Department: 1 International Center for New-Structured Materials (ICNSM), Laboratory of New-Structured Materials, Department of Materials Science and Engineering
•A collective phase transition is dependent on the coverage on Au(111) while a hexamer phase is independent on coverage on Bi-3×√3-Au(111) surface.•The results reveal the competing between intermolecular interactions and interfacial interactions.•There is no GNRs formed on Bi-3×√3-Au(111) after annealing.•Density functional theory (DFT) calculations confirm the configuration change of DBBA molecule on Au(111) and Bi-3×√3-Au(111) surface and the important role of the substrate assistance to form GNRs.The initial growth behaviors of nonplanar 10,10′-dibromo-9,9′-bianthryl (DBBA) molecules on the Au(111) substrates, which is either pristine or Bi-3 × √3-Au(111), at low deposition rates have been systematically investigated using low temperature scanning tunneling microscopy (LT-STM) and density functional theories (DFT) calculations. The effects of such substrates on the subsequent graphene nanoribbons (GNRs) formation are addressed. On clean Au(111), DBBA molecules self-assemble into highly ordered commensurate single-molecule chains along <112¯>Au at a coverage of 0.8 monolayer (ML), and collectively transit into long-range ordered commensurate double-molecule chains along <11¯0>Au but with many single-molecule vacancies at a coverage of 1.2 ML, revealing the delicate competing between intermolecular interactions and molecule-substrate interfacial interactions. The interfacial interactions are further tuned by introducing bismuth to form a Bi-3 × √3-Au(111)surface, where DBBA molecules self-assemble into an unique hexamer phase due to the enhanced intermolecular interactions via CH…π and halogen bonds. DFT calculations confirm the proposed molecular configuration change of single DBBA molecule when adsorbed on different substrates. The calculated difference in CBr bond gives further insight into why no GNRs formed on Bi-3 × √3-Au(111).Download high-res image (174KB)Download full-size image
In this work, we demonstrate a first attempt at understanding the catalytic mechanism of nanosized Co in reducing the dehydrogenation temperature of the Li–B–N–H hydrogen storage system by experimental observation and theoretical calculation. A nanosized Co@C composite (Co particles <10 nm) is successfully synthesized by casting a furfuryl alcohol-filled, Co-based metal–organic framework, MOF-74(Co), at 700 °C. Adding small quantities of the prepared nanosized Co@C composite significantly reduces the dehydrogenation temperature of the LiBH4–2LiNH2 system. The 5 wt% Co@C-containing sample releases approximately 10.0 wt% hydrogen at 130–230 °C with a peak temperature of 210 °C, which is reduced by 125 °C from that of the pristine sample. During hydrogen desorption, nanosized Co remains in the metallic state and only works as a catalyst to reduce the kinetic barriers of hydrogen release from the LiBH4–2LiNH2 system. Ab initio calculations reveal that the presence of a Co catalyst induces a redistribution of charge, which not only weakens the chemical H–B bonding but also enhances the electrostatic interactions between Hδ+ in the NH2 groups and Hδ− in the BH4 groups, consequently reducing the energy barriers for the formation of H2 molecules. This explains the low-temperature dehydrogenation behaviour of the Co-catalysed Li–B–N–H systems.
In this work, we demonstrate a first attempt at understanding the catalytic mechanism of nanosized Co in reducing the dehydrogenation temperature of the Li–B–N–H hydrogen storage system by experimental observation and theoretical calculation. A nanosized Co@C composite (Co particles <10 nm) is successfully synthesized by casting a furfuryl alcohol-filled, Co-based metal–organic framework, MOF-74(Co), at 700 °C. Adding small quantities of the prepared nanosized Co@C composite significantly reduces the dehydrogenation temperature of the LiBH4–2LiNH2 system. The 5 wt% Co@C-containing sample releases approximately 10.0 wt% hydrogen at 130–230 °C with a peak temperature of 210 °C, which is reduced by 125 °C from that of the pristine sample. During hydrogen desorption, nanosized Co remains in the metallic state and only works as a catalyst to reduce the kinetic barriers of hydrogen release from the LiBH4–2LiNH2 system. Ab initio calculations reveal that the presence of a Co catalyst induces a redistribution of charge, which not only weakens the chemical H–B bonding but also enhances the electrostatic interactions between Hδ+ in the NH2 groups and Hδ− in the BH4 groups, consequently reducing the energy barriers for the formation of H2 molecules. This explains the low-temperature dehydrogenation behaviour of the Co-catalysed Li–B–N–H systems.
Co-reporter:Pei Yang;Bo Tai;Weikang Wu;Jian-Min Zhang;Feng Wang;Shan Guan;Wei Guo;Shengyuan A. Yang
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 24) pp:16189-16197
Publication Date(Web):2017/06/21
DOI:10.1039/C7CP01953J
Perovskite oxide materials have been attracting significant attention due to their rich physical and chemical properties. With its proven stability and bio-compatibility, we suggest the lanthanide-doped perovskite to be a promising material for biological luminescence applications. Here, taking CaTiO3 as a concrete example, we systematically investigate its doping properties using first-principles computational methods. We determine the conditions allowing the growth of CaTiO3 against various competing phases. We obtain the formation energies of various intrinsic point defects in the material. The doping configuration and the charge state of the lanthanide dopants are determined. We find that for heavier elements in the lanthanide family, the substitution at the Ca site is favored under p-type growth conditions and tends to be trivalent, whereas the substitution at the Ti site is favored under n-type growth conditions and tends to be divalent. And for lighter elements in the family, the substitution at the Ca site is more favored for most cases and the dopant is more likely to be trivalent. By tuning the growth conditions, one could control the valence state of the lanthanide dopant, which in turn controls the luminescence spectra. We collect and identify the emission peaks in the infrared biological window, based on which possible doping schemes are suggested for bio-labeling and imaging applications.
Novel phenomena appear when two different oxide materials are combined together to form an interface. For example, at the interface of LaAlO3/SrTiO3, two-dimensional conductive states form to avoid the polar discontinuity, and magnetic properties are found at such an interface. In this work, we propose a new type of interface between two nonmagnetic and nonpolar oxides that could host a magnetic state, where it is the ferroelectric polarization discontinuity instead of the polar discontinuity that leads to the charge transfer, forming the interfacial magnetic state. As a concrete example, we investigate by first-principles calculations the heterostructures made of ferroelectric perovskite oxide PbTiO3 and nonferroelectric polarized oxide TiO2. We show that charge is transferred to the interfacial layer forming an interfacial ferromagnetic ordering that may persist up to room temperature. Especially, the strong coupling between bulk ferroelectric polarization and interface ferromagnetism represents a new type of magnetoelectric effect, which provides an ideal platform for exploring the intriguing interfacial multiferroics. The findings here are important not only for fundamental science but also for promising applications in nanoscale electronics and spintronics.Keywords: ferroelectric polarization discontinuity; first-principles; interfacial multiferroics; perovskite oxide heterostructures; spin polarization;
Co-reporter:Yao Wang, Shan-Shan Wang, Yunhao Lu, Jianzhong Jiang, and Shengyuan A. Yang
Nano Letters 2016 Volume 16(Issue 7) pp:4576-4582
Publication Date(Web):June 16, 2016
DOI:10.1021/acs.nanolett.6b01841
The change of bonding status, typically occurring only in chemical processes, could dramatically alter the material properties. Here, we show that a tunable breaking and forming of a diatomic bond can be achieved through physical means, i.e., by a moderate biaxial strain, in the newly discovered MoN2 two-dimensional (2D) material. On the basis of first-principles calculations, we predict that as the lattice parameter is increased under strain, there exists an isostructural phase transition at which the N–N distance has a sudden drop, corresponding to the transition from a N–N nonbonding state to a N–N single bond state. Remarkably, the bonding change also induces a magnetic phase transition, during which the magnetic moments transfer from the N(2p) sublattice to the Mo(4d) sublattice; meanwhile, the type of magnetic coupling is changed from ferromagnetic to antiferromagnetic. We provide a physical picture for understanding these striking effects. The discovery is not only of great scientific interest in exploring unusual phase transitions in low-dimensional systems, but it also reveals the great potential of the 2D MoN2 material in the nanoscale mechanical, electronic, and spintronic applications.
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).
Journal of Alloys and Compounds 2014 Volume 613() pp:55-61
Publication Date(Web):15 November 2014
DOI:10.1016/j.jallcom.2014.06.005
•The SOC effect affects the cohesion energy of crystal phase.•The effect of SOC was reduced due to random local atomic structures in liquids.•The local geometrical structures also affect the melting points.•Both SOC effect and local atomic structures are important for melting point difference.The origin of different melting points between Al2Cu and Al2Au has been studied using ab initio molecular dynamics simulations. Cohesive energy, electronic structures and structure information of both crystal and liquid phases have been analyzed. It is found that spin orbital coupling (SOC) plays an important role on the cohesive energy of crystal phase, consistent with the different melting points of these two alloys. Whereas, it seems that SOC has no effect on the formation energy and structure of liquid phase. Possible mechanism of reduced SOC effect at liquid phase is proposed. Our results are helpful to understand the glass formation ability difference between Al2Cu and Al2Au.
Co-reporter:Yinzhu Jiang, Dan Zhang, Yong Li, Tianzhi Yuan, Naoufal Bahlawane, Chu Liang, Wenping Sun, Yunhao Lu, Mi Yan
Nano Energy 2014 Volume 4() pp:23-30
Publication Date(Web):March 2014
DOI:10.1016/j.nanoen.2013.12.001
•A high-performance amorphous Fe2O3 anode is developed for lithium ion batteries.•Amorphization of TMOs may offer a new perspective for high performance LIB anodes.•A capacity of ~1600 mA h g−1 is sustained after 500 cycles at 1 A g−1.•A specific capacity of ~460 mA h g−1 is achieved using an ultra-large 20 A g−1.Despite their widespread application state-of-the-art lithium batteries are still highly limited in terms of capacity, lifetime and safety upon high charging rate. The development of advanced Li-ion batteries with high energy/power density relies increasingly on transition metal oxides. Their conversion reactions enable a combined high capacity and enhanced safety. Nevertheless, their practical application is severely limited by the insufficient cycling stability, poor rate capability and large voltage hysteresis which impact the lifetime and the performance of the battery. Here we report the exceptionally high-performance of an amorphous Fe2O3 anode, which largely outperforms its crystalline counterpart. Besides the advantageous narrow voltage hysteresis, this material exhibits a new breakthrough in terms of cycling stability and rate capacity. A highly reversible charge–discharge capacity of ~1600 mA h g−1 was observed after 500 cycles using a current density of 1000 mA g−1. A specific capacity of ~460 mA h g−1 was achieved using the ever reported large current density of 20,000 mA g−1 (~20 C), which opens venues for high power applications. The amorphous nature of Fe2O3 anode yields a unique electrochemical behavior and enhanced capacitive storage, which drives the overall electrochemical performance. This work demonstrates that amorphous transition metal oxides (a-TMO) based materials may offer a new perspective towards the development of high performing anodes for the next-generation of Li-ion batteries.
Based on first-principles electronic structure calculations and molecular dynamics simulations, a possible reaction pathway for fabricating half-metallic Mo-borine sandwich molecular wires on a hydrogen-passivated Si(001) surface is presented. The molecular wire is chemically bonded to the silicon surface and is stable up to room temperature. Interestingly, the essential properties of the molecular wire are not significantly affected by the Si substrate. Furthermore, their electronic and magnetic properties are tunable by an external electric field, which allows the molecular wire to function as a molecular switch or a basic component for information storage devices, leading to applications in future molecular electronic and spintronic devices.
Adsorption of Mn adatom on PbTe(1 1 1) surface is investigated by first-principle calculations. A subsurface substitutional adsorption mechanism is found. MnTe bond is stronger and shorter than PbTe bond. This leads to competition. Because of stronger MnTe bond, Mn atoms prefer to be deep into bulk crystal in order to maximum the number of MnTe bond. But the MnTe bonds cannot relax to gain their maximum strength because of the rigidity of the bulk crystal. At the outmost surface layer Mn atoms can relax maximum but the number of MnTe bond is only half of that in bulk. The 2nd layer is the best choice and Mn atoms prefer to form a pattern, in well agreement with recent experimental work. More importantly, its magnetic state is strain-dependent and this opens a new avenue to fabricate spintronics and spin caloritronics with a high tunneling magnetothermopower based on PbTe.
