Modification of Shockley surface state by long-chain n-alkane: Photoemission study on tetratetracontane/Au(111) interface

Modification of quasi two-dimensional surface electron system on Au(111) with adsorption of long-chain n-alkane molecule n-CH₃(CH₂)₄₂CH₃ (tetratetracontane: TTC) was investigated by angle-resolved photoemission spectroscopy. Significant modification of the energy band structure of the Shockley surface state was induced by the adsorption of TTC monolayer with “flat-on” structure. The energy shift of the Shockley surface state toward the Fermi level reaches about 160 meV at Γ? point (k = 0 Å^− 1). The possible origin of the stabilization of the surface electron system with TTC monolayer is discussed.     

Photoconductive properties of organic-inorganic hybrid perovskite (C6H13NH3)2(CH3NH3)m − 1PbmI3m + 1:TiO2 nanocomposites device structure

Photoconductive devices, with remarkable photoconductive performance, of fluorine doped tin oxide/TiO₂/(C₆H₁₃NH₃)₂(CH₃NH₃)_m − 1Pb_mI_3m + 1 (m = 1, 2):TiO₂/Pt were fabricated. An electron injection mechanism from the (C₆H₁₃NH₃)₂(CH₃NH₃)_m − 1Pb_mI_3m + 1 (m = 1, 2) to TiO₂ was proposed for the photoconductive effects, where organic-inorganic hybrid perovskite (C₆H₁₃NH₃)₂(CH₃NH₃)_m − 1Pb_mI_3m + 1 (m = 1, 2), self-organized into mesoscopic TiO₂ films from solution directly, served as the electron donor. The photoconductive performance of the devices can be adjusted by the inorganic sheet thickness (tuned by m) of the hybrid perovskite. The photocurrent value increased as m value increased at the same illumination. Further, when bias voltage was 1.0 V, the ratio of photocurrent and dark current for (C₆H₁₃NH₃)₂(CH₃NH₃)_2⁻ Pb₂I₇:TiO₂ reached as high as 7.05 × 10³. The devices could be potentially used as light detectors and light-controlled switch.     

Structural study of CH3S self-assembled monolayers on Au(111)

We present preliminary results of an experimental investigation of ordered phases of CH₃S chemisorbed on Au(111). The self-assembled monolayer has been grown by dosing dimethyl disulfide in ultrahigh vacuum at different substrate temperatures between 200 K and 320 K and following different protocols. The monolayers have been characterized by means of low-energy He atom scattering with time-of-flight detection in a temperature range between 150 K and 300 K. The observed diffraction patterns show that the main periodicity is well-described by the (3 × 4) overlayer of the Au(111) lattice, coexisting with the (√3 × √3) periodicity, in agreement with previous results obtained by means of low-energy electron diffraction.     

An efficient dye-sensitized solar cell based on a functionalized-triarylamine dye

A new functionalized-triarylamine dye (MXD10) has been designed, synthesized, and characterized. Two CH₃(CH₂)₄CH=CH- units were introduced into triphenylamine for improvement of light harvesting, suppression of dye aggregation and retardation of charge recombination. Photophysical, electrochemical and photovoltaic measurements are in accord with the molecular design. Device based on MXD10 gave a maximum power conversion efficiency of 6.47% under simulated AM 1.5 irradiation (100 mW cm⁻²) with J_SC = 15 mA/cm², V_OC = 635 mV, and ff = 0.68.     

Intermediate structural phases in rare-earth substituted BiFeO3

The room-temperature crystal structure and local ferroelectric properties of Bi_0.85RE_0.15FeO₃ (RE = Sm, Gd, Dy) polycrystalline samples have been investigated by X-ray diffraction (XRD) and piezoresponse force microscopy (PFM) techniques. XRD measurements show that the rare-earth substitution causes the transformation of R3c structure typical of BiFeO₃ to yield orthorhombic phases with √2a × 2√2a × 2a and √2a × 2a × √2a superlattices (a is the parameter of the cubic perovskite subcell). Results of PFM investigations imply that both the orthorhombic phases are polar. The models describing crystal structure of the phases are discussed.     

Detection of deposition rate of plasma-polymerized acrylate and methacrylate derivatives using quartz crystal microbalance

The deposition rates of plasma-polymerized (pp-)films of 12 acrylate derivatives (CH₂CHCOOR: substitution R is H, CH₃, CHCH₂, CH₂CH₃, CH₂CH₂CH₃, (CH₂)₃CH₃, C(CH₃)₃, CH₂CH(CH₃)₂, CH₂(CH₂)₄CH₃, CH₂CF₃, CH₂CF₂CF₃, CH₂(CF₂)₂CF₃), and 12 methacrylate derivatives (CH₂CCH₃COOR′: substitution R′ is H, CH₃, CHCH₂, CH₂CH₃, CH₂CH₂CH₃, (CH₂)₃CH₃, C(CH₃)₃, CH₂CH(CH₃)₂, CH₂(CH₂)₄CH₃, CH₂CF₃, CH₂CF₂CF₃, CH₂(CF₂)₂CF₃) are determined by the quartz crystal microbalance technique. Using the same polymerization conditions (100 W RF and 100 Pa vapor pressure) for the various monomers, it is found that the deposition rates were proportional to the polymerization time. The average deposition rate of pp-acrylate derivatives is larger than that of pp-methacrylate derivatives without pp-hexylacrylate. The average deposition rate of pp-fluoroalkylacrylates was higher than 7-25 times that of pp-alkylacrylate, and the average deposition rate of pp-fluoroalkylmethacrylates was higher than 10-31 times that of pp-alkylmethacrylates, respectively. The average deposition rate of pp-film depends on the chemical structure of the monomer suggesting different mechanisms under plasma-polymerization.     

M2Y8(SiO4)6O2: Tb (M = Ca, Sr) phosphors: Sol-gel synthesis from N-2-aminoethylic-3-aminopropyldiethoxysilane and different photoluminescence behavior

M₂Y₈(SiO₄)₆O₂: Tb³⁺ (M = Ca, Sr) phosphors have been synthesized with a new silicon source silane crosslinking reagent (N-2-aminoethylic-3-aminopropyldiethoxysilane [NH₂(CH₂)₂NH(CH₂)₃SiCH₃(OCH₃)₂], abbreviated as AEAPMMS) through the sol-gel process, both of which present the characteristic emission ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) of Tb³⁺ ions. It is interesting to be found that the high energy level blue emission (⁵D₃ → ⁷F_J (J = 6, 5, 4, 3) transition) still can be found in the emission spectrum of Ca₂Y₈(SiO₄)₆O₂: Tb³⁺ while it disappears in the emission spectrum of Sr₂Y₈(SiO₄)₆O₂: Tb³⁺ for the cross-relaxation-induced quenching.     

Effect of etching on dielectric constant and surface composition of SiCOH low-k films in inductively coupled fluorocarbon plasmas

SiCOH low-k (k = 2.8) film etched in fluorocarbon (CF₄ and CHF₃) inductively coupled plasmas was characterized in this work. The surface composition and molecular structures of the low-k films after etching in the CF₄, CHF₃, CF₄/Ar, and CHF₃/Ar plasmas were characterized. A higher etch rate was observed with the CF₄ plasmas than with the CHF₃ plasmas. The etch rate of the low-k film in the CF₄ plasmas was decreased and the etch rate in the CHF₃ plasmas was increased by the Ar addition. After etching the low-k films, a decrease in the dielectric constant of up to 0.19 was observed. The thickness of the fluorocarbon (CF_x) layer and CF_x (x = 1, 2, 3)-to-carbon ratio obtained from the XPS C 1s peak increased with decreasing etch rate. The k-value was correlated with amount of Si-CH₃ and Si-O related groups determined from the Fourier transform infrared (FT-IR) spectrum. The Si-O related peaks were markedly decreased after etching in the CF₄ and CF₄/Ar plasmas. The lower k-value was attributed to the increase of the Si-CH₃/Si-O ratio after etching low-k film.     

Evaluation of monolayers and mixed monolayers formed from mercaptobenzothiazole and decanethiol as sensing platforms

In this investigation, the characterisation of monolayer and mixed monolayers formed from mercaptobenzothiazole (MBT) and decanethiol (DT) has been carried out with cyclic voltammetry. The SAMs have been tested for their stability and electron transfer blocking properties. The redox probes used in the present study are [Fe(CN)₆]⁴⁻, [Ru(NH₃)₆]²⁺ and Cu underpotential deposition (upd). The electron transfer kinetics is investigated in acid and neutral pH range. Electron transfer kinetics is altered by the nature of charge on the redox probe and the charge on the monolayer. Electron transfer kinetics of negatively charged redox probes like ferrocyanide ions is blocked when the surface pK_a<pH_medium and at pK_a>pH_medium reversible features is observed for negatively charged probes. An exactly reverse effect is observed in the case of positively charged redox species like [Ru(NH₃)₆]^2+/3+.Cu under potential deposition studies reflects the structural integrity and compactness of the SAM layer. The utility of these monolayers and mixed monolayer for selective sensing of dopamine is discussed based on their ability to discriminate between positively and negatively charged redox species at different pH.     

Synthesis,structure and optical studies of inorganic–organic hybrid semiconductor,NH3(CH2)12NH3PbI4

Synthesis, crystal structure and optical properties of two-dimensional layered inorganic–organic hybrid NH₃(CH₂)₁₂NH₃PbI₄ are presented. Intercalation strategy has also been used to fabricate single crystal and thin films of the same. As thin film, they are well oriented and stacked along the [l 0 0] direction with strong room-temperature excitonic absorption and emission characteristics. Exciton features were correlated with the relative inorganic network crumpling and conformation of alkylammonium chains. The structural features are compared with those of similar hybrid, (H(CH₂)₁₂NH₃)₂PbI₄.     

[NH3(CH2)2NH3][Co(SO4)2(H2O)4]: Chemical preparation, crystal structure, thermal decomposition and magnetic properties

Cobalt ethylenediammonium bis(sulfate) tetrahydrate, [NH₃(CH₂)₂NH₃][Co(SO₄)₂(H₂O)₄], has been synthesised by slow evaporation at room temperature. It crystallises in the triclinic system, space group , with the unit cell parameters: a = 6.8033(2), b = 7.0705(2), c = 7.2192(3) Å, α = 74.909(2)°, β = 72.291(2)°, γ = 79.167(2)°, Z = 1 and V = 317.16(2) Å³. The Co(II) atom is octahedrally coordinated by four water molecules and two sulfate tetrahedra leading to trimeric units [Co(SO₄)₂(H₂O)₄]. These units are linked to each other and to the ethylenediammonium cations through OW-H…O and N-H…O hydrogen bonds, respectively. The zero-dimensional structure is described as an alternation between cationic and anionic layers along the crystallographic b-axis. The dehydration of the precursor proceeds through three stages leading to crystalline intermediary hydrate phases and an anhydrous compound. The magnetic measurements show that the title compound is predominantly paramagnetic with weak antiferromagnetic interactions.     

Preparation and properties of fluorinated aliphatic alcohols/silica nanocomposites – Application to the encapsulation of anatase titanium oxide nanoparticles into these composite cores

A variety of fluorinated aliphatic alcohols [R_F-CH₂CH₂OH; R_F = CF₃(CF₂)₃CH₂(CF₂)₅, CF₃(CF₂)_n; n = 3, 5, 7] were applied to the preparation of the corresponding fluorinated alcohols/silica nanocomposites [R_F-CH₂CH₂OH/SiO₂] through the sol–gel reactions with tetraethoxysilane (TEOS) and silica nanoparticles under alkaline conditions. R_F-CH₂CH₂OH/SiO₂ nanocomposites thus obtained have a good dispersibility and stability in not only water but also traditional organic solvents such as methanol, ethanol, 1,2-dichloroethane and tetrahydrofuran. FE–SEM (field emission scanning electron microscopy) and dynamic light scattering (DLS) measurements show that these composites are nanometer size-controlled fine particles in methanol. These fluorinated nanocomposites were also applied to the surface modification of glass to exhibit a superhydrophilic characteristic with a superoleophobicity on the modified surface. Interestingly, R_F-CH₂CH₂OH/SiO₂ nanocomposites were found to exhibit no weight loss behavior corresponding to the contents of the alcohols in the composites even after calcination at 800 °C. In addition, anatase TiO₂ nanoparticles (an-TiO₂) were effectively encapsulated into R_F-CH₂CH₂OH/SiO₂ nanocomposite cores under the similar sol–gel reactions to give the corresponding fluorinated alcohol/SiO₂/an-TiO₂ nanocomposites. These obtained nanocomposites can give a higher photocatalytic activity even after calcination at 1000 °C for the decolorization of methylene blue under UV light irradiation than that of the an-TiO₂ nanoparticles under the similar conditions, although the parent TiO₂ nanoparticles after calcination were unable to give a photocatalytic activity.     

The development of the gadolinium surface state

The critical coverage for formation of the a₁(d_3z²-r² and s) symmetry gadolinium surface state appears to be in region of one monolayer for gadolinium on W(1 1 2) and is evident from a change in the density of states in the region near the Fermi level and a change in the band symmetry. Below one monolayer coverage, strong hybridization between the Gd overlayer and the W(1 1 2) surface dominates the electronic structure.     

Diffusion of self-assembled monolayers of thiols on the gold surfaces covered with polydimethylsiloxane stamps

Thiols can diffuse and form self-assembled monolayers (SAMs) on the gold surfaces covered with polydimethylsiloxane (PDMS) stamps. For the first time, with cells as the indicator of how far alkanethiols had diffused to form SAM, we studied the growth dynamics of SAMs of HS(CH₂)₁₁(OCH₂CH₂)₃OH (EG₃) and HS(CH₂)₁₁(OCH₂CH₂)₆OH (EG₆) on the gold surfaces covered with PDMS stamps. The growth of SAMs is well described by one-dimensional diffusion from a line source of concentration, with surface diffusion coefficient of 193.4 ± 19.2 μm²/min (EG₃) and 95.8 ± 18.9 μm²/min (EG₆).     

Sol-gel derived fluoridated hydroxyapatite films

Fluoridated hydroxyapatite [Ca₅(PO₄)₃(OH)_xF_1−x] films have reasonably good bioactivity and stability in the body, they could behave better than hydroxyapatite films in medical applications. In this work, a sol-gel method was adopted to prepare fluoridated hydroxyapatite films on titanium alloy. Three kinds of fluorine-containing reagents CF₃COOH, HPF₆ and NH₄PF₆ were selected to add into mixed Ca(NO₃)₂-P₂O₅ ethanol solutions to form dipping sols. The dipping sol with CF₃COOH led to an apatite film in which fluorine could not be detected in EDS. While the dipping sol, with HPF₆ or NH₄PF₆, could result in fluoridated hydroxyapatite films. The incorporation of fluorine could be attributed to the reactions of both HPF₆ or NH₄PF₆ with the mixed Ca(NO₃)₂-P₂O₅ ethanol solution to form nano-sized CaF₂ particles, which in turn, react with other species to form fluoridated hydroxyapatite during the film formation at 600 °C. Among the three fluorine-containing reagents, HPF₆ was the best because its dipping sol was more stable and the resulting films had better morphology.     

Proliferation of osteoblasts and fibroblasts on model surfaces of varying roughness and surface chemistry

Physical and chemical properties of the surfaces of implants are of considerable interest for dental and orthopedic applications. We used self-assembled monolayers (SAMs) terminated by various functional chemical groups to study the effect of surface chemistry on cell behavior. Cell morphology and proliferation on silicon wafers of various roughnesses and topographies created by chemical etching in caustic solution and by corundum sandblasting were analyzed as well. Water contact angle data indicated that oxidized wafer surfaces displayed high hydrophilicity, modification with poly(ethylene glycol) (PEG) created a hydrophilic surface, and an amino group (NH₂) led to a moderately wettable surface. A hydrophobic surface was formed by hydrocarbon chains terminated by CH₃, but this hydrophobicity was even further increased by a fluorocarbon (CF₃) group. Cell proliferation on these surfaces was different depending primarily on the chemistry of the terminating groups rather than on wettability. Cell proliferation on CH₃ was as high as on NH₂ and hydrophilic oxidized surfaces, but significantly lower on CF₃. Precoating of silicon wafers with cell culture serum had no significant influence on cell proliferation. Scanning electron microscopy indicated a very weak initial cell-surface contact on CF₃. The cell number of osteoblasts was significantly lower on sandblasted surfaces compared with other rough surfaces but no differences were detected with 3T3 mouse fibroblasts. The different surface roughnesses and topographies were recognized by MG-63 osteoblasts. The cells spread well on smooth surfaces but appeared smaller on a rough and unique pyramid-shaped surface and on a rough sandblasted surface.     

Comparison for the crystal structure,synthesis and microwave dielectric properties of alkaline earth orthophosphates

A₃(PO₄)₂ compounds have different crystal structures when A sites are occupied by Ca or heavy alkaline earth metal atoms (Sr or Ba). The compounds with isomorphous crystal structure were synthesized by solid-state reaction method when the A-site atoms were Sr or Ba, and their crystal structure and microstructure of the sintered ceramics were investigated by X-ray powder diffraction (XRD) and scanning electron microscope (SEM), respectively. The microwave dielectric properties were measured using a network analyzer. It was found that Ba₃(PO₄)₂ could be sintered at 1060 °C, while the α-Sr₃(PO₄)₂ ceramics that has a smaller Sr²⁺ ionic radius, could be sintered at 1200 °C, and higher relative densities were obtained. The dielectric constant (?) of the α-Sr₃(PO₄)₂ is higher than that of Ba₃(PO₄)₂, but Ba₃(PO₄)₂ has a higher Q × f value than that of β-Ca₃(PO₄)₂ and α-Sr₃(PO₄)₂, which could be interpreted by the differences in ionic polarizability and bond strength. The temperature coefficients of resonant frequency (τ_f) for all samples with isomorphous crystal structure have positive values, ranging between +11 and +66 ppm °C⁻¹.     

Very-low temperature specific heat of Torlon

The specific heat of Torlon has been measured in the 0.15-4.2 K temperature range. Data below 1 K can be represented by c(T) = P₁T^1+δ + P₂T³, with P₁ = (5.41 ± 0.08)·10⁻⁶J K^−(2+δ) g⁻¹, P₂ = (2.82 ± 0.03) ·10⁻⁵JK⁻⁴g⁻¹ and δ = 0.28 ± 0.01, as predicted by the tunnelling theory. Above 1 K, the behaviour of c(T) is similar to that of other amorphous materials and can be expressed as: c(T) = P · T^Ω with P = (2.68 ± 0.07)·10⁻⁵JK^Ω+1g⁻¹ and Ω = 3.32 ± 0.02.     

Structural and mechanical properties of titanium and titanium diboride monolayers and Ti/TiB2 multilayers

Nano-multilayers represent a new class of engineering materials that are made up of alternating nanometer scale layers of two different components. In the present work a titanium (Ti) monolayer was combined with titanium diboride (TiB₂) to form a Ti/TiB₂ nano-multilayer. Designed experimental parameters enabled an evaluation of the effects of direct current bias voltage (U_b) and bilayer thickness (Λ) during multilayer deposition on the mechanical properties of reactively sputtered Ti/TiB₂ multilayer films. Their nanostructures and mechanical properties were characterized and analyzed using X-ray photoelectron spectroscopy (XPS), low-angle and high-angle X-ray diffraction (XRD), plan-view and cross-sectional high-resolution transmission electron microscopy (HRTEM), and microindentation measurements. Under the optimal bias voltage of U_b = − 60 V, it was found that Λ (varied from 1.1 to 9.8 nm) was the most important factor which dominated the nanostructure and hardness. The hardness values obtained varied from 12 GPa for Ti and 15 GPa for TiB₂ monolayers, up to 33 GPa for the hardest Ti/TiB₂ multilayer at Λ = 1.9 nm. The observed hardness enhancement correlated to the layer thickness, followed a relation similar to the Hall-Petch strengthening dependence, with a generalized power of ∼ 0.6. In addition, the structural barriers between two materials (hcp Ti/amorphous TiB₂) and stress relaxation at interfaces within multilayer films resulted in a reduction of crack propagation and high-hardness.     

Synthesis of tadpole-shaped Au nanoparticles using a Langmuir monolayer of fluorocarbon surfactant

Tadpole-shaped nanoplates, linearly arranged nanoparticles and triangular and hexagonal nanoplates were synthesized under a Langmuir monolayer of a cationic fluorocarbon surfactant, FC-4 (C₃F₇O(CF(CF₃)CF₂O)₂CF(CF₃)CONH(CH₂)₃N⁺(C₂H₅)₂CH₃I^?) through interfacial reduction of AuCl₄^? by formaldehyde gas. Reports about such tadpole-shaped nanoparticles are relatively scarce. The predominantly plate-like particles are mainly nearly perfect triangular and hexagonal nanocrystals, of micrometer scale in diameter. The Au nanoparticles are characterized using transmission electron microscopy (TEM) and selected-area electron diffraction (SAED). The atomically flat planar surfaces of the Au nanoplates correspond to {111} planes and the lateral surfaces are {110} planes. The surface pressure strongly influences the formation of different Au nanostructures. A potential mechanism of such diverse morphologies is also discussed.