Currently the synthesis of plasmonic nanoparticles for sensing applications mostly focuses on their shape because it is believed that nanoparticles with sharp tips provide higher sensitivities than those without. Herein, by measuring and analyzing the sensitivities of more than 74 types of nanoparticles of various shapes, sizes, and compositions, we found that, contrary to this common belief, the correlation between shape and sensitivity is much weaker than that between aspect ratio and sensitivity. Among all the parameters investigated here, including size, shape, composition, aspect ratio, crosssectional area, and initial plasmonic resonance frequency, the aspect ratio (R) is the key parameter that controls the nanoparticle sensitivity (S) following an empirical equation, S = 46.87R + 109.37. Other parameters have much less influence on the nanoparticle sensitivity to refractive index changes. The stronger dependence of the sensitivity on aspect ratio than on shape encourages us to reassess the current focus of nanoparticle synthesis chemistry. In addition, the S−R linear relationship determined here can be used as a design rule for future synthesis and fabrication of highly sensitive nanomaterials for chemical, biological, biomedical, and environmental sensing.

In-plane anisotropic two-dimensional (2D) materials, emerging as an intriguing type of 2D family, provide an ideal platform for designing and fabrication of optoelectronic devices. Exploring air-stable and strong inplane anisotropic 2D materials is still challenging and promising for polarized photodetection. Herein, SiP 2 , a 2D IV−V semiconductor, is successfully prepared and introduced into an in-plane anisotropic 2D family. The basic characterizations combined with theoretical calculations reveal 2D SiP 2 to exhibit an intrinsically low-symmetry structure, the in-plane anisotropy of phonon vibrations, and an anisotropically dispersed band structure. Moreover, the photodetector based on 2D SiP 2 exhibits high performance with a high detectivity of 10 12 Jones, a large light on/ off ratio of 10 3 , a low dark current of 10 −13 A, and a fast response speed of 3 ms. Furthermore, 2D SiP 2 demonstrates a high anisotropic photodetection with an anisotropic ratio up to 2. In addition, the polarization-sensitive photodetector presents a dichroic ratio of 1.6 due to the intrinsic linear dichroism. These good characteristics make 2D SiP 2 a promising candidate as an in-plane anisotropic semiconductor for high-sensitivity and polarized optoelectronic applications.

The in‐plane anisotropic feature of 2D layered materials has captured enormous research interest due to their application in polarization‐sensitive photodetection. Here, silicon phosphide (SiP), as a novel member of group IV–V 2D materials, is first introduced to the anisotropic 2D materials family with a high in‐plane anisotropy. The low‐symmetry structure, optical and optoelectronic properties are investigated systematically. Impressively, the photodetectors based on 2D SiP demonstrate high performance with low dark current, a fast response speed of 30 µs, and a strong anisotropic photoresponse with an anisotropic factor of 2.9. Furthermore, a strong polarization‐sensitive photodetector with a dichroic ratio up to 2.3 is realized based on the intrinsic linear dichroism of 2D SiP. This work not only provides an insight into the in‐plane anisotropic properties of 2D SiP, but also sheds light on its great potentials in anisotropic optoelectronic applications.

photonics and optoelectronics is the lack of materials with broad-band optical response and strong light-matter interaction. Therefore, it is an urgent need and many efforts have been devoted to searching for this kind of novel materials. [2][3][4][5] The broad-band optical response of 2D nanomaterial is related to the unique band structure and electronic properties. [1] Graphene exhibits a wide-spectral photonic response from ultraviolet to the radio-wave regimes owing to its gapless and conical-shape band structure. However, lack of intrinsic bandgap makes graphene-based devices suffer from relatively small on/off ratio, large dark current, and poor photo response. The relative low absorption and high non-saturable loss of graphene in optical response limit its extensive applications. [6][7][8][9] Following graphene, the most studied 2D transition metal dichalcogenides (TMDCs) possess a bandgap ranging from 1.0 to 2.0 eV, indicating their practical optoelectronic applications are not available in midinfrared (MIR) wavelength range. [10,11] After graphene and TMDCs, black phosphorus (BP), the most thermodynamically stable allotrope of phosphorus, has been thoroughly studied as a novel 2D layered material since early 2014. [12] It has triggered significant interests in both scientific research and potential electronic, optoelectronic, and biomedicine applications because of its unique and exotic properties. [13][14][15] Layered BP has a direct bandgap with layer-dependent variation over ≈0.3-2.0 eV, which gives rise to broad-band optical properties from visible to MIR region. The intrinsic layer-dependent direct bandgap gives rise to high on/off ratio and low dark current for electronic devices and makes BP an appropriate 2D material for MIR photonic applications. Moreover, the bandgap of BP can be efficiently tuned by electrical gating, which should pave the way for optoelectronic devices. [16] BP presents puckered structure with in-plane anisotropy, which results in specific dichroic optical properties of light absorption and photoluminescence. [17] However, easy oxidation under ambient environment is the biggest obstacle that significantly impedes its practical applications. [14,[18][19][20][21][22] Therefore, how to improve the long-term stability of BP has become a challenge.Germanium phosphide (GeP), a typical 2D group IV-V semiconductor, has attracted significant attention due to the advantages of higher thermodynamic stability than black phosphorus (BP), widely tunable bandgap, high carrier mobility, and in-plane anisotropy. However, its photonic and optoelectronic properties have not been extensively explored so far. Herein, large size and high-quality GeP single bulk crystal is successfully grown by flux method and stripped into 2D nanosheets with liquid phase exfoliation (LPE) and spin-coating methods. The broad-band photonic and optoelectronic properties of 2D GeP nanosheets are systematically investigated. First principles calculations are performed to verify its widely tunable bandgap from 0.43 eV f...

Despite the impressive progresses in terahertz (THz) sources and detection, there is still a big challenge for high performance active optoelectronic THz devices such as THz modulators. All‐optically controlled THz modulators with large modulation depth (MD) and wide modulation bandwidth are of great importance for the THz technology. Herein, a MoTe2/Si van der Waals (vdWs) heterostructure is rationally designed as all‐optical THz modulator by taking advantage of their similar band alignment and easy integration with Si complementary metal‐oxide‐semiconductor (CMOS). The MoTe2/Si modulator presents an ultrasensitive THz modulation performance with a MD of 99.9% under a low illumination power of 300 mW at 1064 nm. This is a record MD for TMDCs‐based all‐optically controlled THz modulators to date. Moreover, the MoTe2/Si modulator exhibits broadband modulation performance with a wide frequency range from 0.3 to 2.0 THz. The high modulation performance under low illumination power is beneficial for practical application with low energy consumption and easy heat dissipation, which is advantageous to modulator chip. This work validates a facile protocol for fabricating high performance THz modulators and paves the way for their practical applications in THz technology.