Creating and studying nanostructures with controlled sizes and prescribed properties are among the most urgent problems. Their solution is expected to trigger revolutionary changes in nanoelectronics, nanomechanics, biology, medicine, material science, and other fields of science.
At the Rzhanov Institute of Semiconductor Physics of the Siberian Branch of the Russian Academy of Sciences (ISP SB RAS), the research team headed by V. Ya. Prints, doctor of physics and mathematics, has developed a unique precision technology for creating three-dimensional nanostructures and nanosystems, which provides molecular-scale accuracy of production of semiconductor, metallic, and hybrid nanostructures.
Grown in vacuum
The technical basis for the new technology is the process of molecular-beam epitaxy, controlled layer-by-layer deposition of atoms in superhigh vacuum. This process allows growing complex heterostructures, which are uniform over the area, from various substances with extremely high, atomic-scale accuracy, monolayer by monolayer.
The nanoobjects proper are formed at the next stage with the use of selective etching of a specially created so-called sacrificial layer in this heterostructure resembling a sandwich. As this layer is removed, elastic forces make a thin two-layer film roll into a nanotube.
This method can be used to obtain nanoshells of versatile shapes: tubes, spirals, rings, hemispheres, and periodic nanocorrugated structures. The authors of this technology believe this is the only possible method for creating such a variety of nanoobjects with a certain atomic structure.
To date, nanotubes of semiconductor materials employed to study the properties of a two-dimensional electron gas on cylindrical surfaces and tubes with a micron-scale diameter to be used as micro- and nanosyringes in cell biology and medicine have been produced. Hot-wire anemometers based on tubes with nanometer thickness of the walls are more sensitive than conventional gauges for gas flow in terms of measuring velocity fluctuations in turbulent flows, and have a faster response speed.
On the way to cap of darkness
The high quality of the grown heterostructures provides curved and rolled nanostructures, including shells up to several centimeters long, with atomically smooth walls uniform in thickness. The method for the formation of curved and rolled heterostructures can be readily matched with the technology of microchip production. Moreover, using the methods of controlled directional bending and rolling, which were developed at the Institute, it is possible to create many objects with different configurations on one substrate and to assemble three-dimensional structures based on the interaction between the rolling objects.
For this purpose, multilayer structures containing several bilayers separated by sacrificial layers are grown by the method of molecular beam epitaxy. Etching produces periodic arrays of bound three-dimensional structures filling the entire substrate surface. Such micro- and nanostructures are the basis for creating principally new two-dimensional and three-dimensional chiral (optically active) materials.
In 2006, scientists from the UK and US demonstrated a negative refraction index and invisibility of objects located behind such a metamaterial for gigahertz wavelengths. Based on an array of such nanoshells, the Institute pioneered in creating an artificial optically active medium for terahertz wavelengths; materials with a negative refraction index necessary to create invisible screens, superlenses, and other unique devices are under development. The authors of the technology believe that their technique offers a transition to shorter wavelengths, down to the optical range.
This is a direct path to the realization of the long-term dream of the humankind about a cap of darkness. Apparently, it should not be long before the implementation of this dream, since more than 20 leading institutes worldwide work on the basis of the technology first developed at the Novosibirsk Academgorodok.
Unfortunately, it is next to impossible to ensure conditions for obtaining extremely pure, perfect, and uniform-over-the-area multilayer heterostructures on the Earth. A principal technological breakthrough in creating more perfect nanoobjects for facilities of molecular beam epitaxy may be transportation of these facilities to outer space.
High vacuum formed using the molecular screen effect near orbital stations will provide nanostructures of a much better quality. The idea of bringing such technological facilities to outer space seems fantastic, but it has a good chance to become realistic in the near future.