Thickness Of TiO2 Layer Research Articles

Thickness dependence of device parameters in solid state dye sensitized solar cells

A solid-state dye-sensitized solar cell (SDSC) was fabricated with a very thin (~ 650 nm) mesoporous TiO2 electrode and a donor-antenna (D-A) dye by using 2,2',7,7'- tetrakis - (N,N-di-p-methoxyphenyl-amine) 9,9'- spirobifluorene (Spiro OMeTAD) as hole conductor. A highly transparent thin electrode sensitized with D-A dye showed a short circuit current (Isc) of 4.10mA/cm2, an open circuit voltage (Voc) of 782 mV and an efficiency of 1.79 % at an illumination intensity of 100 mW/cm2 (1 sun, AM 1.5G). TiCl4 treatment of mesoporous TiO2 layer resulted in Isc of 6.18 mA/cm2, Voc of 737 mV and an efficiency of 2.12% at the same illumination intensity. This investigation demonstrates the possibility of fabrication of SDSC by way of using a very thin and transparent TiO2 electrode together with a high molar extinction coefficient D-A dye, and the effect of TiO2 layer thickness on solid-state solar cell performances is discussed. Keywords: Donor - antenna dye, sensitization, solid-state dyesensitized solar cell, TiO2, transparent electrode. Doi: 10.4038/jnsfsr.v39i1.2921 J.Natn.Sci.Foundation Sri Lanka 2011 39 (1): 35-42

Urea Effect on Strong Electrorheological Response of Novel Core-Shell Nanoparticles

Electrorheological (ER) fluids are regarded as smart materials with potential for application in various industries because of the controllable viscosity, the reversibly and fast response. In this paper, core-shell structured Ni/Ti/Urea nanoparticles, as an ER material, were prepared by a sol-gel method. TEM, XRD and FT-IR spectra demonstrated that the Ni nanoparticles have been homogeneously coated with a 2 nm thick layer of TiO2 containing polar groups. The polar groups were caused by the introduction of urea. The ER effect of the fluids of Ni/Ti/Urea particles in silicone oil was investigated under a DC electric field. It is found that the ER fluids of the urea-doped Ni/TiO2/Urea particles have a high ER activity, which is 10 times that of the particles containing no urea. The polar groups in the particles are the intrinsic reasons for the enhancement of electrorheological effect.

Micro-arc oxidation of Ti6Al4V and Ti6Al7Nb alloys for biomedical applications

In the present study, the in-vitro biological responses of two competitive titanium alloys (Ti6Al4V and Ti6Al7Nb) were investigated after modifying their surfaces by the micro-arc oxidation (MAO) process conducted in a (CH3COO)2Ca·H2O and Na3PO4 containing electrolyte under identical electrical parameters and exposure time. After the process, the surfaces of the alloys were covered with a thick (approx. 10μm) TiO2 layer exhibiting different characteristics. The oxide layer of the Ti6Al4V alloy was porous and contained hydroxyapatite precipitates whereas the oxide layer of the Ti6Al7Nb alloy showed a more grainy appearance and contained calcium titanate precipitates. Simulated body fluid (SBF) and cell culture tests were conducted to compare the biological performance of the alloys. Even though oxidized alloys exhibited somewhat similar response in SBF tests, the number of SAOS-2 cells attached to the oxide layer of the Ti6Al4V alloy was greater than that of the Ti6Al7Nb alloy.

Characterization of Dye-Sensitized Solar Cell with Different Nanoparticle sizes

ABSTRACTThe Dye-sensitized Solar Cell (DSSC) has been regarded as the next-generation solar cell because of its simple and low cost fabrication process. The experiments for optimizing the cell efficiency were carried out in this work include varying the TiO2 layer thickness on the working electrode and determining the most favorable nanoparticle size in the TiO2 paste. The TiO2 electrode or working electrode was fabricated using screen printing technique with the Coatema tool with thicknesses ranging from ~20 to 66 μm. It was observed that both open circuit voltage and short circuit current were found to have measurable dependence on the TiO2 layer thickness. The open circuit voltage changed from 0.77 to 0.82 V and correspondingly the short circuit current also varied from ~19 to 23 mA/cm2 depending on the TiO2 layer thickness. Additionally, the cell with 40 μm TiO2 thickness showed 9.06% photo conversion efficiency compared to 6.4% and 8.5% efficiency obtained for the cells with 20 μm and 66 μm TiO2 thicknesses respectively. The second part of the experiment was conducted using three different nanoparticle sizes of 13 nm, 20 nm and 37nm in the TiO2 layer to identify optimum nanoparticle size by maintaining the TiO2 film thickness at 40 μm. The cell with 20 nm size nanoparticle, in combination with 40 μm TiO2 thickness showed 11.2% efficiency that is in par or slightly better than the efficiency value reported for the DSSC in the literature as of now. The work described in this paper showed best possible values for the TiO2 layer thickness and nanoparticle size in the TiO2 for obtaining improved cell efficiency of 11.2%.

