Silicon <i>pn</i> junction imaging and characterizations using sensitivity enhanced Kelvin probe force microscopy

Kikukawa, Atsushi; Hosaka, Sumio; Imura, R.

doi:10.1063/1.113780

Cited by 286 publications

(164 citation statements)

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“…The force and force gradient at f m modulates the cantilever fundamental mechanical resonance (frequency f 0 ) creating sidebands at f 0 þ f m and f 0 À f m . The f 0 þ f m sideband is detected at the second mechanical resonance of the cantilever using standard AFM methods 3,4 (see supplemental information 12 b).…”

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Raman spectroscopy and microscopy based on mechanical force detection

Rajapaksa

Wickramasinghe

2011

Applied Physics Letters

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The Raman effect is typically observed by irradiating a sample with an intense light source and detecting the minute amount of frequency shifted scattered light. We demonstrate that Raman molecular vibrational resonances can be detected directly through an entirely different mechanism-namely, a force measurement. We create a force interaction through optical parametric down conversion between stimulated, Raman excited, molecules on a surface and a cantilevered nanometer scale probe tip brought very close to it. Spectroscopy and microscopy on clusters of molecules have been performed. Single molecules within such clusters are clearly resolved in the Raman micrographs. The technique can be readily extended to perform pump probe experiments for measuring inter-and intramolecular couplings and conformational changes at the single molecule level. The Raman effect 1 is one of the most widely used phenomenon in chemical spectroscopy. Over the past 80 years, this effect has been measured by irradiating the sample with intense monochromatic light and detecting the minute amount (one part in 10 9 ) of frequency shifted scattered light. A typical Raman setup utilizes a high rejection, low insertion loss, long pass filter to reject the incident pump light. This is followed by a sensitive detector coupled to a high resolution spectrometer to record the molecular vibrational spectrum. We present initial results on an entirely different mechanism for detecting the Raman effect. It is based on the force interaction between a Raman excited molecule and a scanning probe microscope probe tip. The ability to measure the Raman effect using a non-optical channel is important because the weak Raman signal can be detected in zero optical background, providing similar sensitivity advantages to that offered by photoacoustic spectroscopy. 2 Furthermore, since we do not need a spectrometer for the measurement, the resolution of the technique can be improved by several orders of magnitude as compared with conventional techniques, since it is only limited by the spectral bandwidth of the lasers used and not by the spectrometer resolution; for diode lasers, this bandwidth can be as narrow as 100 kHz. We present images from our Raman Probe Force Microscope of molecular clusters where single molecules can be discerned within them due to their orientation differences.The concept of our scheme can be understood by referring to Figure 1. Two collinear optical beams-a pump beam at frequency m 1 and a stimulating beam at frequency m 2 -are focused to a diffraction limited spot on the sample surface to efficiently stimulate molecular vibrations at frequency (m 1 À m 2 ). The stimulating beam at frequency m 2 is tunable, allowing (m 1 À m 2 ) to be tuned through the various Raman vibrational resonances. We probe the force interaction between the excited oscillating molecules and a cantilevered, gold coated, scanning probe microscope tip approached within nm range of the sample surface as the force interaction is modulated at frequency f m . The force ...

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Raman spectroscopy and microscopy based on mechanical force detection

Rajapaksa

Wickramasinghe

2011

Applied Physics Letters

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“…Even earlier, the second mode of oscillation of an AFM cantilever was employed for the detection of the surface potential, simultaneously with the regular topography measurement in a Kelvin probe force microscope ͑KPFM͒. 9 In this method an ac bias at the frequency of the second oscillation mode is applied to the sample ͑or the tip͒, which induces cantilever oscillation at this frequency. If an additional dc bias is adjusted correctly to compensate for the electrostatic force between the tip and the sample, the oscillation at this frequency will vanish and the dc bias will correspond to the contact potential ͑CP͒ between the tip and the sample.…”

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Special cantilever geometry for the access of higher oscillation modes in atomic force microscopy

Sadewasser

Villanueva

Plaza

2006

Applied Physics Letters

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Employing higher oscillation modes of microcantilevers promises higher sensitivity when applied as sensors, for example, for mass detection or in atomic force microscopy. Introducing a special cantilever geometry, we show that the relation between the resonance frequencies of the first and second resonance modes can be modified to separate them further or to bring them closer together. In atomic force microscopy the latter is of special interest as the photodiode of the beam deflection detection limits the accessible frequency range. Using finite element simulations, we optimized the design of the modified cantilever geometry for a maximum reduction of the frequency of the second oscillation mode with respect to the first mode. Cantilevers were fabricated by silicon micromachining and subsequently utilized in an ultrahigh vacuum Kelvin probe force microscope imaging the surface potential of C 60 on graphite.

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“…The lock-in amplifier can apply DC and AC bias voltages [V dc and V ac cos(2πf m t), respectively] between a tip and a sample, detect a modulation frequency (f m ) component of electrostatic force, and feedback control V dc to obtain CPD (V CPD ). We adopted amplitude modulation KFM (AM-KFM) [23] and set f m to the 1st resonance (f 1 =67 kHz) of an Au-coated cantilever (PPP-FMAu, Nanoworld). For simultaneous topography imaging, the cantilever oscillated at the 2nd resonance (f 2 =401.2 kHz).…”

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confidence: 99%