Titanium Buffer Layer Research Articles

TiSZ-reinforced hydroxyapatite coatings on magnesium substrate with titanium interlayer

ABSTRACT In this study, pure and 10% wt. Titania-Stabilised Zirconia (TiSZ) -reinforced Hydroxyapatite (HA) coatings were deposited on magnesium substrate using plasma spray as a single layer and double layer with an HVOF sprayed Ti bond coat. The coated specimens were characterised by X-ray diffraction (XRD) analysis, and scanning electron microscopy equipped with energy dispersive spectroscopy (SEM, EDS). Rockwell-C adhesion and scratch tests were performed. The corrosion behaviours in simulated body fluid (SBF) of coatings were investigated by an electrochemical corrosion test. Analyses confirmed successful coating with a dense titanium buffer layer. The double-layered HA-titanium combination offered superior corrosion resistance compared to single layers. While adding TiSZ enhanced adhesion, it compromised scratch resistance. The titanium bond coat had minimal impact on adhesion and cohesion behaviour of coatings.

Magnetic nanostructures with defined magnetic states fabricated by focused ion beam

A comparative analysis of the effects of Ga+-focused ion beam (FIB) on the magnetic properties of nanostructures was conducted in this study. It shows that the FIB cuts that cause the structures to switch from the initial vortex to the single-domain (“snake-like”) states do not require complete physical separation of the elements. Numerical simulations indicate that a remaining 3–5 nm or less magnetic material in a 20–30 nm thick permalloy layer can cause the switching. These results were partially confirmed experimentally, where grooves with a depth between 15–30 nm caused the switching. The addition of a titanium buffer layer significantly improves the accuracy and quality of the FIB cuts by reducing the amount of redeposited material.

Coevaporation of Doped Inorganic Carrier‐Selective Layers for High‐Performance Inverted Planar Perovskite Solar Cells

Inorganic carrier‐selective layers (CSLs), whose conductivity can be effectively tuned by doping, offer low‐cost and stable alternatives for their organic counterparts in perovskite solar cells (PSCs). Herein, a dual‐source electron‐beam co‐evaporation method for the controlled deposition of copper‐doped nickel oxide (Cu:NiO) and tungsten‐doped niobium oxide (W:Nb2O5) as hole and electron transport layers, respectively, is used. The mechanisms for the improved conductivity using dopants are investigated. Owing to the improved conductivity and optimized band alignment of the doped CSLs, the all‐inorganic‐CSLs‐based PSCs achieve a maximum power conversion efficiency (PCE) of 20.47%. Furthermore, a thin titanium buffer layer is inserted between W:Nb2O5 and the silver electrode to prevent halide ingression and improve band alignment. This leads to a further improvement of PCE to 21.32% and long‐term stability (1200 h) after encapsulation. Finally, the large‐scale applicability of the doped CSLs by coevaporation is demonstrated for the device with 1 cm2 area showing a PCE of over 19%. The results demonstrate the potential application of the coevaporated CSLs with controlled doping in PSCs for commercialization.

Simplified patterning process for the selective 1D ZnO nanorods growth

A novel patterning method for the selective growth of ZnO nanorods has been developed, which can avoid any etching steps and longtime lift-off processes. In the simplified process, the deposition of a titanium buffer layer is omitted, and a 50 nm ZnO thin-film seed layer is deposited by e-beam evaporation directly onto the silicon patterned with the photoresist. The omitted titanium buffer layer has been observed to result in the absence of the ZnO seed layer on the photoresist. Then, the ZnO nanorods with diameters ranging from 50 to 500 nm have been found to grow hydrothermally only on the regions without the photoresist. The photoresist remains on the substrate after the hydrothermal growth, which can protect areas from the polluted solution and unwanted nanorods. After all processes, the photoresist can be removed easily by the solvent without any unwanted damage of nanorods. With this simplified method, ZnO nanorods can be synthesized and patterned with only one step of lithography, which can be used for novel ZnO based devices.

