Ti-Si Bonds Research Articles

Damage microstructures in Ti3SiC2 under successive Xe-He-H ions irradiation and annealing process

Ti3SiC2 is recognized as a promising candidate material for nuclear energy applications; however, the microstructural defects resulting from complex irradiation processes remain elusive. This study investigates the microstructural evolution of Ti3SiC2 under sequential Xe-He-H ions irradiation at room temperature, followed by annealing at 900 °C, employing both experimental and first-principles computational approaches. A reverse phase transformation occurred following He irradiation, indicating that He facilitates the remote migration and recombination of Si vacancies through the formation of He-Si pairs during annealing. Post-annealing, the Xe-irradiated sample exhibited a widespread distribution of small Xe bubbles, whereas larger bubbles were prevalent at peak damage regions in the samples subjected to Xe+He and Xe+He+H irradiation. Concurrently, Si-rich precipitates with distinct distribution patterns were observed in samples irradiated with Xe, Xe+He, and Xe+He+H ions, significantly affecting the hardness. First-principles calculations reveal that the distinct damage profiles are primarily attributed to the dynamic behaviors of Si interstitials. The Ti-Si bonds are relatively weak and easily broken, leading to abundant Si interstitials in Xe ion irradiation, and He enhances Si diffusion. Conversely, H enhances Si segregation by preventing He from capturing Si interstitials. Within the TiC grains, He promotes Si migration, causing an approximately 700-fold increase in Si diffusivity at 900 °C. The Si segregation leads to the nucleation of 〈110〉 dislocation loops, culminating in the formation of distinctive strip-like Si clusters. This study elucidates the formation mechanism of Si segregation within Ti3SiC2, providing valuable insights for the design of irradiation-resistant materials.

Effects of alloying elements on the generalized stacking fault energy of Ti5Si3: A first principle study

Influences of six alloying elements on the generalized-stacking-fault (GSF) energy in Ti5Si3 (Ti60Si36) were investigated by the first-principle methods. The GSF energy curve of Ti5Si3 (Ti60Si36) is plotted in the basal{0001}<112¯0>, prism{11¯00}[0001] and pyramidal {21¯1¯2}1/3<21¯1¯3¯>slip system after alloying with six alloying elements. According to the calculation results, the addition of alloying elements will result in a significant decrease of GSF energy, which can promote the generation of prismatic stacking defects and enhance the plasticity of Ti5Si3. In the basal {0001}<112¯0>, prism{11¯00}[0001] and pyramidal {21¯1¯2}1/3<21¯1¯3¯>slip systems, the γus of the possible slip locations decreases gradually with increasing difference in atomic size between Ti and alloying elements. At the same time, through the calculation of elastic constant, it is analyzed that the plasticity of Ti5Si3 will raise first and then fall after the addition of Al atoms with different contents. The addition of alloying elements will decrease the GSF energy, which is caused by the weakening of Ti‒Si bonds. This work may have guiding significance for the alloying design of Ti5Si3 intermetallic compounds.

Improved Contact Resistivity and Transconductance for Sub-10 nm FinFET Technology by Laser-Induced Contact Silicide

Ultra-violet laser thermal annealing (LTA) is proposed to form contact TiSix for sub-10 nm FinFETs. Compared to conventional rapid thermal annealing (RTA), LTA process leads to reduced total series resistance (RTotal) by 10.1∼16.1% and 13.0∼15.3% which corresponds to enhanced transconductance (gm) by 7.7∼9.8% and 5.9∼9.0% for N-/P-FinFETs respectively due to improved contact resistivity (ρc) by 69% arising from more orderly local Ti-Si bonds and smoother TiSix/Si interface. There is also no concern of LTA process in terms of comparable off-state/junction leakage and reliability by hot carrier stress. In addition, LTA is VLSI-compatible without adding any process complexity. These promising properties enable LTA to further unleash the performance of FinFETs.

