A. K. M. Maidul Islam

Alumina-Supported Cu(II), A Versatile and Recyclable Catalyst for Regioselective Ring Opening of Aziridines and Epoxides and Subsequent Cyclization to Functionalized 1,4-Benzoxazines and 1,4-Benzodioxanes

An easily accessible catalyst, alumina-supported copper(II), efficiently catalyzes the ring opening of aziridines and epoxides followed by cyclization of the corresponding intermediate to produce a variety of functionalized 1,4-benzoxazines and 1,4-benzodioxanes, respectively, in one pot without any ligand in high yields. The ring cleavages of aziridines and epoxides are highly regioselective. The catalyst is inexpensive, non-air-sensitive, environmentally friendly, and recyclable. The function of the catalyst and the reaction pathway are postulated. This protocol is successfully utilized for the formation of three carbon-heteroatom bonds, namely, C-O, C-N, and C-S, in one pot.

Crystalline growth of rubrene film enhanced by vertical ordering in cadmium arachidate multilayer substrate.

The growth of highly crystalline rubrene thin films for organic field effect transistor (OFET) application remains a challenge. Here, we report on the vapor-deposited growth of rubrene films on the substrates made of cadmium arachidate (CdA) multilayers deposited onto SiO2/Si(100) via the Langmuir-Blodgett technique. The CdA films, containing 2n+1 layers, with integer n ranging from 0 to 4, are surface-terminated identically by the methyl group but exhibit the thickness-dependent morphology. The morphology and structure of both CdA and rubrene films are characterized by X-ray reflectivity (XRR), X-ray diffraction (XRD), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and atomic force microscopy (AFM). Crystalline rubrene films, evidenced by XRD and marked by platelet features in AFM images, become observable when grown onto the CdA layer thicker than 5L. XRD data show that vertical ordering, that is, ordering along surface normal, of CdA multilayer substrates exerts a strong influence in promoting the crystalline growth of rubrene films. This promoted growth is not due to the surface energy of CdA layer but derived from the additional interaction localized between rubrene and CdA island sidewall and presumably strengthened by a close dimensional match between the a-axis of rubrene lattice and the layer spacing of CdA multilayer. The best OFET mobility is recorded for 9L CdA substrate and reaches 6.7 × 10(-2) cm(2) V(-1) s(-1), presumably limited by the roughness of the interface between CdA and rubrene films.

Characterization of Langmuir−Blodgett Film Using Differential Charging in X-ray Photoelectron Spectroscopy

Differential charging is often regarded as a problem in X-ray photoelectron spectroscopy (XPS) studies, especially for insulating or partially conducting samples. Neutralization techniques have been developed to circumvent this effect. Instead of neutralizing the positive charge, which is often the technique to obtain good quality data, it is possible to exploit this phenomenon to get useful information about the sample. An attempt is made here to use this differential charging to study the mono- and multilayer Langmuir-Blodgett (LB) films of cadmium arachidate on silicon substrate. The surface potential was probed by measuring XPS line shift with respect to their neutral position and was found to have correlation with the thickness of the films. No differential charging was observed in the monolayer LB film where there was only one layer of cadmium headgroup. Significant differential charging was observed for multilayer films, the total charging as well as the differential charging in these films increase with increasing number of layers. Angle-resolved XPS measurements were performed to obtain additional information about the structure of the films. Charging of the upper layer of the films close to the vacuum interface was found to be less compared to that of the interior. The discrete cadmium layers were found to be more differentially charged compared to the continuous hydrocarbon stacks in the multilayer LB films. Charging of the discrete cadmium layers has been utilized to obtain quantitative information of the multilayer LB films.

Effect of temperature in synthesis of silver nanoparticles in triblock copolymer micellar solution

Knowing that poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) in aqueous solution is thermoresponsive, the effect of temperature on formation and stabilisation of silver nanoparticles has been investigated systematically. Synthesis of silver nanoparticles was achieved from silver ammonia complex [Ag(NH3)2]+ in aqueous solution of hydroxyl terminated PEO–PPO–PEO at four different temperatures. A non-Arrhenius behaviour for the rate of silver reduction with temperature was observed. The hydrodynamic diameter of the composite coils suddenly increased at certain intermediate time indicating sudden agglomeration of individual micelles to form bigger network structures. The size and the distribution of the nanoparticles show a bimodal distribution at the lowest temperature. At intermediate temperature, particles of the smallest size with a narrow distribution was achieved. At the highest temperature, a bunch-like particle morphology was found. Chemical changes in polymer properties were observed at higher temperatures. The results suggest that at a lower temperature, a change in polymer morphology play an important role in controlling the particle size and their distribution, whereas at a higher temperature, this role is shifted to the chemical change of the polymer. At an intermediate temperature, a balance between the two effects provides the optimum condition for formation of silver nanoparticles of small size and narrow distribution.

Characterization of RF Sputter-Deposited Ultra Thin PZT Films and Its Interface With Substrate

Lead Zirconate Titanate [Pb(Zr,Ti)O3, PZT] thin films have been extensively studied due to their possible applications in ferroelectric and piezoelectric devices. This work deals with the synthesis and characterization of ultra thin PZT films of thickness ∼100 nm deposited on Si/SiO2/TiO2/Pt(111) by RF Magnetron Sputtering under optimized deposition and post-annealing conditions. Various techniques like XRD, XPS, SIMS, SEM and TEM, have been employed to characterize the film nanostructure and the interface quality in the post-annealed films. Though the XRD results showed the formation of ∼87 vol% perovskite phase with 111 orientation, the films failed to show good electrical and ferroelectric properties. In XPS study of annealed PZT films, Pb was found to exist in both oxidised and metallic states. Both SIMS depth profiling and STEM-EDX line profile results showed that there is an enrichment of Pb along the PZT/Pt interface. This suggests interdiffusion of the elements in the film during post-annealing. It is concluded that interdiffusion of the chemical species during annealing results in Pb enrichment at the film substrate interface. In addition, the presence of ∼13% non-ferroelectric pyrochlore phase as well as some amount of Pb species present in metallic state further degrades the film quality.

Evolution of orbital phases with particle size in nanoscale stoichiometric LaMnO3

The thermodynamically stable long-range orbital order in bulk LaMnO3 becomes metastable at nanoscale around a critical particle size dC 20 nm. The orbital order–disorder transition switches from reversible to irreversible at dC while the resistance in the orbital ordered state decays by 2%–4% over a time scale of ∼3000s. At well below dC, of course, a stable orbital disordered phase emerges. The orthorhombic distortion of the underlying crystallographic structure (space group Pbnm) decreases systematically with the decrease in particle size and at far below dC (e.g., at ∼10 nm), the structure becomes cubic (space group Pm3−m). Using the crystallographic and electrical resistance data, a phase diagram has been constructed showing the evolution of different orbital phases as a function of particle size across 10 nm to bulk for stoichiometric LaMnO3.

Improvement of rubrene thin film transistor with self assembled monolayer of octadecyltrichlorosilane (OTS)

We have fabricated organic thin film transistors (OTFTs) using rubrene as an active layer with untreated SiO2 and OTS modified SiO2 gate dielectrics. The effect of the OTS treatment on the electric characteristics of OTFT was investigated. As a result of OTS modification, we can improve the mobility to 0.12×10−2 cm2/V.S and IOn/IOff ratio to 0.98×105.