Thick TiO2 Research Articles

Quantum Dot/TiO2 Nanocomposite-Based Photoelectrochemical Sensor for Enhanced H2O2 Detection Applied for Cell Monitoring and Visualization.

This workexploits the possibility of using CdSe/ZnS quantum dot (QD)-electrodes to monitor the metabolism of living cells based on photoelectrochemical (PEC) measurements. To realize that, the PEC setup is improved with respect to an enhanced photocurrent signal, better stability, and an increased signal-to-noise ratio, but also for a better biocompatibility of the sensor surface on which cells have been grown. To achieve this, a QD-TiO2 heterojunction is introduced with the help of atomic layer deposition (ALD). The heterojunction reduces the charge carrier recombination inside the semiconductor nanoparticles and improves the drift behavior. The PEC performance is carefully analyzed by adjusting the TiO2 thickness and combining this strategy with multilayer immobilizations of QDs. The optimal thickness of this coating is ≈5nm; here, photocurrent generation can be enhanced significantly (e.g., for a single QD layer electrode by more than one order of magnitude at 0V vs Ag/AgCl). The resulting optimized electrode is used for hydrogen peroxide (H2O2) sensing with a good sensitivity down to µmolar concentrations, reusability, stability, response rate, and repeatability. Finally, the sensing system is applied to monitor the activity of cells directly grown on top of the electrode surface.

Photocatalytic Edge Growth of Conductive Gold Lines On Microstructured TiO2-ITO Substrates.

Titanium dioxide is well-known for its excellent photocatalytic properties. UV-controlled photodeposition of gold on TiO2 is achieved by photocatalytic reduction of precursor ions from a tetrachloroauric solution. During the growth process on the surface, clusters grow from nucleation centers and coalescence is observed for sufficiently long UV illumination times, resulting in gold structures with complex shapes. Here, we hypothesize and demonstrate that the growth process is altered by employing an ITO sublayer below the TiO2 layer. Photocatalytic gold growth experiments on a microstructured thin film stack of 6 nm ITO and 70 nm TiO2 lead to strongly localized gold growth along the edge of the patterned area. A conductive gold line with a height of 3.8 μm is achieved along the edge of the TiO2-coated region, while gold growth on the surface of TiO2 is effectively suppressed. For substrates coated only with ITO or TiO2, no edge growth is observed. Furthermore, for an 845 nm thick TiO2 layer, either with or without ITO sublayer, gold growth on the TiO2 surface is dominant. Thus, for the effective steering of electrons to the edge, both the ITO sublayer and a sufficiently thin TiO2 layer are necessary. This modified method of photocatalytic deposition─electrons photogeneration in a thin layer, collection in a dedicated conductive sublayer, and growth by reduction at a different position─opens opportunities for localized material deposition. We are in particular aiming at extending the toolbox of neuromorphic engineering by providing a technical implementation of stimulus-controlled dynamic formation of directional conductive interlinks.

Enhancing SERS sensitivity of semiconductors through constructing CuO@TiO2 heterojunctions via atomic layer deposition

Semiconductors hold great promise for surface-enhanced Raman scattering (SERS) applications. Various strategies have been proposed to address the challenge of low SERS sensitivity in semiconductors, with the construction of heterojunctions being among the most effective approaches. In this study, CuO@TiO2 heterojunctions were fabricated by depositing a precisely controlled layer of TiO2 film onto the surface of CuO nanowires (CuO NWs) using the atomic layer deposition (ALD) technique. This approach significantly enhances the SERS sensitivity of CuO NWs, and the SERS performance of the semiconductor heterojunction can be further optimized by accurately adjusting the thickness of TiO2. The SERS activity exhibits systematic variations with the TiO2 thickness across the CuO@TiO2-Rhodamine 6G (R6G) system, with the optimal SERS performance of the heterojunction substrate achieved at a TiO2 thickness of 250 cycles. This finding highlights the substantial influence of TiO2 coating thickness on the photo-induced charge transfer (PICT) processes within the CuO@TiO2-R6G system. Furthermore, CuO@TiO2 heterojunctions demonstrate exceptional stability and uniformity. As a result, this study holds significant importance in enhancing the SERS performance of oxide semiconductors, designing optimal semiconductor heterojunction SERS substrates, and investigating thickness-dependent charge transfer mechanisms in semiconductors.

