Chalcogen Assisted Enhanced Atomic Orbital Interaction at TMDs - Metal Interface & Chalcogen Passivation of TMD Channel For Overall Performance Boost of 2D TMD FETs

Metal-semiconductor interface is a bottleneck for efficient transport of charge carriers through Transition Metal Dichalcogenide (TMD) based field-effect transistors (FETs). Injection of charge carriers across such interfaces is mostly limited by Schottky barrier at the contacts which must be reduced to achieve highly efficient contacts for carrier injection into the channel. Here we introduce a universal approach involving dry chemistry to enhance atomic orbital interaction between various TMDs (MoS2, WS2, MoSe2 and WSe2) & metal contacts has been experimentally demonstrated. Quantum chemistry between TMDs, Chalcogens and metals has been explored using detailed atomistic (DFT & NEGF) simulations, which is then verified using Raman, PL and XPS investigations. Atomistic investigations revealed lower contact resistance due to enhanced orbital interaction and unique physics of charge sharing between constituent atoms in TMDs with introduced Chalcogen atoms which is subsequently validated through experiments. Besides contact engineering, which lowered contact resistance by 72, 86, 1.8, 13 times in MoS2, WS2, MoSe2 and WSe2 respectively, a novel approach to cure / passivate dangling bonds present at the 2D TMD channel surface has been demonstrated. While the contact engineering improved the ON-state performance (ION, gm, mobility and RON) of 2D TMD FETs by orders of magnitude, Chalcogen based channel passivation was found to improve gate control (IOFF, SS, & VTH) significantly. This resulted in an overall performance boost. The engineered TMD FETs were shown to have performance on par with best reported till date

Disosiasi H2S dalam Gas Alam pada Temperatur Ruang Menggunakan Katalisator MgO: Pengaruh Jumlah Katalis dan Laju Alir Massa

The presence of H2S in natural gas is very detrimental to ammonia industry because it can poison and deactivate steam reforming catalysts. In the ammonia plant Pusri-IB PT. Pusri Palembang, H2S was separated in the Desulfurizer Unit (201-D) by adsorption using ZnO adsorbent at low temperature (28 ° C). Unfortunately, in this process the ZnO adsorbent cannot be regenerated so that within one year the ZnO adsorbent will be saturated with sulfur. The alternative process of H2S separation is to dissociate H2S into its constituent elements (hydrogen and sulfur) with catalytic process. The magnesium oxide catalyst was chosen because magnesium oxide is a metal oxide compound widely known in the catalysis process and has two active sites. The highest H2S conversion that can be achieved by MgO catalyst is 92.29%. Unlike ZnO, MgO does not absorb H2S, but catalyzes the dissociation of H2S into hydrogen and solid sulfur without being changed consumed by the reaction itself so that the MgO catalyst has a longer life time than the ZnO adsorbent.A B S T R A KKandungan H2S dalam gas alam sangat merugikan bagi industri amoniak karena dapat meracuni dan mendeaktivasi katalis steam reforming. Di pabrik amoniak Pusri-IB PT. Pusri Palembang, H2S dipisahkan di Unit Desulfurizer (201-D) secara adsorpsi dengan menggunakan adsorben ZnO pada temperatur rendah (28 ° C). Namun sangat disayangkan, pada proses ini adsorben ZnO tidak dapat diregenerasi sehingga dalam kurun waktu satu tahun adsorben ZnO akan jenuh oleh sulfur. Salah satu alternatif proses pemisahan H2S adalah dengan mendisosiasi H2S menjadi unsur penyusunnya yaitu hidrogen dan sulfur dengan bantuan katalis. Katalis magnesium oksida dipilih karena magnesium oksida merupakan senyawa metal oksida yang penggunaannya sudah dikenal luas dalam proses katalisis serta memiliki dua gugus aktif. Konversi H2S tertinggi yang dapat dicapai katalis MgO adalah sebesar 92,29%. Berbeda halnya dengan ZnO, MgO tidak menyerap H2S, namun mengkatalisis proses disosiasi H2S menjadi hidrogen dan sulfur padat tanpa mengalami perubahan atau terkonsumsi oleh reaksi itu sendiri sehingga katalis MgO memiliki life time yang lebih lama dibanding adsorben ZnO.

Evidence of quasi-intramolecular redox reactions during thermal decomposition of ammonium hydroxodisulfitoferriate(III), (NH4)(2)[Fe(OH)(SO3)(2)]center dot H2O

Synthesis of ammonium hydroxodisulfitoferriate(III), (diammonium catena-{bis(mu (2)-sulfito-kappa O,kappa O)-mu (2)-hydroxo-kappa O-2}ferrate(III) monohydrate) (NH4)(2)[Fe(OH)(SO3)(2)]center dot H2O (compound 1) and its thermal behavior is reported. The compound is stable in air. Its thermal decomposition proceeds without the expected quasi-intramolecular oxidation of sulfite ion with ferric ions. The disproportionation reaction of the ammonium sulfite, formed from the evolved NH3, SO2 and H2O in the main decomposition stage of 1, results in the formation of ammonium sulfate and ammonium sulfide. The ammonium sulfide is unstable at the decomposition temperature of 1 (150 A degrees C) and transforms into NH3 and H2S which immediately forms elementary sulfur by reaction with SO2. The formation and decomposition of other intermediate compounds like (NH4)(2)SnOx (n = 2, x = 3 and n = 3, x = 6) results in the same decomposition products (S, SO2 and NH3). Two basic iron sulfates, formed in different ratios during synthesizing experiments performed under N-2 or in the presence of air, have been detected as solid intermediates which contain ammonium ions. The final decomposition product was proved to be alpha-Fe2O3 (mineral name hematite)

Advanced Electrochemical Analysis for Complex Electrode Applications

This thesis has investigated several complex situations that may be encountered in electrochemical studies. Three main situations have been examined, they include the formation of polymer films on electrode surfaces during measurements, a novel nanocatalyst modified electrode surfaces, and organised carbon nanotube (CNT) structures on electrode surfaces. These have been utilised for different electrochemical applications owing to their dissimilar properties. Voltammetric techniques of cyclic voltammetry (CV), square wave voltammetry (SWV) and Fourier transformed large amplitude ac voltammetry (FTACV) have been utilised to examine these reactions. Chapter 3 reports the investigation of catechol oxidation and subsequent polymerisation through crosslinking with D-glucosamine or chitosan. Hydrogel can be formed on the electrode surface during the process, which changes the viscosity of the solution and thus affects the diffusion of chemical species. This process has been examined by several voltammetric techniques. A further examination of the chemical system has also been conducted using FTACV for the first time. Chapter 4 describes the preparation of carbon microsphere supported molybdenum disulfide. The material has been utilised as electrocatalysts for hydrogen evolution reaction (HER) in acidic media, and the performance tested by traditional linear sweep voltammetry (LSV) and advanced FTACV techniques. The FTACV technique has been used for the first time for HER processes. In addition, the synthesised particles have also been used for thermal catalytic decomposition of hydrogen sulfide, which shows a significant improvement in the conversion rate over conventional examples. Chapter 5 demonstrates the direct growth of vertically aligned CNT forests on a gold electrode. The electrochemical response of the fabricated electrode has also been examined with ferrocyanide as the redox species. Furthermore, the immobilisation of anthraquinone onto CNT forest has been attempted. The fabricated electrode was utilised as a pH sensor via CV and SWV, and both indicates a well correlated pH-potential relationship in the pH range of 2 to 12. The sensor has also been assessed by the FTACV technique.Schlumberger Gould Research Campus for Research Excellence and Technological Enterprise (CREATE) programme in Singapor