Application of atomic force microscopy to detect edge of mask contaminations that may hinder titanium silicide formation

An atomic force microscope (AFM) was used to study anomalies in the titanium disilicide formation of narrow (0.26 μm) poly lines at the edge of n+ and p+ implant masks; a special test structure was designed both for morphological and electrical evaluations. On poly lines along the borders of the n+ mask, before titanium deposition, the AFM was able to detect some material build-up exactly on the locations where the silicide is severely reduced in thickness or interrupted, as inferred by electrical data and SEM analysis on finished samples. A carbon (or nitrogen) atom knock-on during the arsenic implant was invoked to explain the observed local hindering of the silicide formation.     

Formation mechanism of silicide nanoparticles by induction thermal plasmas

The condensation mechanism of metal mixture in thermal plasmas was investigated experimentally and numerically to prepare nanoparticles of silicon base intermetallic compounds. Silicon powder premixed with metal powder (Mo, Ti, Co, Fe, Cr, or Mn) was introduced into the plasma. The nanoparticles were prepared on condition that metal vapor was quickly quenched by the water-cooled copper coil. The nucleation rate expression was used for the estimation of critical saturation ratio. The nucleation temperature of the metal almost corresponds to the melting temperature, while silicon has wide liquid range between the nucleation and melting temperature, resulting in better preparation of silicide. For Mo–Si system, nucleation position of Mo is different from that of Si. Therefore, quenching position has strong effect on the particle composition of molybdenum silicide nanoparticles.     

Oxidation mechanism of W substituted Mo-Si-B alloys

The oxidation mechanism of a Mo₅₅W₁₅Si₁₅B₁₅ alloy was established, and the effects of W content, oxidation temperature and microstructural length scale were determined. In addition to influencing the oxidation mechanism, the addition of W also destabilized the A15 phase which is consistent with our previous experiments in ternary Mo-W-Si alloys [1]. Microstructural investigation of the oxidized alloy revealed entrapped tungsten oxides at temperatures below 1300 °C, which volatilize above 1400–1500 °C. The presence of WO₃ in the oxide scale interrupts the surface coverage by the glassy borosilicate, thereby adversely affecting the oxidation behavior. In order to determine the effects of length scale, the microstructural evolution during the transient oxidation of cast and sintered alloys, with different microstructural length scales, was studied at 1100 and 1400 °C. Finer microstructure promoted faster borosilicate surface coverage at 1400 °C.     

Microstructure and oxidation behaviors at 800°C and 1250°C of MoSi2/ReSi2/NbSi2 compound coating prepared by electrodeposition and then pack cementation

MoRe duplex film has been electrodeposited from aqueous solution innovatively and then applied to fabricate protective silicide coating for the NbTiSi based alloy successively. The XRD, SEM and EDS results indicated the formation of MoSi₂/ReSi₂/NbSi₂ compound coating after halide reactivated pack cementation (HAPC) treatment. Pesting oxidation of MoSi₂ layer was suppressed and the NbTiSi based alloy was effectively protected at 800?°C with a mass gain of 0.48?mg?cm^?2 after oxidation for 100?h. At 1250?°C, continuous mass gain was observed with a mass gain of 2.6?mg?cm^?2 after exposure of 10?h. The synergistic combination of MoSi₂ and NbSi₂ layer enabled admirable protection of the substrate, in which MoSi₂ layer worked as the major anti-oxidation coating and the NbSi₂ layer could be a reservoir for Si. The contrast experiments indicate that ReSi₂ layer could improve the integrity and adherence of MoSi₂ layer, reduce the outward diffusion of alloying elements and oxidation of NbSi₂ layer, and then improve oxidation resistance of the compound coating ultimately.     

Phase growth in an amorphous Si–Cu system,as shown by a combination of SNMS,XPS, XRD and APT techniques

It is shown, by the combination of secondary neutral mass spectrometry (SNMS), X-ray diffraction and atom probe tomography (APT), that the growth of a Cu₃Si crystalline layer between amorphous Si and nanocrystalline Cu thin films at 408 K follows a linear law and the shifts of the Cu₃Si/Cu and Cu₃Si/amorphous Si interfaces contribute approximately equally to the growth of this phase. It is also illustrated that the Si atoms diffuse rapidly into the grain boundaries of the nanocrystalline Cu, leading to Si segregation on the outer surface and to an increase in the overall Si content inside the Cu layer. Both the SNMS and APT results indicate that, even during the deposition of Cu on the amorphous Si, an intermixed region (of about 10 nm thick) is formed at the interface. This readily transforms into a homogeneous Cu₃Si crystalline reaction layer which grows further, apparently following an interface-controlled linear kinetics.     

