Ion Beam Mixing Effects Research Articles

Epitaxial growth of a deposited amorphous Si layer formed on hydrogen-terminated Si(001) surfaces by ion beam induced epitaxial crystallization combined with ion beam mixing

We have investigated the crystallization process of an amorphous Si layer deposited on hydrogen-terminated Si(001) surfaces by ion beam induced epitaxial crystallization (IBIEC) combined with the ion beam mixing (IBMX) method, aiming at the clarification of the essential IBMX effect on crystallization. In this study, we deposited a 10−15 nm thick amorphous Si layer on clean and two kinds of H-terminated Si(001) surfaces of dihydride (DH) and monohydride (MH), and then carried out the IBMX by 10-keV Si+ ion irradiation with a fluence of 1 × 1015 ions cm−2 at RT near the amorphous/crystalline interface followed by the IBIEC treatment by 180-keV Ar+ ion irradiation with fluences of 5 × 1015 and 1 × 1016 ions cm−2 at 300 °C–500 °C. The thickness of the crystallized layer was quantitatively measured by the Rutherford backscattering channeling method. We found that the epitaxial crystallization of the amorphous Si layer formed on both DH and MH surfaces can be realized by IBMX followed by IBIEC treatments at significantly lower temperatures than 500 °C in all processes. This fact suggests that the epitaxial crystallization of the amorphous layer formed on the crystalline substrate surface terminated by the obstructive layer is effectively enhanced, regardless of the structure and coverage of the interfacial layers. It should be emphasized that the IBIEC combined with IBMX treatments make it possible to epitaxially crystallize the amorphous layers formed on obstructive layers covering crystalline substrates at significantly low temperatures.

Interface mediated enhanced mixing of multilayered Ni-Bi thin films by swift heavy ion irradiation

We report the effect of ion beam mixing of Ni/Bi multilayers using 100MeV Au ions as a function of irradiation fluences. X-ray diffraction study reveals the higher magnitude of NiBi3 and NiBi phases compared to elemental Ni and Bi after ion irradiation. We observe an evolution of grainy structures to a molten-like surface with increasing ion fluences. These features were also reflected in the Rutherford Backscattering spectrometry spectra, in terms of the enhanced mixing with increasing ion fluences. The experimental findings were understood on the basis of inelastic thermal spike model calculations.

Ion beam-mixing effects in nearly lattice-matched AlInN/GaN heterostructures by swift heavy ion irradiation

Ion beam-induced intermixing is of great interest and has been observed in various systems such as metal–semiconductor interfaces. However, similar effects in III-nitrides have not been studied in any detail, yet. In the present study, swift heavy ion-induced intermixing of nearly lattice-matched Al(1−x) In x N/GaN heterostructures have been investigated using Rutherford backscattering spectrometry and high-resolution X-ray diffraction techniques. Inter-diffusion of Ga and In elements across the Al(1−x) In x N/GaN interface and the consequent formation of a new mixed quaternary alloy (AlGaInN) layer have been observed. The influence of electronic energy loss of SHI on intermixing effects has been studied.

The Effect of Ion Beam-Mixing on Deposited Si Anodes for High Capacity Li Ion Batteries

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Control of interface properties, layer quality and interdiffusion in selected nanoscaled heterostructures

Applications of ion beam techniques (IBA and IBMM) on nanoscaled thin films of selected materials (e.g. magnetite Fe 3 O 4, uranium nitride UN) are presented. 1 MeV Ar + and Kr + ion beam with different ion fluences in the range of 1015–1017 ions cm −2 have been used to modify the film interfaces. Selected heterostructure interfaces were treated by subsequent thermal annealing. By analyzing the results obtained for the films in three different states (as-deposition, after annealing and after ion irradiation), the effects of ion beam mixing and interdiffusion were determined.

Mass transport in ion–nanostructure interactions

Recently, interesting differences for ion–uniform film and ion–nanostructure interaction phenomena, particularly relating to ion beam mixing effects have been reported. Upon irradiation with 1.5MeV Au2+ ions on isolated Au nanostructures on silicon substrate, a higher probability of crater formation, larger sputtered particle size and its coverage and enhanced sputtering yield compared to the continuous films of Au on Si substrate were observed. Ion bombardment at high flux (≈6.3×1012ionscm−2s−1) showed a dramatic mass transport from nanostructures extending up to a distance of about 60nm into the substrate, much beyond their size. In this paper, RBS/Channeling results would be presented to elucidate on the arrangement of re-distributed gold atoms location in silicon and silicide matrix. Scanning transmission electron microscopy (STEM, with high angle annular dark field imaging) was used to complement the RBS results in determining the unusual mass transport and under ion–nanostructure interaction. The amorphous nature of the silicon matrix, that is deduced from both the RBS/Channeling and from TEM measurements, is an important factor in enhanced diffusion process resulting in dramatic mass flow.

