bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Resonance Raman Spectroscopy Studies in 2D and 1D Nanocarbons
Authors: Souza Filho Antonio G G 
Published: February 2020

Raman spectroscopy is a nondestructive tool widely used to characterize a variety of nanomaterials including the novel 2D and 1D systems such as graphene and MoS2, linear carbon chains, among others. Since electrons and phonons are specially coupled to each other due to the reduced dimensionality, this technique provides detailed information about the structure and electronic properties of theses layered systems thus allowing one to probe in the phonon spectra the numbers of layers and their interactions with the environment. Most of these 2D materials are on substrate and the understanding on how the substrate affects the physical properties of these atomic thickness layers is a key point for fully characterize the materials. In this regard, strain is an important variable to take into account because the adhesion of the layered materials depends on the nature of the substrate and a key question is how the strain is transferred from a given substrate to the 2D material, for instance.
The use of hydrostatic pressure has been an effective method modulate the interactions between the 2D materials with substrates and environment and Raman spectroscopy has been important for investigating these strained 2D nanomaterials because the Raman cross section of these low dimensional materials is very large.
In this talk, we discuss recent results obtained for high-pressure Raman studies of graphene (mono- and bilayer) and MoS2 (mono-, bi-, tri- and many layers) sitting on substrate. Depending on the pressure transmitting medium, the pressure-induced changes in the Raman modes frequency at different rates, which has been attributed to different strain transferred from the substrate to the 2D materials. In the case of MoS2, the behavior of Raman modes suggested that a biaxial stress is transmitted from substrate to the MoS2 layers by means of the substrate deformation due to pressure and the magnitude of such stress transfer is found to be dependent of the number of layers. We also discuss the effects of strain on the vibrational properties of linear carbon chains encapsulated in carbon nanotubes.
(Invited) Open-Cage Fullerene C60 Derivatives Encapsulating a Paramagnetic Molecule
Authors: Murata Yasujiro 
Published: February 2020

Organic electron spin systems have received much attention owing to their broad interests in medicine, quantum device, molecular magnetism, and etc. Fullerene C60 has an inner space which is suitable to accommodate a variety of small molecules. In this work, we constructed organic electron spin systems, O2@openC60 and NO@openC60, by encapsulation of the molecules inside an open-cage C60 derivative with high crystallinity and solubility. In the case of O2@openC60, the EPR signals were observed and the paramagnetic behaviour was demonstrated above 3 K without an antiferromagnetic transition.[1] In the case of NO@openC60, however, sharp 1H NMR signals were observed with remarkable paramagnetic shifts despite the encapsulation of the paramagnetic molecule. Although an NO molecule is known to be inactive in ESR measurements due to the intrinsic orbital angular momentum, the ESR signal of NO@openC60 was detected below 40 K owing to the symmetry breaking.[2]
[1] A Stable, Soluble, and Crystalline Supramolecular System with a Triplet Ground State
Futagoishi, T.; Aharen, T.; Kato, T.; Kato, A.; Ihara, T.; Tada, T.; Murata, M.; Wakamiya, A.; Kageyama, H.; Kanemitsu, Y.; Murata, Y. Angew. Chem. Int. Ed. 2017, 56, 4261-4265.
[2] Construction of a Metal-Free Electron Spin System by Encapsulation of an NO Molecule inside an Open-Cage Fullerene C60 Derivative
Hasegawa, S.; Hashikawa, Y.; Kato, T.; Murata, Y. Angew. Chem. Int. Ed. 2018, 57, 12804-12808.
(Invited) Photoinduced Charge Separation in Several Dyads Involving Fullerenes
Authors: Solà Miquel , Stasyuk Antony J. , Stasyuk Olga A. , Voityuk Alexander A. 
Published: February 2020

Conversion of the sunlight into chemical energy is considered to be one of the most important and fundamental chemical reactions in nature. A broad variety of artificial photosynthetic systems based on dyads, triads and up to pentads involving electron donor and acceptor moieties have been designed and synthesized in order to investigate artificial photoinduced energy and electron transfer processes. In this work, we discuss a series of computational studies that involves the photoinduced charge separation in metal-cluster encapsulated triphenylamine-[80]fullerenes,[1]
in a transition-metal complex linked to a fullerene moiety,[2] in an all-fullerene hetero-dumbbell formed by two fullerene units, namely C60 as the electron acceptor component and endohedral Lu3N@C80 as the donor unit,[3] and in four akamptisomers of quinoxalinoporphyrin–[60]fullerene complex.[4]

