Boron-doped zinc oxide thin films prepared by sol-gel technique

Multilayer transparent conducting boron-doped zinc oxide films have been prepared on glass substrates by the sol gel dip coating process. Zinc acetate solutions of 0.4 M in isopropanol stabilized by diethanolamine and doped with boron tri-i-propoxide were used. Each layer was fired at 400–650^∘C in a conventional furnace for 30 min. Selected samples were vacuum annealed at 400–450^∘C for 1 h to improve their electrical properties. The electrical resistivity curve with doping shows a minimum around 0.8 at.%. Excess boron caused a drop of the carrier mobility without acting as donors. Post-deposition annealing sequence was crucial for dopant partial regeneration. Films with an average optical transmittance exceeding 90% can be achieved reproducibly.     

Synthesis of mesoporous SiO2 glass by a novel chemical method

A novel five-step method for fabricating mesoporous SiO₂ glass was described in this paper, which consists of: (1) formation of colloidal suspension of Zn(OH)₂, (2) synthesis of silica sol, (3) mixture of Zn(OH)₂ colloidal suspension and silica sol to form nano-ZnO embedded precursor glass, (4) annealing of the precursor glass, and (5) treating nano-ZnO embedded glass with HCl to obtain the mesoporous glass. The mesostructure of the glass was investigated by X-ray diffraction (XRD), field emission scanning electron microscope (SEM), and BET surface area analysis. The average pore size distribution is in the range of 3.7 nm, and the surface area is as high as 496.5 m²/g.     

Influence of Li<Superscript>+</Superscript> dopants on the properties of the ZnO piezoelectric films

ZnO piezoelectric films with the preferred 002-orientation were prepared by sol-gel method. The annealing temperature was 600^∘C and the resistivity of the ZnO film was 1 × 10⁶ Ω ⋅ cm. Li₂CO₃ and LiCl were added respectively into ZnO precursor as source of Li⁺-ion. The molar ratio of [Li⁺]/[Zn^{2 +}] was 0.05. It is observed that the annealing temperature for forming preferred 002-orientation of ZnO films decreases from 660 to 550^∘ C after Li₂CO₃ being doped. When Li₂CO₃ and LiCl are doped, the resistivity of ZnO films increases to 10⁸Ω ⋅ cm and 10⁹Ω ⋅ cm, respectively, with an annealing temperature of 550^∘ C. When annealing temperature is 600^∘ C, the resistivity of the ZnO film with LiCl dopant increases to 10⁷Ω cm. The influence mechanism of the two dopants on the properties of the ZnO films is analyzed.     

Hydrophobic properties and color effects of hybrid silica spin-coatings on cellulose matrix

A novel sol–gel derived organic–inorganic hybrid silica sol consisting of organic direct red dye 4BS and inorganic silica (SiO₂) is successfully synthesized by adding coupling agent γ-chloropropyltriethoxysilane (CPTS). Hybrid silica coatings are deposited on cellulose matrix surface via spin-coating approach to introduce effective hydrophobic and color properties. Compared to the dye hybrid silica sol (DHSS), the particle size of CPTS/dye hybrid silica sol (CDHSS) increases from 64.51 to 129.70 nm, while the surface tension reduces from 34.27 × 10⁻³ N m⁻¹ to 31.22 × 10⁻³ N m⁻¹. The hydrostatic pressure of the cellulose matrix coating with CDHSS is 4530.5 Pa, the contact angle is 131.48°, and the wetting time is ~150 min, which attributes to the alkyl chloride aliphatic chain and sharp micro-surface roughness of the hybrid coatings validated directly by AFM and SEM images. The K/S value (5.15) of the cellulose matrix coated with CPTS/dye hybrid silica (CMCCDHS) is 12.44% higher than that of the cellulose matrix coated with dye hybrid silica (CMCDHS), and increased by 30.38% relative to the control coated sample. The maximum absorption wavelengths of the matrixes treated with different processes are the same as the maximum absorption wavelength of the silica sols (510 nm).     

