The modification of the atomic configuration of pristine carbon and related nanomaterials via surface functionalization is a perfect way of control their opto-electronic properties [1-12]. However, it is worth noting that a very detailed analysis of this atomic configuration and concentration of the different species of these heteroatomic/functionalized nanostructures is highly required to determine their impact on the electronic/optoelectronic properties of these nanomaterials. In this sense, TEM is an essential tool to perform such studies [1-10]. In particular, spatially resolved electron energy loss spectroscopy (SR-EELS), developed in an aberration-corrected TEM (having access to a close to 1 angstrom electron probe), is the most powerful technique to achieve these goals.

In this contribution, we present a detailed study of the atomic configuration of different 1D (NTs) and 2D systems via SR-EELS. We have examined the different chemical species present in these nanostructures, determined their average concentration as well as their spatial distribution and studied their chemical environment and bonding [4-12]. These works provide very rich information about these hybrid and complex nanomaterials, opening fascinating perspectives for optoelectronic applications of such nano-systems.

References

[1] R. Arenal, X. Blase, A. Loiseau, Advances in Physics 59, 101 (2010).

[2] P. Ayala, R. Arenal, A. Rubio, A. Loiseau, T. Pichler, Rev. Mod. Phys. 82, 1843 (2010).

[3] R. Arenal, K. March, C.P. Ewels, X. Rocquefelte, M. Kociak, A. Loiseau, O. Stéphan, Nano Lett. 14, 5509 (2014).

[4] A. Setaro, M. Adeli, M. Glaeske, D. Przyrembel, T. Bisswanger, G. Gordeev, M. Weinelt, R. Arenal, R. Haag, S. Reich, Nature Comm. 8, 14281 (2017).

[5] L. Alvarez, et al., J. Phys. Chem. C 119, 5203 (2015).

[6] R. Arenal, L. Alvarez, J.-L. Bantignies, to be submitted.

[7] K. Huth, M. Gläske, K. Achazi, G. Gordeev, S. Kumar, R. Arenal, S. K. Sharma, M. Adeli, A. Setaro, S. Reich, R. Haag, Small (2018).

[8] R. Vitoria, Y. Sayed-Ahmad, M. Pelaez-Fernandez, C. Bittencourt, R. Arenal, C.P. Ewels, N. Tagmatarchis, Nature 2D Materials (2017).

[9] L. Vallan, R. Canton-Vitoria, H.B. Gobeze, Y. Jang, R. Arenal, A.M. Benito, W.K. Maser, F. D’Souza, N. Tagmatarchis, JACS (2018).

[10] R. Canton-Vitoria, T. Scharl, A. Stergiou, A. Cadranel, R. Arenal, D.M Guldi, N. Tagmatarchis, Angewandte (2019).

[11] A. Kagkoura, R. Arenal, N. Tagmatarchis. Adv. Funct. Mat. (2021).

[12] Research supported by the Spanish MCIN (PID2019-104739GB-100/AEI/10.13039/501100011033), the Government of Aragon through project DGA E13_23R and EU Horizon MagGraphZyme (101068591) program.

