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Terahertz metamaterial sensing (TMS) is a new interdisciplinary technology. A TMS system employs terahertz waves as the pumping source, these then interact with the sample and carry the substance information, e.g., refractive index, absorption spectra. These properties are relevant to the molecular rotation and vibration states produced by a surface‐plasmon‐polariton‐like effect. TMS technology is usually characterized by large penetration depth and high sensitivity. Owing to these advantages, TMS may be used for ultratrace detection and consequently has a wide range of practical applications in biomedicine, food safety, environmental monitoring, industry and agriculture, material characterization, and safety inspection. Furthermore, TMS performance is determined not only by the structural topology of metamaterials, but also by their compositions and substrates. This paper reviews the essential fundamentals, relevant applications, and recent advances in TMS technology with a focus on the influence of material selection on TMS performance. This review is envisaged to be used as a key reference for developing TMS‐based functional devices with enhanced characteristics. [ABSTRACT FROM AUTHOR]

Simultaneous realization of high quality factor (Q), sensitivity, and figure of merit (FOM) play a pivotal role in building the THz sensor. For such purpose, we propose an all-polymeric Bloch surface wave (BSW) structure that supports a bright BSW mode and a dark surface Fano state that is embedded in the continuum, both of which coupled to the same radiation channels. The existence of the sharp dip with a maximum depth of Fano line could be interpreted with the physics of Friedrich–Wintgen bound states in the continuum (FW-BICs), because of the destructive interference between bright BSW and dark surface Fano modes. A strong angular- and frequency-dependent Q was found. Related influential factors to Q value may also include an asymmetric arrangement of top and grating layers, together with the weak coupling provided by photonic crystals. One numerically optimized design shows a quality factor Q of the Fano mode as 23,670, which is almost two orders higher than that in conventional metallic-metamaterial-based designs. The optimized sensitivity can numerically reach 4.34 THz/RIU in the frequency domain, which is one order higher than that reported in all-dielectric metasurfaces. We infer the high sensitivity is related to the phase-matching condition provided by near-subwavelength gratings. The associated FOM can reach 8857/RIU. Besides, the proposed design also numerically demonstrates high sensitivity in the angular domain ∼125.5°/RIU. Considering it poses no specific requirement for materials that own high contrast of permittivity in the THz regime, large interfacing area, the mechanical and chemical robustness offered by polymers and low cost in fabrication, such all-polymeric BSW structure that supports novel Fano resonance in THz window may give access to rich applications in hazardous gas detection and label-free bio-sensing. [ABSTRACT FROM AUTHOR]

In this report, the strong-dependence of low-frequency (terahertz) vibrational dynamics on weak and long-range forces in crystals is leveraged to determine the bulk magnetic configuration of iron phosphate – a promising material for cathodes in lithium ion batteries. We demonstrate that terahertz time-domain spectroscopy – coupled with quantum mechanical simulations – can discern between various spin configurations in FePO4. Furthermore, the results of this work unambiguously show that the well-accepted space group symmetry for FePO4 is incorrect, and the low-frequency spectroscopic measurements provide a clearer picture of the correct structure over the gold-standard of X-ray diffraction. This work opens the door for characterizing, predicting, and interpreting crystalline magnetic ordering using low-frequency vibrational spectroscopy. [ABSTRACT FROM AUTHOR]

Complementary split-ring resonator (CSRR) metasurfaces present interesting applications in terahertz biosensing. Indium tin oxide (ITO) is an essential optoelectronic material because of its optical transparency, high conductivity, and good stability. In this letter, we innovatively suggest that ITO-based CSRR metasurfaces can excite multi-peaks resonance in 0.1–2 THz by numerical simulation and experimental measurements. The multi-peak-resonance presents red-shift characteristics with the increasing external radius of the split-ring. The experimental results are in close agreement with the numerical values, which may indicate that the proposed ITO-based CSRR metasurfaces may play a significant role in visible terahertz biosensing applications. [ABSTRACT FROM AUTHOR]

Surface structuring is one of the most effective strategies for achieving water-repellent and self-cleaning surface properties of silicon surface. Here, through a silver nanoparticle-assisted HF/HNO3 etching process, we create a series of hierarchical silicon surface structures consisting of (110)-(100)-(110) oriented zigzag nanowires engraved in pyramids. The morphology of the hierarchical structure exhibits a strong dependence on the HNO3 concentration, which renders the hierarchical structures tunable and allows us to analyze the formation mechanism of the structures. The optimized hierarchical structure exhibits excellent superhydrophobic property, achieving a contact angle (CA) of 158° and CA hysteresis (CAH) of 1.2° without any surface treatment. The morphology-superhydrophobicity relation is systematically studied, based on which a microscopic model is proposed to describe how CA and CAH are affected by water penetration depth in the hierarchical structures. [ABSTRACT FROM AUTHOR]

