O3 reached 0.07846 min−1 under the combined light irradiation and ultrasonic, meanwhile 95 % Rh B can be degraded within 20 min and nearly 100 % in 60 min with eminent cycling stability, which is brilliant than previous reports on KNN-based catalyst. This work provides not only a novel piezo-photocatalytic degradation material but also a built-in electric field and defect synergy strategy for boosting carrier separation.

A Bayesian approach for CT reconstruction with defect detection for subsea pipelines

Subsea pipelines can be inspected via 2D cross-sectional x-ray computed tomography (CT). Traditional reconstruction methods produce an image of the pipe’s interior that can be post-processed for detection of possible defects. In this paper we propose a novel Bayesian CT reconstruction method with built-in defect detection. We decompose the reconstruction into a sum of two images; one containing the overall pipe structure, and one containing defects, and infer the images simultaneously in a Gibbs scheme. Our method requires that prior information about the two images is very distinct, i.e. the first image should contain the large-scale and layered pipe structure, and the second image should contain small, coherent defects. We demonstrate our methodology with numerical experiments using synthetic and real CT data from scans of subsea pipes in cases with full and limited data. Experiments demonstrate the effectiveness of the proposed method in various data settings, with reconstruction quality comparable to existing techniques, while also providing defect detection with uncertainty quantification.

Molecular Ferroelectrics-Driven High-Performance Perovskite Solar Cells.

The nonradiative recombination of electrons and holes has been identified as the main cause of energy loss in hybrid organic-inorganic perovskite solar cells (PSCs). Sufficient built-in field and defect passivation can facilitate effective separation of electron-hole pairs to address the crucial issues. For the first time, we introduce a homochiral molecular ferroelectric into a PSC to enlarge the built-in electric field of the perovskite film, thereby facilitating effective charge separation and transportation. As a consequence of similarities in ionic structure, the molecular ferroelectric component of the PSC passivates the defects in the active perovskite layers, thereby inducing an approximately eightfold enhancement in photoluminescence intensity and reducing electron trap-state density. The photovoltaic molecular ferroelectric PSCs achieve a power conversion efficiency as high as 21.78 %.

Significance of powder feedstock characteristics in defect suppression of additively manufactured Inconel 718

The characteristics of powder applied in electron beam powder-bed fusion (EB-PBF) play a vital role in the process stability and final part performance. We use two types of Inconel 718 alloy powders for experiments, namely, (i) imperfect spherical and (ii) spherical powders. They have similar particle size distributions but are different in geometry and built-in defect. The forming qualities concerning surface topography, density, and internal defect of the EB-PBF-built samples prepared using two types of powders are characterized under the same processing conditions. In particular, the forming qualities are further compared under the optimal process condition to highlight the decisive role of powder features. Notably, different powder geometries with distinct surface feature inevitably affect the heat transfer during melting. The significance of powder feedstock characteristics in defect suppression is clarified with the aid of numerical simulations. The experimental results show that compared to spherical powders, fabrication using imperfect spherical powders is more likely to evoke lack–of–fusion and excessive melting under low and high energy conditions, respectively. Thus, spherical powders have a broader process window in ensuring a higher density and smoother surface than that of imperfect spherical powders. Moreover, in the sample built with spherical powders, the high cooling and solidification rates evaluated by numerical simulations result in the suppression of the interdendritic voids.

Electron number density measurements from the frequency shift of a plasma defect state in a one-dimensional photonic crystal

We describe the use of a plasma-functionalized vacancy defect in a one-dimensional microwave photonic crystal to experimentally measure the electron number density of glow discharges at 5–40 torr. The photonic crystal consists of spaced alumina plates with a built-in void defect that breaks the repeating symmetry of the layers, resulting in narrow defect transmission peaks within relatively deep bandgaps. We exploit the sensitivity of the defect transmission at 28 GHz to varying plasma density to measure electron number densities as low as 2 × 109 cm−3. Defect energy shifts are proportional to plasma density, in reasonable agreement with theoretical predictions of photonic crystal performance. At higher discharge current densities and discharge pressure, we see a departure from the model predictions, largely attributable to the heating of the alumina structure, causing expansion and changes in the lattice parameter that counteract the effect of the increased plasma density on the defect state frequency.

