S. V. Golod

Freestanding SiGe/Si/Cr and SiGe/Si/SixNy/Cr microtubes

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.

Study of the properties of artificial anisotropic structures with high chirality

The chiral properties of an artificial anisotropic structure composed of microhelices are numerically simulated using the example of a sample developed by a team of authors from the Institute of Semiconductor Physics of the Russian Academy of Sciences. It is shown that this artificial structure can exhibit strong chiral properties in the THz range. Analytical expressions for the dielectric, magnetic, and chiral susceptibilities of the structure are derived on the condition of strong gyrotropy. The calculated values of the angle of the electromagnetic-wave polarization plane rotation and the circular dichroism are compared with the experimental results.

Manufacturing chiral electromagnetic metamaterials by directional rolling of strained heterofilms

We show that THz chiral metamaterials consisting of large regular arrays of metal–semiconductor microhelices can be manufactured from strained heterofilms by directional rolling. We also report the results of an experimental study of the electromagnetic properties of such arrays.

Comparison of various methods for transferring graphene and few layer graphene grown by chemical vapor deposition to an insulating SiO2/Si substrate

The objective of this study is to compare the results of transferring graphene and few layer graphene (FKG) up to 5 nm thick, grown by chemical vapor deposition (CVD) at a reduced pressure to a SiO2/Si substrate using four different polymer films. The chosen transfer methods are based on the most promising (according to published data) materials: polymethyl methacrylate, polydimethylsiloxane, thermoscotch, and polycarbonate. It is shown that the most promising transfer method (minimum resistance and maximum carrier mobility) lies in the use of polycarbonate thin films with their dissolution in chloroform. In this case, the following parameters are steadily obtained: the graphene and FLG resistance is 250–900 Ω/□ and the carrier mobility is 900–2500 cm2/(V s).

Investigation of electromagnetic properties of a high absorptive, weakly reflective metamaterial—substrate system with compensated chirality

In the present paper, a theoretical and experimental study of a highly absorptive, weakly reflective coating designed and fabricated on the basis of 3D THz resonant elements is reported. Transmission and reflection of electromagnetic waves from the metamaterial-substrate structure involving a highly absorptive, weakly reflective array of artificial bi-anisotropic elements were analyzed. The samples contained paired right-handed and left-handed helices, due to the fact that the chirality was compensated. The parameters of helices were optimized to achieve roughly identical values of dielectric permittivity and magnetic permeability. As a result, the metamaterial exhibited weak reflectivity in the vicinity of resonance frequency. On the other hand, effective resonance properties of the helices were tuned to ensure substantial absorption of THz radiation. Analytical expressions for the coefficients of radiation reflection and transmission in the samples were derived by solving a boundary-value problem for th...

Terahertz-range chiral metamaterials based on helices made of metal-semiconductor nanofilms

Chiral metamaterials of the terahertz range are formed by means of rolling of strained nanofilms. Structural elements of these metamaterials are metal-semiconductor microhelices. Resonant optical activity of new metamaterials in the terahertz range is demonstrated. Arrays of model wire helices are formed and tested in the microwave range.

Polarization rotation of THz radiation by an array of helices.

Novel approach to controlling polarization of THz radiation is introduced. Polarization plane rotation of transmitted wave by a monolayer of precise microhelices was demonstrated by experiments on the Novosibirsk free electron laser. It had strongly resonant character. Modulation of polarization opens up new possibilities in communication, biomedical, chemistry, security, imaging and spectroscopy applications.

Surface melting of copper during graphene growth by chemical vapour deposition

Evidence for the presence of a liquid phase on a copper surface during graphene growth by chemical vapour deposition at temperatures of 1000 and 1050 °C has been experimentally obtained. It was established that, first, the liquid phase forms a groove structure and bubble-like nanoobjects on the copper surface. Second, the liquid phase promotes the propagation of the wavy relief of a growing graphene film to the adjacent copper, and, third, the surface flows of the liquid phase can influence the waviness and orientation of the graphene islands. From the obtained data, it was concluded that surface melting plays an important role in graphene formation by chemical vapour deposition at temperatures below the melting point of copper.

Terahertz metamaterials and systems based on rolled-up 3D elements: designs, technological approaches, and properties

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.

Investigation of the properties of weakly reflective metamaterials with compensated chirality

The properties of an artificial anisotropic structure formed by microhelices have been numerically simulated by the example of a specially designed sample. The sample contains paired helices with right- and left-handed twisting directions, due to which the metamaterial chirality is compensated for. Helices are characterized by precalculated optimal parameters; as a result, the permittivity and permeability of metamaterial are approximately equal. Therefore, the wave impedance of the structure is close to the impedance of free space in the frequency range near 2 THz and the reflection of normally incident electromagnetic waves is weak. A boundary problem is solved and an analytical expression is obtained for the reflection and transmission coefficients of an electromagnetic wave passing through the structure. The simulated properties of the structure are compared with experimental results.