Narrow Results

The convergence of terahertz spectroscopy and single molecule experimentation offers significant promise of enhancement in sensitivity and selectivity in molecular recognition, identification and quantitation germane to military and security applications. This paper provides a brief overview of the constraints set by single molecule recognition systems and reports the results of experiments which address fundamental barriers to the integration of large, patterned bio-compatible molecular opto-electronic systems with silicon based microelectronic systems. Central to this thrust is an approach involving sequential epitaxy on surface bound single stranded DNA one-dimensional substrates. The challenge of producing highly structured macromolecular substrates, which are necessary in order to implement molecular nanolithography, has been addressed experimentally by combining “designer” synthetic DNA with biosynthetically derived plasmid components. By design, these one dimensional templates are composed of domains which contain sites which are recognized, and therefore addressable by either complementary DNA sequences and/or selected enzymes. Such design is necessary in order to access the nominal 2 nm linewidth potential resolution of nanolithography on these one-dimensional substrates. The recognition and binding properties of DNA ensure that the lithographic process is intrinsically self-organizing, and therefore self-aligning, a necessity for assembly processes at the requisite resolution. Another requirement of this molecular epitaxy approach is that the substrate must be immobilized. The challenge of robust surface immobilization is being addressed via the production of the equivalent of molecular tube sockets. In this application, multi-valent core-shell fluorescent quantum dots provide a mechanism to prepare surface attachment sites with a pre-determined 1:1 attachment site : substrate (DNA) molecule ratio.

Localization property in the disordered few-chain DNA systems with a long-range correlation is numerically investigated. We apply the chain system with the correlated disorder in the interchain and/or intrachain hoppings to the simple model of a double strand of DNA. Numerical results for the density of states and the Lyapunov exponent of the wave function in the two- or three-chain models are given. It is found that the correlation effect enhances the localization length (the inverse least non-negative Lyapunov exponent) around the band center.

Ground state properties of zinc-blende structures ZnS and ZnSe are investigated from first principles using plane wave basis, projector augmented wave method and local orbital-dependent potential, as well as a basis set of Gaussian-type functions with hybrid functionals for the approximation of exchange-correlation energy. The results of DFT calculations with the LDA, LDA+U, GGA, GGA+U, BLYP, B3P86, P3PW, BH-HP, KMLYP and B3LYP approximations are compared. It is shown that the hybrid functional B3LYP provides an accurate quantitative description of the structural, electronic and vibrational properties of ZnS and ZnSe in comparison with experimental data.

The structural, electronic, magnetic properties of Mn₃XC (X=Al, Zn and Ga) antiperovskites have been investigated using first principles calculations based on Full-Potential Linearized Augmented Plane-Wave (FP-LAPW) method. Generalized Gradient Approximation with parameterization by Perdew (GGA-PBESol) is used to take into account the electron exchange–correlation interaction. Structural optimization is performed by fitting calculated data (energy-volume) to Birch–Murnaghan equation of state. Lattice constants increase in the order Mn₃AlC$\to$Mn₃GaC$\to$Mn₃ZnC. Electronic results show that there is no bandgap near the Fermi level. While the magnetism in these compounds is derived mainly from Mn atom. Finally, thermodynamic properties, including bulk modulus, heat capacities, thermal expansion and Grüneisen parameter, are computed using quasi-harmonic Debye model and analyzed in detail.

This work performs a computational prediction on SnSe₂ and Te-doped bilayer material. Doping the Te element onto SnSe₂ can lead to a decrease in bandgap $E_g$ energy (from 1.95 eV to 0.94 eV) and cause a drop in both conduction band (CB) and valence band (VB), apart from the valence band maximum (VBM). This may lead to an increase in electrical conductivity. The decrease in $g_2$ parameter may result in an impact on electronic effective mass and transport properties when the SnSe₂ bilayer is doped with Te. A redshift observed on both the optical absorption and the dielectric constant plots may suggest that a tensile force could be possibly induced when we dope the SnSe₂ compound. The identical elastic constants of C${}_{14}$ and C${}_{65}$ evaluated could describe the nature of the close-packed hexagonal bilayer. Finally, the ductility slightly increases when we mix the Te element onto the SnSe₂ alloy. It is also worth noting that both SnSe₂ and Te-doped are dynamically stable, according to the phonon dispersion.

