C60 Molecules Research Articles

Structure Formation of C60 on Insulating CaF2 Substrates: Matching Experiments with Simulations

AbstractThe epitaxial growth of metallic thin films has been studied intensively, leading to computational models that can predict diverse morphologies depending on thermodynamic and kinetic growth parameters. Much less is known about thin films of organic molecules. Here kinetic Monte Carlo simulations to study buckyball C60 molecules on dielectric CaF2(111) substrates is employed. This system undergoes a transition from mostly one‐layered growth to two‐layered growth of triangular cluster morphologies as the temperature is raised. Even though simplified, these simulations still require a large set of parametrized rates for the elementary transitions, the determination of which has been challenging. Here recent results for these parameters to measure cluster densities and second layer occupations are employed. Simulation snapshots of cluster morphologies are compared in a wide range of temperatures to test to which extent rate models can match the experimental observations. While adjustments to free diffusion parameters are necessary to reproduce the experimentally observed cluster densities and sizes, the cluster morphologies are excellently reproduced without further adjustments.

Enhanced Uptake and Phototoxicity of C60@albumin Hybrids by Folate Bioconjugation.

Fullerenes are considered excellent photosensitizers, being highly suitable for photodynamic therapy (PDT). A lack of water solubility and low biocompatibility are, in many instances, still hampering the full exploitation of their potential in nanomedicine. Here, we used human serum albumin (HSA) to disperse fullerenes by binding up to five fullerene cages inside the hydrophobic cavities. Albumin was bioconjugated with folic acid to specifically address the folate receptors that are usually overexpressed in several solid tumors. Concurrently, tetramethylrhodamine isothiocyanate, TRITC, a tag for imaging, was conjugated to C60@HSA in order to build an effective phototheranostic platform. The in vitro experiments demonstrated that: (i) HSA disperses C60 molecules in a physiological environment, (ii) HSA, upon C60 binding, maintains its biological identity and biocompatibility, (iii) the C60@HSA complex shows a significant visible-light-induced production of reactive oxygen species, and (iv) folate bioconjugation improves both the internalization and the PDT-induced phototoxicity of the C60@HSA complex in HeLa cells.

Joule Heating in Single-Molecule Point Contacts Studied by Tip-Enhanced Raman Spectroscopy.

Heating and cooling in current-carrying molecular junctions is a crucial issue in molecular electronics. The microscopic mechanism involves complex factors such as energy inputs, molecular properties, electrode materials, and molecule-electrode coupling. To gain an in-depth understanding, it is a desired experiment to assess vibrational population that represents the energy distribution stored within the molecule. Here, we demonstrate the direct observation of vibrational heating in a single C60 molecule by means of tip-enhanced Raman spectroscopy (TERS). The heating of respective vibrational modes is monitored by anti-Stokes Raman scattering in the TERS spectra. The precise control of the gap distance in the single-molecule junction allows us to reveal a qualitatively different heating mechanism in distinct electron transport regimes, namely, the tunneling and single-molecule point contact (SMPC) regimes. Strong Joule heating via inelastic electron-vibration scattering occurs in the SMPC regime, whereas optical heating is predominant in the tunneling regime. The strong Joule heating at the SMPC also leads to a pronounced red shift of the Raman peak position and line width broadening. Furthermore, by examining the SMPC with several types of contact surfaces, we show that the heating efficiency is related to the current density at the SMPC and the vibrational dissipation channels into the electrode.

Room temperature synthesis of water-soluble spherical particles of a uniform diameter composed of carbon nanobelts and C60 molecules

A carbon nanobelt (CNB) is a loop of fused benzene rings and a C60 molecule is a football shaped fullerene composed of 60 carbon atoms. In this study, we synthesize uniform spherical particles composed of (6,6)CNBs and C60 molecules in 1,2-dichlorobenzene at room temperature via bottom-up self-assembly, setting the molar concentrations of (6,6)CNBs and C60 molecules at appropriate values, and find that the particles are monodisperse even in water. The present room temperature synthetic methodology may well be applied to the creation of nano/micro structures/materials using basic carbon nano units such as cycloparaphenylene (CPP, carbon nanorings) and fullerenes; e.g., C60, C70 and C59N.

Efficient Exciton Dislocation and Ultrafast Charge Extraction in CsPbI3 Perovskite Quantum Dots by Using Fullerene Derivative as Semiconductor Ligand.

