Diffusion Of Bi Research Articles

Effect of the underlayer (Ag, Ti or Bi) on the magnetic properties of Fe/Pt multilayer films

Fe/Pt multilayer films with an Ag, Ti or Bi underlayer were prepared by magnetron sputtering and effect of the underlayer on the magnetic properties of annealed Fe/Pt multilayer films was also investigated. Our results demonstrate that Ag underlayer has little effect on the in-plane coercivity H c of the Fe/Pt multilayer film due to the formation of Ag and L1 0-FePt phases in the films. The H c of Ti/[Fe/Pt] 13 film keeps on rising with the increasing annealing temperature T a up to 500 °C and then decreases with the further increasing T a. The reason should be attributed to the formation of some intermetallic compounds between Ti and Fe; Pt at a high T a which is harmful to the structure of L1 0-FePt. The H c of [Fe/Pt] 13 films is enhanced by the Bi underlayer, which can be understood by considering the promotion of the L1 0-FePt phase by Bi diffusion.

Interdiffusion of adsorbed Pb and Bi on Cu(1 0 0)

The impingement and interdiffusion of adsorbed Pb and Bi layers spreading from separated 3D pure bulk sources on Cu(1 0 0) has been studied, at T = 513 K, by in situ scanning Auger microscopy. When the leading edges of the pure Pb and Bi diffusion profiles impinge, they both consist of low-coverage lattice gas surface alloyed phases. In these low-coverage phases, Pb displaces surface alloyed Bi and the point of intersection of the profiles drifts towards the Bi source. These features lead to the conclusion that Pb atoms are more strongly bound at surface alloyed sites in Cu(1 0 0) than Bi atoms. Once the total coverage (Pb + Bi) on the substrate reaches about one monolayer, Pb and Bi are dealloyed from the substrate, and the interdiffusion profiles become essentially symmetric. Pb and Bi mix in all proportions, with an interdiffusion coefficient of ∼10 −13 m 2/s. This is considerably smaller than the self-diffusion coefficients previously observed for pure Pb and Bi in their respective high-coverage phases, indicating that the mechanism of interdiffusion is different from that of self-diffusion. As interdiffusion proceeds, the point of intersection of the Pb and Bi profiles reverses its drift direction, leading to the conclusion that binding of Bi atoms to the Cu(1 0 0) substrate is stronger than that of Pb atoms in the highest-coverage surface dealloyed layers.

Low-temperature ordering and enhanced coercivity of L1-FePt thin film promoted by a Bi underlayer

We have studied L10-FePt thin films with a Bi underlayer. Experimental results show that the ordering temperature of the L10-FePt film can be lowered down to 300–350°C and the in-plane coercivity HC of the film is obviously enhanced by introduction of a Bi underlayer. After annealing at 400°C for 20min, a Bi∕FePt film realizes a HC of 13.5kOe and the ratio of the remnant magnetization Mr to the saturation one MS of as high as 0.93. The reduction of the ordering temperature and the enhanced magnetic properties of L10-FePt films can be understood by considering the large diffusivities of Fe and Pt associated with Bi diffusion.

Impact of surface phase transitions and structure on surface diffusion profiles of Pb and Bi over Cu(1 0 0)

Surface diffusion of Pb and Bi over Cu(1 0 0) surfaces has been studied by scanning Auger microscopy techniques. The diffusion profiles of Pb and Bi have been found to be quite different. The results show that three major factors control the shapes of the surface diffusion profiles: (a) First order phase transitions, which lead to phase coexistence over specified coverage ranges, tend to produce abrupt changes in coverage versus distance profiles; (b) profiles can be affected by the existence of significant differences in the diffusion coefficients of the various phases present, and by the possibility (c) of important changes in diffusivity within a given phase, as a function of coverage, due to interactions between the diffusing atoms. In addition, it has been shown that the strong connection between diffusion profile shapes and the 2D phase diagram allows certain features of the 2D phase diagram to be determined from diffusion profiles.