Anodic Deposition of Ultrathin TiO2 Film with Blocking Layer and Anchoring Layer for Dye-Sensitized Solar Cells

Ultrathin anatase TiO2 films were coated on the fluorine-doped tin oxide (FTO) glass by anodic electrodeposition followed by annealing at 450°C before the formation of thick TiO2 layer. The electrodeposited TiO2 films were more compact structure near the FTO surface (inner layer), and became less compact further away from the surface (outer layer). The outer layer of film deposited at 10 μA cm−2 was composed of granular nanoparticles and that of film deposited at 5 μA cm−2 was composed of short nanorods. The inner compact layer could act as a blocking layer to suppress the charge recombination. The outer loose layer could provide an anchoring layer for a better electrical contact between FTO and thick TiO2 layer. The photoelectron conversion efficiency (η) of dye-sensitized solar cell (DSC) using TiO2-coated FTO deposited at 10 μA cm−2 was 6.9%, which is higher than that of DSC using bare FTO (6.5%). The outer anchoring layer composed of short nanorods deposited at 5 μA cm−2 could significantly reduce the interfacial contact resistance between FTO and main TiO2 layer. Therefore, η of DSC was further increased to 7.1% after employing the TiO2-coated FTO deposited at 5 μA cm−2.

Synchrotron X-ray Photoemission Study of NiTi Surface Oxidation with Hyperthermal Oxygen Molecular Beam

We report results of our detailed studies on the initial oxidation process of NiTi with a 2 eV hyperthermal oxygen molecular beam (HOMB) and thermal O2 in the backfilling. The oxidation processes are monitored by X-ray photoemission spectroscopy measurements in conjunction with synchrotron radiation. In the oxide formation process at higher O coverage, HOMB has the advantage in the dissociation process of O2 molecule and can grow TiO2 layers with the underlying TiOx-rich and/or Ni-rich layers even at room temperature. Surface annealing enhances the diffusion atoms and as a result, the efficiency of Ti oxide formation. We succeeded in fabricating thick Ni-free TiO2 layer, possibly blue colored rutile TiO2, combining HOMB and surface annealing.

Oxidation of TiNi surface with hyperthermal oxygen molecular beams

We report results of our detailed studies on the initial oxidation process of TiNi with a 2eV hyperthermal oxygen molecular beam (HOMB) and thermal O2 in the backfilling. The oxidation processes are monitored by X-ray photoemission spectroscopy (XPS) measurements in conjunction with synchrotron radiation (SR). In the early stage of oxidation, the precursor mediated dissociative adsorption is the dominant reaction mechanism. In the oxide formation process at higher O coverage, HOMB has the advantage in the dissociation process of O2 molecule and can grow TiO2 layers with the underlying TiOx-rich and/or Ni-rich layers. We succeeded in fabricating thick Ni-free TiO2 layer, possibly blue colored rutile TiO2, combining HOMB and surface annealing.

Perylene imide dyes for solid-state dye-sensitized solar cells: Spectroscopy, energy levels and photovoltaic performance

We report the solid-state dye-sensitized solar cell performances of perylene imide using nanoporous TiO2 electrodes. Solid-state dye-sensitized solar cells were fabricated using the organic hole-transporting medium (HTM) 2,2′7,7′-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9′-spirobifluorene (spiro-OMeTAD). The experimental ELUMO levels of perylene imide dyes are found to be 3.75 and 3.77eV, respectively. Therefore, perylene imide dyes can inject electrons to the conduction band of titanium dioxide in organic dye-sensitized solar cells. TiO2 thin films of about 2μm in thicknesses were prepared. Both preparation and thickness of the compact TiO2 layer were optimized using spray pyrolysis. The studies revealed that an optimum film thickness of 130–150nm of compact TiO2 yielded the best rectifying behavior and SDSC performance. In this work, our goal was to investigate the performance of perylene sensitizers in connection with spiro-OMeTAD hole transport material. Short-circuit current densities, open circuit voltages and overall conversion efficiencies of the solar cell with 2,2′7,7′-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9′-spirobifluorene(spiro-OMeTAD) as a hole conductor and perylene imide as sensitizer on mesoporous TiO2 were investigated.

