Electrical-field activated sintering and forming of micro-components

As the demand for miniature products has increased significantly, so also has the need for these products to be produced in a rapid, flexible and cost efficient manner. The application of electroplasticity shows significant potential to produce the components by using powder materials. Nevertheless, previous research has shown that there are still significant challenges to be met in order to achieve increased relative densification of product samples and simplification of the processes. The process concept in this study comprises the combination of electrical-field activated sintering and forming processes. Therefore, the aims of the research were to develop the process concept for the manufacture of micro-components and to design the die sets along with other tooling for machine setup to enable the forming of micro-components from powder materials. A comprehensive literature review on micro-manufacturing, size effects, powder metallurgy and the electroplasticity process has been conducted. The development of the die sets for the process has been described, followed by a series of experiments. The FE thermal-electrical analysis was also carried out to study the heating flows of the die sets development during the process. In this research, titanium (Ti) and titanium tin alloy (90Ti10Sn) have been selected for the main powder materials tested for both vacuum and open-air process environment by using a Gleeble® 3800 testing system and Projection Welding machine respectively. Meanwhile, for the additional experiment, copper (Cu) has been selected to be tested in the open-air process environment by using a Projection Welding machine with die sets prepared by the Micro-FAST project. Based on the data collected, this efficient process has the potential to produce components with a high relative density of around 98%. Changes of the particles concerning deformation and breaking are crucial in the course of achieving the densification which differs from a conventional sintering process

Photovoltaic technologies photo-thermal challenges: Thin active layer solar cells significance

Massive energy demand and source of energy usages is the key root of global emission and climate change. Solar photovoltaic (PV) is low carbon energy technology currently 3.2% share of global electricity supply. The rapid progress of solar PV is vastly related to increase energy efficiency and lessening of active materials usage. This paper solar PV present significance and most prospective PV materials technical challenges are reviewed for its future advancement. Among the challenges solar energy absorption-related dynamic photo-thermal effect on cells or modules is vital. Transparent passivation contact materials with lower temperature coefficient (TC) and thin active layer resulted in lowering both dynamic photo-thermal outcome and optical to electrical energy gap. Thin active layer minor bulk recombination and sub-band parasitic absorption lessening purpose transparent conductive materials (TCM) based proper band barrier heterointerface is impending. It can optimize desired band absorption and photo-coupling with selective carrier induces greater efficiency. Earlier research though explains it on carrier selectivity prejudice, but how it can lessen the near infrared band optical and associated thermal influence is essential to illustrated. Passivation and TC interrelations hence, field related drift is control over diffusion process loss in advanced bifacial and thin active layer PV technology. Loss lessening pathways thin wafer-based Si, thin film CdTe, organic and perovskite photo coupling with advanced TCM, thus, Si/CdTe and Si/perovskite tandem cells along with OSC building integrated transparent photovoltaic technologies advancement pathways are reported

Synthesis of Poly(hydroxamic acid) Ligand from Polymer Grafted Khaya Cellulose for Transition Metals Extraction

A cellulose-graft-poly(methyl acrylate) was synthesized by free radical initiating process and the ester functional groups were converted into the hydroxamic acid ligand. The intermediate and final products are characterized by FT-IR, FESEM, HR-TEM and XPS technique. The pH of the solution acts as a key factor in achieving optical color signals of metalcomplexation. The reflectance spectra of the[Cu-ligand]n+ complex was found to be a highest absorbance at 99.8 % at pH 6 and it was increased upon increasing of Cu2+ ion concentrations and a broad peak at 700 nm was observed which indicated the charge transfer (π-π transition) metals-Cu complex. The adsorption capacity of copper was found to be superior (336 mg g-1)rather than other transition metals such as Fe3+, Co3+, Cr3+, Ni2+, Mn2+ and Zn2+ were 310, 295, 288, 250, 248 and 225 mg g-1, respectively at pH 6. The experimental data of all metal ions fitted significantly with the pseudo-second-order rate equation. The transition metal ions sorption onto ligand were well fitted with the Langmuir isotherm model (R2>0.99), which suggested that the cellulose-based adsorbent known as poly(hydroxamic acid) ligand surface is homogenous and monolayer. The reusability of the poly(hydroxamic acid) ligand was checked by the sorption/desorption process up to ten cycles without any significant loss in its original sensing and removal performances

Reversible hysteresis inversion in MoS₂ field effect transistors

MoS2 devices: variable temperature measurements unveil reversible hysteresis mechanisms Defects and traps in MoS2 van der Pauw devices give rise to a hysteresis inversion mechanism which is reversible with temperature. A team led by Saurabh Lodha at the Indian Institute of Technology Bombay performed variable temperature hysteresis measurements on four- and two-terminal MoS2 devices, both suspended and supported on a SiO2 substrate. The onset of a clockwise hysteresis at room temperature was attributed to intrinsic MoS2 defects, whereas an additional mechanism resulting in an anticlockwise hysteresis was observed at higher temperature, and attributed to extrinsic charge trapping and de-trapping between the oxide and the silicon gate. By leveraging the temperature dependence of the hysteresis in MoS2, the authors developed a non-volatile memory and a temperature sensor

