Monolayer Ti Research Articles

High Sensitivity Surface Plasmon Resonance Sensor Based on Two-Dimensional MXene and Transition Metal Dichalcogenide: A Theoretical Study.

MXene, a new class of two-dimensional nanomaterials, have drawn increasing attention as emerging materials for sensing applications. However, MXene-based surface plasmon resonance sensors remain largely unexplored. In this work, we theoretically show that the sensitivity of the surface plasmon resonance sensor can be significantly enhanced by combining two-dimensional MXene and transition metal dichalcogenides. A high sensitivity of /RIU (refractive index unit) with a sensitivity enhancement of 41.43% was achieved in aqueous solutions (refractive index ∼1.33) with the employment of monolayer MXene and five layers of at a 633 nm excitation wavelength. The integration of MXene with a conventional surface plasmon resonance sensor provides a promising approach for bio- and chemical sensing, thus opening up new opportunities for highly sensitive surface plasmon resonance sensors using two-dimensional nanomaterials.

Synthesis and microstructural characterization of nanoscale multilayer TiAlN/TaN coatings deposited by DC magnetron sputtering

(Ti,Al)N coatings have become the most used option for the protection of different industrial tools due to their excellent properties like high hardness and low wear rate, which is maintained until temperatures of 700 °C are achieved by the formation of a dense and stable layer of Al2O3. Additionally, TaN coatings have proved to be an appropriate alternative to conventional coatings with great potential in different applications, due to their high chemical stability and corrosion resistance. These aspects motivated the combination of both coatings in a multilayer structure at the nanometric scale. In this work, novel coatings of (Ti,Al)N/TaN were deposited on AISI H13 hot work tool steel by a self-manufactured DC magnetron sputtering vacuum chamber without target shutter. In order to obtain coatings with different decreasing periods, four substrate rotation speeds were used: 0.2 rpm, 0.5 rpm, 1.0 rpm, and 3.0 rpm. In addition to the multilayer coatings, the monolayers of (Ti,Al)N and TaN were deposited for comparison purposes. Using AFM, it was possible to observe that both the roughness and the grain size decreased from 17 to 13 nm and from 165 to 137 nm, respectively, as the substrate rotation speed increased. The monolayer coatings (Ti,Al)N and TaN exhibited an fcc crystal structure with growth directions (111) and (200), respectively. On the other hand, for the multilayer coating (Ti,Al)N/TaN, a change in the preferential direction corresponding to the TaN from [200] to [111] was identified. In the SEM images of the multilayers, a microstructure of columnar growth was observed, which is densified with an increased rotation speed of the substrates, and the multilayers are no longer observed for the highest speeds and the smallest periods. Using plan-view TEM images and selected area EDS, it was possible to suggest the formation of a nanoscale-structured multilayer with a well-defined interface between TiAlN and TaN. Regarding the residual stresses of the coatings, it was possible to observe that with the increase in the substrate rotation speed during the deposition, the stresses decreased progressively, reaching values up to − 1.51 GPa, significantly lower than both TiAlN (− 7.09 GPa) and TaN (− 8.66 GPa) monolayer coatings.

Tribological and cutting performance of TiAlCrN films with different Cr contents deposited with multilayered structure

Abstract Increasing requirements on high speed and dry cutting applications open up new demands on the quality of cutting tool materials. In this study, we evaluated the effect of Cr additions on the properties of Ti(Al)N/Cr(Al)N multilayered films deposited by magnetron sputtering. In particular, we studied the high temperature tribological properties and the cutting performance in real service drilling tests and compared the results with a monolayer Ti 0.47 Al 0.46 N reference film. Dry sliding experiments were performed using a pin-on-disc tribometer at room temperature and at 650 °C with Al 2 O 3 balls as counterparts. The drilling performance of the coatings was evaluated at cutting speeds in the range of 50–200 m/min. Wear of the drills in different zones (chisel edge and flank edge) was mapped after every 15 holes.

