Ti Adhesion Layer Research Articles

Fabrication of Ag micro-particles based on stress-induced migration by using multilayered structure with artificial holes array.

Silver micro/nanomaterials have attracted a great deal of attention due to their superior physicochemical properties. The atomic migration driven by electromigration or stress-induced migration has been demonstrated to be a promising method for the fabrication of metallic micro-/nanomaterials because of the advantage of simple processing. However, how to realize the controllable fabrication and mass production is still the critical technical problem for the method to be used in large-scale industrial applications. In this paper, the multilayered samples consisted of copper foil substrate, Ti adhesive layer, Ag film, and TiN passivation layer and with arrays of artificial holes on the passivation layer were applied to prepare arrays of Ag micro-particles. For the purpose of controllable fabrication, stress-induced migration experiments combined with finite element simulation were applied to analyze the influence of the passivation layer thickness and the heating temperature on the atom migration and Ag particles growing behavior. And the relationship between size of the fabricated Ag particles and the processing parameters of stress-induced migration experiments were also investigated. As a result, a proper structure size of the multilayered samples and heating temperature were recommended, which can be used for the Ag micro-particles controllable fabrication and mass production.

Ion-Beam-Induced Structure Fragmentation and Dewetting in Au/Ti Films

We investigate the formation of Au structures by continuing fragmentation of a Au film separated from Si (100) substrate by a Ti adhesion layer. The ion-beam processing uses 2 keV Cs+ projectiles. It induces the formation of a large variety of structures with dimensions from tens of microns down to a few nanometers, and shapes that include flat Au islands and clusters of Au nanoparticles. We identify different fragmentation mechanisms. In one pathway, Au structures are formed as pinch-off droplets detached from large Au islands undergoing solid-state dewetting. In a second pathway, a continuing cracking fragmentation produces Au structures with a wide range of sizes and shows self-similarity, expressed in a power law for volume distribution of fragments Vα with α= -2.03±0.05. The measured α value is consistent with theoretical results in the literature modelling strong impact fragmentation. In the last stage of fragmentation evolution, Au nanostructures are spread over a texturized Si background. They assume shapes close to hemispherical, reflecting the increasing relevance of surface tension as dimensions decrease.

Adhesion-Enhanced Vertically Oriented Graphene on Titanium-Covered Quartz Glass toward High-Stability Light-Dimming-Related Applications

Improving the adhesion property of graphene directly grown on an insulating substrate is essential for promoting the reliability and durability of the related applications. However, effective approaches have rarely been reported, especially for vertically oriented graphene (VG) films grown on insulating templates. To tackle this, we have developed a facile synthetic strategy by introducing an ultrathin (10 nm-thick) titanium (Ti) film on a quartz glass substrate as the adhesion layer, for plasma-enhanced chemical vapor deposition (PECVD) growth of VG films. This synthetic process induces the formation of Ti, oxygen (O), carbon (C)-containing adhesion layer (Ti (O, C)), offering improved interfacial adhesion due to the formation of chemical bonds among Ti and C atoms. Dramatically improved surface and interface stabilities have been achieved, with regard to its counterpart without a Ti adhesion layer. Moreover, we have also realized precise controls of the transparent/conductive property, surface roughness, and hydrophobicity, etc., by varying the VG film growth time. We have also demonstrated the very intriguing application potentials of the hybrids in light-dimming related fields, that is, electro-heating defogging lenses and neutral density filters toward medical endoscope defogging and camera photography.

Thermally induced reactions of monolayer WS2 with Au-Ti substrates

The thermal stability of WS2 flakes is studied after integration into a device structure with a Si/SiO2 substrate, a Ti adhesion layer and a Au-contact layer. WS2 /Au/Ti is commonly used in catalytic and electronic devices, and its thermal stability is important for extended operation and mitigation of breakdown at local hot-spots during operation. The thermal stability is severely impacted by rapid diffusion of Ti into and through the polycrystalline Au. Thin film samples of Au/Ti, with and without an exfoliated WS2 monolayer, were annealed sequentially from 275 to 625 °C in vacuum. The near-surface chemical information was extracted with X-ray photoelectron spectroscopy for each annealing step. Ti from the sticking layer, which is buried under 25 nm of Au, diffuses into the near surface region, and initiates a wide range of reactions forming: Ti oxide, carbide, sulfide and a Ti-Au alloy, mainly Au2Ti. WS2 experiences S loss for T > 350 °C and forms Ti-sulfide for T > 600 °C. Higher thermal loads spanning the same temperature range lead to coalescence within the nanocrystalline Au layer, limiting grain boundary diffusion of Ti. The results provide insight on the stability of the WS2/Au/Ti material system which impacts its performance in catalytic and electronic applications.