Effects of ion beam mixing of silicon carbide film deposited onto metallic materials for application to nuclear hydrogen production

The effects of ion beam mixing of the SiC film coated on metallic substrates were studied, aiming at developing highly sustainable materials at above 1173K in SO3/SO2 ambience. Firstly, ∼50nm thick SiC films were deposited by e-beam evaporative method on stainless 316L, Inconel 800H, Inconel 690, and Hastelloy-X substrates, followed by the 100keV (Ar and N) ions bombardment to mix the interfacial region. After ion beam mixing, additional ∼500nm thick SiC film was deposited onto the ion bombarded SiC film. Samples with and without ion beam mixing were immersed in 50% H2SO4 solution for 1h with heating the solution up at 573K. The film in the as-deposited sample was completely removed during the immersion, while the ion beam mixed sample exhibited no detachment of the deposited film. The corrosion of non-ion beam-mixed sample initiated from non-deposited metallic surface and then propagated to the film deposited region, flaking-off the film from the edge. The interface formed by ion beam mixing seems to be protective against the corrosion. The SiC film/metallic substrates were heated up to 1223K. The film deposited on the stainless steel substrate was completely peeled off, while the films deposited on Ni-based alloys all sustained. This is due to the difference of thermal stresses between the film and substrate materials. The best materials combination in our experimental scheme is the SiC film and the Hastelloy-X, because their thermal properties are more similar than for the other materials combinations.

Orientation dependent ion beam mixing of Ta/Si interfaces

Ta/Si interfaces were systematically studied concerning ion beam mixing effects. Tantalum was evaporated on silicon of (100) and (111) orientation using the molecular beam epitaxy (MBE) method. The samples were then irradiated with 1.85MeV and 6MeV Ar, 90keV O and 90keV C. Rutherford backscattering spectroscopy (RBS) was used to examine mixing effects. Atomic force microscopy (AFM) was applied for investigating the surface roughness. Ballistic mixing, radiation enhanced diffusion and thermal spike effects were found in both systems. Si substrates of the orientation (100) led to smaller mixing rates at the Ta/Si interface as compared to Si(111).

On the lifetime of wall conditioning layers

Motivated by the large-scale application of tungsten as first wall material in the tokamak ASDEX Upgrade, we performed a numerical study about the erosion behaviour of boron films from carbon and tungsten substrates using the Monte-Carlo code TRIDYN. We compared the erosion caused by monoenergetic ions as well as the case of a plasma with a temperature of 10eV containing boron as an impurity. In both cases we obtained, that on tungsten substrates a pure tungsten surface film is formed with some boron inventory buried underneath. For a carbon substrate, however, the boron inventory depletes slowly due to ion beam mixing effects in the case of monoenergetic ion bombardment. In the case of a thermal plasma containing boron as an impurity, an equilibrium boron surface concentration is established at high fluences. This boron concentration is strongly enhanced as compared to the boron impurity concentration in the plasma.

Ion-beam-induced embedded nanostructures and nanoscale mixing

Megaelectron volts ion-induced effects for discontinuous gold nanoislands and for continuous gold films on silicon substrate have been studied. Irradiation was carried out with 1.5MeV Au2+ ions at room temperature to various fluences. Cross-sectional transmission electron microscopy and Rutherford backscattering spectrometry are used to study the ion-beam mixing in Au∕Si systems. At a fluence of 1×1014ionscm−2, a material push-in effect and a metastable Au-Si phase formation have been observed for Au nanoislands, while no push in or mixing has been observed for the case of continuous films. The mixed phase of Au-Si system is found to be crystalline in nature. The material push- in and ion-beam mixing effects that are observed in case of nanoislands appear to be due to combined effect of capillary driving force, ion-induced viscous flow, and ion-induced energy spike effects.

The effect of silicon ion implantation on the structure of tantalum–silicon contacts

The effect of ion beam mixing on the formation of tantalum–silicon contacts was studied. Silicon implantation into 50 nm Ta layers on n +-Si (1 0 0) was carried out at temperatures from 150 to 500 °C and fluences between 1×10 15 and 1×10 17 Si/cm 2. The microstructural changes were characterized by Auger electron spectroscopy, X-ray diffraction and cross-sectional transmission electron microscopy. The contact resistance was measured before and after implantation using the four-point Kelvin method. Implantation at low temperature (∼150 °C) leads to the formation of an amorphous Ta(Si) interface-layer. The width of the mixed layer increases linearly with implanted dose and temperature. Substrate amorphization results in an increase of the contact resistance. An improved contact resistance was achieved by implantation with 5×10 16 Si/cm 2 at 400 °C. TaSi 2 formation at the interface was observed in this case.