This work investigates the effect of band structure, optical spectra, computed elastic coefficients, Bulk-to-Shear modulus ratio, Young’s modulus and Poisson’s ratio in metal selenide compounds and their influence on electronic, optical, and elastic properties of bulk crystals using density functional theory (DFT). By studying the structural and geometrical parameters, we show that the V–VI group compound has a direct bandgap of 0.887eV and the band structure can be explained by a partial density of states (PDOS) plot. By using Pugh’s formation, the bulk-to-shear ratio can be significant in precisely determining the ductility of a material. Poisson’s ratio can provide information to examine whether the lattice crystal is ionic or covalent. Our elastic data show that the orthorhombic system is found to be unstable. The optical spectra (high absorption coefficient of $1.78\times 10^5$cm${}^{-1}$, dielectric coefficient of 8.61 and reflective index of 2.93) of our current work would be beneficial to explore the applications of optoelectronic devices, especially in light-harvesting materials, covering the UV region. Our findings advance the knowledge of the structural, electronic, optical, vibrational, and mechanical properties of Sb₂Se₃, the key to their use, and explained the potential applications in photovoltaics perspectives.

The computational predictions of transition-metal tri-chalcogenide (TMTCs) were performed using ab initio density functional theory (DFT) to investigate the electronic band structure, the partial density of states (PDOS), optical absorptions, dielectric functions, complex conductivity, reflectivity, refractive index, electron loss, the Poisson’s ratio, Young’s modulus, bulk-to-shear ratio, and phonon dispersion. The bandgap is measured from the valence band maximum (VBM) to the conduction band minimum (CBM) with the G–Z transitions. This suggests that the material is an indirect bandgap semiconductor. The electronic bandgap ($E_g)$ is significantly improved with nonlocal hybrid functionals, especially in HSE0s, with $E_g$ of 1.0eV, which is in excellent agreement with the experimental data. However, our data shows that the HF-LDA exchange correlations significantly overestimate the $E_g$ with 7.33eV. Also, our optical absorption data indicates a high absorption coefficient of about $2.9\times 10^5$cm${}^{-1}$. The absorption peak of 7.4eV indicates TiS₃ can be applied in vacuum ultra-violet (VUV) applications. The reflectivity is also shown to be high, with over 90% of light being reflected. The mechanical stability of the monoclinic system can be testified by our elastic coefficients and the phonon dispersions.

Based on the density functional theory (DFT) calculations, the structural, electronic, optical and thermoelectric properties of the MnFeTe Heuslerene compound have been investigated. The total energy change curve in terms of volume refers to the ground state point and equilibrium volume. By applying mBJ approximation, this compound has perfect half-metallic behavior of 100% spin polarization at the Fermi level with 7${}_{\mu B}$ magnetic moment. Optical calculations show that the semiconductor behavior with an optical absorption gap occurred by incident light perpendicular to the MnFeTe Heuslerene plane. The figure of merit coefficient (ZT) has reached 3.5 at 50K temperature, which makes it an excellent candidate for thermoelectric applications. Also, the power factor (PF) of this compound has reached its maximum value at room temperature.

A $4\times 4\times 4$ and 765eV (sufficient to converge the results) have been used to explore the electronic, optical, mechanical, and vibrational properties using ab initio code CASTEP with hybrid functionals. A wide indirect F–Z bandgap energy of 3.77eV has been reported. Our partial density of states plot further shows the valence band is made of O 2p and Ag 4d electron orbitals, while Ag S orbitals and N O 2p states contribute to the conduction band bottom (CBM), among the upper conduction band consisting of Ag 4p, O 2$s2p$ and N 2p electron orbitals. In our optical data, a high absorption coefficient of $2.57\times 10^5$ cm${}^{-1}$ has been found, and a relatively low 20% reflectivity simply indicates a high absorption of the material. Although our mechanical data cannot determine the material ductility/brittleness with the B/G ratio, we can report a Poisson’s ratio value of −2.04 in this work. On the other hand, the phonon dispersion and the density of the phonon state plot report may indicate the mechanical instability of the system. The negative Poisson’s ratio (NPR) we provide may hint at the possibility of using AgNO₃ as a promising anode in a group I/II elements (Mg, K, Na)-ion battery.

