Conducting micro-and nanotubes and free-standing flexible helical microcoils have been fabricated from strained Ge x Si 1−x /Si heterolayers. The fabrication technique was based on self-rolling of a thin highly strained epitaxial Ge x Si 1−x /Si bifilm detached from the substrate by selective etching of a sacrificial layer in a roll-shaped tube. The obtained tube diameters varied from 10 nm to 13 µm, depending on the thickness and lattice mismatch of the GeSi/Si bilayer. GeSi/Si tubes and helical coils, up to 70 nm in diameter, exhibit good conducting properties and high mechanical strength.

We report on hybrid microtubes and rings fabricated from rolled-up strained metal–semiconductor SiGe/Si/Cr and metal–insulator–semiconductor SiGe/Si/SixNy/Cr films. For making suspended microtubes, a method of directional rolling of the patterned films by anisotropic underetching of silicon substrate was introduced. It is shown quantitatively that Cr and SixNy layers are highly strained, the tensile stress being sufficient to cause the rolling-up of the hybrid films into microtubes of preset diameter. The proposed controllable and reproducible technology is promising for fabricating cylindrical-shaped microcapacitors, induction coils, transistors, and building blocks of microelectromechanical devices.

Electromagnetic metamaterials opened the way to extraordinary manipulation of radiation. Terahertz (THz) and optical metamaterials are usually fabricated by traditional planar-patterning approaches, while the majority of practical applications require metamaterials with 3D resonators. Making arrays of precise 3D micro- and nanoresonators is still a challenging problem. Here we present a versatile set of approaches to fabrication of metamaterials with 3D resonators rolled-up from strained films, demonstrate novel THz metamaterials/systems, and show giant polarization rotation by several chiral metamaterials/systems. The polarization spectra of chiral metamaterials on semiconductor substrates exhibit ultrasharp quasiperiodic peaks. Application of 3D printing allowed assembling more complex systems, including the bianisotropic system with optimal microhelices, which showed an extreme polarization azimuth rotation of 85° with drop by 150° at a frequency shift of 0.4%. We refer the quasiperiodic peaks in the polarization spectra of metamaterial systems to the interplay of different resonances, including peculiar chiral waveguide resonance. Formed metamaterials cannot be made by any other presently available technology. All steps of presented fabrication approaches are parallel, IC-compatible and allow mass fabrication with scaling of rolled-up resonators up to visible frequencies. We anticipate that the rolled-up meta-atoms will be ideal building blocks for future generations of commercial metamaterials, devices and systems on their basis.

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Controllable formation and properties of solid single-crystal micro-and nanoshells of various shapes (tubes and spirals, vertically positioned rings and cylinders, and bent and trough-shaped cantilevers) are briefly reviewed, and new results are given. The shells and complicated structures of prescribed size and shape are formed with the use of elastic energy of initial strained SiGe/Si films of nanometer thickness and methods of highly selective and directed detachment of the films from the silicon substrates. It is experimentally demonstrated that the diameters of the fabricated SiGe/Si nanotubes are several times smaller than the values predicted by the continuum elasticity theory. The properties of the shells made of semiconductor and hybrid (metal-semiconductor and metal-dielectricsemiconductor) films and their applications in micro-and nanoscale electrical engineering are discussed.

of semiconductor technology, such as consecutive lithographic steps with layers alignment, and the deposition and chemical etching of materials, are used. Besides, for preventing the capillary sticking of 3D microstructures and nanostructures, special treatments of surfaces and the supercritical drying technique are used after liquid-etching and resistdevelopment steps. [15,16] In ref.[17], a method was proposed for fabrication of microhelices and nanohelices from elastically strained thin semiconductor strips detached, with the help of selective etching of a sacrificial layer, from the substrate and then rolled in classically shaped 3D helices. The latter approach, combined with supercritical drying, [16] was successively employed for forming, on a GaAs substrate, a chiral metamaterial in the form of a single-layer array of 14.5 µm diameter 3D microhelices fabricated from a strained hybrid semiconductor-metal (In 0.2 Ga 0.8 As/GaAs/Ti/Au) films. [18,19] It was shown that the maximum polarization-plane rotation angle for terahertz radiation having passed the heliceson-substrate system reached 17° at 2.1 THz frequency. A close value for the polarization-plane rotation angle of terahertz radiation, 14°, was also obtained using a structure that involved 3D metal gammadion-shaped elements located directly on the surface of pyramidal trenches etched in a silicon substrate. [20] Experimental data obtained for both chiral metamaterials proved a high effectiveness of the interaction of electromagnetic radiation with the 3D conducting microresonators, thus encouraging the workers to spent further efforts on the search for simpler and cheaper technological solutions.Today, rapid progress in the development of additive technologies [21,22] opens up wide opportunities in the field of 3D chiral resonator elements, 3D metamaterials, and photonic crystals. [23][24][25] A number of sequential 3D printing methods have enabled the point-by-point formation of free-standing conducting helices for chiral metamaterials active in a broad range of radiation wavelengths, from microwave (MW) to optical frequencies. Those methods can be classed to several groups. First, these are methods including the electrochemical and chemical deposition of metals onto the surface of printed 3D polymer structures: i) filling of helically shaped channels with a metal [9,26] and ii) covering of free-standing 3D helical microcarcasses with a metal. [27] Second, this is the growth of An original design for chiral metasurfaces formation is proposed. The hybrid fabrication approach is based on the 3D printing of polymer substrates with a shape-generating "helical" relief, molding, and subsequent shadow metal deposition. The formed double-layer grating of multiturn metal helices rotates the polarization plane of sub-terahertz and microwave radiation through an angle in excess of 40°. Both experimentally and in numerical simulations, it is demonstrated that re-reflection phenomena occur in the "metal helixpolymer substrate" hybrid structure. Those phenomena per...

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