CsPbI3 quantum dots (QDs) are of great interest in new-generation photovoltaics (PVs) due to their excellent optoelectronic properties. The long and insulative ligands protect their phase stability and enable superior photoluminescence quantum yield, however, limiting charge transportation and extraction in PV devices. In this work, we use a fullerene derivative with the carboxylic anchor group ([SAM]C60) as the semiconductor ligand and build the type II heterojunction system of CsPbI3 QDs and [SAM]C60 molecules. We find their combination enables obvious exciton dislocation and highly efficient photogenerated charge extraction. After the introduction of [SAM]C60, the exciton-binding energy of CsPbI3 decreases from 30 meV to 7 meV and the fluorescence emission mechanism also exhibits obvious changes. Transient absorption spectroscopy visualizes a ~5 ps electron extraction rate in this system. The findings gained here may guide the development of perovskite QD devices.

Hollow Spherical Fullerene Obtained by Kinetically Controlled Liquid-Liquid Interfacial Precipitation.

Nanomaterials with hollow structures are expected to exhibit new functionalities for materials engineering. Here we report the fabrication of fullerene (C60 ) spheres having different hollow structures by using a kinetically controlled liquid-liquid interfacial precipitation (KC-LLIP) method. For this purpose, 1,2-ethylenediamine (EDA) was used as a covalent cross-linker of C60 molecules to form C60 -EDA shells, while in-situ generated EDA-sulfur (EDA-S) droplets were applied as 'yolks' being eliminated by washing following formation of the yolk-shell structure, leading to hollow structures. Porous spheres, string hollow spheres, hollow spheres, and open hollow spheres have been synthesized by controlling the kinetics of nucleation of C60 -EDA and the template EDA-S growth. Isopropanol was used as an additive to control the discrepancy in growth rates of C60 -EDA and EDA-S. This simple KC-LLIP preparation method is expected to facilitate the large-scale fabrication and application of structured C60 spheres in materials science and technology.

Molecular insight into C60-grafted graphene oxide as a novel reverse osmosis membrane with low energy consumption for seawater desalination

In this study, via molecular dynamics simulations, the performance of the cross-sectional and flat pure GO and GO/C60 membranes for seawater desalination have been investigated and compared. The simulation results demonstrate that the flat and cross-sectional pure GO membranes, despite 100 % salt rejection, due to low interlayer spacing show an additional resistance on the water permeation that exhibit low water flux even at high pressures. While, the cross-sectional GO/C60 membrane with high interlayer spacing provides a tunnel with a high effective area for high water flux even at low pressure. Also, this membrane shows a 100 % salt rejection due to the steric effects caused by C60 molecules. The flat GO/C60 membrane with misalignment and offsetting slits on the layers shows an additional resistance on the water permeation which decreases the water flux compared to the cross-sectional GO/C60 by diversion of water flow. Therefore, cross-sectional GO/C60 membrane with a high water flux and salt rejection at low pressure, provides a great potential for energy-efficient seawater desalination by RO process.

Guest-Host Raman under Liquid Nitrogen Spectroscopy for the Acquisition of Improved Vibrational Spectra of Solids.

Guest-host Raman under liquid nitrogen spectroscopy (GHRUNS) is introduced whereby solid-state guest molecules are isolated inside cage-like host environments for the facile acquisition of their Raman spectra. This convenient method features reduced fluorescence, the analysis of populations in their ground states, and increased signal to noise ratios. Samples are also preserved through the reduction of thermal degradation and oxidation. To demonstrate the benefits of this new method, Raman spectra of the ubiquitous molecule C60 inside a cage of water ice are presented. Using this technique, a new normal mode of C60 is elucidated. The GHRUNS methodology is of interest to those seeking to acquire and characterize the vibrational spectra, structure, and properties of emissive, air-sensitive molecules.

Collision-Induced C60 Rovibrational Relaxation Probed by State-Resolved Nonlinear Spectroscopy

Quantum state-resolved spectroscopy was recently achieved for C60 molecules when cooled by buffer gas collisions and probed with a midinfrared frequency comb. This rovibrational quantum state resolution for the largest molecule on record is facilitated by the remarkable symmetry and rigidity of C60, which also present new opportunities and challenges to explore energy transfer between quantum states in this many-atom system. Here we combine state-specific optical pumping, buffer gas collisions, and ultrasensitive intracavity nonlinear spectroscopy to initiate and probe the rotation-vibration energy transfer and relaxation. This approach provides the first detailed characterization of C60 collisional energy transfer for a variety of collision partners, and determines the rotational and vibrational inelastic collision cross sections. These results compare well with our theoretical modeling of the collisions, and establish a route towards quantum state control of a new class of unprecedentedly large molecules.

