Tray Research Articles (Page 1)

The article proposes a model of friction of graphite, which is a stack of graphene sheets. The model is based on the thickness of the surface layer, which for graphite is 3 monolayers of graphene. Large internal stresses arise in the surface layer, leading to the occurrence of dislocations and nanocracks. The friction process can be described as a process of elastic-plastic deformation of the surface layer. For graphene, an important role in friction on graphite is played by the nanolayer, which is a quantum nanostructure. Graphene friction occurs in a stepwise manner, taking into account the Tamm states of the surface. It is shown that friction is accompanied by oscillatory and dissipative processes, the formation of a turbulent fragment, and self-organization in the form of Benard cells. A formula has been obtained that can serve as a criterion for selecting an antifriction coating made of graphene or its composites. The terahertz radiation we predicted in graphene refers to surface plasmon-polaritons (plasmons). The most promising approach to creating effective terahertz radiation detectors is the use of nanostructures as a sensitive element. These nanostructures include graphene and graphene-like materials. The proposed model opens a new approach for theoretical and experimental research of processes in nanotribology.

Abstract We have investigated the generation of plasma oscillations of photogenerated carriers contributing to the terahertz wave radiation in a GaAs layer structure by using pairs of ultrashort optical pulses. The frequency of the terahertz wave is increased under the condition that the two optical pulses were irradiated at the same time, which originates from the change in the plasma frequency due to effective increase in photogenerated carrier density. Moreover, the frequency changes even when there is no temporal overlapping of the optical pulses. This indicates that the populations of carriers excited at different times collectively perform the plasma oscillation.

Abstract A highly sensitive terahertz (THz) wave parametric upconversion detector was demonstrated based on KTiOPO 4 (KTP) crystal pumped by a nanosecond 1064-nm laser. The effects of pump energy on the detection sensitivity were studied in this experiment, where the upconversion signal and spontaneous noise were both amplified linearly with the increase of pump energy. The minimum detectable THz wave energy of 57.6 aJ was realized at 5.74 THz under higher pump energy, which gives the dynamic range of 104 dB and noise equivalent power (NEP) of 147.8 fW/Hz 1/2 . It was three orders of magnitude higher than that of bolometer. Moreover, a rapid-response detection in the THz frequency range of 5.24-6.14 THz was achieved. This THz parametric upconversion detector based on KTP crystal can provide a technical solution to achieve high-sensitive THz detection in a wide THz region.

Abstract This paper presents a comprehensive quantitative comparison between Terahertz (THz) communication and optical wireless communication (OWC) technologies, with a focus on indoor and outdoor deployment scenarios. For indoor environments, we compare THz and vertical-cavity surface-emitting laser (VCSEL)-based OWC systems by incorporating misalignment effects using a multi-ray THz channel model with antenna patterns and a Gaussian beam model for VCSELs. Unified beamwidth assumptions enable consistent evaluation. We further develop power consumption models capturing THz phase noise, VCSEL nonlinearities, and photodetector bandwidth-area tradeoffs, facilitating a detailed energy efficiency analysis under multi-transmitter coverage. For outdoor scenarios, we survey existing stochastic channel models that characterize path loss, pointing errors, and small-scale fading for both THz and free space optics (FSO) links. These models are applied to unmanned aerial vehicle (UAV)-based use cases to evaluate communication robustness under dynamic conditions. Our findings highlight critical performance tradeoffs and deployment challenges, offering insights into the relative advantages of THz and OWC technologies in diverse environments.

