Direct measurement instrument for lattice spacing on regular crystalline surfaces using a scanning tunneling microscope and laser interferometry

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A two-dimensional (2D) encoder with picometre resolution using multi-tunnelling-probes scanning tunnelling microscope (MTP-STM) as detector units and a regular crystalline lattice as a reference is proposed. In experiments to demonstrate the method, a highly oriented pyrolytic graphite (HOPG) crystal is utilized as the reference. The MTP-STM heads, which are set upon a sample stage, observe multi-points which satisfy some relationship on the HOPG crystalline surface on the sample stage, and the relative 2D displacement between the MTP-STM heads and the sample stage can be determined from the multi-current signals of the multi-points. Two unit lattice vectors on the HOPG crystalline surface with length and intersection angle of 0.246 nm and 60°, respectively, are utilized as 2D displacement references. 2D displacement of the sample stage on which the HOPG crystal is placed can be calculated using the linear sum of the two unit lattice vectors, derived from a linear operation of the multi-current signals. Displacement interpolation less than the lattice spacing of the HOPG crystal can also be performed. To determine the linear sum of the two unit vectors as the 2D displacement, the multi-points to be observed with the MTP-STM must be properly positioned according to the 2D atomic structure of the HOPG crystal. In the experiments, the proposed method is compared with a capacitance sensor whose resolution is improved to approximately 0.1 nm by limiting the sensor's bandwidth to 300 Hz. In order to obtain suitable multi-current signals of the properly positioned multi-points in semi-real-time, lateral dither modulations are applied to the STM probes. The results show that the proposed method has the capability to measure 2D lateral displacements with a resolution on the order of 10 pm with a maximum measurement speed of 100 nm s−1 or more.

Section: Three-point Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Two-dimensional encoder with picometre resolution using lattice spacing on regular crystalline surface as standard

Aketagawa

Honda

Ishige

et al. 2007

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“…where δ ij is Kronecker's delta; lattice spacing of the HOPG crystal |a i | is 0.246 nm [10], and the intersectional angle between a 1 and a 2 is 60 • . The displacement vector r from the point O to the center of the dithered STM tip can be calculated using a linear sum of unit lattice vectors a 1 and a 2 as…”

Section: Principle Of An Atom Encodermentioning

confidence: 99%

“…The STM, which is popular in surface engineering, is capable of observing an atomic image of the crystalline surface. On the other hand, a lattice spacing of approximately 0.246 nm [10] if the HOPG crystalline surface is uniform and stable over a long range when the crystals are stress free. In the previous paper, one or two mono-crystalline areas of the HOPG surface are utilized as 2D references, and observed by one or two lateral-dithered STM tip(s).…”

Section: Introductionmentioning

confidence: 99%

A two-dimensional atom encoder using one lateral-dithered scanning tunneling microscope (STM) tip and a regular crystalline lattice

Chaikool

Aketagawa

Okuyama

2009

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In this paper, we propose a new 2D displacement atom encoder using only one lateral-dithered scanning tunneling microscope (STM) tip and one mono-crystalline area of the highly oriented pyrolytic graphite (HOPG) crystal. A high-speed lateral circular dither modulation with proper amplitude is applied to a tip scanner to position the STM tip on six specific points on the HOPG crystalline surface. Multi-tunneling-current signals obtained from the six specific points are utilized to determine the lateral 2D displacement based on the two unit lattice vectors on the HOPG crystalline surface. In addition, the interpolation method can be used in the newly proposed method to measure displacement less than the lattice spacing. In the paper, instrumentation and experiments of the new 2D displacement measurement technique are discussed. The experimental results show that the proposed technique has the capability to measure 2D displacement with a resolution of 10 pm order.

“…The experiments were performed for both the new tracking controller with the enhanced STM stiffness and the simple PI controller with the normal STM stiffness which was tuned manually. In the experiments, the graphite crystal, whose lattice spacing is about 0.25 nm [6], was utilized as the reference. The tunnelling current and the bias voltage were 2 nA and 50 mV, respectively.…”

Section: Stabilization Experimentsmentioning

confidence: 99%

Real-time atomic encoder using scanning tunnelling microscope and regular crystalline surface

Aketagawa¹,

Takada²,

Rerkkumsup³

et al. 2006

In this paper, we demonstrate a technique for highly stable atom-tracking control of a scanning tunnelling microscope (STM) tip by referring to an atomic point on a regular crystalline surface. We also demonstrate an atomic encoder using ‘atom-by-atom’ step control along a crystalline axis. A graphite crystal, whose lattice spacing is approximately 0.25 nm, was utilized as the reference material. To enhance the stability of the atom-tracking control in the presence of external disturbances, a robust controller, consisting of an integrator, a tracer and limiter units, was developed. Experimental results show that the proposed method has high capability for maintaining the atom-tracking control without any jumping of the STM tip to adjoining atoms, even in a noisy environment. This method was also applied to atom-step control of the STM tip by referring to a specific crystalline axis. Atom-stepping control along a crystalline axis over a range of 200 atoms and at a rate of 10 atoms s−1 was performed and demonstrated without missing the atomic array.