B. Song

Graphene on Au(111): A Highly Conductive Material with Excellent Adsorption Properties for High-Resolution Bio/Nanodetection and Identification

Based on numerical simulations and experimental studies, we show that a composite material which consists of a sheet of graphene on a Au(111) surface exhibits both an excellent conductivity and the ability to stably adsorb biomolecules. If we use this material as a substrate, the signal-to-noise ratios can be greatly enhanced. The key to this unique property is that graphene can stably adsorb carbon-based rings, which are widely present in biomolecules, due to pi-stacking interactions while the substrate retains the excellent conductivity of gold. Remarkably, the signal-to-noise ratio is found to be so high that the signal is clearly distinguishable for different nucleobases when an ssDNA is placed on this graphene-on-Au(111) material. Our finding opens opportunities for a range of bio/nano-applications including single-DNA-molecule-based biodevices and biosensors, particularly, high-accuracy sequencing of DNA strands with repeating segments.

Observation of glassy ferromagnetism in Al-doped 4H-SiC.

Glassy ferromagnetism is observed in diluted magnetic semiconductor Al-doped 4H-SiC. We propose a possible explanation for the origin of ferromagnetism order that is the coeffect of sp(2)/sp(3) configuration along with the structural defects. This result unambiguously demonstrates the existence of intrinsic ferromagnetism order in nonmagnetic sp systems.

Observation of spin-glass behavior in antiperovskite Mn3GaN

The dc magnetization, ac susceptibility, and isothermal remanent magnetization measurements are carried out for antiperovskite Mn3GaN. Strong indication for a frozen state with freeing temperature of Tf at ∼133K is found, determined from the difference between field-cooled and zero-field-cooled magnetizations. The ac susceptibility measurements show a peak around Tf, with the peak position shifting as a function of the driving frequency f and magnetic field H, respectively. Relaxation effects are observed after switching the external magnetic field below Tf. These findings consistently demonstrate that Mn3GaN exhibits a canonical spin-glass state at low temperature.

Nucleobase adsorbed at graphene devices: Enhance bio-sensorics

Graphene as a good material for sensing single small molecules is hardly believed to identify bio-molecules via electrical currents. This is because bio-molecules tend to bind to graphene through non-covalent bonds, such as π-π stacking interaction, which is not customarily considered to induce a clear perturbation of the graphene electronic structure. In contrast to these expectations, we demonstrate that oxygen in nucleobases adsorbed on graphene with π-π stacking interaction can clearly alter the electric current even in water at room temperature. This property allows us to devise the strategies employing graphene as material of choice in bio-sensorics, bio-chips.

Anomalous conductance response of DNA wires under stretching.

The complex mechanisms governing charge migration in DNA oligomers reflect the rich structural and electronic properties of the molecule of life. Controlling the mechanical stability of DNA nanowires in charge transport experiments is a requisite for identifying intrinsic issues responsible for long-range charge transfers. By merging density-functional theory based calculations and model Hamiltonian approaches, we have studied DNA quantum transport during the stretching-twisting process of poly(GC) DNA oligomers. During the stretching process, local maxima in the charge transfer integral t between two nearest-neighbor GC pairs arise from the competition between stretching and twisting. This is reflected in local maxima for the conductance, which depend very sensitively on the coupling to the electrodes. In the case of DNA-electrode couplings smaller than t, the conductance versus stretching distance saturates to plateau in agreement with recent experimental observations.

Cation⊗3π: cooperative interaction of a cation and three benzenes with an anomalous order in binding energy.

Cation-π or cation-π-π interaction between one cation and one or two structures bearing rich π-electrons (such as benzene, aromatic rings, graphene, and carbon nanotubes) plays a ubiquitous role in various areas. Here, we analyzed a new type interaction, cation⊗3π, whereby one cation simultaneously binds with three separate π-electron-rich structures. Surprisingly, we found an anomalous increase in the order of the one-benzene binding strength of the cation⊗3π interaction, with K(+) > Na(+) > Li(+). This was at odds with the conventional ranking of the binding strength which usually increases as the radii of the cations decrease. The key to the present unexpected observations was the cooperative interaction of the cation with the three benzenes and also between the three benzenes, in which a steric-exclusion effect between the three benzenes played an important role. Moreover, the binding energy of cation⊗3π was comparable to cation⊗2π for K(+) and Na(+), showing the particular importance of cation⊗3π interaction in biological systems.

Observation of spin-glass behavior in antiperovskite compound Mn3Cu0.7Ga0.3N

We present a detailed study of magnetic properties of antiperovsite compound Mn3Cu0.7Ga0.3N. Ac susceptibility measurements show a peak around “freezing temperature” (Tf), with the peak position shifting as a function of the driving frequency f and magnetic field H. Magnetic relaxation measurements show a slow decay of the remanent magnetization with time below Tf. These findings consistently demonstrate the existence of spin-glass states in Mn3Cu0.7Ga0.3N. The behavior may be attributed to either a small amount of disorder, arising from the random occupation of 1a sites in the space group Pm-3m by mixed Cu/Ga atoms, or the common frustration, or both.

Irreversible Denaturation of Proteins through Aluminum‐Induced Formation of Backbone Ring Structures

A combination of abu2005initio calculations, circular dichroism, nuclear magnetic resonance, and X-ray photoelectron spectroscopy has shown that aluminum ions can induce the formation of backbone ring structures in a wide range of peptides, including neurodegenerative disease related motifs. These ring structures greatly destabilize the protein and result in irreversible denaturation. This behavior benefits from the ability of aluminum ions to form chemical bonds simultaneously with the amide nitrogen and carbonyl oxygen atoms on the peptide backbone.

Structural and magnetic properties of (Al, Fe)-codoped SiC

In this study, as a first attempt, we choose Al and transition metals (TMs), Fe, as codoping atoms to synthesize (Al, TM)-codoped SiC. X-ray diffraction and Raman analysis showed that a series of single-phase codoped 4H-SiC samples were obtained and no trace of any other impurity phases, such as Fe3Si and polytypes of other types of SiC, was found. Measurement of magnetic properties showed that codoping by Al and Fe elements changed the original glassy ferromagnetism (FM) features in Al-doped SiC and induced a robust room temperature FM order that gradually dominated (Al, Fe)-codoped 4H-SiC with increase in Fe content. The contribution of Al elements to the magnetic properties of (Al, Fe)-codoped 4H-SiC can be neglected and the magnetic origin should be ascribed to be induced by Fe doping. The only major role of Al is to stabilize the codoped crystal structure as 4H- single phase. As the first investigation on (Al, TM)-codoped SiC, this study opens a new pathway to obtain TM-doped SiC-based diluted magnetic semiconductors with a high Tc via the codoping strategy.

Anomalous I-V curve for mono-atomic carbon chains

The electronic transport properties of mono-atomic carbon chains were studied theoretically using a combination of density functional theory and the non-equilibrium Greens functions method. The I-V curves for the chains composed of an even number of atoms and attached to gold electrodes through sulfur exhibit two plateaus where the current becomes bias independent. In contrast, when the number of carbon atoms in the chain is odd, the electric current simply increases monotonically with bias. This peculiar behavior is attributed to dimerization of the chains, directly resulting from their one-dimensional nature. The finding is expected to be helpful in designing molecular devices, such as carbon-chain-based transistors and sensors, for nanoscale and biological applications.