Influence of Glass Surface Modification on Thin Film Copper Electrodes

We investigate the impact of the glass surface on the structural and electrical properties of Ti/Cu film stacks as well as single Ti adhesion layer, by modifying Corning® Eagle XG® glass surfaces using four acids common in TFT-LCD microfabrication processes. Atomic force microscopy results indicate significant change of the surface topography of Ti and Cu, particularly found on hydrofluoric acid treated glass surfaces. The film microstructures are characterized by a comprehensive analysis using Bragg, grazing incidence and in-plane X-ray diffraction, and X-ray reflectivity methods as well as the transmission electron microscopy. The sheet resistance was measured using the four-point probe method. We demonstrate the role of the glass surface state through its impact on the structural and electrical properties of Ti/Cu electrodes emanating from glass surface treatments.

Development of thermal barrier coatings using reactive pulsed dc magnetron sputtering for thermal protection of titanium alloys

There is a need to thermally protect titanium (Ti) alloys so that they can be used in high temperature environments, such as during hypersonic flight. In this study, a thermal barrier coating (TBC) system was developed using reactive magnetron sputtering. The coating system consists of a nickel chromium aluminum yttrium (NiCrAlY) bond coat and an yttria-stabilized zirconia (YSZ) top coat. The YSZ layer was deposited by reactive pulsed direct current (DC) magnetron sputtering a Zr-Y target in a gas mixture comprised of argon (Ar) and oxygen (O2). The pulsed DC magnetron sputtering process used closed-loop control with the cathode voltage as the feedback signal. The YSZ coatings were deposited at different cathode voltage feedback signals. The phase structure, elemental composition, microstructure, and thickness of the YSZ coatings were examined by different means. It was found that up to 69% of the metallic deposition rate can be achieved for obtaining near stoichiometric YSZ coatings. The YSZ coatings exhibit single cubic phase structure with an Y2O3% in the range from 6.5 mol% to 8 mol%. The developed TBC consists of a 2 μm Ti adhesion layer, a 30 μm NiCrAlY bond coat, and a 40 μm YSZ top coat deposited on Ti-6Al-4 V substrate. The NiCrAlY layer exhibited a dense structure and the YSZ layer exhibited a porous columnar grain structure. The TBC showed excellent adhesion on Ti-6Al-4 V. The coated Ti-6Al-4 V was annealed from 800 °C to 1000 °C in air to evaluate the thermal protection capability of the coating. No degradation of the TBC was observed and the Ti-6Al-4 V alloy preserved fine gains and desired mechanical properties up to 900 °C. However, the coating showed horizontal cracks and degradation at the interface between the Ti-6Al-4 V substrate and the NiCrAlY bond coat at 1000 °C. It is assumed that the outward diffusion of Al from the Ti alloy led to the coating failure at the interface. This indicates that new diffusion barrier layers are needed as part of the TBC system.

Influence of titanium adhesion layer on performance of β-Ga2O3 solar-blind photodetector

The influence of a titanium (Ti) adhesion layer on the ductility of thin Au film well bonded with β-Ga2O3 film on a flexible substrate were investigated with the quality of β-Ga2O3 deep-ultraviolet photodetector. The photodetector fabricated with Ti adhesion layer exhibits excellent photoelectric performance and stability. The photocurrent obtained by the Ti/Au bilayer-device (3.1 × 10−8 A) is significantly greater than that of an Au electrode-device (1.7 × 10−8 A) at 10 V under a flat state. After 250 bending cycles, the photoresponsivity of the Au electrode-device declined approximately 20 times, while little photoresponsivity degradation was observed in the Ti/Au bilayer-device. Additionally, more suppression of the deformation and cracks was observed in the Au film with Ti adhesion layer than the Au grown directly on the β-Ga2O3 films. These results reveal the importance of the adhesion layer in promoting the photodetector.

