A New Scanning Method for Fast Atomic Force Microscopy

Abstract

In recent years, the atomic force microscope (AFM) has become an important tool in nanotechnology research. It was first conceived to generate 3-D images of conducting as well as nonconducting surfaces with a high degree of accuracy. Presently, it is also being used in applications that involve manipulation of material surfaces at a nanoscale. In this paper, we describe a new scanning method for fast atomic force microscopy. In this technique, the sample is scanned in a spiral pattern instead of the well-established raster pattern. A constant angular velocity spiral scan can be produced by applying single frequency cosine and sine signals with slowly varying amplitudes to the x-axis and y-axis of AFM nanopositioner, respectively. The use of single-frequency input signals allows the scanner to move at high speeds without exciting the mechanical resonance of the device. Alternatively, the frequency of the sinusoidal set points can be varied to maintain a constant linear velocity (CLV) while a spiral trajectory is being traced. Thus, producing a CLV spiral. These scan methods can be incorporated into most modern AFMs with minimal effort since they can be implemented in software using the existing hardware. Experimental results obtained by implementing the method on a commercial AFM indicate that high-quality images can be generated at scan frequencies well beyond the raster scans.

A generalized negative imaginary lemma and Riccati-based static state-feedback negative imaginary synthesis

“…The transformation (15) can be constructed such that A 11 has all of its eigenvalues in the closed left half of the complex plane and A 22 has all of its eigenvalues in the open right half of the complex plane; i.e., A 22 is an anti-stable matrix. (12) with C 1 B 2 non-singular A f , B f ,B 1 , U, A 11 , A 12 , A 22 , B f 1 , B f 2 , B 11 and B 22 as in (15)- (17), where A 22 is the anti-stable block of the A f matrix.…”

“…For instance, a positive position feedback control scheme based on the NI stability result provided in [1,2] is used to design a novel compensation method for a coupled fuselage-rotor mode of a rotary wing unmanned aerial vehicle in [13]. In [14,15], the NI stability result is applied to nanopositioning in an atomic force microscope. An identification algorithm which enforces an NI constraint is proposed in [3] for estimating model parameters, following which an integral resonant controller is designed for damping vibrations in flexible structures.…”

Design of an Inertially Counterbalanced $Z$ -Nanopositioner for High-Speed Atomic Force Microscopy

“…Sinusoidal signals were used to drive the fast axis of the nanopositioner in order to avoid excitation of the lateral resonant modes. Sinusoidal signals have been used in tuning fork AFM [21], [41] and some other high-speed nonraster scan patterns AFM [42], [43]. 200 × 200 pixel resolution images were obtained at line rates of 10, 100, and 200 Hz.…”

Control Methods in Data-Storage Systems

“…In particular, two methods that have been proposed are based on tracking spiral [235], [236] and cycloid-like trajectories [237]. The main advantage of these methods is that for a mechanical scanner it is much easier to track a smooth trajectory, rather than a raster pattern with sharp corners.…”