Characteristics of Pt/BiFeO3/TiO2/Si capacitors with TiO2 layer formed by liquid-delivery metal organic chemical vapor deposition

Metal-ferroelectric-insulator-semiconductor (MFIS) capacitors with 250 nm thick BiFeO3 (BFO) ferroelectric film and 150 nm thick TiO2 layer on silicon substrate have been fabricated and characterized. TiO2 was deposited on Si substrate by liquid delivery metal-organic chemical vapor deposition (LD-MOCVD) process. The microstructure and the electrical properties of the Pt/BFO/TiO2/Si capacitors were studied. TiO2 demonstrates excellent insulating properties on Si substrate. The MFIS structure showed clockwise capacitance-voltage hysteresis loops due to the ferroelectric polarization of BFO. The maximum memory window is 3.51 V. When sweeping voltages decreased from ±14 to ±6 V, the memory window width decreased from 3.51 to 1.11 V. The leakage current of the film was of the order of 10−8 A/cm2 at an applied voltage of 4 V.

Design of self-cleaning TiO2 coating on clay roofing tiles

The phenomenon of heterogeneous photocatalysis takes place in the degradation process of many organic contaminants on solid surfaces. Photocatalysis is based on the excitation of the semiconductor by irradiation with supraband gap photons and the migration of electron-hole pairs to the surface of the photocatalysts, leading to the reaction of the holes with adsorbed H2O and OH− to form hydroxyl radicals. Due to the stability and photosensitivity of TiO2 semiconductors, this system is well studied and is of great interest from an ecological and industrial point of view for use in the field of building materials. Clay roofing tiles, due to their long-term exploitation, are subject to physical, chemical and biological degradation that leads to deterioration. Ceramic systems have a high percentage of total porosity and considering their non-tolerance of organic coating, the use of surface active materials (SAM) that induce porosity in TiO2 coatings is of vital significance. Photocatalytic coatings applied on clay roofing tiles under industrial conditions were designed by varying the quantity of TiO2 (mass/cm2) on the tile surface (thin and thick TiO2 layer). The positive changes in specific surface area and mesopore structure of the designed coatings were made by the addition of PEG 600 as a surface active material. It was shown that a thin photocatalytic layer (0.399 mg suspension/cm2 tile surface), applied onto ceramic tiles under industrial conditions, had better photocatalytic activity in methylene blue decomposition, hydrophilicity and antimicrobial activity than a thick photocatalytic coating (0.885 mg suspension/cm2).

SELF-CLEANING GLASS BASED ON ACID-TREATED TiO<sub>2</sub> FILMS WITH PALMITIC ACID AS MODEL POLLUTANT

Preparation and characterization of self-cleaning glass based on acid-treated TiO2 films as well as evaluation on their self-cleaning properties have been carried out. Palmitic acid photodegradation was used as model pollutant. Acid-treated TiO2 powders were deposited on glass surface by using spraying technique. The XRD results showed that acid-treated TiO2 film exhibited decreased anatase crystalline size. The corresponding SEM images showed porous surface morphology. Layer densification was observed as the film thickness increased. TiO2 photocatalytic activity increased as the length of UV radiation increased. Best results were obtained at experimental condition of 35 hours UV radiation time. It is also observed that the thickness of TiO2 layers influenced the efficiency of palmitic acid photodegradation. The film with 1.661 µm thick TiO2 layers and 6.933 mg weight (0.7164 mg/cm2) could degrade 97.54 % mg palmitic acid/cm2 thin film. Keywords: TiO2 films, acid treatment, self-cleaning glass

WE‐E‐204B‐04: TiO2 Nanotube Field Emitter as a New Cold Cathode for X‐Ray Generation

Introduction/Purpose: Titanium dioxide (TiO2) nanotubes (NTs) grown by anodization are proposed as a new candidate for a cold cathode X‐ray source. This kind of oxide nanotube can potentially be an excellent choice to overcome the major limitations that exist in relation to carbon nanotubes (CNT). Being an oxide, TiO2 is not affected by residual oxygen present in the tube in contrast to CNTs, which can severely degrade from exposure to oxygen. Second, since TiO2 nanotubes are grown on a titanium (Ti) sheet as the latter oxidizes, a good electrical contact between TiO2 nanotube film and conductive Ti substrate is guaranteed. On the other hand, poor electrical contact between CNT and deposited substrate causes heating effects. The goal of this work was to simulate the effect of the NT parameters on field TiO2 NT emission properties. Methods: The field emission from two sources was considered: 1) from the top of NTs, and 2) the bottom of the NTs which serve as a thin semiconductor layer. Numerical calculations were performed to study the dependence of field emission on NT parameters for each emission mechanism. The calculations were performed in Matlab. Results: It is shown that the current decreased significantly with an increase of NT diameter, while it increased with the height of NTs. The rate of current increase with diameter is stronger for smaller diameter NTs. Regarding field emission from the bottom of the TiO2 layer, this current is strongly dependent on the TiO2 layer thickness and decreases as the latter increases. This current linearly increases with an increase of TiO2 electron charge carrier concentration. Conclusions: Effect of TiO2 NT geometrical and physical parameters on field emission can be simulated and the results can be used as a guide for design purposes.

