Conformal TiO2 Research Articles

Screen-Assisted Self-Spreading of TiO2 Precursor Solution on FTO Substrates for High-Quality Electron Transport Layers in Perovskite Solar Cells.

The electron transport layer (ETL) plays a critical role in efficient and stable perovskite solar cells (PSCs). The current effective method for the large-scale preparation of metal oxide ETLs is mainly based on expensive sputtering processes. Here, a screen-assisted self-spreading method is proposed as a novel approach to prepare uniformly thin and conformal TiO2 films on a rough fluorine-doped tin oxide (FTO) substrate as an ETL in planar PSCs. The TiO2 ETL deposited by this method exhibited good coverage and homogeneity on the rough FTO substrate, thereby minimizing interfacial recombination. The photovoltaic performance of the PSCs fabricated by this method is superior to that of the cells fabricated by spin coating, especially in terms of the fill factor. The performance enhancement can be attributed to the complete coverage of the FTO substrate by the conformal TiO2 film, confirming the effectiveness and reliability of the proposed method for the preparation of the TiO2 ETL. The advantages of this method lie in its scalability to prepare oxide films with a large area, eliminating the requirement of complex equipment, such as spinners, sputters, or physical vapor deposition equipment.

Conformal TiO2 Aerogel-Like Films by Plasma Deposition: from Omniphobic Antireflective Coatings to Perovskite Solar Cell Photoelectrodes.

The ability to control the porosity of thin oxide films is a key factor determining their properties. Despite the abundance of dry processes for synthesizing oxide porous layers, a high porosity range is typically achieved by spin-coating-based wet chemical methods. Besides, special techniques such as supercritical drying are required to replace the pore liquid with air while maintaining the porous network. In this study, we propose a new method for the fabrication of ultraporous titanium dioxide thin films at room or mild temperatures (T ≤ 120 °C) by a sequential process involving plasma deposition and etching. These films are conformal to the substrate topography even for high-aspect-ratio substrates and show percolated porosity values above 85% that are comparable to those of advanced aerogels. The films deposited at room temperature are amorphous. However, they become partly crystalline at slightly higher temperatures, presenting a distribution of anatase clusters embedded in the sponge-like open porous structure. Surprisingly, the porous structure remains after annealing the films at 450 °C in air, which increases the fraction of embedded anatase nanocrystals. The films are antireflective, omniphobic, and photoactive, becoming superhydrophilic when subjected to ultraviolet light irradiation. The supported, percolated, and nanoporous structure can be used as an electron-conducting electrode in perovskite solar cells. The properties of the cells depend on the aerogel-like film thickness, which reaches efficiencies close to those of commercial mesoporous anatase electrodes. This generic solvent-free synthesis is scalable and applicable to ultrahigh porous conformal oxides of different compositions, with potential applications in photonics, optoelectronics, energy storage, and controlled wetting.

Microwave-Absorbing Foams with Adjustable Absorption Frequency and Structural Coloration.

Microwave-absorbing materials with regulatable absorption frequency and optical camouflage hold great significance in intelligent electronic devices and advanced stealth technology. Herein, we present an innovative microwave-absorbing foam that can dynamically tune microwave absorption frequencies via a simple mechanical compression while in parallel enabling optical camouflage over broad spectral ranges by adjusting the structural colors. The vivid colors spanning different color categories generated from thin-film interference can be precisely regulated by adjusting the thickness of the conformal TiO2 coatings on Ni/melamine foam. Enhanced interfacial and defect-induced polarizations resulting from the introduction of TiO2 coating synergistically contribute to the dielectric attenuation performance. Consequently, such a foam exhibits exceptional microwave absorption capabilities, and the absorption frequency can be dynamically tuned from the S band to the Ku band by manipulating its compression ratio. Additionally, simulation calculations validate the adjustable electromagnetic wave loss behavior, offering valuable insights for the development of next-generation intelligent electromagnetic devices across diverse fields.