Early stages in the self-organization of Si nanopatterns induced by ion bombardment

We reveal early stages of self-organization of nanopatterns created by 2 keV Cs+ ion-beam irradiation of a Si surface coated with Au and a Ti adhesion layer. After ion-beam etching of the metallic layers, at normal incidence, we first observe distinct transient stages: (I) a dewetting-like pattern of grooves in the Si amorphized layer, sparsely populated with holes, followed by (II) the coexistence of rounded mounds and faceted holes distributed on a flat surface, the latter being an indication of the decisive role played by the crystalline/amorphous interface. Subsequently, the system evolves to stage III, a nanopattern of densely packed nanodots convoluted with a long-wavelength surface corrugation. A momentum-space analysis shows that stages (I) and (II) are identified, respectively, with channel-type and sphere-type quasi order.

Thin Ti adhesion layer breaks bottleneck to hot hole relaxation in Au films.

Slow relaxation of highly excited (hot) charge carriers can be used to increase efficiencies of solar cells and related devices as it allows hot carriers to be extracted and utilized before they relax and lose energy. Using a combination of real-time density functional theory and nonadiabatic molecular dynamics, we demonstrate that nonradiative relaxation of excited holes in an Au film slows down 30-fold as holes relax across the energy range -2 to -1.5 eV below the Fermi level. This effect arises due to sharp decreases in density of states (DOS) and reduced hole-phonon coupling in this energy range. Furthermore, to improve adhesion, a thin film of transition metal, such as Ti, is often inserted between the noble metal layer and its underlying substrate; we demonstrate that this adhesion layer completely eliminates the hot-hole bottleneck because it significantly, 7-fold per atom, increases the DOS in the critical energy region between -1.5 eV and the Fermi level, and because Ti atoms are 4-times lighter than Au atoms, high frequency phonons are introduced and increase the charge-phonon coupling. The detailed ab initio analysis of the charge-phonon scattering emphasizes the nonequilibrium nature of the relaxation processes and provides important insights into the energy flow in metal films. The study suggests that energy losses to heat can be greatly reduced by judicious selection of adhesion layers that do not involve light atoms and have relatively low DOS in the relevant energy range. Inversely, narrow Ti adhesion layers assist heat dissipation needed in electronics applications.

Feasibility of ZnO and Zn Seed Layers for Growth of Vertically Aligned and High-Quality ZnO Nanorods by the Sonochemical Method

The role of both zinc oxide (ZnO) and zinc (Zn) seed layers were evaluated for the growth of vertically aligned high-quality zinc oxide (ZnO) nanorods by the sonochemical method. A total of four samples categorized into two groups were evaluated, with a different type and thickness of seed layer for the first group - ZnO, 85 nm and the second group - Zn, 55 nm respectively. This was after depositing Ti (10 nm) as the adhesion layer on p-type Si (111) substrates for two samples, and without the adhesion layer on the others. All depositions were carried out using RF-sputtering. The effects of the seed layers on the growth of vertically aligned high-quality ZnO nanorods were systematically studied using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) analysis and transmission electron microscopy (TEM). Results show that the type and thickness of a seed layer are key parameters to the synthesis of high quality ZnO nanorods. Results also show that the Ti (10 nm) adhesion layer did not affect the growth surface-to-volume ratio of the ZnO nanorods and the ZnO nanorods synthesized using ZnO (85 nm) as seed layer has a better surface-to-volume ratio compared to that using Zn (55 nm) as seed layer, with and without the adhesion layer.

Less is More: Improved Thermal Stability and Plasmonic Response in Au Films via the Use of SubNanometer Ti Adhesion Layers.