References

[1] J. P. Martínez, M. Solà and A. A. Voityuk. Chem. Eur. J. 22 (2016) 17305.
[2] A. J. Stasyuk, O. A. Stasyuk, S. Filippone, N. Martín, M. Solà and A. A. Voityuk. Chem. Eur. J., 24 (2018) 13020.
[3] Manuscript in preparation
[4] A. J. Stasyuk, O. A. Stasyuk, M. Solà and A. A. Voityuk. Chem. Eur. J., 2019, ASAP, DOI: 10.1002/chem.201804999

Figure 1
(Invited) Prato Addition to M3n@C80(M = Y, Gd): Mono, Bis, and Higher Adducts
Authors: Semivrazhskaya Olesya , Safwan Aroua , Yamakoshi Yoko 
Published: February 2020

Regiocontrol of mutiple fullerene derivatization is important for producing derivatives with specific functions. In previous reports,[1]it was found that bis 1,3-dipolar cycloaddition (Prato reaction) can proceed in a regioselective manner in the case of trimetallic nitride template endohedral metallofullerene, (TNT-EMFM3N@C80, M = Sc, Lu, Y, Gd), while less regioselectivity is usually observed in the case of C60. This is presumably due to the effect of the endohedral metal cluster inside the C80and – especially in case of bis-addition reaction – the position of second addition sites seem to be dependent on the ionic radii of the metal. In this study, we used a larger excess of the dipole in the Prato reaction of M3N@C80(M = Y, Gd). After a short reaction interval, sufficient amounts of tri and tetra adducts were obtained, in addition to the bis-adducts. Although the adducts were not single isomers (four tris-adducts and mono-tetra adduct), the reaction occurred in regioselective manners. All generated tris- and tetra-adducts of M3N@C80 (M = Y, Gd) were isolated by HPLC. The structures of the tris-and tetra-adducts of Y3N@C80were established by 1H and 13C NMR.
Reference:
[1]. Aroua, S.; Garcia-Borràs, M.; Bölter M. F.;, Osuna, S.*; Yamakoshi, Y.*: Endohedral Metal-Induced Regioselective Formation of Bis-Prato Adduct of Y3N@Ih-C80 and Gd3N@Ih-C80, J. Am. Chem. Soc.
2015, 137, 58-61; Cerón, M. R.; Izquierdo, M.; Garcia-Borràs, M.; Lee, S. S.; Stevenson, S.; Osuna, S.; Eshegoyen, L.: Bis-1,3-dipolar Cycloadditions on Endohedral Fullerenes M3N@Ih-C80 (M = Sc, Lu): Remarkable Endohedral-Cluster Regiochemical Control, J. Am. Chem. Soc.
2015, 137, 11775 – 11782.
(Invited) Uranium-Based Endohedral Fullerenes: Completely Unexpected and Unusual Cage Structures Dictated By the Tetracationic Lanthanide Metal Ion
Authors: Echegoyen Luis , Cai Wenting , Poblet Josep M. , Feng Lai , Morales-Martinez Roser , Rodriguez-Fortea Antonio , Chen Ning 
Published: February 2020

For the first time, actinide endohedral metallofullerenes (EMFs) with non-IPR carbon cages, U@C80, Th@C80 and U@C76, were successfully synthesized and fully characterized by mass spectrometry, single crystal X-ray diffractometry, UV-vis-NIR, Raman and cyclic voltammetry. Crystallographic analysis revealed that the U@C80 and Th@C80 shared the same non-IPR cage of C
1(28324)-C80, and U@C76 was assigned to non-IPR U@C
1(17418)-C76. All of these cages are chiral and have never been reported before. DFT calculations show that the stabilization of these unique non-IPR fullerenes originates from a four electron transfer, a significant degree of covalency and the resulting strong host-guest interactions between the actinide ions and the fullerene cages.
We now have a complete family of U@C2n compounds, and this family will be presented and discussed in detail.
Effect of Structural Properties on the Photoelectrochemical Performance of Transition Metal Dichalcogenides
Authors: Tóth Peter S. , Szabó Gábor , Janáky Csaba 
Published: February 2020