Formation of MoSi2 and Al doped MoSi2 coatings on molybdenum base TZM (Mo–0.5Ti–0.1Zr–0.02C) alloy

Formation of aluminium (Al) doped molybdenum di-silicide (MoSi₂) coatings was studied to improve the high temperature oxidation behavior of TZM (Mo–0.5Ti–0.1Zr–0.02C) alloy. The pack composition of the halide activated pack cementation process was successfully optimized to form silicide and Al doped silicide coatings on the TZM alloy substrates. Mo(Si, Al)₂ phase was found to form at the outer layer of the coating prepared by doping Al in MoSi₂. A change in composition of the phases with increase in coating temperature was detected with Al doping, whereas un-doped silicide coating process was dominated by the formation and growth of MoSi₂ phase. Oxidation test and the characterization studies using SEM, EDS, XRD, and micro-hardness measurements indicated the improved performance of Al doped silicide coating during high temperature oxidation in dry air due to the formation of the protective alumina scale.     

Pd/a-Si:H界面反应研究

本文使用IERS(干涉增强喇曼散射),TEM和SIMS等方法研究了Pd/a-Si:H界面反应的热退火行为,发现Pd/a-Si:H界面在室温下形成非晶互混层;经160℃退火,形成晶态Pd_2Si相,比Pd/c-Si界面反应温度低;经500℃退火,未与Pd反应的非晶硅出现晶化现象。本文还观察了界面反应过程中氢的行为,发现由于界面反应,导致a-Si:H中的氢在较低温度下就开始释放。     

Al/TiSi_2/Si系统与肖特基势垒二极管的热稳定性

本文用x射线衍射及I—V测量法研究了Al/TiSi_2/Si系统热稳定性及肖特基势垒特性。热稳定性的研究结果表明;系统在550℃以下退火是热稳定的;在更高的温度下退火,Al开始与TiSi_2起反应,形成了(Ti_7Al_5)Si-(12)三元化合物。在进行电特性研究时,发现系统在450℃退火时,Al已渗透TiSi_2而使肖特基势垒二极管失效。     

Magnetisation of bulk Mn11Si19 and Mn4Si7

The purpose of this paper is to determine by experiment whether Mn₁₁Si₁₉ and Mn₄Si₇ in their bulk states have a finite magnetic moment or not. Magnetisation measurements were carried out on these materials using both SQUID system and Kerr rotation system. The high quality samples were grown using the temperature gradient solution growth method. SQUID measurements revealed that Mn₁₁Si₁₉ has finite magnetism while Mn₄Si₇ does not in their bulk states. It was also confirmed that Mn₄Si₇ became magnetic and Mn₁₁Si₁₉ got to exhibit a distinctive hysteresis in their powdery state. The enhancement of magnetism implied that the surface of the samples was to a great extent linked to its magnetism.     

Development of in-situ composite surface on mild steel by laser surface alloying with silicon and its remelting

In the present study, an attempt has been made to develop in-situ iron silicide dispersed surface on mild steel substrate by laser surface alloying with silicon using a high-power continuous wave CO₂ laser. The effect of laser surface remelting of the alloyed surface using argon and nitrogen (with and without graphite coating) as shrouding environment has also been studied. The microstructure of laser surface alloyed mild steel with silicon consists of uniformly dispersed iron silicide in grain refined α-iron matrix with an improved microhardness to 575 VHN as compared to 150 VHN of as-received mild steel substrate. Surface remelting in Ar atmosphere coarsened the microstructure and reduced the area fraction of silicide and hence, reduction in the microhardness to 450 VHN. Surface remelting in nitrogen increased the microhardness to 740 VHN due to the formation of iron nitrides in addition to the presence of silicides. Graphite coating prior to remelting improved the microhardness to 800 VHN due to the presence of martensites along with nitrides and silicides. A maximum enhancement in wear resistance was achieved when remelting was done in nitrogen environment with carbon deposition. The mechanism of wear was found to be predominantly abrasive in nature as compared to adhesive and oxidative in as-received mild steel.