TiO2 Surface Layer Research Articles

The effect of Ti-based surface layer on AlSi thin film as a high-performance anode for the lithium-ion battery

Significant volume changes during cycling and the instability of the solid electrolyte interphase (SEI) are the main challenges that limit the practical application of silicon-based anodes. TiN and TiO2 were selected as surface layers and deposited on the HCl-etched AlSi (AlSi’) thin films by atomic layer deposition (ALD) to enhance the electrochemical performance of the anode. The surface layers with excellent mechanical strength can effectively suppress the volume expansion of the AlSi thin film and maintain excellent electrical contact between the film and the substrate during cycling. The effects of TiN and TiO2 surface layers on the composition and growth of the SEI layer on the AlSi’ film anode have been discussed in detail. The TiO2 surface layer was found to inhibit the continuous growth of the SEI layer and promote the formation of a mechanically robust and stable SEI layer. The AlSi’/TiO2(8 nm) anode shows a high initial discharge capacity of 2802 mA h g-1 with an initial coulomb efficiency (ICE) of 88% at 0.8 A g-1, and it maintains a capacity retention rate of 83% after 500 cycles. Moreover, the AlSi’/TiO2(8 nm) anode exhibits outstanding rate performance, as it sustains a capacity of 1710 mA h g-1 after 500 cycles at 5 A g-1, and maintains a capacity above 1032 mA h g-1 even at 30 A g-1.

Analysis of Shape-Memory-Alloy Fiber Interface Strength for Optimization of Self-Healing Composites

Self-healing materials, possessing an innate ability to mend damage and restore structural strength, have tremendous potential to improve safety and reliability, especially in space applications where recovery or manual performance of repairs may be prohibitive, dangerous, or impossible. Self-healing metallic materials developed with Nickel Titanium (NiTi) Shape Memory Alloy (SMA) reinforcement showed a promising prospect for recovering from larger scale damage. However, NiTi is known to form an inert oxide (TiO2) surface layer that is extremely hard to attach to. In this research, to promote better strength between the fiber and matrix, TiO2 surface layer has been removed by etching the NiTi wires in an inert environment and a pull test has been performed to evaluate the resulting change in adhesion strength between the fiber and metallic matrix. The experimental investigation of these interface fracture scenarios will enable the efficient design of composite materials.

Seeking the Oxidation Mechanism of Debris in the Fretting Wear of Titanium Functionalized by Surface Laser Treatments

Surface laser treatment (SLT) using nanosecond IR lasers has been shown to improve the tribological behaviour of titanium. Here, we studied the fretting wear of SLT-functionalized pure titanium in a mixture of reactive gases O2 (20 vol.%) + N2 (80 vol.%). The contact geometry was a ball on a plane and the ball was made of bearing steel. The very small amplitude of relative displacement between reciprocating parts in fretting wear makes the evacuation of wear particles difficult. Moreover, the oxidation mechanism of the debris depends on the accessibility of the surrounding atmosphere to the tribological contact. This work focused in the analysis of debris generation and oxidation mechanisms, and sought to differentiate the role of oxygen forming part of the ambient O2 + N2 gas mixture from oxygen present in the surface layer of the SL-treated titanium. Before the fretting test, the surface of the commercially pure titanium plates was treated with a laser under a mixture of O2 + N2 gases with oxygen enriched in the 18O isotope. Then, the fretting tests were performed in regular air containing natural oxygen. Micro-Raman spectroscopy and ion beam analysis (IBA) techniques were used to analyse the TiO2 surface layers and fretting scars. Iron oxide particles were identified by Raman spectroscopy and IBA as the third body in the tribological contact. The spatial distribution of 18O, Ti, 16O and Fe in the fretting scars was studied by IBA. The analysis showed that the areas containing high concentrations of Fe displayed also high concentrations of 16O, but smaller concentrations of 18O and Ti. Therefore, it was concluded that tribological contact allows the oxidation of iron debris by its reaction with ambient air.