Diamond(001)–Si(001) and Si(001)–Ti(0001) interfaces: A density functional theory study

Peeling is considered to be the main technical obstacle for coating applications. There are many factors that affect the peeling process of coatings. The interfacial properties of the coating and substrate play a crucial role in the peeling process. In this study, the work of adhesion (Wad), interface energy (γi), and electronic structure of diamond (001)–Si(001) and Si(001)–Ti (0001) interface models have been investigated using first-principles calculations. The results indicate that the diamond (001)–Si(001) interface exhibits larger Wad and smaller γi values when compared with the Si(001)–Ti (0001) interface. However, the Wad of diamond–diamond, Si–Si, and Ti–Ti is 15.92, 4.92, and 3.84 J/m2, respectively. When compared with the two interface models, the Wad of Ti–Ti is the smallest, indicating that it will be the first to undergo deformation during the shear process. In addition, analysis of the charge density difference and density of states revealed that the interfacial Ti–Si bond is a covalent–metallic bond, which is much weaker than the Si–C bond (covalent bond), and therefore, the Si(001)–Ti (0001) structure is more inclined to delaminate.

Diamond(001)–Si(001) and Si(001)–Ti(0001) interfaces: A density functional theory study

Peeling is considered to be the main technical obstacle for coating applications. There are many factors that affect the peeling process of coatings. The interfacial properties of the coating and substrate play a crucial role in the peeling process. In this study, the work of adhesion (Wad), interface energy (γi), and electronic structure of diamond(001)–Si(001) and Si(001)–Ti(0001) interface models have been investigated using first-principles calculations. The results indicate that the diamond(001)–Si(001) interface exhibits larger Wad and smaller γi values when compared with the Si(001)–Ti(0001) interface. However, the Wad of diamond–diamond, Si–Si, and Ti–Ti is 15.92, 4.92, and 3.84 J/m2, respectively. When compared with the two interface models, the Wad of Ti–Ti is the smallest, indicating that it will be the first to undergo deformation during the shear process. In addition, analysis of the charge density difference and density of states revealed that the interfacial Ti–Si bond is a covalent–metallic bond, which is much weaker than the Si–C bond (covalent bond), and therefore, the Si(001)–Ti(0001) structure is more inclined to delaminate.

Novel Synthesis of Red Phosphorus Nanodot/Ti3C2Tx MXenes from Low-Cost Ti3SiC2 MAX Phases for Superior Lithium- and Sodium-Ion Batteries.

MXenes, synthesized from MAX, have emerged as new energy-storage materials for a good combination of metallic conductivity and rich surface chemistry. The reported MXenes are synthesized mostly from Al-based MAX. It is still a big challenge to synthesize MXenes from abundant Si-based MAX because of its strong Ti-Si bonds. Here, we report for the first time a high-energy ultrasonic cell-crushing extraction method to successfully prepare Ti3C2Tx MXenes from Si-based MAX using a single low-concentration etchant. This novel strategy for preparing MXenes has a high extraction efficiency and is a fast preparation process of less than 2 h for selective etching of Si. Furthermore, through the high-energy ball-milling technology, unique P-O-Ti bonded red phosphorus nanodot/Ti3C2Tx (PTCT) composites were successfully prepared, which enable superior electrochemical performance in lithium- and sodium-ion batteries because of the double-morphology structure, where the amorphous nano red phosphorus particles were strongly absorbed to Ti3C2Tx MXene sheets, facilitating the transport of alkali ions during cycling processes. This novel synthesis method of Ti3C2Tx MXenes from Si-based MAX and unique P-O-Ti bonded PTCT composites opens a new door for preparing high-performance MXene-based materials and facilitating the development of low-cost MXenes and other two-dimensional materials for next-generation energy storage.

Effect of amorphous silicon interlayer on the adherence of amorphous hydrogenated carbon coatings deposited on several metallic surfaces

The effect of an amorphous hydrogenated silicon (a-Si:H) interlayer on the adherence of amorphous hydrogenated carbon (a-C:H) coatings deposited on four metallic surfaces: AISI M2 steel, AISI 304 stainless steel, Nitinol alloy, and Ti6Al4V alloy was studied. The interlayers and the coatings were deposited employing an asymmetrical bipolar pulsed-DC PECVD system with an active screen. Multilayer a-C:H coatings were also deposited, with the aim of obtaining thicker films. The interlayers were synthetized by varying the applied negative pulse amplitude from −0.8 kV to −10 kV, keeping their thickness constant at 250 nm. The coatings' adhesion was evaluated using classical scratch and VDI 3198 indentation tests. Raman spectroscopy was used to analyze the films' atomic arrangements. The total compressive stress was determined through the measurement of the substrate curvature before and after the film deposition, while nanoindentation experiments allowed determining the films' hardness and elastic modulus. In order to determine the chemical bonding between a-Si:H and the metallic surfaces, X-ray photoelectron spectroscopy (XPS) was used. The obtained results showed high values of critical loads, allowing a high degree of adherence of the a-C:H coatings to all the metallic materials. The highest Lc1 critical load values (≥25 N) were determined when the a-Si:H interlayers were deposited using the highest negative applied voltage (from −6 kV to −10 kV) on the Nitinol alloy surfaces. The XPS results suggested that the high degree of adhesion of the a-C:H coatings to Nitinol could be attributed to chemical bonds of TiSi and NiSi formed in the interface, while for the Ti6Al4V alloy the TiSi bonds predominated. On the other hand, on steel surfaces the adhesion was due to FeSi bonds. A combination of a modified pulsed-DC PECVD system with an active screen and an a-Si:H interlayer allowed depositing hard, adherent, and low-stress a-C:H coatings.

Self-propagating high-temperature synthesis in the Ti-Si-C system: Features of product patterning

Nanolaminate Ti3SiC2-based material is prepared by self-propagating high-temperature synthesis (SHS) from elements, and the processes of its phase and structure formation is investigated. The Ti3SiC2 content in combustion products grows with an increase in the lifetime of the melt. The stratification observed at the level of the crystal structure results in the pronounced nanolaminate structure of Ti3SiC2 grains. The formation of the Ti3SiC2 phase occurs behind the combustion front with the interaction of stoichiometric TiC with the melt based on Ti-Si. Quantum-chemical calculations show that the formation of Ti-Si bonds is energetically preferable to Ti-C bond formation. A comparison of TiC and Ti3SiC2 crystal structures allow the assumption to be made that the laminate shape of Ti3SiC2 crystals is caused by the accumulation of structure discrepancies and hence by a lack of conjugation between the crystals.

Titanium-induced charge of Si(0 0 1) surface dependent on local configuration

High-resolution X-ray photoemission spectroscopy (XPS) was applied to Ti-deposited Si(001) surfaces, which were structurally characterized by means of scanning tunneling microscopy (STM). Negative chemical shift of Si due to Ti deposition was assigned to the distorted TiSi bonds formed on the surface. The shift was reduced when a Ti sank beneath a Si dimer. Silicidation resulted in a positive shift to the TiSi bonding. The charge on the Si atoms near Ti was estimated through preliminary natural bonding orbital (NBO) calculation. We show that the shifts can be explained in terms of the sensitivity of charges of Si near Ti to the local structure near the dimer.

High-temperature neutron diffraction and the temperature-dependent crystal structures of theMAXphasesTi3SiC2andTi3GeC2

Herein, we report on the crystal structures of the isostructural Ti3SiC2 and Ti3GeC2 phases determined by Rietveld analysis of neutron diffraction data in the 100° to 1100 ° C temperature range. The results show that the Si and Ge atoms vibrate anisotropically with the highest amplitudes and within the basal planes. The equivalent isotropic thermal motion behavior does not differ significantly between the two phases; the anisotropic thermal motion, interatomic distances, and bond angles, however, show strikingly different behavior. Furthermore, while the Ti-Si bonds increase linearly with increasing temperature, the Ti-Ge bonds apparently do not. The anisotropic motion of the Ge atoms in the basal plane with the correlated motion between the Ti and the Ge atoms is invoked as a possible explanation. The volume expansions are 9.00.1 10 �6 K �1 and 8.70.1 10 �6 K �1 for Ti3SiC2 and Ti3GeC2, respectively; the expansions along the a and c axes are a

Cleavage fracture in Ti 3SiC 2 from first-principles

Using ab initio full-potential linearized plane wave calculations, we studied the cleavage characteristics for three basal planes in Ti 3 SiC 2 and found that the habit cleavage should be between the Ti and Si hexagonal layers. The estimations of fracture properties under tensile stress showed a significant stretching of the Ti–Si bonds before failure that may explain the damage tolerance of Ti 3 SiC 2 .

A systematic investigation of work function in advanced metal gate–HfO 2–SiO 2 structures with bevel oxide

This paper presents for the first time the work function extraction for chemical vapor deposition (CVD)-TiN and poly-Si work functions on atomic layer deposition (ALD)-HfO 2 and high temperature SiO 2 (HTO) for a wide range of EOT values. The measurements were performed on bevel oxide structures with various SiO 2 thicknesses from 0 to 12 nm. Our results reveal that the work functions of both TiN and poly-Si gates highly depend on the underlying dielectrics especially in the case of TiN on HTO films. It is found that the leakage current also depends on the dielectric stacks. When TiN is formed on the HTO film, its work function has two distinct values depending on the HTO thickness; this indicates that Ti Si bonds strongly affect the work function variation. Both TiN on HTO and poly-Si on HfO 2 show the work function shifts to about 4.3 eV, suggesting a pinning level in both structures.