Formulation of Model Defects Suitable for the Resonance Regime

A method to account for model deficiencies in nuclear data evaluations in the resonance regime is proposed. The method follows the ideas of Schnabel and coworkers and relies on Gaussian processes with a novel problemadapted ansatz for the covariance matrix of model uncertainties extending the formalism to the energy region of resonances. The method was used to evaluate a set of schematic but realistic neutron reaction data generated by an R-matrix code and a well defined model defect. Using the extended ansatz for model defects the Bayesian evaluation successfully recovered the built-in model defect in size and structure thus demonstrating the applicability of the method.

Development of a novel 20 kV 0.1 Hz very low frequency cosine‐rectangular voltage generator for multi‐functional insulation testing of MV power cables

This study covers research and development efforts to develop, design and test a novel very low frequency cosine-rectangular voltage generator (CRVG) specialised not only for a withstand test, but also a partial discharge (PD) test of standard medium voltage (MV) cross-linked polyethylene power cables. The system schematic and operating principle of the proposed system are presented and described. The cosinusoidal polarity reversing process is realised through L–C series resonance. A charging and discharging switch is developed by means of an insulated gate bipolar transistor series-connected semiconductor switch. A laboratory prototype is assembled and tested. Maximum output voltage of the proposed CRVG is measured as 20 kV, which is in accordance with the expected acceptance test voltage level given in IEEE standard 400.2. Finally, the proposed system is applied to PD detection of a 300 m cable circuit with a built-in artificial defect, and the PD locating results are presented, proving the system's feasibility.

Impact of bias potential and layer arrangement on thermal stability of arc evaporated Al-Cr-N coatings

Cathodic arc evaporated homogenously grown as well as multilayered AlxCr1−xN coatings were prepared using AlxCr1−x targets with compositions of x=0.7, 0.75, 0.85, and 0.9 and bias potentials of −40, −80, and −120V. The mechanical properties of the as deposited coatings can be significantly increased by increasing the applied bias potential, but the thermal stability, with respect to phase decomposition and CrN dissociation to cubic Cr under N2-release, is reduced. The built-in defect density, intermixing of individual higher and lower Al-containing layers, and especially the fraction of phase boundaries within multi-phased coatings are extremely influenced by the bias potential. Due to the reduced thermal stability, the hardness gain by increasing the bias potential is already lost for Ta≥600°C in (as deposited) single-phase cubic structured coatings. Therefore, the Al0·7Cr0.3N coatings prepared with −40V outperform their −120V bias counterparts in hardness already for Ta≥600 °C. This is different for the multilayer coatings comprising cubic and hexagonal wurtzite type phases. Although, the thermal stability with respect to structural changes is also reduced with increasing bias, their mechanical properties are less influenced by the annealing treatment. Especially the Al0·75Cr0.25N/Al0·9Cr0.1N multilayers exhibit excellent hardness values of 30±3GPa over the entire annealing temperature range up to 1100°C, when prepared with −120V bias. Here, the increased bias during deposition leads to dense coatings and the arrangement with high Al-containing layers provides an improved resistance against decomposition and CrN dissociation.

Thermo-electric analysis of the interconnection of the LHC main superconducting bus bars

Spurred by the question of the maximum allowable energy for the operation of the Large Hadron Collider (LHC), we have progressed in the understanding of the thermo-electric behavior of the 13kA superconducting bus bars interconnecting its main magnets. A deep insight of the underlying mechanisms is required to ensure the protection of the accelerator against undesired effects of resistive transitions. This is especially important in case of defective interconnections which can jeopardize the operation of the whole LHC.In this paper we present a numerical model of the interconnections between the main dipole and quadrupole magnets, validated against experimental tests of an interconnection sample with a purposely built-in defect. We consider defective interconnections featuring a lack of bonding among the superconducting cables and the copper stabilizer components, such as those that could be present in the machine. We evaluate the critical defect length limiting the maximum allowable current for powering the magnets. We determine the dependence of the critical defect length on different parameters as the heat transfer towards the cooling helium bath, the quality of manufacturing, the operating conditions and the protection system parameters, and discuss the relevant mechanisms.