Preparation of pH-sensitive surface based on mixed oxides of titanium and iridium for early detection of inflammation around the implant

The surface of an implant used during operation is a preferred site for the attachment of harmful microorganisms. These subsequently affect the surrounding tissue with their metabolic products, including the tissue's pH. The possibility of sensing the pH around the implant could be a way of detecting the infection in the early stages. Transition metal oxides can be used for these applications. The most common alloys used for the manufacture of implants are titanium alloys which are characterized by a passive TiO2 surface layer that can be modified. In this work, the Ti–6Al–4V alloy whose surface was nanostructured was used. Iridium particles were subsequently deposited on the prepared surface by various methods to increase the sensitivity to pH change. The potentiostatic mode was chosen as the most suitable method of deposition. Energy dispersive analysis and X-ray photoelectron spectroscopy verified the success of iridium particle deposition. The electrochemical response was measured in a physiological saline solution and monitoring the open circuit potential change proved to be the most appropriate sensing method. After subsequent oxidation process, the prepared surface showed a sensitivity of 64 mV/pH at 37 °C.

Improving the Electron Transport Performance of TiO2 Film by Regulating TiCl4 Post-Treatment for High-Efficiency Carbon-Based Perovskite Solar Cells.

Titanium oxide (TiO2 ) has been widely used as an electron transport layer (ETL) in perovskite solar cells (PSCs). Typically, TiCl4 post-treatment is indispensable for modifying the surfaces of TiO2 ETL to improve the electron transport performance. However, it is challenging to produce the preferred anatase phase-dominated TiO2 by the TiCl4 post-treatment due to the higher thermodynamic stability of the rutile phase. In this work, a mild continuous pH control strategy for effectively regulating the hydrolysis process of TiCl4 post-treatment is proposed. As the weak organic base, urea has been demonstrated can maintain a moderate pH decrease during the hydrolysis process of TiCl4 while keeping the hydrolysis process relatively mild due to the ultra-weak alkalinity. The improved pH environment is beneficial for the formation of anatase TiO2 . Consequently, a uniform anatase-dominated TiO2 surface layer is formed on the mesoporous TiO2 , resulting in reduced defect density and superior band energy level. The interfacial charge recombination is effectively suppressed, and the charge extraction efficiency is improved simultaneously in the fabricated solar cells. The efficiency of the fabricated carbon electrode-based PSCs (C-PSCs) is improved from 16.63% to 18.08%, which is the highest for C-PSCs based on wide-bandgap perovskites.

The effects of radio frequency atmospheric pressure plasma and thermal treatment on the hydrogenation of TiO2 thin film

The effects of radio frequency (RF) atmospheric pressure (AP) He/H2 plasma and thermal treatment on the hydrogenation of TiO2 thin films were investigated and compared in this work. The color of the original TiO2 film changes from white to black after being hydrogenated in He/H2 plasma at 160 W (gas temperature ∼381 °C) within 5 min, while the color of the thermally treated TiO2 film did not change significantly even in pure H2 or He/H2 atmosphere with higher temperature (470 °C) and longer time (30 min). This indicated that a more effective hydrogenation reaction happened through RF AP He/H2 plasma treatment than through pure H2 or He/H2 thermal treatment. The color change of TiO2 film was measured based on the Commission Internationale d’Eclairage L*a*b* color space system. Hydrogenated TiO2 film displayed improved visible light absorption with increased plasma power. The morphology of the cauliflower-like nanoparticles of the TiO2 film surface remained unchanged after plasma processing. X-ray photoelectron spectroscopy results showed that the contents of Ti3+ species and Ti–OH bonds in the plasma-hydrogenated black TiO2 increased compared with those in the thermally treated TiO2. X-ray diffraction (XRD) patterns and Raman spectra indicated that plasma would destroy the crystal structure of the TiO2 surface layer, while thermal annealing would increase the overall crystallinity. The different trends of XRD and Raman spectra results suggested that plasma modification on the TiO2 surface layer is more drastic than on its inner layer, which was also consistent with transmission electron microscopy results. Optical emission spectra results suggest that numerous active species were generated during RF AP He/H2 plasma processing, while there were no peaks detected from thermal processing. A possible mechanism for the TiO2 hydrogenation process by plasma has been proposed. Numerous active species were generated in the bulk plasma region, accelerated in the sheath region, and bumped toward the TiO2 film, which will react with the TiO2 surface to form OVs and disordered layers. This leads to the tailoring of the band gap of black TiO2 and causes its light absorption to extend into the visible region.