A new star-shaped donor-acceptor molecule has been synthesized for application as the donor material in solution-processed bulk-heterojunction organic solar cells (OSCs). The molecule consists of a triphenylamine (TPA) unit as the core and a donor unit with three arms containing benzo[1,2,5]thiadiazole (BT) acceptor units and 5,5″-dihexyl-2,2′:3′,2″-terthiophene (tTh) end groups. The molecule, denoted S(TPA-BT-tTh), exhibits a broad absorption band in the wavelength range 300-650 nm and high hole mobility of 1.1×10 cm V s. An OSC device based on S(TPA-BT-tTh) as donor and [6,6]-phenyl C-butyric acid methyl ester (PCBM) as the acceptor (1:3, w/ w) exhibited a power conversion efficiency of 2.28% with a short circuit current density of 6.39 mA/cm under illumination of AM.1.5, 100 mW/cm. [ABSTRACT FROM AUTHOR]

A new two-dimensional-conjugated polymer (PBDTT3-TPA) containing benzodithiophene (BDT) and a side chain isolation comonomer is designed and synthesized. Interestingly, PBDTT3-TPA is compatible with higher lowest unoccupied molecular level (LUMO) acceptors of indene-C60 bisadduct (ICBA), and polymer solar cells based on PBDTT3-TPA/ICBA show an open-circuit voltage ( VOC) of ca. 0.80 V and a power conversion efficiency of 2.48% under AM1.5G illumination of at 100 mW cm−2. Furthermore, the energy loss in the corresponding fullerene acceptor devices is discussed, and the increase in the observed VOC is explained quantitatively by the up-shifted LUMO energy of ICBA (0.17 eV) and the reduced saturation current ( JSO) in the blends. [ABSTRACT FROM AUTHOR]

THz waves have interesting applications in refractive index sensing. A THz gas sensor based on the guided Bloch surface wave resonance (GBSWR) in a one-dimensional photonic crystal (1DPhC), which consists of periodic polycarbonate (PC) layers and polyvinylidene fluoride (PVDF) layers, has been proposed. Numerical results based on finite element method (FEM) show that the photonic band gap that confines Bloch surface waves (BSWs) lies in the regime of 11.54 to 21.43 THz, in which THz wave can transmit in both PC and PVDF with the ignored absorption. The calculated sensitivity of hazardous gas HCN in angle is found to be 118.6°/RIU (and the corresponding figure of merit (FOM) is 227) and the sensitivity in frequency is 4.7 THz/RIU (the corresponding FOM is 301.3). The proposed structure may also be used for monitoring hazardous gases which show absorption to the incident THz wave. Further results show that for N2O gas, the maximum sensitivity goes up to 644 (transmittance unit/ one unit of the imaginary part of the refractive index). The proposed design may find applications in the detection of dangerous gases. [ABSTRACT FROM AUTHOR]

Hybrid nanostructured silicon–organic solar cells have been pursued as a low‐cost solution for silicon photovoltaic devices. However, it is difficult for the organic semiconductor, typically poly(3,4‐ethylenedioxythiophene):polystyrene (PEDOT:PSS), to fully cover the nanostructured silicon surface due to the high surface tension of the polymer solution and the small size of the cavities in nanostructured silicon. As a result, the performance of the hybrid solar cells is limited by the defect‐induced surface recombination and poor hole extraction. In this work, an inorganic hole‐transporting layer, copper(I) thiocyanate (CuSCN), is introduced between silicon nanowire (SiNW) and PEDOT:PSS to improve the junction quality. The effect of CuSCN on as‐fabricated SiNW and tetramethylammonium hydroxide (TMAH)‐treated SiNW structures is examined, and it is shown that in both cases CuSCN can well cover the SiNW surface due to the easy penetration of its solution into the silicon nanostructure. As a result, the power conversion efficiency of the solar cells has been dramatically improved from 7.68% to 10.5% for as‐fabricated SiNW‐based‐hybrid cells, and from 10.75% to 12.24% for TMAH‐passivated SiNW‐based‐hybrid cells, suggesting that the double hole‐transporting layer approach can effectively improve the junction quality in hybrid organic‐nanostructured silicon‐based devices. An inorganic hole‐transporting layer, copper(I) thiocyanate (CuSCN), is introduced between silicon nanowire (SiNW) and poly(3,4‐ethylenedioxythiophene):polystyrene (PEDOT:PSS) to improve the junction quality. The power conversion efficiency of the solar cells has been dramatically improved 10.75–12.24%, suggesting that the double hole‐transporting layer approach can effectively improve the junction quality in hybrid organic‐nanostructured silicon based devices. [ABSTRACT FROM AUTHOR]