Chip-scale, electrically tunable, continuous-wave, coherent terahertz (THz) radiation sources are critical for emerging applications in sensing, imaging, spectroscopy, communications, space, and quantum technologies. Here, we demonstrate a robust source-on-a-chip THz emitter based on a layered high-temperature superconductor, engineered with an elliptical microcavity and capable of sustained coherent emission over an unprecedented operational lifetime exceeding 11 years. This compact THz source operates up to 60 K (with T c ≈ 90 K), delivering stable radiation in the 0.7–0.8 THz range, with on-chip electrical tunability from 100 GHz to 1 THz. Coherence arises from the phase-locked oscillation of intrinsic Josephson junction arrays, resonantly coupled to transverse electromagnetic modes within the cavity, analogous to a laser cavity, yielding collective macroscopic oscillations. THz emission remains detectable across an approximately 0.5-m free-space open-air link at room temperature. We analyse the cavity-mode structure and extract THz photon generation rates up to approximately 503 photons fs − 1 in cryogenic conditions and 50–260 photons ps − 1 over the air. These results demonstrate, for the first time, sustained and electrically tunable coherent THz emission from superconductors over multiyear timescales, defining another class of robust, chip-integrated THz lasers with applications in scalable THz and quantum technologies.

Abstract Metasurfaces composed of van der Waals materials exhibit extreme anisotropy and strong subwavelength confinement, enabling precise control of mid-infrared and terahertz waves for advanced photonic and optoelectronic applications. Among their intriguing phenomena, canalization – characterized by nearly diffraction-free propagation – offers significant potential for nanoscale light manipulation and enhanced light–matter interactions. Recently, gratings were demonstrated to induce synthetic transverse optical (STO) resonances, facilitating canalization perpendicular to the ribbon axis. In this study, we introduce a novel canalization mechanism by sandwiching a grating of hBN ribbons between graphene layers. The hybrid structure achieves orthogonal redirection of STO-induced canalization through the coupling plasmon polaritons in graphene and phonon polaritons in the hBN ribbons, achieving beam widths of approximately 300 nm (∼ λ 0 /20, where λ 0 is the free-space wavelength) across the spectral range of 1,470–1,510 cm −1 . Detailed analyses were conducted by varying graphene’s Fermi energy and geometric parameters, elucidating key field characteristics and spatial evolution of the canalization. Moreover, practical feasibility is demonstrated through simulated experimental antenna-launched excitation. Our finding holds promise for the development of polariton canalizations in diverse vdW material systems and facilitating on-chip photonic applications.

α-Sn has recently been attracting significant interest due to its unique electronic properties. However, alternative strategies to the conventional epitaxial growth on InSb to stabilize it at room temperature and the ability to manipulate its bandgap are still a challenge. In this work, a complementary metal oxide semiconductor (CMOS)-compatible process employing microwave irradiation is used to synthetize α-Sn nanoparticles (NPs) of different size on a Si substrate. Morphological characterizations suggest the possibility to control the average Sn NPs size by means of a combined dewetting and coalescence process induced by the microwaves on Sn films. Transmission Electron Microscopy (TEM) and Synchrotron Radiation-Grazing Incidence X-ray Diffraction (SR-GIXRD) analyses confirm the stabilization of the α-Sn phase within an oxide shell, while X-ray Photoelectron Spectroscopy (XPS) measurements allow tracking the oxide shell evolution and reveal the opening of a bandgap. Optical investigation demonstrates unprecedented tunability of the ultranarrow bandgap energy of α-Sn between 64 and 137 meV (15-35 THz). The observed bandgap modulation with NPs size is consistent with a quantum confinement effect, which suggests the proposed approach as an effective strategy for tuning the α-Sn bandgap and broadening its potential for a CMOS-compatible integration in next-generation terahertz technologies.

Unveiling the anisotropy and mechanism of magnetic alignment of graphene in polymer composites for efficient absorption of THz radiations (0.3–3.0 THz)

Twisted THz radiation from a prebunched relativistic electron beam using an ion channel guiding and helical magnetic wiggler

Terahertz sensing of trace analytes via weak value amplification.