Surface-redox sodium-ion storage in anatase titanium oxide

Sodium-ion storage technologies are promising candidates for large-scale grid systems due to the abundance and low cost of sodium. However, compared to well-understood lithium-ion storage mechanisms, sodium-ion storage remains relatively unexplored. Herein, we systematically determine the sodium-ion storage properties of anatase titanium dioxide (TiO2(A)). During the initial sodiation process, a thin surface layer (~3 to 5 nm) of crystalline TiO2(A) becomes amorphous but still undergoes Ti4+/Ti3+ redox reactions. A model explaining the role of the amorphous layer and the dependence of the specific capacity on the size of TiO2(A) nanoparticles is proposed. Amorphous nanoparticles of ~10 nm seem to be optimum in terms of achieving high specific capacity, on the order of 200 mAh g−1, at high charge/discharge rates. Kinetic studies of TiO2(A) nanoparticles indicate that sodium-ion storage is due to a surface-redox mechanism that is not dependent on nanoparticle size in contrast to the lithiation of TiO2(A) which is a diffusion-limited intercalation process. The surface-redox properties of TiO2(A) result in excellent rate capability, cycling stability and low overpotentials. Moreover, tailoring the surface-redox mechanism enables thick electrodes of TiO2(A) to retain high rate properties, and represents a promising direction for high-power sodium-ion storage.

CO Oxidation over Pd Catalyst Supported on Porous TiO2 Prepared by Plasma Electrolytic Oxidation (PEO) of a Ti Metallic Carrier.

A porous TiO2 layer was prepared with the plasma electrolytic oxidation (PEO) of Ti. In a further step, Pd was deposited on the TiO2 surface layer using the adsorption method. The activity of the Pd/TiO2/Ti catalyst was investigated during the oxidation of CO to CO2 in a mixture of air with 5% CO. The structure of the catalytic active layer was studied using a scanning electron microscope equipped with an energy dispersive spectrometer (SEM-EDS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), inductively coupled plasma mass spectrometry (ICP-MS), and X-ray diffraction (XRD). The PEO process provided a porous TiO2 layer with a uniform thickness in the range of 5–10 µm, which is desirable for the production of Pd-supported catalysts. A TOF-SIMS analysis showed the formation of Pd nanoparticles after the adsorption treatment. The conversion of CO to CO2 in all samples was achieved at 150–280 °C, depending on the concentration of Pd. The composition of Pd/ TiO2/Ti was determined using ICP-MS. The optimum concentration of Pd on the surface of the catalyst was approximately 0.14% wt. This concentration was obtained when a 0.4% PdCl2 solution was used in the adsorption process. Increasing the concentration of PdCl2 did not lead to a further improvement in the activity of Pd/ TiO2/Ti.

Transformations of the Microstructure and Phase Compositions of Titanium Alloys during Ultrasonic Impact Treatment Part II: Ti-6Al-4V Titanium Alloy

Experimental and theoretical studies enabled the reveal of patterns of the microstructure formation in the surface layer of Ti-6Al-4V titanium alloy subjected to ultrasonic impact treatment. The mixed amorphous and nanocrystalline structure of the 200 nm thick uppermost surface layer of titanium dioxide TiO2 was demonstrated using transmission electron microscopy. The 5 µm thick intermediate layer containing nanocrystalline α grains, and the 50–60 µm thick lower layer containing fragmented α-Ti grains with retained β phase were also observed. The refinement of the β-Ti phase during ultrasonic impact treatment was accompanied by the formation of the orthorhombic (α″) martensitic phase. Molecular dynamics simulation of strains of a vanadium-doped titanium crystallite subjected to ultrasonic impact treatment revealed the formation of striped dislocation substructures as well as the development of reversible β→α phase transformations. Ab initio calculations of the atomic structure of V-doped Ti crystallites containing α, β or α″ phases of titanium were carried out. On the basis of the results of the experimental observations, a molecular dynamics simulation and ab initio calculations a mechanism was proposed, which associated the development of the strain-induced β→α″ phase transformations in Ti-6Al-4V alloy with the presence of oxygen. The role of the electronic subsystem in the development of the strain-induced phase transformations was discussed.

