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1. Real-Time In Situ Observation of CsPbBr3 Perovskite Nanoplatelets Transforming into Nanosheets

Author

Prabhakaran, Aarya, Dang, Zhiya, Dhall, Rohan, Camerin, Fabrizio, Marín-Aguilar, Susana, Dhanabalan, Balaji, Castelli, Andrea, Brescia, Rosaria, Manna, Liberato, Dijkstra, Marjolein, and Arciniegas, Milena P

Subjects
Macromolecular and Materials Chemistry, Chemical Sciences, Physical Chemistry, in situ TEM, in situ heating, perovskite nanoplatelets, self-assembly, shape transformation, Nanoscience & Nanotechnology
Abstract

The manipulation of nano-objects through heating is an effective strategy for inducing structural modifications and therefore changing the optoelectronic properties of semiconducting materials. Despite its potential, the underlying mechanism of the structural transformations remains elusive, largely due to the challenges associated with their in situ observations. To address these issues, we synthesize temperature-sensitive CsPbBr3 perovskite nanoplatelets and investigate their structural evolution at the nanoscale using in situ heating transmission electron microscopy. We observe the morphological changes that start from the self-assembly of the nanoplatelets into ribbons on a substrate. We identify several paths of merging nanoplates within ribbons that ultimately lead to the formation of nanosheets dispersed randomly on the substrate. These observations are supported by molecular dynamics simulations. We correlate the various paths for merging to the random orientation of the initial ribbons along with the ligand mobility (especially from the edges of the nanoplatelets). This leads to the preferential growth of individual nanosheets and the merging of neighboring ones. These processes enable the creation of structures with tunable emission, ranging from blue to green, all from a single material. Our real-time observations of the transformation of perovskite 2D nanocrystals reveal a route to achieve large-area nanosheets by controlling the initial orientation of the self-assembled objects with potential for large-scale applications.

Published
2023

2. Temperature Driven Transformation of CsPbBr$_3$ Nanoplatelets into Mosaic Nanotiles in Solution through Self-Assembly

Author

Dang, Zhiya, Dhanabalan, Balaji, Castelli, Andrea, Dhall, Rohan, Bustillo, Karen C., Marchelli, Dorwal, Spirito, Davide, Petralanda, Urko, Shamsi, Javad, Manna, Liberato, Krahne, Roman, and Arciniegas, Milena P.

Subjects
Physics - Applied Physics, Physics - Chemical Physics
Abstract

Two-dimensional colloidal halide perovskite nanocrystals are promising materials for light emitting applications. In addition, they can be used as components to create a variety of materials through physical and chemical transformations. Recent studies focused on nanoplatelets that are able to self-assemble and transform on solid substrates. Yet, the mechanism behind the process and the atomic arrangement of their assemblies remain unclear. Here, we present the transformation of self-assembled stacks of CsPbBr$_3$ nanoplatelets in solution, capturing the different stages of the process by keeping the solutions at room temperature and monitoring the nanocrystal morphology over a period of a few months. Using ex-situ transmission electron microscopy and surface analysis, we demonstrate that the transformation mechanism can be understood as oriented attachment, proceeding through the following steps: i) desorption of the ligands from the particles surfaces, causing the merging of nanoplatelet stacks, which first form nanobelts; ii) merging of neighboring nanobelts that form more extended nanoplates; and iii) attachment of nanobelts and nanoplates, which create objects with an atomic structure that resemble a mosaic made of broken nanotiles. We reveal that the starting nanoplatelets merge seamlessly and defect-free on an atomic scale in small and thin nanobelts. However, aged nanobelts and nanoplates, which are mainly stabilized by amine/ammonium ions, link through a bilayer of CsBr. In this case, the atomic columns of neighboring perovskite lattices shift by a half-unit-cell, forming Ruddlesden-Popper planar faults., Comment: 28 pages, 5 Figures

Published
2020
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3. Directional Anisotropy of the Vibrational Modes in 2D Layered Perovskites

Author

Dhanabalan, Balaji, Leng, Yu-Chen, Biffi, Giulia, Lin, Miao-Ling, Tan, Ping-Heng, Infante, Ivan, Manna, Liberato, Arciniegas, Milena P., and Krahne, Roman

Subjects
Physics - Chemical Physics, Condensed Matter - Materials Science
Abstract