Resistive switching characteristics of a modified active electrode and Ti buffer layer in Cu[sbnd]Se-based atomic switch

Atomic switches are well-known promising candidates for future application in non-volatile logic memory devices. The resistive switching characteristics of these devices depend on the formation of a conductive filament (CF) by active metal electrodes. However, the formation of a stable CF is still a challenge owing to filament overgrowth in the solid electrolyte. To achieve controlled CF growth, we have used a modified active electrode with different CuxSe1−x composition ratios (0.01 < x < 0.45) and a titanium (Ti) buffer layer. The optimum composition was determined to be Cu0.11Se0.89/Ti (2.5 nm) for which excellent resistive switching properties were observed, such as a high on/off ratio of 104, low operating voltage, uniform resistance distribution, ten-year data retention at 85 °C, and uniform endurance (2000 cycles). The improvement is can be described from the high controllability of the oxidation-reduction reaction rate of the optimized CuSe modified active electrode by the means of Ti buffer layer and the TiO bond formation at the Ti/Al2O3 interface. In addition, depth profiles of the conductive filament based on Cu0.11Se0.89 with a Ti buffer layer were studied by performing current atomic force microscopy (I-AFM) to evaluate the enhancements in electrical performance and reliability resulting from the insertion of the Ti buffer layer.

High performance top-gated multilayer WSe2 field effect transistors

In this paper, high performance top-gated WSe2 field effect transistor (FET) devices are demonstrated via a two-step remote plasma assisted ALD process. High-quality, low-leakage aluminum oxide (Al2O3) gate dielectric layers are deposited onto the WSe2 channel using a remote plasma assisted ALD process with an ultrathin (∼1 nm) titanium buffer layer. The first few nanometers (∼2 nm) of the Al2O3 dielectric film is deposited at relatively low temperature (i.e. 50 °C) and remainder of the film is deposited at 150 °C to ensure the conformal coating of Al2O3 on the WSe2 surface. Additionally, an ultra-thin titanium buffer layer is introduced at the WSe2 channel surface prior to ALD process to mitigate oxygen plasma induced doping effects. Excellent device characteristics with current on–off ratio in excess of 106 and a field effect mobility as high as 70.1 cm2 V–1 s–1 are achieved in a few-layer WSe2 FET device with a 30 nm Al2O3 top-gate dielectric. With further investigation and careful optimization, this method can play an important role for the realization of high performance top gated FETs for future optoelectronic device applications.

Poly-4-vinylphenol (PVP) and Poly(melamine-co-formaldehyde) (PMF)-Based Atomic Switching Device and Its Application to Logic Gate Circuits with Low Operating Voltage.

In this study, we demonstrate a high-performance solid polymer electrolyte (SPE) atomic switching device with low SET/RESET voltages (0.25 and -0.5 V, respectively), high on/off-current ratio (105), excellent cyclic endurance (>103), and long retention time (>104 s), where poly-4-vinylphenol (PVP)/poly(melamine-co-formaldehyde) (PMF) is used as an SPE layer. To accomplish these excellent device performance parameters, we reduce the off-current level of the PVP/PMF atomic switching device by improving the electrical insulating property of the PVP/PMF electrolyte through adjustment of the number of cross-linked chains. We then apply a titanium buffer layer to the PVP/PMF switching device for further improvement of bipolar switching behavior and device stability. In addition, we first implement SPE atomic switch-based logic AND and OR circuits with low operating voltages below 2 V by integrating 5 × 5 arrays of PVP/PMF switching devices on the flexible substrate. In particular, this low operating voltage of our logic circuits was much lower than that (>5 V) of the circuits configured by polymer resistive random access memory. This research successfully presents the feasibility of PVP/PMF atomic switches for flexible integrated circuits for next-generation electronic applications.

Biodegradable bi-layered coatings shaped by dipping of Ti films followed by the EPD of gelatin/hydroxyapatite composites

The work describes the incorporation of hydroxyapatite (HA) into gelatin (GN) films that gels on cooling shaped using electrophoretic deposition (EPD) on stainless steel substrates. Titanium buffer layer (Ti) prepared by dip coating was inserted to improve the bonding strength between HA/GN layer and substrate. Then suspensions composed of 1vol% of HA/GN (76/24, 61/39, 50/50wt/wt) were formulated to shape a bilayer structure Ti-HA/GN. Rheological properties of HA/GN suspensions, including the evolution of their viscoelastic behaviour at room conditions and at gelling temperature, were studied to determine the gel strength. Results demonstrate that the measurement of the suspension viscosity, its frequency dependent behaviour and the strength of its internal structure, are excellent tools to characterize slurry with regard to its suitability for shaping the polymer/ceramic composite by EPD. Obtained results confirmed the shaping of a bilayer system, growing by sequential dipping of Ti films and EPD of HA/GN coatings.

Research on titanium nitride thin films deposited by reactive magnetron sputtering for MEMS applications

Titanium nitride can be used among other materials as diffusion barrier for MEMS (microelectromechanical systems) applications. The aim of this study is to elaborate and to characterize at nanoscale titanium nitride thin films. The thin films were deposited by reactive magnetron sputtering on silicon substrates using a 99.99% purity titanium target. Different deposition parameters were employed. The deposition temperature, deposition time, substrate bias voltage and the presence/absence of a titanium buffer layer are the parameters that were modified. The so-obtained films were then investigated by atomic force microscopy. A significant impact of the deposition parameters on the determined mechanical and tribological characteristics was highlighted. The results showed that the titanium nitride thin films deposited for 20min at room temperature without the presence of a titanium buffer layer when a negative bias of −90V was applied to the substrate is characterized by the best tribological and mechanical behavior.

Characteristics of the epitaxy of InGaN-based light-emitting diodes grown by nanoscale epitaxial lateral overgrowth using a nitrided titanium buffer layer

In this work, a buffer layer of nitrided titanium (Ti) achieved through the nitridation of a Ti metal layer on a sapphire substrate was used for the epitaxial growth of InGaN-based light-emitting diodes (LEDs) achieved by low pressure metal-organic chemical vapor deposition. The effect of in-situ Ti metal nitridation on the performance of these InGaN-based LEDs was then investigated. It was very clear that the use of the nitrided Ti buffer layer (NTBL) induced the formation of a nanoscale epitaxial lateral overgrowth layer during the epitaxial growth. When evaluated by Raman spectroscopy, this epi-layer exhibited large in-plane compressive stress releasing with a Raman shift value of 567.9 cm-1. Cathodoluminescence spectroscopy and transmission electron microscopy results indicated that the InGaN-based LEDs with an NTBL have improved crystal quality, with a low threading dislocations density being yielded via the strain relaxation in the InGaN-based LEDs. Based on the results mentioned above, the electroluminescence results indicate that the light performance of InGaN-based LEDs with an NTBL can be enhanced by 45% and 42% at 20 mA and 100 mA, respectively. These results suggest that the strain relaxation and quality improvement in the GaN epilayer could be responsible for the enhancement of emission power.

Suppression of phase transitions in Pd thin films by insertion of a Ti buffer layer

We investigated the effects of a thin titanium (Ti) buffer layer on structural changes and electrical responses of palladium (Pd) thin films. A Ti buffer layer was inserted between a Pd film and the substrate, with varying thickness from 0.5 to 80 nm. Unlike pure Pd films, Ti-buffered Pd films showed no structural deformations after cyclic exposure to hydrogen gas, leading to a linear relationship between sensitivity and hydrogen gas concentration over the measured concentration range of 0 to 2%. This was attributed to the suppression of phase transitions from the α to the β phase in Pd films, due to the reinforced film adhesion by the inserted Ti layer. Our results highlight the practical usability of Pd thin films as reliable and sensible hydrogen sensors, enabled simply by the insertion of a thin Ti buffer layer.

Titanium buffer layer for improved field emission of CNT based cold cathode

Carbon nanotube (CNT) based cold cathodes are considered to be the most promising material for fabrication of next generation high-performance flat panel displays and vacuum microelectronic devices. Adhesion of CNTs with the substrate and the contact resistance between them are two of the important issues to be addressed in CNT based field emission (FE) devices. Here in this work, a buffer layer of titanium (Ti) is deposited prior to the catalyst deposition and the growth was carried out using chemical vapor deposition (CVD) technique. There was significant increase in emission current density from 10 mA/cm 2 to 30 mA/cm 2 at the field of 4 V/μm by the use of titanium buffer layer due to much less dense growth of CNTs of smaller diameter. Field emission results suggest that the adhesion of the CNTs to the substrate has improved. The titanium buffer layer has also lowered the contact resistance between the CNTs and the substrate because of which a stable emission of 30 mA for a longer duration was obtained.

Investigation of hydroxyapatite coated polyether ether ketone composites by gas plasma sprays

