Atomically resolved imaging by low-temperature frequency-modulation atomic force microscopy using a quartz length-extension resonator

An, Toshu; Nishio, Takahiro; Eguchi, Toyoaki; Ono, Masahiro; Nomura, Atsushi; Akiyama, Kotone; Hasegawa, Yukio

doi:10.1063/1.2830937

Cited by 42 publications

(32 citation statements)

References 29 publications

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“…For the needle sensor, reasonable Q values are 15 000 at room temperature and 80 000 at 4 K. 30 For the qPlus sensor, Q ≈ 3000 at room temperature, reaching up to 200 000 at 4 K. 42 Thus, at room temperature the thermal contribution to the minimal detectable force gradient is δk ts thermal = 6 mN/m per √ Hz for the needle sensor and δk ts thermal = 3 mN/m per √ Hz for the qPlus sensor. At T = 4 K, the minimal detectable force gradient is δk ts thermal = 390 μN/m per √ Hz for the needle sensor and δk ts thermal = 40 μN/m per √ Hz for the qPlus sensor.…”

Section: B Thermal Noisementioning

confidence: 99%

Comparison of force sensors for atomic force microscopy based on quartz tuning forks and length-extensional resonators

et al. 2011

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The force sensor is key to the performance of atomic force microscopy (AFM). Nowadays, most atomic force microscopes use micromachined force sensors made from silicon, but piezoelectric quartz sensors are being applied at an increasing rate, mainly in vacuum. These self-sensing force sensors allow a relatively easy upgrade of a scanning tunneling microscope to a combined scanning tunneling/atomic force microscope. Two fundamentally different types of quartz sensors have achieved atomic resolution: the "needle sensor," which is based on a length-extensional resonator, and the "qPlus sensor," which is based on a tuning fork. Here, we calculate and measure the noise characteristics of these sensors. We find four noise sources: deflection detector noise, thermal noise, oscillator noise, and thermal drift noise. We calculate the effect of these noise sources as a factor of sensor stiffness, bandwidth, and oscillation amplitude. We find that for self-sensing quartz sensors, the deflection detector noise is independent of sensor stiffness, while the remaining three noise sources increase strongly with sensor stiffness. Deflection detector noise increases with bandwidth to the power of 1.5, while thermal noise and oscillator noise are proportional to the square root of the bandwidth. Thermal drift noise, however, is inversely proportional to bandwidth. The first three noise sources are inversely proportional to amplitude while thermal drift noise is independent of the amplitude. Thus, we show that the earlier finding that quoted an optimal signal-to-noise ratio for oscillation amplitudes similar to the range of the forces is still correct when considering all four frequency noise contributions. Finally, we suggest how the signal-to-noise ratio of the sensors can be improved further, we briefly discuss the challenges of mounting tips, and we compare the noise performance of self-sensing quartz sensors and optically detected Si cantilevers.

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Section: B Thermal Noisementioning

confidence: 99%

Comparison of force sensors for atomic force microscopy based on quartz tuning forks and length-extensional resonators

et al. 2011

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“…To control the tip-surface interaction force, we used the shift in the resonance frequency (f) of the qLER which vibrated at ~1 MHz (Q factor ~45 000) with an amplitude of 0.1 nm. [11,12,15] In our setup, the tip-surface distance (the tunneling barrier) was ~0.5 nm on H-terminated surfaces. [16] When a bias voltage (V S ) was applied between the probe and the Si pad, mean tunneling current was recorded at each position of the probe tip.…”

Section: Tunneling Current Mapsmentioning

confidence: 99%

“…Improved resolution and easy navigation to nanowire devices were achieved due to integration of STM and AFM operation by the use of a force sensor consisting of a sharp tungsten probe attached to a quartz length extension resonator (qLER) cantilever. [11,12] We have already reported on photocarrent distriution in Si stripes separated by SiO 2 films, [13] and the built-in potential mapping of a p-n junction under the optimized probe-sample gap. [14] Here, we demonstrate high-resolution characterization of small SOI nanowires by using M-SPM.…”

Section: Introductionmentioning

confidence: 99%

Nanoscale Characterization of Silicon-On-Insulator Nanowires by Multimode Scanning Probe Microscopy

Bolotov

Tada

Morita

et al. 2013

Trans. Mat. Res. Soc. Japan

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Structural and electronic properties of silicon-on-insulator (SOI) nanowires with a cross section area of 2020 nm 2 were investigated with high spatial resolution by multimode scanning probe microscopy (MSPM) in the constant force mode. The position-dependent tunneling current was measured in the interior of the Si nanowires whose surfaces were terminated with hydrogen and with ultrathin thermal oxide. The current value and fluctuations were reduced for Si nanowires terminated with an ultrathin oxide layer (~0.3 nm), indicating the homogeneous surface passivation. The tunneling current decreased within a distance of ~300 nm from the Si pad electrode for both types of surface termination. Calculations of the tunneling current were performed based on the macroscopic conduction model including the conductance contributions of the nanowire volume and the surface states. In the model, the bulk carrier concentration and the surface state density were tuned to fit the experimental data for the small Si nanowires. The results support the length-dependent conductance of thin Si nanowires, demonstrating the ability of the technique for characterization of modern silicon-on-insulator devices.

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“…In our technique, the interaction force gradient between the metal probe tip and the surface was detected as a shift in the resonance frequency (f) of an quartz length extension resonator (qLER) which vibrated at ~1 MHz (Q factor ~35 000) with an amplitude of 0.2 nm. [22,23], All measurements were performed at room temperature in an ultra-high vacuum chamber (a residual pressure of ~1.410 -7 Pa). To avoid surface contaminations, the chamber was connected to the processing/oxidation chamber through a vacuum transfer port.…”

Section: Built-in Potential Measurementsmentioning

confidence: 99%

Built-in Potential Mapping of Silicon Field Effect Transistor Cross Sections by Multimode Scanning Probe Microscopy

Bolotov

Tada

Arimoto

et al. 2013

Trans. Mat. Res. Soc. Japan

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Fig 1. AFM topograph of cross sectional Si(110) surface with two MOSFETs (L G 35 nm) after final processing step. Color scale is 2.5 nm. Built-in potential maps of metal-oxide-semiconductor field effect transistors (MOSFETs) with gate lengths of 30 and 150 nm were measured on cross sectional Si(110) surfaces covered with ultra-thin oxide. The maps were obtained by measuring the contact potential difference (CPD) using multimode scanning probe microscopy (MSPM) with a vibrating probe in the constant force mode. The improved spatial resolution and the sensitivity to the electrostatic potential were achieved for an optimal probe-sample gap (~1 nm) and vibration amplitude of 0.2 nm. The capability and challenges of the measurement method are discussed by comparing measured CPD maps with device simulation results.

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Atomically resolved imaging by low-temperature frequency-modulation atomic force microscopy using a quartz length-extension resonator

Cited by 42 publications

References 29 publications

Comparison of force sensors for atomic force microscopy based on quartz tuning forks and length-extensional resonators

Comparison of force sensors for atomic force microscopy based on quartz tuning forks and length-extensional resonators

Nanoscale Characterization of Silicon-On-Insulator Nanowires by Multimode Scanning Probe Microscopy

Built-in Potential Mapping of Silicon Field Effect Transistor Cross Sections by Multimode Scanning Probe Microscopy

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