Study Of Subsurface Imaging Via Kelvin Probe Force Mircoscopy

Since scanning tunnel microscopy (STM) is invented, scanning probe microscopy (SPM) is one of the most important tool for probing nanoscale physical properties of sample. To meet different applications, a lot of variants have been developed, such as electrostatic force microscopy (EFM) for probing electric properties, acoustic atomic force microscopy (Acoustic AFM) for probing mechanical properties and Kelvin probe force microscopy (KPFM) for probing potential distribution. As advance in microelec-tronics and nanocomposites science, the demand of new SPM technology for probing not only surface properties but also subsurface properties is rising.To meet this need, this paper aims to investigate using KPFM as subsurface imag-ing tool of metal nanofillers buried in polymer and 3D reconstruction method of dis-persion of nanofillers in nanocomposites based on 2nd harmonic amplitude. To achieve this research goal, study is conducted in following aspects:First, we investigate factors which affects quality of imaging results when probing subsurface structure. Selection of imaging parameters is very important, such as system parameters like distance of tip and sample, radius of tip, angle of tip cone and sample factors like relative dielectric of polymer, size and buried depth of nanofiller. In this paper, an analytical model and finite element analysis (FEA) model of tip sample metal substrate system is proposed to analyze relationship between electrostatic force on tip and imaging parameters. The results show that to achieve best imaging quality small tip-sample distance and appropriate tip radius (about 1.5 times of radius of nanofiller) is preferred, while angle of tip cone is less important. For sample factors, appropriate relative dielectric (between 4 - 10), big diameter and small buried depth is best.Second, preparation of nanocomposites sample and subsurface imaging experi-ment analysis. Sample is prepared by spin coating with carbon nanotube (CNT) as filler and 4—4-oxydianiline and an equimolar amount 3—3,4—4-benzophenone tetracar-boxylic dianhydride as polymer. Via 2nd harmonic amplitude of tip, subsurface CNT structure is detected. Several images are acquired with different tip sample distance and show that as distance increases contrast of CNT structure fades, which is in accordance with results of system parameters.Third, exploring 3D reconstruction method of dispersion of nanofiller in polymer. KPFM 2nd harmonic amplitude image only shows 2D dispersion of nanofiller, but some- times 3D dispersion is more preferred. As diameter and buried depth of nanofiller will affect nearing distribution of electrostatic force, we investigate the relationship between diameter and buried depth and distribution properties of electrostatic force, which is described by peak force and full width at half maximum (FWHM), and investigate 3D reconstruction method utilizing this relationship.Finally, difference about subsurface imaging of KPFM and contact resonance atomic force microscopy (CR-AFM) is researched. Because of different imaging principle, KPFM can probe nanofiller with relative bigger buried depth, but has poorer lateral resolution.