The use of a metallic adhesion layer is known to increase the thermo-mechanical stability of Au thin films against solid-state dewetting, but in turn results in damping of the plasmonic response, reducing their utility in applications such as heat-assisted magnetic recording (HAMR). In this work, 50 nm Au films with Ti adhesion layers ranging in thickness from 0 to 5 nm were fabricated, and their thermal stability, electrical resistivity, and plasmonic response were measured. Subnanometer adhesion layers are demonstrated to significantly increase the stability of the thin films against dewetting at elevated temperatures (>200 °C), compared to more commonly used adhesion layer thicknesses that are in the range of 2-5 nm. For adhesion layers thicker than 1 nm, the diffusion of excess Ti through Au grain boundaries and subsequent oxidation was determined to result in degradation of the film. This mechanism was confirmed using transmission electron microscopy and X-ray photoelectron spectroscopy on annealed 0.5 and 5 nm adhesion layer samples. The superiority of subnanometer adhesion layers was further demonstrated through measurements of the surface-plasmon polariton resonance; those with thinner adhesion layers possessed both a stronger and spectrally sharper resonance. These results have relevance beyond HAMR to all Ti/Au systems operating at elevated temperatures.

Controlling morphology and texture of sputter-deposited Pd films by tuning the surface topography of the (Ti) adhesive layer

In this work, the effect of the deposition parameters of a magnetron sputtered Ti adhesive intermediate layer on the morphology and hydrogen absorption properties of thin Pd films of about 100 nm was investigated. The insertion of an adhesive layer between a Pd film and a rigid substrate usually suppresses or reduces hydrogen absorption. In this study, it is shown that by tuning the surface topography of the intermediate layer the morphology, crystallographic texture and hydrogen absorption properties of the Pd film can be controlled. The surface topography of the Ti layer was characterized using atomic force microscopy. The surface topography strongly depends on the Ti deposition conditions and can vary from widely spread large islands to densely packed small-grained islands depending on thickness (between 1 and 6 nm) and sputter pressure (0.4 and 3 Pa). TEM and XRD analysis led to the conclusion that rough Ti intermediate layers result in Pd films with an open columnar structure with small voids, and a weak and broad (111) texture. Smooth Ti intermediate layers promote the formation of Pd films with a dense columnar structure with fewer voids, and a strong and sharp (111) texture. Changes in the Pd adatom surface diffusion and shadowing effects are the main cause of the observed differences. Pd films with an open columnar morphology and weaker texture show better hydrogen absorption properties with respect to absorption capacity and kinetics of the films with dense columnar morphology. By tuning the surface topography of the Ti adhesive layer, Pd films with controlled morphology and texture can be prepared such that no delamination from the substrate occurs without compromising on absorption properties.

Structural, magnetic and magnetostrictive properties of Fe83Ga17 films with a Ti adhesion layer

Abstract In this study, Fe83Ga17 thin films are deposited on Si(1 0 0) and Si(1 1 1) substrates with a Ti layer by using DC magnetron sputtering. The addition of Ti layer does not significantly change the magnetic and magnetostrictive properties of the Fe-Ga film, however it can effectively prevent the abscission of film during heat treatment. The Fe83Ga17 films deposited on Si(1 0 0) and Ti/Si(1 0 0) have relatively small coercive forces, low saturation magnetic fields, and the magnetostriction curves are easily saturated in a low field. The magnetostriction of Fe83Ga17 on Ti/Si(1 0 0) can reach 105 ppm. The Fe83Ga17 thin films on Si(1 1 1) and Ti/Si(1 1 1) have large saturation magnetic fields (about 61Oe) and the magnetostriction curve shows linearity, which can be used in magnetic field detection, micro actuators and magnetoelectric (ME) devices. Dendritic domains and stripe domains are observed in these samples due to the influence of different internal stresses. After a vacuum heat treatment, the internal stress was released. At the same time, the structure of both the dendritic domains and stripe domains turns into a dot domain. The EBSD results show that annealed Fe-Ga films sputtered on a Ti layer have a very weak texture.