Sulfur‐Supplemented Vapor Transport Deposition of Sb2S3 and Sb2(S,Se)3 for High‐Performance Hydrogen Evolution Photocathodes

Chalcogen vacancy has long been recognized as a detrimental deep‐level defect that can induce severe charge recombination and diminish the quasi‐Fermi‐level splitting in Sb2S3 and Sb2Se3, especially when they are prepared by physical vapor deposition in vacuum. In order to counter this limitation, a sulfur‐supplemented vapor transport deposition technique is proposed, which intentionally introduces low pressure sulfur vapor and can thus afford low‐defect‐density antimony chalcogenide films. The resultant photocathodes modified with conformal TiO2 protection layer and Pt cocatalyst demonstrate a photocurrent as high as 20 mA cm−2 along with a much improved fill factor and onset potential, achieving an applied bias photoconversion efficiency above 1%. This work highlights the importance of the vacancy defect passivation and the preferential crystalline orientation in the film in promoting the photocathode performance.

Stability enhancement and patterning of silver nanowire networks by conformal TiO2 coating for flexible transparent conductive electrodes

Stability enhancement and patterning of silver nanowire networks by conformal TiO2 coating for flexible transparent conductive electrodes

Excellent conformality of atmospheric-pressure plasma-enhanced spatial atomic layer deposition with subsecond plasma exposure times

Atmospheric-pressure spatial atomic layer deposition (s-ALD) has emerged as a scalable deposition technique combining the advantages of ALD with high deposition rates, suitable for low-cost and high-volume applications. There is a growing interest in atmospheric-pressure plasma-enhanced spatial ALD (PE-s-ALD), e.g., to allow for deposition at reduced temperatures or for materials that are otherwise difficult to prepare by thermal ALD. For low-pressure PE-ALD, conformal films on high aspect ratio features have been achieved despite plasma radical recombination, and the aspects influencing conformality are fairly well understood. This work addresses surface recombination and conformality for atmospheric-pressure PE-s-ALD films. We demonstrate that conformality can be achieved for SiO2 and TiO2 films deposited by atmospheric-pressure PE-s-ALD inside high-aspect-ratio trenches with short plasma exposure times. Using plasma exposure of 0.73 s results in conformal SiO2 and TiO2 films in structures with aspect ratios of 74 and 219, respectively. Additionally, the recombination probabilities of oxygen radicals at atmospheric pressure are extracted to be 4×10−4 for SiO2 and 6×10−5 for TiO2. These results demonstrate that atmospheric-pressure PE-s-ALD can be used for conformal and high-speed depositions on 3D substrates.

Quantified Uniformity and Selectivity of TiO2 Films in 45‐nm Half Pitch Patterns Using Area‐Selective Deposition Supercycles

AbstractArea‐selective deposition (ASD) shows great promise for sub‐10 nm manufacturing in nanoelectronics, but significant challenges remain in scaling to ultrasmall dimensions and understanding feature‐dependent nonuniformity and selectivity loss. This work addresses these problems by simultaneously quantifying uniformity and selectivity for passivation/deposition/etch supercycles in 45 nm half‐pitch TiN/SiO2 line/space patterns. This work employs three selective processes that are uniquely suited for supercycle processing: dimethylamino‐trimethylsilane (DMA‐TMS) inhibition, TiO2 atomic layer deposition (ALD), and HBr/BCl3 plasma etch. The DMA‐TMS inhibition selectively passivates the SiO2 nongrowth surface without affecting deposition on the TiN and TiO2 growth surfaces. The plasma etch removes TiO2 defect particles at a faster rate than the conformal TiO2 film or SiO2 lines. Using three supercycles of this process, this work demonstrates 8 nm of TiO2 with 88% uniformity and ≈100% selectivity according to transmission electron microscopy (TEM), a 2×improvement in film thickness from previous reports in similar nanoscale patterns. Integrated consideration of uniformity and selectivity at specific feature scales will facilitate the effective design of selective deposition processes for nanoscale electronic devices.

