Yunhao Lu

Bio: Yunhao Lu is an academic researcher from Zhejiang University. The author has contributed to research in topics: Graphene & Band gap. The author has an hindex of 42, co-authored 163 publications receiving 11029 citations. Previous affiliations of Yunhao Lu include National University of Singapore.

Simultaneous phase and size control of upconversion nanocrystals through lanthanide doping

Abstract: Doping is a widely applied technological process in materials science that involves incorporating atoms or ions of appropriate elements into host lattices to yield hybrid materials with desirable properties and functions. For nanocrystalline materials, doping is of fundamental importance in stabilizing a specific crystallographic phase, modifying electronic properties, modulating magnetism as well as tuning emission properties. Here we describe a material system in which doping influences the growth process to give simultaneous control over the crystallographic phase, size and optical emission properties of the resulting nanocrystals. We show that NaYF(4) nanocrystals can be rationally tuned in size (down to ten nanometres), phase (cubic or hexagonal) and upconversion emission colour (green to blue) through use of trivalent lanthanide dopant ions introduced at precisely defined concentrations. We use first-principles calculations to confirm that the influence of lanthanide doping on crystal phase and size arises from a strong dependence on the size and dipole polarizability of the substitutional dopant ion. Our results suggest that the doping-induced structural and size transition, demonstrated here in NaYF(4) upconversion nanocrystals, could be extended to other lanthanide-doped nanocrystal systems for applications ranging from luminescent biological labels to volumetric three-dimensional displays.

Uniaxial strain on graphene: Raman spectroscopy study and band-gap opening.

Abstract: Graphene was deposited on a transparent and flexible substrate, and tensile strain up to ∼0.8% was loaded by stretching the substrate in one direction. Raman spectra of strained graphene show significant red shifts of 2D and G band (−27.8 and −14.2 cm−1 per 1% strain, respectively) because of the elongation of the carbon−carbon bonds. This indicates that uniaxial strain has been successfully applied on graphene. We also proposed that, by applying uniaxial strain on graphene, tunable band gap at K point can be realized. First-principle calculations predicted a band-gap opening of ∼300 meV for graphene under 1% uniaxial tensile strain. The strained graphene provides an alternative way to experimentally tune the band gap of graphene, which would be more efficient and more controllable than other methods that are used to open the band gap in graphene. Moreover, our results suggest that the flexible substrate is ready for such a strain process, and Raman spectroscopy can be used as an ultrasensitive method to ...

Uniaxial Strain on Graphene: Raman Spectroscopy Study and Band-Gap

Abstract: Graphene was deposited on a transparent andflexible substrate, and tensile strain up to0.8% was loaded by stretching the substrate in one direction. Raman spectra of strained graphene show significant red shifts of 2D and G band (27.8 and14.2 cm 1 per 1% strain, respectively) because of the elongation of the carboncarbon bonds. This indicates that uniaxial strain has been successfully applied on graphene. We also proposedthat,byapplyinguniaxialstrainongraphene,tunablebandgapatKpointcanberealized.First-principle calculations predicted a band-gap opening of300 meV for graphene under 1% uniaxial tensile strain. The strained graphene provides an alternative way to experimentally tune the band gap of graphene, which would be more efficient and more controllable than other methods that are used to open the band gap in graphene. Moreover,ourresultssuggestthattheflexiblesubstrateisreadyforsuchastrainprocess,andRamanspectroscopy can be used as an ultrasensitive method to determine the strain.

Metal-Embedded Graphene: A Possible Catalyst with High Activity

Abstract: The catalytic activity of Au-embedded graphene is investigated by the first-principle method using the CO oxidation as a benchmark probe. The first step of CO oxidation catalyzed by the Au-embedded graphene is most likely to proceed with the Langmuir−Hinshelwood reaction (CO + O2 → OOCO → CO2 +O), and the energy barrier is as low as 0.31 eV. The second step of the oxidation would be the Eley−Rideal reaction (CO + O → CO2) with a much smaller energy barrier (0.18 eV). The partially filled d states of Au are localized around the Fermi level due to the interactions between Au and the neighboring carbon atoms. The high activity of Au-embedded graphene may be attributed to the electronic resonance among electronic states of CO, O2, and the Au atom, particularly, among the d states of the Au atom and the antibonding 2π* states of CO and O2. This opens a new avenue to fabricate low cost and high activity carbon-based catalyst.

Prussian Blue@C Composite as an Ultrahigh-Rate and Long-Life Sodium-Ion Battery Cathode

Abstract: Rechargeable sodium ion batteries (SIBs) are surfacing as promising candidates for applications in large-scale energy-storage systems. Prussian blue (PB) and its analogues (PBAs) have been considered as potential cathodes because of their rigid open framework and low-cost synthesis. Nevertheless, PBAs suffer from inferior rate capability and poor cycling stability resulting from the low electronic conductivity and deficiencies in the PBAs framework. Herein, to understand the vacancy-impacted sodium storage and Na-insertion reaction kinetics, we report on an in-situ synthesized PB@C composite as a high-performance SIB cathode. Perfectly shaped, nanosized PB cubes were grown directly on carbon chains, assuring fast charge transfer and Na-ion diffusion. The existence of [Fe(CN)6] vacancies in the PB crystal is found to greatly degrade the electrochemical activity of the FeLS(C) redox couple via first-principles computation. Superior reaction kinetics are demonstrated for the redox reactions of the FeHS(N) couple, which rely on the partial insertion of Na ions to enhance the electron conduction. The synergistic effects of the structure and morphology results in the PB@C composite achieving an unprecedented rate capability and outstanding cycling stability (77.5 mAh g−1 at 90 C, 90 mAh g−1 after 2000 cycles at 20 C with 90% capacity retention).

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Raman spectroscopy as a versatile tool for studying the properties of graphene

Abstract: Raman spectroscopy is an integral part of graphene research. It is used to determine the number and orientation of layers, the quality and types of edge, and the effects of perturbations, such as electric and magnetic fields, strain, doping, disorder and functional groups. This, in turn, provides insight into all sp(2)-bonded carbon allotropes, because graphene is their fundamental building block. Here we review the state of the art, future directions and open questions in Raman spectroscopy of graphene. We describe essential physical processes whose importance has only recently been recognized, such as the various types of resonance at play, and the role of quantum interference. We update all basic concepts and notations, and propose a terminology that is able to describe any result in literature. We finally highlight the potential of Raman spectroscopy for layered materials other than graphene.

Functionalization of Graphene: Covalent and Non-Covalent Approaches, Derivatives and Applications

Abstract: Approaches, Derivatives and Applications Vasilios Georgakilas,† Michal Otyepka,‡ Athanasios B. Bourlinos,‡ Vimlesh Chandra, Namdong Kim, K. Christian Kemp, Pavel Hobza,‡,§,⊥ Radek Zboril,*,‡ and Kwang S. Kim* †Institute of Materials Science, NCSR “Demokritos”, Ag. Paraskevi Attikis, 15310 Athens, Greece ‡Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacky University Olomouc, 17. listopadu 12, 771 46 Olomouc, Czech Republic Center for Superfunctional Materials, Department of Chemistry, Pohang University of Science and Technology, San 31, Hyojadong, Namgu, Pohang 790-784, Korea Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, v.v.i., Flemingovo naḿ. 2, 166 10 Prague 6, Czech Republic