Synthesis of poly(hydroxamic acid) ligand from polymer grafted corn-cob cellulose for transition metals extraction

Poly(hydroxamic acid) ligand was synthesized using ester functionalities of cellulose-graft-poly(methyl acrylate) copolymer, and products are characterized by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy analysis. The poly(hydroxamic acid) ligand was utilized for the sensing and removal of transition metal ions form aqueous solutions. The solution pH is found a key factor for the optical detection of metal ions, and the reflectance spectra of the [Cu-ligand]n+ complex were observed to be the highest absorbance 99.5% at pH?6. With the increase of Cu2+ ion concentration, the reflectance spectra were increased, and a broad peak at 705?nm indicated that the charge transfer (p-p transition) complex was formed. The adsorption capacity with copper was found to be superior, 320?mg?g-1, and adsorption capacities for other transition metal ions were also found to be good such as Fe3+, Mn2+, Co3+, Cr3+, Ni2+, and Zn2+ were 255, 260, 300, 280, 233, and 223?mg?g-1, respectively, at pH?6. The experimental data show that all metal ions fitted well with the pseudo-second-order rate equation. The sorption results of the transition metal ions onto ligand were well fitted with Langmuir isotherm model (R2?>?0.98), which implies the homogenous and monolayer character of poly(hydroxamic acid) ligand surface. Eleven cycles sorption/desorption process were applied to verify the reusability of this adsorbent. The investigation of sorption and extraction efficiency in each cycle indicated that this new type of adsorbent can be recycled in many cycles with no significant loss in its original detection and removal capability

Bio-waste corn–cob cellulose supported poly (amidoxime) palladium nanoparticles for Suzuki-Miyaura cross-coupling reactions

Waste corn-cob cellulose supported poly(amidoxime) palladium nanoparticles (PdNs@PA) were prepared by the surface modification of waste corn-cob cellulose through graft co-polymerization and subsequent amidoximation. The supported nanoperticles showed high catalytic activity (45-400 mol ppm) towards Suzuki-Miyaura cross-coupling of aryl bromides/chlorides with organoboronic acids to give the corresponding biaryl products up to 99 % yield with high turnover number (TON) 19777 and turnover frequency (TOF) 4944 h−1. The PdNs@PA was easily recovered from the reaction mixture and reused several times without significant loss of its catalytic activity

Enhanced reliability of vertical strained impact ionization MOSFET incorporating dielectric pocket for ultra-sensitive biosensor applications

Fast switching with an enhanced reliability device structure of Vertical Strained Impact Ionization MOSFET incorporating Dielectric Pocket (VESIMOS-DP) has been successfully design, simulated and analyzed in this paper. Ultra-low power with low subthreshold swing (S) and high breakdown voltage are imperative for ultra-sensitive biosensors. Impact ionization MOSFET (IMOS) is predicted to be capable of S as low as 20 mV/dec, which is much lower than Conventional MOSFET (CMOS). There are significant drop in subthreshold slope (S) while threshold voltage is increase as the body doping concentration increases. S value for DP place at source side is higher (S 24.4 mV/decade) as compared at the drain side (S 18.9 mV/decade) intrinsic region. The vicinity of DP near the drain region reduces charge sharing effects associated with the source and thus improves impact ionization rate. The introduction of a Dielectric Pocket (DP) is believed to be able to minimize the PBT effect while improving the reliability of the device by attaining higher breakdown voltage. Consequently, with the reduced of alloy scattering, the electron mobility has been improved by 22%. In many aspects, it is revealed that the incorporation of DP enhanced the reliability of VESIMOS for future development of nanoelectronic devices

Chaotic variability of the Atlantic meridional overturning circulation at subannual time scales

This study describes the intra- to interannual variability of the Atlantic meridional overturning circulation (AMOC) and the relative dynamical contributions to the total variability in an eddy-resolving 1/128 resolution ocean model. Based on a 53-yr-long hindcast and two 4-yr-long ensembles, we assess the total AMOC variability as well as the variability arising from small differences in the ocean initial state that rapidly imprints on the mesoscale eddy fields and subsequently on large-scale features. This initial-condition-dependent variability will henceforth be referred to as “chaotic” variability. We find that intra-annual AMOC fluctuations are mainly driven by the atmospheric forcing, with the chaotic variability fraction never exceeding 26% of the total variance in the whole meridional Atlantic domain. To understand the nature of the chaotic variability we decompose the AMOC (into its Ekman, geostrophic, barotropic, and residual components). The barotropic and geostrophic AMOC contributions exhibit strong, partly compensating fluctuations, which are linked to chaotic spatial variations of currents over topography. In the North Atlantic, the largest chaotic divergence of ensemble members is found around 248, 388, and 648N. At 26.58N, where the AMOC is monitored by the RAPID– MOCHA array, the chaotic fraction of the AMOC variability is 10%. This fraction is slightly overestimated with the reconstruction methodology as used in the observations (∼15%). This higher fraction of chaotic variability is due to the barotropic contribution not being completely captured by the monitoring system. We look at the strong AMOC decline observed in 2009/10 and find that the ensemble spread (our measure for chaotic variability) was not particularly large during this event