Optimization of electrolyte co-additives, TiO2 thickness, and dye concentration for the enhanced performance of dye-sensitized solar cells

Optimization of electrolyte co-additives, TiO2 thickness, and dye concentration for the enhanced performance of dye-sensitized solar cells

Rapid Determination of the Optimum Thickness of Doped TiO2 Nanotubes Layer by Local Photoelectrochemistry and Operando Properties Extraction by Data Modeling.

In this work, the optimal thickness of TiO2, M‐doped, N‐doped, and (M:N) codoped TiO2 (with M = Nb or Ta) nanotubes (NTs) for photoelectrochemical (PEC) water splitting is determined, in one step through local photoelectrochemical analysis of electrodes with variable thickness of the photoactive material. A simple anodization method allows the growth, on a single electrode, of aligned doped TiO2 nanotubes whose length gradually changes from 0 to 15 μm. The external quantum efficiency (EQE) as a function of the NTs film thickness is measured using a small beam of UV or visible light to scan the surface and locally trigger the oxygen evolution reaction (OER). The results provide the optimal NT layer thickness for each type of doped TiO2‐NTs and demonstrate that if the (M:N) codoped TiO2‐NTs have the best activity in the visible region, the optimal layer thickness is reduced compared to TiO2 or M:doped TiO2‐NTs. Additionally, by fitting the data with a model that incorporates charge carrier transfer and light absorption mechanisms in the film, it becomes possible to evaluate in operando the interfacial charge transfer, absorption coefficient or majority carrier mean path which are important properties of semiconducting (SC) materials for PEC applications.This article is protected by copyright. All rights reserved.

Achieving a Double Advantage Through Design of TiO2/C Interlaced Coating for Si Anode

AbstractMultifunctional coating strategy shows promising prospective in advancing Si‐based anodes towards practical applications in Li‐ion batteries. Dual coating of amorphous carbon and TiO2 shows demonstrable advantages owing to high elasticity of amorphous carbon and mechanical toughness of TiO2. However, for past design of Si@C@TiO2 composite electrode, wherein C and TiO2 are configured layer‐by‐layer, a long‐standing problem exists as that a thin TiO2 coating is insufficient to stabilize the electrode's architecture while a thick one prevents the core active material of Si far from fully electrochemically utilization due to the too strong structural constraint effect. Herein, it presents that a facial heat treatment of Si@C@TiO2 with thick enough TiO2 can readily avert the problem. Such a strategy promotes the capacity utilization rate from 39% to 61% for the initial cycle and from 43% to 85% after 200 cycles. Model structure of C/TiO2 multilayer films is employed to reveal the role of the heat treatment. It finds that the heat treatment can transform a layer‐by‐layer structure of C@TiO2 into an interlaced structure of C/TiO2 which exhibits a dual advantage in withstanding mechanical strain and simultaneously promoting Li‐ion storage and electron/Li‐ion transport.

Photocatalytic degradation of methylene blue by TiO2/Nd2O3 composite thin films

To improve the photocatalytic property of TiO2 thin films, the composite thin films of TiO2/Nd2O3 structure were fabricated by electron-beam physical vapor deposition method, and the photocatalytic property of the fabricated films was experimentally studied in the present work. The XRD and Raman analyses show that the TiO2/Nd2O3 films are mainly hexagonal crystalline phase of Nd2O3. The XPS analysis for the chemical state changes of Ti, O and Nd of the basic elements in the films is confirming the electron flow in the internal electric field which generated in the TiO2/Nd2O3 films. The surface morphology shows the lattice distortion which affects the changes in the energy band structure. Moreover, the formation of n-n homojunctions improved the separation efficiency of electrons and holes, and enhanced the catalytic activity. The photocatalytic performance for the methylene blue target dye shows that the sample with TiO2 thickness of 20–25 nm has better performance, high degradation efficiency and high reaction rate.