Morphological Characteristics of Au Films Deposited on Ti: A Combined SEM-AFM Study

Deposited Au films and coatings are, nowadays, routinely used as active or passive elements in several innovative electronic, optoelectronic, sensing, and energy devices. In these devices, the physical properties of the Au films are strongly determined by the films nanoscale structure. In addition, in these devices, often, a layer of Ti is employed to promote adhesion and, so, influencing the nanoscale structure of the deposited Au film. In this work, we present experimental analysis on the nanoscale cross-section and surface morphology of Au films deposited on Ti. In particular, we sputter-deposited thick (>100 nm thickness) Au films on Ti foils and we used Scanning Electron Microscopy to analyze the films cross-sectional and surface morphology as a function of the Au film thickness and deposition angle. In addition, we analyzed the Au films surface morphology by Atomic Force Microscopy which allowed quantifying the films surface roughness versus the film thickness and deposition angle. The results establish a relation between the Au films cross-sectional and surface morphologies and surface roughness to the film thickness and deposition angle. These results allow setting a general working framework to obtain Au films on Ti with specific morphological and topographic properties for desired applications in which the Ti adhesion layer is needed for Au.

Strong Influence of Ti Adhesion Layer on Electron-Phonon Relaxation in Thin Gold Films: Ab Initio Nonadiabatic Molecular Dynamics.

Electron-phonon relaxation in thin metal films is an important consideration for many ultrasmall devices and ultrafast applications. Recent time-resolved experiments demonstrate a significant, more than a factor of five, increase in the electron-phonon coupling and acceleration in the electron-phonon relaxation rate when a narrow Ti adhesion layer is introduced between an Au film and a nonmetal substrate. Using nonadiabatic molecular dynamics combined with real-time time-dependent density functional theory, we identify the reasons that give rise to this strong effect. First, the Ti layer greatly enhances the density of states (DOS) in the energy region starting at 1 eV below the Fermi level and extending several electronvolts above it. Second, Ti atoms are four times lighter than Au atoms and therefore generate larger nonadiabatic (NA) electron-phonon coupling. Because the transition rates depend on coupling and DOS, both the factors accelerate the dynamics. Showing good agreement with the experiments, the time-domain atomistic simulations provide a detailed mechanistic understanding of the electron-phonon relaxation dynamics in thin gold films and related nanomaterials.

Influence of Ti and Cr Adhesion Layers on Ultrathin Au Films.

Efficient adhesion of gold thin films on dielectric or semiconductor substrates is essential in applications and research within plasmonics, metamaterials, 2D materials, and nanoelectronics. As a consequence of the relentless downscaling in nanoscience and technology, the thicknesses of adhesion layer and overlayer have reached tens of nanometers, and it is unclear if our current understanding is sufficient. In this report, we investigated how Cr and Ti adhesion layers influence the nanostructure of 2-20 nm thin Au films by means of high-resolution electron microscopy, complemented with atomic force microscopy and X-ray photoelectron spectroscopy. Pure Au films were compared to Ti/Au and Cr/Au bilayer systems. Both Ti and Cr had a striking impact on grain size and crystal orientation of the Au overlayer, which we interpret as the adhesion layer-enhanced wetting of Au and the formation of chemical bonds between the layers. Ti formed a uniform layer under the Au overlayer. Cr interdiffused with the Au layer forming a Cr-Au alloy. The crystal orientation of the Au layers was mainly [111] for all thin-film systems. The results showed that both adhesion layers were partially oxidized, and oxidation sources were scrutinized and found. A difference in bilayer electrical resistivity between Ti/Au and Cr/Au systems was measured and compared. On the basis of these results, a revised and more detailed adhesion layer model for both Ti/Au and Cr/Au systems was proposed. Finally, the implications of the results were analyzed, and recommendations for the selection of adhesion layers for nano-optics and nanoelectronics applications are presented.

