Adhesion and bonding of the Al/TiC interface

The electronic structure and adhesion of Al/TiC(0 0 1) interface are examined by density functional theory. Our results show the preferred configuration is the Al atom above the ceramic’s metalloid atom. The calculated adhesion explains the conflicting experimental results of the W_ad from the aspect of the establishing different chemical equilibrium bonds at the different temperatures. By applying several analysis methods we have thoroughly characterized the interfacial electronic structure. For the Ti-site the interfacial Al and Ti atoms form the metal/covalent bond, while for the C-site the interfacial Al and C atoms form the polar covalent interaction. In addition, we examine the effects of Mg and Si alloying elements at the interface, and find that Mg greatly deteriorates the interface and Si slightly improves the interface. The cleavage may take place preferentially at the interface with the help of interface strain energy, especially with the addition of Mg. This is in good agreement with the experimental result.     

Interfacial reaction of intermetallic compounds of ultrasonic-assisted brazed joints between dissimilar alloys of Ti6Al4V and Al4Cu1Mg

Ultrasonic-assisted brazing of Al4Cu1Mg and Ti6Al4V using Zn-based filler metal (without and with Si) has been investigated. Before brazing, the Ti6Al4V samples were pre-treated by hot-dip aluminizing and ultrasonic dipping in a molten filler metal bath in order to control the formation of intermetallic compounds between the Ti6Al4V samples and the filler metal. The results show that the TiAl(3) phase was formed in the interface between the Ti6Al4V substrate and the aluminized coating. For the Zn-based filler metal without Si, the Ti6Al4V interfacial area of the brazed joint did not change under the effect of the ultrasonic wave, and only consisted of the TiAl(3) phase. For the Zn-based filler metal with Si, the TiAl(3) phase disappeared and a Ti(7)Al(5)Si(12) phase was formed at the interfacial area of the brazed joints under the effect of the ultrasonic wave. Due to the TiAl(3) phase completely changing to a Ti(7)Al(5)Si(12) phase, the morphology of the intermetallic compounds changed from a block-like shape into a lamellar-like structure. The highest shear strength of 138MPa was obtained from the brazed joint free of the block-like TiAl(3) phase.     

Interaction behaviors at the interface between liquid Al–Si and solid Ti–6Al–4V in ultrasonic-assisted brazing in air

Power ultrasonic vibration (20 kHz, 6 μm) was applied to assist the interaction between a liquid Al–Si alloy and solid Ti–6Al–4V substrate in air. The interaction behaviors, including breakage of the oxide film on the Ti–6Al–4V surface, chemical dissolution of solid Ti–6Al–4V, and interfacial chemical reactions, were investigated. Experimental results showed that numerous 2–20 μm diameter-sized pits formed on the Ti–6Al–4V surface. Propagation of ultrasonic waves in the liquid Al–Si alloy resulted in ultrasonic cavitation. When this cavitation occurred at or near the liquid/solid interface, many complex effects were generated at the small zones during the bubble implosion, including micro-jets, hot spots, and acoustic streaming. The breakage behavior of oxide films on the solid Ti–6Al–4V substrate, excessive chemical dissolution of solid Ti–6Al–4V into liquid Al–Si, abnormal interfacial chemical reactions at the interface, and phase transformation between the intermetallic compounds could be wholly ascribed to these ultrasonic effects. An effective bond between Al–Si and Ti–6Al–4V can be produced by ultrasonic-assisted brazing in air.     

Epitaxial growth of bcc Fe films on Al(1 0 0) surfaces using Ti as an interface stabilizer

An approach is described to promote epitaxial growth of thin metal films on single-crystal metal substrates by stabilizing the interface with an extremely thin metallic interlayer. A single atomic layer of a metal is deposited at the interface, Ti on Al(1 0 0) in this case, prior to the growth of the metal film of interest to produce an epitaxial interface in a system that is otherwise characterized by interdiffusion and disorder. The stabilized interface reduces interdiffusion and serves as a template for ordered film growth. Using Rutherford backscattering and channeling techniques along with low-energy electron diffraction and low-energy He⁺ scattering, it is demonstrated that an atomically thin layer of Ti metal deposited at the Fe-Al interface, a system well known for considerable intermixing at room temperature, reduces interdiffusion and promotes the epitaxial growth of Fe films on the Al(1 0 0) surface. The decrease in ion scattering yield for Al atoms, Fe-Fe shadowing and long-range order of the surface suggest that the epitaxial growth of Fe is greatly improved when the Ti interlayer is introduced prior to Fe deposition. Off-normal ion channeling experiments provide clear evidence for the bcc structure of Fe on the Ti/Al(1 0 0) template with the measured average (1 0 0) interplanar distance of 1.44 Å in the Fe overlayer.     