The effect of a Bi underlayer on FePt thin film

In this paper, the FePt films with Bi underlayer were prepared by dc magnetron sputtering on glass substrates. The L10-FePt films were obtained after the deposited samples were subjected to vacuum annealing at various temperatures. The effect of a Bi underlayer on the ordering temperature and magnetic properties of FePt films was studied. Experimental results show that the FePt film can realize the low-temperature ordering at 350℃ after introduction of a Bi underlayer. Moreover, the Bi underlayer can also obviously enhance the coercivity Hc of the film and enlarge the concentration range of FePt films with high Hc. We studied the distribution of Bi atoms by X-ray photoelectron spectroscopy and the change of crystal structure of FePt films by X-ray diffraction. The cause of the above observatious is associated with enhanced ordering degree of FePt films by the Bi diffusion during annealing process.

Solute-Driven Melting Kinetics in the Sn-Bi System

AbstractThe goal of the present study was to gain insight into the mechanisms and behavior of solute driven melting processes. Solute-driven melting refers to melting whose driving force originates from a change in composition, i.e., solute content, rather than a change in temperature. This kind of melting has been known to cause casting defects in superalloys and other metals.An experimental apparatus was designed and a series of experiments were carried out on Sn-Bi alloys. The apparatus involved diffusing Bi into solid Sn cast inside a glass capillary to cause it to melt. The Bi source was an enriched liquid Sn-Bi alloy contained in a reservoir. The Sn in the capillary was kept at a constant temperature below its melting point so that the melting was caused by the increasing Bi composition. The progression of the interface was monitored by quenching the process at various times for the same conditions.The apparatus was successful in delivering data for the displacement of the interface against time. It was found that interface position was approximately proportional to the square root of time, and so the process may be diffusion controlled as conjectured in previous literature. Rough calculations are made relating the temperature and supersaturation to the displacement coefficient A in the equation z = At½ where z is displacement and t is time. By comparing data at different temperatures with the same supersaturation, an activation energy Q of ~60,000J/mol is calculated. This value is between the activations energies for diffusion of Bi through the liquid and the solid. Suggestions for modification of the apparatus to include in-situ interface monitoring are made.

Grain boundary diffusion and segregation of Bi in Cu: radiotracer measurements in B and C diffusion regimes

Grain boundary (GB) radiotracer diffusion of 207Bi in polycrystalline Cu was measured in Harrison's B (1198–843 K) and C (659–536 K) kinetic regimes. In the B regime the triple product P= s· δ· D gb (where s is the segregation factor and δ the GB width) was found to obey the Arrhenius law P=6.6×10 −12×exp (−102.8 kJ mol −1/ RT) m 3 s −1. The measurements in the C regime yielded the temperature dependence of the Bi GB diffusion coefficient D gb in Cu, D gb=0.24×exp (−156.2 kJ mol −1/ RT) m 2 s −1. Assuming that δ≅5×10 −10 m the segregation factor s of Bi in Cu was determined in the limit of very dilute solute concentration to follow an Arrhenius dependence s= s 0exp(−Δ H s/ RT) with the pre-exponential factor s 0=0.054 and the segregation enthalpy Δ H s=−53.4 kJ mol −1.

Diffusion kinetics of Bi and Pb–Bi monolayer precursing films on Cu(1 1 1)

We have used Auger electron spectroscopy to study the diffusive spreading and adsorption of pure Bi and Pb–11 at.%Bi precursing films on Cu(111) surfaces, from droplets of the respective materials. The Bi diffusion coefficient (DBi) increases with Bi-coverage. However, in the intermediate coverage range, DBi remains approximately constant, which is presumably due to the formation of an ordered Bi hexagonal overlayer. In the case of Pb–Bi alloy spreading, the presence of Bi slows down the Pb diffusion kinetics significantly. The kinetics of Bi spreading are also slower in the presence of Pb, but the effect is less marked. The equilibrium concentrations both at the Pb–Bi drop surface, and in the surrounding precursing film, were found to be Bi-enriched.

Diffusion kinetics of Bi and Pb?Bi monolayer precursing films on Cu(111)

We have used Auger electron spectroscopy to study the diffusive spreading and adsorption of pure Bi and Pb–11 at.%Bi precursing films on Cu(1 1 1) surfaces, from droplets of the respective materials. The Bi diffusion coefficient ( D Bi ) increases with Bi-coverage. However, in the intermediate coverage range, D Bi remains approximately constant, which is presumably due to the formation of an ordered Bi hexagonal overlayer. In the case of Pb–Bi alloy spreading, the presence of Bi slows down the Pb diffusion kinetics significantly. The kinetics of Bi spreading are also slower in the presence of Pb, but the effect is less marked. The equilibrium concentrations both at the Pb–Bi drop surface, and in the surrounding precursing film, were found to be Bi-enriched.

Effect of Bi 4Ti 3O 12 seeding layer on the structural and ferroelectric properties of Bi 3.25La 0.75Ti 3O 12 thin films fabricated by a metalorganic decomposition method

Ferroelectric Bi 3.25La 0.75Ti 3O 12 (BLT) thin films with Bi 4Ti 3O 12 (BTO) seeding layers were deposited onto a Pt/Ti/SiO 2/Si substrate using a metalorganic decomposition method. The effects of variation in the thickness on the microstructural and ferroelectric characteristics were investigated. The BLT thin films with 5-nm-thick BTO seeding layers with a Pt bottom electrode showed that the presence of BTO seeding layer induced a significant change in the crystallinity. This results in an improvement of the (1 1 7) orientation compared with BLT thin films without the BTO seeding layer. The 5-nm-thick BTO seeding layer in the BLT/BTO/Pt/Ti/SiO 2/Si structure also prevents the diffusion of Bi into the Pt bottom electrode. The BLT thin films with 5-nm-thick BTO seeding layers showed larger remanent polarization and better fatigue properties compared with the films without the seeding layer. The remanent polarization (2 P r) of BLT thin films without seeding layer and with 5-nm-thick BTO seeding layer annealed at 650 °C were 20.6 and 30 μC/cm 2, respectively.

Diffusion of Bi, Er and Eu implanted into S1813 photoresist

We report on the diffusion of Bi, Er and Eu in the photoresist S1813. The implantation of Bi into the resist at low energies ( E=20 keV) and fluences ( Φ=10 12 cm −2) allowed us to minimize both radiation damage and cluster formation. The impurity redistribution in the samples annealed between 100 and 300 °C was determined using the Rutherford backscattering technique. The results for Bi indicate regular thermal diffusion with an activation energy of E a=680 meV. At higher fluences, the trapping in radiation-induced defects influence the migration behavior. However, the activation energy is hardly influenced (650 meV for implanted Bi at 5 × 10 12 cm −2). Both the lanthanides Er and Eu implanted into the resist at fluences of 5 × 10 12 and 10 13 at/cm 2 show quite a similar behavior as Bi implanted at the highest fluence with similar values for the activation energy ( E a(Eu)=525 meV and E a(Er)=530 meV).

Diffusion of Sr, Bi, and Ta in amorphous SiO 2

Diffusion of Sr, Bi, and Ta in SiO 2 was studied to determine diffusion coefficients and diffusion mechanisms of these elements in the amorphous material. Technological motivation is the introduction of strontium bismuth tantalate (SBT) as ferroelectric material for nonvolatile memories. Diffusion from an SBT layer into a thin layer of SiO 2 was promoted by annealing at 800°C for times ranging from 1 to 24 h . Concentration profiles of the diffusing elements in the SiO 2 layer were recorded by secondary ion mass spectroscopy (SIMS). The measured profiles were compared to profiles derived from calculations for different diffusion mechanisms. The theoretical profile best matching the form of the measured profile was fitted to the experimental data, yielding information about the diffusion mechanism and the diffusion coefficient. The diffusion coefficient of Sr is in the range of 10 −15 cm 2/ s at 800°C and 10 −14 cm 2/ s for Bi. It was found out that Sr and Bi react with vacancies in the SiO 2, forming fast-moving complexes. Tantalum shows no measurable diffusion in this time and temperature range. No information is available about the exact nature of the different Sr and Bi species, since SIMS can only detect elements but not their binding situation. Only indirect indications lead to the theory that vacancies play a role in the transformation from slow- to fast-moving species. Theoretical calculations of the behavior of the elements in SiO 2 may help to solve this problem.