Monolayer Sc2CO2: A Promising Candidate as a SO2 Gas Sensor or Capturer

Toxic gaseous SO2 adsorption on O-terminated M2CO2 (M = Sc, Hf, Zr, and Ti) monolayers has been studied by means of first-principle calculations. It is demonstrated that monolayer Sc2CO2 is most preferred for the SO2 molecule with suitable adsorption strength and apparent charge transfer. Moreover, the electronic conductivity of Sc2CO2 displays a sharp increase after the adsorption of SO2. In particular, the adsorption strength of SO2 on Sc2CO2 can be further enhanced or weakened by applying tensile strains or controlling external electronic fields, which is greatly desirable to realize the capture or reversible release of toxic SO2 gas. These distinctive features endow the Sc2CO2 monolayer with high selectivity and sensitivity as a potential candidate for SO2 gas sensor, as well as efficient control for gaseous SO2 capture.

Tensile property improvement in Ti/Al clad sheets fabricated by twin-roll casting and annealing

A new fabrication method of Ti/Al clad sheet by bonding a thin Ti sheet on to Al alloy melt during twin-roll casting was presented to broaden industrial applications of Ti alloys. In the twin-roll-cast Ti/Al clad sheet, a homogeneously solidified microstructure existed in the cast Al side, while a Ti/Al interface did not contain pores, cracks, or lateral delamination, which indicated a successful fabrication. When this cast sheet was annealed at 400 °C, metallurgical bonding was expanded by interfacial diffusion, thereby leading to improvement in tensile properties. After the 600 °C-annealing, a TiAl3 intermetallic compound was formed at the Ti/Al interface, which deteriorated tensile properties because of its brittle characteristics. The yield and tensile strengths of the 400 °C-30-min-annealed sheet (132 MPa and 218 MPa, respectively) were higher than those (103 MPa and 203 MPa, respectively) calculated by a rule of mixtures using tensile properties of a 5052-O Al alloy and a pure Ti. Its ductility was also higher than that of 5052-O Al alloy (25%) or pure Ti (25%) because the strain at the interfacial delamination point reached 41%. The 400 °C-30-min-annealed sheet showed the overall homogenous deformation behavior by complimenting drawbacks of mono-layer of Al or Ti.

Growth of HfO2/TiO2 nanolaminates by atomic layer deposition and HfO2-TiO2 by atomic partial layer deposition

A novel growth technique, called atomic partial layer deposition (APLD), has been proposed to expand the applications of, and the research in, atomic layer deposition (ALD). This technique allows the possibility for the fabrication of well-controlled alloys on a single atomic layer scale. To demonstrate the capabilities of this technique, samples of HfO2 and TiO2 were prepared as conventional ALD nanolaminates through the repeated exposure of the separated metal-precursor and reactant. Subsequently, HfO2-TiO2 APLD growth mode samples were obtained by varying the precursor doses and exposure times to obtain a fractional coverage in the monolayer of Hf and Ti. The thickness and structure of the samples were studied by X-ray reflectivity. The surface topography was studied using atomic force microscopy along with Kelvin probe force microscopy for surface potential mapping. Clear differences on the surface, compared with the conventional HfO2/TiO2 ALD nanolaminates, were observed, which confirmed the HfO2-TiO2 APLD growth. The films were analyzed using X-ray photoelectron spectroscopy (XPS) depth profile scans and angle resolved XPS, where well-defined HfO2 and TiO2 contributions were found for both the conventional and APLD mode samples, and an additional contribution, assigned to a ternary phase Hf-Ti-O, in the APLD grown films was observed. This result confirms that Hf and Ti form an alloy in a monolayer by APLD mode growth.

