Single-component Layers Research Articles

Application of Metal Oxide Nanoparticles in the Field of Potentiometric Sensors: A Review.

Recently, there has been rapid development of electrochemical sensors, and there have been numerous reports in the literature that describe new constructions with improved performance parameters. Undoubtedly, this is due to the fact that those sensors are characterized by very good analytical parameters, and at the same time, they are cheap and easy to use, which distinguishes them from other analytical tools. One of the trends observed in their development is the search for new functional materials. This review focuses on potentiometric sensors designed with the use of various metal oxides. Metal oxides, because of their remarkable properties including high electrical capacity and mixed ion-electron conductivity, have found applications as both sensing layers (e.g., of screen-printing pH sensors) or solid-contact layers and paste components in solid-contact and paste-ion-selective electrodes. All the mentioned applications of metal oxides are described in the scope of the paper. This paper presents a survey on the use of metal oxides in the field of the potentiometry method as both single-component layers and as a component of hybrid materials. Metal oxides are allowed to obtain potentiometric sensors of all-solid-state construction characterized by remarkable analytical parameters. These new types of sensors exhibit properties that are competitive with those of the commonly used conventional electrodes. Different construction solutions and various metal oxides were compared in the scope of this review based on their analytical parameters.

Friction titration measurements of electrochemically generated mixed alkylthiol monolayers on polycrystalline gold

An electrochemical procedure was used to generate a heterogeneous mixed monolayer composed of 1-undecanethiol (UDT) and 11-mercaptoundecanoic acid (MUA) on polycrystalline gold and the interface was characterized over a range of solution pH using Lateral Force Microscopy (LFM). To generate the heterogeneous mixture, a single component layer of UDT was formed on the gold electrode and portions were removed by reductively desorbing molecules selectively from the Au(111) facets. The voids created by this method were backfilled with MUA using either short-term passive incubation or electrochemically assisted deposition and LFM was used to gather friction maps of the surface in pH adjusted KClO4. From pH 3 to 8, the friction of both UDT and MUA zones in the mixed layer were relatively constant but above this range, the friction of the MUA regions increased significantly. The elevated friction was attributed to the ionization of the MUA groups since pH induced frictional differences were not observed when backfilling with the non-ionizable thiol 11-mercapto-1-undecanol (MUD). The relative difference in friction between the MUA and UDT zones were fit to a modified Henderson-Hasselbach equation to extract the apparent surface pKa (or pK1/2) of MUA bound to the Au(111) facets. The results were similar for both passive and electrochemically backfilled MUA and rendered a pK1/2 of 10.3 ± 0.8. The elevated pK1/2 was attributed to hydrogen bonding of the COOH groups when tightly packed on Au(111) as well as the presence of UDT, which created a local hydrophobic environment near the MUA molecules.

Mixing Poly(ethylene glycol) and Poly(2-alkyl-2-oxazoline)s Enhances Hydration and Viscoelasticity of Polymer Brushes and Determines Their Nanotribological and Antifouling Properties.

Poly(2-alkyl-2-oxazoline)s (PAOXAs) have progressively emerged as suitable alternatives for replacing poly(ethylene glycol) (PEG) in a variety of biomaterial-related applications, especially in the designing of polymer brush-based biointerfaces because of their stealth properties and chemical robustness. When equimolar mixtures of PEG and PAOXAs are assembled on surfaces to yield mixed polymer brushes, the interfacial physicochemical properties of the obtained films are significantly altered, in some cases, surpassing the biopassive and lubricious characteristics displayed by single-component PAOXA and PEG counterparts. With a combination of variable angle spectroscopic ellipsometry, quartz crystal microbalance with dissipation, and atomic force microscopy-based methods, we demonstrate thatmixing of PEG brushes with equimolar amounts of PAOXA grafts determines an increment in film's hydration and viscoelasticity. In the case of mixtures of PEG and poly(2-methyl-2-oxazoline) or poly(2-ethyl-2-oxazoline), brushes displaying full inertness toward serum proteins and improved lubricity with respect to the corresponding single-component layers can be generated, while providing a multifunctional surface that substantially enlarges the applicability of the designed coatings.

Molecular-Level Realignment in Donor–Acceptor Bilayer Blends on Metals

Molecular bilayers made up of a donor–acceptor blend in contact with the metal and capped with a single-component layer show a tunable energy level alignment at both metal–organic and organic–organic interfaces. To ensure sharp heteromolecular interfaces, a contact layer is formed by a stable blend of pentacene (PEN) and perfluorinated copper phthalocyanine (F16CuPc) on Au(111) and Ag(111) and of perfluoropentacene (PFP) and copper phthalocyanine (CuPc) on Ag(111). Core-level and valence band photoemission reveal that, upon capping with pure F16CuPc, CuPc, and PEN, the electronic states of both contact and capping layers “realign” with respect to the monolayer and the multilayer references. The sign of the shift depends clearly on whether the capping layer is donor-like (PEN, CuPc) or acceptor-like (F16CuPc). As revealed by NEXAFS, the shift in electronic levels of the contact layer upon capping leads to a spectral density variation across the Fermi edge (EF); i.e., it induces molecule/metal charge transfer.

Multi-Component Organic Layers on Metal Substrates.

Increasingly high hopes are being placed on organic semiconductors for a variety of applications. Progress along these lines, however, requires the design and growth of increasingly complex systems with well-defined structural and electronic properties. These issues have been studied and reviewed extensively in single-component layers, but the focus is gradually shifting towards more complex and functional multi-component assemblies such as donor-acceptor networks. These blends show different properties from those of the corresponding single-component layers, and the understanding on how these properties depend on the different supramolecular environment of multi-component assemblies is crucial for the advancement of organic devices. Here, our understanding of two-dimensional multi-component layers on solid substrates is reviewed. Regarding the structure, the driving forces behind the self-assembly of these systems are described. Regarding the electronic properties, recent insights into how these are affected as the molecule's supramolecular environment changes are explained. Key information for the design and controlled growth of complex, functional multicomponent structures by self-assembly is summarized.

Defect-sealing of Al2O3/ZrO2 multilayer for barrier coating by plasma-enhanced atomic layer deposition process

Barrier layers were coated by plasma enhanced atomic layer deposition. They had inevitable defects for several reasons and these defects deteriorated the diffusion barrier properties. The size of the pinhole defect decreased with the increase of the layer thickness resulting in enhanced barrier properties, until the thickness reached 20nm for a single-component aluminum oxide (Al2O3) or zirconium oxide (ZrO2) layer. No more enhancement of barrier properties was observed with a further increase of layer thickness, since the defects tended to grow in single-component layers. Alternation of Al2O3 and ZrO2 layers prevented defect growth by covering the defects with another component, and enhanced the barrier properties when compared with single-component layers. Increase of the number of Al2O3/ZrO2 stacks with the same total layer thickness remarkably reduced the water vapor transmission rates value to below 5×10−5g/m2day at 38°C and 100% relative humidity. The Al2O3/ZrO2 multilayer formed on a polyethylene naphthalate substrate at optimized conditions showed light transmittance greater than 86% at a wavelength of 550nm, for application as flexible display substrate.

Cathodoluminescence of Double Layers of Phosphor Particles

We present radiance measurements of particle layers of ZnO:Zn, Y2O3:Eu and Y2O2S:Eu bombarded with electrons at anode voltages between 1 and 15 kV. The layers described in this work refer to single component layers, double layers and two component mixtures. The phosphor layers are deposited on ITO-coated glass slides by settling; the efficiency of the cathodoluminescence is determined by summing the radiances and luminances in the reflected and transmitted modes respectively. The efficiency of a double layer of Y2O3:Eu on top of ZnO:Zn at high electron energy is significantly larger than the efficiency of a corresponding layer in which the two components are mixed. This result is interpreted in terms of the penetration-model, which predicts a larger efficiency for a high-voltage phosphor on top of a low-voltage phosphor. When a layer of the low-voltage phosphor ZnO:Zn is on top of the high-voltage phosphor Y2O3:Eu, we also observe a higher efficiency than that of the corresponding layer with both components mixed. In this case the efficiency increases due to suppression of charging in the Y2O3:Eu layer. Double layers of ZnO:Zn and Y2O2S:Eu did not show enhanced efficiency, because the size of the Y2O2S:Eu particles was too large to evoke the penetration effect.

Photoconductivity Enhancement in Multilayers of CdSe and CdTe Quantum Dots

Charge separation at the interface between CdSe and CdTe quantum dots was investigated by comparing the photoconductivity of films consisting of only CdSe or CdTe quantum dots to that of films with alternating layers of CdSe and CdTe quantum dots. The photoconductivity for alternating layers is three times higher than for the single component layers. Different possible mechanisms are discussed, and it is concluded that the dissociation of photoexcited excitons into spatially separated mobile charge carriers at the CdSe/CdTe QD interfaces is the most likely explanation. Given that the yield of charge carrier photogeneration in the multilayer sample is at most one, and under the assumption that the mobility of QD layers in unchanged, we conclude that the yield of charge carrier photogeneration in the single component samples is at most one-third. The thickness of the individual CdSe and CdTe layers was varied, resulting in different distances between the CdSe/CdTe interfaces. The photoconductivity increased with respect to films of only CdSe or CdTe when these interfaces were separated by only one or two quantum dot layers, which implies that exciton diffusion is inefficient.

Study of two-component colloidal particles at air/water interfaces using Langmuir–Blodgett techniques

One and two-component colloidal particles, sulfate-treated polystyrene (S-PS), aldehyde-sulfate (AS-PS), and carboxylate-treated polystyrene particles (C-PS), were assembled at air/water interfaces by injecting particle dispersions. Surface pressure–area ( π– A) isotherms were measured using the Langmuir–Blodgett technique. The isotherms for S-PS particles are reversible and independent of barrier speeds during the compression/relaxation cycles. The normalized isotherms of S-PS/AS-PS and S-PS/C-PS particle mixtures lie between those of single species. In addition, the self-assembled structures of particles were transferred onto mica substrates and characterized using a laser scanning confocal microscope. The morphology of the two-component layer has the characteristics of both single component layers with no significant phase separation. Finally, we have explored the potential applicability of a purely additive group contribution analysis to surface pressure–area isotherms.

ToF‐SIMS investigations of adsorbed proteins on dental titanium

AbstractTwo model proteins, bovine serum albumin (BSA) and lysozyme (LSZ), were used to study adsorption behavior on dental titanium by time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). Protein films were prepared as single component layers and as mixtures of the two proteins. Additionally, the behavior of consecutive adsorption of both proteins was investigated. The obtained data were analyzed by means of principal component analysis (PCA). Dental titanium samples with a layer consisting of simply one protein could be separated from each other by selecting amino acid related peaks and using PCA or samples coated with a mixture of both proteins, the differentiation was also possible. The partial displacement of LSZ molecules by BSA was shown in the case of simultaneous adsorption. The consecutive adsorption of BSA and subsequently LSZ resulted in layers with a bigger amount of LSZ than of BSA compared to the layers obtained by simultaneous adsorption.

Cross‐Linked Multilayers of Poly(vinyl amine) as a Single Component and Their Interaction with Proteins

Novel multilayer thin films that consist solely of cross-linked single component layers are generated by a selective cross-linking of the poly(vinyl amine) (PVAm) layers in [PVAm/poly(acrylic acid) (PAA)](n) thin films constructed either on silica particles or silicon wafers, followed by the removal of PAA. The surface topography of the (PVAm)(n) multilayer thin films, before and after the adsorption of human serum albumin (HSA), has been studied by atomic force microscopy on the freeze-dried films. The decrease of the average roughness of the film after the adsorption of HSA showed the protein was adsorbed into the (PVAm)(n) film making these films potential reservoirs for proteins.

Charge transport and recombination in bulk heterojunction solar cells containing a dicyanoimidazole‐based molecular acceptor

AbstractCarrier transport and recombination have been studied in single component layers and blends of the soluble PPV‐derivative poly[2,5‐dimethoxy‐1,4‐phenylenevinylene‐2‐methoxy‐5‐(2‐ethyl‐hexyloxy)‐1,4‐phenylenevinylene] (M3EH‐PPV) and the small molecule acceptor 4,7‐bis(2‐(1‐hexyl‐4,5‐dicyanoimidazole‐2‐yl)vinyl) benzo[c][1,2,5]‐thiadiazole (HV‐BT). Measurements on single carrier devices show significantly smaller electron mobility in the blend compared to the pure HV‐BT layer, which is suggestive of the formation of isolated clusters of the acceptor in a continuous polymer matrix. The significant change in fill factor (FF) with increasing illumination intensity is consistently explained by a model taking into account bimolecular recombination and space charge effects. The decay of the carrier density after photoexcitation has been studied by performing photo‐CELIV measurements on pure and blend layers. It is found that the decay at long delay times follows a power‐law dependence, which is, however, not consistent with a Langevin‐type bimolecular recombination of free charges. A good description of the data is obtained by assuming trimolecular recombination to govern the charge carrier dynamics in these systems.

Customized Electronic Coupling in Self‐Assembled Donor–Acceptor Nanostructures

AbstractCharge transfer processes between donor–acceptor complexes and metallic electrodes are at the heart of novel organic optoelectronic devices such as solar cells. Here, a combined approach of surface‐sensitive microscopy, synchrotron radiation spectroscopy, and state‐of‐the‐art ab initio calculations is used to demonstrate the delicate balance that exists between intermolecular and molecule–substrate interactions, hybridization, and charge transfer in model donor–acceptor assemblies at metal‐organic interfaces. It is shown that charge transfer and chemical properties of interfaces based on single component layers cannot be naively extrapolated to binary donor–acceptor assemblies. In particular, studying the self‐assembly of supramolecular nanostructures on Cu(111), composed of fluorinated copper‐phthalocyanines (F16CuPc) and diindenoperylene (DIP), it is found that, in reference to the associated single component layers, the donor (DIP) decouples electronically from the metal surface, while the acceptor (F16CuPc) suffers strong hybridization with the substrate.

Non‐Covalent Interactions in Supramolecular Assemblies Investigated with Electron Spectroscopies

A new view: A picture of the different non-covalent interactions relevant for the self-assembly of organic layers and their spectroscopic fingerprints is provided (see figure). In particular, state-of-the-art spectroscopic measurements are performed for supramolecular assemblies, comparing the electronic structure of single-component layers with that of binary organic layers.

Protein films adsorbed on experimental dental materials: ToF-SIMS with multivariate data analysis

The proteins lysozyme, amylase, and bovine serum albumin (BSA) were adsorbed on two experimental dental materials, made of fluoroapatite particles embedded in polymer matrices, and on silicon wafers. The protein films were prepared as single-component layers, as binary mixtures, and as double layers. These systems were investigated by time-of-flight secondary ion mass spectrometry (ToF-SIMS) and the multivariate data analysis technique of discriminant principal-component analysis (DPCA). During adsorption of a single protein film on to the solid surfaces, the three proteins could be clearly distinguished by the scores of their mass spectra after selection of amino acid-related peaks and DPCA. Furthermore, very similar results were obtained on the two different fluoroapatite substrates. For samples coated with binary layers of two proteins adsorbed simultaneously, it was found for both substrate types that BSA shows the strongest ability to adsorb followed by lysozyme, while amylase has the smallest ability. By contrast, the consecutive adsorption of two protein layers showed a strong influence of substrate type on the adsorption ability of the proteins.

Direct numerical simulation of a transitional temporal mixing layer laden with multicomponent-fuel evaporating drops using continuous thermodynamics

A model of a temporal three-dimensional mixing layer laden with fuel drops of a liquid containing a large number of species is derived. The fuel model is based on continuous thermodynamics, whereby the composition is statistically described through a distribution function parametrized on the species molar weight. The drop temperature is initially lower than that of the carrier gas, leading to drop heat up and evaporation. The model describing the changes in the multicomponent (MC) fuel drop composition and in the gas phase composition due to evaporation encompasses only two more conservation equations when compared with the equivalent single-component (SC) fuel formulation. Single drop results of a MC fuel having a sharply peaked distribution are shown to compare favorably with a validated SC-fuel drop simulation. Then, single drop comparisons are performed between results from MC fuel and a representative SC fuel used as a surrogate of the MC fuel. Further, two mixing layer simulations are conducted with a MC fuel and they are compared to representative SC-fuel simulations conducted elsewhere. Examination of the results shows that although the global layer characteristics are generally similar in the SC and MC situations, the MC layers display a higher momentum-thickness-based Reynolds number at transition. Vorticity analysis shows that the SC layers exhibit larger vortical activity than their MC counterpart. An examination of the drop organization at transition shows more structure and an increased drop-number density for MC simulations in regions of moderate and high strain. These results are primarily attributed to the slower evaporation of MC-fuel drops than of their SC counterpart. This slower evaporation is due to the lower volatility of the higher molar weight species, and also to condensation of already-evaporated species on drops that are transported in regions of different gas composition. The more volatile species released in the gas phase earlier during the drop lifetime reside in the lower stream while intermediary molar weight species, which egress after the drops are entrained in the mixing layer, reside in the mixing layer and form there a very heterogeneous mixture; the heavier species that evaporate later during the drop lifetime tend to reside in regions of high drop number density. This leads to a segregation of species in the gas phase based on the relative evaporation time from the drops. The ensemble-average drop temperature becomes eventually larger/smaller than the initial drop temperature in MC/SC simulations. Neither this species segregation nor the drop temperature variation with respect to the initial temperature or as a function of the mass loading can be captured by the SC-fuel simulations.

Properties of surface layers produced from a metallorganic titanium compound under glow discharge conditions

A prospective line in the development of thermochemical treatments under glow discharge conditions is to work out new techniques of producing multicomponent layers, e.g. composite layers, by combining various treatments such as plasma nitriding and the PACVD methods. The combined properties, appropriately selected and complementary to one another, of the single-component layers obtained using one of these processes, permit widening the application range of these layers. This paper specifies the conditions under which the multicomponent layers of Ti(NCO) type and composite layers of the nitrided + Ti(NCO) type can be produced on steel. The optimum temperature of the process is 500 °C. The composite layers nitrided + Ti(NCO) type have a good resistance to both corrosion and frictional wear. Spectral investigations by optical emission spectroscopy have shown that the active particles that take part in the formation of the Ti(NCO) layer are: titanium ions (Ti +) and atoms, nitrogen particles (N +, N 2 +, NH), oxygen atoms and CN radicals coming from the gaseous atmosphere and nitrogen from the prenitrided steels.

Properties of Surface Layers Produced from a Metalorganic Titanium Compound Under Glow Discharge Conditions

A prospective line in the development of thermo-chemical treatments under glow discharge conditions is to work out new techniques of producing multicomponent layers, e.g., composite layers, by combining various treatments, such as e.g. plasma nitriding and the PACVD method. The combined properties, appropriately selected and complementary to one another, of the single-component layers obtained using one of these processes, permit widening the application range of the layers. The paper specifies the conditions under which the multicomponent layers of Ti(OCN) type and composite layers of the nitrided + TiN or nitrided + Ti(OCN) type can be produced on steel. The structure and properties of the layers thus obtained are also described.

Effect of absorption perturbation on the reflectivity of a quarter-wave distributed Bragg reflector

Reported is a mathematical analysis and derivation of a formula for the change of reflectivity of a quarter-wave distributed Bragg reflector (DBR) owing to weak absorption in the mirror layers. From the analysis, the individual contribution of each absorptive mirror layer of a perturbed DBR to the reduction of its reflectivity can be determined. In the limit of small loss, the analytical expression provides a very good estimate of change in reflectivity with absorption perturbation present in any single component layer or an arbitrary combination of component layers of the DBR.

One and two component adsorption layers of n-hexane and benzene on graphite studied by2H NMR spectroscopy

Deuteron (2H) nuclear magnetic resonance (NMR) spectra were measured at temperatures between 300 and 90 K for n-hexane (C6D14), benzene (C6D6), and a mixture of n-hexane and benzene (C6D14/C6H6 and C6H14/C6D6) adsorbed on the graphitized carbon black Carbopack B. The amounts adsorbed correspond to one monolayer coverage of each substance for both the single and the two-component adsorption. The single component layers each undergo a two-dimensional (2D) fluid/solid phase transition spread over a 30–40 K interval centred at about the transition temperatures reported from diffraction studies. The surface diffusion coefficients in the 2D fluid regime are reported. On cooling to temperatures of about 200 to 160 K, three-dimensional benzene crystallites are formed leaving the n-hexane component in the one monolayer 2D fluid state. On further cooling, the n-hexane layer undergoes a 2D fluid/solid phase transition analogous to the corresponding one-component case.