First-principles study of Ti 3AC 2 (A = Si, Al) (0 0 1) surfaces

We have systematically studied the mechanical properties and surface properties of (1 × 1) Ti 3AC 2 (A = Si, Al) (0 0 1) using the density functional theory (DFT). The calculated cleavage energy for each possible cleavage site shows that Ti–Si and Ti–Al are the weakest layers, while the Ti–C layer is the strongest one. It reveals that the main difference between Ti 3SiC 2 and Ti 3AlC 2 is that the Ti–Si bond is stronger than the Ti–Al bond. This shows the different mechanical and surface properties between them. The surface rumpling and surface energy of Ti 3SiC 2 and Ti 3AlC 2 are calculated. The study shows that the cleavage energy affects both the surface rumpling and the surface energy. The higher the cleavage energy, the larger the surface energy and surface rumpling. Furthermore, the most stable surface structures are predicted for different experimental conditions. The predicted surface structures agree with the available experimental results.

On the impact of TiN film thickness variations on the effective work function of poly-Si/TiN/SiO/sub 2/ and poly-Si/TiN/HfSiON gate stacks

The impact of TiN film thickness variations on the effective work function (WF) of poly-Si/TiN/SiO/sub 2/ and poly-Si/TiN/HfSiON interfaces has been investigated. The electrical signatures of these gate stacks indicate that the concentration of Hf-Ti and Ti-Si bonds at the (poly-Si/TiN)/HfSiON and (poly-Si/TiN)/SiO/sub 2/ interface plays a significant role on the control of the gate stacks' WF. The density of these interfacial bonds and the related work function changes are correlated to the degree of nucleation of the TiN film on the dielectric.

Study of nanocrystalline TiN/Si 3N 4 thin films deposited using a dual ion beam method

A dual ion beam system is used to produce hard nanocomposite TiN/Si 3N 4 coatings on Si. Cross-sectional high resolution transmission electron microscopy analysis of the coatings shows that ion assistance causes microstructure to change from the non-assisted columnar form to one where there are small crystals present in an amorphous percolation network. For an unheated Si substrate, the microhardness increases with increasing ion-assist energy from 24 to 29 GPa, whereas for a deposition substrate at 400 °C, the microhardness values are 7–8 GPa or higher. The value of microhardness does not change even when coatings are annealed in vacuum at 1000 °C, showing that these coatings have high thermal stability. X-ray photoelectron spectroscopy data indicate that the –Ti–N–Si– bonds expected when the percolation network is formed are present only for substrate temperatures above 600 °C and that Ti–Si bonds form at lower temperature and during excess ion bombardment.

Topology of charge density and elastic anisotropy of Ti3SiC2polymorphs

Using an all-electron, full potential first-principles method, we have investigated the topology of charge density and elastic anisotropy of Ti3SiC2polymorphs comparatively. By analyzing the charge density topology, it was found that the Ti–Si bonds are weaker in β than in α, resulting in a destabilizing effect and lower Young’s modulus in directions betweenaandcaxes for β. On the other hand, the Si–C bonds (absent in α) are formed in β in thecdirection. The formation of the Si–C bonds not only mitigates the destabilizing effect of the weaker Ti–Si bonds, but also results in larger Young’s modulus in thecdirection. In contrast to the high elastic anisotrophy, the elastic anisotropy of Ti3SiC2is very low.

Nonclassical titanocene silyl hydrides.

