No.10 - June 2006
FEATURED EQUIPMENT: Dynamic imaging of nano-scale features
Optical Video Nano Microscopy
Introduction
Drawings, 3D models and pictures often accompany the verbal or written description of tiny objects like carbon nanotubes or nanowires that can be hardly seen even by the most sophisticated tools. Since the visual information is the primary source for human comprehension of reality, sometimes not just one, but a continuous stream of images is required when we are dealing with dynamically active objects. For example, the motion of molecular structures, and especially that of biological structures, is the result of specific thermal and functional activity. In this case, collecting adequate and sufficient information proves critically important for understanding, analyzing and controlling an object and its dynamic behavior.
Generally, using atomic force microscopy (AFM) and scanning tunneling microscopy (STM) tools raises two primary concerns.
The first concern regards the uncertainty of whether the state of structural integrity was preserved after probing the molecular structure with a mechanical tip. The van der Waals interactions between the molecular structure and the tip could alter the structural integrity, which would render the topological description ambiguous.
The second concern takes into account the fact that nanostructures are rather dynamic than static. Therefore, the accuracy of the topological description is directly proportional to the speed of data acquisition.
Regarding carbon nanotubes, their structure attracts a lot of attention for potential applications in semiconductor industry, as conductors with zero resistance, and for biomedical applications, as drug delivery systems. Their size ranges between one and several nanometers in diameter and their length reaches about 100 nm. But most important is that any distortion in their straightness induces significant losses in conductivity. Such distortions could be of mechanical nature, since vibrations could produce twisting and banding of individual nanotubes and nanotubes assembly.
The frequency and amplitude of such vibrations is of a particular interest. These vibrations are, probably, in the range of tens or even hundreds of megahertz with their amplitude reaching several nanometers. To identify and measure such dynamic behavior, the tool?s resolution has to be at least two Angstroms, and the speed of data acquisition in the GHz range.
In principle, at the nano level, the whole idea of a common reference system becomes an obstacle for precise image acquisition and metrology. The reason is that the speed of sequentially, point by point, data collection has to be at least one order of magnitude greater then the potential velocity of the observed nano assembly. Such capabilities do not exist today and they seem potentially impossible.
A more reasonable approach would be the simultaneous acquisition of multiple values for different points during a single acquisition step. In this case, the relationship between different points throughout the structure will be preserved and an accurate metrology could be performed relative to any point designated as the reference. This approach is more likely to help the scientific and industrial community to deal with nano-structural problems in a more accurate and efficient manner.
AngstroVision?s long-standing strategy resides on the understanding of a simple fact: the current imaging microscopy will reach its theoretical limits when industry will move into the quantum domain. For this reason, AngstroVision Inc. has developed and patented a fundamentally new technology that is the first to allow a real-time acquisition of high-resolution 3-D video images from the nano-world. The data gathered is metrologically accurate, and can be acquired non-destructively in a wide range of environments without requiring any preparation of samples, and at very high speed. As a result, apart from all other imaging and metrology devices, the new technology offers the opportunity to advance and dominate many application areas and to significantly influence the development of the semiconductor, materials, biotechnology and nanotechnology fields.
Technology description
The technology uses quantum interference effect to create simultaneously many thousands of tiny optical probes, which are acting similarly to the mechanical tips in scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The configuration of all optical probes, in this case, remains the same during image acquisition. There is no physical interaction, like van der Waals forces, between probes. Material interaction occurs only at the quantum level.
Lateral and vertical resolution is defined as a relative displacement of each probe from the reference location and can be calibrated as a fraction of the wavelength of the coherent light source. Each probe is acting independently, yet simultaneously, measuring vertical elevation at the appropriate probe location. As a result, the topological description is more accurate and can be acquired at greater speed.
The three key areas of AngstroVision?s intellectual property are:
1. a method for achieving high resolution in all three dimensions
2. the system design and configuration and
3. the image processing algorithms, which take into account the interference patterns and transform them into 3-D topographical data.
System performance
The current prototype, built for demonstrating the proof-of-principle, produces 3-D images with a vertical resolution of 2 nm and 10 nm for the lateral resolution. It captures data at 30 frames per second with an effective imaging rate of 1 frame per second. The system resolution is adjustable and the device can operate as any classical optical microscope. Field depth varies from 1 μm to several mm with a working distance of 13mm. AngstroVision believes that a substantial improvement in system performance is possible and a resolution of less than one nanometer is practically achievable. The speed of data capture strongly depends on camera performance and it can be significantly increased. Two samples of images taken by breadboard are below. Both images are 10um x 10um field of view. Figure 1 shows the Ni poles:100 nm high, 250 nm wide and 750 nm pitch. Figure 2 is an image of carbon nanotubes.
Figure 2: Carbon nanotubes
Conclusion
The introduction of AngstroVision?s technology opens a new opportunity in the field of scientific discovery, for its original approach toward unique phenomena that occur at atomic or molecular level and yield materials with extraordinary properties, useful in many industrial applications.