Influence of Zn doping on electrical and optical properties of multilayered tin oxide thin films

In this study, the electrical and optical properties of Zn doped tin oxide films prepared using sol-gel spin coating process have been investigated. The SnO² : Zn multi-coating films were deposited at optimum deposition conditions using a hydroalcoholic solution consisting of stannous chloride and zinc chloride. Films with Zn doping levels from 0–10 wt% in solution are developed. The results of electrical measurements indicate that the sheet resistance of the deposited films increases with increasing Zn doping concentration and several superimposed coatings are necessary to reach expected low sheet resistance. Films with three coatings show minimum sheet resistance of 1–479 kΩ/ in the case of undoped SnO₂ and 77 kΩ/ for 5 wt% Zn doped SnO₂ when coated on glass substrate. In the case of single layer SnO₂ film, absorption edge is 3.57 eV and when doped with Zn absorption edge shifts towards lower energies (longer wavelengths). The absorption edge lies in the range of 3.489-3.557 eV depending upon the Zn doping concentration. The direct and indirect transitions and their dependence on dopant concentration and number of coatings are presented.     

Poly(p-phenylene vinylene) light-emitting devices prepared via the precursor route onto indium tin oxide and fluorine-doped tin dioxide substrates

For the preparation of organic light-emitting devices (LEDs) an optically transparent and electrically conducting thin film is needed as anode. Usually, a glass substrate coated with indium tin oxide (ITO) is used. We show that ITO is unsuitable in the case of poly(p-phenylene vinylene) (PPV) prepared by the precursor route. We have found that a reaction in which hydrogen chloride is eliminated during the thermal conversion to PPV and the ITO takes place. Scanning electron microscopy investigations of the ITO-PPV interface demonstrates that indium chloride compounds, e.g., InCl3 crystals with dimensions up to 40 μm, are produced. Photoluminescence measurements reveal that the fluorescence efficiency is quenched by a factor of 2–23 in the case of ITO compared with PPV converted onto usual glass. In a second step we have investigated LEDs prepared from PPV in the ITO/PPV/Al configuration in order to obtain information about the process responsible for the degradation of these devices. We shall show that the formation of the above-mentioned indium chloride compounds is one possible degradation mechanism and is responsible for the relative short lifetimes of these LEDs. To overcome this problem we propose to use fluorine-doped tin dioxide (FTO) instead of ITO. Finally, we show the results obtained for LEDs in the FTO/PPV/Al configuration and compare them with ITO/PPV/Al devices. This revised version was published online in November 2006 with corrections to the Cover Date.     

Enhanced optical and hydrophilic properties of Si and Cd co-doped TiO<Subscript>2</Subscript> thin films

In this study, preparation of Si and Cd co doped (5 mol% Si and 5–20 mol% Cd) TiO₂ dip-coated thin films on glass substrates via sol–gel process have been investigated. The samples were characterized by X-ray diffraction (XRD) and Scanning electron microscopy analysis after heat treatments. XRD results suggested that adding dopants has a great effect on crystallinity and particle size of TiO₂. Titania rutile phase formation was inhibited by Si⁴⁺ and promoted by Cd²⁺ doping. But the effect of Cd doped appeared at high concentration. Accordingly, the thin films showed various water contact angles. The water contact angles changed from 69.0° to 9.6° by changing the content of Cd doped.     

New transparent conductive films: FTO coated ITO

New transparent conductive films, fluorine doped tin oxide (FTO) films coated on indium-tin-oxide (ITO) films, were developed. These transparent conductive films were prepared by the spray pyrolysis deposition method at a substrate temperature of 350 °C in ITO and 400 °C in FTO. For ITO deposition, an ethanol solution of indium(III) chloride, InCl₃·4H₂O, and tin(II) chloride, SnCl₂·2H₂O [Sn/(In+Sn), 5 at.%] was sprayed on a Corning #7059 glass substrate (100×100×1.1 mm³). After the deposition, FTO films were consecutively deposited for protecting oxidation of ITO films. FTO deposition was carried out by an ethanol solution of tin(IV) chloride, SnCl₄·5H₂O within the saturated water solution of NH₄F. These new transparent conductive films achieved the lowest resistivity of 1.4×10⁻⁴ Ω cm and the optical transmittance of more than 80% in the visible range of the spectrum. The electrical resistance of these new transparent conductive films increased by less than 10% even when exposed to high temperatures of 300-600 °C for 1 h in the air.     