The vibrational modes in organic/inorganic layered perovskites are of fundamental importance for their optoelectronic properties. The hierarchical architecture of the Ruddlesden-Popper phase of these materials allows for distinct directionality of the vibrational modes withrespect to the main axes of the pseudocubic lattice in the octahedral plane. Here, we study the directionality of the fundamental phonon modes in single exfoliated Ruddlesden-Popper perovskite flakes with polarized Raman spectroscopy at ultralow-frequencies. A wealth of Raman bands is distinguished in the range from 15-150 cm-1 (2-15 meV), whose features depend on the organic cation species, on temperature, and on the direction of the linear polarization of the incident light. By controlling the angle of the linear polarization of the excitation laser with respect to the in-plane axes of the octahedral layer, we gain detailed information on the symmetry of the vibrational modes. The choice of two different organic moieties, phenethylammonium (PEA) and butylammonium (BA) allows to discern the influence of the linker molecules, evidencing strong anisotropy of the vibrations for the (PEA)2PbBr4 samples. Temperature dependent Raman measurements reveal that the broad phonon bands observed at room temperature consist of a series of sharp modes, and that such mode splitting strongly differs for the different organic moieties and vibrational bands., Comment: 25 pages, 4 figures

Published
2020
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4. Core/Shell CdSe/CdS Bone-Shaped Nanocrystals with a Thick and Anisotropic Shell as Optical Emitters

Author

Castelli, Andrea, Dhanabalan, Balaji, Polovitsyn, Anatolii, Caligiuri, Vincenzo, Di Stasio, Francesco, Scarpellini, Alice, Brescia, Rosaria, Palei, Milan, Martin-Garcia, Beatriz, Prato, Mirko, Manna, Liberato, Moreels, Iwan, Krahne, Roman, and Arciniegas, Milena P.

Subjects
Physics - Chemical Physics
Abstract

Colloidal core/shell nanocrystals are key materials for optoelectronics, enabling control over essential properties via precise engineering of the shape, thickness, and crystal lattice structure of their shell. Here, we apply the growth protocol for CdS branched nanocrystals on CdSe nanoplatelet seeds and obtain bone-shaped heterostructures with a highly anisotropic shell. Surprisingly, the nanoplatelets withstand the high growth temperature of 350 {\deg}C and we obtain structures with a CdSe nanoplatelet core that is overcoated by a shell of cubic CdS, on top of which tetrahedral CdS structures with hexagonal lattice are formed. These complex core/shell nanocrystals show a bandedge emission around 657 nm with a photoluminescence quantum yield of ca. 42 % in solution, which is also retained in thin films. Interestingly, the nanocrystals manifest simultaneous red and green emission, and the relatively long wavelength of the green emission indicates charge recombination at the cubic/hexagonal interface of the CdS shell. The nanocrystal films show amplified spontaneous emission, random lasing, and distributed feedback lasing when the material is deposited on suitable gratings. Our work stimulates the design and fabrication of more exotic core/shell heterostructures where charge carrier delocalization, dipole moment, and other optical and electrical properties can be engineered., Comment: 26 pages, 6 figures, 1 table

Published
2020
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5. Unveiling the Secrets of tunable emission color coordinates in Sn-based layered related perovskite- structures

Author

Prabhakaran, Aarya, primary, Arciniegas, Milena P., additional, Andrusenko, Iryna, additional, Pianetti, Andrea, additional, Lauciello, Simone, additional, Prato, Mirko, additional, Dhanabalan, Balaji, additional, Solokha, Pavlo, additional, Gemmi, Mauro, additional, Brovelli, Sergio, additional, Manna, Liberato, additional, and Marras, Sergio, additional

Published
2023
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6. Real-Time In Situ Observation of CsPbBr3 Perovskite Nanoplatelets Transforming into Nanosheets

Author

Sub Soft Condensed Matter, Soft Condensed Matter and Biophysics, Prabhakaran, Aarya, Dang, Zhiya, Dhall, Rohan, Camerin, Fabrizio, Marín-Aguilar, Susana, Dhanabalan, Balaji, Castelli, Andrea, Brescia, Rosaria, Manna, Liberato, Dijkstra, Marjolein, Arciniegas, Milena P., Sub Soft Condensed Matter, Soft Condensed Matter and Biophysics, Prabhakaran, Aarya, Dang, Zhiya, Dhall, Rohan, Camerin, Fabrizio, Marín-Aguilar, Susana, Dhanabalan, Balaji, Castelli, Andrea, Brescia, Rosaria, Manna, Liberato, Dijkstra, Marjolein, and Arciniegas, Milena P.