High performance polyether ether ketone (PEEK) composites exhibit great potential to be tailored for implants according to specific requirements. Hydroxyapatite (HA) coatings were also proved to improve the efficiency after medical implantations. It is therefore desired to develop high quality HA coated PEEK composites by gas plasma spray. Two different HA powders were evaluated, and a high temperature sensing system was employed to monitor the surface temperature and flying velocity for the plasma spray process. The composites were also immersed in simulate body fluids to reveal in-vitro characteristics for implant designs. The results showed that the smaller and more spherical HA powder was more favorable in producing HA coating. A titanium (Ti) buffer layer could be pre-deposited to further improve HA coating quality. The HA coating thickness was therefore about 30–40 μm and the surface roughness was 4.9 μm. In addition, the effects of gas plasma spray parameters, such as Ar/He carrying gas flow rate, plasma power, spray distance and powder feeding rate, on the powder surface temperature and flying velocity have been investigated. The flying velocity increased from 250–300 to 440–490 m/s, when a second He gas source was added to the 40 L/min Ar carrying gas. It also increased from 437 to 451 m/s when the applied current was raised from 400 to 450 A. However, the HA powder flying velocity was decreased with both increasing spray distance and powder feeding rate. It decreased from 451 to 441 m/s while the feeding rate was increased from 18 g/min to 30 g/min. It also gradually decreased from 486 to 438 m/s while the spray distance was increased from 50 to 85 mm. The powder surface temperature decreased from 2850 °C to 2735 °C from the same batch of experiments.

Density control of carbon nanofibers on titanium buffer layer using electroplated Ni catalyst

With a view to controlling the density of carbon nanofibers (CNFs), the density of Ni catalysts was varied using direct current (dc) electroplating technique coupled with titanium (Ti) buffer layer which is deposited between catalytic layer and substrate. The dc electroplating technique is used for the deposition and formation of islands of Ni catalysts simultaneously, without any additional process. The islands of Ni catalysts were formed on the substrate with Ti buffer layer, while the smooth and continuous film of Ni catalyst was formed on the substrate without the Ti buffer layer, using the same electroplating process. The site density of Ni catalysts was controlled via the dc electroplating technique coupled with the deposition of Ti buffer layer successfully. Then, CNFs were synthesized using a direct current plasma enhanced chemical vapor deposition (dc-PECVD) system at a temperature of 480°C. The morphologies of the electroplated Ni catalysts and CNFs were compared at different electroplating cond...

Characterization of (Ba1−x,Srx)TiO3 thin films deposited on Pt/Ti/SiO2/Si substrates with different Ti buffer layer thicknesses

(Ba1−x,Srx)TiO3 (BST) films were deposited on Pt/Ti/SiO2/Si substrates with various Ti buffer layer thicknesses by metalorganic chemical vapor deposition. The deposition rate and surface morphologies of the BST films were strongly dependent on the titanium buffer layer thickness. The deposition rate of BST films linearly increases with increasing Ti thickness. Titanium diffusion through the platinum bottom electrode played an important role as a nucleation site for BST growth. The 50 nm thick BST films deposited on Pt/Ti/SiO2/Si substrates with a Ti thickness of 50 nm have a dielectric constant of 190 and a dissipation factor of 0.025 at 100 kHz. The films showed symmetrical J-V characteristics with respect to the bias polarity and leakage current density of 8.0×10−7 A/cm2 at an applied voltage of 1 V. The optimal thickness of the Ti buffer layer in Pt/Ti/SiO2/Si substrates is important to obtain good electrical properties of BST films.

Selective deposition of CrO 2 films on glass substrates

Crystalline films of ferromagnetic chromium dioxide were deposited onto glass substrates using a vapor transport technique. Buffer layers of oxidized titanium were used to aid the nucleation of the films. Because the CrO 2 films did not nucleate on the bare glass, selective deposition could be realized by patterning the titanium buffer layer.

Effects of Titanium Buffer Layer on Lead-Zirconate-Titanate Crystallization Processes in Sol-Gel Deposition Technique

Effects of the Ti buffer layer on crystallization processes of lead-zirconate-titanate (PZT) films by the sol-gel deposition technique were investigated. The Ti buffer layer was deposited on a Pt/TiN/SiO2/Si substrate by electron beam evaporation at the back-pressure of 1×10-11 Torr. Homogeneous crystalline PZT film of perovskite structure with fine grains were successfully obtained on the substrate with a Ti buffer layer. In contrast, a rosette-structure film which consists of large grains surrounded by a second phase was formed on a pure Pt surface. Ti existing at the interface between Pt and PZT acts as nuclei, and affects the growth of fine grains. Furthermore, leakage current density was drastically reduced from 5×10-5 A/cm2 to 6×10-9 A/cm2 at 4 V for 200-nm-thick film formed on a substrate with a buffer layer. Crystalline orientations and microstructures of PZT films were strongly dependent on the equivalent thickness of the buffer layer and there was an optimum thickness. When the equivalent thickness of the buffer layer was 2 nm, PZT showed <111>-preferred orientation and a homogeneous film structure with fine grains on the <111>-oriented Pt/SiO2/Si substrate.