Photocatalytic degradation of methylene blue by anatase TiO2 coating

AbstractPhotocatalytic coatings have the potential to contribute to the purification of water via an advanced oxidation process (AOP). A commonly used method for analyzing the mechanism of the photocatalytic performance of a given reactor type is to document the degradation behavior in a solution containing methylene blue. However, since methylene blue is rather unstable, the degradation results should be viewed critically. In this work, the degradation behavior of a test solution with methylene blue on quartz glass surfaces coated with photocatalytic titanium dioxide (TiO2) of the anatase modification was investigated through a variety of different light sources. The coating was deposited by physical vapor deposition (PVD) with the reactive pulsed DC magnetron sputtering ion plating (MSIP) method described in the study by Desch and Lake, while the quartz glasses were coated with a 100 nm thick TiO2 coating on the outside. The same glasses were used for all experiments with TiO2. In the determination of the degradation rate, additional experiments were performed using pure quartz glass without any coating, which made it possible to examine the influence of different light sources on the degradation rate of methylene blue in general. Three different light sources, namely UV‐A, UV‐C, and simple fluorescent lamps were used in this study. The concentration of methylene blue was recorded by photo spectrometer in 10‐min increments throughout the experiment and the experiments were performed for 24 h in all cases. Our data indicates that the methylene blue test is a poor method because the degradation rate is not clearly differentiable due to the low stability of the test substance. Without including reference testing in the absence of a catalyst, data may be subject to misinterpretation.

Increasing the wear resistance of hip prostheses components using micro-nanostructured thin layers

Evaluation of micro-nanostructured thin layers applicability for increasing the lifetime of rehabilitation systems, mainly hip prostheses, is the aim of the present research. This because, the final objective of the complete project is to improve the quality of human prostheses using micro-nanostructured thin layers. In order to realize these researches, 0.5, 1, and 1.5 µm thick thin layers of TiN and TiO2, were deposited on substrates made of materials currently used for hip prostheses – M30NW steel and CoCr – using physical deposition methods, respectively Cathodic Arc (CA), Direct Current (DC) sputtering and High-Power Impulse Magnetron Sputtering (HiPIMS). After tribological and nanoindentation tests, the 1.5 μm thick TiN and TiO2 thin layers deposited on the steel and CoCr substrates using the DC sputtering method presented superior mechanical properties. Functional characterization of a total hip prosthesis, that have had components coated with these thin layers presented an increased resistance to fatigue wear. After comparative analysis, the main conclusion of the realized researches was that TiN layers with a thickness of 1.5 μm have an increased resistance to fatigue wear in comparison with TiO2 layers, when both are deposited by DC sputtering on M30NW steel and CoCr substrates. It was observed that 1.5 μm thick TiN layers ensures a prolongation by 15% of the lifetime of femoral heads compared to those uncoated.

Effect of dissolved precursors on corrosion characteristics of Ni-based alloy Inconel 625, stainless steel 316L and titanium alloy TA2 in acidic and neutral supercritical water: A comparative study

This work investigated the corrosion characteristics of nickel-based alloy Inconel 625, stainless steel 316L (SS 316L), and commercial grade 2 titanium alloy (TA2) in ZrO(NO3)2-containing and ZrO(NO3)2/KOH-containing supercritical water (SCW) at 400 °C and 25 MPa. During ZrO(NO3)2-containing SCW exposure, Inconel 625 undergoes pitting and intergranular corrosion, while SS 316L and TA2 suffer uniform corrosion. Based on corrosion rate and metal oxide stability, the corrosion resistance follows an order of TA2 > Inconel 625 > SS 316L. The addition of KOH reduces the intergranular corrosion sensitivity of Inconel 625, and leads to different oxide distribution of SS 316L. The thick TiO2 oxide layer mixed with ZrO2 formed in ZrO(NO3)2/KOH-containing SCW enables TA2 to exhibit superior corrosion resistance than Inconel 625 and SS 316L.

Silver-infused TiO2 nanowires and unveiling their potential for superior wastewater dye remediations.

Silver infused ultrathin TiO2 nanowires (NWs) were synthesized via a single step solvothermal approach. The crystallinity, structure, and morphology were determined to understand the physicochemical nature of the nanocomposites. The catalytic efficiency of the newly synthesized nanocatalysts was tested for the textile waste treatment taking methylene blue (MB) as model pollutant under solar light irradiations. Nearly 96% photodegradation efficiency for MB was achieved within 20 min. Furthermore, the recyclability of the photocatalyst was also studied, and the material remained stable and effective up to four consecutive runs. RESEARCH HIGHLIGHTS: Precise size-controlled synthesis of Ag-incorporated titania nanowires (ATNWs) Controlled aspect ratios, with tunable lengths and diameters (100-3 nm) via precursor and surfactant optimization Demonstrated ATNWs' efficiency in degrading toxic dye, methylene blue (MB) 96% photodegradation efficiency for MB achieved within 20 min using 3 nm thick annealed TiO2 NWs Recyclability efficiency of photocatalyst, which remained stable and effective for up to four consecutive runs.

Transparent and hard TiO2/Au electromagnetic shielding antireflection coatings on aircraft canopy PMMA organic glass

This research addresses the critical need for a highly stable and transparent electromagnetic shielding coating for aircraft PMMA windows and canopies, crucial for safeguarding against electromagnetic interference and enhancing aircraft stealth capabilities. The study presents the novel design, deposition and investigation of transparent coatings, specifically TiO2/Au, on PMMA organic glass cockpit canopies. Optimization of TiO2 and Au film thicknesses is achieved through simulation using TFcalc software, incorporating polarization and optical constants data obtained in this study. The experiments reveal that the deposition of TiO2/Au/TiO2 on PMMA results in fogging, reducing transparency, while novel TiO2/Au coating does not exhibit this issue. The TiO2/Au configuration, featuring a TiO2 layer approximately 30 nm thick and an Au film ranging from 11 to 15 nm in thickness, demonstrates outstanding attributes, including a remarkable transparency level of approximately 70–80% and robust electromagnetic interference shielding efficiency within the range of 19–29 dB across S, C, X, and Ku bands of electromagnetic waves. These exceptional performance characteristics position it as an ideal choice for aviation applications. The synergy of the stable Au and durable TiO2 components, with their high hardness and self-cleaning properties, extends its potential utility to a diverse array of applications.

Calcium isotope variability among ocean islands reveals the physical and lithological controls on mantle partial melting