Ion beam induced modification of lattice strains in In 0.1Ga 0.9As/GaAs system

The effects of 150 MeV Ag ion irradiation on the molecular beam epitaxially grown In 0.1Ga 0.9As/GaAs samples have been studied using high resolution X-ray diffraction (HRXRD). Our earlier experiments suggest that the compressive strain will decrease due to ion beam mixing effects in an initially strained system. Similarly a tensile strain will be induced in an initially lattice matched system. These studies are being performed to explore the possibility of spatial bandgap tuning for the integration of optoelectronics circuits. Here we present a systematic study to understand the effects of ion fluence and the initial strain/layer thickness on the modification of strain. Strain measurements are performed using HRXRD by determining the angular shift in the layer peak position with respect to that of the substrate peak. Substrate peak broadens with ion fluence due to the implantation effects at the end of the ion range (∼13 μm). However, the thin InGaAs layer and the substrate region near to this layer will not be affected. It is shown that the Swift Heavy Ion induced mixing can alter the lattice strain at room temperature without loss of the quality of the structure.

Rutherford backscattering and secondary ion mass spectrometry investigation of Mg:Ag–tris(8-hydroxy quinoline) aluminum interfaces

The presence or absence of silver diffusion from Mg:Ag cathodes in tris(8-hydroxy quinoline) aluminum (Alq3) type organic light emitting diodes (OLEDs) has been investigated by Rutherford backscattering (RBS) and secondary ion mass spectrometry (SIMS). Comparison of experimental and simulated RBS data indicated a very abrupt Ag–Alq3 interface, consistent with there being no uniform diffusion of silver into the organic layer of the OLED during deposition, i.e. <0.5 at.% Ag in the first 20% of the organic layer. Silver diffusion through the organic layers of an OLED cannot, therefore, be the root cause of common electrical shorting problems. SIMS profiles of the same sample were obtained using O2+, O− and Ar+ primary ion beams, and in each case different depth profiles were obtained. The variation in the SIMS results is due to ion beam mixing effects, matrix effects and migration of metal ions in an electrostatic field created by a charged surface. It was concluded, therefore, that SIMS is not a suitable technique for studying metal-on-organic interfaces.

Modified physical properties by ion-beam mixing of Fe–Si multilayered films

We investigated the effect of ion-beam mixing (IBM) on the physical properties of Fe–Si multilayerd films (MLF). By the magnetic, magneto-optical, optical and structural studies, it was found that the IBM results in a formation of metastable B2-phase Fe2Si wih a perfect crystalline structure, a low coercivity and a Curie temperature of about 550 K. An annealing at 720 K of the ion-beam mixed Fe–Si MLF further destroys the layered structure at the bottom and also decomposes Fe2Si to form a metastable magnetically-hard Fe5Si3 phase and, presumably, Fe3Si.

Direct patterning of nanometer-scale silicide structures by focused ion-beam implantation through a thin barrier layer

Recently several new approaches have been proposed to manufacture silicide structures using mask-less techniques. We have developed a new technique for direct patterning and formation of cobalt silicide structures using focused ion-beam (FIB) implantation. Utilizing the effects of ion-beam mixing and properties of thin barrier oxides, silicide lines with dimensions down to 170 nm were produced on (100) silicon substrates using the FIB. The process involves the ion implantation of 200 keV As++ through a cobalt thin film. A thin (∼2 nm) oxide (SiOx) at the Si/Co interface acts as a selective reaction barrier. Ion-beam mixing was instrumental in fracturing of the oxide layer, thereby allowing the silicidation reaction to proceed across the boundary during subsequent rapid thermal anneal treatments. Diffusion controlled reactions advanced rapidly in the implanted areas, while it is inhibited elsewhere. A threshold dose of 3×1015 cm−2 was required for process initiation. Four-terminal resistance test structures were formed for electrical measurements. Reported resistivity was in the range of 12 to 23±1 μΩ cm.

Study of magnetic multilayers by RBS with nanometer resolution

The interface roughness of thermally grown giant magnetoresistance (GMR) multilayers was investigated with nanometer depth scale by Rutherford backscattering spectroscopy (RBS) using a high-resolution magnetic spectrograph. Co/Cu multilayers were prepared by electron beam evaporation under ultra-high vacuum conditions in an MBE system. The samples were measured by RBS under several scattering angles to obtain the concentration depth profiles. Ion beam mixing effects deduced from the experimental data and theoretical models were used to unfold the experimental spectra, giving the initial interface roughness. It is shown that the interface roughness, comparable to the amount of surface roughness, is probably not responsible for the extremely weak GMR effect, found in this type of samples.

Ion beam mixing of Ni/Al multilayer structure at different temperatures

A multilayer structure composed of 10 sputter-deposited alternating Ni and Al thin films with an average composition of Ni 0.50Al 0.50 was ion mixed at different temperatures between −145°C and +430°C. Ion mixing of Ni/Al multilayers was performed in an implanter using 350 keV Ar ions at a dose of 1×10 16 ions cm −2. The ion range of about 180 nm was estimated with the TRIM 95 computer code. The as-deposited and ion-mixed specimens were characterized by Auger electron spectroscopy (AES) depth profiling. The AES depth profiles of the ion- and heat-treated Ni/Al multilayer structures allowed a quantitative determination of interface widths which indicated different migration lengths of atoms at the interfaces in the early stage of the mixing process. Generally, the effect of ion beam mixing increased with increasing temperature. Extended X-ray absorption fine structure spectroscopy (EXAFS) revealed the presence of the NiAl phase in the samples ion mixed at temperatures of 280 and 330°C. In the sample treated at 430°C, the AES has shown the formation of homogeneous nickel–aluminum layer. X-ray diffraction (XRD) has indicated that the layer is textured and probably composed of the NiAl and Ni 2Al 3 phases.

Inner wall coating of cylinders by plasma immersion ion implantation for corrosion protection

Hollow workpieces such as cylinders are often required to exhibit better performance in wear and corrosion behaviour than the material the workpiece is made of can offer. The problem can be overcome when a protective coating is deposited onto the inner walls. However, coating inner walls by means of physical vapour deposition techniques is difficult because the material to be deposited has to enter the hollow object under very flat angles to the wall, depending on the ratio of aperture to inner diameter. This problem can be overcome when the source of the material to be deposited is located inside the workpiece. This is possible when sputter coating with ions is performed. A sputter target is located inside the workpiece. Energetic ions extracted from a plasma in which the workpiece is immersed are accelerated towards the workpiece, enter it and impinge onto the sputter target. Thus, material is sputtered onto the inner wall. At the same time, ions impinge onto the growing film and lead to ion beam mixing effects. This technique has been tested with cylinders made of different materials and with different sputter target materials. The deposited films are well adhering and dense and may act as protective coatings against corrosion. This is shown for corrosion of iron in acetic acid, pitting corrosion of aluminium in sodium chloride solution, and hydrogen embrittlement of tantalum in hydrochloric acid.

Effects of ion beam mixing on the depth profiles of thin metal layer in TiO 2

Thin films of TiO 2 prepared by a sol–gel method were irradiated with 100 keV Ar ions. A bilayer (Mo/TiO 2) and multilayers (TiO 2/Mo,Cr,Ag/TiO 2) of the thin metal films and TiO 2 were used. After the irradiation, concentration profiles and the structure of the surface layer were studied by Rutherford backscattering spectroscopy (RBS), X-ray photoelectron spectroscopy (XPS) and glancing angle X-ray diffraction (G-XRD). It was found that a ballistic mixing was predominant in the redistribution of Mo and Cr atoms embedded in TiO 2, and oxides of Mo and Cr were decomposed in metallic states with increasing ion fluence. In the case of TiO 2/Ag/TiO 2, Ag colloids were formed in process of a dip-coating of the sol–gel method, and the Ag atoms were dispersed into deeper layer by a grain boundary diffusion. Ion beam mixing in the TiO 2 films produced a slight increase in the optical absorption of visible light.

Investigation of ion beam mixing effects in Ta/Pd bilayers deposited on Si

This paper presents a study of the effects of As + ion irradiation and vacuum thermal treatments on Ta/Pd bilayers on silicon. The layers were deposited by DC sputtering to the thickness of 60 nm (Pd) and 45 nm (Ta) on (111)Si wafers. The Ta/Pd/Si structures were then implanted with 300, 400 and 500 keV As + ions at room temperature (RT), to the doses from 0.5–1·10 16 ions cm −2. Thermal treatments of samples were performed in vacuum at 900°C, for 10 min. Characterizations were performed by Rutherford backscattering spectroscopy and X-ray diffraction. It was found that intermixing of the components at Ta/Pd and Pd/Si interfaces depends on the value of damage energy F D deposited by the incident ions at the interfaces. Ion bombardment at room temperature induces the formation of Pd 2Si phase with polycrystalline structure. Post-implantation annealing at 900°C made possible the growth of PdSi silicide. Then, the reaction of Ta with Si is enhanced by rapid silicon diffusion through already formed PdSi phase. Consequently, the formation of TaSi 2 and Ta 3Si silicides at the Ta/PdSi interface occurred.