2D materials towards ultrafast photonic applications

Zhang L., Fahad S., Wu H., Dong T., Chen Z., Zhang Z., Liu R., Zhai X., Li X., Fei X., Song Q., Wang Z., Chen L., Sun C., Peng Y., et. al.

We developed a size-controlled intercalation method to prepare Sb nanosheets. A distinct size-dependent nonlinear optical response, unveiling the strong influence of the scale of the Sb nanosheets on the carrier dynamics was observed.

Liu M., Wei Z., Luo A., Xu W., Luo Z.

Abstract Due to the exotic electronic and optical properties, two-dimensional (2D) materials, such as graphene, topological insulators, transition metal dichalcogenides, black phosphorus, MXenes, graphitic carbon nitride, metal-organic frameworks, and so on, have attracted enormous interest in the scientific communities dealing with electronics and photonics. Combing the 2D materials with the microfiber, the 2D material-decorated microfiber photonic devices could be assembled. They offer the advantages of a high nonlinear effect, all fiber structure, high damage threshold, and so on, which play important roles in fields of pulse shaping and all-optical signal processing. In this review, first, we introduce the fabrication methods of 2D material-decorated microfiber photonic devices. Then the pulse generation and the nonlinear soliton dynamics based on pulse shaping method in fiber lasers and all-optical signal processing based on 2D material-decorated microfiber photonic devices, such as optical modulator and wavelength converter, are summarized, respectively. Finally, the challenges and opportunities in the future development of 2D material-decorated microfiber photonic devices are given. It is believed that 2D material-decorated microfiber photonic devices will develop rapidly and open new opportunities in the related fields.

Huang Z., Ma B., Wang H., Li N., Liu R., Zhang Z., Zhang X., Zhao J., Zheng P., Wang Q., Zhang H.

Two-dimensional (2D) CsPb2Br5 exhibits intriguing functions in enhancing the performance of optoelectronic devices in terms of environmental stability and luminescence properties when composited with other perovskites in different dimensionalities. We built a type I three-dimensional (3D) CsPbBr3/2D CsPb2Br5 heterojunction through phase transition where CsPbBr3 quantum dots in situ grew into 2D CsPb2Br5. A thorough growth mechanism study in combination with excited state dynamic investigations via femtosecond spectroscopy and first-principles calculations revealed that the type I hierarchy enhanced the stability of the heterojunction and spurred its luminous quantum yield by prolonging the lifetime of photogenerated carriers. Mixing the heterojunction with other phosphors yielded white-light-emitting diodes with a color rendering index of 94%. The work thus not only offered one new avenue for building heterojunctions by using the "soft crystal" nature of perovskites but also disentangled the enhanced luminescence mechanism of the heterojunction that can be harnessed for promising applications in the luminescence and display fields.

Xiao Q., Li X., Zhang Z., Hu C., Dun G., Sun B., Peng Y., Wang Q., Zheng Z., Zhang H.

Zhai X., Huang Y., Feng Z., Zhang X., Wang Q.

All-inorganic metal halide perovskites are a new emerging star following organometallic halide perovskites, thanks to their outstanding optoelectronic properties and relatively higher stability at the same time. Our group has contributed in this field through developing novel fabrication methods for perovskite micro/nano crystals, cesium lead halide perovskite quantum dots (CsPbX3 QDs) in particular, and investigating their photoinduced excited-state dynamics via various time-resolved spectroscopic techniques. Therefore in this chapter, we focus on the review of (nonlinear) optical properties and dynamics of CsPbX3 QDs. The chapter is organized as the followings: immediately after Sect. 6.1 of Introduction, Sect. 6.2 summarizes current preparation methods and focuses on mechanosynthesis (ball milling technique strategy), a methodology we are among the earliest groups to advocate. Section 6.3 details the photoinduced excited-state dynamics of perovskite QDs as fast as femtosecond (fs) scale, through different time-resolved spectroscopic tools including fluorescence lifetime measurement, fs transient absorption spectroscopy, streak camera, etc. Section 6.4 reviews the applications of CsPbX3 QDs stemming from their unique optical/electronic properties: optoelectronic devices, photocatalysis, nanolasers, and particularly nonlinear optics. The final Sect. 6.5 is Perspectives, which gives the thoughts for the future trend of the field from the authors. To sum up, all-inorganic perovskite QDs have thrived in the optoelectronic field. Numerous new experimental findings and applications of them are springing up every day. As an exciting new territory, there is much to be explored through joint efforts of researchers from varied background of physics, chemistry, optics, electronics, engineering, etc., through employing powerful methodologies like ultrafast spectroscopy.