Based on density functional theory, structural, electronic, magneto-optic, and thermoelectric properties of RbCaN₂ and RbCaO₂, Heuslerene compounds have been calculated. These compounds have the ground state points with total magnetic moment of 1.0${\mu }_B$, which represents their ferromagnetic behavior. The RbCaN₂ Heuslerene has the half-metallic nature and RbCaO₂ case is a magnetic semiconductor. The Kerr angle of the RbCaN₂ Heuslerene has two relatively peaks at the energies of 5.5eV to 7.0eV, but for the RbCaO₂ compound, this diagram is wider in a larger energy range. Faraday angle peaks occurred at 6.2eV and 6.8eV for RbCaN₂ and RbCaO₂ compounds, which indicates the polarization of the light irradiated to them at these energies. It was observed that both compounds show high thermoelectric quality at temperatures higher than the room-temperature, and both compounds are suitable for power generator applications.

In this paper, using density functional theory (DFT), we present a systematic computational investigation on ZrCl₄ in respect of electronic, structural, optical, mechanical properties, which is of great interest in semiconductor physics. Our results show that the metal tetrachloride is a mechanically stable semiconductor with a wide indirect bandgap of $E_g^{\mathrm{\text{HSE}}03}=4.82$eV ($E_g^{\mathrm{\text{GGA}}}=3.56$eV). ZrCl₄ could behave as a brittle material and could be covalent. According to our optical data, a reflectivity of 27.6% could suggest a good material absorption characteristic on the studied material, with a high absorption coefficient of up to $1.61\times 10^5$cm${}^{-1}$. On the partial density of states plot, the hybridization of electron orbitals between Cl 3p⁵ states in the valence band and transition Zr 4d² states in the conduction band is also observed. Our findings advance the fundamental understanding of ZrCl₄ material and provide important insights in electronic/optoelectronic applications.

In this work, a novel stishovite–aluminum alloy with chemical formula SiO₂–Al–SiO₂ is proposed. The structural, electronic and optical properties were obtained using GGA-PBE functional. The study of electronic properties of SiO₂–Al–SiO₂ shows that it has a bandgap energy at 22 meV, compared to a much wider energy gap inside stishovite. The band structure of SiO₂–Al–SiO₂ reported in this work indicates that the SiO₂–Al alloy proposed is found to be a semi-metal. Also, we report a reflectivity of 73% (2.53 eV) and 70% (7.97 eV), based on 8.36 nm of its total thickness. The strong optical absorption at 2.11 eV and 5.79 eV is suggesting the SiO₂–Al–SiO₂ can be used as both visible part (orange) sensing and the UV photodetectors. Thus, the SiO₂–Al alloy can have potential application in optoelectronic device fabrications.

In this paper, the electronic, optical, elastic, mechanical, and vibrational properties of glass B₂O₃ have been investigated. Simulations have been carried out including the P3₁21 structure. Our nonlocal empirical hybrid has accurately described the electronic band structure and band gap energy $E_g$ of the material. Our optical absorption plot has correctly identified the type of the glass B₂O₃ structure. The absorption plot also shows the interband indirect transitions from the valance O 2p¹ to conduction B 2p⁴ orbitals. We have also included the elastic constants and phonon dispersions to test the dynamic stability of the systems. Our theoretical findings bear fundamental interests in the development of complicated amorphous nanostructures.

Using ab initio first-principles calculations, we investigate the structural, electronic, optical, and vibrational properties of Silver Sulphide Ag₃S and Selenide Ag₃Se with nonlocal hybrids exchange-correlation functional. With our computational predictions, we manage to classify the material to be Fermi-Dirac semi-metal, rather than Weyl metal. Our calculated results show that the electronic band in between the Fermi-Dirac cone shifts downward when we replace the element Sulphide S with Selenide Se. The obtained optical results such as absorption coefficients and dielectric functions (conductivity, reflectivity, etc.) are similar for both Ag₃S and Ag₃Se. A high absorption coefficient of $2\times 10^5$ cm${}^{-1}$ has been reported, and about 50% of light is reflected. In Raman spectra, the A${}_{\mathrm{\text{g}}}^{\mathrm{\text{X}}\text{-}\mathrm{\text{X}}}$ managed to shift downward when replacing the element X, sulphide S with selenide Se, while the A${}_{\mathrm{\text{g}}}^{\mathrm{\text{rigid}}}$ shifts upward (to higher wavelength). The rotation and vibration of the bonding between atoms have also been explained. The calculated results of Silver-VI compounds provide useful information in the exploitation of more complicated structures.

Ab Initio density functional theory (DFT) simulations have been employed to systematically explore the electronic, optical, elastic, mechanical and vibrational properties. In this study, we revealed that $\gamma$-CuI has a wide direct bandgap energy of 3.21 eV, is pure covalent and brittle. We also found that the core level is made up of I s electron orbitals, the valence band is constructed with I p orbitals, and the Cu s orbital states mainly contribute to the conduction band minimum (CBM). The reflectivity of CuI is reported to be low (35.9% for the light reflected), showing high material absorption. A high absorption coefficient of $2.31\times 10^5{\mathrm{\text{cm}}}^{-1}$ is also reported. The elastic and mechanical properties can further confirm the mechanical stability of the CuI system, derived from DFT-calculated elastic constants and phonon dispersion from density functional perturbation theory (DFPT) calculations.

In this paper, the structural, electronic, optical, and mechanical properties of the hexagonal Ceria CeO₂ have been studied with hybrid functionals. The rare-earth oxide compound exhibits a $\mathrm{\Gamma }-M$ indirect bandgap, with a bandgap energy of 2.706 eV. The electronic bandstructure has been described in detail in terms of orbital states. The rare-earth Ce f orbital contributes to the conduction band and transitional Ce d, O s electron orbitals to the valence bands. Our optical spectra also fully explain the structural and electronic properties of the material. (i.e. atomic-bonding, density or capacity inside Cerium oxide system, and the excitation of electrons to transfer from valence O 2p to conduction Ce f orbitals, leading to orbital hybridizations, etc.). Finally, our elastic coefficients verify the mechanical stability of our Ceria system. Our bandgap energy found is in excellent agreement with the experimental data. A high optical absorption coefficient of up to $1\times 10^5$ cm${}^{-1}$ is found, indicating a good material absorption within the ultraviolet C (UVC) range. The findings of this work would be beneficial to both theoretical and experimental research works to explore the potential applications of CeO₂ in optoelectronics devices.

Based on the density functional theory, the electronic, optical and thermoelectric properties of the Cu₂FeSnS₄ two-dimensional (2D) structure are investigated. The total energy of unit cell changes the curve in terms of its volume which indicates an equilibrium volume for this compound. The density of states and band structure show that the compound has half-metallic behavior with an electron gap of 0.7eV at up spin. The merit coefficient at high spin up to room temperature is in the range of 0.9 and is stable, making it a suitable option for thermoelectric applications.

The structural, electronic, optical, mechanical and vibrational properties of hexagonal Di-Tellurium-Tungsten (Te₂W) are exploited with a hybrid Heyd–Scuseria–Ernzerhof 2003 (HSE03) functional and semi-local general gradient approximation (GGA) scheme using ab initio density functional theory (DFT) calculations. The structural and electronic properties have been analyzed with the band structure and electron orbitals from the partial density of states (PDOS). Our reflectivity data from optical spectra explain its applications over mechanical engineering such as lubricant oils, further with the fact that the refractive index results obtained suggest the possibility of deploying Te₂W material over optical displays. Our work finalizes by testifying the physical and mechanical stability, with our DFT-calculated elastic coefficients along with its criteria, mechanical moduli and phonon data provided. In general, our non-local hybrid functional corrects the band structure and bandgap energy $E_g$ extremely well, over the traditional semi-local exchange-correlation functional.

Electronic Three-Dimensional Atlas of Acupuncture.

The article is about the use of software in the Singapore biomed research industry.