| 1. |
- Ayub, Rabia, et al.
(författare)
-
Cyclopropyl Group : An Excited-State Aromaticity Indicator?
- 2017
-
Ingår i: Chemistry - A European Journal. - : Wiley-VCH Verlag. - 0947-6539 .- 1521-3765. ; 23:55, s. 13684-13695
-
Tidskriftsartikel (refereegranskat)abstract
- The cyclopropyl (cPr) group, which is a well-known probe for detecting radical character at atoms to which it is connected, is tested as an indicator for aromaticity in the first ππ* triplet and singlet excited states (T1 and S1). Baird's rule says that the π-electron counts for aromaticity and antiaromaticity in the T1 and S1 states are opposite to Hückel's rule in the ground state (S0). Our hypothesis is that the cPr group, as a result of Baird's rule, will remain closed when attached to an excited-state aromatic ring, enabling it to be used as an indicator to distinguish excited-state aromatic rings from excited-state antiaromatic and nonaromatic rings. Quantum chemical calculations and photoreactivity experiments support our hypothesis; calculated aromaticity indices reveal that openings of cPr substituents on [4n]annulenes ruin the excited-state aromaticity in energetically unfavorable processes. Yet, polycyclic compounds influenced by excited-state aromaticity (e.g., biphenylene), as well as 4nπ-electron heterocycles with two or more heteroatoms represent limitations.
|
|
| 2. |
- Chen, Zhang, et al.
(författare)
-
Making monolayer graphene photoluminescent by electron-beam-activated fluorination approach
- 2023
-
Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 608
-
Tidskriftsartikel (refereegranskat)abstract
- The past one and half decades have witnessed a tremendous development of graphene electronics, and the key to the success of graphene is its exceptional properties. The lacking of an inherent bandgap endows graphene with excellent electrical properties but considerably limits its applications in light-emitting and high-performance graphene-based devices. Herein, an approach for the direct writing of semiconducting and photoluminescent fluorinated graphene (C4F) patterns on monolayer graphene by an optimized electron-beam-activated fluorination technique is reported. A series of characterization approaches, such as atomic force microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy were used to demonstrate the successful preparation of C4F for maskless lithography. Specially, a sharp and strong photoluminescence located at the purple light range of ∼380 nm was observed in C4F, demonstrating a desirable semiconducting nature, and the bandgap was further confirmed by follow-up electrical measurements, where the C4F filed-effect transistor exhibited a p-type semiconductor behavior and significantly enhanced on/off ratio. Therefore, this work provides a novel technique for the fabrication of graphene devices for promising electronic and optoelectronic applications, but also opens a route towards the tailoring and engineering of electronic properties of graphene.
|
|
| 3. |
- Deligkiozi, Ioanna, et al.
(författare)
-
Synthesis and characterization of new azobenzene-containing bis pentacyanoferrate(II) stoppered push-pull [2]rotaxanes, with alpha- and beta-cyclodextrin. Towards highly medium responsive dyes
- 2015
-
Ingår i: Dyes and pigments. - : Elsevier BV. - 0143-7208 .- 1873-3743. ; 113, s. 709-722
-
Tidskriftsartikel (refereegranskat)abstract
- The solvatochromic behavior of novel synthesized azo-containing viologen-based rotaxanes, combining push-pull linear and alpha or beta-cyclodextrin macrocyclic components is examined. These rotaxanes are stoppered by pentacyanoferrate(II) units. The latter stabilize these systems and furthermore act as strong electron donors. These units are linked to strong electron withdrawing viologen units thus giving rise to an exceptionally intense solvatochromic behavior. Suitable solvent polarity scales and Linear Solvation Energy Relationships (LSERs) were employed in order to rationalize the solvent polarity effects observed, both specific and non-specific ones. The results for the title compounds as well as their Cyclodextrin-Free-Dumbbell (CFD) like analogue, are compared to recent published solvatochromic data regarding similar smaller pentacyanoferrate(II) complexes as well as other highly solvatochromic compounds. Structural effects on the solvatochromic intensity as well as the contribution of different solvent-solute interactions are rationalized and quantified. (C) 2014 Elsevier Ltd. All rights reserved.
|
|
| 4. |
- Duan, Tianbo, 1992-, et al.