Cathodoluminescence defectoscopy of ZnS and ZnSe crystals

The quality and reliability of microelectronic materials can be dramatically changed by point and linear defects, which occur in specimens naturally, or which can be deliberately introduced. The control of defect distribution requires a measurement method capable of investigating the defects on a micrometer scale. This article surveys some of the opportunities for the control of defects in solids by using a combination of different cathodoluminescence modes including color cathodoluminescence (CCL) in the scanning electron microscope (SEM) with computer graphics. The method of cathodoluminescence defectoscopy was applied to microcharacterization of commercial wide-band-gap II–VI semiconductors (ZnS, ZnSe) as well as to the thin diffusion layers formed in these materials in the process of annealing. The luminescence topography of the radiative centres distribution at different Al and Bi concentrations was investigated and a model of two-polar and dissociative diffusion of Zn, Al and Bi from the melt to the crystal volume was proposed.

A comparison of Ti/Pt and TiN/Pt electrodes used with ferroelectric SrBi 2Ta 2O 9 films

The effects of Ti and TiN adhesion layers, used below the Pt bottom electrode, on the purity, phase distribution and electrical properties of ferroelectric SrBi 2Ta 2O 9 (SBT) thin films have been examined and compared. Changes in electrode morphology were observed as a function of temperature, using atomic force microscopy (AFM) and scanning electron microscopy (SEM). A distinct improvement was seen when TiN is used; there are fewer shorting capacitors and the remnant polarisation of the ferroelectric increases markedly. However, the adhesion is not as good. Secondary ion mass spectrometry (SIMS) shows that when Ti/Pt bottom electrodes are used, Ti diffuses through the Pt film causing spurious phases to crystallise in the SBT film. These depth profiles also show evidence of Bi diffusion to the surface of the oxide film and through the Pt towards Ti rich regions.

Cathodoluminescence Defectoscopy of II-VI Compounds

The quality and reliability of microelectronic materials can be dramatically changed by point and linear defects, which occur in specimens naturally, or which can be deliberately introduced. The control of defect distribution requires a measurement method capable of investigating the defects on a micrometer scale. This article surveys some of the opportunities for the control of defects in solids by using a combination of different cathodoluminescence modes including colour cathodoluminescence (CCL) in the scanning electron microscope (SEM) with computer graphics. The method of cathodoluminescence defectoscopy was applied to microcharacterization of commercial wide-band-gap II-VI semiconductors (ZnS, ZnSe) as well as to the thin diffusion layers formed in these materials in the process of annealing. The luminescence topography of the radiative centre distribution at different Al and Bi concentrations was investigated and a model of two-polar and dissociative diffusion of Zn, Al and Bi from the melt to the crystal volume was proposed.

Improvement in ferroelectric properties of SrBi2Ta2O9 thin films with Bi2O3 buffer layers by liquid-delivery metalorganic chemical-vapor deposition

Ferroelectric SrBi2Ta2O9 (SBT) thin films were deposited onto the Bi2O3 buffered Pt/Ti/SiO2/Si substrates using liquid-delivery metalorganic chemical-vapor deposition. The SBT films with a 5-nm-thick Bi2O3 buffer layer on a Pt bottom electrode showed (115) orientation stronger than those without the Bi2O3 buffer layer after annealing at 750 °C. The Bi2O3 buffer layer in Pt/Bi2O3/SBT/Bi2O3/Pt/Ti/SiO2/Si capacitors effectively prevents the evaporation of Bi through the Pt top electrode and diffusion of Bi into the Pt bottom electrode. The remanent polarization and leakage current densities of SBT films with Bi2O3 buffer layers were improved significantly in comparison with those for the films without the Bi2O3 buffer layer. The remanent polarization (2Pr) and coercive field (Ec) of SBT films without and with the Bi2O3 buffer layer annealed at 750 °C were 12 and 23 μC/cm2, 57 and 38 kV/cm at an applied voltage of 5 V, respectively.

