Ion beam mixing of Al/Fe binary systems

Ion beam mixing of Al layers on Fe and Fe layers on Al are studied by irradiation with 200 keV Xe⁺-ions at room temperature as a function of the thickness of the top layer and of the ion fluence from 5×10¹⁵ to 7.5×10¹⁶ions/cm². Deconvolution procedures are needed to separate the influence of the ion sputter profiling by AES from the ion beam induced mixing effects. Auger electron spectroscopy data reveal that the mixing induced diffusivity ought to be considered as a function of concentration. The diffusion coefficients are evaluated by the Boltzmann-Matano method. A strong dependence of the diffusion coefficients and also the mixing efficiencies from the ion dose, the depth of the interface and the nuclear energy deposition were observed. Results are discussed in terms of the diffusional and collisional mixing as well as chemical affinity of both Fe and Al.     

Xenon-beam-induced atomic transport through Cr/Al and Cr2N/Al interfaces

Cr layers (60–75 nm) on Al substrates and Cr₂N layers (40–120 nm) on Al+3 wt.% Mg substrates were irradiated at 80 K and 300 K with 150–900 keV Xe-ions. The ion-beam-induced interface mixing was analyzed by means of Rutherford Backscattering Spectrometry (RBS). Both systems exhibit fairly small mixing rates, with those of Cr/Al being enhanced at 300 K target temperature, due to radiation-enhanced diffusion. The observed interface broadening is compared with predictions of ballistic and thermal spike mixing models. The low-temperature mixing rates in the system Cr/Al are underestimated by the ballistic model, but are rather well reproduced by local spike models. Mixing in the Cr₂N/Al system at both temperatures, on the other hand, seems to be rather well described by the ballistic model.     

Protection against corrosion of iron alloys by aluminized coatings produced using two different processes

Aluminized coatings were produced on iron by means of two different processes: electron beam deposition under UHV of Al on iron samples previously covered with ⁵⁷Fe films, and hot-dipping of iron samples in molten aluminium. Aluminized samples were submitted to thermal treatments in order to promote interdiffusion at the Fe–Al interface and favour the formation of Fe–Al intermetallic compounds of composition suitable to protect the underlying iron from oxidation. Phase composition, structure and morphology of both as deposited and thermally treated coatings were characterized by means of X-ray diffraction, Mössbauer spectroscopy and metallographic techniques. Significant differences among the effects of the Fe–Al interdiffusion occurring for Al layers produced with the two processes are pointed out and discussed.     

The use of macroscopic modelling of intermetallic phases in aluminium alloys in the study of ferricyanide accelerated chromate conversion coatings

Chromate conversion coatings are used on aluminium alloys, primarily for their renowned corrosion resistant properties. Although these coatings are in common industrial use, neither the protection mechanisms, nor the coating interation with the intermetallic precipitation phases are fully understood. Macroscopic models have been developed in order to represent the galvanic cells present in aluminium alloys due to the presence of such intermetallic particles. Particles modelled include CuAl₂, FeAl₃ and Cu₂FeAl₇, all know to be cathodic to the aluminium matrix. Variations in deposition, both in composition and thickness, are indicative of the mechanisms of deposition over each phase. Characterisation of the coating deposition was carried out using X-ray photoelectron spectroscopy, Rutherford backscattering spectroscopy, Auger electron spectroscopy, scanning electron microscopy with X-ray analysis. Depositional characteristics have been determined for each phase. The coating on the intermetallic phases is primarily Al oxide, and is significantly thinner than the coating on the matrix. This coating on the matrix consists mainly of a mixed Cr/Al oxide. The coating on the intermetallic phases was only one tenth the thickness of the matrix coating, and contained higher levels of Fe, Al and O. Matrix coating chemistry predominated with Cr, O, Fe and N, indicative of a chromate conversion coating. The mechanism for reduced rates of deposition over intermetallic phases was found to be affected by fluorine ion attack leading to intermetallic de-alloying and decomposition of Fe(CN)₆²⁻ accelerator into amide groups on the matrix.     

Structure, properties and applications of thin Fe--Al layers

Fe-Al alloys show interesting physical properties and offer some special industrial applications. There are phase transitions combined with changes in the magnetic behaviour. Another interesting fact is the excellent oxidation and corrosion resistance of iron aluminides even at high temperatures. Thin Fe-Al layers can be produced in different ways. Ion beam methods are able to produce surface layers on bulk material modifying the initial properties completely. The properties depend strongly on the phase structure induced by the preparation process. 57-Fe Mössbauer spectroscopy, and in the case of surface layers conversion electron Mössbauer spectroscopy, is very suitable to identify this phase structure. In the present work, it is described for Al implanted Fe layers. Depending on implantation dose and energy both magnetic and non-magnetic phases can be produced. Due to the inhomogeneous distribution of Al in the Fe target a layer structure of different phases can be created. Moreover, due to double implantation an Fe-Si-Al alloy can be prepared.     