Defect Prevention and Detection in Software for Automated Test Equipment

This paper describes a test application development tool designed with a high degree of defect prevention and detection built-in. While this tool is specific to a particular tester, the PT3800, the approach that it uses may be employed for other ATE. The PT3800 tester is the successor of a more than 20 year-old tester, the PT3300. The development of the PT3800 provided an opportunity to improve the test application development experience. The result was the creation of a test application development tool known as the PT3800 AM creation, revision and archiving tool, or PACRAT (AM refers to automated media, specifically test application source code). This paper details the built-in defect prevention and detection techniques employed by PACRAT.

Built-in defect of a biological pericardial aortic prosthesis?

We report a case on an early complication of a biological pericardial tissue valve in the aortic position that required emergency replacement. One of the three leaflets of the valve was stuck open in a fixed-open position and would not unfold in diastole. This resulted in severe aortic insufficiency, diagnosed by standard postoperatory echocardiography and confirmed in the operating room.

Magnetorefractive effect in manganites

The magnetotrans mittance and magnetoreflectance of manganite films and one-dimensional magnetophotonic crystals containing a manganite film as a defect are calculated. The calculations demonstrate that the magnetotransmittance and magnetoreflectance of manganites with a colossal magnetoresistance can be treated as a manifestation of the magnetorefractive effect. The magnitude of the magnetorefractive effect in transmission can reach 20–40% at low temperatures. The effect in reflection amounts to 1–2% for a 300-nm-thick film and can be substantially amplified through multibeam interference in the symmetric and antisymmetric structures of magnetophotonic crystals with a built-in defect.

Built-in Self-test and Defect Tolerance in Molecular Electronics-based Nanofabrics

We propose a built-in self-test (BIST) procedure for nanofabrics implemented using chemically assembled electronic nanotechnology. Several fault detection configurations are presented to target stuck-at faults, shorts, opens, and connection faults in nanoblocks and switchblocks. The detectability of multiple faults in blocks within the nanofabric is also considered. We present an adaptive recovery procedure through which we can identify defect-free nanoblocks and switchblocks in the nanofabric-under-test. The proposed BIST, recovery, and defect tolerance procedures are based on the reconfiguration of the nanofabric to achieve complete fault coverage for different types of faults. We show that a large fraction of defect-free blocks can be recovered using a small number of BIST configurations. We also present simple bounds on the recovery that can be achieved for a given defect density. Simulation results are presented for various nanofabric sizes, different defect densities, and for random and clustered defects. The proposed BIST procedure is well suited for regular and dense architectures that have high defect densities.

A NAND Flash Memory Controller for SD/MMC Flash Memory Card

In this paper, a novel NAND flash memory controller was designed. A t-EC w-bit parallel Bose-Chaudhuri-Hocquengham (BCH) error-correction code (ECC) was designed for correcting the random bit errors of the flash memory chip, which is suitable for the randomly bit errors property and parallel I/O interface of the NAND-type flash memory. A code-banking mechanism was designed for the tradeoffs between the controller cost and the in-system programmability (ISP) support. With the ISP functionality and the Flash parameters programmed in the reserved area of the flash memory chip during the card production stage, the function for supporting various kinds of NAND flash memory could be provided by a single controller. In addition, built-in defect management and wear-leveling algorithm enhanced the product life cycle and reliability. Dual channel accessing of the Flash memory provided the good performance in data transfer rate. With respect to the proposed controller architecture, a real secure digital card (SD)/multimedia card (MMC) flash memory card controller chip was designed and implemented with UMC 0.18 mum CMOS process. Experimental results show the designed circuit can fully comply with the system specifications and shows the good performances

Enhancement of the magnetorefractive effect in magnetophotonic crystals

The magnetorefractive effect in a one-dimensional magnetophotonic crystal, more specifically, a photonic crystal (SiO2/Ta2O5) containing a built-in defect in the form of a thin layer of the Co-(Al-O) magnetic nanocomposite, is studied in a computer simulation experiment. The structure of the unit cell of the photonic crystal in which most of the field energy is concentrated in cells nearest to the defect is determined. This makes it possible to increase the defect-mode Q factor and, owing to the multiple passage of light along the defect, to enhance the magnetorefractive effect by more than one order of magnitude as compared to a thin film on a substrate and by two orders of magnitude as compared to thick films. The reflectance of these structures in an applied magnetic field can be as high as 60%.