Interfacial engineering of nanostructured photoanode in fiber dye‐sensitized solar cells for self‐charging power systems

AbstractSolar cells offer an environmentally sustainable and convenient option for power source of next‐generation wearable electronics. Due to the advantages of low cost, easy fabrication and deformation, fiber dye‐sensitized solar cells (FDSSCs) are required to be suitable for the available wearable electronics. Herein, through introduced nanopillar arrays over the Ti wire and atomic layer deposition of conformal TiO2 layer to make the photoanode, the energy conversion efficiency of the FDSSCs is improved by 45%. The FDSSCs are combined with planar microsupercapacitor (MSC) clusters to make self‐charging power system on a polymer sheet. The interdigital finger electrodes of MSC were obtained in a single‐step method by laser‐inducing on a polyimide film, and two series can be charged up to 1.8 V in 30 s by the FDSSCs under solar irradiation. This power sheet can be attached to various surfaces such as skin, cloths, and electronic devices for practical applications.image

ALD coated polypropylene hernia meshes for prevention of mesh-related post-surgery complications: an experimental study in animals

In this work, thermal atomic layer deposition (ALD) was used to synthesize vanadium (V)-doped TiO2 thin nanofilm on polypropylene (PP) hernia meshes. Multiple layers of (Al2O3 + TiVO x ) nano-films were coated on the PP hernia mesh surface to provide a layer with a total thickness of 38 nm to improve its antibacterial properties, thereby, prevent mesh-related post-surgery complications. Highly conformal V-doped TiO2 nanofilm were deposited on PP mesh at a temperature of 85 °C. Rats and rabbits have been used to evaluate the tissue reaction on coated PP hernia meshes and biomechanical testing of the healed tissue. Five rabbits and ten rats have been implanted with ALD coated and uncoated (control) PP meshes into the back of rats and abdominal wall of rabbits. Histology of the mesh-adjacent tissues and electron microscopy of the explanted mesh surface were performed to characterize host tissue response to the implanted PP meshes. The effect of V-doped TiO2 coating on a living organism and fibroblast functions and bacterial activities were studied. The present results indicated that ALD coating improves adhesion properties and exhibited enhanced antibacterial activity compared to uncoated PP mesh. It was shown that V-doped TiO2 coatings were highly effective in inhibiting S. aureus and E. coli adhesion and exhibited excellent antibacterial activity. We found that V-doping of TiO2, unlike bare TiO2, allows generated and further procured strong redox reactions which effectively kills bacteria under visible light. We have reported comparative analysis of the use of undoped (bare) TiO2 and V-doped TiO2 as a coating for PP meshes and their action in biological environment and preventing biofilms formation compared with uncoated PP meshes. The PP meshes coated with V-doped TiO2 showed significantly lower shrinkage rates compared with an identical PP mesh without a coating. We have shown that ALD coatings provide non-adhesive and functional (antibacterial) properties.

Mesoporous Ultrathin In2O3 Nanosheet Cocatalysts on a Silicon Nanowire Photoanode for Efficient Photoelectrochemical Water Splitting.

Vertical Si nanowire (NW) arrays are a promising photoanode material in the photoelectrochemical (PEC) water splitting field because of their highly efficient light absorption capability and large surface areas for PEC reactions. However, Si NW arrays always suffer from high overpotential, low photocurrent density, and low applied bias photon-to-current efficiency (ABPE) due to their low surface catalytic activity and intense charge recombination. Here, we report an efficient oxygen evolution cocatalyst of optically transparent, mesoporous ultrathin (2.47 nm thick) In2O3 nanosheets, which are coupled on the top of Si NW arrays. Combined with a conformal TiO2 thin film as an intermediate protective layer, this Si NW/TiO2/In2O3 (2.47 nm) heterostructured photoanode exhibited an extremely low onset potential of 0.6 V vs reversible hydrogen electrode (RHE). The Si NW/TiO2/In2O3 (2.47 nm) photoanode also showed a high photocurrent density of 27 mA cm-2 at 1.23 V vs RHE, more than 1 order of magnitude higher than that of the Si NW/TiO2 photoanodes. This improvement in solar water splitting performance was attributed to the significantly promoted charge injection efficiency as a result of the In2O3 nanosheet coupling. This work presents a promising pathway for developing efficient Si-based photoanodes by coupling ultrathin 2D cocatalysts.