Ion-beam-mixing induced amorphization of Fe/Zr multilayers

The Ar-ion-beam-mixing of the Fe/Zr multilayers is studied by conversion electron Mössbauer spectroscopy. The dependence of the amorphization process on ion dose is studied in detail for two sample thicknesses with an Fe to Zr ratio of 1 and modulation wavelength of 20 and 60 nm. Experimental results are compared with the predictions of the ballistic cascade and thermal spike models of mixing.     

Formation of metallic nanophases in silica by ion beam mixing. Part II: cluster formation

2 matrix by ion-beam mixing of SiO₂/Ag multilayers is studied via Rutherford backscattering spectrometry, optical absorption, and transmission electron microscopy experiments. In a first step, irradiation with MeV heavy ions transforms the continuous Ag layers into a string of micrometer-sized Ag inclusions. This mechanism can be attributed to lateral segregation of metallic atoms induced by irradiation. In a second step, the Ag inclusions are broken up by incoming ions and Ag nanoclusters are formed by agglomeration of mobile Ag atoms. The latter mechanism is likely due to a combination of ballistic mixing and radiation-induced segregation or radiation-enhanced diffusion processes. The size of the metallic nanoclusters formed depends also on the irradiation temperature. Received: 27 October 1997/Accepted: 3 February 1998     

PLD方法制备的纳米Fe/Al薄膜的结构及应力分析

 采用PLD方法制备了Fe/Al合金薄膜，研究了Fe/Al合金薄膜的物相、结构、应力等。研究表明薄膜的沉积速率随着衬底温度的升高而降低。原子力显微镜（AFM）图像显示，薄膜表面平整、致密且光滑，均方根粗糙度小于1 nm。等离子体发射谱（ICP）表明Fe/Al原子比为1∶1。X射线小角衍射（XRD）分析表明薄膜中的物相是Al_0.5Fe_0.5，Al_0.5Fe_0.5晶体具有简单立方结构(SC)，晶格常数为0.297 nm，平均晶粒尺寸为81.74 nm，平均微畸变为0.007 6。     

Amorphization of Fe/Al: bulk and thin-film effects

The amorphous non-equilibrium state of the system Fe/Al is studied in bulk and thin-film systems. For bulk samples prepared by ion-beam mixing of laser-deposited multilayers, a bcc solid solution is found for alloys with up to 70 at. % Al. Around 75 at. % Al a Fe₂Al₅-like crystalline phase is found. An amorphous state with Fe₂Al₅-like short-range order is found for 80 at. % Al. In thin films, for example the amorphous Al-rich transition layer of a laser-deposited Fe/Al multilayer, the amorphous state can exist for up to 30 at. % Fe due to the high interfacial energy. By ion-beam mixing at low temperatures (about 140 K) an oversaturation with 40 at. % Fe can be achieved.     

Fe/Al混合膜的PLD法制备及表面分析

 采用脉冲激光气相沉积（PLD）技术制备了Fe/Al混合膜,测量了该混合膜的光电子能谱（XPS）,并采用原子力显微镜（AFM）、扫描电子显微镜（SEM）对Fe/Al混合膜作了表面分析。结果表明：Fe/Al混合膜的表面粗糙度对衬底温度有明显的依赖性, 随着衬底温度的升高,薄膜的表面逐渐变得平滑,膜层变得致密,在200 ℃衬底温度下制得了均方根（rms）粗糙度为0.154 nm、具有原子尺度光滑性的Fe/Al混合膜, 膜中Fe和Al分布比较均匀,其成分比约为1∶3,同时XPS分析也表明Fe/Al混合膜暴露在空气中后表面形成了Al₂O₃和FeO氧化层。     

Investigation of magnetic properties in 57Fe/Al multilayers

Fe/Al multilayer thin films prepared by ion beam sputtering, with an overall atomic concentration ratio of Fe/Al = 1:2 have been studied by x-ray diffraction spectroscopy (XRD), X-ray reflectivity (XRR) and D.C. Magnetization. These studies show the formation of Fe–Al intermetallic layers. Two magnetic regions and transition temperatures of 473 and 533 K are evident from magnetization studies. Conversion Electron Mössbauer Spectroscopy (CEMS) shows formation of off-stoichiometric Fe₃Al like phase and phases consisting of pure Fe and Fe-rich extended Fe–Al solutions.     

The effect of deposition temperature on the intermixing and microstructure of Fe/Ni thin film

The physical vapour deposition of Ni atoms on α-Fe(001) surface under different deposition temperatures were simulated by molecular dynamics to study the intermixing and microstructure of the interfacial region. The results indicate that Ni atoms hardly penetrate into Fe substrate while Fe atoms easily diffuse into Ni deposition layers. The thickness of the intermixing region is temperature-dependent, with high temperatures yielding larger thicknesses. The deposited layers are mainly composed of amorphous phase due to the abnormal deposition behaviour of Ni and Fe. In the deposited Ni-rich phase, the relatively stable metallic compound B₂ structured FeNi is found under high deposition temperature conditions.     

Direct synthesis of β-FeSi2 by ion beam mixing of Fe/Si bilayers

The iron di-silicide #-FeSi₂ is a promising direct band gap semiconductor but difficult to produce. Here, the successful direct synthesis of this phase by ion beam mixing of Fe/Si bilayers at temperatures in the range of 450 to 550 °C is reported. The obtained single-phase #-FeSi₂ layers and their structure are confirmed by Rutherford backscattering spectrometry, X-ray diffraction and conversion electron Mössbauer spectroscopy.     

