Consider how far it is from New York to Los Angeles. Now compare that distance to the length of the “l” in “Angeles”. That’s roughly how one meter compares to one nanometer.
A nanometer—one billionth of a meter—is a very small distance almost any way you look at it. One nanometer is about six times the width of a carbon atom. Distances of tens of nanometers are barely significant in much present-day technology, in which “identical” precision machine parts differ that much or more in size with little discernable effect on how well the machines work. But these tiny distances are becoming significant in the new field of nanotechnology --the study of manipulating matter on an atomic and molecular scale.
For some nanotechnical devices, the precise placement of each atom can be important, which is still a challenge for mass-producing them. On the other hand, some nanotechnical devices only require small size, without needing great precision in their atomic structure to perform their basic function, though their quality might improve if their atoms could be positioned reliably.
In one way current nanotechnology resembles the new laser technology of the mid-20th century—current nanotechnology has a few immediate uses, plus the potential to do many other revolutionary things if certain technical problems can be overcome. Recent nanotechnology patents available through the OSTI DOepatents database provide a sample of both the potential and the technical challenges. Some of these patents relate to actual nanometer-scale devices, while others focus on ways to make nanoscale structural elements.
One new nanoscale device (U.S. Patent 8,110,796)[DOepatents], a result of work at George Washington University in Washington, DC, is used to help control production of organic molecule and biomolecule samples so their masses can be measured by mass spectrometry. Laser light has long been used to desorb sample molecules from the surfaces of materials to be analyzed, but the number of molecules produced correlates only roughly with the energy of the laser pulse. The new device, a sample holder that has quasiperiodic structure with features measured in nanometers (similar to the laser wavelength), responds differently to different polarizations of the laser light, thus enabling control of the molecule production by controlling the incident laser pulses’ polarization.
Nanocrystals can be used as lasers themselves to amplify light. This has been problematic, though: if a nanocrystal is in a state in which it can amplify an incident photon, the state is either one that doesn't often last very long, limiting the opportunity to amplify a photon, or one in which the photon is about as likely to be absorbed as amplified. U.S. Patent 8,098,700,[DOepatents] based on research at Los Alamos National Laboratory, describes a way to prepare nanocrystals that avoids both problems.
Another device, recently patented by Lawrence Berkeley National Laboratory (U.S. Patent 8,120,448)[DOepatents] that doesn’t involve interaction with light, is a nanoscale high-frequency electromechanical oscillator. This is a common type of electronic component in a very small size. This device consists of a nanotube placed between source and drain electrodes and above a gate electrode. The nanotube has metal beads along its length that serve as adjustable clamps, so the nanotube segments between the beads have the widest vibrations. Frequencies are determined by the length of the vibrating segments, just as are the frequencies of strings in a musical instrument. This oscillator could be used to produce a regular electronic vibration at microwave frequencies.
U.S. Patent 8,093,474,[DOepatents] assigned to Lawrence Livermore National Laboratory, describes a method for making structures that are rather similar to those in the Lawrence Berkeley patent—nearly-equal sized metal spheres spaced regularly along nanowires—but with a quite different use in mind: data storage and retrieval. This patent envisions using electrical charges or their absence on the metal spheres to represent binary digits.
The nanowire-growing method described in the Lawrence Livermore patent produces structures that have some variation in the size of their components. Producing nanotubes to precise specifications is a problem addressed using several techniques described in different patents. Another U.S. patent based on Lawrence Berkeley National Laboratory research (number 8,093,494)[DOepatents] describes how to make nanotubes of particular sizes by accreting nanocrystals layer by layer, using masks to direct where the layers will form. A patent issued to Rice University (number 8,124,503)[DOepatents] describes a different way to control the diameter of growing carbon nanotubes by treating the catalyst particle on which the nanotube grows. Yet another approach, exemplified by a Northwestern University patent (number 8,110,125),[DOepatents] is to produce nanotubes in a wide range of sizes with both left- and right-handed chirality, and then sort them by size and handedness and pick out the ones you want. This avoids any need to modify the nanotubes in ways that could remove their useful properties.
U.S. Patent 8,119,571,[DOepatents] based on Oak Ridge National Laboratory research, tells how an ordered array of nanostructures incorporated into electronic devices can give the devices improved or enhanced performance, or even new properties. The fabrication methods described in the patent produce columns of nanodots or nanorods whose diameters are in the range of 2 to 100 nanometers, in arrays in which over 80% of the columns are aligned within 60 degrees of perpendicular to the device layer—a limited but possibly significant degree of ordering.
Early techniques for assembling nanocrystals into ordered arrangements have had their limitations. Examples include making the nanocrystals insoluble in water (a problem in using them, e.g., for biological imaging) or making the assembled structures weak or unstable. U.S. Patent 8,092,595,[DOepatents] which describes research results from Sandia National Laboratories, reports how to solve these problems by adding a solution of hydrophobic core material in an organic solvent to a surfactant-in-water solution, removing at least a portion of the organic solvent to form a micellar solution of nanocrystals, and then adding a coassembling material under specified reaction conditions to form an ordered nanocrystal array. The usefulness of the array depends on what sort of nanocrystals it is made from and how they are arranged.
One other patent (number 8,124,583)[DOepatents] deals with the use of nanofibers to produce large pieces of material for particular uses. Research at Northwestern University has led to a way to grow minerals uniformly on nanofiber bundles or gels. The key word here is “uniformly”. Under appropriate conditions, peptide-aphiphile nanofibers can induce hydroxyapatite crystals to grow on their surfaces much as collagen fibrils induce similar crystal growth in bone. Unless the growth is uniform, though, the crystals that form first inhibit the diffusion of reagents into the bundle or gel interior and preclude growth of a larger homogeneous structure. This is one of the technical problems that the invention solves, which makes it useful for such medical applications as bone or tooth regeneration in mammals, and for nonmedical applications like coating hard surfaces on substrates.
Prepared by Dr. William N. Watson, Physicist
DOE Office of Scientific and Technical Information