Characterization and optimization of the detection sensitivity of an atomic force microscope for small cantilevers (original) (raw)

A detailed analysis of the optical beam deflection technique for use in atomic force microscopy

Journal of Applied Physics, 1992

A Michelson interferometer and an optical beam deflection configuration (both shot noise and diffraction limited) are compared for application in an atomic force microscope. The comparison shows that the optical beam deflection method and the interferometer have essentially the same sensitivity. This remarkable result is explained by indicating the physical equivalence of both methods. Furthermore, various configurations using optical beam deflection are discussed. All the setups are capable of detecting the cantilever displacements with atomic resolution in a 10 kHz bandwidth.

MODEL OF THE CANTILEVER USED AS A WEAK FORCE SENSOR IN ATOMIC FORCE MICROSCOPY

2005

New types of weak forces measurements with Atomic Force Microscope (AFM) are very challenging for experimental physics and call for new studies on control strategies operating the AFM. It is thus necessary to first develop a precise model of the cantilever with its sharp tip, in interaction with the scanned sample. This paper presents a model of the cantilever, that is based on beam theory and taking into account the influence of the long distance interaction forces.

Calibrating laser beam deflection systems for use in atomic force microscopes and cantilever sensors

Applied Physics Letters, 2006

Most atomic force microscopes and cantilever-based sensors use an optical laser beam detection system to monitor cantilever deflections. We have developed a working model that accurately describes the way in which a position sensitive photodetector interprets the deflection of a cantilever in these instruments. This model exactly predicts the numerical relationship between the measured photodetector signal and the actual cantilever deflection. In addition, the model is used to optimize the geometry of such laser deflection systems, which greatly simplifies the use of any cantilever-based instrument that uses a laser beam detection system.

Characteristics and Functionality of Cantilevers and Scanners in Atomic Force Microscopy

Materials

In this paper, we provide a systematic review of atomic force microscopy (AFM), a fast-developing technique that embraces scanners, controllers, and cantilevers. The main objectives of this review are to analyze the available technical solutions of AFM, including the limitations and problems. The main questions the review addresses are the problems of working in contact, noncontact, and tapping AFM modes. We do not include applications of AFM but rather the design of different parts and operation modes. Since the main part of AFM is the cantilever, we focused on its operation and design. Information from scientific articles published over the last 5 years is provided. Many articles in this period disclose minor amendments in the mechanical system but suggest innovative AFM control and imaging algorithms. Some of them are based on artificial intelligence. During operation, control of cantilever dynamic characteristics can be achieved by magnetic field, electrostatic, or aerodynamic f...

Improved atomic force microscopy cantilever performance by partial reflective coating

Beilstein Journal of Nanotechnology, 2015

Optical beam deflection systems are widely used in cantilever based atomic force microscopy (AFM). Most commercial cantilevers have a reflective metal coating on the detector side to increase the reflectivity in order to achieve a high signal on the photodiode. Although the reflective coating is usually much thinner than the cantilever, it can still significantly contribute to the damping of the cantilever, leading to a lower mechanical quality factor (Q-factor). In dynamic mode operation in high vacuum, a cantilever with a high Q-factor is desired in order to achieve a lower minimal detectable force. The reflective coating can also increase the low-frequency force noise. In contact mode and force spectroscopy, a cantilever with minimal low-frequency force noise is desirable. We present a study on cantilevers with a partial reflective coating on the detector side. For this study, soft (≈0.01 N/m) and stiff (≈28 N/m) rectangular cantilevers were used with a custom partial coating at ...

Interdigital cantilevers for atomic force microscopy

Applied Physics Letters, 1996

We present a sensor for the atomic force microscope ͑AFM͒ where a silicon cantilever is micromachined into the shape of interdigitated fingers that form a diffraction grating. When detecting a force, alternating fingers are displaced while remaining fingers are held fixed. This creates a phase sensitive diffraction grating, allowing the cantilever displacement to be determined by measuring the intensity of diffracted modes. This cantilever can be used with a standard AFM without modification while achieving the sensitivity of the interferometer and maintaining the simplicity of the optical lever. Since optical interference occurs between alternating fingers that are fabricated on the cantilever, laser intensity rather than position can be measured by crudely positioning a photodiode. We estimate that the rms noise of this sensor in a 10 hz-1 kHz bandwidth is ϳ0.02 Å and present images of graphite with atomic resolution.

Monitoring of an atomic force microscope cantilever with a compact disk pickup

Review of Scientific Instruments, 1999

In the present study we test a compact disk pickup as the cantilever position sensor in an atomic force microscope ͑AFM͒. The pickup is placed on top of the optical microscope used for the visual inspection and alignment of the specimen. The AFM is also equipped with its own cantilever movement sensor system. Both the built-in and the new detection devices are simultaneously active for comparison purposes. Two different measurements are performed in sequence on the same sample each using one sensor at a time as the error signal source for the AFM feedback loop. The pickup has demonstrated good sensitivity as well as excellent performance in terms of compactness, reliability, and cost.

Finite Element Study Of The Metrological Aspects Of Atomic Force Microscope Cantilevers

In this paper we compare two dierent calibration methods for cantilevers used in contact mode Atomic Force Microscopy: the dimensional method and the nite element method (FEM). Each method is used for the accurate calculation of the normal cantilever stiness kz, a parameter crucial for the AFM images acquired with a constant-force load. The dimensional method was restricted to tipless rectangular and trapezoidal cantilevers whereas FEM allowed us to compare levers of dierent geometries: tipless rectangular, tipless trapezoidal 2D, tipless trapezoidal 3D and trapezoidal 3D with a pyramidal tip at the free end. The FE models were initially validated by the equations provided by beam theory and data from literature and then were used to produce our results.

Exploiting cantilever curvature for noise reduction in atomic force microscopy

The Review of scientific instruments, 2011

Optical beam deflection is a widely used method for detecting the deflection of atomic force microscope (AFM) cantilevers. This paper presents a first order derivation for the angular detection noise density which determines the lower limit for deflection sensing. Surprisingly, the cantilever radius of curvature, commonly not considered, plays a crucial role and can be exploited to decrease angular detection noise. We demonstrate a reduction in angular detection shot noise of more than an order of magnitude on a home-built AFM with a commercial 450 μm long cantilever by exploiting the optical properties of the cantilever curvature caused by the reflective gold coating. Lastly, we demonstrate how cantilever curvature can be responsible for up to 45% of the variability in the measured sensitivity of cantilevers on commercially available AFMs.