The application of nanotechnology is the practical manipulation of materials at nanoscale, placing molecules and atoms precisely in order to obtain desired functionality. Unlike working at microscale typical of most miniaturization to date, novel properties arise at nanoscale, displaying characteristics that seem inconsistent with the classical laws of physics. These novel properties can be exploited to create materials with unheralded densities and levels of integration, leading to the introduction of new uses, new devices, and new classes of applications.

Scientists and engineers need practical tools to realize the attributes and further gains possible through nanotechnology. Their tools must be able to identify and image atomic structure across a wide range of materials, and do so in a time- and -cost-effective manner. The Imago LEAP^® Microscope is the only 3D atom probe that meets all criteria.

Imago's patented Local Electrode technology led to the first practical, effective three-dimensional atom probe (3DAP), delivering statistically significant results in hours rather than days. This enables:

• A field of view 50 times larger than earlier 3DAPs; the difference between looking at the outside world through a wide-open door, instead of through a peep hole.
• Data collection a thousand times faster than conventional 3DAPs, allowing users to run dozens of experiments in a day, compared to one or two a week.
• Simplified specimen preparation and handling, with specimens made on planar surfaces such as wafers made using a variety of methods already familiar to TEM users.

What's more, Imago's state-of-the-art laser and voltage pulsers, detectors, and associated electronics deliver unparalleled precision, accuracy, and performance.

Time-of-flight mass spectrometry identifies individual atoms by their elements or isotopes, while point-projection microscopy identifies where atoms were originally located in the specimen (i.e., in 3D). The atom probe microscope uses the principles of both time-of-flight mass spectroscopy and point-projection microscopy to identify individual elements and to locate them within the bulk of a material.

As in transmission electron microscopy (TEM), the user creates a specimen. Instead of the thin foil familiar to users of TEMs, the atom probe specimen is a small pointed tip (microtip) with a ~100nm radius of curvature (item #1 in the figure). This microtip can be carved into a wafer using commonly available techniques such as the focused ion beam. Several other techniques can be used to make the tips either before or after the film is deposited, and with or without the use of a focused ion-beam tool.

The specimen is then inserted into a cryogenically cooled, UHV analysis chamber. The analysis chamber is cryogenically cooled to freeze out atomic motion. It is at ultrahigh vacuum to allow individual atoms to be identified without interference from the environment.

A positive voltage is applied to the specimen via the voltage pulser (item #2 in the figure). The positive voltage attracts electrons and results in the creation of positive ions. These ions are repelled from the specimen and pulled toward a position-sensitive detector.

Under an identical voltage differential, lighter ions (those from lighter elements, shown in green) will reach the detector quicker than their heavier counterparts (depicted in red). To accurately measure the time of departure of the ion, the positive voltage is typically pulsed. The arrival time of the ion is recorded by a set of timing devices on the single particle detector. This detector operates under the principle of a delay line detector. The time-of-flight of the ion identifies the mass-to-charge of the ion, which provides the elemental identity, so the atomic species is obtained. The numbers of atoms of various elements that hit the detector are recorded and a mass spectrum is extrapolated.

The location of the atom in the specimen is determined from the ion's hit position on the delay line detector (item #3 in the figure). The x and y coordinates of the hit relate to the ion's original position on the specimen. It is a fundamental rule of physics that neither potential lines nor atomic flight paths can intersect or cross each other; therefore, an ion that hits the detector to the right of another ion must have been located to its right on the specimen. The depth, or z dimension, is provided by the sequence (time) of the ion hit on the detector. Placing the detector at a distance away from the specimen magnifies the tip of the specimen. The specimen has a curvature (r) on the order of nanometers. The detector (d) is millimeters away from the specimen. This configuration magnifies the specimen by a million X (r/d multiplied by a constant).

In due course, atoms from the surface ionize, exposing another layer of atoms under them. This process of field ionization continues until the specimen has been fully analyzed, and provides a 3D image of the entire specimen. In this technique, the specimen is the primary optic, so there are fairly stringent considerations for the conductivity, interface strength, and geometry of the specimen.