Wang Z., Sun H., Zhang Q., Feng J., Zhang J., Li Y., Ning C.

Semiconductors that can provide optical gain at extremely low carrier density levels are critically important for applications such as energy efficient nanolasers. However, all current semiconductor lasers are based on traditional semiconductor materials that require extremely high density levels above the so-called Mott transition to realize optical gain. The new emerging 2D materials provide unprecedented opportunities for studying new excitonic physics and exploring new optical gain mechanisms at much lower density levels due to the strong Coulomb interaction and co-existence and mutual conversion of excitonic complexes. Here, we report a new gain mechanism involving charged excitons or trions in electrically gated 2D molybdenum ditelluride well below the Mott density. Our combined experimental and modelling study not only reveals the complex interplay of excitonic complexes well below the Mott transition but also establishes 2D materials as a new class of gain materials at densities 4–5 orders of magnitude lower than those of conventional semiconductors and provides a foundation for lasing at ultralow injection levels for future energy efficient photonic devices. Additionally, our study could help reconcile recent conflicting results on 2D materials: While 2D material-based lasers have been demonstrated at extremely low densities with spectral features dominated by various excitonic complexes, optical gain was only observed in experiments at densities several orders of magnitude higher, beyond the Mott density. We believe that our results could lead to more systematic studies on the relationship between the mutual conversion of excitonic species and the existence of optical gain well below the Mott transition. A new mechanism for amplifying optical signals in two-dimensional semiconductors could be used to develop nano-sized lasers with little input power. When high-energy photons strike a semiconductor they produce excitons – pairs comprising an excited electron and the positively-charged ‘hole’ that it leaves behind, or even trions - states comprising two electrons and one hole, or one electron and two holes. However, scientists have so far limited understanding of the many exotic exciton states that can exist and mutually convert. Cun-Zheng Ning at Tsinghua University in Beijing and co-workers studied ultra-thin single and dual layers of molybdenum ditelluride, and observed a complex interplay between excitons and trions. The trion states enabled the system to show optical gain – a vital property for lasers - despite being orders of magnitude below the so-called Mott transition density, a minimum condition for optical gain in conventional semiconductors.

Liu W., Liu M., Liu X., Wang X., Deng H., Lei M., Wei Z., Wei Z.

Gao L., Li C., Huang W., Mei S., Lin H., Ou Q., Zhang Y., Guo J., Zhang F., Xu S., Zhang H.

2D transition metal carbides or nitrides, known as MXenes, are a new family of 2D materials with close to 30 members experimentally synthesized and dozens more theoretically investigated. Because o...

Guo X., Liu R., Hu D., Hu H., Wei Z., Wang R., Dai Y., Cheng Y., Chen K., Liu K., Zhang G., Zhu X., Sun Z., Yang X., Dai Q.

All-optical modulators are attracting significant attention due to their intrinsic perspective on high-speed, low-loss, and broadband performance, which are promising to replace their electrical counterparts for future information communication technology. However, high-power consumption and large footprint remain obstacles for the prevailing nonlinear optical methods due to the weak photon-photon interaction. Here, efficient all-optical mid-infrared plasmonic waveguide and free-space modulators in atomically thin graphene-MoS2 heterostructures based on the ultrafast and efficient doping of graphene with the photogenerated carrier in the monolayer MoS2 are reported. Plasmonic modulation of 44 cm-1 is demonstrated by an LED with light intensity down to 0.15 mW cm-2 , which is four orders of magnitude smaller than the prevailing graphene nonlinear all-optical modulators (≈103 mW cm-2 ). The ultrafast carrier transfer and recombination time of photogenerated carriers in the heterostructure may achieve ultrafast modulation of the graphene plasmon. The demonstration of the efficient all-optical mid-infrared plasmonic modulators, with chip-scale integrability and deep-sub wavelength light field confinement derived from the van der Waals heterostructures, may be an important step toward on-chip all-optical devices.

