Research Highlights

Marginally twisted bilayer graphene with large Bernal stacked domains involves symmetry-breaking features with domain boundaries that exhibit topological edge states normally obscured by trivial bands. A vertical electric field can activate these edge states through inversion symmetry breaking and opening a bandgap around the edge state energy. However, harnessing pristine topological states at the Fermi level without violent electric or magnetic bias remains challenging, particularly above room temperature. Here, we demonstrate that thermal biasing can break the vertically stacked lattice symmetry of twisted bilayer graphene via the interatomic Seebeck effect, enabling thermoelectric imaging of topological edge states at tunable Fermi levels above room temperature. The high spatial resolution in the imaging is achieved through atomic-scale thermopower generation between a metallic tip and the sample, reflecting the local electronic band structure and its derivative features of twisted bilayer graphene at the Fermi level. Our findings suggest that thermal biasing provides a sensitive, non-destructive method for symmetry breaking and topological state imaging above room temperature, making it a practical and accessible approach.

https://doi.org/10.1038/s41467-025-57194-x

While the shape-dependent quantum confinement (QC) effect in anisotropic semiconductor nanocrystals has been extensively studied, the QC in facet-specified polyhedral quantum dots (QDs) remains underexplored. Recently, tetrahedral nanocrystals have gained prominence in III–V nanocrystal synthesis. In our study, we successfully synthesized well-faceted tetrahedral InAs QDs with a first excitonic absorption extending up to 1700 nm. We observed an unconventional sizing curve, indicating weaker confinement than for equivalently volumed spherical QDs. The (111) surface states of InAs QDs persist at the conduction band minimum state even after ligand passivation with a significantly reduced band gap, which places tetrahedral QDs at lower energies in the sizing curve. Consequently, films composed of tetrahedral QDs demonstrate an extended photoresponse into the short-wave infrared region, compared to isovolume spherical QD films.

https://pubs.acs.org/doi/10.1021/jacs.4c00966

Phase transition points can be used to critically reduce the ionic migration activation energy, which is important for realizing high-performance electrolytes at low temperatures. Here, we demonstrate a route toward low-temperature thermionic conduction in solids, by exploiting the critically lowered activation energy associated with oxygen transport in Ca-substituted bismuth ferrite (Bi1-xCaxFeO3-δ) films. Our demonstration relies on the finding that a compositional phase transition occurs by varying Ca doping ratio across xCa ≃ 0.45 between two structural phases with oxygen-vacancy channel ordering along <100> or <110> crystal axis, respectively. Regardless of the atomic-scale irregularity in defect distribution at the doping ratio, the activation energy is largely suppressed to 0.43 eV, compared with ~0.9 eV measured in otherwise rigid phases. From first-principles calculations, we propose that the effective short-range attraction between two positively charged oxygen vacancies sharing lattice deformation not only forms the defect orders but also suppresses the activation energy through concerted hopping.

https://doi.org/10.1038/s41467-022-32826-8

The microscopic origins of thermopower have been investigated to design efficient thermoelectric devices, but strongly correlated quantum states such as charge density waves and Mott insulating phase remain to be explored for atomic-scale thermopower engineering. Here, we report on thermopower and phonon puddles in the charge density wave states in 1T-TaS2, probed by scanning thermoelectric microscopy. The Star-of-David clusters of atoms in 1T-TaS2 exhibit counterintuitive variations in thermopower with broken three-fold symmetry at the atomic scale, originating from the localized nature of valence electrons and their interlayer coupling in the Mott insulating charge density waves phase of 1T-TaS2. Additionally, phonon puddles are observed with a spatial range shorter than the conventional mean free path of phonons, revealing the phonon propagation and scattering in the subsurface structures of 1T-TaS2.

https://doi.org/10.1038/s41467-022-32226-y

Friction-driven static electrification is familiar and fundamental in daily life, industry, and technology, but its basics have long been unknown and have continually perplexed scientists from ancient Greece to the modern high-tech era. Despite its simple manifestation, triboelectric charging is believed to be very complex because of the unresolvable interfacial interaction between two rubbing materials. Here, we for the first time reveal a simple physics of triboelectric charging and triboelectric series based on friction-originated thermoelectric charging effects at the interface, characterized by the material density (𝜌), specific heat (𝑐), thermal conductivity (𝑘), and Seebeck coefficient (𝑆) of each material. We demonstrate that energy dissipational heat at the interface induces temperature variations in the materials and thus develops electrostatic potentials that will initiate thermoelectric charging across the interface. We find that the trends and quantities of triboelectric charging for various polymers, metals, semiconductors, and even lightning clouds are simply governed by the triboelectric factor 𝜉=𝑆/√𝜌⁢𝑐⁢𝑘. The triboelectric figure-of-merit is expressed with the triboelectric power 𝐾=𝜉⁢√𝑡/𝜋, of which the difference can be maximized up to 1.2 V/W cm-2 at the friction time 𝑡 = 1 s. Our findings will bring significant opportunities for microscopic understanding and management of triboelectricity or static electrification.

https://doi.org/10.1103/PhysRevResearch.4.023131

Thermal energy transport across the interfaces of physically and chemically modified graphene with two metals, Al and Cu, was investigated by measuring thermal conductance using the time-domain thermoreflectance method. Graphene was processed using a He2+ ion-beam with a Gaussian distribution or by exposure to ultraviolet/O3, which generates structural or chemical disorder, respectively. Hereby, we could monitor changes in the thermal conductance in response to varying degrees of disorder. We find that the measured conductance increases as the density of the physical disorder increases, but undergoes an abrupt modulation with increasing degrees of chemical modification, which decreases at first and then increases considerably. Moreover, we find that the conductance varies inverse proportionally to the average distance between the structural defects in the graphene, implying a strong in-plane influence of phonon kinetics on interfacial heat flow. We attribute the bimodal results to an interplay between the distinct effects on graphene’s vibrational modes exerted by graphene modification and by the scattering of modes.

https://www.nature.com/articles/srep34428

The photoluminescence (PL) origin of bright blue emission arising from intrinsic states in graphene quantum dots (GQDs) is investigated. The bright PL of intercalatively acquired GQDs is attributed to favorably formed subdomains composed of four to seven carbon hexagons. Random and harsh oxidation which hinders the energetically favorable formation of subdomains causes weak and redshifted PL.

https://doi.org/10.1002/adma.201600616

Wet chemical synthesis of covalent III-V colloidal quantum dots (CQDs) has been challenging because of uncontrolled surfaces and a poor understanding of surface–ligand interactions. We report a simple acid-free approach to synthesize highly crystalline indium phosphide CQDs in the unique tetrahedral shape by using tris(dimethylamino) phosphine and indium trichloride as the phosphorus and indium precursors, dissolved in oleylamine. Our chemical analyses indicate that both the oleylamine and chloride ligands participate in the stabilization of tetrahedral-shaped InP CQDs covered with cation-rich (111) facets. Based on density functional theory calculations, we propose that fractional dangling electrons of the In-rich (111) surface could be completely passivated by three halide and one primary amine ligands per the (2×2) surface unit, satisfying the 8-electron rule. This halide–amine co-passivation strategy will benefit the synthesis of stable III-V CQDs with controlled surfaces.

https://doi.org/10.1002/ange.201600289

Energy-efficient CO2 capture is a stringent demand for green and sustainable energy supply. Strong adsorption is desirable for high capacity and selective capture at ambient conditions but unfavorable for regeneration of adsorbents by a simple pressure control process. Here we present highly regenerative and selective CO2 capture by carbon nitride functionalized porous reduced graphene oxide aerogel surface. The resultant structure demonstrates large CO2adsorption capacity at ambient conditions (0.43 mmol·g–1) and high CO2 selectivity against N2 yet retains regenerability to desorb 98% CO2 by simple pressure swing. First-principles thermodynamics calculations revealed that microporous edges of graphitic carbon nitride offer the optimal CO2 adsorption by induced dipole interaction and allows excellent CO2 selectivity as well as facile regenerability. This work identifies a customized route to reversible gas capture using metal-free, two-dimensional carbonaceous materials, which can be extended to other useful applications.

https://pubs.acs.org/doi/full/10.1021/acsnano.5b03400

Youngtak Oh et al, ACS Nano - August 2015

Axial coordinations of diatomic NO molecules to metalloporphyrins play key roles in dynamic processes of biological functions such as blood pressure control and immune response. Probing such reactions at the single molecule level is essential to understand their physical mechanisms but has been rarely performed. Here we report on our single molecule dissociation experiments of diatomic NO from NO–Co-porphyrin complexes describing its dissociation mechanisms. Under tunneling junctions of scanning tunneling microscope, both positive and negative energy pulses gave rise to dissociations of NO with threshold voltages, +0.68 and −0.74 V at 0.1 nA tunneling current on Au(111). From the observed power law relations between dissociation rate and tunneling current, we argue that the dissociations were inelastically induced with molecular orbital resonances by stochastically tunneling electrons, which is supported with our density functional theory calculations. Our study shows that single molecule dissociation experiments can be used to probe reaction mechanisms in a variety of axial coordinations between small molecules and metalloporphyrins.

https://doi.org/10.1021/acsnano.5b03466

Howon Kim et al, ACS Nano - July 2015

The fast degradation of lead selenide (PbSe) nanocrystal quantum dots (NQDs) in ambient conditions impedes widespread deployment of the highly excitonic, thus versatile, colloidal NQDs. Here we report a simple in situ post-synthetic halide salt treatment that results in size-independent air stability of PbSe NQDs without significantly altering their optoelectronic characteristics. From TEM, NMR, and XPS results and DFT calculations, we propose that the unprecedented size-independent air stability of the PbSe NQDs can be attributed to the successful passivation of under-coordinated PbSe(100) facets with atomically thin PbX2 (X = Cl, Br, I) adlayers. Conductive films made of halide-treated ultrastable PbSe NQDs exhibit markedly improved air stability and behave as an n-type channel in a field-effect transistor. Our simple in situ wet-chemical passivation scheme will enable broader utilization of PbSe NQDs in ambient conditions in many optoelectronic applications.

https://doi.org/10.1021/ja503957r

Ju Young Woo et al, JACS - June 2014

The atomic variations of electronic wave functions at the surface and electron scattering near a defect have been detected unprecedentedly by tracing thermoelectric voltages given a temperature bias [Cho et al., Nat. Mater. 12, 913 (2013)]. Because thermoelectricity, or the Seebeck effect, is associated with heat-induced electron diffusion, how the thermoelectric signal is related to the atomic-scale wave functions and what the role of the temperature is at such a length scale remain very unclear. Here we show that coherent electron and heat transport through a pointlike contact produces an atomic Seebeck effect, which is described by the mesoscopic Seebeck coefficient multiplied by an effective temperature drop at the interface. The mesoscopic Seebeck coefficient is approximately proportional to the logarithmic energy derivative of local density of states at the Fermi energy. We deduced that the effective temperature drop at the tip-sample junction could vary at a subangstrom scale depending on atom-to-atom interaction at the interface. A computer-based simulation method of thermoelectric images is proposed, and a point defect in graphene was identified by comparing experiment and the simulation of thermoelectric imaging.

http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.112.136601

E.-S. Lee et al, PRL - April 2014

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사이언스타임즈: https://www.sciencetimes.co.kr/nscvrg/view/menu/248?searchCategory=220&nscvrgSn=122892

Controlling and sensing spin states of magnetic molecules at the single-molecule level is essential for spintronic molecular device applications. Here, we demonstrate that spin states of Co–porphyrin on Au(111) can be reversibly switched over by binding and unbinding of the NO molecule and can be sensed using scanning tunneling microscopy and spectroscopy (STM and STS). Before NO exposure, Co–porphryin showed a clear zero-bias peak, a signature of Kondo effect in STS, whereas after NO exposures, it formed a molecular complex, NO–Co–porphyrin, that did not show any zero-bias feature, implying that the Kondo effect was switched off by binding of NO. The Kondo effect could be switched back on by unbinding of NO through single-molecule manipulation or thermal desorption. Our density functional theory calculation results explain the observations with pairing of unpaired spins in dz2 and ppπ* orbitals of Co–porphyrin and NO, respectively. Our study opens up ways to control molecular spin state and Kondo effect by means of enormous variety of bimolecular binding and unbinding reactions on metallic surfaces.

http://pubs.acs.org/doi/abs/10.1021/nn4039595

H. Kim et al, ACS Nano - Sep. 2013

It has been widely accepted that enhanced dihydrogen adsorption is required for room-temperature hydrogen storage on nanostructured porous materials. Here we report, based on results of first-principles total energy and vibrational spectrum calculations, finite-temperature adsorption and desorption thermodynamics of hydrogen molecules that are adsorbed on the metal center of metal-porphyrin-incorporated graphene. We have revealed that the room-temperature hydrogen storage is achievable not only with the enhanced adsorption enthalpy, but also with soft-mode driven vibrational entropy of the adsorbed dihydrogen molecule. The soft vibration modes mostly result from multiple orbital coupling between the hydrogen molecule and the buckled metal center, for example, in Ca-porphyrin-incorporated graphene. Our study suggests that the current design strategy for room-temperature hydrogen storage materials should be modified with explicitly taking the finite-temperature vibration thermodynamics into account.

http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.111.066102

Woo et al., Phys. Rev. Lett. - July 2013

Heat is a familiar form of energy transported from a hot side to a colder side of an object, but not a notion associated with microscopic measurements of electronic properties. A temperature difference within a material causes charge carriers, electrons or holes to diffuse along the temperature gradient inducing a thermoelectric voltage. Here we show that local thermoelectric measurements can yield high-sensitivity imaging of structural disorder on the atomic and nanometre scales. The thermopower measurement acts to amplify the variations in the local density of states at the Fermi level, giving high differential contrast in thermoelectric signals. Using this imaging technique, we uncovered point defects in the first layer of epitaxial graphene, which generate soliton-like domain-wall line patterns separating regions of the different interlayer stacking of the second graphene layer.

https://www.nature.com/articles/nmat3708

Cho et al, Nature Mater. - July 2013

Ambient stability of colloidal nanocrystal quantum dots (QDs) is imperative for low-cost, high-efficiency QD photovoltaics. We synthesized air-stable, ultrasmall PbS QDs with diameter (D) down to 1.5 nm, and found an abrupt transition at D ≈ 4 nm in the air stability as the QD size was varied from 1.5 to 7.5 nm. X-ray photoemission spectroscopy measurements and density functional theory calculations reveal that the stability transition is closely associated with the shape transition of oleate-capped QDs from octahedron to cuboctahedron, driven by steric hindrance and thus size-dependent surface energy of oleate-passivated Pb-rich QD facets. This microscopic understanding of the surface chemistry on ultrasmall QDs, up to a few nanometers, should be very useful for precisely and accurately controlling physicochemical properties of colloidal QDs such as doping polarity, carrier mobility, air stability, and hot-carrier dynamics for solar cell applications.