Influence of Cr additions on the structure and oxidation resistance of multilayered TiAlCrN films

Ti1−xAlxN coatings with NaCl-type structure have been widely used in advanced machining and other high temperature applications due to their excellent mechanical, thermal and tribological properties. Here, we investigated the influence of Cr additions on the structure, mechanical properties and oxidation resistance, including the oxide scale characterization, of multilayered TiAlN/CrAlN coatings deposited by magnetron sputtering. The properties of Cr rich coatings were compared to a TiAlN film deposited as reference. XRD diffraction analysis revealed that all coatings showed an fcc NaCl-type structure. However, for the TiAlN monolayer Ti and Al are forming a solid solution whilst, for Cr rich coatings, a multilayer structure alternating TiAlN and CrAlN layers, also forming solid solutions, was grown as a result of the geometry of the targets distribution inside the deposition chamber in combination with a slow rotation of the sample holder and a sufficiently high deposition rate. TGA measurements showed that Cr additions increased the oxidation performance of the coatings. For Ti0.47Al0.46N, dual oxide layers occur when tested at 800°C, being the porous inner one of TiO2 and the outer a compact and continuous layer of Al-oxide which protects the coating from the oxidation. At 900°C the oxidation resistance of this film degraded due to the fast Ti ions diffusion to the surface which impedes the formation of the continuous and protective Al oxide layer. Cr rich coatings showed different oxides scales depending on their chemical composition. For Ti0.30Al0.46Cr0.26N and Ti0.28Al0.34Cr0.42N, a Ti-O rich layer is formed on the top of a protective Al-Cr-O layer when the samples were tested at 900°C and 1000°C, being the oxide layers thicker for the higher temperature. Concerning the coating with the highest Cr content (Ti0.28Al0.31Cr0.51N), a compact and continuous Cr(Al)2O3 oxide layer was formed at 900 and 1000°C with residual TiO2 islands on the top, contributing for a significant enhancement of the oxidation resistance.

Formation of atomically ordered and chemically selective Si-O-Ti monolayer on Si0.5Ge0.5(110) for a MIS structure via H2O2(g) functionalization.

Si0.5Ge0.5(110) surfaces were passivated and functionalized using atomic H, hydrogen peroxide (H2O2), and either tetrakis(dimethylamino)titanium (TDMAT) or titanium tetrachloride (TiCl4) and studied in situ with multiple spectroscopic techniques. To passivate the dangling bonds, atomic H and H2O2(g) were utilized and scanning tunneling spectroscopy (STS) demonstrated unpinning of the surface Fermi level. The H2O2(g) could also be used to functionalize the surface for metal atomic layer deposition. After subsequent TDMAT or TiCl4 dosing followed by a post-deposition annealing, scanning tunneling microscopy demonstrated that a thermally stable and well-ordered monolayer of TiOx was deposited on Si0.5Ge0.5(110), and X-ray photoelectron spectroscopy verified that the interfaces only contained Si-O-Ti bonds and a complete absence of GeOx. STS measurements confirmed a TiOx monolayer without mid-gap and conduction band edge states, which should be an ideal ultrathin insulating layer in a metal-insulator-semiconductor structure. Regardless of the Ti precursors, the final Ti density and electronic structure were identical since the Ti bonding is limited by the high coordination of Ti to O.

Novel multilayer arrangement of conductive layers traps the electromagnetic interferences by multiple internal reflections at high frequency in the far field

The use of the wireless cellular phone is increasing dramatically, and this use can disturb the electronic circuits function with an electromagnetic interference (EMI). Metals are particularly suitable as shielding material against (EMI) due to their high electrical conductivity, but there are a few drawbacks to the use of metal as a shielding material. The weight of the ‘heavy’ metal can be classified as an issue in the case of full metal shielding, especially in the applications where mass should be as low as possible. The purpose behind this study is to ameliorate the shielding of electronic circuit by using multilayer structure. We propose a new multilayer structure shield based on an alumina dielectric layer (Al2O3) sandwiched between two conductive layers of Titanium for better protection against electromagnetic waves. The simulation results prove that the proposed multilayer structure displays more effectiveness of electromagnetic shielding, and a better performance in high frequencies than the Ti monolayer structure, which is achieved due to the impedance mismatch of our structure. Moreover, this multilayer structure has a lighter weight, lower cost, and more efficient shielding than the monolayer structure.