Shi H., Li M., Shaygan Nia A., Wang M., Park S., Zhang Z., Lohe M.R., Yang S., Feng X.

Because of its thickness-dependent direct bandgap and exceptional optoelectronic properties, indium(III) selenide (In2 Se3 ) has emerged as an important semiconductor for electronics and optoelectronics. However, the scalable synthesis of defect-free In2 Se3 flakes remains a significant barrier for its practical applications. Here, a facile electrochemical strategy is presented for the ultrafast delamination of bulk layered In2 Se3 crystals in nonaqueous media, resulting in high-yield (83%) production of defect-free In2 Se3 flakes with large lateral size (up to 26 µm). The intercalation of tetrahexylammonium (THA+ ) ions mainly creates stage-3 intercalated compounds in which every three layers of In2 Se3 are occupied by one layer of THA molecules. The subsequent exfoliation leads to a majority of trilayer In2 Se3 nanosheets. As a proof of concept, solution-processed, large-area (400 µm × 20 µm) thin-film photodetectors embedded with the exfoliated In2 Se3 flakes reveal ultrafast response time with a rise and decay of 41 and 39 ms, respectively, and efficient responsivity (1 mA W-1 ). Such performance surpasses most of the state-of-the-art thin-film photodetectors based on transition metal dichalcogenides.

Marcaud G., Serna S., Panaghiotis K., Alonso-Ramos C., Le Roux X., Berciano M., Maroutian T., Agnus G., Aubert P., Jollivet A., Ruiz-Caridad A., Largeau L., Isac N., Cassan E., Matzen S., et. al.

Nonlinear all-optical technology is an ultimate route for the next-generation ultrafast signal processing of optical communication systems. New nonlinear functionalities need to be implemented in photonics, and complex oxides are considered as promising candidates due to their wide panel of attributes. In this context, yttria-stabilized zirconia (YSZ) stands out, thanks to its ability to be epitaxially grown on silicon, adapting the lattice for the crystalline oxide family of materials. We report, for the first time to the best of our knowledge, a detailed theoretical and experimental study about the third-order nonlinear susceptibility in crystalline YSZ. Via self-phase modulation-induced broadening and considering the in-plane orientation of YSZ, we experimentally obtained an effective Kerr coefficient of n^2YSZ=4.0±2×10−19  m2·W−1 in an 8% (mole fraction) YSZ waveguide. In agreement with the theoretically predicted n^2YSZ=1.3×10−19  m2·  W−1, the third-order nonlinear coefficient of YSZ is comparable with the one of silicon nitride, which is already being used in nonlinear optics. These promising results are a new step toward the implementation of functional oxides for nonlinear optical applications.

Lu Y., Chen J., Chen T., Shu Y., Chang R., Sheng Y., Shautsova V., Mkhize N., Holdway P., Bhaskaran H., Warner J.H.

A chemical vapor deposition method is developed for thickness-controlled (one to four layers), uniform, and continuous films of both defective gallium(II) sulfide (GaS): GaS0.87 and stoichiometric GaS. The unique degradation mechanism of GaS0.87 with X-ray photoelectron spectroscopy and annular dark-field scanning transmission electron microscopy is studied, and it is found that the poor stability and weak optical signal from GaS are strongly related to photo-induced oxidation at defects. An enhanced stability of the stoichiometric GaS is demonstrated under laser and strong UV light, and by controlling defects in GaS, the photoresponse range can be changed from vis-to-UV to UV-discriminating. The stoichiometric GaS is suitable for large-scale, UV-sensitive, high-performance photodetector arrays for information encoding under large vis-light noise, with short response time (

Xiao Q., Hu C., Wu H., Ren Y., Li X., Yang Q., Dun G., Huang Z., Peng Y., Yan F., Wang Q., Zhang H.

An effective solution to scalable exfoliation of large lateral sized antimonene nanosheets is developed. