Heterologous expression of xylanase gene from bacillus sp. in e. coli bl21 (DE3)

Xylanase gene of 642 bp with molecular weight 23kDa which was isolated from indigenous Bacillus sp. The isolated xylanase gene from indigenous Bacillus sp. was cloned into pET expression vector to obtain a high level expression of this recombinant family 11 xylanase in expression host E.coli BL21 (DE3). This attempt to clone the gene was initiated with the extraction of xylanase gene previously isolated from pGEM®-T easy cloning vector. The cloning vector was digested with restriction endonuclease and the xylanase insert was cloned into pET41(a) and transformed into E.coli BL21(DE3) via heat shock transformation. The expression was attempted to be observed through formation of halos in congo red staining method. Qualitative xylanase screening showed no detectable xylanase activity. This was predicted to be due to reasons like improper framing (frameshift) of cloned xylanase gene to LacZ promoter or incapability of E.coli BL21(DE3) to grow optimally in M9 minimal media with corn cob xylan source. It is highly recommended to get the full sequence of recombinant pET41(a)-Xyn to confirm the position of ligation of xylanase gene. The minimal media should also be altered in salt composition for optimized growth of E.coli BL21 (DE3)

Reactive plasma cleaning and restoration of transition metal dichalcogenide monolayers

The cleaning of two-dimensional (2D) materials is an essential step in the fabrication of future devices, leveraging their unique physical, optical, and chemical properties. Part of these emerging 2D materials are transition metal dichalcogenides (TMDs). So far there is limited understanding of the cleaning of “monolayer” TMD materials. In this study, we report on the use of downstream H2 plasma to clean the surface of monolayer WS2 grown by MOCVD. We demonstrate that high-temperature processing is essential, allowing to maximize the removal rate of polymers and to mitigate damage caused to the WS2 in the form of sulfur vacancies. We show that low temperature in situ carbonyl sulfide (OCS) soak is an efficient way to resulfurize the material, besides high-temperature H2S annealing. The cleaning processes and mechanisms elucidated in this work are tested on back-gated field-effect transistors, confirming that transport properties of WS2 devices can be maintained by the combination of H2 plasma cleaning and OCS restoration. The low-damage plasma cleaning based on H2 and OCS is very reproducible, fast (completed in a few minutes) and uses a 300 mm industrial plasma etch system qualified for standard semiconductor pilot production. This process is, therefore, expected to enable the industrial scale-up of 2D-based devices, co-integrated with silicon technology

A novel technique for detoxification of phenol from wastewater: Nanoparticle Assisted Nano Filtration (NANF)

© 2016 Naidu et al. Background: Phenol is one of the most versatile and important organic compound. It is also a growing concern as water pollutants due to its high persistence and toxicity. Removal of Phenol from wastewaters was investigated using a novel nanoparticle adsorption and nanofiltration technique named as Nanoparticle Assisted Nano Filtration (NANF). Methods: The nanoparticle used for NANF study were silver nanoparticles and synthesized to three distinct average particle sizes of 10 nm, 40 nm and 70 nm. The effect of nanoparticle size, their concentrations and their tri and diparticle combinations upon phenol removal were studied. Results: Total surface areas (TSA) for various particle size and concentrations have been calculated and the highest was 4710 × 1012 nm2 for 10 nm particles and 180 ppm concentration while the lowest was for 2461 × 1011 for 70 nm and 60 ppm concentrations. Tri and diparticle studies showed more phenol removal % than that of their individual particles, particularly for using small particles on large membrane pore size and large particles at low concentrations. These results have also been confirmed with COD and toxicity removal studies. Conclusions: The combination of nanoparticles adsorption and nanofiltration results in high phenol removal and mineralization, leading to the conclusion that NANF has very high potential for treating toxic chemical wastewaters

Process Integration for Graphene Tunnel Field Effect Transistors

CMOS scaling over the years has brought great improvements in the computational speed, density and cost of microprocessors. However, scaling is approaching its limits owing to the difficulty in reducing the supply voltage with conventional MOSFETs having at best a subthreshold swing of 60mv/decade. A possible alternative is Tunnel FETs (TFETs) where carrier transport happens through band-to-band tunneling as opposed to thermal injection in MOSFETs. While silicon and III-V semiconductors have been investigated in this context, carbon-based and the large family of transition metal dichalcogenides offer more material flexibility and better electrostatic control. Bilayer Graphene (BLG) has the interesting property that an appreciable band gap can be induced electrostatically. Additionally, its low effective mass (0.05me), direct bandgap and ultra-thin body make it highly suitable for TFETs. Theoretical studies for BLG TFETs have shown promising results, although practical implementation requires several technical hurdles to be overcome. To address some of these, process modules for realization of BLG TFET have been developed in this dissertation. Channel-Length Scaling: To replace conventional Si MOSFETs, graphene and other 2D materials should demonstrate superior behavior in the short-channel devices. Thus, a recipe for fabricating devices with a channel length down to 40nm was developed and demonstrated in the lab. Also, MoS2 devices were fabricated with this recipe and their electrical properties were compared over a range of channel-lengths. Contact-doping on Single-Layer Graphene (SLG): BLG TFET architectures exploiting the effect of charge transfer between metal and graphene to realize abrupt P-i-N structure has been proposed in literature. An experimental study towards quantifying doping by metal on large area SLG was performed with Transfer Length method (TLM). Coupled with the scaling module, CVD graphene was used to obtain a statistical variation of various electrical parameters crucial for realization of logic devices. Also, an evaluation using a model based on Landauer-Buttiker formalism was performed to understand the electrostatic and geometric factors for designing P-N junctions. Further, suggestions regarding extending the results to BLG has been proposed. Gate-Stack on Graphene: Gate-dielectric scaling is very important for enabling overall device scaling. Due to weak Vander Waals’ interaction between graphene layers, growing a reliable oxide on graphene channel has been a challenge. In this work, a low temperature Atomic Layer Deposition (ALD) recipe for high k-dielectrics - Aluminum oxide (Al2O3) - over graphene has been developed and investigated through physical and electrical characterization.Electronic Components, Technology and Materials GroupMicroelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc