Xerogel Films Research Articles

An electrochemical investigation on (MoO3+PVP+PVA) nanobelts for lithium batteries

Molybdenum trioxide (MoO3) xerogel films modified with poly(vinyl alcohol)+poly(vinyl pyrrolidone) (PVP+PVA) polyblends were obtained by ion-exchange method with sol-gel technique. Investigations were conducted using X-ray “diffractometry”, Fourier transform infrared spectroscopy, and cyclic voltammetry. The results show that the H atoms in polyblend are H-bonded with the O atoms in the Mo=O bonds of MoO3 xerogel, which effectively shield the electrostatic interaction between MoO3 interlayer and Li+ ions when MoO3 xerogel is modified by the intercalation of (PVP+PVA). The reversibility of the insertion/extraction of Li+ ions is greatly improved by the modification with polyblend of MoO3 nanocomposite films. MoO3 and (PVP+PVA) x MoO3 (x = 0, 0.5) nanobelts were obtained by a simple hydrothermal process from MoO3 sol. The electrochemical cells with configuration Li/(LiPF6+EC+DMC)/MoO3 modified by (PVP+PVA) were fabricated and their discharge profiles studied.

GeO 2 based high k dielectric material synthesized by sol–gel process

Recently, there has been lot of research on new high dielectric constant (high k) materials for use in future generations of ultra-large scale integrated circuits (ULSI). There are number of requirements for the new high k materials, such as high dielectric constant, thermal stability (400 °C or higher), high mechanical strength, and good adhesion to neighboring layers. Keeping in view the properties required for the replacement of existing SiO 2 dielectrics, new high k dielectric material based on GeO 2 has been synthesized. Polycrystalline GeO 2 thin films have been deposited by simple, and cost effective sol–gel spin coating process. The obtained xerogel films of germanium oxide have been annealed at 400 °C, 600 °C and 800 °C for 3 h in argon atmosphere. Elemental composition, morphology, and phase analysis have been measured by employing X-ray photoelectron spectroscopy, scanning electron microscopy, and X-ray diffraction techniques, respectively. The formation of the hexagonal GeO 2 phase at and above 400 °C has been reported. The composition of the annealed films have been measured and found to be 68 at.% of O, 32 at.% of Ge for GeO 2, which are close to the stoichiometry of the GeO 2.

Modification of chemical performance of dopants in xerogel films with entrapped ionic liquid

The effect of ionic liquid (IL), 1-butyl-3-methylimidazolium chloride [C4mim][Cl], entrapment on the properties of the xerogel films is described. This has been investigated by evaluation of the behavior of sulfonephthalein pH indicators entrapped in a xerogel matrix formed by tetraethoxysilane (TEOS) and vinyltriethoxysilane (VTEOS) with co-entrapped ionic liquid. We report that co-doping of the ionic liquid with pH indicators within the xerogel matrix significantly modifies the performance of primary dopants such as acidic constants and pH indicating ranges but the spectral intensity depends on the structure of the indicator. Increase in pH indicating ranges in the presence of ionic liquid can be advantageously used for designing pH optodes with a wider determination range. IL–xerogel modified films showed increased wettability, hydrophilicity, reduced gel shrinkage and faster response times compared to the unmodified silica matrix. The reason for such modification is explained mainly based upon changes in the environment of the indicator caused by an increase in hydrophilicity in the presence of IL as well as ionic interactions between the indicator and IL. The long term stability of the xerogel films was investigated over at least fifteen months.

Determination of Young's modulus and yield stress of porous low-k materials by nanoindentation

In the present study, the concept of the ‘effectively shaped indenter’ was used to analyse nanoindentation data of rather soft films on hard substrates. This approach was introduced for monolithic materials by Pharr and co-workers some years ago [G.M. Pharr, A. Bolshakov: J. Mater. Res. 17 (2002) 2660, A. Bolshakov, W.C. Oliver, G.M. Pharr, MRS Symp. Proc 356 (1995) 675]. Substrate to layer moduli ratios range from nearly 60 to 160. With such soft and brittle materials (Young's modulus nearly 3 GPa or smaller, yield strength around 100 MPa), no completely elastic measurements can be performed even at low loads. Hence, an established method for the determination of yield stresses by means of nanoindentation, namely that of loading-partial-unloading [N. Schwarzer: ASME J. Tribology 122 (2000) 672, T. Chudoba, N. Schwarzer, F. Richter: Thin Solid Films 355–356 (1999) 284, T. Chudoba, N. Schwarzer, F. Richter: Surf. Coat. Technol. 127 (2000) 9] was not applicable. However, the ‘effectively shaped indenter concept’ allows one to separate the elastic stresses due to the penetration from the residual stresses caused by the inelastic deformation, assuming that their influence on the elastic stress field is small. Thus, by using this approach critical yield stresses of soft porous materials have been obtained. Additionally, the Young's modulus of these materials has also been determined by means of laser-generated surface acoustic wave (LSAW) measurements and the Oliver and Pharr method. In the latter case, a special extrapolation method for the indentation modulus had to be applied to correct for the substrate influence. The results by the different methods are compared and their deviations are discussed. As there is no complete solution available for the correction of the substrate influence on Young's modulus of the film when plastic deformation occurs during indentation, the authors are searching for an approach to approximate the elastic properties of a soft film on a hard substrate. It seems that the determination of the Young's modulus of very soft films cannot be separated from the determination of the yield stress. As an example for a low-k material actually of interest, porous silica xerogel films on silicon with porosities of 38 up to 51 vol.% were investigated.

Nitric Oxide-Releasing Xerogel-Based Fiber-Optic pH Sensors

A xerogel-based optical pH sensor capable of releasing low levels of nitric oxide (NO) and measuring changes in solution pH is reported. Through simple dip-coating procedures, aminoalkoxysilane-based xerogel films modified with N-diazeniumdiolate NO donor precursors and the fluorescent pH indicator seminaphthorhodamine-1 carboxylate (SNARF-1) were sequentially deposited onto optical fibers. The resulting sensors were characterized by fast and linear response to pH throughout the physiological range (pH 7.0-7.8). Real-time chemiluminescence measurements confirmed that the presence of the overlying SNARF-1-containing TMOS layer did not have an inhibitory effect on N-diazeniumdiolate formation or NO release, and the NO-releasing coatings were capable of maintaining NO fluxes >0.4 pmol/cm(2) s up to 16 h. In vitro blood compatibility studies using porcine platelets confirmed the expected thromboresistivity of the NO-releasing xerogel coatings.

O2-Responsive Chemical Sensors Based on Hybrid Xerogels That Contain Fluorinated Precursors

We report the development and analytical figures of merit associated with several new O(2)-responsive sensor materials. These new sensing materials are formed by sequestering the luminophore tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) ([Ru(dpp)(3)](2+)) within hybrid xerogels that are composed of two of the following methoxysilanes: tetramethoxysilane, n-propyl-trimethoxysilane, 3,3,3-trifluoropropyl-trimethoxysilane, phenethyl-trimethoxysilane, and pentafluorophenylpropyl-trimethoxysilane. Steady-state and time-resolved luminescence measurements are used to investigate these hybrid xerogel-based sensor materials and elucidate the underlying reasons for the observed performance. The results show that many of the [Ru(dpp)(3)](2+)-doped composites form visually uniform, crack-free xerogel films that can be used to construct O(2) sensors that have linear calibration curves and excellent long-term stability. To the best of our knowledge, the [Ru(dpp)(3)](2+)-doped fluorinated hybrid xerogels also exhibit the highest O(2) sensitivity of any reported [Ru(dpp)(3)](2+)-based sensor platform.

Vibrational spectra of metals treated with allyltrimethoxysilane sol–gel and self-assembled monolayer of allytrichlorosilane

A sol–gel has been prepared by using allyltrimethoxysilane (ATMS) as precursor, ethanol as homogenizer as well as solvent, and hydrochloric acid as catalyst. The sol–gel was employed for the coating treatment of aluminum. Self-assembled monolayer (SAM) with allyltrichlorosilane (ATCS) is another method used for the metal surface treatment in the present work. The treated metal surfaces were characterized with reflection adsorption infrared spectra (RAIR). Detailed interpretation and vibrational assignment have been given to the collected IR spectra of the sol–gel, xerogel and surface films of ATMS and the SAM of ATCS on aluminum as well as pure silanes. A series of investigation of the UV exposure and temperature effects has been carried out. Results from the investigation indicate that the UV radiation exposure or the high temperature thermal treatment will induce a chemical process on the organosilica coated surfaces.

Self-Assembled π-Nanotapes as Donor Scaffolds for Selective and Thermally Gated Fluorescence Resonance Energy Transfer (FRET)

Self-assembled nanotapes of a few tailor-made oligo(p-phenylenevinylene)s (OPVs) have been prepared and used as supramolecular donor scaffold to study the fluorescence resonance energy transfer (FRET) to a suitable acceptor. In nonpolar solvents, FRET occurs with nearly 63-81% efficiency, exclusively from the self-assembled OPVs to entrapped Rhodamine B, resulting in the quenching of the donor emission with concomitant formation of the acceptor emission at 625 nm. The efficiency of FRET is considerably influenced by the ability of the OPVs to form the self-assembled aggregates and hence could be controlled by structural variation of the molecules, and polarity of the solvent. Most importantly, FRET could be controlled by temperature as a result of the thermally reversible self-assembly process. The FRET efficiency was significantly enhanced (ca. 90%) in a xerogel film of the OPV1 which is dispersed with relatively less amount of the acceptor (33 mol %), when compared to that of the aggregates in dodecane gel. FRET is not efficient in polar solvents due to weak self-organization of the chromophores. These results indicate that energy transfer occurs exclusively from the self-assembled donor and not directly from the individual donor molecules. The present study illustrates that the self-assembly of chromophores facilitates temperature and solvent controlled FRET within pi-conjugated nanostructures.

Structural, morphological, wettability and thermal resistance properties of hydro-oleophobic thin films prepared by a wet chemical process

The structural properties of fluorine containing polymer compounds make them highly attractive materials for hydro-oleophobic applications. However, most of these exhibit low surface energy and poor adhesion on the substrates. In the present investigation, crack free, smooth and uniform thin films of poly[4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole]-co-tetrafluoroethylene (TFD-co-TFE) with good adhesion have been deposited by wet chemical spin-coating technique on polished AISI 440C steel substrates. The as-deposited films (xerogel films) have been subjected to annealing for 1h at different temperatures ranging from 100 to 500°C in an argon atmosphere. The size growth of the nano-hemispheres increased from 8nm for xerogel film to 28nm for film annealed at 400°C. It was found that as the annealing temperature increased from 100 to 400°C, nano-hemisphere-like structures were formed, which in turn have shown increase in the water contact angle from 122° to 147° and oil (peanut) contact angle from 85° to 96°. No change in the water contact angle (122°) has been observed when the films deposited at room temperature were heated in air from 30 to 80°C as well as exposed to steam for 8 days for 8h/day indicating thermal stability of the film.

Preparation and electrochemical properties of vanadium pentoxide aerogel film derived at the ambient pressure

V 2O 5 aerogel materials has received much significant attention recently as it can be used as highly promising cathodic materials for Li-ion batteries. A novel kind of V 2O 5 aerogel materials, ambient dried V 2O 5 aerogel films were reported in this paper. The films were deposited by the dip-coating method and dipped into acetone and cyclohexane by turn to exchange the solvent in the films. Atomic force microscopy (AFM), X-ray diffraction topography (XRD), ellipsometry, and electrochemical measurements were employed to characterize the aerogel films. The porosity of the aerogel films is 56%, 16% higher than that of the xerogel films when dried at 120 °C. The aerogel films have the higher capacity, as well as better reversibility than those of the xerogel films. The improvement of the capacity can be ascribed to the increase of porosity as well as the pore diameters after the solvent exchange.

Effect of preparation conditions on the ordering of structural elements in vanadium pentoxide xerogels

Vanadium(V) oxide xerogels with an ordered laminar structure are of considerable interest in modern inorganic chemistry [1]. They combine the ease of intercalation of inorganic ions [2] or organic molecules [3] into the interlayer space and the presence of a transition metal ions with variable oxidation states, giving rise to nonlinear electrical and, in some cases, magnetic characteristics. Hybrid inorganic‐organic materials based on xerogels of vanadium(V) oxide and its nanotubular forms [4] attract considerable attention due to their unique physical and unusual physicochemical and rheological properties, which enable their use as cathode materials for lithium batteries [5], chemical sensors [6], electrochromic materials [7], and catalysts [8]. Vanadium(V) oxide xerogels can be prepared by hydrolysis of organic derivatives of vanadic acid, by polycondensation of vanadates in an aqueous solution in an acid medium, and by decomposition of peroxovanadium(V) compounds upon dissolution of the crystalline oxide in hydrogen peroxide [1, 9, 11]. The mechanisms of these processes are essentially different; therefore, it is important to elucidate the structural features of the xerogels as a function of the preparation method. Small-angle X-ray scattering, which is a standard method for measuring the kinetics of gel condensation in solutions [10], can also be used rather efficiently to study the structural features of xerogels. This study reveals the correlation between the chemical prehistory and the structural organization of samples obtained. Complex analysis of small-angle X-ray scattering (SAXS) patterns of xerogel films synthesized by different methods was carried out for the first time and possible models for description of their structure were considered. Colloid solutions of vanadium(V) oxide for the formation of xerogel films were prepared by three procedures (table). According to method A, analytical grade crystalline V 2 O 5 (0.5 g) was dissolved in 15% H 2 O 2 (30 mL) by slow addition of V 2 O 5 powder to the hydrogen peroxide solution [11]. After the oxygen evolution ceased, the solution became yellow. Heating the solution to ~40°C gave a dark red solution, which was kept under ambient conditions for 7 days until a xerogel film formed. According to method B, the gel was obtained by hydrolysis of tert -butyl metavanadate VO(OC(CH 3 ) 3 ) 3 . The ester was synthesized [11] by refluxing a mixture of calcined vanadium(V) oxide with excess tert -butyl alcohol in the presence of a desiccant (silica gel) for 7 h. The resulting mixture was separated by distillation at 81°C . Hydrolysis was carried out by mixing the ester with an equal volume of water (an excess) for the preparation of bulk samples or under ambient conditions. In method C, polycondensation of V took place in an aqueous solution of sodium vanadate on acidification. A colloid solution of V 2 O 5 · n H 2 O was obtained by

Luminescence Quenching of Eu(III) Carboxylates by Cu(II) in a Composite Polymer Xerogel Film†

Three Eu(III) luminescent compounds were separately entrapped in a xerogel porous silica matrix and finely ground particles of it were deposited on a glass support with polyvinylacetate (PVAc) as a binder to build a thin film sensor. These 3 devices were immersed in aqueous solutions of Cu(II) and the content of this metal was evaluated by emission-quenching experiments. The sensor containing the highly luminescent antenna chelate of diethylenetriaminepentaacetic acid (dtpa) sensitized with Coumarin120 rendered the largest Stern-Volmer constant (K(SV) = 1.49 x 10(4) M(-1)), showing no leaching of the Eu(III) complex to the aqueous solution and a reproducible value of the luminescence ratio between water and Cu(II) solution. The in situ sensor we developed can measure the concentration of Cu(II) in aqueous media down to the ppm level by emission-quenching experiments. This methodology permits a simple calibration of the sensor and an easy to use reusable device.