Effect of Synthesis on Quality, Electronic Properties and Environmental Stability of Individual Monolayer Ti3C2 MXene Flakes

2D transition metal carbide Ti3C2Tx (T stands for surface termination), the most widely studied MXene, has shown outstanding electrochemical properties and promise for a number of bulk applications. However, electronic properties of individual MXene flakes, which are important for understanding the potential of these materials, remain largely unexplored. Herein, a modified synthetic method is reported for producing high‐quality monolayer Ti3C2Tx flakes. Field‐effect transistors (FETs) based on monolayer Ti3C2Tx flakes are fabricated and their electronic properties are measured. Individual Ti3C2Tx flakes exhibit a high conductivity of 4600 ± 1100 S cm−1 and field‐effect electron mobility of 2.6 ± 0.7 cm2 V−1 s−1. The resistivity of multilayer Ti3C2Tx films is only one order of magnitude higher than the resistivity of individual flakes, which indicates a surprisingly good electron transport through the surface terminations of different flakes, unlike in many other 2D materials. Finally, the fabricated FETs are used to investigate the environmental stability and kinetics of oxidation of Ti3C2Tx flakes in humid air. The high‐quality Ti3C2Tx flakes are reasonably stable and remain highly conductive even after their exposure to air for more than 24 h. It is demonstrated that after the initial exponential decay the conductivity of Ti3C2Tx flakes linearly decreases with time, which is consistent with their edge oxidation.

Electronic properties of the FeSe/STO interface from first-principle calculations

We perform first-principle calculations of the FeSe monolayer on STO with the focus on three central aspects. First, compared to experiment, the bulk lattice constant of FeSe is too small in LDA, PBEsol and Perdew–Burgke–Ernzerhof (PBE) type exchange-correlation (xc) functionals while in bulk SrTiO3 (STO) LDA over-binds, PBE under-binds and PBEsol agrees best with experiment. Thus, the strain in the FeSe monolayer on STO depends on the xc functional and, especially in the non-magnetic state, is strongly overestimated and best described in PBEsol. In agreement with earlier work, we find that the band structure of the checkerboard antiferromagnetic configuration agrees best with experiment where, in addition, the relative strain on FeSe is best described. Second, our focus is on the crystal structure of the interface itself. The FeSe/STO distance depends weakly on the presence of magnetism and PBE results agree best with recent experimental data. We find that a double -layer below the FeSe relaxes to a structure in disagreement with experimental data. On the other hand, considering the effect of oxygen-vacancies in the single terminated slab within the virtual crystal approximation, in agreement with recent experiment, the FeSe monolayer Ti layer distance increases for a small vacancy concentration (<20%). Third, we investigate the charge-transfer to FeSe due to oxygen-vacancies in STO. Interestingly, we find negligible charge transfer for small concentrations—only above 20% a significant charge transfer is observed.

Electron channeling in TiO2 coated Cu layers

Electron transport in metal conductors with ∼5–30 nm width is dominated by surface scattering. In situ transport measurements as a function of surface chemistry demonstrate that the primary parameter determining the surface scattering specularity is the localized surface density of states at the Fermi level N(Ef). In particular, the measured sheet resistance of epitaxial Cu(001) layers with thickness dCu = 9–25 nm increases when coated with dTi = 0.1–4.0 monolayers (MLs) of Ti, but decreases again during exposure to 37 Pa of O2. These resistivity changes are a function of dCu and dTi and are due to a transition from partially specular electron scattering at the Cu surface to completely diffuse scattering at the Cu–Ti interface, and the recovery of surface specularity as the Ti is oxidized. X-ray reflectivity and photoelectron spectroscopy indicate the formation of a 0.47 ± 0.03 nm thick Cu2O surface layer on top of the TiO2–Cu2O during air exposure, while density functional calculations of TiOx cap layers as a function of x = 0–2 and dTi = 0.25–1.0 ML show a reduction of N(Ef) by up to a factor of four. This reduction is proposed to be the key cause for the recovery of surface specularity and results in electron confinement and channeling in the Cu layer upon Ti oxidation. Transport measurements at 293 and 77 K confirm the channeling and demonstrate the potential for high-conductivity metal nanowires by quantifying the surface specularity parameter p = 0.67 ± 0.05, 0.00 ± 0.05, and 0.35 ± 0.05 at the Cu–vacuum, Cu–Ti, and Cu–TiO2 interfaces.