Cu diffusion into Ag during BSCCO tape processing

Diffusion studies of (Bi,Pb) 2Sr 2Ca 2Cu 3O 10 and Bi 2Sr 2CaCu 2O 8 tapes wrapped in Ag show that Cu of the ceramic diffuses into the Ag sheath during annealing that results in a decrease of the Cu content of the ceramic. The diffusion coefficient has been determined to range between about 1.4×10 −11 and 2.9×10 −11 cm 2 s −1 at temperatures between 790°C and 860°C. A diffusion of Bi, Pb, Sr, and Ca into Ag has not been observed.

Control of bismuth volatility in SBT by vanadium doping

The volatility of bismuth (Bi) presents difficulty in the integration of ferroelectric strontium bismuth tantalate (SrBi2Ta2O9 or SBT) thin films for FeRAM applications. This paper presents preliminary results indicating that the Bi volatility problem may be controlled by the addition of vanadium (V) to SBT. A series of V-doped SBT films (∼150 nm), of a nominal composition SrBi2.2(Ta1-xVx)2O9 with x = 0, 0.01, and 0.07, were deposited on Pt/SiO2/Si wafers by sol-gel processing. XRD and SEM revealed a polycrystalline morphology and a vanadium solubility in SBT of at least 7%. SBT with 7% V-doping exhibited little structural damage from a forming gas anneal. 7% V-doping also limited Bi diffusion into Pt bottom electrodes and increased the surface Bi 4f7/2 electron binding energies. The ferroelectric and polarization fatigue properties did not improve with V-doping, which was attributed to oxygen vacancy formation due to acceptor doping. Vanadium stabilized Bi in the SBT matrix by reducing from the pentavalent to the tetravalent state, which provided the free energy to either oxidize bismuth or prevent the reduction of bismuth.

Atomic-scale quantitative elemental analysis of boundary layers in a SrTiO3ceramic condenser by high-angle annular dark-field electron microscopy

Abstract Atomic-resolution high-angle annular dark-field (HAADF) scanning transmission electron microscopy was quantitatively performed for a boundary layer semiconducting SrTiO3 ceramic condenser which has a Bi diffusion layer near the boundary in each grain. With the aid of HAADF image simulation it was found that the Sr sites in the diffusion later are replaced by Bi atoms with a concentration of 14at.%. In a few lattice layers near the edge of the grain, the Bi concentration abruptly increased. The Bi concentration of every Sr or Ti(O) column, along the [001] incident electron beam, was estimated from the simulation taking account of the lattice distortion, which was caused as a result of the substitution of Bi atoms, giving a high ratio of Bi to Sr and Ti atoms. It is also concluded that the simulation is indispensable for HAADF microscopy analysis of a crystal with distorted lattice.

Influence of annealing temperature on ferroelectric properties of SrBi2Ta2O9 thin films prepared by off-axis radio frequency magnetron sputtering

Ferroelectric SrBi2Ta2O9 (SBT) thin films were deposited on Pt/TiOx/SiO2/Si substrates using the off-axis radio frequency magnetron sputtering technique. X-ray diffraction and atomic force microscopy experiments showed that the crystallization of SBT thin films at >700 °C correlated with the formation of rod-like grains. Cross-sectional field emission scanning electron microscopy images revealed that the apparent thickness of SBT decreased while the thickness of Pt increased as the annealing temperature was increased. The apparent decrease in the thickness of SBT was attributed to crystallization and densification in the film whereas the apparent increase in Pt thickness was due to diffusion of Ti and Bi into the Pt layer. This diffusion at high annealing temperatures (800 °C and above) alters the Pt purity and degrades the Pt as the bottom electrode for the ferroelectric capacitor. Good insulating properties were obtained when the SBT film was annealed at 700 and 750 °C whereas higher leakage currents were observed at annealing temperatures >800 °C. A remnant polarization (Pr) of 4.35 μC/cm2 and coercive field (Ec) of 31.5 kV/cm were obtained for the SBT thin film annealed at 750 °C with a leakage current density of <10−7 A/cm2.