Published
2023

7. Stable Sn-Based Hybrid Perovskite-Related Structures with Tunable Color Coordinates via Organic Cations in Low-Temperature Synthesis

Author

Prabhakaran, Aarya, primary, Dhanabalan, Balaji, additional, Andrusenko, Iryna, additional, Pianetti, Andrea, additional, Lauciello, Simone, additional, Prato, Mirko, additional, Marras, Sergio, additional, Solokha, Pavlo, additional, Gemmi, Mauro, additional, Brovelli, Sergio, additional, Manna, Liberato, additional, and Arciniegas, Milena P., additional

Published
2023
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10. Two-dimensional material-based printed photonics: a review

Author

Francis, Bibi Mary, primary, Ponraj, Joice Sophia, additional, Dhanabalan, Balaji, additional, Manavalan, Rajesh Kumar, additional, Veluswamy, Pandiyarasan, additional, Yin, Peng, additional, Al-Hartomy, Omar A, additional, Al-Ghamdi, Ahmed, additional, Wageh, Swelm, additional, Zhang, Han, additional, and Dhanabalan, Sathish Chander, additional

Published
2022
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11. Highly Emitting Perovskite Nanocrystals with 2-Year Stability in Water through an Automated Polymer Encapsulation for Bioimaging

Author

Avugadda, Sahitya Kumar, primary, Castelli, Andrea, additional, Dhanabalan, Balaji, additional, Fernandez, Tamara, additional, Silvestri, Niccolo, additional, Collantes, Cynthia, additional, Baranov, Dmitry, additional, Imran, Muhammad, additional, Manna, Liberato, additional, Pellegrino, Teresa, additional, and Arciniegas, Milena P., additional

Published
2022
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12. Correlating symmetries of low-frequency vibrations and self-trapped excitons in layered perovskites for light emission with different colors

Author

European Commission, Ministero degli Affari Esteri e della Cooperazione Internazionale, National Natural Science Foundation of China, China Postdoctoral Science Foundation, National Key Research and Development Program (China), Lin, Miao-Ling, Dhanabalan, Balaji, Biffi, Giulia, Leng, Yu-Chen, Kutkan, Seda, Arciniegas, Milena P., Tan, Ping-Heng, Krahne, Roman, European Commission, Ministero degli Affari Esteri e della Cooperazione Internazionale, National Natural Science Foundation of China, China Postdoctoral Science Foundation, National Key Research and Development Program (China), Lin, Miao-Ling, Dhanabalan, Balaji, Biffi, Giulia, Leng, Yu-Chen, Kutkan, Seda, Arciniegas, Milena P., Tan, Ping-Heng, and Krahne, Roman

Abstract

The soft hybrid organic–inorganic structure of two-dimensional layered perovskites (2DLPs) enables broadband emission at room temperature from a single material, which makes 2DLPs promising sources for solid-state white lighting, yet with low efficiency. The underlying photophysics involves self-trapping of excitons favored by distortions of the inorganic lattice and coupling to phonons, where the mechanism is still under debate. 2DLPs with different organic moieties and emission ranging from self-trapped exciton (STE)-dominated white light to blue band-edge photoluminescence are investigated. Detailed insights into the directional symmetries of phonon modes are gained using angle-resolved polarized Raman spectroscopy and are correlated to the temperature-dependence of the STE emission. It is demonstrated that weak STE bands at low-temperature are linked to in-plane phonons, and efficient room-temperature STE emission to more complex coupling to several phonon modes with out-of-plane components. Thereby, a unique view is provided into the lattice deformations and recombination dynamics that are key to designing more efficient materials.

Published
2022

17. Real-Time In Situ Observation of CsPbBr3Perovskite Nanoplatelets Transforming into Nanosheets

Author

Prabhakaran, Aarya, Dang, Zhiya, Dhall, Rohan, Camerin, Fabrizio, Marín-Aguilar, Susana, Dhanabalan, Balaji, Castelli, Andrea, Brescia, Rosaria, Manna, Liberato, Dijkstra, Marjolein, and Arciniegas, Milena P.

Abstract

The manipulation of nano-objects through heating is an effective strategy for inducing structural modifications and therefore changing the optoelectronic properties of semiconducting materials. Despite its potential, the underlying mechanism of the structural transformations remains elusive, largely due to the challenges associated with their in situ observations. To address these issues, we synthesize temperature-sensitive CsPbBr3perovskite nanoplatelets and investigate their structural evolution at the nanoscale using in situ heating transmission electron microscopy. We observe the morphological changes that start from the self-assembly of the nanoplatelets into ribbons on a substrate. We identify several paths of merging nanoplates within ribbons that ultimately lead to the formation of nanosheets dispersed randomly on the substrate. These observations are supported by molecular dynamics simulations. We correlate the various paths for merging to the random orientation of the initial ribbons along with the ligand mobility (especially from the edges of the nanoplatelets). This leads to the preferential growth of individual nanosheets and the merging of neighboring ones. These processes enable the creation of structures with tunable emission, ranging from blue to green, all from a single material. Our real-time observations of the transformation of perovskite 2D nanocrystals reveal a route to achieve large-area nanosheets by controlling the initial orientation of the self-assembled objects with potential for large-scale applications.