Two-dimensional (2D) hybrid organic-inorganic perovskite (HOIP) crystals represent a promising class of scintillating materials for wide-energy radiation detection. Current research focuses on lead halide perovskites based on phenethylammonium (PEA), butylammonium (BA), and benzylammonium (BZA) A₂BX₄ (A= PEA, BA, BZA; B= Pb, Sn, Cu, Mn; X= Cl, Br, I), garnering considerable interest within the scientific community. These crystals exhibit favorable optical and scintillation properties, including high light yields (LY), minimal afterglow, and fast scintillation decay times, making them well-suited for applications in X-ray imaging and rapid timing. Noteworthy is their exceptional environmental resilience, achieving a record LY > 10 photons/keV and scintillation decay times < 10 ns. However, further enhancement of structural, optical, and scintillation properties requires a comprehensive study of crystal growth optimization through organic ligands, ion doping, and halide exchange. This study delves into the impact of structural variations on the optical and scintillating properties of 2D HOIP crystals using a low-temperature solution process. Our comprehensive investigation employs various techniques, including X-ray diffraction, photoluminescence (PL), time-resolved PL, radioluminescence (RL), thermoluminescence, and scintillation measurements. The first approach involves introducing BZA to PEA, resulting in narrowed PL spectra and enhanced electron-hole transfer efficiency. Moreover, the use of mixed organic ligands increases the percentage of the fast component in scintillation decay time > 70% compared to individual ligand crystals (< 20%), advantageous for the scintillation process. The second approach incorporates ion doping, such as Li and Rb, leading to enhanced crystal emission with a noticeable redshift in radioluminescence. Optimum ion doping (< 5%) achieves a reduced bandgap, enhancing LY to 25%. The final approach, halide exchange, (e.g., bromide to iodide in PEA₂PbX₄; X=Br, I), results in RL spectra in the red band, enhancing compatibility with silicon detectors for standard CMOS technologies. The decay time features fast components (0.5 and 4.5 ns), constituting approximately 12% of the total LY, ensuring optimal performance for timing applications. This work underscores the crucial role of organic ligands, ion doping, and halide exchange in radiation imaging, holding promise for applications such as positron-emission and photon-counting-computed tomography.

Humanity is searching for alternate sources to replace its non-sustainable sources of energies, especially fossil fuels, as global warming reaches alarming heights. In material science, new materials are developed to pursue renewable ways to generate green energy. Perovskites are growingly gaining attention in this field because of having modifiable structures and tuneable bandgaps that further increase their photocatalytic performances. Proton exchange increases photocatalytic hydrogen production by exchanging the interlayer atoms with hydrated protons and it facilitates easier exfoliation for the preparation of two-dimensional nanomaterials from layered structures. Single-atom metal doping is used to enhance photocatalytic activity by introducing new energy levels to the structure and generally, noble metals are used in single-atom and co-catalyst doping. In this study, the effects of Sn doping, as a cheap alternative, and proton exchange on a Dion-Jacobson layered perovskite, CsLaTa₂O₇ (CLTO) were investigated. The photocatalytic efficiencies of the proton exchanged HLaTa₂O₇ (HLTO) and the Sn-doped, proton exchanged HLaTa_2-xSn_xO₇ (Sn-HLTO) were determined by photocatalytic hydrogen evolution reactions. The amount of hydrogen evolved by HLTO was 2-fold of the pristine CLTO while Sn-HLTO, which has an optimum 1.5% Sn:Ta doping, evolved almost 15 times more hydrogen than HLTO.

Electron microscopy and spectroscopy are widely used to characterize various low-dimensional materials. Identifying the atomic structures and/or measurements of local optical properties are of great importance in designing nanoscale devices based on functionalized nanostructures. Electron energy-loss spectroscopy (EELS) has been used for elemental identification in transmission electron microscopes (TEM) by using core-level excitations. Recent developments of monochromators after the e-beam guns have enabled us to access optical and vibrational information from the valence EELS ranges of novel materials. Here we show our latest studies to develop the possibilities of EELS applied for low-dimensional hybrid/functionalized materials. Examples for atomic defects in in-plane hybrid TMDCs[1], monolayer structures of metal chlorides intercalated in bi-layer graphene[2, 3], surface adatoms for catalysis[4], isotopically heterogeneous graphene[5], and some forms of novel 1D/2D hybrid structures[6] will be shown.

[1] Y.-C. Lin et al., Adv. Mater., (2021) 2007819

[2] Y.-C. Lin et al., Adv. Mater. (2021) 2105898

[3] Y.-C. Lin et al., Nano Lett., (2021) 21, 10386-10391

[4] S. Wu et al., J. Am. Chem. Soc., (2021) 143, 9105-9112

[5] R. Senga et al. Nature (2022) 603 68-73

[6] J. Zhou et al. Nature (2022) 609 46-51

[7] The works presented here are supported by JST-CREST and ERC MORE-TEM projects.