Investigation of fullerene motion on thermally activated gold substrates with different shapes

In the current study, the regime of motion of fullerene molecules on substrates with different shapes at a range of specific temperatures has been investigated. To do so, the potential energy of fullerene molecules was analyzed using the classical molecular dynamics method. C20, C36, C50, C60, C72, C76, C80, and C90 fullerene molecules were selected due to their spherical shapes with different sizes. In addition, to completely analyze the behavior of these molecules, different gold substrates, including flat, concave, the top side of the step (upward step), and the downside of the step (downward step) substrates, were considered. Specifying the regime of the motion at different temperatures is one of the main goals of this study. For this purpose, we have studied the translational and rotational motions of fullerene molecules independently. In the first step of the investigation, Lennard-Jones potential energy of fullerene molecules was calculated. Subsequently, the regime of motion of different fullerenes has been classified, based on their displacement and sliding velocity. Our findings indicated that C60 is appropriate in less than 5% of the conditions. However, C20, C76 and C80 molecules were found to be appropriate candidates in most cases in different conditions while they were incompetent only in seven situations. As far as a straight-line movement is considered, the concave geometry demonstrated a better performance compared to the other substrates. In addition, C72 indicated less favorable performance concerning the range of movement and diffusion coefficients. All in all, our investigation helps to understand the performance of different fullerene molecules on gold substrates and find their probable application, especially as a wheel in nano-machine structures.

Tuning 3C-SiC(100)/Si(100) Heterostructure Interface Quality

We report a systematic spectroscopic and structural investigation of 3C-silicon carbide (3C-SiC) films grown on Si(100)-(2 × 1) by codeposition of C60 molecules and Si atoms in ultrahigh-vacuum conditions. This work focuses on reducing the macroscopic defects formed at the interface in Si-SiC heterojunctions. A wide range of parameters influence the growth process, including the substrate deposition temperature, the relative effusion fluxes of C60 and Si, and the clean Si(100) surface order. By adjusting the Si and C60 deposition rates, it is possible to reduce the Si atom diffusion from the substrate and control both the surface morphology and the specific formation of the C-rich c(2 × 2) or Si-rich 3 × 2 ordered surfaces. Our results show that the growth of 3C-SiC on flat and good quality Si substrates is a crucial and necessary starting point to obtaining good quality 3C-SiC/Si interfaces with a minimum number of defects.

Nanographene Metallaprisms: Structure, Stimulated Transformation, and Emission Enhancement.

Nanographenes are inclined to assemble into stacked columnar structures that are stabilized by π-π interactions, whereas other supramolecular structures of nanographenes, such as prisms and cages, are rarely investigated. Herein, a diazananographene was synthesized, and then assembled with a coordination unit, thereby producing a triangular metallaprism. After adding C60 or C70 , the triangular metallaprism was transformed into a square tetramer, which encapsulated a pair of C60 or C70 molecules. The formed host-guest complex demonstrated efficient energy transfer from the diazananographene shell to the C60 cores. The emission intensity of the capsulated C60 was enhanced remarkably, compared with free C60 , due to an increased quantum yield and optical absorption coefficient. This work demonstrates the versatility of nanographene-based supramolecular architectures beyond columnar stacking and their ability to enhance the emission of otherwise non-emissive fullerene.

Nanographene Metallaprisms: Structure, Stimulated Transformation, and Emission Enhancement

AbstractNanographenes are inclined to assemble into stacked columnar structures that are stabilized by π‐π interactions, whereas other supramolecular structures of nanographenes, such as prisms and cages, are rarely investigated. Herein, a diazananographene was synthesized, and then assembled with a coordination unit, thereby producing a triangular metallaprism. After adding C60 or C70, the triangular metallaprism was transformed into a square tetramer, which encapsulated a pair of C60 or C70 molecules. The formed host‐guest complex demonstrated efficient energy transfer from the diazananographene shell to the C60 cores. The emission intensity of the capsulated C60 was enhanced remarkably, compared with free C60, due to an increased quantum yield and optical absorption coefficient. This work demonstrates the versatility of nanographene‐based supramolecular architectures beyond columnar stacking and their ability to enhance the emission of otherwise non‐emissive fullerene.