Formation of the Si/Ti interface

The formation of the Si/Ti interface during the deposition of silicon on titanium polycrystalline substrates has been studied at room temperature (RT) using X-ray photoelectron spectroscopy (XPS), angle-resolved XPS (ARXPS), ultraviolet photoelectron spectroscopy (UPS) and ion scattering spectroscopy (ISS). The experimental results are consistent with a two-stage mechanism for Si growth: a first stage characterized by the simultaneous formation of a uniform titanium silicide layer, that reaches a limiting thickness of ∼3 monolayer (ML), and pure silicon islands 1 ML thick that grow on top of this layer up to coalescence, followed by a second stage in which pure silicon islands, with an average thickness of 9 ML, grow on top of the uniform titanium silicide layer + pure silicon ML structure formed during the first stage. As a whole, pure silicon species grows according to a Stranski-Krastanov mechanism, where the first ML is formed during the first stage and the islands during the second stage. The comparison of Ti/Si and Si/Ti interfaces shows that the structure and composition of the interface do not depend substantially on the deposition sequence, suggesting that the bulk chemistry of the compound formed at the interface dominates over the surface kinetics and the bulk substrate chemistry in determining the composition and structure of the interface.     

Influence of MgO and ZrO2 buffer layers on dielectric properties of Ba(Zr0.20Ti0.80)O3 thin films prepared by sol-gel processing

Ba(Zr_0.20Ti_0.80)O₃ (BZT) thin films are deposited on Pt(1 1 1)/Ti/SiO₂/Si, MgO and ZrO₂ buffered Pt(1 1 1)/Ti/SiO₂/Si substrates by a sol-gel process. The BZT thin films directly grown on Pt(1 1 1)/Ti/SiO₂/Si substrates exhibit highly (1 1 1) preferred orientation, while the films deposited on Pt(1 1 1)/Ti/SiO₂/Si substrates with MgO and ZrO₂ buffer layers show highly (1 1 0) preferred orientation. At 100 kHz, dielectric constants are 417, 311 and 321 for the BZT thin films grown on Pt(1 1 1)/Ti/SiO₂/Si, MgO and ZrO₂ buffered Pt(1 1 1)/Ti/SiO₂/Si substrates, respectively. The difference in dielectric properties of three BZT films can be attributed to the series capacitance effect, interface conditions and their orientations.     

Multinuclear (27Al, 29Si, 47,49Ti) solid-state NMR of titanium substituted zeolite USY

Multinuclear solid-state NMR spectroscopy, employing 29Si MAS,27Al MAS/3Q-MAS and (47,49)Ti wide-line experiments, has been used for the structural characterization of titanium substituted ultra-stable zeolite Y (Ti-USY). 27Al MAS experiments show the presence of aluminum in four (Al(IV)), five (Al(V)), and six (Al(VI)) coordination, whereas the multiplicity within Al(IV) and Al(VI) is revealed by 27Al 3Q-MAS experiments. Two different tetrahedral and octahedral Al environments are resolved and their isotropic chemical shifts (delta(CS)) and second-order quadrupole interaction parameters (P(Q)) have been determined by a graphical analysis of the 3Q-MAS spectra. The emergence of signal with higher intensity at -101 ppm in the 29Si MAS spectrum of Ti-USY samples indicates the possible occurrence of Q4(3Si,1Ti) type silicon environments due to titanium substitution in the faujasite framework. High-field (11.74T) operation, using a probehead specially designed to handle a large sample volume, has enabled the acquisition of 47,49Ti static spectra and identification of the titanium environment in the zeolite. The chemical shielding and electric field gradient tensors for the titanium environment in the zeolite have been determined by a computer simulation of the quadrupolar broadened static 47,49Ti NMR spectra.     

Metal contacts to n-GaN

Al, Au, Ti/Al and Ti/Au contacts were prepared on n-GaN and annealed up to 900 °C. The structure, phase and morphology were studied by cross-sectional transmission and scanning electron microscopy as well as by X-ray diffraction (XRD), the electrical behaviour by current-voltage measurements. It was obtained that annealing resulted in interdiffusion, lateral diffusion along the surface, alloying and bowling up of the metal layers. The current-voltage characteristics of as-deposited Al and Ti/Al contacts were linear, while the Au and Ti/Au contacts exhibited rectifying behaviour. Except the Ti/Au contact which became linear, the contacts degraded during heat treatment at 900 °C. The surface of Au and Ti/Au contacts annealed at 900 °C have shown fractal-like structures revealed by scanning electron microscopy. Transmission electron microscopy and XRD investigations of the Ti/Au contact revealed that Au diffused into the n-GaN layer at 900 °C. X-ray diffraction examinations showed, that new Ti₂N, Au₂Ga and Ga₃Ti₂ interface phases formed in Ti/Au contact at 900 °C, new Ti₂N phase formed in Ti/Al contact at 700 and 900 °C, as well as new AlN interface phase developed in Ti/Al contact at 900 °C.     

(Ti,Al,Si,C)N nanocomposite coatings synthesized by plasma-enhanced magnetron sputtering

Materials’ surface service property could be enhanced by transition metal nitride hard coatings due to their high hardness, wear and high temperature oxidation resistance, but the higher friction coefficient (0.4-0.9) of which aroused terrible abrasion. In this work, quinternary (Ti,Al,Si,C)N hard coating 3-4 μm was synthesized at 300 °C using plasma enhanced magnetron sputtering system. It was found that the coating's columnar crystals structure was restrained obviously with the increase of C content and a non-columnar crystals growth mode was indicated at the C content of 33.5 at.%. Both the XRD and TEM showed that the (Ti,Al,Si,C)N hard coatings had unique nanocomposite structures composed of nanocrystalline and amorphous nc-(Ti,Al)(C,N)/nc-AlN/a-Si₃N₄/a-Si/a-C. However, the coatings were still super hard with the highest hardness of 41 GPa in spite of the carbon incorporation. That a-C could facilitate the graphitization process during the friction process which could improve the coating's tribological performance. Therefore, that nanocomposite (Ti,Al,Si,C)N coatings with higher hardness (>36 GPa) and a lower friction coefficient (<0.2) could be synthesized and enhance the tribological performance and surface properties profoundly.     

Ultrathin amorphous Ti–Al film used as a diffusion barrier for copper metallization

The viability of ultrathin amorphous Ti–Al film (～4 nm) as a diffusion barrier layer between Cu and Si for the application in Si-based ultra-large scale integration (ULSI) has been investigated. The Cu/Ti–Al/Si heterostructures are annealed in a high vacuum at various temperatures. There is no impurity peaks in the X-ray diffraction patterns for the samples up to annealing temperature of 800 ^°C, although the island-like grains were observed on the surface of the 800 ^°C annealed sample due to dewetting and agglomeration of the Cu film. No inter-reactions can be found from the images of transmission electron microscopy and Ti–Al is still amorphous after high-temperature annealing. These results indicate that Ti–Al film can effectively separate Cu from Si at high temperatures, and that the amorphous ultrathin Ti–Al film can be a very good barrier layer for Cu metallization.     

Study of Ni/Si(1 0 0) solid-state reaction with Al addition

The characteristics of Ni/Si(1 0 0) solid-state reaction with Al addition (Ni/Al/Si(1 0 0), Ni/Al/Ni/Si(1 0 0) and Al/Ni/Si(1 0 0)) is studied. Ni and Al films were deposited on Si(1 0 0) substrate by ion beam sputtering. The solid-state reaction between metal films and Si was performed by rapid thermal annealing. The sheet resistance of the formed silicide film was measured by four-point probe method. The X-ray diffraction (XRD) was employed to detect the phases in the silicide film. The Auger electron spectroscopy was applied to reveal the element profiles in depth. The influence of Al addition on the Schottky barrier heights of the formed silicide/Si diodes was investigated by current-voltage measurements. The experimental results show that NiSi forms even with the addition of Al, although the formation temperature correspondingly changes. It is revealed that Ni silicidation is accompanied with Al diffusion in Ni film toward the film top surface and Al is the dominant diffusion species in Ni/Al system. However, no Ni_xAl_y phase is detected in the films and no significant Schottky barrier height modulation by the addition of Al is observed.     

基于第一性原理的Si/SiC、Al/SiC界面成键特性和结合强度对比研究

采用半固态搅拌铸造法制备Al Si7-Si C复合材料，并利用真空压铸工艺实现了其近净成形，结合第一性原理计算方法研究了共晶Si对Si C颗粒和基体界面结合强度的影响.结果显示，在Al Si7-Si C复合材料中，发现较为严重的共晶Si偏析现象，当Si C颗粒同时处于共晶Si和α-Al边界时，形成了少量的共晶Si夹杂、被大量共晶Si包裹、完全被共晶Si包裹三种典型的界面.第一性原理计算结果显示，在C端和Si端的Si/Si C界面中，弛豫后top Si¹配位方式具有最大的粘附功，与Al/Si C界面相比，Si/Si C界面具有更高的结合强度.Si偏析相提高了界面处的电荷密度，因而具有更好的界面结构稳定性.     

