Block Copolymer Nanostructures for Inorganic Oxide Nanopatterning

Self-assembled nature of block copolymer (BCP) makes them ideal for emerging technologies in nanometer scale. The micro phase separation between two or more dissimilar polymer blocks of BCP leads to uniform periodic nanostructures of different domains of dimension in the range of 5-100 nm, good for the development of emerging microelectronic and optoelectronics devices. Molecular weight and chain architecture of each blocks govern the morphology evolution; gives different structure like spherical, micelles, lamellae, cylindrical, gyroid etc. The morphology evolution of BCP nanostructure also depends on different external factors as well. In the first work of this thesis, three external factors temperature, BCP thickness and brush layer which influences microphase separation and orientation of the BCP have been varied to study their influence on a cylinder forming BCP poly (styrene-block-methyl methacrylate (PS-b-PMMA). The well-organized periodic nanostructure of BCPs can be used as template to make inorganic nanopattern. In this work, titanium dioxide (TiO2) with unique structural and functional properties has been selected as inorganic material. In the second and third work of this thesis, I have used the same cylinder forming PS-b-PMMA as a template to deposit TiO2 nanodots using two different inorganic deposition methods. In the second work, room temperature pulse laser deposition (PLD) and in the third work wet chemical method were used to deposit TiO2 nanodots. Scanning electron microscope (SEM), energy dispersive x-ray spectroscopy (EDS), x-ray diffraction (XRD), and photoluminescence (PL) were used to characterize BCP and TiO2 nanostructures

Crystal Growth and Property Tuning of Layered Magnetic Topological Semimetals

The demand for energy-efficient devices has been growing rapidly due to the need for data-driven technologies and the global energy crisis. As device size approaches the atomic scale, the miniaturization of electronic devices may stop in the near future unless fundamentally new materials or device concepts are developed. The emergent topological materials with exotic properties show remarkable robustness against crystal lattice defects, which are promising for next-generation technology. These materials host exotic properties such as high mobility, large magnetoresistance, chiral anomaly, and surface Fermi arcs, etc. Among various topological materials, the ZrSiS-family materials exhibit two types of Dirac states, which provide opportunities to tune topological states by varying different parameters. The magnetic version of ZrSiS-family compounds, LnSbTe (Ln = lanthanide), hosts inherent magnetism, providing a novel platform to study the interplay between magnetism and exotic quantum states.With this motivation, this research is focused on the synthesis of single-crystal and characterization of previously unexplored magnetic topological nodal line semimetals LnSbTe. The compounds NdSbTe and SmSbTe exhibit antiferromagnetic ground states and enhanced electronic correlations. The magnetization and heat capacity measurements suggest the possible existence of magnetic frustration in tetragonally crystallized SmSbTe. Furthermore, the evolution of electronic and magnetic properties was studied with varying composition

High-resolution hyperfine spectroscopy of excited states using electromagnetically-induced transparency

We use the phenomenon of electromagnetically-induced transparency in a three-level atomic system for hyperfine spectroscopy of upper states that are not directly coupled to the ground state. The three levels form a ladder system: the probe laser couples the ground state to the lower excited state, while the control laser couples the two upper states. As the frequency of the control laser is scanned, the probe absorption shows transparency peaks whenever the control laser is resonant with a hyperfine level of the upper state. As an illustration of the technique, we measure hyperfine structure in the $7S_{1/2}$ states of $^{85}$Rb and $^{87}$Rb, and obtain an improvement of more than an order of magnitude over previous values.Comment: 7 pages, 6 figure

Quinolines and Related Compounds as Potential Antimalarials

Various 4-and 8-aminoquinoline derivatives having different substituents in the side chain and in the nucleus have been discussed in respect of their antimalarial activity and tolerance dosages. The effect of the incorporation of different moieties e.g. piperazine, piperidine and quinoline itself has also been highlighted. Certain quinoline quinones and benzoquinones as effective antimalarial agents have also been described

The proposed Nepal-China trans-border railway in Nepal’s collective imagination

Nepal-China relations have been amicable since the establishment of diplomatic ties in 1955. Consequently, the image of China in Nepal’s collective imagination has remained positive. This imagination reached new heights when China welcomed the promulgation of Nepal's new constitution in September 2015, while India, opposed to the promulgation, imposed an embargo. The Indian embargo not only undermined Nepali sovereignty by disapproving of the contents of the new constitution, but also compelled Nepal to think about lessening its dependency on India. The most obvious route was to expand trans-border connectivity with China. In March 2016, Nepal and China inked a ‘historic’ trade deal aiming to expand trans-border connectivity including a much-hyped trans-border railway link. Drawing broad public support, the deal had the effect of revitalising Nepali aspirations of coming out of an ‘India-locked’ trade and transit. This article examines opposing voices regarding the significance of this shift. On the one hand, there are those that embrace expansion of Nepal-China cross-border railway connectivity. Here, hopes are that railway connectivity will shift Nepal’s destiny away from dependence on India. On the other hand, many are wary that such a project is unaffordable, technically difficult, and most importantly, it plays into China’s interests in South Asian sub-regional geopolitics

Generalized H-fold sumset and Subsequence sum

Let $A$ and $H$ be nonempty finite sets of integers and positive integers, respectively. The generalized $H$-fold sumset, denoted by $H^{(r)}A$, is the union of the sumsets $h^{(r)}A$ for $h\in H$ where, the sumset $h^{(r)}A$ is the set of all integers that can be represented as a sum of $h$ elements from $A$ with no summand in the representation appearing more than $r$ times. In this paper, we find the optimal lower bound for the cardinality of $H^{(r)}A$, i.e., for $|H^{(r)}A|$ and the structure of the underlying sets $A$ and $H$ when $|H^{(r)}A|$ is equal to the optimal lower bound in the cases $A$ contains only positive integers and $A$ contains only nonnegative integers. This generalizes recent results of Bhanja. Furthermore, with a particular set $H$, since $H^{(r)}A$ generalizes subsequence sum and hence subset sum, we get several results of subsequence sums and subset sums as special cases.Comment: To be appear in C. R. Math. Acad. Sci. Paris, 25 page

Extended inverse theorems for hh-fold sumsets in integers

Let $h \geq 2$, $k \geq 5$ be integers and $A$ be a nonempty finite set of $k$ integers. Very recently, Tang and Xing studied extended inverse theorems for $hk-h+1 < \left|hA\right| \leq hk+2h-3$. In this paper, we extend the work of Tang and Xing and study all possible inverse theorems for $hk-h+1<\left|hA\right| \leq hk+3h-4$. Furthermore, we give a range of $|hA|$ for which inverse problems are not possible.Comment: To be appear in contrib. discrete math., 17 pages, correct some typographical errors, Statement and proof of some results change