http://pubs.acs.org/doi/abs/10.1021/ja400948t

Choi et al, J. Am. Chem. Soc. - Mar. 2013

Atomically thin graphene is an ideal model system for studying nanoscale friction due to its intrinsic two-dimensional (2D) anisotropy. Furthermore, modulating its tribological properties could be an important milestone for graphene-based micro- and nanomechanical devices. Here, we report unexpectedly enhanced nanoscale friction on chemically modified graphene and a relevant theoretical analysis associated with flexural phonons. Ultrahigh vacuum friction force microscopy measurements show that nanoscale friction on the graphene surface increases by a factor of 6 after fluorination of the surface, while the adhesion force is slightly reduced. Density functional theory calculations show that the out-of-plane bending stiffness of graphene increases up to 4-fold after fluorination. Thus, the less compliant F-graphene exhibits more friction. This indicates that the mechanics of tip-to-graphene nanoscale friction would be characteristically different from that of conventional solid-on-solid contact and would be dominated by the out-of-plane bending stiffness of the chemically modified graphene. We propose that damping via flexural phonons could be a main source for frictional energy dissipation in 2D systems such as graphene.

https://pubs.acs.org/doi/10.1021/nl204019k

Kwon et al, Nano Lett. - Jun. 25, 2012

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Nature Research Highlight: https://doi.org/10.1038/487143b

연합뉴스: https://v.daum.net/v/20120702104707945

대전 CBS: https://v.daum.net/v/20120702115718710

YTN Science24: https://science.ytn.co.kr/program/view.php?mcd=0030&key=201207031037238686

Despite being one of the most important thermodynamic variables, pH has yet to be incorporated into first-principles thermodynamics to calculate stability of acidic and basic solutes in aqueous solutions. By treating the solutes as defects in homogeneous liquids, we formulate a first-principles approach to calculate their formation energies under protonchemical potential, or pH, based on explicit molecular dynamics. The method draws analogy to first-principle calculations of defect formation energies under electron chemical potential, or Fermi energy, in semiconductors. From this, we propose a simple pictorial representation of the general theory of acid-base chemistry. By performing first-principles molecular dynamics of liquid water models with solutes, we apply the formulation to calculate formation energies of various neutral and charged solutes such as H+, OH−, NH3, NH4+, HCOOH, and HCOO− in water. The deduced auto-dissociation constant of water and the difference in the pKa values of NH3 and HCOOH show good agreement with known experimental values. Our first-principles approach can be further extended and applied to other bio- and electro-chemical molecules such as amino acids and redox reaction couples that could exist in aqueous environments to understand their thermodynamic stability.

https://doi.org/10.1063/1.3700442

Y. -H. Kim, K. Kim, S. B. Zhang, J. Chem. Phys. - Apr. 6, 2012

We report the theory and synthesis of sub-nanosized gold clusters on reduced graphene oxide (r-GOs). The Au sub-nanoclusters were found to be nucleated and grown at defects of the r-GOs, particularly on nitrogen-induced defects from density functional theory investigation. The resulting Au/r-GOs exhibit an improvement of bulk electrical conductivities and a reduced ratio of the intensity of the D band to that of the G band (ID/IG), compared to the r-GOs without Au nanoclusters. The unique decrease of the ID/IG was demonstrated to be related to the filling of subnano-sized Au clusters on the r-GOs, presumably owing to enhancing the flat geometry of the graphene nanosheets.

https://doi.org/10.1039/C2JM16195H

H. Y. Koo et al, J. Mater. Chem. - Mar. 22, 2012

The development of short-to-medium-range order in atomic arrangements has generally been observed in noncrystalline solid systems such as metallic glasses. Whether such medium-range order (MRO) can exist in materials at well above their melting or glass-transition temperature has been a long-standing important scientific issue. Here, using ab initio molecular dynamics simulations, we show that a novel, persistent MRO exists in liquid Al-Cu alloys near the composition of CuAl3. The correlated atomic motions associated with the MRO give rise to a substantially enhanced viscosity in the vicinity of the composition. The component of the MRO liquid state gradually decreases with increasing temperature, and it disappears above a crossover temperature TLLC. The continuous liquid-liquid crossover through a percolationlike transition leads to a pronounced heat capacity peak at TLLC.

