Photothermal Spectroscopic Measurements by Dual Sampling Method in Intermittent-Contact-Mode Atomic Force Microscopy

Abstract

We have proposed a dual sampling method in intermittent-contact-mode atomic force microscopy with a piezoresistive cantilever for photothermal (PT) measurements. This method realizes a sensitive detection of thermal expansion in a sample by excluding crosstalk from photoabsorption signals generated at the piezoresistive sensor on the cantilever. We have confirmed the feasibility of this method through the excitation photon energy dependence of the PT signal measured on Si and GaAs.

Photothermal spectroscopy by atomic force microscopy on Cu(In,Ga)Se2 solar cell materials

“…2(a) shows our experimental setup for the PT measurements, which was based on a commercial AFM system (SPI4000/SPA300HV, Hitachi High-Tech Science Corp., Japan) operated at room temperature in nitrogen gas at 1 atm. In the PT measurements, the sample surface was illuminated by an intermittent light and scanned by AFM, and the output of the deflection sensor for the AFM cantilever was sampled by a home-made DS circuit [14]. Then, the periodical change in output signal from the DS circuit at the modulation frequency of the incident light, which corresponded to periodical thermal expansion caused by the intermittent light illumination, was extracted by the lock-in amplifier and treated as the PT signal [14].…”

“…In the PT measurements, the sample surface was illuminated by an intermittent light and scanned by AFM, and the output of the deflection sensor for the AFM cantilever was sampled by a home-made DS circuit [14]. Then, the periodical change in output signal from the DS circuit at the modulation frequency of the incident light, which corresponded to periodical thermal expansion caused by the intermittent light illumination, was extracted by the lock-in amplifier and treated as the PT signal [14]. To avoid the influence of stray light on the PT measurements, a Si piezoresistive cantilever (PRC-DF40P, Hitachi High-Tech Science Corp., Japan) was used.…”

“…In this study, we performed photothermal (PT) measurements on the CIGS solar cells by the dual sampling (DS) method in atomic force microscopy (AFM) under near-infrared excitation, which we originally proposed [14,15]. Because the PT signal corresponds to a value of thermal expansion caused by the non-radiative recombination of the photocarriers, we expected that the PT measurements by AFM on the solar cells would allow us to investigate nonradiative recombination properties locally.…”

“…(a) Experimental setup for the photothermal (PT) measurements by the dual sampling (DS) atomic force microscopy (AFM) method[14], and (b) light sources for the PT measurements. For the latter, (i) a Ti:Al 2 O 3 laser in continuous wave mode, with central photon energy of 1.38 eV, was used for photo-excitation above the CIGS bandgap, and (ii) a near-infrared laser diode with central photon energy of 0.78 or 0.89 eV was used for photo-excitation below the bandgap.…”

Photothermal spectroscopy on multicrystalline silicon solar cell materials by dual sampling method in atomic force microscopy

“…To investigate such a property, in this study, we have performed photothermal (PT) measurement by dual sampling method in atomic force microscopy (DS-AFM) under near-infrared light excitation [1] [2]. We observed the distribution of the PT signal around some grain boundaries (GBs) and discuss the origins of the enhanced PT signal by comparison with the surface potential distributions observed by Kelvin probe force microscopy (KFM) and with the results of photoluminescence (PL) measurements.…”