The Study of Selected Properties of Ti EB PVD Coating Deposited Onto Inner Tube Surface at Low Temperature

This study investigates the selected properties of the thin Ti coating applied by activated evaporation EB PVD technique. This technique was used for the deposition of Ti thin coating onto inner surface of OKhN3 MFA steel tubes. Deposition process was carried out at temperature 200°C. Conventional type of coatings - monolayer Ti - was analyzed by standard techniques for surface status and quality assessment - coating thickness, chemical composition by EDX analysis, adhesion, hardness, roughness, and growth direction of columns at room temperature. Ti monolayer achieved roughness Ra equal from 0.42 μm to 0.47 μm. The resulting hardness was from 2 GPa to 8.5 GPa depending on the sample location inside the vacuum chamber. Placing of the coated surface also affected the direction of grain growth of Ti coating columns. The angles α of grain growth were found to be from 40° to 60°. Angle α increased two to three times more than the incidence angle β (from 12° to 28°) of evaporated Ti particles. Values of the adhesion measured along the Ti growth direction were mostly higher (up to 10%) or the same as those measured perpendicular to it.

Effect of strain on the magnetic states of transition-metal atoms doped monolayer WS2

The effects of transition-metal atoms doping and elastic strain on the magnetic properties of monolayer WS2 are investigated by the first-principles calculation. Firstly, we investigate the magnetic properties of a series of 3d transition-metal atoms (from Sc to Zn) doped monolayer WS2. Our calculations show that doping of transition-metal atoms from Sc to Cr results in nonmagnetic states, while Mn, Fe, Co, Ni, Cu and Zn doping can induce magnetism in WS2 monolayer. The localized nonbonding 3d electrons of TM atoms lead to the formation of magnetic moments. Meanwhile, our calculations indicate that the elastic strain can be used to manipulate the spin polarization of TM-3d orbital. Specifically, the magnetic moment of Fe and Co-doped monolayer WS2 increase with the increase of tensile strain, while the magnetic moment of Mn, Ni, Cu and Zn-doped WS2 monolayer initially increase and then decrease with the increase of tensile strain. On the other hand, the magnetic moment of Fe, Co, Mn, Ni, Cu and Zn-doped WS2 monolayers decrease with the increase of compressive strain. While the magnetic moment of Sc, Ti, V and Cr-doped WS2 monolayers remain 0μB independent of tensile strain and compressive strain.

Titanium induced polarity inversion in ordered (In,Ga)N/GaN nanocolumns

We report on the formation of polarity inversion in ordered (In,Ga)N/GaN nanocolumns grown on a Ti-masked GaN-buffered sapphire substrate by plasma assisted molecular beam epitaxy. High-resolution transmission electron microscopy and electron energy-loss spectroscopy reveal a stacking fault-like planar defect at the homoepitaxial GaN interface due to Ti incorporation, triggering the generation of N-polar domains in Ga-polar nanocolumns. Density functional theory calculations are applied to clarify the atomic configurations of a Ti monolayer occupation on the GaN (0002) plane and to prove the inversion effect. The polarity inversion leads to an enhanced indium incorporation in the subsequent (In,Ga)N segment of the nanocolumn. This study provides a deeper understanding of the effects of Ti mask in the well-controlled selective area growth of (In,Ga)N/GaN nanocolumns.

Tuning the electronic structures and magnetism of two-dimensional porous C2N via transition metal embedding.