Published
2023
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18. Developing Metal-Halide Layered Perovskite Nanomaterials for Optoelectronics

Author

DHANABALAN, BALAJI

Subjects
White emission, Polarized Raman spectroscopy, Settore ING-IND/22 - Scienza e Tecnologia dei Materiali, Ruddlesden−Popper structure, Deep-blue emission, Organic cations, 2D layered perovskites, Mechanical emission switching
Abstract

The abundant chemical tunability along with outstanding optoelectronic properties of the 2D metal-halide layered perovskite materials, as well as the potential prospect on understanding the structure-property relationships at the molecular level, provide enormous opportunity for the scientific community on designing new and efficient 2D metal-halide layered perovskites for a specific optoelectronic application. These materials still require attention on understanding their fundamental electronic properties and on controlling their synthesis parameters to produce high quality materials. Moreover, the synergy between the organic and inorganic compounds in these systems further opens up the possibility to unlock novel optoelectronic properties by simply integrating many other available functional organic molecules into these structures. This thesis is dedicated to the synthesis of 2D lead-bromide Ruddlesden Popper layered perovskite materials through a simple synthesis technique and by using different organic molecules. It targets a full investigation of the photo-physical properties of the as synthesized materials. Moreover, it presents detailed studies on the effect of structural rigidity and electron-phonon interaction provided by organic molecules on the emission efficiencies of 2D layered perovskites, and their emission tunability by using organic molecules with different architectures. In a more technological view, this thesis summarizes the work performed on the integration of 2D layered perovskites in polymer films and their emission enhancement by mechanical stress.

Published
2021
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21. Engineering the Optical Emission and Robustness of Metal‐Halide Layered Perovskites through Ligand Accommodation

Author

Dhanabalan, Balaji, primary, Biffi, Giulia, additional, Moliterni, Anna, additional, Olieric, Vincent, additional, Giannini, Cinzia, additional, Saleh, Gabriele, additional, Ponet, Louis, additional, Prato, Mirko, additional, Imran, Muhammad, additional, Manna, Liberato, additional, Krahne, Roman, additional, Artyukhin, Sergey, additional, and Arciniegas, Milena P., additional

Published
2021
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26. Surface‐Dependent Properties and Tunable Photodetection of CsPbBr3 Microcrystals Grown on Functional Substrates.

Author

Abiedh, Khouloud, Dhanabalan, Balaji, Kutkan, Seda, Lauciello, Simone, Pasquale, Lea, Toma, Andrea, Salerno, Marco, Arciniegas, Milena P., Hassen, Fredj, and Krahne, Roman

Subjects
*ATOMIC force microscopy, *CURRENT-voltage curves, *SINGLE crystals, *THIN films, *METAL halides, *CURVES
Abstract

All‐inorganic metal halide perovskites are highly attractive materials for optoelectronics and are typically implemented as thin films, nanocrystals, and single crystals with macroscopic and millimeter‐size dimensions. Single crystals with regular shapes in the micrometer range are less explored and present an interesting alternative when a well‐defined and spatially localized response is desired. Here, CsPbBr3 microcrystals are fabricated by simple and fast drop‐casting of a precursor solution on several substrates that for the growth process are heated to temperatures in the range from 80 to 150 °C. The microcrystals have a cubic shape and feature a pyramidal cavity on their top surface that forms due to faster growth at the edges once the growing crystal is attached to the substrate. Distinct heterogeneity in the photoluminescence (PL) and conductivity of the different facets are measured by µ‐PL and conductive atomic force microscopy experiments. Toward device applications, the authors contact single microcrystals on conductive substrates mechanically with a micromanipulator tip. They observe diode‐like current–voltage curves and good photodetector functionality, obtaining a high responsivity of 150–300 A W−1 in the blue–green spectral region under forward bias, and a sharp detection band centered around 540 nm with peak responsivity close to 0.7 A W−1 under reverse bias. [ABSTRACT FROM AUTHOR]

Published
2022
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27. Temperature-Driven Transformation of CsPbBr3 Nanoplatelets into Mosaic Nanotiles in Solution through Self-Assembly