Hydroxyl groups in metal hydroxides exhibit bond terminability and high reactivity, leading to unique crystal structures and functionalities not found in metal oxides or nitrides. Particularly, surface hydroxyl groups offer a platform for emerging applications such as electrochemical catalysts, nano-catalyst supports, seed layers for metal-organic frameworks, and adsorbents. While metal hydroxides have predominantly been studied on powder and polycrystalline thin film forms, oriented/epitaxial thin films have rarely been reported due to their instability at high temperatures. In this study, the low-temperature topochemical synthesis strategy^[1] is utilized, where layered oxide thin films are converted to layered hydroxide thin films while maintaining an orientation relationship with the substrate. We focus on cobalt hydroxides as a model system and discuss the detailed synthesis of orientated layered hydroxide thin films.

^[1] T. Sudare et al., Chem. Mater. 2022, 34, 23, 10681–10690.

Characterisation of the exact chemical composition of solution-processed and functionalisation 2D materials is still a challenging tast. Typically, a combination Raman spectroscopy, XPS, TGA-MS and electron-microscopy based EDX is used. Some reports also complement this portfolio with IR vibrational spectrocopy in the MIR rand which is suitable to detect organic functionalities which are physisorbed or chemisorbed on the surface. However, any quantitative information is lacking and a destinction between physisorption (of e.g. solvent) and covalently-grafted moieties is hardly possible.

In this talk, we address this by systematic studies of solution-processed and/or functionalised MoS2 nanosheets as model substance, where we extend the spectroscopic range to the FIR, where Mo-S vibrations can be discerned. This is possible through diffuse-reflectance Fourier transform IR spectroscopy (DRIFT) in CsI matrix. Through normalisation to the Mo-S vibrations, it is possible to obtain semi-quantitative information on the amount of organic molecules associated with the MoS2 surface. By using this technique, we first investigate the purity of the starting materials and develop washing procedures to remove as much physisorbed solvent and surfactant after exfoliation and size selection as possible as a starting point for further derivatisation. We then subject the purified nanosheets to functionalisation with diazonium salt to investigate the reactivity of nanosheets produced by different exfoliation strategies in the liquid phase.

In contrast to the tremendous efforts dedicated to the exploration of graphene and inorganic 2D crystals, there has been much less development in organic 2D crystalline materials, including the bottom-up organic/polymer synthesis of graphene nanoribbons, 2D metal-organic frameworks, 2D polymers/supramolecular polymers, as well as the supramolecular approach to 2D organic nanostructures. One of the central chemical challenges is to realize a controlled polymerization in two distinct dimensions under thermodynamic/kinetic control in solution and at the surface/interface. In this talk, we will present our recent efforts in bottom-up synthetic approaches toward novel organic 2D crystals with structural control at the atomic/molecular level. On-water surface chemistry provides a powerful synthetic platform by exploiting water-surface confinement and enhanced chemical reactivity and selectivity. We will particularly present a surfactant-monolayer assisted interfacial synthesis (SMAIS) method that is highly efficient in promoting the programmable assembly of precursor monomers on the water surface and subsequent 1D/2D polymerization in a controlled manner. 2D conjugated polymers and coordination polymers belong to such material classes. The unique 2D crystal structures with possible tailoring of conjugated building blocks and conjugation lengths, tunable pore sizes and thicknesses, as well as impressive electronic structures, make them highly promising for a range of applications in electronics, optoelectronics, and spintronics. Other physicochemical phenomena and application potential of organic 2D crystals, such as in membranes and energy devices, will also be discussed.

Adsorption-mediated methods for environmental pollution control are suitable as they are cost-effective and easy to use. Porous materials can play an important role in adsorption studies. Herein, we have synthesized a p-n heterostructure of phosphorene and metal oxide using a simple hydrothermal approach. The synthesized material is porous in nature, with a surface area of 127.44 m²/g and a pore volume of about 1.73 nm with appreciable thermal stability. As the material is microporous, we have used them for the adsorption of CO₂ gas and dye. For CO₂ adsorption, we have determined the CO₂ gas uptake according to the mass balance principle of the ideal gas equation, and it was found to be about 21.478 mol/kg. We have also studied different isotherm models to check the adsorption phenomena. Moreover, for dye adsorption, we have chosen xanthene-derived rose bengal (RB) dye, which shows a removal percentage of about 92.02 %. In the case of dye adsorption, the material shows good reusability and significant adsorption up to five cycles.