Silver coated bioactive glass particles for wound healing applications

Bioactive glass particles (0.42SiO₂–0.15CaO–0.23Na₂O–0.20ZnO) of varying size (<90 μm and 425–850 μm) were synthesized and coated with silver (Ag) to produce Ag coated particles (PAg). These were compared against the uncoated analogous particles (Pcon.). Surface area analysis determined that Ag coating of the glass particles resulted in increased the surface area from 2.90 to 9.12 m²/g (90 μm) and 1.09–7.71 m²/g (425–850 μm). Scanning electron microscopy determined that the Ag coating remained at the surface and there was little diffusion through the bulk. Antibacterial (Escherichia coli—13 mm and Staphylococcus epidermidis—12 mm) and antifungal testing (Candida albicans—7.7 mm) determined that small Ag-coated glass particles exhibited the largest inhibition zones compared to uncoated particles. pH analysis determined an overall higher pH consider in the smaller particles, where after 24 h the large uncoated and Ag coated particles were 8.27 and 8.74 respectively, while the smaller uncoated and Ag coated particles attained pH values of 9.63 and 9.35 respectively.     

Synthesis and light-emitting properties of poly[9-(4′-tert-butyl-phenylenemethene)-fluoroene-co-9,9-dioctylfluorene]

A novel copolymer, poly[9-(4′-tert-butyl-phenylenemethene)-fluoroene-co-9,9-dioctylfluorene], has been synthesized through the Yamamoto coupling method. The copolymer has good solubility and thermal stability with a glass transition temperature at 85 °C. The PL spectrum of the copolymer shows a maximum emission peak at 530 nm. A polymer light-emitting diode (PLED) with the configuration ITO/PEDOT/copolymer/Ca/Al has been fabricated. The device emits green light with an emission peak at 540 nm. A maximum brightness of 603 cd/m² was achieved at a drive voltage of 24.3 V.     

Structural and electrical properties of perovskite ruthenate-based lead-free thick film resistors on alumina and LTCC

CaRuO₃ perovskite-based lead-free thick-film resistors (TFRs) were prepared on 96%-alumina and Low Temperature Co-fired Ceramic (LTCC) substrates. The microstructure evolution, possible interactions, and electrical properties of resistors were investigated. The hot and cold TCR values of all the resistors were measured in the temperature range (+20 to +120 ^∘C) and (+20 to −120 ^∘C), respectively. TFRs with 25% by vol. of CaRuO₃ on alumina exhibit a sheet resistance R_s = 5kΩ/sq. with hot and cold TCR of 225 and 470 ppm/^∘C respectively, whereas the same composition gives 1.2 kΩ/sq., 16.5 kΩ/sq. and 0.7 kΩ/sq. for co-fired, post-fired resistors on LTCC and buried resistors, respectively. The hot (HTCR) and cold (CTCR) values were evaluated; HTCR = 190 ppm/^∘C and CTCR = 314 ppm/^∘C were found for co-fired structures; HTCR = 216 ppm/^∘C and CTCR = 205 ppm/^∘C for post-fired samples and HTCR = 520 ppm/^∘C and CTCR = 350 ppm/^∘C for buried in LTCC structures.     

Fabrication of silica glass containing yellow oxynitride phosphor by the sol–gel process

Abstract

We have prepared silica glass by the sol–gel method and studied its ability to disperse the Ca-α-SiAlON:Eu²⁺ phosphor for application in white light emitting diodes (LEDs). The emission color generated by irradiating doped glass with a blue LED at 450 nm depended on the concentration of SiAlON and the glass thickness, resulting in nearly white light. The luminescence efficiency of 1-mm-thick glass depended on the SiAlON concentration, and was highest at 4 wt% SiAlON.     