Photoluminescence properties of Er3+-doped Al2O3 film synthesized from Er-ion-implanted γ-AlOOH xerogel

The Er3+-doped Al2O3 films were prepared by sintering Er-ion-implanted γ-AlOOH xerogel films on SiO2/Si(100) substrates. In a cycle, the γ-AlOOH xerogel films about 50 nm thick were dip-coated using aluminium isopropoxide-derived γ-AlOOH sols; the Er ions were then implanted into the γ-AlOOH xerogel films using an ion energy of 45 keV with different doses of 5×1014 to 1×1016 ions cm−2. Er3+-doped Al2O3 films were formed after 1, 2, and 4 cycles of dip-coating and implantation at different sintering temperatures of 800–1200 °C. The photoluminescence (PL) spectra were observed with a main peak at 1.533 μm and a side peak at 1.549 μm for all the Er3+-doped Al2O3 films. The intensity of PL peak of the Er3+-doped Al2O3 film obtained after 4 cycles with 5×1015 ions cm−2 dose at every cycle and sintered at 900 °C for 5 h, increased by about 10 and 3 times compared with that of the films obtained after 1 and 2 cycles. At the same sintering temperature of 900 °C, the intensity of PL peak of the Er3+-doped Al2O3 films first increased with the increase of dose from 5×1014 to 5×1015 ions cm−2 at every cycle, and then a saturation tendency was observed when the dose further was increased to 1×1016 ions cm−2. For the samples using 5×1015 ions cm−2 dose at every cycle, the PL intensity increased with the increase of sintering temperature from 800 to 1200 °C.

1.54μm photoluminescence from Er-doped sol–gel derived In2O3 films embedded in porous anodic alumina

Abstract Porous anodic alumina matrices covered with spin-on erbium-doped In 2 O 3 xerogel films have been synthesized and investigated by photoluminescence (PL) spectroscopy. At room temperature an emission at 1.54 μm associated with 4 I 13/2 → 4 I 15/2 transitions of Er 3+ ions has been observed for the excitation wavelength of 302 nm, i.e. above the band gap of In 2 O 3 host. The intensity of this emission increases about six times with the increasing of the annealing temperature from 600 to 1000 °C. An absence of Er-related emission peaks for the excitation wavelength beneath the absorption edge of In 2 O 3 xerogel (532 nm) suggest an energy transfer from the In 2 O 3 host to erbium-related luminescence centers. The role of thermal processing of sol–gel derived indium oxide film in the enhancement of the 1.54 μm light emission from Er 3+ ions is discussed.

A usable concept for the indentation of thin porous films

Abstract The paper deals with the application of Pharr's concept of the effectively shaped indenter as well as an extension of that concept – referred to as extrapolation method – on the determination of the yield strength of porous thin films. As an example, a 1066 nm thick porous SiO2 xerogel film having a porosity of about 50% and an average pore size in the range 3 – 4 nm was investigated. Three different spherical indenters with radii of 1.4, 3.11 and 110 µm were used in this investigation. Depending on the indenter radius and the applied load the physical nature of the sample deformation was different eaking the one or the other of the two methods more suitable for analysis. We found that the data received with the large indenter could be well analysed using Pharr's concept, while for the twg smaller indenters the extrapolation method had to be used. The yield strength values obtained with the two methods were in remarkable agreement 109 vs. 99 MPa).

Electrochemical properties of vanadium pentoxide xerogel films

Vanadium pentoxide xerogel (VXG) films were prepared by rapid quenching, then coin type 2016 size lithium rechargeable batteries were assembled and tested with the VXG film electrodes and lithium anodes. Electrochemical impedance spectroscopy (EIS) analysis result reveals the expected response for intercalation, except that there is almost no Warburg (diffusion) component. Analyses results of cyclic voltammetry (CV), constant discharge (CD) and discharge-charge(DC) indicate that the sample achieves a high initial discharge specific capacity of approximate 400 mA · h/g and a corresponding efficiency of 97 % in the voltage diapason of 1.5–4.0 V with a draining current of 60 mA/g. Its preservation ratio of capacity still keeps as high as 85 % even after 100 cycles. The good electrochemical performance indicates that VXG film material is a promising cathode for lithium rechargeable batteries.