Keywords: Phosphorene; metal oxide; Phosphorene-metal oxide composite; CO2 adsorption; anionic dye adsorption.

The efficient and cost-effective detection of harmful volatile organic compounds (VOCs) is a major health and environmental concern in industrialised societies. To this end, tailor-made porous coordination polymers are emerging as promising molecular sensing materials due to their responsiveness to a wide range of external stimuli. Low-dimensional non-porous coordination polymers (npCPs), capable of accommodating molecules through internal lattice reorganisation[1,2], are unusual materials with applications in sensing and selective gas adsorption[3].

In this talk, we present low-dimensional npCPs with remarkable sensing activity[4].The desorption of interstitial host molecules is accompanied by magneto-structural transitions that are readily detectable in the optical and electronic properties of the material. These structural changes, and hence the (opto)electronic readout, are reversible upon exposure to the source vapours. In addition, the insitu replacement of these weakly bound source host molecules by others leads to a different optical response[5]. Thus, the colour and conduction properties are determined by the weakly bound molecules in the lattice.

These findings open the door to a novel concept of non-porous switchable protonic conductors and capacitive sensors that operate at low humidity and with selectivity for different molecules. These materials can therefore provide a versatile platform for the fabrication of tailor-made detectors with a variety of readout options from optical, magnetic to electron transport measurements.

References

[1] E. Coronado, M. Giménez-Marqués, G. M. Espallargas, L. Brammer, Nat. Commun. 2012, 3, 828.

[2] J. Sánchez Costa, S. Rodríguez-Jiménez, G. A. Craig, B. Barth, C. M. Beavers, S. J. Teat, G. Aromí, J. Am. Chem. Soc. 2014, 136, 3869.

[3] S. Rodríguez-Jiménez, H. L. Feltham, S. Brooker, Angew. Chemie - Int. Ed. 2016, 55, 15067.

[4] E. Resines-Urien, E. Burzurí, E. Fernandez-Bartolome, M.A. García García-Tuñón, P. de la Presa, R. Poloni, S. J. Teat and J. Sanchez Costa, Chem. Sci., 2019,10, 6612-6616.

[5] A. Develioglu, E. Resines-Urien, R. Poloni, L. Martín-Pérez, J. Sanchez Costa and E. Burzurí, Adv. Sci. 2021, 2102619.

Two dimensional transition metal dichalcogenides (TMDCs) nanomaterials have recently become of large research interest due to their potential broad range of applications spanning from photonics1, and nanoelectronics to energy storage.2 Previous studies from our group reported the first observation of chiroptical properties in MoS2 produced via top-down exfoliation in the presence of a chiral inductor.3 However, top-down processes such as liquid-phase exfoliation are affected by several drawbacks, including a large degree of heterogeneity in the materials produced as well as poor control of nanostructure morphology. Due to these intrinsic issues related to the synthetic procedure, the fine control of the optical and chiroptical properties, the understanding of the origin of the symmetry break, as well as applications of the nanomaterials are challenging. For these reasons, we are currently investigating other strategies to produce chiral two-dimensional TMDCs with higher control of the nanomaterials’ morphology.

In particular, our investigation covers the introduction of chirality in bottom-up colloidal two-dimensional TMDCs. Bottom-up syntheses are well-known procedures successfully applied to produce high-quality 2D TMDCs nanostructures with high control on morphology, crystallographic structure and chemical composition.4-6 Our observations demonstrate the induction of chirality in MoS2 and WS2 nanocrystals prepared by bottom-up synthesis, using post-synthetic passivation in the presence of chiral amines. Moreover, particular attention is dedicated to the origin of chirality. Thanks to the superior control on morphology accessible by bottom-up methods this strategy allows for the production of high quality 2D chiral nanostructures.

