M. K. Bera

Silver(I)-catalyzed dual activation of propargylic alcohol and aziridine/azetidine: triggering ring-opening and endo-selective ring-closing in a cascade.

[Ag(COD)(2)]PF(6) catalyzes the reaction between propargyl alcohols and N-tosylaziridines/azetidines leading to a diverse range of N,O-heterocycles, namely, oxazines, oxazepines, and oxazocines via ring-opening and ring-closing in a cascade.

Ag(I)-Catalyzed Regioselective Ring-Opening of N-Tosylaziridine and N-Tosylazetidine with S-, O-, and N-Nucleophiles and Tethered Dinucleophiles

[Ag(COD)(2)]PF(6) catalyzes the ring-opening of N-tosylaziridines and -azetidines with alcohols, amines, thiols, and related tethered 1,2-ethane dinucleophiles. Initial rate studies and DFT-based evaluation of stepwise energetics suggest an inverse relationship between the nucleophilic reactivity of a heteroatom donor and its binding affinity to cationic Ag(I).

Leakage current characteristics and the energy band diagram of Al/ZrO2/Si0.3Ge0.7 hetero-MIS structures

Zirconium oxide (ZrO2) films have been deposited on Ge-rich SiGe heterolayers at 150 ?C by the microwave plasma enhanced chemical vapour deposition (PECVD) technique using zirconium tetra-tert-butoxide. The possible conduction mechanisms in deposited ZrO2 films have been investigated at both room and high temperature. It is found that the conduction mechanism is dominated by Schottky emission at a low electric field (E 1.2 MV cm?1). The extracted trap energy is about 0.78 eV from the conduction band of ZrO2. It is shown that the current in ZrO2 films exhibits strong temperature dependence at a low electric field. The trapping behaviour of the charge carriers in thin ZrO2 gate dielectric stacks during constant gate voltage stress of metal?oxide?semiconductor capacitors has also been investigated.

Silver(I)−Diene Complexes as Versatile Catalysts for the C-Arylation of N-Tosylaziridines: Mechanistic Insight from In Situ Diagnostics

Silver(I) complex [Ag(diene)(2)](+)Y(-) (where diene = cyclooctadiene, norbornadiene, and 1,3-cyclohexadiene; Y(-) = PF(6)(-), BF(4)(-)) efficiently catalyzes the arylation of N-tosylaziridines with arenes and heteroarenes under ambient condition to provide the corresponding beta-aryl amine derivatives with excellent regioselectivity. To understand the nature of substrate activation, and initial bond breaking/making steps, the following studies were conducted with the help of in situ NMR ((1)H, (31)P, (109)Ag) and ESI-MS probe: (I) evaluation of Hammett reaction constant (rho); (II) correlation of initial rate (k) versus cone angle (theta) of ligand L for reactions mediated by [Ag(COD)(2)]PF(6)/L (where L is a phosphine or a phosphite ligand); (III) identification of silver-arene intermediates in solution; and (IV) correlation of initial rate (k) with Delta(HOMO-LUMO) of [Ag(diene)(2)]PF(6) obtained from preliminary DFT studies. Study I led to a rho-value of -0.586, indicating that the extent of electrophilic perturbation is considerably less than a typical Lewis acid catalyzed process. Study II indicated that initial rate (k) increases with concomitant increase in theta, as well with Delta(31)P((complex-ligand)), which corroborates to a mechanism involving prior ligand dissociation. Study III showed the plausible formation of [Ag(diene)(arene)](+) and [Ag(arene)(2)](+) as reactive species in solution. Study IV showed that the dependence of initial rate (k) with diene ligand is in the order COD > NBD > CHD; which corresponds well with the order of hardness of the respective Ag(I) complexes.

Analysis of interface states of Al/TiO2/Si0.3Ge0.7 MIS structures using the conductance technique

TiO2 films have been deposited at a low temperature (~150 ?C) using titanium tetrakis isopropoxide (TTIP) as an organometallic precursor on Si0.3Ge0.7 heterolayers by a microwave plasma-enhanced chemical vapour deposition system. Interfacial properties of the as-deposited films have been characterized using capacitance?voltage and conductance?voltage techniques measured at different frequencies. The energy distribution of interface states and the relaxation time have been determined from Gp/? versus ? analysis. A Dit level of Al/TiO2/SiGe MIS capacitors in the range of 2.87 ? 1011 eV?1 cm?2 (in EC-0.446) eV to 5.04 ? 1011 eV?1 cm?2 (in EC-0.696) eV has been observed from conductance measurements.

Effects of annealing on the electrical properties of TiO2 films deposited on Ge-rich SiGe substrates

Titanium oxide (TiO2) high-k dielectric layers were deposited on the Si0.3Ge0.7 substrates by plasma enhanced chemical vapor deposition (PECVD) at low temperature (150°C). To study the effects of annealing on the electrical properties, the TiO2 films were annealed in pure nitrogen ambient in the temperature range of 400–600°C. Good electrical performance for the gate dielectrics was observed for the dielectric films annealed up to 500°C, in terms of interface state density, leakage current, and charge trapping properties. Annealing at 600°C is found to degrade the electrical properties due to Ge segregation and subsequent diffusion into the TiO2 layer. Schottky emission was found to be the dominant leakage current conduction mechanism in PECVD TiO2 films.

Rapid thermal oxidation of Ge-rich Si1−xGex heterolayers

Rapid thermal oxidation (RTO) of the Ge-rich (x=0.7)Si1−xGex heterolayer is reported. In particular, the structural modifications of SiGe films during oxidation process and the dependence of the oxidation kinetics on Ge content, oxidation temperature, and oxide thickness have been studied. The segregation mechanism of Ge at the oxide∕SiGe interface is discussed. Interface properties of the RTO-grown oxides studied using high-frequency capacitance-voltage (C-V) characteristics of metal-oxide-semiconductor capacitors are also reported.

Charge trapping properties of ultra-thin TiO2 films on strained-Si

Ultra-thin high-k titanium oxide (equivalent oxide thickness ~2.2 nm) films have been deposited on strained-Si/relaxed-SiGe heterolayers using microwave plasma at 1000 s) is observed for as-deposited TiO2 under high constant voltage stress.

Internal Photoemission Study on Reliability of Ultra-thin Zirconium Oxide Films on Strained-Si

As scaling laws become less effective in boosting performance for CMOS devices for 90 nm and below, substrate- and process-induced strain engineering are playing an ever increasing role in performance enhancement. Strained-Si MOSFETs are also attractive for high speed and low power applications (Maiti et al., 2007). Ultra thin SiO2 gate dielectrics, of less than 1.5 nm in thickness, are needed for the 45 nm technology node and beyond. In order to reduce the leakage current, an extensive search for alternative high dielectric constant (high-k) gate materials that would probably replace the SiO2 for the sub-45 nm CMOS technologies is being pursued. In this article, we report for the first time, the results of the internal photoemission (IPE) study on reliability properties of microwave-plasma deposited high-k gate dielectric (ZrO2) films on strained-Si/SiGe heterolayers. The kinetics of charge trapping/detrapping and its chemical nature have been investigated through IPE and electron paramagnetic resonance study.

Paramagnetic defects and charge trapping in TaYOx gate dielectrics on strained-Si

Charge trapping kinetics and chemical nature of defects present in Al/TaYOx/strained-Si/Si0.8Ge0.2 MIS capacitors have been studied using internal photoemission and magnetic resonance. Reliability characteristics have been studied using CVS and CCS techniques. Results of electron paramagnetic resonance (EPR) and internal photoemission (IPE) studies on the charge trapping behavior are reported.