(författare)
-
Towards Ballistic Transport CVD Graphene by Controlled Removal of Polymer Residues
- 2022
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 33:49, s. 495704-
-
Tidskriftsartikel (refereegranskat)abstract
- Polymer-assisted wet transfer of chemical vapor deposited (CVD) graphene has achieved great success towards the true potential for large-scale electronic applications, while the lack of an efficient polymer removal method has been regarded as a crucial factor for realizing high carrier mobility in graphene devices. Hereby, we report an efficient and facile method to clean polymer residues on graphene surface by merely employing solvent mixture of isopropanol (IPA) and water (H2O). Raman spectroscopy shows an intact crystal structure of graphene after treatment, and the x-ray photoelectron spectroscopy indicates a significant decrease in the C–O and C=O bond signals, which is mainly attributed to the removal of polymer residues and further confirmed by subsequent atomic force microscopy analysis. More importantly, our gated measurements demonstrate that the proposed approach has resulted in a 3-fold increase of the carrier mobility in CVD graphene with the electron mobility close to 10 000 cm2 V−1 S−1, corresponding to an electron mean free path beyond 100 nm. This intrigues the promising application for this novel method in achieving ballistic transport for CVD graphene devices.
|
|
| 5. |
- Li, Hu, 1986-, et al.
(författare)
-
Click Chemistry Enabling Covalent and Non-Covalent Modifications of Graphene with (Poly)saccharides
- 2021
-
Ingår i: Polymers. - BASEL SWITZERLAND : MDPI. - 2073-4360. ; 13:1
-
Forskningsöversikt (refereegranskat)abstract
- Graphene is a material with outstanding properties and numerous potential applications in a wide range of research and technology areas, spanning from electronics, energy materials, sensors, and actuators to life-science and many more. However, the insolubility and poor dispersibility of graphene are two major problems hampering its use in certain applications. Tethering mono-, di-, or even poly-saccharides on graphene through click-chemistry is gaining more and more attention as a key modification approach leading to new graphene-based materials (GBM) with improved hydrophilicity and substantial dispersibility in polar solvents, e.g., water. The attachment of (poly)saccharides on graphene further renders the final GBMs biocompatible and could open new routes to novel biomedical and environmental applications. In this review, recent modifications of graphene and other carbon rich materials (CRMs) through click chemistry are reviewed.
|
|
| 6. |
- Li, Hu, 1986-, et al.
(författare)
-
Direct measurement of the surface energy of single-walled carbon nanotubes through atomic force microscopy
- 2019
-
Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 126:6
-
Tidskriftsartikel (refereegranskat)abstract
- Surface energy in nanomaterials is an essential parameter demonstrating a key role in their surface interactions and their functionalization aptitude. In this work, a new and facile methodology based on atomic force microscopy for the measurement of the surface energy of single-walled carbon nanotubes (SWCNTs) is reported. The proposed approach starts with the calibration based on a well-studied material, graphite, and the precision of the technique is confirmed by the measurement of the surface energy of multiwalled carbon nanotubes. Our measurements show that SWCNTs display a surface energy of 52.8mJ/m(2), which is in very good agreement with theoretical predictions of the measured property. Our experimental approach is essentially applicable to other nano-objects in contrast to conventional wet angle methods which are currently employed mainly in bulk materials.
|
|
| 7. |
- Li, Hu, 1986-, et al.
(författare)
-
Fabrication of BP2T functionalized graphene via non-covalent π-π stacking interactions for enhanced ammonia detection
- 2021
-
Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 11:57, s. 35982-35987
-
Tidskriftsartikel (refereegranskat)abstract
- Graphene has stimulated great enthusiasm in a variety of fields, while its chemically inert surface still remains challenging for functionalization towards various applications. Herein, we report an approach to fabricate non-covalently functionalized graphene by employing pi-pi stacking interactions, which has potentialities for enhanced ammonia detection. 5,5 '-Di(4-biphenylyl)-2,2 '-bithiophene (BP2T) molecules are used in our work for the non-covalent functionalization through strong pi-pi interactions of aromatic structures with graphene, and systematic investigations by employing various spectroscopic and microscopic characterization methods confirm the successful non-covalent attachment of the BP2T on the top of graphene. From our gas sensing experiments, the BP2T functionalized graphene is promising for ammonia sensing with a 3-fold higher sensitivity comparing to that of the pristine graphene, which is mainly attributed to the enhanced binding energy between the ammonia and BP2T molecules derived by employing the Langmuir isotherm model. This work provides essential evidence of the pi-pi stacking interactions between graphene and aromatic molecules, and the reported approach also has the potential to be widely employed in a variety of graphene functionalizations for chemical detection.