Layered transition metal dichalcogenides (TMDCs) have become promising candidates for photoelectrochemical (PEC) studies from the 80’s. Both n- and p-type MoSe2, and WSe2 materials were studied in photoelectrocatalytic reactions using model redox couples and hydrogen evolution reaction. (1-2) Exfoliation of the bulk, layered crystals to single- and few-layered two-dimensional (2D) nanosheets leads to new physical phenomena, different from their bulk counterparts. (3) The electrochemical properties of 2D nanoflakes −which define the performance of these materials in energy-related applications− depends on their structural properties. These structural features include the number of layers, the basal/edge planes, and the defect density. (4-5) Therefore, to employ 2D nanosheets for energy conversion and storage we need to understand their fundamental PEC properties, using an approach with spatial resolution.
In our study, TMDCs samples, MoSe2, WSe2, and MoWSe2 nanosheets were mechanically exfoliated to get bulk, few-layered, and monolayer specimens. The number of layers, and defect density in the separated nanosheets were characterised by Raman spectroscopy and atomic force microscopy. Our recently developed custom-designed microdroplet cell-based photoelectrochemical approach was applied to identify the structural parts and to measure the PEC activity of the flakes (10-50 μm droplets in diameter). PEC measurements, including photovoltammetry, photocurrent transient analysis, and quantum efficiency were carried out to reveal the role of structural properties on the light harvesting, charge transport, and recombination properties of TMDCs. We have determined the band diagrams of these materials using bandgap values from PEC studies and work functions achieved from ambient pressure photoemission spectroscopy (APS) and surface photovoltage spectroscopy (SPS) measurements. Our photoelectrochemical microscopy technique also allowed to probe the PEC reactivity of novel member of 2D family, such as MoWSe2 mixed transition metal dichalcogenide. Finally, I demonstrate the use of model reversible redox species (K4[Fe(CN)6], (NH4)2[IrCl6]) to mimic photoelectrocatalytic processes.
(1) F. R. F. Fan, H. S. White, B. L. Wheeler, A. J. Bard; J. Am. Chem. Soc. 1980, 102, 5142-5148
(2) W. Kautek, H. Gerischer; Ber. Bunsenges. Phys. Chem. 1980, 84, 645-653
(3) K. S. Novoselov, D. Jiang, F. Schedin, T. J. Booth, V. V. Khotkevich, S. V. Morozov, A. K. Geim; PNAS, 2005, 102, 10451-10453
(4) P. S. Toth, A. T. Valota, M. Velický, I. A. Kinloch, K. S. Novoselov, E. W. Hill, R. A. W. Dryfe; Chem. Sci., 2014, 5, 582-589
(5) M. Velický, M. A. Bissett, C. R. Woods, P. S. Toth, T. Georgiou, I. A. Kinloch, K. S. Novoselov, R. A. W. Dryfe; Nano Lett., 2016, 16, 2023-2032
Tackling Electrons in Two-Dimensional Materials for Electronic and Energy Applications
Authors: Liu Yuanyue 
Published: February 2020

Two-dimensional (2D) materials have shown great potential for many applications such as electrocatalysis and electronics. However, their developments are impeded by a number of significant challenges, many of which root in the 'problems of electrons'. On the physics side, the electrons/holes in current 2D semiconductors do not move fast enough under electric field (i.e. low mobility), impeding their use in high-performance electronics and optoelectronics. On the chemistry side, the current 2D electrocatalysts still suffer from relatively low activity/selectivity, hindering their use in efficient energy conversion. These challenges urge for an improved understanding of the electrons in 2D materials, and using these insights to design/discover 2D host materials with better performance.
Here I will discuss our recent progress in understanding the chemistry and physics of electrons in 2D materials for electronic and energy applications. Specifically, I will show (1) what limits the intrinsic carrier mobility of two dimensional metal dichalcogenides, and how to find high-mobility 2D semiconductors [1]; (2) the significant impact of charge on electrochemical reactions of 2D materials, which is often neglected in modeling their electrochemistry, and the implications for energy applications [2].
[1] D. Kim, J. Shi, Y. Liu, JACS, 2018, 140, 9127
[2] L. Cheng, Y. Liu, JACS, 2018 DOI: 10.1021/jacs.8b07871
Transition Metal Salts Additive as Antioxidant or Metal Oxide Decorator during Electrochemical Exfoliation of Graphite?
Authors: Ejigu Andinet , Fujisawa Kazunori , Spencer Ben F. , Wang Bin , Terrones Mauricio , Kinloch Ian A , Dryfe Robert AW 
Published: February 2020