Impact of Different Intermediate Layers on the Morphology and Crystallinity of TiO2 Grown on Carbon Nanotubes by Atomic Layer Deposition

AbstractNanocomposites of TiO2 and carbon nanotubes (CNTs) have been extensively studied in photocatalysis, sensing, and energy conversion and storage over the last decade. The unique properties of these nanocomposites are greatly dependent on the morphology, crystallinity, and homogeneity of the TiO2 coating. However, a fine control of the film microstructure is still challenging due to limited understanding of early stages of the TiO2 growth. The presence of an intermediate buffer layer can induce remarkable changes in the morphological and structural characteristics of the coatings. Here, TiO2 films deposited by atomic layer deposition (ALD) on CNTs without and with different intermediate layers (Al2O3 and ZnO) have been systematically investigated. Compared to bare CNTs, it is suggested that these two intermediate layers with higher surface energy can lead to a delay of the TiO2 crystallization, ultimately resulting in the growth of conformal and crystalline TiO2 films. This study demonstrates a strategy to tailor the microstructure and the properties of thin films via ALD by applying intermediate layers and provides information about the role of surface energy of the substrate in crystallization and growth behavior of ALD thin films.

Dendritic CuBi2O4 Array Photocathode Coated with Conformal TiO2 Protection Layer for Efficient and Stable Photoelectrochemical Hydrogen Evolution Reaction

Short carrier diffusion length and poor photostability are two major bottlenecks limiting the application of CuBi2O4 as a competitive candidate for photoelectrochemical (PEC) hydrogen evolution reaction (HER). To overcome the bottlenecks, we develop a novel template-assisted synthesis strategy to prepare the CuBi2O4 dendrites and then protect the dendritic structure with a conformal nanometer-thick TiO2 passivation layer. The obtained CuBi2O4/TiO2 composite dendrites exhibit high activity for the PEC HER with a photocurrent density of ca. 0.90 mA cm–2 at 0.200 V vs reversible hydrogen electrode (RHE) in neutral solution, and this value is among the highest reported on CuBi2O4-based photocathodes at the same potential. Moreover, the CuBi2O4/TiO2 dendrites show a high photostability with the photocurrent density being stabilized at ca. 0.36 mA cm–2 (88.8% of its original value) after 6 h measurements at a high applied potential of 0.600 V vs RHE, which is superior to all CuBi2O4-based photocathodes reported recently in the literature. This work provides an effective strategy to improve the activity and stability of the copper-oxide-based materials for the HER via constructing a dendritic structure and protecting the structure with a nanoscale TiO2 passivation layer.

In situ biomineralization-constructed superhydrophilic and underwater superoleophobic PVDF-TiO2 membranes for superior antifouling separation of oil-in-water emulsions

In situ construction has emerged for fabricating superwetting PVDF membranes with uniform organic coatings and improved resistance to oil fouling, but it remains almost unexplored to apply this strategy to attain durable inorganic coatings and prepare superior antifouling PVDF membranes. Herein, we developed a novel in situ biomineralization method to fabricate superhydrophilic and underwater superoleophobic PVDF-TiO2 membranes with conformal TiO2 coatings on both the top and internal surfaces. An initial flux of 400 L m−2 h−1 (LMH) with a final flux of 200 LMH at 2.5 h under 0.1 bar, oil rejection higher than 99.7%, and highly stable cycling performance (5 cycles at 130 min each) were achieved on crossflow filtration of surfactant-stabilized oil-in-water emulsions. We used a new “flux map” to make a relatively fair comparison among the reported membranes, which suggested the superior performance of our PVDF-TiO2 membrane. The demonstrated exceptional performance was attributed to the low oil adhesion and great hydrophilicity enabled by the durable and superwetting coatings composed of densely packed TiO2 nanoparticles on the entire membrane, as well as to the relatively smooth top surface with an appropriate surface pore size that alleviate the oils being trapped by the surface structures.