A DFT study of the electronic, optical, and mechanical properties of a recently synthesized monolayer fullerene network

Closely packed quasi-hexagonal and quasi-tetragonal crystalline phase of C60 molecules (named qHPC60) was recently synthesized. Here, we used GGA-PBE based DFT simulations to investigate the optoelectronic and mechanical properties of qHPC60 monolayers. qHPC60 has a moderate direct electronic bandgap, with anisotropic mechanical properties. Their elastic modulus ranges between 50–62 GPa. The results for optical properties suggest that qHPC60 can act as a UV collector for photon energies up to 5.5 eV since it presents low reflectivity and refractive index greater than one. The estimated optical bandgap (1.5–1.6 eV) is in very good agreement with the experimental one (1.6 eV).

Free Energy Landscapes, Diffusion Coefficients, and Kinetic Rates from Transition Paths.

We address the problem of constructing accurate mathematical models of the dynamics of complex systems projected on a collective variable. To this aim we introduce a conceptually simple yet effective algorithm for estimating the parameters of Langevin and Fokker-Planck equations from a set of short, possibly out-of-equilibrium molecular dynamics trajectories, obtained for instance from transition path sampling or as relaxation from high free-energy configurations. The approach maximizes the model likelihood based on any explicit expression of the short-time propagator, hence it can be applied to different evolution equations. We demonstrate the numerical efficiency and robustness of the algorithm on model systems, and we apply it to reconstruct the projected dynamics of pairs of C60 and C240 fullerene molecules in explicit water. Our methodology allows reconstructing the accurate thermodynamics and kinetics of activated processes, namely free energy landscapes, diffusion coefficients, and kinetic rates. Compared to existing enhanced sampling methods, we directly exploit short unbiased trajectories at a competitive computational cost.

Mechanical Properties of Cubene Crystals.

The fullerene family, whose most popular members are the spherical C and C molecules, has recently added a new member, the cube-shaped carbon molecule C called a cubene. A molecular crystal based on fullerenes is called fullerite. In this work, based on relaxational molecular dynamics, two fullerites based on cubenes are described for the first time, one of which belongs to the cubic system, and the other to the triclinic system. Potential energy per atom, elastic constants, and mechanical stress components are calculated as functions of lattice strain. It has been established that the cubic cubene crystal is metastable, while the triclinic crystal is presumably the crystalline phase in the ground state (the potential energies per atom for these two structures are −0.0452 and −0.0480 eV, respectively).The cubic phase has a lower density than the monoclinic one (volumes per cubene are 101 and 97.7 Å). The elastic constants for the monoclinic phase are approximately 4% higher than those for the cubic phase. The presented results are the first step in studying the physical and mechanical properties of C fullerite, which may have potential for hydrogen storage and other applications. In the future, the influence of temperature on the properties of cubenes will be analyzed.

(Invited) Nucleation and Growth of Small Atomic Aggregates into Superatom Nanoclusters