The titanocene silyl hydride complexes [Ti(Cp)2(PMe3)(H)(SiR3)] [SiR3=SiMePhCl (6), SiPh2Cl (7), SiMeCl2 (8), SiCl3 (9)] were prepared by HSiR3 addition to [Ti(Cp)2(PMe3)2] and were studied by NMR and IR spectroscopy, X-ray diffraction (for 6, 8, and 9), and DFT calculations. Spectroscopic and structural data established that these complexes exhibit nonclassical Ti-H-Si-Cl interligand hypervalent interactions. In particular, the observation of silicon-hydride coupling constants J(Si,H) in 6-9 in the range 22-40 Hz, the signs of which we found to be negative for 8 and 9, is conclusive evidence of the presence of a direct Si-H bond. The analogous reaction of [Ti(Cp)2(PMe3)2] with HSi(OEt)3 does not afford the expected classical silyl hydride complex [Ti(Cp)2(PMe3)(H)[Si(OEt)3]], and instead NMR-silent titanium (apparently TiIII) complex(es) and the silane redistribution product Si(OEt)4 are formed. The structural data and DFT calculations for the compounds [Ti(Cp)2(PMe3)(H)(SiR3)] show that the strength of interligand hypervalent interactions in the chlorosilyl complexes decreases as the number of chloro groups on silicon increases. However, in the absence of an Si-bound electron-withdrawing group trans to the Si-H moiety, a silane sigma complex is formed, characterized by a long Ti-Si bond of 2.658 A and short Si-H contact of 1.840 A in the model complex [Ti(Cp)2(PMe3)(H)(SiMe3)]. Both the silane sigma complexes and silyl hydride complexes with interligand hypervalent interactions exhibit bond paths between the silicon and hydride atoms in Atoms in Molecules (AIM) studies. To date a classical titanocene phosphane silyl hydride complex without any Si-H interaction has not been observed, and therefore titanocene silyl hydrides are, depending on the nature of the R groups on Si, either silane sigma complexes or compounds with an interligand hypervalent interaction.

MCSCF Study of Multiple Bonding between Ti and the Main-Group Elements C, Si, N, and P

The nature of the multiple bonding of H2TiEH2 (E = C, Si) and H2TiEH (E = N, P) molecules has been investigated with the multiconfiguration SCF (MCSCF) method. It is shown that the Ti−C and Ti−P bond lengths decrease with bond rotation, whereas the Ti−Si bond length increases. MCSCF geometry optimization shows that Ti−N has triple-bond character with a linear Ti−N−H bond angle that results from strong back-bonding from the N lone pair into the empty Ti d orbitals. The rotation barrier and bond dissociation energy for TiE are estimated with the MCSCF + multireference second-order perturbation theory (MRMP2) method. The singlet rotation barriers in TiC, TiSi, and TiP are estimated to be 15.9, 8.6, and 9.3 kcal/mol, respectively. The TiC and TiSi bond dissociation energies are estimated to be 83.4 and 56.9 kcal/mol, respectively. The Ti⋮N triple-bond energy is about 30 kcal/mol larger than that of the carbon species, whereas the energy of the TiP bond is about 8 kcal/mol smaller than that of the silicon species.

Kinetics of the C49–C54 phase transition in TiSi 2: New indications from sheet resistance, infrared spectroscopy and molecular dynamics simulations

The kinetics and mechanism of the C49C54 polymorphic transformation in titanium disilicides thin films were investigated by sheet resistance and optical spectroscopy. Fine grained C49 films were prepared by depositing Ti films on heated amorphous silicon substrates. The transformation to the C54 phase occurred after rapid thermal processing at temperatures between 700 and 775°C. The time to transform the film at a fixed temperature decreases with the grain size and no strain can be detected during the transformation. The activation energy for the transformation is 3.9±0.2 eV. Total energy calculations suggests that the activation energy is associated to the breaking of TiSi bonds during the massive-reconstructive transformation.

Very High Frequency Plasma Enhanced Chemical Vapor Deposition of TiSix/TiN1-xSix Barrier Films

Very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) of titaniumsilicide /titaniumnitride barrier films using the silane reduction process with a TiCl4 source is described. VHF plasma, which is denser than a conventional RF plasma, produces a large number of excited species. The silane reduction process, which supplies excited species such as SiHx radicals and SiHx + ions as reductants in plasma, promotes dissociation of TiCl4 precursors more than a conventional hydrogen reduction process. Therefore, the VHF-PECVD with the silane reduction process forms high quality titaniumsilicide/titaniumnitride barrier films, which have a low Cl content (<0.2 at.%). In the silane reduction process, the Ti–Si bond is simultaneously formed into the bond structure, resulting in depositing Si-containing films of TiSix or TiN1-x Six . The resistivity of TiSix or TiN1-x Six is about 100 µ Ω· cm. The surface morphology of TiSix films is very smooth and the structure of TiN1-x Six films is amorphous.