Biocompatibility and Mechanical Stability of Nanopatterned Titanium Films on Stainless Steel Vascular Stents

Nanoporous ceramic coatings such as titania are promoted to produce drug-free cardiovascular stents with a low risk of in-stent restenosis (ISR) because of their selectivity towards vascular cell proliferation. The brittle coatings applied on stents are prone to cracking because they are subjected to plastic deformation during implantation. This study aims to overcome this problem by using a unique process without refraining from biocompatibility. Accordingly, a titanium film with 1 µm thickness was deposited on 316 LVM stainless-steel sheets using magnetron sputtering. Then, the samples were anodized to produce nanoporous oxide. The nanoporous oxide was removed by ultrasonication, leaving an approximately 500 nm metallic titanium layer with a nanopatterned surface. XPS studies revealed the presence of a 5 nm-thick TiO2 surface layer with a trace amount of fluorinated titanium on nanopatterned surfaces. Oxygen plasma treatment of the nanopatterned surface produced an additional 5 nm-thick fluoride-free oxide layer. The samples did not exhibit any cracking or spallation during plastic deformation. Cell viability studies showed that nanopatterned surfaces stimulate endothelial cell proliferation while reducing the proliferation of smooth muscle cells. Plasma treatment further accelerated the proliferation of endothelial cells. Activation of blood platelets did not occur on oxygen plasma-treated, fluoride-free nanopatterned surfaces. The presented surface treatment method can also be applied to other stent materials such as CoCr, nitinol, and orthopedic implants.

Thermal nanoimprint lithography of sodium hyaluronate solutions with gas permeable inorganic hybrid mold for cosmetic and pharmaceutical applications

Gas-permeable inorganic hybrid mold that hybridized the surface layer of TiO2–SiO2 gas-permeable polymer using the sol–gel method and the lower layer of porous maraging steel by a metal three-dimensional printer was developed for fluid function materials containing high concentrations of water and volatile solvents. Thermal nanoimprint lithography was used to fabricate the advanced high-resolution needle patterning of sodium hyaluronate containing volatile solvents to broaden the application area of fluid function materials such as cosmetics and pharmaceuticals.

Improved SERS sensitivity of TiO2 nanorod films by annealing in vacuum

In this paper, substoichiometric TiO2-x nanorod films were prepared by vacuum annealing treatment of TiO2 nanorod films for an optimized period of time as a simple and effective method. As surface-enhanced Raman scattering (SERS) substrates, the TiO2-x nanorod films show good stability and high sensitivity because of the detection limit of Rhodamine 6G (R6G) as low as 10−6 M. By combining photoluminescence (PL), UV–vis diffuse reflectance, Raman and electrical measurement, a high density of electronic states related to oxygen vacancy below the Fermi level has been identified in the reduced TiO2−x. Besides, X-ray photoelectron spectroscopy (XPS) analysis exhibits an ultra-thin TiO2 layer was formed at the outmost surface of TiO2-x. The effect of the TiO2 surface layer includes two aspects: (a) providing abundant regenerated surface oxygen-vacancy-associated levels to promote charge transfer between analyte and substrate under illumination of visible light; and (b) protecting oxygen vacancy from further oxidation to improve the stability of SERS performance of TiO2.

Degradation-resistant TiO2@Sn anodes for high-capacity lithium-ion batteries

As the demand for higher-performance batteries has increased, so has the body of research on theoretical high-capacity anode materials. However, the research has been hindered because the high-capacity anode material properties and interactions are not well understood, largely due to the difficulty of observing cycling in situ. Using electrochemical scanning transmission electron microscopy (ec-STEM), we report the real-time observation and electrochemical analysis of pristine tin (Sn) and titanium dioxide-coated Sn (TiO2@Sn) electrodes during lithiation/delithiation. As expected, we observed a volume expansion of the pristine Sn electrodes during lithiation, but we further observed that the expansion was followed by Sn detachment from the current collector. Remarkably, although the TiO2@Sn electrodes also exhibited similar volume expansion during lithiation, they showed no evidence of Sn detachment. We found that the TiO2 surface layer acted as an electrochemically activated artificial solid-electrolyte interphase that serves to conduct Li ions. As a physical coating, it mechanically prevented Sn detachment following volume changes during cycling, providing significant degradation resistance and 80% Coulombic efficiency for a complete lithiation/delithiation cycle. Interestingly, upon delithiation, TiO2@Sn electrode displayed a self-healing mechanism of small pore formation in the Sn particle followed by agglomeration into several larger pores as delithiation continued.

