Generation of Tunable Terahertz Waves from Tailored Versatile Spintronic Meta-Antenna Arrays.

Broadband spintronic terahertz (THz) radiation can be efficiently generated by spin-to-charge current conversion in a ferromagnetic/nonmagnetic heterostructure. There had been many studies on realizing the enhancement or the modulation of spintronic terahertz waves. However, reported devices so far focus on implementing certain specific modulation methods, either related to the spintronic stacks or related to the metamaterial structures. In this study, a set of femtosecond laser-driven versatile spintronic terahertz devices are proposed by integrating meta-antenna structures with W/CoFeB/Pt nanolayer stacks. These monolithic integrated devices exhibit spintronic terahertz wave emission, spectral modulation, and polarization manipulation simultaneously. The terahertz pulses are generated within the ferromagnetic heterostructure interfaces and transmitted along the metallic structures, leading to the modulation of the spintronic terahertz waves. Results have shown that the center-frequency shift is up to 140 GHz and the value of ellipticity can reach 0.6, demonstrating a set of integrated and efficient spintronic terahertz devices to modulate the emitted wave. In addition, compared with the slotline antenna, the maximum peak value of the bandpass band is enhanced up to 1.63 times by carefully designing the metamaterial structure. The spintronic meta-antenna array proposed here paves an integrated way for the manipulation of spintronic terahertz optoelectronic devices.

Generation of tailored terahertz waves from monolithic integrated metamaterials onto spintronic terahertz emitters.

Recently emerging spintronic terahertz (THz) emitters, featuring many appreciable merits such as low-cost, high efficiency, ultrabroadband, and ease of integration, offer multifaceted capabilities not only in understanding the fundamental ultrafast magnetism physics but also for exploring multifarious practical applications. Integration of various flexible and tunable functions at the source such as polarization manipulation, amplitude tailoring, phase modulation, and radiation beam steering with the spintronic THz emitters and their derivatives can yield more compact and elegant devices. Here, we demonstrate a monolithic metamaterial integrated onto a W/CoFeB/Pt THz nanoemitter for a purpose-designed functionality of the electromagnetically induced transparency analog. Through elaborate engineering the asymmetry degree and geometric parameters of the metamaterial structure, we successfully verified the feasibility of monolithic modulations for the radiated THz waves. The integrated device was eventually compared with a set of stand-alone metamaterial positioning scenarios, and the negligible frequency difference between two of the positioning schemes further manifests almost an ideal realization of the proposed monolithic integrated metamaterial device with a spintronic THz emitter. We believe that such adaptable and scalable devices may make valuable contributions to the designable spintronic THz devices with pre-shaping THz waves and enable chip-scale spintronic THz optics, sensing, and imaging.

Near-field Terahertz Sensing of HeLa Cells and Pseudomonas Based on Monolithic Integrated Metamaterials with a Spintronic Terahertz Emitter.

Label-free biosensors operating within the terahertz (THz) spectra have helped to unlock a myriad of potential THz applications, ranging from biomaterial detection to point-of-care diagnostics. However, the THz wave diffraction limit and the lack of emitter-integrated THz biosensors hinder the proliferation of high-resolution near-field label-free THz biosensing. Here, a monolithic THz emission biosensor (TEB) is achieved for the first time by integrating asymmetric double-split ring resonator metamaterials with a ferromagnetic heterojunction spintronic THz emitter. This device exhibits an electromagnetically induced transparency window with a resonance frequency of 1.02 THz and a spintronic THz radiation source with a bandwidth of 900 GHz, which are integrated on a fused silica substrate monolithically for the first time. It was observed that the resonance frequency experienced a red-shift behavior with increasing concentration of HeLa cells and Pseudomonas because of the strong interaction between the spintronic THz radiation and the biological samples on the metamaterials. The spatial frequency red-shift resolution is ∼0.01 THz with a Pseudomonas concentration increase from ∼0.5 × 104 to ∼1 × 104/mL. The monolithic THz biosensor is also sensitive to the sample concentration distribution with a 15.68 sensitivity under a spatial resolution of 500 µm, which is determined by the infrared pump light diffraction limit. This TEB shows great potential for high-resolution near-field biosensing applications of trace biological samples.

Magnetic Cell Centrifuge Platform Performance Study with Different Microsieve Pore Geometries.

The detection and analysis of circulating tumor cells (CTCs) plays a crucial role in clinical practice. However, the heterogeneity and rarity of CTCs make their capture and separation from peripheral blood very difficult while maintaining their structural integrity and viability. We previously demonstrated the effectiveness of the Magnetic Cell Centrifuge Platform (MCCP), which combined the magnetic-labeling cell separation mechanism with the size-based method. In this paper, a comparison of the effectiveness of different microsieve pore geometries toward MCCP is demonstrated to improve the yield of the target cell capture. Firstly, models of a trapped cell with rectangular and circular pore geometries are presented to compare the contact force using finite element numerical simulations. The device performance is then evaluated with both constant pressure and constant flow rate experimental conditions. In addition, the efficient isolation of magnetically labeled Hela cells with red fluorescent proteins (target cells) from Hela cells with green fluorescent protein (background cells) is validated. The experimental results show that the circular sieves yield 97% purity of the target cells from the sample with a throughput of up to 2 µL/s and 66-fold sample enrichment. This finding will pave the way for the design of a higher efficient MCCP systems.