One of the challenges in nucleation and growth of small atomic aggregates is to develop the novel research field of solid-state chemistry and material science using gas-phase-synthesized superatom nanoclusters. Among various superatoms, the greatest advantage of the central-atom-encapsulating binary superatoms, such as M@Si16, is that their electronic structures can be designed by optimizing the central metal atom M while retaining the geometrical symmetry of the Si16 cage [1], as shown in the figure below. We have systematically investigated the nucleation and growth of M@Si16 superatoms with gas-phase mass spectrometry, and then performed the surface immobilization of the M@Si16 cations and anions on a substrate monodispersively with the size-selective soft-landing. Initial products prepared via the surface immobilization of M@Si16 superatoms on solid surfaces decorated with monolayer films of C60 molecules were investigated using scanning tunneling microscopy (STM) [2] and X-ray photoelectron spectroscopy (XPS) [3]. Furthermore, we have developed a large-scale synthesis method for M@Si16 (M = Ti and Ta) by scaling up the clean dry-process with a high-power impulse magnetron sputtering (HiPIMS, nanojima®) [4] and by a direct liquid embedded trapping (DiLET) method [5]. The spectroscopic results reveal that the structures of soft-landed and isolated M@Si16 superatoms are the metal-encapsulating tetrahedral silicon-cage (METS) [5,6].Furthermore, superatoms of group-5 metals (M = V, Nb, and Ta) encapsulating Si16 cage nanoclusters (M@Si16) can be efficiently generated to form assembled films [7]. Temperature-dependent current–voltage (I–V) characteristics of the M@Si16 assembled films revealed that the electrical conduction mechanism is not band transport, but hopping transport with Efros–Shklovskii variable range hopping for all central M atoms [8]. The results show that electrons involved in conduction are strongly correlated to localized electronic states.[1] K. Koyasu, A. Nakajima, et al. J. Am. Chem. Soc. 127, 4998 (2005).[2] M. Nakaya, A. Nakajima, et al. Nanoscale, 6, 14702 (2014).[3] M. Shibuta, A. Nakajima, et al. J. Am. Chem. Soc. 137, 14015 (2015).[4] C. H. Zhang, A. Nakajima, et al. J. Phys. Chem. A 117, 10211 (2013).[5] H. Tsunoyama, A. Nakajima, et al. J. Phys. Chem. C 121, 20507 (2017).[6] H. Tsunoyama, A. Nakajima, et al. Acc. Chem. Res. 51, 1735 (2018).[7] M. Shibuta, A. Nakajima, et al. J. Phys. Chem. C, 124, 28108 (2020).[8] T. Yokoyama, A. Nakajima, et al. J. Phys. Chem. C, 125, 18420 (2021). Figure 1

Electrostatic properties of two-dimensional C60 polymer thin films under an external electric field

Electrostatic properties of different C60 thin films under external electric fields have been investigated from first-principle total-energy calculations. Density functional theory calculations combined with the effective screening medium method reveal that the electrostatic properties of C60 thin films in an electric field strongly depend on the arrangement and conformation of the C60 molecules. The relative permittivity across the thin films exhibits clear a positional dependence resulting from the π electron distribution within the films. An electrostatic polarization is uniformly induced by weak electric fields, typically 0.1 V nm−1, because of the semiconducting electronic structure of the thin films, whereas the polarization is highly concentrated in the outermost C60 layer under strong electric fields of 0.5 V nm−1.

The molecular dynamics study of vacancy defect influence on carbon nanotube performance as drug delivery system

In the current research, we described atomic vacancy defect influence on nanopumping performance of CNT structure with molecular dynamics (MD) method (for the first time). In our simulations, CNT structure is defined in the presence of C20 molecule and Au tips in the nanopumping process. Temperature and potential energy convergence after 1 ns indicated the atomic stability in defined systems, which this result arises from the appropriate settings inside the MD box. Also, the nanopumping process was detected after 0.26 ps for the CNT structure without any vacancy defect. By atomic defect implementation to C-based nanotube, the nano-pumping performance of this tube was disrupted. Numerically, by inserting 1% vacancy to pristine CNT, the nanopumping was detected after 0.29 ps. Furthermore, MD outputs predicted by implementing vacancy defect with a larger 10% ratio, nanopumping process doesn't occur. On the other hand, by nanopumping parameters optimization in defected CNT (with 1% defect), this atomic process (nanopumping) occurs after 0.24 ps.

Periodic corner holes on the Si(111)-7×7 surface can trap silver atoms

Advancement in nanotechnology to a large extent depends on the ability to manipulate materials at the atomistic level, including positioning single atoms on the active sites of the surfaces of interest, promoting strong chemical bonding. Here, we report a long-time confinement of a single Ag atom inside a corner hole (CH) of the technologically relevant Si(111)-7×7 surface, which has comparable size as a fullerene C60 molecule with a single dangling bond at the bottom center. Experiments reveal that a set of 17 Ag atoms stays entrapped in the CH for the entire duration of experiment, 4 days and 7 h. Warming up the surface to about 150 °C degrees forces the Ag atoms out of the CH within a few minutes. The processes of entrapment and diffusion are temperature dependent. Theoretical calculations based on density functional theory support the experimental results confirming the highest adsorption energy at the CH for the Ag atom, and suggest that other elements such as Li, Na, Cu, Au, F and I may display similar behavior. The capability of atomic manipulation at room temperature makes this effect particularly attractive for building single atom devices and possibly developing new engineering and nano-manufacturing methods.