Analysis of structural transformations and fluctuation effects in the nanosized nickel films in the vicinity of the melting point

Abstract

Metal films are widely employed in integrated cir cuits for the creation of active and passive elements. Recent interest in low dimensional conductors has been driven mainly by the applications in microelec tronics and other branches of science and technology. Conductors whose typical dimensions are less than 100 nm are called nanosized conductors.It is known that melting point T m of low dimen sional conductors (e.g., thin metal films), which char acterizes the beginning of the dispersion of the sample into droplets, is significantly lower than the melting point of bulk materials due to the dimensional effect in melting [1,2]. The surface energy determines the dependences of the phase transition temperatures on the film thickness and dimensions of small crystallites. The calculated and experimental results show signifi cant variations in the phase transition temperature in low dimensional conductors with variations in the film thickness [1-3].In particular, Gromov et al.[3] demonstrated the experimental dependence of the melting point of thin nickel films on the Al 2 O 3 surface on the film thickness in accordance with which the melting point of the nickel film with a thickness of 10 nm (T ≈ 800 K) is lower than the melting point of bulk nickel by about 900 K.In this work, we employ the scanning probe microscopy (SPM) in the study of the effect of heating temperature on the structure of the Ni film with an original thickness of 20 nm that is deposited on the sil icon oxide substrate (the thickness of the thermally grown silicon oxide SiO 2 is about 1 µm). Thin Ni film is deposited using the magnetron sputtering in the argon medium at a pressure of 7 × 10 -3 mmHg, a residual gas pressure in the chamber of no greater than 10 -5 mmHg, and room temperature. Then, we employ photolithography to create Ni film samples on the substrate.The main purpose of this work is the interpretation of the experimental results from [4], in accordance with which significant positive fluctuations of the resistance (or voltage across the sample at the given current) are observed in the vicinity of the melting point of the nanosized Ni films upon gradual slow heating. The results indicate an increase in the film resistance upon heating.For the interpretation of the above results, we use the SPM for the imaging of the surfaces of thin nickel films that are heated to different temperatures [5]. The analysis of the topology of thin nickel films is supple mented with the estimation of variations in the mean thickness upon heating to different temperatures due to the structural transformation in the film.Using the SPM, we study the surface topology of the nickel films at room temperature (T = 300 K) and determine the mean thickness: h = 20 ± 2 nm. Then, we perform the slow heating of the film samples. Figure 1 demonstrates the surface topologies of the nickel film samples with original thicknesses of 20 ± 2 nm after heating to temperatures of about 712, 737, and 752 K. The sample is heated in a vacuum chamber with a residual gas pressure of ...

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