László Kotis

Unexpectedly high sputtering yield of carbon at grazing angle of incidence ion bombardment

The relative sputtering yield of amorphous carbon with respect to polycrystalline nickel at Ar-ion bombardment was determined by means of Auger electron spectroscopy depth profiling as a function of the angle of incidence and projectile energy in the ranges of 49°–88° and 0.3–1keV, respectively. It was found that the relative sputtering yield YC∕YNi strongly increases with angle of incidence from 49° to 82°. At around 80° the sputtering yield of C is higher than that of Ni. Above 82° no dependence on the angle of incidence was found. The relative sputtering yield weakly depends on the energy of the projectile. The experimental results will be explained by the help of transport of ion in solid (TRIM) simulations.

Asymmetric transient enhanced intermixing in Pt/Ti

The ion-sputtering induced intermixing is studied by Monte Carlo transport of ions in matter (TRIM), molecular-dynamics (MD) simulations, and Auger electron spectroscopy depth profiling (AES-DP) analysis in Pt/Ti/Si substrate (Pt/Ti) and Ta/Ti/Pt/Si substrate (Ti/Pt) multilayers. Experimental evidence is found for the asymmetry of intermixing in Pt/Ti, and in Ti/Pt. In Ti/Pt we obtain a much weaker interdiffusion (broadening at the interface) than in Pt/Ti. The unexpected enhancement of the interdiffusion of the Pt atoms into the Ti substrate has also been demonstrated by simulations. We are able to capture the essential features of intermixing using TRIM and MD simulations for ion-beam sputtering and find reasonable values for interface broadening which can be compared with the experimental measurements. We explain the asymmetry of IM by the possible occurrence of transient enhanced diffusion in Pt/Ti which manifests in the exponential high diffusity tail of the AES concentration profile.

Ion beam mixing by focused ion beam

Si amorphous (41 nm)/Cr polycrystalline (46 nm) multilayer structure was irradiated by 30 keV Ga+ ions with fluences in the range of 25−820 ions∕nm2 using a focused ion beam. The effect of irradiation on the concentration distribution was studied by Auger electron spectroscopy depth profiling, cross-sectional transmission electron microscopy, and atomic force microscopy. The ion irradiation did not result in roughening on the free surface. On the other hand, the Ga+ irradiation produced a strongly mixed region around the first Si/Cr interface. The thickness of mixed region depends on the Ga+ fluence and it is joined to the pure Cr matrix with an unusual sharp interface. With increasing fluence the width of the mixed region increases but the interface between the mixed layer and pure Cr remains sharp. TRIDYN simulation failed to reproduce this behavior. Assuming that the Ga+ irradiation induces asymmetric mixing, that is during the mixing process the Cr can enter the Si layer, but the Si cannot enter the C...

Producing metastable nanophase with sharp interface by means of focused ion beam irradiation

Amorphous carbon/nickel double layers were irradiated by 30 keV Ga+ ions via focused ion beam. The effect of irradiation on the concentration distribution of all constituents was studied by Auger electron spectroscopy depth profiling and cross sectional transmission electron microscopy, while the morphology change of the sample was determined by atomic force microscopy. The Ga+ ion irradiation results in the formation of metastable Ni3C layer with a uniform thickness. The C/Ni3C and Ni3C/Ni interfaces were found to be sharp up to a fluence of 200 Ga+ ions/nm2.

Monte Carlo calculation of backscattering factor for Ni–C multilayer system

Auger electron spectroscopy (AES) depth profiles using the NiMVV (61 eV), CKLL (272 eV) and NiLMM (848 eV) lines were recorded for a 3 × (Ni(40 nm)/C(28 nm))/Si substrate sample. It was found that the Auger intensities corresponding to pure regions of the depth profile changed with depth. The behaviour of the change was different for the different layers and different Auger lines. The changes can be attributed to the change in the backscattering factor (BF) as the thickness of the sample changes due to the sputter removal. Zommer and Jablonski developed a Monte Carlo (MC) algorithm to calculate the BF for systems with a buried layer. This algorithm was applied to the present case; the intensities of the monitored Auger lines were calculated for the sample with decreasing thickness similarly to the Auger depth profiling. The agreement between the measured and calculated AES depth profiles is excellent. The MC calculation verifies that several layers contribute to the BF and thus the expressions developed for overlayer/substrate systems cannot be used.

Influence of layer microstructure on the double nucleation process in Cu/Mg multilayers

We have investigated by differential scanning calorimetry the thermal evolution of Cu∕Mg multilayers with different modulation lengths, ranging from 7∕28to30∕120nm. The Cu and Mg layers were grown by sequential evaporation in an electron beam deposition system. The phase identification and layer microstructure were determined by cross-section transmission electron microscopy, Rutherford backscattering, and scanning electron microscopy with focused ion beam for sample preparation. Upon heating, the intermetallic CuMg2 forms at the interfaces until coalescence is reached and thickens through a diffusion-limited process. Cross-section transmission electron microscopy observations show a distinct microstructure at the top and bottom of the as-prepared Mg layers, while no significant differences were seen in the Cu layers. We show that this effect is responsible for the observed asymmetry in the nucleation process between the Cu on Mg and the Mg on Cu interfaces. By modeling the calorimetric data we determine ...

Growing imbedded Ni3C-rich layer with sharp interfaces by means of ion beam mixing of C/Ni layers

C/Ni bilayers of various layer thicknesses (20?40?nm) were ion bombarded using Ga+ and Ni+ projectiles of energies 20 and 30?keV. Ion bombardment resulted in the growth of a Ni3C rich layer with the following features: (a) sharp carbon/Ni3C rich layer interface, (b) the amount of Ni3C produced by the irradiation proportional to the square root of the fluence and dependent on the type of projectile, (c) good correlation between the distribution of vacancies produced by the ion bombardment and the distribution of Ni3C. The formation of the metastable Ni3C compound was explained by a vacancy-assisted process. The sharp interface is the consequence of a relaxation process removing the intermixed Ni from the carbon layer. The square root of fluence dependence of the thickness of the Ni3C-rich layer can be explained by a usual diffusion equation considering moving boundaries.