Major geodynamic processes, including mantle convection and plate tectonics, govern the exchange of mass between Earth's interior and its surface. These processes drive mass-transfer mechanisms such as partial melting and crustal recycling, which have generated a lithologically and compositionally heterogeneous mantle over time. Ocean island basalts (OIB) directly sample these heterogeneities, making them excellent tools to constrain the mantle’s dynamic geochemical evolution. In this study, we probe the connection between crustal recycling, mantle mineralogy, and partial melting using the stable Ca isotope compositions of OIB, ultimately contextualizing their Ca isotope variability using conventional mantle “endmember” components including DMM, HIMU, EM-1, and EM-2. Using the state-of-the-art Nu Sapphire collision cell MC-ICP-MS, we measured the Ca isotope compositions of 27 well-characterized OIB samples from 11 different ocean island groups. By supplementing our new data with additional high-precision Ca isotope measurements from the literature, we create an expanded dataset consisting of 15 ocean islands, facilitating a global-scale investigation of Ca isotope variability among hotspots. Our findings reveal that island-averaged Ca isotope compositions form two distinct groups on the basis of their radiogenic isotope compositions. The first group, consisting of OIB with un-enriched radiogenic isotope compositions (non-EM-type), exhibits robust negative correlations with both lithospheric thickness and primitive TiO2 contents, providing compelling evidence that Ca isotopes are sensitive to the degree of partial melting (F) as well as to the effects of crustal recycling. This joint signal appears to trace the process of decompression melting beneath oceanic lithosphere of variable thickness, as recycled lithologies rich in garnet and pyroxene (i.e., pyroxenites)—which generate large solid-melt Ca isotope fractionations—disproportionally control the Ca isotope composition of the final aggregate melt when F is limited by thick overlying lithosphere. In contrast, the island-averaged Ca isotope compositions of OIB with enriched radiogenic isotope compositions (EM-type) form a distinctly light negative correlation with primitive TiO2 contents without exhibiting a relationship with lithospheric thickness. In addition to lithology-dependent partial melting effects, the Ca isotope compositions of EM-type OIB appear to be sensitive to the compositional effects of crustal recycling, which may explain their decoupling from the physical controls of partial melting. Calcium isotopes show exceptional potential for elucidating the origin of both enriched and ultra-depleted mantle sources, emphasizing the need to prioritize localities with these signatures in future studies.

Pt/GO/TiO2 room–temperature hydrogen sensing Schottky diode: High resistance to humidity interference endowed by the graphene oxide interlayer

Room–temperature hydrogen sensors usually suffer from dramatic response drop in humid air. Aiming to solve such issue of H2 sensing Schottky diodes, a platinum/graphene oxide/titanium dioxide (Pt/GO/TiO2) Schottky diode is designed. The GO interlayer between the 50–nm–thick Pt nanolayer and TiO2 substrate significantly improves resistance to humidity interference. Remarkably, the diode with a GO loading of 0.969 mg cm−2 exhibits a response retention rate (RRH95%/Rdry) of nearly 100%. To reveal the mechanism for the improved anti–humidity performance, the H2O adsorption behavior of Pt/GO/TiO2 diode was investigated by quartz crystal microbalance and near ambient pressure X–ray photoelectron spectroscopy. H2O molecules are absent on the Pt surface of Pt/GO/TiO2 in water vapor. This is a result of the H2O adsorption effect of the GO interlayer, which stems from the superior H2O adsorption ability of the GO interlayer and causes the diffusion of H2O molecules adsorbed on the Pt surface into the GO interlayer through nanochannels in the Pt nanolayer. Additionally, the GO interlayer serves as a blocking layer for the diffusion of hydroxyl species generated on the TiO2 surface to the Pt nanolayer. Such hydroxyl blocking effect prevents the consumption of adsorbed H atoms at the Pt/GO interface.

Sodium adsorption on nanometer-thick TiO2 channel thin-film transistors for enhanced drain currents

Sodium adsorption on nanometer-thick-TiO2-channel thin-film transistors (TFTs) are examined for enhancing the drain current. In the TFTs, the channel thickness of TiO2 is set as thin as ∼16 nm. The TiO2 film is deposited by atomic layer deposition using plasma excited humified Ar, followed by crystallization into the anatase phase by thermal annealing at 500 °C in air. The gate oxide is a 300 nm thick SiO2 film, which is grown on a highly doped n+ Si substrate. The n+ Si substrate is used as the gate electrode. The drain and source electrodes of Ti are deposited by an electron beam evaporation at room temperature. The TiO2 channel is covered with multiple layers of aluminum silicate and SiO2 films to enhance the Na sorptivity. The multiple films consist of combinations of 1 nm thick SiO2 and 0.16 nm thick aluminum silicate. The channel length and width are 60 and 1000 μm, respectively. The TFT without the Na adsorption exhibits a field effect mobility of ∼0.5 cm2/V s, where the drain current is recorded around 30 μA with a gate voltage of 10 V. With immersion of the TFT in a 10 mM NaCl solution, the drain current is enhanced to the order of mA. The simulation with an equivalent circuit with source and drain resistances suggests that the field effect mobility is enhanced to ∼30 cm2/V s with the adsorption of Na. In this paper, we discuss the operation mechanism of the Na adsorbed TiO2 TFT and its applicability as TFT-based high current switch devices and sensors.