Although terahertz (THz) metasurfaces based on bound states in the continuum (BIC) have garnered significant attention in biomedical applications, their technical implementation in high-sensitivity cancer cells detection remains a critical challenge. In this work, we present a THz biosensor employing dual split-ring resonator (DSRR) arrays quasi-bound states in the continuum (Q-BIC). Numerical simulations reveal a high-Q resonance dip at 2.35 THz with a detection sensitivity of 522 GHz/RIU. Experimentally, the performance was validated by detecting normal cells (murine splenocytes) and three cancer cell lines (LLC, LoVo, and MC38). In addition, analysis of cell type discrimination was achieved by integrating machine learning algorithms to project high dimensional spectral data into a low-dimensional space. This study establishes a label-free approach for long-term cellular monitoring, advancing THz technology as an innovative platform for practical biomedical applications.

Design and Analysis of 1-Bit and 2-Bit Coding Metamaterial for RCS Reduction in the Terahertz Band

Tunable Polarization Magnetooptical Effects at Scattering of Terahertz Radiation from Graphene Nanoribbon Gratings in a Magnetic Field

Magnetoplasmonic Effects Induced by Diffraction of Terahertz Waves on Magnetically Biased Graphene Metasurfaces

Bound states in the continuum (BICs) and exceptional points (EPs), as two distinct physical singularities represented by complex frequencies in non-Hermitian systems, have garnered significant attention and clear definitions in their respective fields in recent years. They share overlapping applications in areas such as high-sensitivity sensing and laser emission. However, the transition between the two, inspired by these intersections, remains largely unexplored. In this work, we reveal the transition process in a non-Hermitian two-mode system, evolving from one bound singularity to a two-dimensional exceptional ring, where the EP is the coalescent state of the quasi-Friedrich-Wintgen (FW)-BIC. This phenomenon is experimentally validated through pored dielectric metasurfaces in terahertz band. Furthermore, external pumping induced photocarriers as the dissipative perturbation, facilitates the breaking of degeneracy in the complex eigenfrequency and enables dynamic EP switching. Finally, we experimentally demonstrate a switchable terahertz beam deflection driven by the phase singularities of the EP. These findings are instrumental in advancing the development of compact devices for sensing and wavefront control within non-Hermitian systems.

Abstract Yellow organic crystals, like BNA, MNA, and NMBA, can be used to generate terahertz (THz) pulses of light through optical rectification of infrared ultrafast laser pulses. When producing THz with these organic crystals, one needs to consider that 1) their damage thresholds are low due to having low melting points and 2) Fresnel reflection losses due to multiple interfaces reduce the efficiency of the generated THz output. In this work, new heterogeneous multi‐layer “sandwich” structures are developed with these yellow organic crystals by 1) fusing them to sapphire plates to permit the crystal to withstand higher laser fluences and 2) using an index‐matching fluid (liquid crystal MBBA) to decrease Fresnel reflection losses and improve the THz output. It is shown that the sapphire plates increase the damage threshold of these yellow organic crystals by a factor of two or more, thus allowing the crystals to generate higher THz electric fields. Furthermore, it is shown that the THz light output efficiency increases by assembling the yellow crystals into multi‐layered sandwich structures. For some yellow organic crystals, the sandwich structures increase the THz intensity by more than a factor of two.

A two-dimensional electron gas (2DEG) forms at the interface of complex oxides like SrTi O 3 (STO) and LaTi O 3 (LTO), despite each material having a low native conductivity, as a band and a Mott insulator, respectively. The interface 2DEG hosts charge carriers with moderate charge carrier density and mobility that raised interest as a material system for applications like field-effect transistors or detectors. Of particular interest is the integration of these oxide systems in silicon technology. To this end we study the carrier dynamics in a STO/LTO/STO heterostructure epitaxially grown on Si(001) both experimentally and theoretically. Linear THz spectroscopy was performed to analyze the temperature dependent charge carrier density and mobility, which was found to be in the range of 10 12 c m − 2 and 1000 c m 2 V − 1 s − 1 , respectively. Pump-probe measurements revealed a very minor optical nonlinearity caused by hot carriers with a relaxation time of several 10 ps, even at low temperature. Density functional theory calculations with a Hubbard U term on ultrathin STO-capped LTO films on STO/Si(001) show an effective mass of 0.64–0.68 m e .