SRAM design on 65-nm CMOS technology with dynamic sleep transistor for leakage reduction

A 70-Mb SRAM is designed and fabricated on a 65-nm CMOS technology. It features a 0.57-/spl mu/m/sup 2/ 6T SRAM cell with large noise margin down to 0.7 V for low-voltage operation. The fully synchronized subarray contains an integrated leakage reduction scheme with dynamically controlled sleep transistor. SRAM virtual ground in standby is controlled by programmable bias transistors to achieve good voltage control with fine granularity under process skew. It also has a built-in programmable defect screen circuit for high volume manufacturing. The measurements showed that the SRAM leakage can be reduced by 3-5/spl times/ while maintaining the integrity of stored data.

Suppression of impurity interdiffusion in heteroepitaxy by inserting a low-temperature buffer layer in between the epilayer and the substrate

This article demonstrates that interdiffusion, which is inherent in heteroepitaxy, can be well suppressed by inserting a thin buffer layer grown at sufficiently lower temperature with taking a ZnSe/GaAs heteroepitaxy as an example. Two types of samples are prepared by molecular beam epitaxy (MBE): a 1114 Å thick ZnSe epilayer grown on a 150 Å thick low-temperature ZnSe buffer layer on a GaAs (0 0 1) substrate, and a 1356 Å thick ZnSe layer grown directly on GaAs. The composition profile at the heterointerface measured by secondary ion mass spectrometry (SIMS) clearly shows that the Ga diffusion is greatly suppressed in the ZnSe/GaAs system prepared with the low-temperature buffer layers, while considerable Ga interdiffusion from the GaAs substrate into the ZnSe epilayer is observed in the sample without the low-temperature buffer layer. The suppression of interdiffusion is also evidenced by low-temperature photoluminescence (PL) spectroscopy which shows no trace of donor–acceptor pair (DAP) emission at around 2.7 eV normally observed in ZnSe epilayers. In addition to the suppression of interdiffusion, Se reaction with GaAs surfaces is suppressed, which leads to the reduction of built-in defect generation due to heterovalency. Consequently, the ZnSe layer grown on a thin low-temperature ZnSe buffer layer shows high crystallinity as indicated by strong and sharp exciton emission in low-temperature photoluminescence spectrum and narrow X-ray line width.

Local characterization of compositionally graded Pb(Zr,Ti)O 3 thin films by scanning force microscope

Compositionally graded PZT thin film was prepared by a sol–gel technique. Nanoscale domain structure and polarization reversal behavior in an individual grain were investigated by means of scanning force microscopy (SFM) in piezoresponse mode. Domain as small as 30 nm in size was visualized. The observed complex domain contrast was attributed to the crystallographic orientation of the grains and to the built-in potential difference in compositionally graded PZT thin film under an ac field. The built-in potential difference, defect and space charge gave rise to strong domain pinning behavior during the polarization reversal.

Highly sensitive pulsed digital holography for built-in defect analysis with a laser excitation

A highly sensitive method is presented for noninvasive defect analysis on thin structures with a Q-switched double-pulsed ruby laser with frequency doubling (347 nm). In our research we feature an all-optical arrangement, where a focused laser pulse derived from the same ruby laser (694 nm) acts as a built-in synchronous excitation source for digital holographic interferometry. The recordings are made with a CCD camera for capturing two holograms (two states of the specimen) corresponding to the two UV laser pulses with a short time separation (10-50 mus). Subtraction of the phase distribution in two digital holograms gives a fringe phase map that shows the change in deformation of the specimen between the recordings. The advantage of the proposed method is two fold. First, the use of a shorter wavelength results in a higher sensitivity. Second, owing to the induced synchronous built-in optical excitation, the specimen is not subjected to any external physical excitation devices. Experimental results are presented on identification and evaluation of defects in thin metal sheets.

Numerical modelling of ultrasonic wave propagation using the efficient p-version finite element method

In this paper, the new p-version of the finite element method has been used for the numerical modelling of ultrasonic wave propagation in solid media. The p-method involves increasing the polynomial order of the interpolation functions to achieve convergence. This is unlike the conventional h-version in which the number of elements is increased to achieve the same goal. Illustrative examples of wave propagation through an isotropic aluminium block, including a case with a built-in defect in the form of a crack, have been discussed. Also, a convergence criterion has been developed for dynamic problems. The potential to extend this model to other applications such as medical ultrasonics or to a more complex anisotropic medium is significant.