Influence of Fatigue and Bending Strain on Critical Currents of Niobium Superconducting Flexible Cables Containing Ti and Cu Interfacial Layers

Niobium is a viable material for thin-film superconducting flexible microwave cables. To aid in the design of superconducting flexible cables using Nb, it is important to evaluate not only the superconductor electrical performance, but also mechanical reliability performance since these cables should be reasonably robust when flexed. In this paper, we performed fatigue and bending tests on Nb-only and Ti/Nb/Cu multilayer signal lines on flexible Kapton substrates and measured the change in critical current ( $I_c$ ) of these wires. From the fatigue tests, $I_c$ degradation of Nb-only cables occurred at a lower number of cycles than the Ti/Nb/Cu cables. After 250 fatigue cycles, Ti/Nb/Cu wires with the thickest Ti adhesion layer and Cu capping layer exhibited the lowest $I_c$ degradation of $\sim$ 1.2% and 0% in tensile and compressive cases, respectively. From bending tests, where the sample was held in an intentionally curved configuration during testing, $I_c$ degradation of the Nb-only cables was more severe than that of the Ti/Nb/Cu cables during tensile bending and the $I_c$ of Ti/Nb/Cu cables was minimally affected during compressive bending. These results demonstrate that a Ti adhesion layer and Cu capping layer provide reliability enhancement for superconducting Nb flex cables fabricated on Kapton.

Self-Organized Nanoscale Roughness Engineering for Broadband Light Trapping in Thin Film Solar Cells

We present a self-organized method based on defocused ion beam sputtering for nanostructuring glass substrates which feature antireflective and light trapping effects. By irradiating the substrate, capped with a thin gold (Au) film, a self-organized Au nanowire stencil mask is firstly created. The morphology of the mask is then transferred to the glass surface by further irradiating the substrate, finally producing high aspect ratio, uniaxial ripple-like nanostructures whose morphological parameters can be tailored by varying the ion fluence. The effect of a Ti adhesion layer, interposed between glass and Au with the role of inhibiting nanowire dewetting, has also been investigated in order to achieve an improved morphological tunability of the templates. Morphological and optical characterization have been carried out, revealing remarkable light trapping performance for the largest ion fluences. The photon harvesting capability of the nanostructured glass has been tested for different preparation conditions by fabricating thin film amorphous Si solar cells. The comparison of devices grown on textured and flat substrates reveals a relative increase of the short circuit current up to 25%. However, a detrimental impact on the electrical performance is observed with the rougher morphologies endowed with steep v-shaped grooves. We finally demonstrate that post-growth ion beam restructuring of the glass template represents a viable approach toward improved electrical performance.

Surface plasmon damping effects due to Ti adhesion layer in individual gold nanodisks

The adhesion layer used in nanofabrication process of metallic nanostructures affects the surface plasmon modes. We characterize the localized surface plasmon resonances (SPRs) of gold nanodisks of various diameters and heights while varying the thickness of the Ti adhesion layers. Scattering, absorption, and extinction coefficient calculations show a significant dependence of the SPR on the size of nanostructures and the adhesion layer thickness. Comparisons of peak resonance wavelengths of different Ti adhesion layer thicknesses indicate a significant red shift and a reduction in amplitude as the Ti thickness increases. A comparison of spectral broadening of the plasmon mode indicates a linear increase with Ti thickness and percentage. In addition, the decay time of the plasmon mode decreased significantly as the adhesion layer size increases. These observations aid in understanding size dependent adhesion layer effects and optimized fabrication of single nanoplasmonic structures.

Evaluation of Residual Stresses in PVD Coatings by Means of the Curvature Method of Plate

Physical Vapor Deposition (PVD) coatings are primarily designed for metal cutting tools operating in extreme machining and blanking conditions. Residual stresses arising during coating deposition exert an important effect on the service life of the coating through influencing mechanical and tribological properties and adhesion. To determine macroscopic residual stresses, the conventional curvature method was used. As an application, residual stresses in four aluminum based PVD hard coatings, i.e. AlTiN, AlTiSiN, AlCrN, and AlCrSiN, were investigated in the presence of the Ti adhesion layer. Nickel steel plates and steel plates were used as the substrate. Residual stresses were compressive and high (3.0-7.5 GPa) in all coatings. Compressive stresses in coatings are desirable in cohesive tool damage as they strengthen the coating. The values of residual stresses were not significantly dependent on the angle of plate placement (parallel (0°), inclined (45°) and perpendicular (90°)) in relation to the PVD cathode in the deposition chamber. The magnitude of residual stresses is influenced by intrinsic strain at layer growth rather than by thermal stress.