In this theoretical study, we have investigated the two-photon decay of a skew cosh-Gaussian laser (ω0,k0) into two electromagnetic waves (ω1 ,k1), and (ω2,k2), in a collisional magnetized plasma embedded with spherical-shaped nanoclusters, by considering a pre-existing Langmuir wave (ωr,kr) in the plasma. The external magnetic field Bs is oriented perpendicular to the electric field E0 of the skew cosh-Gaussian laser. The interaction of the high-power electric field of a skew cosh-Gaussian laser with the cloud of nanoclusters might have potential to exert a ponderomotive force on the plasma electrons and rapidly transform the nanoclusters into plasma balls, inducing oscillatory velocity to the electron cloud aligned with the electric field of the laser beam. The typical laser intensity is of the order of 1015 Wcm−2. The two-photon decay is enhanced due to the applied ambient magnetic field and strongly depends on the nanocluster plasmon resonance and the phase-matching conditions introduced through the pre-existing Langmuir wave. The resonance condition is achieved at ω0=0.574ωpe and resulting in the maximum growth rate. It is worth noting that the growth rate increases with increasing the skewness parameter and order of the skew cosh-Gaussian laser beam. The findings may be useful in plasma heating and terahertz radiation generation.

ABSTRACT It is of great importance to study the biological effects of terahertz (THz) waves on human cancer cells for their potential future applications in cancer therapy. However, only a few examples of distinct biological effects have been reported due to the lack of strong THz radiation sources. Here, we report our preliminary investigation using a strong THz source at 1.56 THz with an average power of ~ 10 W and an average intensity of ~129.1 mW/cm2 working at a repetition rate of 10 Hz for its macro pulses with duration of ~1 ms and micro pulse duration of ~ 1 ps at a repetition rate of 54.17 MHz from a THz free-electron laser to investigate its biological effects on breast cancer cells in vitro. We observed significant morphological changes in breast cancer cells after 2 hours irradiation and apoptosis after 3 hours irradiation. Most notably, after 4 hours irradiation, we observed obvious cytolysis and the disappearance of most breast cancer cells in the center of the THz beam spot. It is suggested that these biological effects could be attributed mainly to the non-thermal effect of the strong THz waves according to our separate experimental results on the morphological changes of the breast cancer cells induced solely by heat. Our results indicate the potential to leverage the apoptosis and cytolysis of cancer cells induced by strong THz waves for future cancer treatment applications.

Transient or time-resolved electron paramagnetic resonance spectroscopy (TR EPR) is a powerful method for studying various photogenerated paramagnetic species. The use of low-energy quanta, such as terahertz (THz) radiation, as an external stimulus in TR EPR allows the initiation of spin dynamics without generating new paramagnetic species other than those already present in the system. This spin dynamic reflects the return of the system to thermodynamic equilibrium, governed by a spin-lattice relaxation time, T1. The latter, together with a phase memory time, is of paramount importance for the practical implementation of single-molecule magnets and molecular spin qubits. In this work, we present TR EPR spectroscopy with pulsed heating by THz pulses as a versatile spectroscopic method for determining T1 in a wide range of paramagnetic systems. To define the scope of the method, we developed a numerical model based on the Liouville-von Neumann equation, with the equilibrium density matrix defined by the temperature profile of the lattice. Using experimental data obtained for [CoTp2] (cobalt(II) bis[tris(pyrazolyl)borate]) with S = 3/2, we compared the proposed method with two other commonly used techniques: alternating current (AC) magnetometry and pulsed EPR. All three methods were found to be in qualitative agreement and provided complementary information about the relaxation properties. TR EPR spectroscopy showed the orientation dependence of T1. AC magnetometry revealed the dependence of T1 on the value of the external magnetic field, which was attributed in the literature to a field-induced Raman process. Finally, pulsed EPR spectroscopy was found to be biased by strong spectral diffusion.