Based on first-principles calculations, the electronic structures and magnetism are investigated in 3d transition metal (TM)-embedded porous two-dimensional (2D) C2N monolayers. Numerical results indicate that except Mn and Co atoms, other TM atoms can be embedded stably in the 2D C2N monolayer. Moreover, the magnetic moments of the TM-embedded C2N monolayer depend highly on the atomic number of the TM atoms. The Sc, Ti, V, Cr, Mn, Fe, Co and Ni atom-embedded C2N monolayers possess a ferromagnetic ground state, while embedding Cu can induce paramagnetic characteristics in the 2D C2N monolayer. Meanwhile, the Zn-embedded C2N monolayer exhibits a nonmagnetic ground state. These results indicate that the magnetism of 2D C2N monolayers can be tuned via embedding TM atoms.

The band gap modulation of monolayer Ti2CO2 by strain

Monolayer Ti2CO2: indirect–direct band gap transition under biaxial strain of ∼4% and uniaxial strain of ∼6%.

Mixed Ti–O–Si oxide films formation by oxidation of titanium–silicon interfaces

The reaction of oxygen with titanium deposited on Si (100) surfaces has been studied at room temperature and low oxygen pressures, using XPS and ARXPS. The experimental results for Ti growth on Si can be explained using a model involving a two stage mechanism. The first stage is characterized by the formation of a uniform TiSix layer ∼4ML thick and the second one by the formation of metallic titanium that grows following a Stranki–Krastanov mechanism, that is, the formation of a Ti monolayer followed by the growth of Ti islands (7ML thick) over the TiSix layer previously formed. The oxidation of Ti/Si interfaces strongly depends on the interface that is oxidized. For an interface corresponding to the first stage of deposition a Ti–O–Si mixed oxide layer is formed on the near surface. This layer is on top of a multilayer structure which is composed of TiO2 (Ti4+), titanium suboxides along with TiSi (TiSi+Ti1++Ti2++Ti3+), and substrate when going from the outer surface to the substrate whereas for an interface corresponding to the second stage no Ti–O–Si mixed oxide is detected and a Ti0 rich layer is observed between the titanium suboxides and the Si substrate.

Fabrication of thin film TiO2 nanotube arrays on Co–28Cr–6Mo alloy by anodization

Titanium oxide (TiO2) nanotube arrays were prepared by anodization of Ti/Au/Ti trilayer thin film DC sputtered onto forged and cast Co–28Cr–6Mo alloy substrate at 400°C. Two different types of deposited film structures (Ti/Au/Ti trilayer and Ti monolayer), and two deposition temperatures (room temperature and 400°C) were compared in this work. The concentrations of ammonium fluoride (NH4F) and H2O in glycerol electrolyte were varied to study their effect on the formation of TiO2 nanotube arrays on a forged and cast Co–28Cr–6Mo alloy. The results show that Ti/Au/Ti trilayer thin film and elevated temperature sputtered films are favorable for the formation of well-ordered nanotube arrays. The optimized electrolyte concentration for the growth of TiO2 nanotube arrays on forged and cast Co–28Cr–6Mo alloy was obtained. This work contains meaningful results for the application of a TiO2 nanotube coating to a CoCr alloy implant for potential next-generation orthopedic implant surface coatings with improved osseointegrative capabilities.

ENHANCEMENT OF GRAPHENE BINDING ENERGY BY Ti 1ML INTERCALATION BETWEEN GRAPHENE AND METAL SURFACES

We theoretically investigate the effects of intercalation of a thin Ti layer between graphene (Gr) and metal surface ( Au , Ag , Al , Pt , and Pd ) on structural and electronic properties by using the first-principles total energy calculations. We find that the strongest binding energy is realized when 1 monolayer (ML) of Ti is intercalated between Gr and a metal surface independent of the metal atoms, which is 0.08-0.15 eV larger than that for Gr absorbed on a Ti (0001) surface. As the number of Ti layers increases, the binding energy monotonically decreases and converges to that for Gr adsorbed onto the Ti surface. We show that the origin of the enhancement of binding energy can be classified into two classes by considering the affinity of Ti for the metal surfaces.