Theoretical study of Ti and Fe surface alloys on Al(0 0 1) substrate

Accurate density-functional calculations are performed to investigate the formation of Ti and Fe ultrathin alloys on Al(0 0 1) surface. It is demonstrated that a deposition of Ti monolayer on Al(0 0 1) substrate leads to the formation of Al₃Ti surface alloy with Ti atoms arranged according to the L1₂ stacking, distinct from the D0₂₂ structure characteristic of a bulk Al₃Ti compound. A quest for the reason of this distinct atomic arrangement led us to the study of the surface structure of Al₃Ti(0 0 1) compound. It is concluded that even the Al₃Ti(0 0 1) surface is terminated with three layers assuming a L1₂ stacking and hence this stacking fault can be classified as a surface-induced stacking fault. Several possibilities of Fe atoms distributed in the surface region of Al(0 0 1) have been examined. The most stable configuration is the one with the compact Fe monolayer on Al(0 0 1) and covered by one Al monolayer. Lastly, our calculations show that there is no barrier for the penetration of Fe adatoms below the Al(0 0 1) surface; however, such a barrier is present for a Ti-alloyed Al(0 0 1) surface.     

Effects of substrates on the structure and dielectric properties of Ba(Sn0.15Ti0.85)O3 thin films

Ba(Sn_0.15Ti_0.85)O₃ (BTS) thin films were grown on Pt(1 1 1)/Ti/SiO₂/Si and LaNiO₃(LNO)/Pt(1 1 1)/Ti/SiO₂/Si substrates by a sol-gel processing technique, respectively. The BTS thin films deposited on annealed Pt(1 1 1)/Ti/SiO₂/Si and annealed LNO/Pt(1 1 1)/Ti/SiO₂/Si substrates exhibited strong (1 1 1) and perfect (1 0 0) orientations, respectively. The BTS thin films grown on un-annealed Pt(1 1 1)/Ti/SiO₂/Si substrates showed random orientation with intense (1 1 0) peak, while the films deposited on un-annealed LNO/Pt(1 1 1)/Ti/SiO₂/Si substrate exhibited random orientation with intense (1 0 0) peak, respectively. The dielectric constant of the BTS films deposited on annealed Pt(1 1 1)/Ti/SiO₂/Si, annealed LNO/Pt(1 1 1)/Ti/SiO₂/Si, un-annealed Pt(1 1 1)/Ti/SiO₂/Si and un-annealed LNO/Pt(1 1 1)/Ti/SiO₂/Si substrates was 512, 565, 386 and 437, respectively, measured at a frequency of 100 kHz. A high tunability of 49.7% was obtained for the films deposited on annealed LNO/Pt(1 1 1)/Ti/SiO₂/Si substrate, measured at the frequency of 100 kHz with an applied electric field of 200 kV/cm. The high tunability has been attributed to the (1 0 0) texture of the films and larger grain sizes.     

Ion irradiation induced Al-Ti interaction in nano-scaled Al/Ti multilayers

Interactions induced in Al/Ti multilayers by implantation of Ar ions at room temperature were investgated. Initial structures consisted of (Al/Ti) × 5 multilayers deposited by d.c. ion sputtering on Si(1 0 0) wafers, to a total thickness of ∼250 nm. They were irradiated with 200 keV Ar⁺ ions, to the fluences from 5 × 10¹⁵ to 4 × 10¹⁶ ions/cm². It was found that ion irradiation induced a progressed intermixing of the multilayer constituents and Al-Ti nanoalloying for the highest applied fluence. The resulting nanocrystalline structure had a graded composition with non-reacted or interdiffused Al and Ti, and γ-AlTi and AlTi₃ intermetallic phases. Most intense reactivity was observed around mid depth of the multilayers, where most energy was deposited by the impact ions. It is presumed that Al-Ti chemical reaction is triggered by thermal spikes and further enhanced by chemical driving forces. The applied processing can be interesting for fabrication of tightly bond multilayered structures with gradual changes of their composition and properties.     