Molecular-Level Understanding of the Influence of Ions and Water on HMGB1 Adsorption Induced by Surface Hydroxylation of Titanium Implants.

Due to its excellent chemical and mechanical properties, titanium has become the material of choice for orthopedic and dental implants to promote rehabilitation via bone anchorage and osseointegration. Titanium osseointegration is partially related to its capability to form a TiO2 surface layer and its ability to interact with key endogenous proteins immediately upon implantation, establishing the first bone-biomaterial interface. Surgical trauma caused by implantation results in the release of high-mobility group box 1 (HMGB1) protein, which is a prototypic DAMP (damage-associated molecular pattern) with multiple roles in inflammation and tissue healing. To develop different surface strategies that improve the clinical outcome of titanium-based implants by controlling their biological activity, a molecular-scale understanding of HMGB1-surface interactions is desired. Here, we use molecular dynamics (MD) computer simulations to provide direct insight into the HMGB1 interactions and the possible molecular arrangements of HMGB1 on fully hydroxylated and nonhydroxylated rutile (110) TiO2 surfaces. The results establish that HMGB1 is most likely to be adsorbed directly onto the surface regardless of surface hydroxylation, which is undesirable because it could affect its biological activity by causing structural changes to the protein. The hydroxylated TiO2 surface shows a greater affinity for HMGB1 than the nonhydroxylated surface. The water layer on the nonhydroxylated TiO2 surface prevents ions and the protein from directly contacting the surface. However, it was observed that if the ionic strength increases, the total number of ions adsorbed on the two surfaces increases and the protein's direct adsorption ability decreases. These findings will help to understand the HMGB1-TiO2 interactions upon implantation as well as the development of different surface strategies by introducing ions or ionic materials to the titanium implant surface to modulate its interactions with HMGB1 to preserve biological function.

In-Depth Metallurgical and Microstructural Analysis of Oneshape and Heat Treated Onecurve Instruments.

To define surface, mechanical, microstructural and metallurgical features of conventional One-Shape (OShape) and heat-treated OneCurve (OCurve) nickel-titanium instruments. Instruments were analysed by scanning electron microscopy (SEM) on new instruments and after simulated clinical use (SCU). Cyclic fatigue testing was performed and the number of cycles to fracture (NCF) and the length of the fractured instruments were measured (Mann-Whitney test). Fractured instruments during cyclic fatigue testing were then inspected by SEM fractographic analysis. Field emission gun scanning scanning electron microscopy (FEG-SEM), energy-dispersive X-ray spectroscopy (EDX) and micro-Raman spectroscopy were used to assess alloy surface chemistry. Focused ion beam (FIB) was performed to analyse the oxide layer on the surface of OCurve before and after SCU. X-Ray diffraction (XRD), metallographic evaluation and differential scanning calorimetry (DSC) were used to determine martensitic/austenitic phase transformation temperatures. SEM observations on new instruments revealed a smooth regular surface with flattened milling grooves. No wear features were detected after SCU. OCurve exhibited a higher cyclic fatigue resistance (P<0.05), slower crack propagation and a surface layer of TiO2. Metallographic analysis and XRD showed the prevalence of martensitic grains on OCurve instruments that were stable at body temperature as confirmed by DSC analysis. Furthermore, DSC demonstrated a shift in the temperature transformation ranges suggesting an increase of martensite phase in autoclaved OCurve instruments. Heat treatment processes were confirmed as a valid enhancement of the properties of the new generation NiTi instruments. OCurve presented a significant improvement over OShape regarding both mechanical and metallurgical characteristics.