Thermal annealing effects on vanadium pentoxide xerogel films

The effect of water molecules on the conductivity and electrochemical properties of vanadiumpentoxide xerogel was studied in connection with changes of morphology upon thermal annealing atdifferent temperatures. It was demonstrated that the conductivity was increased for the samples heated at150 o C and 270 o C compared to the vanadium pentoxide xerogel. It was also verified a stabilization ofelectrochemical processes of the insertion and de-insertion of lithium ions the structure of thermally annealedvanadium pentoxide.

Inhibition of implant-associated infections via nitric oxide release

The in vivo antibacterial activity of nitric oxide (NO)-releasing xerogel coatings was evaluated against an aggressive subcutaneous Staphylococcus aureus infection in a rat model. The NO-releasing implants were created by coating a medical-grade silicone elastomer with a sol–gel-derived (xerogel) film capable of storing NO. Four of the bare or xerogel-coated silicone materials were subcutaneously implanted into male rats. Ten rats were administered 10 μl of a 10 8 cfu ml −1 S. aureus colony directly into the subcutaneous pocket with the implant prior to wound closure. Infection was quantitatively and qualitatively evaluated after 8 d of implantation with microbiological and histological methods, respectively. A 82% reduction in the number of infected implants was achieved with the NO-releasing coating. Histology revealed that the capsule formation around infected bare silicone rubber controls was immunoactive and that a biofilm may have formed. Capsule formation in response to NO-releasing implants had greater vascularity in comparison with uninoculated or untreated controls. These results suggest that NO-releasing coatings may dramatically reduce the incidence of biomaterial-associated infection.

Electrochemical impedance spectra of V2O5 xerogel films with intercalation of lithium ion

Vanadium pentoxide xerogel films used for lithium rechargeable batteries were prepared from crystalline c-V2O5 by melt quenching method, then the electrochemical process of lithium intercalation into vanadium pentoxide xerogel films was simulated with an equivalent circuit model, which was derived from the mechanism of electrode reactions. Measured electrochemical impedance spectra at various electrode potentials were analyzed by using the complex non-linear least-squares fitting method. The results show that impedance spectra consist of 2 high-to-medium frequency depressed arcs and a low frequency straight line. The high frequency arc is attributed to the absorption reaction of lithium ions into the oxide film, the medium frequency arc is attributed to the charge transfer reaction at the vanadium oxide/electrolyte interface and the low frequency is characterized by a straight line with a phase angle of 45° corresponding to the diffusion of lithium ion through vanadium oxide phase. The experimental and calculated results are compared and discussed focusing on the electrochemical performance and the state of charge of the electrode. Moreover, the high consistence of the fitted values of the model to the experimental data indicates that this mathematical model does give a satisfying description of the intercalation process of vanadium pentoxide xerogel films.

Effects of Thermal Annealing on the Li+ Intercalation Properties of V2O5·nH2O Xerogel Films

V(2)O(5) x nH(2)O xerogel films with n = 1.6, 0.6, and 0.3 have been prepared from the sol-gel route by reacting V(2)O(5) with H(2)O(2) followed by drying under ambient conditions and thermal annealing at 110 and 250 degrees C, respectively. After dehydration, V(2)O(5) crystallizes at 300-330 degrees C, as revealed by thermal gravimetric analysis and X-ray diffraction. Electrochemical characterization demonstrated that V(2)O(5) x 0.3H(2)O film exhibits the best Li(+) intercalation performance, with an initial capacity of 275 mAh/g and a stabilized capacity of 185 mAh/g under a high current density of 100 microA/cm(2) after 50 cycles. Under a low current density of 10 microA/cm(2), the capacity of this film can reach 390 mAh/g. Such an enhanced electrochemical property by thermal treatment is ascribed to the reduced water content, the retained interlayer spacing, and the dominant amorphous phase in the film.