In-situ Coating Of MWNTs With Solgel TiO2 Nanoparticles

Multi-walled carbon nanotubes (MWNTs) were in-situ coated with anatase TiO2 via sol-gel process followed by annealing of the composites using infrared (IR) lamp. SEM results showed that MWNTs were coated with 15-45 nm thick TiO2 layer depending on the composite ratios. Based on the XRD results, MWNTs were found to show heterogeneous nucleation for anatase TiO2 and promote the formation of larger anatase TiO2 crystalline particles with higher crystalline degree. The UV-Vis- NIR characterization indicated the MWNTs also enhanced the sensitivity of TiO2 matrix for both UV and visible light, and the bond edge absorption position of the TiO2 composites shifted toward higher wavelengths with the decrease of MWNTs content. The method could be utilized to fabricate MWNTs /TiO2 composites conveniently.

Ion-beam engineering of Co/TiO2 multilayer nanostructures

Multilayer structures consisting of Co/TiO2 bilayers with partial layer thicknesses varied within several nanometers and a total thickness of up to 100 nm were obtained using the ion-beam sputter deposition method and studied using a combination of analytical techniques. It is shown that, in [Co(2 nm)/TiO2(2 nm)]15, [Co(2 nm)/TiO2(4 nm)]15, and [Co(4 nm)/TiO2(4 nm)]12 structures, the mean-square surface roughness does not exceed 0.9 nm, all partial layers are continuous, all interfaces are plane-parallel and sharp, and the characteristics of each layer are close to those of the corresponding bulk material. The [Co(2 nm)/TiO2(4 nm)]15 structure is characterized by the maximum transparency (exceeding 7% in he visible spectral range. The properties of these multilayer films are promising for applications in magnetooptics and spintronics. The surfaces of [Co(4 nm)/TiO2(2 nm)]15 and [Co(6 nm)/TiO2(2 nm)]12 structures have mean-square roughnesses above 1 nm and exhibit percolations with a surface density of up to 5 × 107 cm−2. A decrease in the partial layer thickness below 2 nm leads to the mixing of layers, while an increase in the thickness of individual TiO2 layers above 6 nm leads to significant differences of the optical transmission spectrum from that of the anatase form of TiO2 and to a decrease in the transparency.

Surface Structure of NiTi Alloy Passivated by Autoclaving

Sterilization of the NiTi alloy in boiling water or steam causes passivation, which results in an amorphous 3.5 nm thick TiO2 layer on the surface. Between the surface and the matrix a transition layer of Ni2O3 and NiO was observed, using the X-ray photoelectron spectroscopy. Differences in sterilization conditions affect the amount of metallic nickel on the surface.

An ALD etch-back method to fabricate high aspect ratio nanopillar arrays for photonic crystal sensors

An IC-compatible technique for photonic crystal sensors is presented here to fabricate dense arrays of high aspect ratios nanopillars, which are made of extremely hard materials that are difficult to shape, such as TiO2. This technique, called Atomic layer deposition ARrays Defined by Etch-back technique (AARDE), can significantly reduce direct bombardment on the functional surfaces and allows the precise control of the size of the densely spaced high pillars. A case study of an array of 1 μm pitch and 1.7 μm high TiO2 pillars is investigated. Starting from 145 nm radius Si rods, the pillars are coated with a 78 nm thick ALD TiO2 layer and subsequently uncapped by a short time plasma etching. The exposed Si cores are then removed and a second ALD deposition is used to refill the opened holes and extend the pillar radius to the desired value.

Sonochemical synthesis of core/Shell structured CdS/TiO2 nanocrystals composites

A simple sonochemical route for the surface coating of titanium dioxide on cadmium sulfide nanocrystal was reported. After 2 h ultrasonic irradiation treatment, the mixture of CdS nanocrystals and tetrabutyl titanate in an aqueous medium yielded CdS/TiO2 nanocrystals composites with core/shell structure. The thickness of TiO2 layer with smooth interface could be easily controlled via changing the concentration of the precursors and the time of irradiation. The core/shell nanocrysrals were characterized by X-ray diffraction, transmission electron microscope and UV-vis spectrometry techniques. The prepared semiconductor composites with particular band structure present appealing properties especially in photochemical activity.