In-Depth Metallurgical and Microstructural Analysis of Oneshape and Heat Treated Onecurve Instruments

Objective:To define surface, mechanical, microstructural and metallurgical features of conventional OneShape (OShape) and heat-treated OneCurve (OCurve) nickel-titanium instruments.Methods:Instruments were analysed by scanning electron microscopy (SEM) on new instruments and after simulated clinical use (SCU). Cyclic fatigue testing was performed and the number of cycles to fracture (NCF) and the length of the fractured instruments were measured (Mann-Whitney test). Fractured instruments during cyclic fatigue testing were then inspected by SEM fractographic analysis. Field emission gun scanning scanning electron microscopy (FEG-SEM), energy-dispersive X-ray spectroscopy (EDX) and micro-Raman spectroscopy were used to assess alloy surface chemistry. Focused ion beam (FIB) was performed to analyse the oxide layer on the surface of OCurve before and after SCU. X-Ray diffraction (XRD), metallographic evaluation and differential scanning calorimetry (DSC) were used to determine martensitic/austenitic phase transformation temperatures.Results:SEM observations on new instruments revealed a smooth regular surface with flattened milling grooves. No wear features were detected after SCU. OCurve exhibited a higher cyclic fatigue resistance (P<0.05), slower crack propagation and a surface layer of TiO2. Metallographic analysis and XRD showed the prevalence of martensitic grains on OCurve instruments that were stable at body temperature as confirmed by DSC analysis. Furthermore, DSC demonstrated a shift in the temperature transformation ranges suggesting an increase of martensite phase in autoclaved OCurve instruments.Conclusion:Heat treatment processes were confirmed as a valid enhancement of the properties of the new generation NiTi instruments. OCurve presented a significant improvement over OShape regarding both mechanical and metallurgical characteristics.

Prevalence of titanium hypersensitivity in patients with titanium implants: A systematic review and meta-analysis

Background:With increase in exposure to titanium in daily life and its use in medical procedures, there is a greater chance for developing titanium hypersensitivity. Our aim and objective is to examine whether patient patients with titanium implants had a greater incidence of titanium hypersensitivity or not. Titanium is widely considered to have good biocompatibility. A passivating surface layer of TiO2 is formed when exposed to air which gives it good corrosion resistance. These properties along with its high strength, lightweight, and improvements in smelting technologies have led to its widespread use as an intraosseous and periosteal implant in dentistry and orthopedics.Materials and Methods:Only case–control studies were used for the meta-analysis. Studies with a sample size of <5 were excluded. Cutaneous and epicutaneous tests were used in the study.Results:Three studies met the inclusion criteria. Titanium hypersensitivity is more prevalent in patients with titanium implants.Conclusions:It is also used in a variety of medical devices such as pacemakers and insulin pumps. Moreover, our external exposure to titanium is increasing. It is used in aerospace, chemical, and automobile industries. It is also used in jewelry, home furnishings, and in making sports and marine equipment. Titanium implants increase the possibility of developing titanium hypersensitivity, and thus, it should be considered as a major factor in unexplained implant failure where other causes have been excluded.

Formation of multi-functional TiO2 surfaces on AA2024 alloy using plasma electrolytic oxidation

Plasma electrolytic oxidation (PEO) was applied to functionalise the surface of AA2024 alloy. A potassium titanium-oxide oxalate dihydrate based aqueous electrolyte was used, which allowed the direct formation of a TiO2 surface layer on the aluminium alloy substrate. The effect of PEO treatment time and the additional presence of anatase particles in the electrolyte solution on the surface layer and its properties (corrosion, wear and photocatalytic activity) were investigated.It was found that the coating thickness and surface morphology are strongly dependent on the PEO processing time. However, the phase composition is not much affected by the treatment time and the main coating phase is rutile with a smaller amount of anatase. Adding additional anatase in the form of particles increases the amount of anatase in the coatings. The additional particle addition has only minor effect on the corrosion resistance, but reduces the wear resistance remarkably. Interestingly, the addition of anatase particles and the PEO treatment time are not effective in increasing the photocatalytic activities of the samples.