|
|
| 8. |
- Li, Hu, 1986-, et al.
(författare)
-
Moiré patterns arising from bilayer graphone/graphene superlattice
- 2020
-
Ingår i: Nano Reseach. - : Springer Nature. - 1998-0124 .- 1998-0000. ; 13:4, s. 1060-1064
-
Tidskriftsartikel (refereegranskat)abstract
- Moiré patterns from two-dimensional (2D) graphene heterostructures assembled via van der Waals interactions have sparked considerable interests in physics with the purpose to tailor the electronic properties of graphene. Here we report for the first time the observation of moiré patterns arising from a bilayer graphone/graphene superlattice produced through direct single-sided hydrogenation of a bilayer graphene on substrate. Compared to pristine graphene, the bilayer superlattice exhibits a rippled surface and two types of moiré patterns are observed: triangular and linear moiré patterns with the periodicities of 11 nm and 8–9 nm, respectively. These moiré patterns are revealed from atomic force microscopy and further confirmed by following fast Fourier transform (FFT) analysis. Density functional theory (DFT) calculations are also performed and the optimized lattice constants of bilayer superlattice heterostructure are in line with our experimental analysis. These findings show that well-defined triangular and linear periodic potentials can be introduced into the graphene system through the single-sided hydrogenation and also open a route towards the tailoring of electronic properties of graphene by various moiré potentials.
|
|
| 9. |
- Li, Hu, 1986-, et al.
(författare)
-
Superior adhesion of graphene nanoscrolls
- 2018
-
Ingår i: Communications Physics. - : Springer Science and Business Media LLC. - 2399-3650. ; 1
-
Tidskriftsartikel (refereegranskat)abstract
- An emerging material in the carbon family, a graphene nanoscroll (GNS) is composed of tubularly scrolled monolayer graphene and has shown superlubricity and large current sustainability, surpassing the properties of monolayer graphene itself. Here we report on the superior adhesion of GNS prepared with a high yield synthesis method that allows for mass production of high quality GNSs. Raman spectra indicate that the GNS still maintains the signature of monolayer graphene, implying the lacking of π-stacking between adjacent layers. Importantly, adhesion measurements using atomic force microscopy reveal these GNSs with height range of 120-130 nm show a 2.5-fold stronger adhesion force than pristine graphene. This result potentially indicates that the GNS has higher adhesion than monolayer graphene and even higher than the liquid-solid and hydrogen-bonding enhanced interfaces which are essential types of adhesions involved in the field of physical adhesions and thus, GNS could be a new candidate for super-strong and lightweight devices.
|
|
| 10. |
- Liu, Jiangwei, et al.
(författare)
-
Experimental observation of size-dependent behavior in surface energy of gold nanoparticles through atomic force microscope
- 2018
-
Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 113:8
-
Tidskriftsartikel (refereegranskat)abstract
- Surface energy plays a key role in the physicochemical interactions of material surfaces, and it is closely related to the unique properties and numerous surface functionalization possibilities of gold nanoparticles. Herein, we have reported an atomic force microscopy based technique to measure the surface energies of different materials in the peakforce quantitative nanomechanical mapping mode. Our study on gold nanoparticles focuses on the particles with diameters ranging from 2 to 14 nm. The experimental results indicate a clear size-dependent behavior in the surface energy of gold nanoparticles when the size is smaller than 5 nm, and the smallest gold nanoparticle displays a threefold higher surface energy compared to bulk gold. Therefore, our experimental results provide essential evidence that can lead to a better understanding of the size-property relationships allowing for process design in gold nanoparticles.
|
|
