Narrow Results

The phase behavior of two components p-quaterphenyl (QP) and polymethyl methacrylate (PMMA)/heptadecanoic acid (HA)) in the Langmuir monolayer was characterized. The surface pressure versus area per molecule isotherms revealed that the area per molecule systematically changed with increasing mole fractions of QP, indicating that repulsive types of interactions were involved between the QP and the matrix molecules (PMMA/HA), leading to the phase separation which in turn stimulated the aggregate formation. Absorption spectroscopy, complemented with scanning electron microscopy (SEM), confirmed the aggregation of QP molecules in the mixed films.

By using the first-principles calculations established on density functional theory (DFT), the electronic aspects of the tetrahexcarbon (TH-carbon) monolayer as a two-dimensional carbon allotrope which is a direct bandgap semiconductor have been investigated under variations of buckling parameter ($\sigma =0,2,4,6$) by the PBE-GGA. Also, optical properties of this nanosheet are projected in out-of-plane polarization in buckling variation situations up to $\sigma =6$. Its optic behaviors in the visible light spectrum match its electronic ones. The results propose that the TH-carbon monolayer is an appropriate material for designing optoelectronic devices.

Electronic and magnetic properties of transition metal (TM) ion-doped monolayer zinc oxide (ML-ZnO) have been analyzed using ab-initio calculations in the frame work of density functional theory. Spin–spin interaction study reveals that Cr, Mn, Fe and Cu doped at Zn site of ML-ZnO show stable ferromagnetic ordering along with the half-metallic behavior for most of the cases. The electronic and magnetic properties of the pristine system can also be modified by using co-doping. 3d orbital electrons of the dopants are primarily responsible for the origin of magnetic moment and the remaining part comes from the 3d and 2p orbital electrons of Zn and O atoms, respectively. Moreover, the magnetic ordering in Fe-doped ML-ZnO can change with the doping distance between the dopants.

In this paper, the electronic structures and magnetic properties of the Cu-doped ZnO monolayer are investigated by means of first-principles methods based on density functional theory. Numerical results show that the Cu dopant can induce the half-metallic ferromagnets in the ZnO monolayer due to the strong p–d coupling. In addition, the semiconductor band gap is also decreased when Zn atom is substituted by Cu atom in the ZnO monolayer. Moreover, the formation energy calculations also indicate that it is energy favorable and relatively easier to incorporate Cu atom into the ZnO monolayer under Zn-rich experimental conditions.

The regularities of the formation of thin Mn/Si (111) nanofilms during solid-phase deposition of Mn on Si under conditions of ultrahigh vacuum ($P=10^{-7}$Pa) and thin Mn₄Si₇/Si (111) nanofilms during annealing of the Mn/Si system have been studied. It has been established that silicon atoms diffuse into the Mn film up to a thickness of $\mathrm{\Theta }=10$–12 monolayers, and Mn in Si up to $\mathrm{\Theta }=8$–10 monolayers, therefore, a transition layer of nonstoichiometric Mn_xSi_y silicide is formed at the Mn–Si interface. After heating at $T=1050$K, the higher manganese silicide (HMS) Mn₄Si₇ is formed. In particular, it was found that the bandgap of Mn₄Si₇is $E_g\approx 0.72$eV, and the electron affinity is $\chi \approx 3$eV and in the work, the optimal thermal diffusion conditions for the formation of stoichiometric Mn₄Si₇ silicide are determined. It is shown that at $T\le 1000$K, a partial formation of a chemical bond between manganese and silicon atoms occurs. At 1100K, a thin Mn₄Si₇ film with a good stoichiometric composition is formed.

In the present communication, the monolayer characteristics of pyrene mixed with stearic acid (SA) at the air–water interface have been reported. The monolayer properties are investigated by recording and analyzing the surface pressure–area per molecule isotherm (π–A) of the pyrene–SA mixed films. It is observed that the pyrene and SA are miscible in the mixed monolayer. This miscibility/nonideality leads to phase separation between the constituent components (pyrene and SA). BAM image of the mixed monolayer confirms the miscibility or nonideal mixing at the mixed monolayer.

The interfacial surface activity of a protein, ovalbumin (OVA) at bare air/water interface in presence and also in absence of electrolyte (KCl) in subphase has been investigated. The surface activity was measured as a function of time. It has been found that, the presence of KCl in aqueous subphase enhances the adsorption rate of the protein. The changes of area/molecule, compressibility, rigidity and unfolding of OVA are trivial up to 10 mM KCl concentration. These properties of OVA, above 10 mM KCl concentration are significant and have been explained in the perspective of DLVO theory and many-body ion–protein dispersion potentials. The presence of high concentration of electrolyte increases the β-structure of OVA, resulting into larger unfolding as well as larger intermolecular aggregates. The overall study indicates that KCl perturbs the OVA monolayer.

Monolayers of thymine amphiphile containing azobenzene chromophore (Azo-Thy) were prepared on various aqueous oligonucleotide (dA₃₀, d(GA)₁₅, d(GGA)₁₀) subphases. Pressure–area isotherms and reflection absorption spectra of the monolayers on dA₃₀ or d(GA)₁₅ solution showed that the H-aggregate of the azobenzene units was formed at higher surface pressure than 25 mN/m. In contrast, the monolayer on an aqueous d(GGA)₁₀ solution did not form any aggregates of the azobenzene units even at high surface pressure. Base-pair formation between Azo-Thy and template d(GGA)₁₀ could give free volume to the azobenzene units in the monolayer to prevent the aggregation of the azobenzene units at the air–water interface.

In order to construct chromophores arrays that precisely controlled their arrangement, monolayers of an azobenzene bearing nucleoamphiphile were prepared on various oligoDNA solutions. Monolayers of the amphiphilic adenine derivative bearing an azobenzene moiety (C₁₂AzoC₅Ade) were prepared on thymidylic acid tetramer (dT4) and octamer (dT8) solutions, and UV-vis reflection absorption spectra of the monolayers were measured to investigate aggregation structures of the azobenzene. The absorption maximum of the monolayer was blue-shifted on the dT4 solution and red-shifted on the dT8 solution. It shows that azobenzene groups in the monolayer have parallel orientation (H aggregate) on the dT4 solution. Though, azobenzene groups have head-to-tail orientation (J aggregates) on the dT8 solution. When monolayers of C₁₂AzoC₅Ade were prepared on the synthesized cyclic oligonucleotides, the absorption spectra were totally different from those of the corresponding linear oligonucleotides.

The methods are presented for fabrication of new nanoscale-organized planar inorganic nanostructures, ultrathin polymeric and nanocomposite films on solid substrates with incorporated nanosized functional and structural building blocks. The methods are based on interfacial synthesis and self-assembly, DNA templating and scaffolding. Ultimately thin monomolecular and multilayer ordered stable polymeric and nanocomposite films containing incorporated ligand-stabilized gold nanoclusters, interfacially in-film grown metallic (Au, Pd) nanoparticles and organized low-dimensional nanostructures were formed. N-alkylated derivatives of poly(4-vinilpyridine) were synthesized and used as water-insoluble amphiphilic polycations to form organized polymeric Langmuir monolayers and novel planar DNA/amphiphilic polycation complexes at the air–aqueous DNA solution interface. The extended net-like and quasi-circular toroidal condensed conformations of deposited planar DNA/amphiphilic polycation complexes were obtained in dependence on the amphiphilic polycation monolayer state during the DNA binding. Planar DNA/amphiphilic polycation complexes were used as nanotemplates for fabrication of organized planar bio-organic–inorganic hybrid nanostructures with ordered nanophase inorganic components (quasi-one-dimensional arrays of semiconductor (CdS) and iron oxide nanoparticles and nanorods) organized in planar matrix of deposited DNA/amphiphilic polycation complex film. The formed nanostructures were characterized by atomic force microscopy and transmission electron microscopy techniques.

A method is presented that enables the determination of transient absorption in Langmuir films made from a monolayer of spiropyran on water. This is achievable even though the optical pathlength of such a monolayer is < 10^-9 m. The approach is to monitor reflectivity changes close to the Brewster angle, where the background of reflected light is minimized. This is the key to the sensitivity of the method. Relatively speaking the small changes in reflectivity due to changes in both real and imaginary parts of the refractive index are easier to observe with the intrinsically low backgrounds at the Brewster angle. Notably using Fresnel equations we can show that the real and imaginary parts of the refractive index can be independently assessed for ultrathin films and monolayers using the approach presented.

The 5,10,15,20-tetrakis(4-sulfophenyl)porphyrin (TPPS₄) and 5-phenyl-10,15,20-tris(4-sulfophenyl)porphyrin (TPPS₃)] were obtained for the first time as the pure sulfonic acid derivatives and characterized for their constitutional structure in the solid state and in water solution. The zwitterionic species in water solutions, above a critical micellar concentration, are stabilized by side-to-side homoassociation to J-aggregates (B-band: 490 nm), but in solids they only give the J-aggregates when water is present in enough amount. Severe dried solids show a zwitterionic species, stabilized by side-to-side interactions, that probably corresponds to the dimer (B-band: 455 nm). The monomeric zwitterion (B-band: 434 nm) is detected in dilute water solutions and its acid/base properties (concentration pK_a(1/2) ≈ 5.0) are not significantly different from those of the acidified solutions of their sodium sulfonate derivatives. However, pure water solutions of TPPS_n, in contrast to those of their sodium salts, show important interactions with hydrophilic surfaces: e.g. TPPS₄ adsorbs on fused quartz forming a monolayer of the free-base porphyrin together with its counter cations. Dilution of the title porphyrins in a solid matrix (e.g.KBr) leads to a free-base porphyrin species with a red-shifted B-band (424 nm) that points to a side-to-side homoassociation, which is in contrast with the typical π-stacked aggregates of the corresponding alkaline metal sulfonato salts.

The generation of singlet oxygen (SO), primarily by using a combination of light and photosensitizers in the presence of a dissolved gas, finds applications in both chemistry and medicine. The efficiency of its formation can be enhanced by immobilization of the photosensitizers. In this work, we have explored the covalent functionalization in suspension of hexahedral slab-like polysilicon microparticles ( $\mu$P, with a largest dimension of three microns) with a model photosensitizer, 5-(4-isothiocyanatophenyl)-10,15,20-(triphenyl)porphyrin (ITC-P), and evaluated the singlet oxygen generation of this photosensitizer in solution and after immobilization (ITC-P-$\mu$P) in suspension. The SO-detection experiment on the functionalized microparticles was performed using a hydrogel as the matrix supporting the microparticles (to avoid their settling), and revealed that ITC-P-$\mu$Pin suspension is capable of generating SO more efficiently than free ITC-P in solution.

The generation of singlet oxygen (SO), primarily by using a combination of light and photosensitizers in the presence of a dissolved gas, finds applications in both chemistry and medicine. The efficiency of its formation can be enhanced by immobilization of the photosensitizers. In this work, we have explored the covalent functionalization in suspension of hexahedral slab-like polysilicon microparticles (μP, with a largest dimension of three microns) with a model photosensitizer, 5-(4-isothiocyanatophenyl)-10,15,20-(triphenyl)porphyrin (ITC-P), and evaluated the singlet oxygen generation of this photosensitizer in solution and after immobilization (ITC-P-μP) in suspension. The SO-detection experiment on the functionalized microparticles was performed using a hydrogel as the matrix supporting the microparticles (to avoid their settling), and revealed that ITC-P-μP in suspension is capable of generating SO more efficiently than free ITC-P in solution.

This study investigates the electronic and structural properties of heterojunctions formed by mono-/bi-layers of graphene on a cerium oxide (CeO₂) substrate. By utilizing first-principles calculations, we analyze the effects of the CeO₂ substrate on graphene’s electronic structure and interfacial properties. The presence of the CeO₂ substrate induces significant modifications in the band structure, including the formation of interface states and changes in the bandgap. The interfacial bonding and lattice matching play crucial roles in determining the heterojunction’s electronic behavior. Furthermore, we examine the charge transfer phenomena and its influence on electrical conductivity and carrier mobility. This research provides insights into the design and optimization of graphene-based devices on CeO₂ substrates for potential electronic and optoelectronic applications.

Monolayers of thymine amphiphile containing azobenzene chromophore (Azo-Thy) were prepared on various aqueous oligonucleotide (dA₃₀, d(GA)₁₅, d(GGA)₁₀) subphases. Pressure–area isotherms and reflection absorption spectra of the monolayers on dA₃₀ or d(GA)₁₅ solution showed that the H-aggregate of the azobenzene units was formed at higher surface pressure than 25 mN/m. In contrast, the monolayer on an aqueous d(GGA)₁₀ solution did not form any aggregates of the azobenzene units even at high surface pressure. Base-pair formation between Azo-Thy and template d(GGA)₁₀ could give free volume to the azobenzene units in the monolayer to prevent the aggregation of the azobenzene units at the air–water interface.

In order to construct chromophores arrays that precisely controlled their arrangement, monolayers of an azobenzene bearing nucleoamphiphile were prepared on various oligoDNA solutions. Monolayers of the amphiphilic adenine derivative bearing an azobenezene moiety (C₁₂AzoC₅Ade) were prepared on thymidylic acid tetramer (dT4) and octamer (dT8) solutions, and UV-vis reflection absorption spectra of the monolayers were measured to investigate aggregation structures of the azobenzene. The absorption maximum of the monolayer was blue-shifted on the dT4 solution and red-shifted on the dT8 solution. It shows that azobenzene groups in the monolayer have parallel orientation (H aggregate) on the dT4 solution. Though, azobenzene groups have head-to-tail orientation (J aggregates) on the dT8 solution. When monolayers of C₁₂AzoC₅Ade were prepared on the synthesized cyclic oligonucleotides, the absorption spectra were totally different from those of the corresponding linear oligonucleotides.