Constructing effective TiO2 nano-coating for high-voltage Ni-rich cathode materials for lithium ion batteries by precise kinetic control

In order to improve the performance of Ni-rich cathode materials for lithium-ion batteries at high cut-off voltage, a highly effective TiO2 nano-coating is constructed on the surface of LiNi0.8Co0.1Mn0.1O2 by precisely controlling the hydrolytic dynamics of Ti4+, and the effect of this coating layer is systematically studied, especially at high upper cut-off voltage. The continuous TiO2 nano-coating layer provides a complete protection for LiNi0.8Co0.1Mn0.1O2 particles and enhances the reversibility of the phase transition between hexagonal and hexagonal (H2→H3) during cycling, which guarantees an excellent cycling stability under high upper cut-off voltage up to 4.5 V. Electrochemical impedance spectroscopy results confirm a stable interface between electrolyte and electrode and the fast kinetics at the surface of the modified sample. High Resolution Transmission Electron Microscopy (HR-TEM) measurement for the cycled electrodes further verifies the slight structure decay of the coated sample comparing with the pristine one. Thus, the modified sample presents excellent cycling stability with capacity retention of 72.2% after 500 cycles and 63.4% after 1000 cycles with the upper cut-off voltage of 4.5 V and 4.3 V, respectively. This work provides a universal method to prepare conformal TiO2 nano-coating and also offer guidance to properly evaluate the function of a coating.

The role of morphology in all-dielectric SERS: A comparison between conformal (T-rex) and non conformal TiO2 shells

All-dielectric optical nanoantennas and resonators are attracting an ever increasing interest for enhanced Raman spectroscopy. These systems can take advantage of many factors that concur to determine their Raman response, including the type of material, refractive index contrast between interfaces, size, shape, roughness and geometrical configuration. However, the relative impact of each one of those terms on the Raman enhancement is still unclear.Here we report the Raman characterization of SiO2@TiO2 semishell microspheres obtained by rf-magnetron sputtering deposition of a TiO2 thin layer on SiO2 cores. The samples were able to significantly amplify Raman scattering in comparison to planar counterparts, however the overall enhancement was very limited with reference to that observed in conformal, smooth and compact TiO2 shell layers obtained by atomic layer deposition. These results demonstrated that geometry is a key factor to maximize the Raman response of these systems and, in general, it is more important than other parameters, such as the surface roughness or even refractive index of the shell layer, which are usually considered crucial for achieving Raman enhancement.

Ultrathin TiO2-coated SiO2 nanoparticles as light scattering centers for quantum dot-sensitized solar cells

SiO2/TiO2 core/shell nanoparticles (ST-NPs) with an ultrathin and conformal TiO2 shell were fabricated via atomic layer deposition (ALD) technique with a specially-designed rotary reactor. We successfully employed the ST-NPs as light scattering centers in a mesoporous TiO2 photoanode in quantum dot (QD)-sensitized solar cells (QDSSCs). ST-NPs enhanced the light scattering in the TiO2 photoanode without deterioration of QD loading behavior. Consequently, visible light absorbance was improved in the PbS QDs-sensitized TiO2 photoanode, and thus the photocurrent density increased from 14 to 17 mA/cm2. Detailed electron microscopy was utilized to reveal the uniqueness of the ultrathin TiO2 shell in ST-NPs, and in-depth electrochemical impedance spectroscopy divulged the increase in photogenerated carrier lifetime and improved recombination resistance for the QDSSC with ST-NPs.

A scalable and biomimetic approach for TiO2 deposition: enabling water splitting by nanostructured WO3 in neutral media as an example

A conformal TiO2 thin layer prepared by a simple biomimetic approach protects WO3 from chemical dissolution at neutral pH.

Atomic Layer Deposition Coating of TiO2 Nano-Thin Films on Magnesium-Zinc Alloys to Enhance Cytocompatibility for Bioresorbable Vascular Stents.

Background and purposeA coronary stent is a well-known cardiovascular medical device implanted to resolve disorders of the circulatory system due to bloodstream narrowing. Since the implanted device interacts with surrounding biological environments, the surface properties of a typical implantable stent play a critical role in its success or failure. Endothelial cell adhesion and proliferation are fundamental criteria needed for the success of a medical device. Metallic coronary stents are commonly used as biomaterial platforms in cardiovascular implants. As a new generation of coronary stents, bioresorbable vascular scaffolds have attracted a great deal of attention among researchers and studies on bioresorbable materials (such as magnesium and zinc) remain a target for further optimization. However, additional surface modification is needed to control the biodegradation of the implant material while promoting biological reactions without the use of drug elution.MethodsHerein, precise temperature and thickness controlled atomic layer deposition (ALD) was utilized to provide a unique and conformal nanoscale TiO2 coating on a customized magnesium-zinc stent alloy.ResultsImpressively, results indicated that this TiO2 nano-thin film coating stimulated coronary arterial endothelial cell adhesion and proliferation with additional features acting as a protective barrier. Data revealed that both surface morphology and surface hydrophilicity contributed to the success of the ALD nanoscale coating, which further acted as a protection layer inhibiting the release of harmful degradation products from the magnesium-zinc stent.ConclusionOverall, the outcome of this in vitro study provided a promising ALD stent coating with unique nano-structural surface properties for increased endothelialization, and as a result, ALD should be further studied for numerous biomedical applications.

Synthesis of CoSe2 nanoparticles embedded in N-doped carbon with conformal TiO2 shell for sodium-ion batteries

CoSe2 is a potential anode material for sodium-ion batteries in terms of their high sodium storage capacity and tunable properties. However, structural degradation and unstable interphase during the reversible sodiation and de-sodiation lead to fast capacity decay. In this work, we develop a nanocomposite architecture based on CoSe2 nanoparticles embedded in N-doped carbon matrix with conformal TiO2 coating (CoSe2@NC@TiO2) by using a metal-organic framework-assisted strategy. The small CoSe2 nanoparticles and N-doped carbon matrix facilitate charge transport and suppress the structural degradation, while the redox-active TiO2 shell further strengthens the structural and interfacial stability without decreasing the capacity. The as-prepared CoSe2@NC@TiO2 nanocomposite particles deliver a reversible sodium storage capacity of 520 mAh g−1 at 0.1 A g−1 with a capacity retention of 78% after 200 cycles, in contrast to the rapid capacity fading after 50 cycles of the pristine CoSe2@NC particles without TiO2 shell.

Al-ZnO/CdS Photoanode Modified with a Triple Functions Conformal TiO2 Film for Enhanced Photoelectrochemical Efficiency and Stability

ZnO/ CdS based nanorod arrays is an excellent class of photoanode materials with high photoelectric response. However, the poor photostability of CdS in aqueous solution seriously prevents its practical application. Although efforts have been made, it still challengeable to improve stability while maintaining initial photocurrent. Herein, a highly efficient photoanode system consisting of Al-doped ZnO nanorod arrays (NRs) served as effective electron-transfer layer and CdS as a light harvesting layer was designed. At last, TiO2 protective layer was deposited onto Al-ZnO/CdS photoanodes through atomic layer deposition (ALD) to enhance the photostability. The integrated Al-ZnO/CdS/TiO2 photoanode exhibits a photocurrent of 11.7 mA/cm2 at 1.23 V versus reversible hydrogen potential (RHE) and conversion efficiency of 5.9 % at 0.48 V versus RHE for 60 ALD TiO2 cycles. More importantly, the photostability of Al-ZnO/CdS/TiO2 photoanode was significantly prolonged comparing with the untreated Al-ZnO/CdS photoanode. The strengthen stability is benefited from the triple functions of ALD TiO2 layer, that is, isolating the direct contact between the photoanode with the surrounding liquid environment, passivating the surface state of the CdS, and capturing as well as storing the photogenerated hole.