arXiv subjects

Santanu Maiti

Publications and source records attributed to Santanu Maiti.

5 recordsLinked to original sources

arXiv2025

3D Electron Diffraction -- The Missing Slice for a Complete Nanoscale Analysis of Organic Solar Cells in TEM

Optimizing the performance of organic solar cells (OSCs) hinges on a comprehensive understanding of their nanostructures, yet traditional characterization methods often fall short, delivering incomplete structural snapshots. We introduce elastically filtered 3D Electron Diffraction (3D ED) as a ground-breaking technique bridging full reciprocal- and real-space structural analysis within a single transmission electron microscope (TEM). Using solvent-vapor annealed DRCN5T:PC71BM, 3D ED reproduces key structural parameters from GIWAXS including lattice spacings, coherence lengths, and mosaicity, while uniquely delivering true in-plane access and direct registration with high-resolution imaging, diffraction imaging and nano-spectroscopy on the same sample. A low-dose, distributed tilt strategy plus energy filtering yields high signal-to-background below damage thresholds. Extension to a second archetypal blend (P3HT:PC71BM; annealing evolution) demonstrates generality. Our findings underscore the transformative potential of 3D ED, particularly in analysing beam-sensitive organic thin films. This paves the way for new avenues in advanced correlative structural characterization of OSCs and holds potential for application to a multitude of other nanostructured materials.

cond-mat.mtrl-sci↗

arXiv2021

Thin Film Growth of Phase-Separating Phthalocyanine-Fullerene Blends: A Combined Experimental and Computational Study

Blended organic thin films have been studied during the last decades due to their applicability in organic solar cells. Although their optical and electronic features have been examined intensively, there is still lack of detailed knowledge about their growth processes and resulting morphologies, which play a key role for the efficiency of optoelectronic devices such as organic solar cells. In this study, pure and blended thin films of copper phthalocyanine (CuPc) and the Buckminster fullerene (C60) were grown by vacuum deposition onto a native silicon oxide substrate at two different substrate temperatures, 310 K and 400 K. The evolution of roughness was followed by in-situ real-time X-ray reflectivity. Crystal orientation, island densities and morphology were examined after the growth by X-ray diffraction experiments and microscopy techniques. The formation of a smooth wetting layer followed by rapid roughening was found in pure CuPc thin films, whereas C60 shows a fast formation of distinct islands at a very early stage of growth. The growth of needle-like CuPc crystals loosing their alignment with the substrate was identified in co-deposited thin films. Furthermore, the data demonstrates that structural features become larger and more pronounced and that the island density decreases by a factor of four when going from 310 K to 400 K. Finally, the key parameters roughness and island density were well reproduced on a smaller scale by kinetic Monte-Carlo simulations of a generic, binary lattice model with simple nearest-neighbor interaction energies.

cond-mat.mtrl-sci↗

arXiv2020

A Neutron Scattering Perspective on the Structure, Softness and Dynamics of the Ligand Shell of PbS Nanocrystals in Solution

Small-angle neutron and X-ray scattering, neutron backscattering and neutron time-of-flight spectroscopy are applied to reveal the structure of the ligand shell, the temperature-dependent diffusion properties and the phonon spectrum of PbS nanocrystals functionalized with oleic acid in deuterated hexane. The nanocrystals decorated with oleic acid as well as the desorbed ligand molecules exhibit simple Brownian diffusion with a Stokes-Einstein temperature-dependence and inhibited freezing. Ligand molecules desorbed from the surface show strong spatial confinement. The phonon spectrum of oleic acid adsorbed to the nanocrystal surface exhibits hybrid modes with a predominant Pb-character. Low-energy surface modes of the NCs are prominent and indicate a large mechanical softness in solution. This work provides comprehensive insights into the ligand-particle interaction of colloidal nanocrystals in solution and highlights its effect on the diffusion and vibrational properties as well as their mechanical softness.

cond-mat.mtrl-sci↗

arXiv2019

Grazing incidence x-ray diffraction studies of lipid-peptide mixed monolayers during shear flow

Grazing Incidence X-ray Diffraction (GIXD) studies of monolayers of biomolecules at the air-water interface give quantitative information of in-plane packing, coherence lengths of the ordered diffracting crystalline domains and the orientation of hydrocarbon chains. Rheo-GIXD measurements revel quantitative changes in the monolayer under shear. Here we report GIXD studies of monolayers of Alamethicin peptide, DPPC lipid and their mixtures at the air-water interface under the application of steady shear stresses. The Alamethicin monolayer and the mixed monolayer show flow jamming transition. On the other hand, pure DPPC monolayer under the constant stress flows steadily with a notable enhancement of area/molecule, coherence length, and the tilt angle with increasing stress, suggesting fusion of nanocrystallites during flow. The DPPC-Alamethicin mixed monolayer shows no significant change in the area/DPPC molecule or in the DPPC chain tilt but the coherence length of both phases (DPPC and Alamethicin) increases suggesting that the crystallites of individual phases are merging to bigger size promoting more separation of phases in the system during flow. Our results show that Rheo-GIXD has the potential to explore in-situ molecular structural changes under rheological conditions for a diverse range of confined biomolecules at the interfaces.

cond-mat.soft↗

arXiv2019

Dye-Sensitized Ternary Copper Chalcogenide Nanocrystals: Optoelectronic Properties, Air Stability and Photosensitivity

We report on the effect of ligand exchange of copper sulphide selenide as well as copper selenide nanocrystals with the organic pi-system Cobalt beta-tetraaminophthalocyanine and analyse changes in the structural, optical as well as electric properties of thin films of these hybrid materials. A strong ligand interaction with the surface of the nanocrystals is revealed by UV-vis absorption and Raman spectroscopy. Grazing-incidence small-angle X-ray scattering studies show a significant contraction in the interparticle distance upon ligand exchange. For copper-deficient copper selenide, this contraction has a negligible effect on electric transport, while for copper-deficient copper sulphide selenide, the conductivity increases by eight orders of magnitude and results in metal-like temperature-dependent transport. We discuss these differences in the light of varying contributions of electronic vs. ionic transport in the two materials and highlight their effect on the stability of the transport properties under ambient conditions. With photocurrent measurements, we demonstrate high optical responsivities of 200-400 A W-1 for the phthalocyanine-capped copper sulphide selenide and emphasize the beneficial role of the organic pi-system in this respect, which acts as an electronic linker and an optical sensitizer at the same time.

cond-mat.mtrl-sci↗