Investigation of formation mechanism of Ti3SiC2 by high pressure and high-temperature synthesis

ABSTRACT

In this paper, synthesis of titanium silicon carbide (Ti₃SiC₂) under high pressure and high-temperature condition has been investigated by using the reactant systems Ti/Si/C, Ti/SiC/TiC, Ti/SiC/C and Ti/TiC/Si. Results reveal that Ti/TiC/Si is unsuited to the synthesis of Ti₃SiC₂ under a high pressure of 2.0?GPa, while an elemental mixture of Ti/Si/C is applicable. By the addition of Al, Ti₃SiC₂ with 95.8?wt% purity was obtained from elemental mixture with a large excess of silicon. The optimum experimental parameters were determined as Ti/Si/Al/C having the molar ratio of 3:1.5:0.5:1.9, holding at 2.0?GPa and 1300?°C for 60?min.     

Surface and interface of Ti(film)/SiC(substrate) system: a soft X-ray emission and photoemission electron microscopy study

We have conducted a soft X-ray emission spectroscopy (SXES) and a photoemission electron microscopy (PEEM) study on the heat-treated Ti/4H–SiC system. This spectro-microscopy approach is an ideal surface and interface characterization techniques due to the non-destructive nature of SXES and the real-time surface imaging of PEEM.

The Si L_2,3 and C K soft X-ray emission spectra, which reflect Si (s+d) states and C p states, respectively, revealed formations of Ti₅Si₃ and TiC in the reacted interfacial region of Ti (50 nm)/4H–SiC(0 0 0 1) sample.

The surface of the Ti films on 4H–SiC samples during heat-treatment up to 850 °C was investigated by PEEM. The variation in brightness in the image of the sample was attributed to the surface deoxidation in the early stage of the treatment and to the formation of reacted region at the later stage. The darkening of the surface could be attributed to the formation of TiC and/or excess C atoms that could have migrated to the surface.     

Epitaxial growth of Al on Si(1 1 1) with Cu buffer layers

The structure of thin Al films grown on Si(1 1 1) with thin Cu buffer layers has been investigated using synchrotron radiation photoemission spectroscopy. A thin Cu(1 1 1) layer between the Si(1 1 1) substrate and an Al film may enhance quantum well effects in the Al film significantly. The strength of quantum well effects has been investigated qualitatively with respect to the thickness of the Cu buffer layer and to the Al film thickness. Deposition of Cu on Si(1 1 1)7 × 7 leads to formation of a disordered silicide layer in an initial regime before a well-ordered Cu(1 1 1) film is formed after deposition of the equivalent of 6 layers of Cu. In the regime below 6 layers of Cu the disorder is transferred to Al layers subsequently grown on top. The initial growth of up to 8 layers of Al on a well-ordered Si/Cu(1 1 1) layer leads to a disordered film due to the lattice mismatch between the two metals. When the Cu buffer layer and the Al over-layer are above 6 and 8 layers, respectively the Al film shows sharp low energy electron diffraction patterns and very sharp quantum well peaks in the valence band spectra signalling good epitaxial growth.     

Origin of ion beam mixing effects on morphological features in solid-phase titanium silicide formation

The origin of the ion beam mixing effect, which causes the formation of smooth silicide films, is investigated for the Ti/Si solid-phase silicidation reaction. Ge ion beam mixing of a conventional Ti/c-Si structure with an oxide-contaminated interface shows an obvious effect when the implant conditions are such that the Ti/Si interface is amorphized. On the other hand, silicidation without ion mixing for Ti/a-Si and Ti/c-Si structures with oxide-free interfaces, prepared by sequential deposition in UHV, results in smooth and rough film surfaces, respectively. This strongly suggests that the ion beam mixing effect primarily comes from the amorphization of the Si substrate surface rather than the destruction of the interfacial oxide film.     

Microstructure of multilayer interface in an Al matrix composite reinforced by TiNi fiber

A multilayer interface was formed in the Al matrix composite which was reinforced by 30% volume fraction of TiNi fiber. The composite was fabricated by pressure infiltration process and the interface between the TiNi fiber and Al matrix was investigated by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). When the TiNi fiber was pre-oxidized in the air at 773 K for 1 h, three layers have been found and characterized in the interface: TiNi–B₂ layer near the TiNi fiber, Ti–Al compound layer with Ti and granular TiO₂ near the Al matrix, and Ti–Ni compound layer between TiNi–B₂ and Ti–Al compound layers. The effect of the multilayer interface on the mechanical properties of the composite was also discussed. The result showed that the uniaxial tensile strength of the composite at room temperature was 318 MPa, which was very close to the theoretical calculation value of 326 MPa. Moreover, the composite with good ductility exhibited a typical ductile-fracture pattern.