Author

Dang, Zhiya, primary, Dhanabalan, Balaji, additional, Castelli, Andrea, additional, Dhall, Rohan, additional, Bustillo, Karen C., additional, Marchelli, Dorwal, additional, Spirito, Davide, additional, Petralanda, Urko, additional, Shamsi, Javad, additional, Manna, Liberato, additional, Krahne, Roman, additional, and Arciniegas, Milena P., additional

Published
2020
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28. Core/Shell CdSe/CdS Bone‐Shaped Nanocrystals with a Thick and Anisotropic Shell as Optical Emitters

Author

Castelli, Andrea, primary, Dhanabalan, Balaji, additional, Polovitsyn, Anatolii, additional, Caligiuri, Vincenzo, additional, Di Stasio, Francesco, additional, Scarpellini, Alice, additional, Brescia, Rosaria, additional, Palei, Milan, additional, Martín‐García, Beatriz, additional, Prato, Mirko, additional, Manna, Liberato, additional, Moreels, Iwan, additional, Krahne, Roman, additional, and Arciniegas, Milena P., additional

Published
2019
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32. Temperature-Driven Transformation of CsPbBr3Nanoplatelets into Mosaic Nanotiles in Solution through Self-Assembly

Author

Dang, Zhiya, Dhanabalan, Balaji, Castelli, Andrea, Dhall, Rohan, Bustillo, Karen C., Marchelli, Dorwal, Spirito, Davide, Petralanda, Urko, Shamsi, Javad, Manna, Liberato, Krahne, Roman, and Arciniegas, Milena P.

Abstract

Two-dimensional colloidal halide perovskite nanocrystals are promising materials for light-emitting applications. Recent studies have focused on nanoplatelets that are able to self-assemble and transform on solid substrates. However, the mechanism behind the process and the atomic arrangement of their assemblies remain unclear. Here, we present a detailed analysis of the transformation of self-assembled stacks of CsPbBr3nanoplatelets in solution over a period of a few months by using ex situ transmission electron microscopy and surface analysis. We demonstrate that the transformation mechanism can be understood as oriented attachment, proceeding through the following steps: (i) desorption of the ligands from the surfaces of the particles, causing the seamless atomic merging of nanoplatelet stacks into nanobelts; (ii) merging of neighboring nanobelts that form more extended nanoplates; and (iii) attachment of nanobelts and nanoplates, forming objects with an atomic structure that resembles a mosaic made of broken nanotiles. We reveal that aged nanobelts and nanoplates, which are mainly stabilized by amine/ammonium ions, link through a bilayer of CsBr, with the atomic columns of neighboring perovskite lattices shifted by a half-unit-cell, forming Ruddlesden–Popper planar faults. We also show, via in situ monitoring of the nanocrystal photoluminescence combined with transmission electron microscopy analysis, that the transformation is temperature driven and that it can take place within tens of minutes in solution and in spin-coated films. Understanding this process gives crucial information for the design and fabrication of perovskite materials, where control over the type and density of defects is desired, stimulating the development of perovskite nanocrystal structures with tailored electronic properties.

Published
2020
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33. Real-Time In Situ Observation of CsPbBr 3 Perovskite Nanoplatelets Transforming into Nanosheets.

Author

Prabhakaran A, Dang Z, Dhall R, Camerin F, Marín-Aguilar S, Dhanabalan B, Castelli A, Brescia R, Manna L, Dijkstra M, and Arciniegas MP

Abstract

The manipulation of nano-objects through heating is an effective strategy for inducing structural modifications and therefore changing the optoelectronic properties of semiconducting materials. Despite its potential, the underlying mechanism of the structural transformations remains elusive, largely due to the challenges associated with their in situ observations. To address these issues, we synthesize temperature-sensitive CsPbBr 3 perovskite nanoplatelets and investigate their structural evolution at the nanoscale using in situ heating transmission electron microscopy. We observe the morphological changes that start from the self-assembly of the nanoplatelets into ribbons on a substrate. We identify several paths of merging nanoplates within ribbons that ultimately lead to the formation of nanosheets dispersed randomly on the substrate. These observations are supported by molecular dynamics simulations. We correlate the various paths for merging to the random orientation of the initial ribbons along with the ligand mobility (especially from the edges of the nanoplatelets). This leads to the preferential growth of individual nanosheets and the merging of neighboring ones. These processes enable the creation of structures with tunable emission, ranging from blue to green, all from a single material. Our real-time observations of the transformation of perovskite 2D nanocrystals reveal a route to achieve large-area nanosheets by controlling the initial orientation of the self-assembled objects with potential for large-scale applications.

Published
2023
Full Text
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