Interfacial phenomena and magnetic properties of Fe/Al multilayers of different thickness

Fe/Al thin film multilayers, differing in the thickness of Fe films (30÷10 Å, were electron-beam evaporated in ultra-high vacuum. Interdiffusion and reaction phenomena occurring during deposition at interfaces were studied by means of conversion electron Mössbauer spectroscopy and Auger electron spectroscopy depth-profiling. Magnetic behavior was investigated by alternating force gradient magnetometry. The formation of Fe–Al solid solution and intermetallic compound is observed. Multilayers are ferromagnetic with magnetization in the film plane for iron film thickness ?15 Å, while exhibiting a superparamagnetic behavior at 10 Å.     

Magnetism of ultrathin Cr layers and Fe/Cr multilayers studied by 119Sn probes

Cr/Sn and Fe/Cr/Sn/Cr multilayers, where monatomic Sn layers are embedded in Cr layers and Fe/Cr multilayers respectively, were prepared by means of ultrahigh-vacuum deposition technique, and the magnetic hyperfine field induced at the ¹¹⁹Sn nuclear sites was examined using conversion electron Mössbauer spectroscopy. The magnetic structures of the Cr layers are inferred from the size and direction of the magnetic hyperfine field transferred at the Sn sites.     

Ion-beam-induced atomic transport and phase formation in the system nickel/antimony

We report on the ion-beam mixing processes of Sb/Ni marker layers and bilayers under the irradiation of ions ranging from He to Pb, at 80 K and at room temperature. The concentration profiles are obtained by Rutherford backscattering spectroscopy with 900 keV -particles. At 80 K, the bilayer mixing rates cannot be reproduced by purely ballistic mixing; the essentially linear scaling of the bilayer mixing rate with the energy F _D deposited at the interface points to local spike formation. A transition to global spike formation seems to be visible for the Pb-irradiations. Additional mixing effects at 300 K are due to radiation enhanced diffusion and scale with F _D. The marker mixing rates at 80 K are reproduced by the ballistic mixing approach, but are equally well described by local spike models. High fluence Xe-irradiations of Sb/Ni bilayers lead to intermetallic phases in the interface region as verified by transmission electron microscopy.     

Stability of FeAl(110) alloy surface structures: a first-principles study

We have studied the stability of FeAl(110) alloy surface structures by first-principles calculations. A general method is employed to determine the allowed chemical potential range for the surface structures of alloys with several bulk ground state structures. We show that there are three stable surface structures, the Fe:Al=1:1, Fe:Al=1:2 and Fe:Al=1:3 surface structures, within the allowed chemical potential range for FeAl bulk. In the three stable surface structures, surface buckling extends deep into the bulk layers. For the Fe:Al=1:1 surface structure, the surface Al atoms displace outwards and surface Fe atoms move inwards relative to their bulk positions. The Fe:Al=1:2 and Fe:Al=1:3 surfaces show large surface rippling due to composition reconstruction of the surface.     

Growth and study of ultrathin insulating SiO2 and MgO layers on the ferromagnetic electrode surface

In this paper, we present the experimental results on the application of the pulsed laser deposition (PLD) method to form functional SiO₂ and MgO layers in contact with Fe₃Si and Fe ferromagnetic electrodes In situ X-ray photoelectron spectroscopy and low-energy ion scattering spectroscopy, in situ conversion electron Mössbauer spectroscopy and Rutherford backscattering and channeling of light ions were used to study the structural properties and morphology of formed ultrathin SiO₂ and MgO layers, as well as the chemical and phase composition of Fe₃ Si/SiO₂ and Fe/MgO interfaces.     

Growth of Ni-Al alloys on Ni(1 1 1): (I) Formation of epitaxial Ni3Al from ultra-thin Al deposits

In this paper we describe the alloying process of ultra-thin Al layers (below 8 × 10¹⁵ Al/cm²) deposited on Ni(1 1 1). For this purpose Auger electron spectroscopy, low energy electron diffraction, and ion beam analysis-channelling measurements have been performed in situ in an ultra-high vacuum chamber. Al deposits formed at low temperature (about 130 K) are strained defective crystalline layers retaining the substrate orientation. Alloying takes place, with very progressive Ni enrichment, in a very broad temperature range between 250 K and 570 K. This feature shows that diffusion of the alloy species is more and more difficult when the Ni concentration increases. At 570 K a crystallographically and chemically ordered Ni₃Al phase is formed, and its order continuously improves upon annealing, up to 750 K. We have shown by ion beam methods that this alloy is three-dimensional, extending up to 16 (1 1 1) planes for the thickest deposits. The Ni₃Al phase can also be obtained directly by Al deposition at 750 K, but its crystalline quality is lower and the layer is probably formed of grains elongated along 〈1 1 −2〉 directions. The Al content of the thin Ni₃Al layers formed mostly dissolves in the bulk above 800 K. However a small amount of Al remains segregated at the Ni crystal surface.