The Journal of Physical Chemistry Letters 2011 Volume 2(Issue 11) pp:1310-1314
Publication Date(Web):May 13, 2011
DOI:10.1021/jz200398d
Systematic study of interaction between graphene and hydroxyls is carried out by first-principles calculations. Although single hydroxyl adsorbed on graphene presents magnetic properties, hydroxyls prefer to adsorb on graphene in pairs without magnetic properties. The formation energy of hydroxyl pairs with graphene is coverage-dependent, and the most stable structure is half-covered by hydroxyl pairs along zigzag chains with alternative sp2 and sp3 hybridization between carbon atoms. The bandgap of this structure is 0.97 eV in GW approximation, close to the bandgap of Si, and this structure is stable at room temperature. It is possible to build graphene-based electronic circuits from graphene hydroxide without the need for cutting or etching.Keywords: bandgap; coverage; DFT; graphene; hydroxide; hydroxyl; oxide;
Co-reporter:Pei Yang, Bo Tai, Weikang Wu, Jian-Min Zhang, Feng Wang, Shan Guan, Wei Guo, Yunhao Lu and Shengyuan A. Yang
Physical Chemistry Chemical Physics 2017 - vol. 19(Issue 24) pp:NaN16197-16197
Publication Date(Web):2017/05/26
DOI:10.1039/C7CP01953J
Perovskite oxide materials have been attracting significant attention due to their rich physical and chemical properties. With its proven stability and bio-compatibility, we suggest the lanthanide-doped perovskite to be a promising material for biological luminescence applications. Here, taking CaTiO3 as a concrete example, we systematically investigate its doping properties using first-principles computational methods. We determine the conditions allowing the growth of CaTiO3 against various competing phases. We obtain the formation energies of various intrinsic point defects in the material. The doping configuration and the charge state of the lanthanide dopants are determined. We find that for heavier elements in the lanthanide family, the substitution at the Ca site is favored under p-type growth conditions and tends to be trivalent, whereas the substitution at the Ti site is favored under n-type growth conditions and tends to be divalent. And for lighter elements in the family, the substitution at the Ca site is more favored for most cases and the dopant is more likely to be trivalent. By tuning the growth conditions, one could control the valence state of the lanthanide dopant, which in turn controls the luminescence spectra. We collect and identify the emission peaks in the infrared biological window, based on which possible doping schemes are suggested for bio-labeling and imaging applications.
In this work, we demonstrate a first attempt at understanding the catalytic mechanism of nanosized Co in reducing the dehydrogenation temperature of the Li–B–N–H hydrogen storage system by experimental observation and theoretical calculation. A nanosized Co@C composite (Co particles <10 nm) is successfully synthesized by casting a furfuryl alcohol-filled, Co-based metal–organic framework, MOF-74(Co), at 700 °C. Adding small quantities of the prepared nanosized Co@C composite significantly reduces the dehydrogenation temperature of the LiBH4–2LiNH2 system. The 5 wt% Co@C-containing sample releases approximately 10.0 wt% hydrogen at 130–230 °C with a peak temperature of 210 °C, which is reduced by 125 °C from that of the pristine sample. During hydrogen desorption, nanosized Co remains in the metallic state and only works as a catalyst to reduce the kinetic barriers of hydrogen release from the LiBH4–2LiNH2 system. Ab initio calculations reveal that the presence of a Co catalyst induces a redistribution of charge, which not only weakens the chemical H–B bonding but also enhances the electrostatic interactions between Hδ+ in the NH2 groups and Hδ− in the BH4 groups, consequently reducing the energy barriers for the formation of H2 molecules. This explains the low-temperature dehydrogenation behaviour of the Co-catalysed Li–B–N–H systems.
In this work, we demonstrate a first attempt at understanding the catalytic mechanism of nanosized Co in reducing the dehydrogenation temperature of the Li–B–N–H hydrogen storage system by experimental observation and theoretical calculation. A nanosized Co@C composite (Co particles <10 nm) is successfully synthesized by casting a furfuryl alcohol-filled, Co-based metal–organic framework, MOF-74(Co), at 700 °C. Adding small quantities of the prepared nanosized Co@C composite significantly reduces the dehydrogenation temperature of the LiBH4–2LiNH2 system. The 5 wt% Co@C-containing sample releases approximately 10.0 wt% hydrogen at 130–230 °C with a peak temperature of 210 °C, which is reduced by 125 °C from that of the pristine sample. During hydrogen desorption, nanosized Co remains in the metallic state and only works as a catalyst to reduce the kinetic barriers of hydrogen release from the LiBH4–2LiNH2 system. Ab initio calculations reveal that the presence of a Co catalyst induces a redistribution of charge, which not only weakens the chemical H–B bonding but also enhances the electrostatic interactions between Hδ+ in the NH2 groups and Hδ− in the BH4 groups, consequently reducing the energy barriers for the formation of H2 molecules. This explains the low-temperature dehydrogenation behaviour of the Co-catalysed Li–B–N–H systems.
