NCAFM2023 Programme Booklet

MEASUREMENT OF ABSOLUTE VALUE OF LOCAL WORK FUNCTION USING VOLTAGE PULSE SCANNING PROBE MICROSCOPY

Emiko Murata 1 , Hibiki Hikasa 1 , Daiki Katsube 2 , Masayuki Abe 3 and Eiichi In ami 1*

1 School of Systems Engineering, Kochi University of Technology, Kami, Kochi 782-8502, Japan. 2 Cluster for Pioneering Research, RIKEN, 2-1 Hirasawa, Wako, Saitama 351-0198, Japan. 3 Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan. Email: inami.eiichi@kochi-tech.ac.jp

The work function is an important physical quantity in devices that utilize electron transport and electron emission. Generally, material surfaces exhibit microscopic roughness and contain local impurities, leading to local variations in the associated work function, known as the local work function (LWF). Therefore, accurately measuring the LWF is crucial for evaluating device performance. Currently, LWF has been measured using scanning tunneling microscopy (STM) and atomic force microscopy (AFM). In STM, information on the local barrier height (LBH), which is approximately equal to the average of the tip and sample work functions, is obtained from the tunneling current as a function of the tip-sample separation It(z). On the other hand, the AFM-based Kelvin probe method can measure the local contact potential difference (LCPD), which represents the difference in work functions between the tip and the sample. In this study, we propose an alternative method to simultaneously measure LBH and LCPD. This method is based on frequency modulation AFM with a conductive tip, where ultrafast voltage pulses synchronized with the cantilever oscillation are applied to the sample (Figure 1). By measuring the tunneling current during the pulse duration with sweeping the trigger delay τ , It(z) can be obtained, allowing analytical determination of the LBH. For this system, furthermore, we previously reported that the LCPD as a function of the tip-sample separation VLCPD(z) can be obtained by measuring the energy dissipation of the oscillating cantilever [1]. Therefore, our method provides simultaneous information on both LBH and LCPD, enabling the evaluation of LWF itself. Further details of the method and their results will be presented in the session.

Fig. 1 Principle of ultrafast voltage pulse SPM

References [1] E. Inami and Y. Sugimoto, Phys. Rev. Lett. 114, 246102 (2015)..

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