Assessment of the Titanium Dioxide Absorption Coefficient by Grazing-Angle Fourier Transform Infrared and Ellipsometric Measurements

Thin films, either deposited or native (i.e., oxide layers), have been widely exploited in different technological fields (e.g., optics, electronics, and biomedicine) to improve the efficiency of devices and extend their range of applications. Among the different physical/chemical characteristics of thin layers that determine their overall properties and therefore their potential for new applications, thickness has been demonstrated to play a pivotal role in affecting different phenomena; this is particularly significant at nanoscale dimensions, since nanostructured materials often behave very differently from their bulk counterparts. For example, thickness affects the microstructure, morphology, and optoelectronic properties of ZnS, ZnO, and Mo-doped indium oxide thin films, as well as the electrical properties of MOS structures in microelectronic and optical devices. In the biomedical field, the thickness of the superficial TiO2 layer affects the biological response of titanium-based materials. Due to its effects on several optical, physical, and biological events, different techniques have been developed to precisely determine the thickness of thin oxide layers, such as, for example, that of SiO2 9 and TiO2. 10 However, the majority of these methods have limitations that can compromise their applicability to a wide range of samples and materials. In addition, these techniques (e.g., X-ray photoelectron spectroscopy (XPS) sputter profiling) may damage the sample surface and alter its micro and nanometric topographical features. One of the most efficient nondestructive methods to precisely measure the thickness of thin organic and inorganic layers is ellipsometry. Infrared (IR) spectroscopy has found increasing applications in materials science, biology, and nanotechnology due to the possibility of determining the surface chemical composition of thin inorganic and molecular layers. However, to our knowledge, this technique has never been used to determine quantitatively the thickness of inorganic thin films. In this work, we demonstrate that ellipsometry and Fourier transform infrared (FT-IR) spectroscopy can be combined to estimate the absorption coefficient and the thickness of IRactive nanometric oxide layers. In particular, we selected the amorphous TiO2 layer present on the surfaces of bulk titanium (cpTi) and Ti6Al4V resulting from natural passivation and chemical oxidation with H2SO4/H2O2 solutions. 28–33 Results from this study will permit the exclusive use of FT-IR to determine the thickness of amorphous titanium dioxide thin films. More generally, our approach can be potentially applied to investigate a wider variety of materials (IR-active thin films deposited on a reflective substrate), without altering their surface topography.

Electric Field Effects on Charge Transport in Polymer/TiO2 Photovoltaic Cells Investigated by Intensity Modulated Photocurrent Spectroscopy

The electric field effects on the charge transport dynamics in bilayer polymer/TiO2 photovoltaic cells are studied by intensity modulated photocurrent spectroscopy (IMPS), for the first time, where a small bias voltage (Va) in the range from −0.1 to 0.2 V is applied to a cell during each IMPS measurement. The bilayer cells consisting of poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) and nanostructured TiO2 are constructed by using a polymer layer thickness l of 350 nm but varied TiO2 layer thicknesses (d = 40 and 65 nm). All the experimental IMPS responses are satisfactorily fitted to the previously developed IMPS model for the bilayer cells at Va = 0 V, providing a detailed analysis of charge transport properties under the applied voltages. It is revealed that the external electric field almost exclusively changes the exciton dissociation rate (S) at the donor/acceptor (D/A) interface, but imposes only a very faint effect on the transport dynamics of photogenerated electrons [ϕn(ω), ...

CdSe Quantum Dot-Sensitized TiO2 Electrodes: Effect of Quantum Dot Coverage and Mode of Attachment

We have investigated the sensitization of nanoporous titanium dioxide by previously synthesized CdSe quantum dots (QDs) protected with trioctylphosphine. Covering the nanoporous TiO2 films with QDs has been achieved using two strategies: (i) direct adsorption from dichoromethane dispersions and (ii) anchoring the QDs through a molecular linker, concretely, mercaptopropionic acid (MPA). In contrast with MPA-mediated adsorption, direct adsorption leads to a high degree of QD aggregation, as revealed by atomic force microscopy (AFM) images obtained with both TiO2 nanoporous films and monocrystalline surfaces. Importantly, at saturation, only 14% of the real surface area of a 5-μm thick P25 TiO2 layer is covered for both attachment modes. For MPA attachment, the incident photon-to-current efficiency (IPCE) increases with the loading, whereas a maximum (close to 40% at the QD excitonic peak) is defined for intermediate coverages in the case of QD direct adsorption. In addition, for equivalent QD loading, IPCE ...