May 12 2004
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In the early 1980s, Gerd Binning and Heinrich Rohrer developed the scanning tunneling microscope (STM) at the IBM Zurich Research Laboratory. In 1986, they won a Noble Prize for their breakthrough achievement.
The STM is operated based on what is known as a tunneling current that begins to flow when a sharp tip proceeds towards a conducting surface at a distance of about 1 nm.
Properties of the Scanning Tunnelling Microscope
The tip is placed on a piezoelectric tube that permits slight movements when a voltage is applied to its electrodes. In this way, the electronics of the STM system regulates the position of the tip such that the tunneling current and, thus, the distance between the tip and the surface are constantly maintained. Simultaneously, a small portion of the sample surface is also scanned. This movement is noted and can be shown as an image of the surface topography.
The individual atoms of a surface can be resolved and exhibited under perfect conditions. An ultrahigh vacuum is needed to prevent sample contamination from the surrounding medium, even though the STM by its nature does not require vacuum to operate, as it operates in both air and under liquids.
The fact that these surfaces look very flat under an STM—the evident height of individual atom being 1/100th to 1/10th of an atomic diameter—is an issue when it comes to studying metal surfaces. Hence, to resolve individual atoms, the distance between the sample and the tip must be constantly maintained within 1/100th of an atomic diameter or greater, that is, approximately 0.002 nm. This not only requires a very high rigidity of the STM as such, but the STM must also be efficiently decoupled from environmental vibrations.
Scanning Tunnelling Microscopy Involvement in Nanotechnology
The STM has the ability to move and position individual atoms. Due to this ability, it has become a significant tool in nanotechnology. In 1982, nanotechnology came out as a workable prospect when IBM researchers used STM to exhibit individual atoms of gold. Later in 1989, another team of researchers from IBM controlled 35 atoms of xenon to design the letters “IBM”. Since then, it has been used as a modern magnetic resonance imaging (MRI) method.
The STM method used by researchers permits the detection of single nuclei detection, but the conventional MRIs can only image several trillion nuclei at a time. The system holds wide implications in identifying single organic molecules, as it can be used in aqueous solutions and would ultimately supplant the present technologies used in microarrays and bio-chips.
Scanning Tunnelling Microscopy Future in Nanotechnology
The highly significant feature of STMs is not the microscope as such, but the cantilever probes with nanoscale tips that are utilized with it. There would be an incredible value in producing probes that can incorporate numerous functions, for example, the detection of optical, magnetic, electrical, and thermal signals at the nanoscale, onto a single tip.
Some disadvantages of the STM method are that it does not offer chemical data about a material and cannot image a three-dimensional sample. This drawback presents an excellent chance for new instrument methods that can attain nanometer-scale resolution, while combining three-dimensionality and multiple-variable measurement.
Both academia and private industry are expected to further continue the demand for metrology tools to eventually observe and control matter at the atomic and molecular level. There would be rapid industrial growth for manufacturers of STM accessories like tips and other instrument developments.