Characterization of spray deposited CoWO<Subscript>4</Subscript> thin films for photovoltaic electrochemical studies

Preparation of Cobalt tungstate (CoWO₄) thin film by spray pyrolysis with ammonical solution as a precursor is presented. The phase and surface morphology characterizations have been carried out by XRD and SEM analysis. The study of optical absorption spectrum in the wavelength range 350 – 850 nm shows direct as well as indirect optical transitions in the thin film material. The d. c. electrical conductivity measurements in the temperature range 310–500 K indicate semiconducting behavior of the thin film. The thin films deposited on fluorine doped tin oxide (FTO) coated conducting glass substrates were used as a photoanode in photovoltaic electrochemical (PVEC) cell with configuration: CoWO₄ | Ce⁴⁺, Ce³⁺ | Pt; 0.1 M in 0.1 N H₂SO₄. The PVEC characterization reveals the fill factor and power conversion efficiency to be 0.36 and 0.62%, respectively. The flat band potential is found to be −0.18 V (SCE).     

Reutilization of waste inert glass from the disposal of polluted dredging spoils by the obtainment of ceramic products for tiles applications

The vitrification treatment has been successfully exploited as a solution for the disposal of polluted dredging spoils from the industrial area close to the Venice Lagoon. The addition of 20% by wt. of glass cullet to the calcined sediments in the vitrification batch provides a suitable chemical composition for the production of an inert glass, despite the compositional variations of the sediments. The obtained waste glass, after being finely ground, has been employed (i) as a raw material for the manufacture of sintered glass-ceramics, by cold pressing and single-step sintering at about 940^∘C, and (ii) as sintering additive (the maximum addition being 10% by wt.) for the manufacture of traditional red single firing ceramic tiles, with a maximum firing temperature of 1186^∘C. Both applications have proved to be promising: in the first case, the sintered glass ceramic product exhibits notable mechanical properties (bending strength > 130 MPa, HV ≈ 6.5 GPa); in the second case, the addition of waste glass does not modify substantially the investigated physical and mechanical properties of the traditional product (water absorption, linear shrinkage, bending strength, planarity).     

Down-shifting in Ce3+–Tb3+ co-doped SiO2–LaF3 nano-glass–ceramics for photon conversion in solar cells

95SiO₂–5LaF₃ sol–gel derived nano-glass–ceramics single doped with Ce³⁺ or Tb³⁺ and co-doped with Ce³⁺–Tb³⁺ were synthesized by thermal treatment of precursor glasses. Precipitation of LaF₃ nanocrystals during ceramming process was confirmed by X-ray diffraction with mean size ranging from 12 to 15 nm. An exhaustive spectroscopic analysis has been carried out. As a result, it was found that the green emission of Tb³⁺ ions was greatly enhanced through down shifting process, due to efficient energy transfer from Ce³⁺ to Tb³⁺ ions in the glass–ceramics, which is favored by the reduction of the interionic distances when the dopant ions are partitioned into LaF₃ nanocrystals. These results suggest the use of these materials to improve the efficiency of solar cells.     

Organic light emitting devices with doped electron transport and hole blocking layers

This study reports on heterostructure OLEDs with n-type molecularly doped electron transport layer and hole blocking layer. The influence of doping on the operating voltage and on light emission performances was investigated. The n-type doping molecule is 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) dispersed into either an 8-(hydroquinoline) aluminum (Alq) electron transport layer (ETL) or a 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (Bathocuproine BCP) hole blocking layer (HBL). The typical device structure is glass substrate/indium tin oxide/PEDOT/TPD–F4-TCNQ/Alq–DCM/BCP/Alq/Mg–Ag where Poly(3,4)ethylenedioxythiophene/Polystyrenesulphonate (PEDOT/PSS) is a hole injecting layer, TPD–F4-TCNQ is a hole transport layer (HTL) made of N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) doped with 2 wt.% of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4-TCNQ) and Alq–DCM is the emitting layer (EML) made of Alq doped with 2 wt.% of 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) orange dye. The modified cathode consists in a combination of a BCP HBL and an Alq ETL where BCP or/and Alq were doped with PBD. Lowest operating voltage (3 V for a luminance of 10 Cd/m²) and brightest devices (6000 Cd/m²) were obtained with a hole blocking bilayer made of BCP doped with 28 wt.% deposited onto an undoped BCP (each one being 5 nm thick). Adding an undoped Alq layer improved the device current efficiency (4 Cd/A) but is detrimental to the operating voltage (6 V for a luminance of 10 Cd/m²). In the absence of real n-type doping with organic molecules, our results point out that the design of molecular doped injection layer at the cathode will need for a compromise between high luminance and efficiency on one hand and low operating voltage on the other hand.     

Effect of pH, temperature and Cl− concentration on electrochemical behavior of NiTi shape memory alloy in artificial saliva

The cooperation of pH, temperature and Cl⁻ concentration on electrochemical behavior of NiTi shape memory alloy in artificial saliva was studied using orthogonal test method. The results showed that the pitting potential for NiTi in artificial saliva decreased at low and high pH; at 25^∘C, the pitting potential was the lowest compared to those at 10^∘C, 37^∘C and 50^∘C; when the Cl⁻ concentration was not less than 0.05 mol/L the pitting potential decreased with the increase of Cl⁻ concentration. The free corrosion potential of austenitic NiTi was lower than that of mixture of austenite and martensite.     

Dielectric response of an epoxy resin when exposed to high temperatures

Epoxy resins are popular insulators that are used for the encapsulation of integrated circuits and for the fabrication of printed circuits boards. As such, it is important to evaluate their reliability when exposed to an environmental stress. This work reports on the influence of a high-temperature thermal stress (400 ^∘C) on the dielectric properties of an acid-anhydride cured DGEBA resin. Gold/epoxy/gold capacitors are used as a test structure. The studied electrical properties are the dielectric constant and the loss factor in the 10⁻¹ Hz100 kHz range, and the DC resistivity. It is found that cycling the sample for several minutes to temperatures as high as 400 ^∘C has almost no effect on its dielectric properties. It is believed that the gold electrodes prevent the thermo-oxidative degradation of the underlying epoxy. Electrical properties are also studied at high temperatures in the 200 ^∘C-400 ^∘C range. Above 200 ^∘C the DC resistivity is considerably increased, as well as the loss in the low-frequency part of the spectrum (< 1kHz). At high frequencies (> 1kHz) the epoxy maintains good dielectric performances up to 400 ^∘C.     

Electroluminescence from ZnS:MnCl2 thin film devices co-doped with MgF2 or MgS

 We report a red shift in the light emission from thin film electroluminescent devices consisting of ZnS co-doped with MgF₂ and MnCl₂ as the phosphor semiconductors and Ta₂O₅ films as insulators. The electroluminescence spectrum shows two peaks at ∼615 nm and at ∼670 nm. The devices have a threshold of about 110 V under 50 Hz a.c driving voltage and show brightness over ∼100 cd/m² at 160 V. The devices are compared with MgS co-doped devices which show green shifted light emission. Received: 28 August 1998 / Reviewed and accepted: 28 September 1998     

Thermal stability and concentration effect in erbium-doped lead fluoroborate glasses

Thermal and optical properties of lead fluoroborate glasses containing Er ions have been investigated. Glass properties of multicomponent oxyfluoride systems have been examined in two ways: with various (a) activator (Er ions) and (b) PbF₂ concentrations. Thermal stability parameter Δ T linearly decreases from 162^∘C to 138^∘C, when PbF₂ content increases from 9 to 72 wt% in glass composition. Non-linear dependence of Δ T stability parameter is observed as a function of activator concentration. The optimal highest values of Δ T factor are obtained for Er concentration in range of 0.5 ÷ 1.5 wt%. Quite intense and long-lived near-infrared photoluminescence of erbium ions at 1.55 μm related to the main ⁴I_13/2–⁴I_15/2 laser transition has been detected in lead fluoroborate glass. Photoluminescence intensity and the ⁴I_13/2 lifetime considerably increase with increasing of PbF₂ concentration. The opposite effect is observed with increasing of activator concentration, which is due to the luminescence quenching. Thus, the ⁴I_13/2 lifetime decreases and this behavior is consistent with non-radiative processes related to the Er–Er interaction increasing.