https://doi.org/10.1103/PhysRevLett.108.115901 

J. Kang et al, Phy. Rev. Lett. - Mar. 13, 2012

Chemically modified graphene platelets, produced via graphene oxide, show great promise in a variety of applications due to their electrical, thermal, barrier and mechanical properties. Understanding the chemical structures of chemically modified graphene platelets will aid in the understanding of their physical properties and facilitate development of chemically modified graphene platelet chemistry. Here we use 13C and 15N solid-state nuclear magnetic resonance spectroscopy and X-ray photoelectron spectroscopy to study the chemical structure of 15N-labelled hydrazine-treated 13C-labelled graphite oxide and unlabelled hydrazine-treated graphene oxide, respectively. These experiments suggest that hydrazine treatment of graphene oxide causes insertion of an aromatic N2 moiety in a five-membered ring at the platelet edges and also restores graphitic networks on the basal planes. Furthermore, density-functional theory calculations support the formation of such N2 structures at the edges and help to elucidate the influence of the aromatic N2 moieties on the electronic structure of chemically modified graphene platelets.

https://www.nature.com/articles/ncomms1643

S. Park et al, Nat. Commun. - Jan. 24 2012

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https://v.daum.net/v/20120125141715394

http://news.unn.net/news/articleView.html?idxno=106571

We report the synthesis of a Fe-porphyrin-like carbon nanotube from conventional plasma-enhanced chemical vapor deposition. Covalent but seamless incorporation of the 5-6-5-6 porphyrinic Fe-N4 moiety into the graphene hexagonal side wall was elucidated by x-ray and ultraviolet photoemission spectroscopies and first-principles electronic structure calculations. The resulting biomimetic nanotube exhibits an excellent oxygen reduction catalytic activity with the extreme structural stability over 0.1×106 cycles, vastly superior to the commercial Pt-C catalyst.

https://doi.org/10.1103/PhysRevLett.106.175502

D. H. Lee, et al., Phys. Rev. Lett. - Apr. 6, 2011

Carbon dioxides (CO2) emitted from large-scale coal-fired power stations or industrial manufacturing plants have to be properly captured to minimize environmental side effects. From results of ab initio calculations using plane waves [PAW-PBE] and localized atomic orbitals [ONIOM(wB97X-D/6-31G*:AM1)], we report strong CO2 adsorption on boron antisite (BN) in boron-rich boron nitride nanotube (BNNT). We have identified two adsorption states: (1) A linear CO2 molecule is physically adsorbed on the BN, showing electron donation from the CO2 lone-pair states to the BN double-acceptor state, and (2) the physisorbed CO2 undergoes a carboxylate-like structural distortion and C═O π-bond breaking due to electron back-donation from BN to CO2. The CO2 chemisorption energy on BN is almost independent of tube diameter and, more importantly, higher than the standard free energy of gaseous CO2 at room temperature. This implies that boron-rich BNNT could capture CO2 effectively at ambient conditions.

http://pubs.acs.org/doi/full/10.1021/ja1101807

H. Choi, et al., J. Am. Chem. Soc. - Feb. 2, 2011

Microscopic understanding of thermal behaviors of metal nanoparticles is important for nanoscale catalysis and thermal energy storage applications. However, it is a challenge to obtain a structural interpretation at the atomic level from measured thermodynamic quantities such as heat capacity. Using first-principles molecular dynamics simulations, we reproduce the size-sensitive heat capacities of AlN clusters with N around 55, which exhibit several distinctive shapes associated with diverse melting behaviors of the clusters. We reveal a clear correlation of the diverse melting behaviors with cluster core symmetries. For the AlN clusters with N = 51−58 and 64, we identify several competing structures with widely different degree of symmetry. The conceptual link between the degree of symmetry (e.g., Td, D2d, and Cs) and solidity of atomic clusters is quantitatively demonstrated through the analysis of the configuration entropy. The size-dependent, diverse melting behaviors of Al clusters originate from the reduced symmetry (Td → D2d → Cs) with increasing the cluster size. In particular, the sudden drop of the melting temperature and appearance of the dip at N = 56 are due to the Td-to-D2d symmetry change, triggered by the surface saturation of the tetrahedral Al55 with the Td symmetry.