The preparation of graphene via electrochemical exfoliation in aqueous solution is considered very attractive in terms of cost, scalability and non-toxicity. However, the quality of graphene produced by this method is inferior to the material produced by methods such as mechanical exfoliation due to the functionalisation of carbon by reactive oxygen radical species derived from water oxidation.1 There is a need to alleviate the effect of these radicals in order to capitalize on the use of anodic electrochemical exfoliation in aqueous solution.
In this presentation, we will describe the use of a new approach, based on the unexpectedly versatile role of transition metal ions to produce high quality graphene via an anodic electrochemical exfoliation route, using sulfate as the intercalating anion.2 Notably, some of the transition metals (Co2+, Fe3+) acted as antioxidants, preventing surface oxidation of graphene, while others (Ru3+, Mn2+, Ir3+) acted as metal oxide decorators (Figure 1). The graphene obtained by electrochemical exfoliation of graphite in the presence of Co2+ is two orders of magnitude more conducting and defect free than the one obtained in the absence of cobalt ion. This Co-treated graphene found to be an excellent cathode material for Aluminum-based batteries in terms of performance and cycling stability. The use of other transition metal ions (Ru3+, Mn2+, Ir3+) in the electrolysis solution resulted in decoration of graphene with the oxide of that metal in a single stage simultaneous process. This process can also allow for producing graphene functionalised with hybrid metal oxides (G-RuO2-Mn3O4) in a one-pot single step process, which can be used as electrodes for supercapacitors (500 F g-1) and as an efficient electrocatalyst for water splitting.

References

1) K. Parvez, Z. S. Wu, R. J. Li, X. J. Liu, R. Graf, X. L. Feng, K. Mullen, J. Am. Chem. Soc.
2014, 136, 6083.
2) A. Ejigu, K. Fujisawa, B. F. Spencer, B. Wang, M. Terrones, I. A. Kinloch, R. A. W. Dryfe, Adv. Funct. Mater.
2018, 28, 1804357.

Figure 1
(Invited) The Role of Defects in Van Der Waals Epitaxy of Transition Metal Dichalcogenides
Authors: Zhang Xiaotian , Choudhury Tanushree , Chubarov Mikhail , Bansal Anushka , Redwing Joan M. 
Published: February 2020

Direct growth of transition metal dichalcogenides (TMDs) such as WS2 and WSe2 on graphene and hexagonal boron nitride (hBN) is of interest for the fabrication of 2D heterostructures as an alternative to exfoliation and 2D layer stacking. This can be challenging, however, given the low surface energy of the basal plane in 2D layered materials which inhibits nucleation and lateral growth of TMD domains. In addition, it is equally probable for TMD domains to orient in two rotational directions (referred to as 0o and 180o domains) on pristine surfaces of hBN and graphene which gives rise to inversion domain boundaries (IDBs) in coalesced films. However, the presence of defects in hBN and graphene can dramatically alter the energy landscape providing a route to control nucleation and epitaxy.
Our recent studies have focused on the epitaxial growth of WSe2, WS2 and related TMD monolayer films by gas source chemical vapor deposition (CVD) on hBN and epitaxial graphene. The CVD process is carried out in a cold-wall reactor using metal hexacarbonyls and hydride chalcogen precursors in a hydrogen carrier gas. In the case of epitaxial graphene, nucleation of WS2 occurs primarily at step edges and terrace defects resulting in different WS2 rotational orientations. In the case of WSe2 growth on hBN, however, single atom vacancies in the hBN were found to act as sites for metal atom trapping which facilitates the nucleation of WSe2 domains on the surface. In this case, the TMD nucleation density can be controlled by manipulating the density of surface atom vacancies which can be achieved through plasma irradiation and annealing in NH3. In addition, the metal atoms break the surface symmetry which leads to a preferred orientation (~95%) for WSe2 domains on hBN. Through careful control of nucleation and extended lateral growth time, fully coalesced WSe2 monolayer films on hBN were achieved which exhibit optical and transport properties superior to comparable films grown on sapphire substrates. The results demonstrate the important role of defects in nucleation and epitaxial growth of 2D heterostructures.
Epitaxial and Atomically Thin Graphene–Metal Hybrid Catalyst Films—the Dual Role of Graphene As the Support and the Chemically-Transparent Protective Cap
Authors: Abdelhafiz Ali , Alamgir Faisal M. 
Published: February 2020