Optimal modeling of perovskite solar cell with graphene oxide as hole transport layer using L32 (28) Taguchi design

Material parameter variations are one of the main contributors affecting the performance of solar cell devices, thus, Taguchi design is employed to optimize the material parameters in attaining maximum power conversion efficiency (PCE). This paper discusses the optimal modeling of the Perovskite solar cell (PSC) with graphene oxide (GO) hole transport layer (HTL) using L32 (28) Taguchi design. The device simulation is conducted using a solar cell capacitance simulator (SCAP), whereas the L32 (28) Taguchi design is used for device optimization. The final results reveal that the L32 (28) Taguchi design has significantly optimized the device parameters in which FTO thickness, FTO donor concentration, TiO2 thickness, TiO2 donor concentration, CH3NH3PbI3-xClx thickness, CH3NH3PbI3-xClx donor concentration, GO thickness and GO acceptor concentration are predictively set to 0.1 µm, 1 x 1020 cm-3, 0.03 µm, 1 x 1020 cm-3, 0.9 µm, 1 x 1020 cm-3, 0.03 µm and 1 x 1020 cm-3 correspondingly. Analysis of variance (ANOVA) reveals that the CH3NH3PbI3-XClX thickness is the most dominant input parameter affecting the PCE of the device. The optimized input parameters yield the maximum attainable PCE of 35.91% with a signal-to-noise ratio (SNR) of 31.11 dB.

Sol-Gel TiO2 Thin Film on Au Nanoparticles for Heterogeneous Plasmonic Photocatalysis.

A new, simple method for preparing substrates for photocatalytic applications under visible light is presented. It is based on the preparation of a dense array of gold nanoparticles (AuNPs) by thermal dewetting of a thin gold film followed by spin-coating of a thin TiO2 film prepared by sol-gel chemistry. The photocatalytic properties of these nanocomposite films are studied by surface-enhanced Raman spectroscopy (SERS) following the N-demethylation reaction of methylene blue as a model reaction. This approach shows that the semiconducting layer on the AuNPs can significantly increase the efficiency of the photoinduced reaction. The SERS study also illustrates the influence of parameters such as TiO2 thickness and position (on or under the AuNPs). Ultimately, this study emphasizes that the primary mechanism behind the N-demethylation reaction is both the increase in extinction and the improved electron transfer facilitated by the semiconducting layer. On the other hand, exclusive reliance on photothermal effects is ruled out.

Selective efficient photocatalytic degradation of antibiotics and direct Z-type migration pathway for hierarchical core-shell TiO2/g-C3N4 composites.

Constructing superior Z-type photocatalytic heterojunction is beneficial to effectively enlarge interface contact, improve the photo-generated carrier separation rate, and retain the high redox ability. In this work, we designed a hierarchical core-shell g-C3N4/TiO2 structure to build Z-type heterojunction via combining simple template method and pyrolysis process. A close-knit Z-type heterojunction was constructed using TiO2 as a thick core and g-C3N4 as an ultra-thin shell. The effects of lamp source, wavelength, tetracycline (TC) concentration, and photocatalyst dose on the degradation performance on TC of g-C3N4/TiO2 were inspected. 0.1TiO2/g-C3N4 photocatalyst had the best degradation rate and highest removal rate within 30min, and its degradation rate was about 49, 23, and 5 times than pure g-C3N4, TiO2, and commercial TiO2/g-C3N4 in respect. Moreover, compared with degradation ability under Xenon lamp, LED irradiation for g-C3N4/TiO2composites showed aremarkable selectivedegradation. The fast and efficient Z-type transfer pathway of 0.1g-C3N4/TiO2 was realized by forming an optimized interface and abundant surface active sites ascribed to the combined action of thick TiO2 core and ultra-thin g-C3N4 shell. In addition, the degradation intermediates were analyzed by LC-MS and suggested pathways of degradation. The work could provide novel design concept to obtain reliable Z-type photocatalysts with hierarchical core-shell structure applied in degradation of antibioticwastewater.

Exploring the impact of electron transport layer thickness and morphology on perovskite infiltration and photoresponse in HTM-free self-powered photodetector

Methylammonium lead Iodide (MAPbI3) is emerging as the frontrunner for high-performance photo-detection due to its superior optoelectronic characteristics and ease of processing. Titanium dioxide (TiO2) is the commonly employed electron transport layer in conventional perovskite-based photodetectors. However, the fundamental understanding of the role of TiO2 morphology and its thickness on the photodetector performance is yet to be explored explicitly. This work systematically investigates the impact of morphology (mesoporous versus compact TiO2 layer) and thickness of the TiO2 layer (50 nm – 3000 nm) on the MAPbI3 photodetector performance. The devices have been fabricated in a hole transport material (HTM)-free architecture with carbon as the top contact. The heterojunction between MAPbI3 and TiO2 renders the device with self-powered capability. The influence of the perovskite sensitisation in the TiO2 electrodes, carrier recombination characteristics and charge-carrier transfer resistances have been studied using photoluminescence and impedance spectroscopy. The TiO2 layer morphology and thickness affected the MAPbI3 infiltration and film formation kinetics. Impedance and photoluminescence spectroscopies reveal that TiO2 layers, with thickness above 460 nm, negatively affected the device performance. An optimum thickness of 460 nm-mesoporous TiO2 layer exhibited a superior responsivity and rise time of 2.9 A/W and 21 ms, respectively. The poor performance at higher thicknesses is due to the increased interfacial charge transfer resistance and charge carrier recombination. This work is the first report of extensive optimisation and study on the impact of TiO2 film morphology and thickness on the MAPbI3 photodetectors. The present work will be a key for modelling and designing high-performance perovskite photodetectors.

Tailoring crystallisation of anatase TiO2 ultra-thin films grown by atomic layer deposition using 2D oxides as growth template

TiO2 ultrathin films are required in many material research areas. The anatase phase was found to be more stable in case of atomic layer deposition growth, nevertheless a critical thickness of around 10 nm appears necessary to obtain crystallization on native silicon oxide on Si (001). This work focuses on direct liquid injection Atomic Layer Deposition (ALD) of TiO2 films with thicknesses about some nanometers, using titanium tetra-isopropoxide as precursor and H2O as oxidant. A particular care to the treatment of ellipsometric measurements is employed. Below the threshold value, films remain amorphous unless the growth starts onto a crystalized surface, a thick TiO2 layer in our case. Here we propose and show the efficiency of 2-dimensional (2D) [Ca2Nb3O10]− and [Ti0.865O2]0.54− nanosheets as seeds at the surface for the crystallization and epitaxy of ultra-thin films of TiO2 below the critical thickness. Furthermore, we show that the structure of the 2D nanosheets determines the growth orientation of the epitaxial anatase, namely (010) for [Ti0.865O2]0.54−, and (100) for [Ca2Nb3O10]−. These results, based on the tailoring of crystal anisotropy via adapted 2D seed nanosheets and low temperature ALD, opens the way for opto-electronics applications of titanium oxide layers of a few unit cells.