http://pubs.acs.org/doi/abs/10.1021/ja107683m

J. Kang et al., J. Am. Chem. Soc. - Dec. 8, 2010

The experimentally observed enhancement of hydrogen adsorption in Cu2-tetracarboxylate paddle-wheel frameworks is investigated by ab initio density-functional theory calculations. We reveal that the puzzling enhancement is due to the effective orbital coupling between the occupied H2 σ and the unoccupied Cu 4s-derived states. The nontrivial dihydrogen-metal σ-s interaction is enabled by a strong localization of the Cu 4s orbital after hybridizing with the neighboring oxygen 2p orbitals. Based on this understanding, we predict that the dihydrogen-metal interaction can be further increased by alloying Cu with s-orbital element Zn or Mg.

https://doi.org/10.1103/PhysRevLett.105.236105

Yong-Hyun Kim et al., Phys. Rev. Lett. - Oct. 27, 2010

Hydrogen spillover on carbon-based systems has been proposed as a viable alternative for room-temperature storage. Given the strength of the C-H bonds, however, it is unclear if spillover indeed takes place in such materials. We performed a first-principles study of H spillover on IRMOF-1. Spillover becomes thermodynamically stable only at high H coverage with a calculated Gibbs free energy of -14 kJ / mol at ambient condition. In general, however, spillover may not proceed due to high-energy states at lower H coverage. We propose that hole doping can substantially lower the energies as well as barriers to enable spillover at ambient conditions.

https://doi.org/10.1103/PhysRevLett.104.236101

K. Lee et al., Phys. Rev. Lett. - June 7, 2010

A new dynamic melting state, which has both solid and liquid characteristics, is revealed from first-principles molecular dynamics simulations of Al55 clusters. In thermal fluctuations near the melting point, the low-energy tetrahedral-like Al55 survives through rapid, collective surface transformations—such as parity conversions and correlated diffusion of two distant vacancies—without losing its structural orders. The emergence of the collective motions is solely due to efficient thermal excitation of soft phonon modes at nanoscale. A series of spontaneous surface reconfigurations result in a mixture or effective flow of surface atoms as is random color shuffling of a Rubik’s cube. This novel flexible solid state (termed as half-solidity) provides useful insights into understanding stability, flexibility, and functionality of nanosystems near or below melting temperatures.

http://pubs.acs.org/doi/abs/10.1021/nn901536a

Movie: http://pubs.acs.org/doi/suppl/10.1021/nn901536a/suppl_file/nn901536a_si_002.mpg

J. Kang et al., ACS Nano - Jan. 8, 2010

Porphyrin is a very important component of natural and artificial catalysis and oxygen delivery in blood. Here, we report that, based on first-principles density-functional calculations, a hydrogenmolecule can be adsorbed non-dissociatively onto Ti-, V-, and Fe-porphyrins, similar to oxygenadsorption in heme-containing proteins, with a significant energy gain, greater than 0.3 eV per H2. The dihydrogen–heme complex will be non-magnetic, as is oxyhemoglobin. In contrast to the backward electron donation of Fe(III)–O2− in oxyhemoglobin, the dihydrogen binding originates from electron donation from H2 to the Fe(II). We have identified that the local symmetry of the transition metal center of porphyrins uniquely determines the binding strength, and, thus, one can even manipulate the strength by intentionally and systematically breaking symmetry.

https://doi.org/10.1039/B913711D

Covered by Phys. Chem. Phys. (Dec. 21, 2009) - Y. -H. Kim et al.

Nano-Bio: Nano Lett. (2007)

Hydrogen Storage: Phys. Rev. Lett. (2006)

Nanocluster Melting: ACS nano (2010)