Mak, K. F. et al. J. Nat. Photonics 2016, 10, 212-226.

Choi, W. et al. Mater. Today 2017, 20, 116− 130.

Purcell-Milton, F. et a.l. ACS Nano 2018, 12, 954-964.

Coogan, A. et al. Mater. Adv. 2021, 2, 146-164.

Liu, Z. et al. J. Am. Chem. Soc. 2022, 144, 4863-4873.

Li, H. et al. J. Am. Chem. Soc. 2014, 136, 3756-3759.

Precise engineering of excited-state interactions between organic molecules and two-dimensional (2D) materials, specifically the manipulation of locally-excited (LE), charge-transfer (CT) excited, and charge-separated (CS) states, still remains a challenge for state-of-the-art photochemistry. In this talk I will give you an overview of our recent results on 2D materials: (1) photoinduced exciplex formation and charge separation by the modulation of the electronic coupling between photoactive molecules (i.e., pyrene and porphyrin) and chemically coverted graphenes; (2) photoinduced energy transfer and switching of its direction by rectangular pi-extension of nanographenes; (3) photoinduced charge separation behavior of transition metal dichlcogenide nanosheet-fullerene inroganic/organic nanohybrid on semiconducting electrodes; (4) observation of a long-lived, highly emissive CT excited state at structurally well-defined hetero-nanostructure interfaces of photoactive pyrene and 2D MoS2 nanosheet via N-benzyl succinimide bridge (Py-Bn-MoS2).

[1] T. Umeyama, J. Baek, J. Mihara, N. V. Tkachenko, H. Imahori, Chem. Commun. 2017, 53, 1025.

[2] T. Umeyama, T. Hanaoka, H. Yamada, Y. Namura, S. Mizuno, T. Ohara, J. Baek, J.-H. Park, Y. Takano, K. Stranius, N. V. Tkachenko, H. Imahori, Chem. Sci. 2019, 10, 6642.

[3] T. Umeyama, T. Ohara, Y. Tsutsui, S. Nakano, S. Seki, H. Imahori, Chem. Eur. J. 2020, 26, 6726.

[4] T. Umeyama, D. Mizutani, Y. Ikeda, W. R. Osterloh, F. Yamamoto, K. Kato, A. Yamakata, M. Higashi, T. Urakami, H. Sato, H. Imahori, Chem. Sci. 2023, 14, 11914.

The development of new functionalities of 2D materials (2Dms) can be achieved by their chemical modifying with a variety of molecules. With this goal, we have been working in the functionalization of transition metal chalcogenides with bistable molecular systems like spin crossover compounds. More recently, we have been dealing with novel strategies to achieve asymmetric functionalization of 2Dms, leading to Janus 2D materials. By functionalizing 2Dms asymmetrically, we can create materials with differently modified surfaces that result in novel properties beyond those of their initial counterparts.  Herein, we would like to present the liquid-phase fabrication strategy that we are developing to be able to prepare these Janus 2D systems.

Additionally, for the characterization of resulting symmetric or asymmetric functionalized systems, the detection limit of spectroscopies like Raman, IR, or XPS is often a problem. These methods also lack detailed spatial resolution and cannot provide information on the homogeneity of the coating. On the other hand, Scanning Probe Microscopy (SPM) allows the study of 2Dms at the nanoscale with excellent lateral resolution. SPM has been widely used for topographic analysis, but it is also a powerful tool for evaluating other properties beyond topography, such as mechanical ones. In this study, we show how SPM adhesion mapping of transition metal chalcogenides 2Dms allows a close inspection of the surface chemical properties. Analyzing adhesion as relative values allows for a simple and robust strategy to distinguish between bare and functionalized layers, improving the reproducibility of measurements. Remarkably, statistical analysis confirms that adhesion values do not depend on the thickness of the layers, proving that it is related only to the most superficial part of the materials. These results demonstrate the potential of simple adhesion SPM measurements to inspect the chemical nature of 2Dms, which may have implications for the scientific community working in this field.