The surface roughness of laser-ablated metal films is evaluated by an atomic force microscope (AFM). The films are deposited on glass substrates using a pulsed Nd:YAG laser. The target is bulk metal such as Ni and Ti. The AFM is confirmed to be a useful tool for measurements of surface roughness on the nanometer scale. Measured values may differ from the real value, depending on the tip radius and the roughness. The reliability of the measured value is discussed in consideration of the locus of the rolling-circle of a tip radius, using simple models. The roughness obtained is 4.3-6.9 nm maximum peak-valley height, and this value is found to be affected by the laser energy density.The laser ablation method has been developed for the preparation of thin films of superconductors [1, 2], semiconductors [3] and metals [4], since the method gives good stoichiometry [5] and the ablated particles have high energy [6]. Although laser-ablated films are so characterized that their surface is finer than that of vacuum-evaporated films [7], the surface roughness and micro-cracks are not negligible. The surface roughness is one of the interesting problems in the film physics and technology. Studies on the composition [5], crystal structure [8] and grain size [9] of the laser-ablated films have been examined, while a report concerning the nanoscale surface roughness has not been made to date.The scanning probe microscope (SPM), which is classified into the scanning tunneling microscope (STM) and the atomic force microscope (AFM), is capable of measurements of surface roughness on the nanometer scale [10]. The STM has been used in roughness measurements [11][12][13] and the reliability of this method is discussed [13]. However, reports concerning surface roughness using the AFM seem to be few [14].In this paper, we describe the roughness evaluation of laser-ablated metal films obtained by the atomic force microscope (AFM), which is devised to detect the changes in the interaction forces between a tip and a sample. Measured values may deviate from the real value, depending on the tip radius and the roughness. We discuss the reliability of the measured value in consideration of the locus of the rollingcircle of a tip radius using simple models.
ExperimentThe schematic of the main part of the laser ablation apparatus used for the present study is shown in Fig. 1. The chamber was evacuated to 5 × 10 −6 Torr using turbo and rotary pumps. The wavelength of the Nd:YAG laser for ablation was 355 nm (the third harmonic), the total energy was 150 mJ/pulse and the pulse width was 5 ns. The target was Ni plate or Ti plate, which was commercially available pure (99.99%) metal. The laser beam was focused on the target at an incidence angle of 60 • from the surface normal and operated at 10 pps. The laser energy density was varied between 1.5 × 10 −2 and 3.0 × 10 −2 J/mm 2 by changing the focusing position [7]. The distance between the slide glass substrate and the target was 30 mm, and the deposition time was 5 min. The laser-ablated plume wa...