Commercialization of polymer electrolyte membrane (PEM) fuel cell materials has been of a great interest over the past decade. At the cathode side, the oxygen reduction reaction (ORR) is the key reaction where sluggish kinetics is present, for which Pt remains the catalyst of choice. In order to leapfrog the current limits to Pt use, three main objectives have to be achieved. First, is a reduction of Pt loading; second, is an enhancement of the mass activity per Pt atom; and third is an increase the catalyst durability. Herein, we demonstrate the dual role of single graphene layer, both as a growth template and as a protective cap for 2D Pt monolayers catalysts, where all three objectives can be achieved.
Using iterative under potential deposition (UPD), atomic layers of Pt catalyst are grown on top of a single layer graphene. X-ray absorption spectroscopic (XAS) and scanning transmission electron microscopy (STEM) analyses show that Pt growth is dictated by the graphene-templated epitaxy. Pt/graphene intimacy induces a localized compressive strain on Pt monolayers ranges 3-10%, owing to structural defects, with an overall compressive strain of 3.5% according to extended x-ray absorption fine structure (EXAFS) analysis. In addition, cyclic voltammetry (CV) analysis shows fully-wetted Pt monolayers coverage of graphene under-layer with only a ~1 nm ultra-thin layer of Pt, while ripening was suppressed as shown through STEM images. Atomic Force Microscopy (AFM) analysis demonstrates that Pt monolayers prefer to follow Frank-van der Merwe growth (i.e. layer-by-layer growth mode) rather than Volmer-Weber growth (i.e. island growth mode), where root mean square (rms) of surface roughness remains quite similar while increasing Pt loading is increased.
Pt/graphene hybrid catalysts show superior catalytic activity for ORR relative to the graphene-free counterparts or state of the art Pt commercial catalyst. A combination of the graphene-imposed compressive strain and electron transfer, push the Pt d-band center up, lowering the overpotential needed for ORR to occur. Furthermore, the graphene/Pt cap hybrid shows the graphene protecting Pt MLs from both dissolution and from ripening, with no Pt loss after 1000 fuel cell operating cycles. Our demonstration of a graphene-Pt hybrid opens the door for graphene/metal or metal/graphene architectures with potential applications in, and not limited to, energy, thermo-electric and electronics field.
Alkali Metal Doped Mono- and Bilayer Graphene: Band Structure, Raman Spectrum and Electronic Transport
Authors: Hell Martin , Ehlen Niels , Falke Yannik , Senkovskiy Boris V. , Petaccia Luca , Szkopek Thomas , Grueneis Alexander 
Published: February 2020

We use ultra-high vacuum (UHV) Raman spectroscopy in tandem with angle-resolved photoemission (ARPES) to investigate the doping-dependent Raman spectrum of epitaxially grown graphene. The evolution of the Raman spectra from pristine to heavily Cs doped graphene up to a carrier concentration of 4.4x10^14 cm-2 is investigated [1]. Renormalization effects reduce the electronic bandwidth at this doping level when graphene is at the onset of the Lifshitz transition. Ultraviolet (UV) light allows to probe the optical transition at the saddle point in the Brillouin zone achieving resonance Raman conditions in close vicinity to the van Hove singularity in the joint density of states. The position of the Raman G band of fully doped graphene/Ir(111) shifts down by 60 cm-1 and the G band asymmetry of Cs doped epitaxial graphene on Ir(111) assumes an unusual strong Fano asymmetry opposite to that of the G band of doped graphene on insulators. We compare these results on Cs doped monolayer graphene to studies of Cs doped bilayer graphene. Growth of bilayer graphene is realized by intercalation of carbon atoms under monolayer graphene using molecular beam epitaxy. We probe each step of the intercalation process using UHV Raman which reveals distinct changes in the linshape. Finally, the graphene is transferred from the metal substrate onto Si wafers and probed by UHV electronic transport during alkali metal deposition. Our work demonstrates high sensitivity towards sensing of alkali atoms and a giant decrease of the four-point resistance by three orders of magnitude upon Cs doping.
[1] M.G.Hell at al. Nano Letters 2018
18 (9), 6045-6056

Figure 1
First-Principles Understanding of Strong Auger Recombination in Hybrid Perovskites
Authors: Shen Jimmy , Zhang Xie , Van de Walle Chris G. 
Published: February 2020

The radiative recombination coefficient of the hybrid perovskites is as high as in typical direct-gap semiconductors [1], facilitating strong light absorption in solar cells and potentially enabling their application in light-emitting diodes (LEDs). Since LEDs operate at higher carrier densities than solar cells, higher-order electron–hole recombination processes can critically affect their efficiency. We have computed Auger recombination coefficients in the prototypical halide perovskite [2], CH3NH3PbI3 (MAPbI3), using first‐principles calculations. Our computed nonradiative Auger coefficients show that strong Auger recombination may suppress the LED’s efficiency. Fortunately, our insights into the origins of the strong Auger recombination indicate potential avenues for engineering to reduce the effect of Auger recombination.
This work was supported by DOE.

[1] Zhang, X, et al. ACS Energy Lett. 3, 2329 (2018).

[2] Shen, J.-X., et al. Adv. Energy Mater. 8, 1801027 (2018).