Thermal Atomic Layer Etching of Gallium Oxide Using Sequential Exposures of HF and Various Metal Precursors

Gallium oxide (Ga2O3) is a transparent semiconducting oxide with a large band gap that has applications for power electronics and optoelectronics. Ga2O3 device fabrication requires etching for many processing steps. In this work, the thermal atomic layer etching (ALE) of Ga2O3 was performed using hydrofluoric acid (HF) and a wide range of different metal precursors including BCl3, AlCl(CH3)2, Al(CH3)3, TiCl4, and Ga(N(CH3)2)3. Because Ga2O3 is not a particularly stable oxide, the B-, Al-, or Ti-containing metal precursors can possibly convert the surface of Ga2O3 to B2O3, Al2O3, or TiO2. These metal precursors can also provide Cl, CH3, and N(CH3)2 ligands for ligand-exchange reactions. Consequently, the thermal ALE of Ga2O3 can occur via “conversion-etch” or fluorination and ligand-exchange reaction pathways. Using sequential HF and BCl3 exposures and in situ spectroscopic ellipsometry techniques, Ga2O3 etch rates were observed to vary from 0.59 to 1.35 Å/cycle at temperatures from 150 to 200 °C, respectively. The Ga2O3 etch rates were also self-limiting versus HF and BCl3 exposure. The lack of BCl3 pressure dependence for the etch rates argued against the conversion-etch mechanism and in favor of a fluorination and ligand-exchange reaction pathway. In situ quartz crystal microbalance techniques also revealed that Ga2O3 could be etched using sequential exposures of HF and various other metal precursors. Ga2O3 etch rates at 250 °C were 1.2, 0.82, 0.85, and 0.23 Å/cycle for AlCl(CH3)2, Al(CH3)3, TiCl4, and Ga(N(CH3)2)3 as the metal precursors, respectively. The mass changes during the individual exposures of HF and the AlCl(CH3)2 and Al(CH3)3 metal precursors argued for a fluorination and ligand-exchange mechanism. The AlCl(CH3)2 and Al(CH3)3 exposures may also lead to some conversion of Ga2O3 to Al2O3. In contrast, the mass changes during the HF and TiCl4 exposures were consistent with the conversion of the surface of Ga2O3 to TiO2 and then the spontaneous removal of the TiO2 surface layer by HF. Distinctly different behavior was observed during the HF and Ga(N(CH3)2)3 exposures. The large mass gain during the Ga(N(CH3)2)3 exposures suggested that Ga(N(CH3)2)3 can adsorb on the fluorinated Ga2O3 surface prior to the ligand-exchange reaction. The wide range of metal precursors that can etch Ga2O3 argues that the ability of these precursors to convert Ga2O3 or to undergo ligand-exchange reactions provides multiple pathways for effective thermal Ga2O3 ALE.

Ultrathin TiO2 surface layer coated TiN nanoparticles in freestanding film for high sulfur loading Li-S battery

A novel structure of ultrathin TiO2 surface layer coated TiN (TiO2@TiN) nanoparticle as polysulfide reservoir which can simultaneously boosts the static trapping and dynamic conversion of LiPS is proposed. TiO2@TiN nanoparticles are found to be uniformly distributed on three dimensional well connected nitrogen doped carbon nanofibers (CNFs) which provide extra chemical adsorption sites and continuous electron transfer pathways. With the synergistic effect of TiO2@TiN and CNFs, TiO2@TiN/CNFs cathode shows exceptionally excellentrate capability by delivering 950 mAh g−1 at current density of 5 mA cm−2 with sulfur loading of 5 mg cm−2. High sulfur utilization by maintaining 6.41 mAh cm−2 after 200 cycles with sulfur loading of 8.0 mg cm−2 is observed. The cycling stability is also confirmed by the discharge capacity of 800 mAh g−1 after 400 cycles with sulfur loading of 4.0 mg cm−2. Moreover, the in-situ conversion, adsorption-conversion and desorption-conversion mechanisms are proposed and confirmed by symmetric batteries and full batteries. This work highlights the superiority of surface chemistry and electrode structure in high sulfur loaded Li-S battery and provides new insights for developing high energy density Li-S battery.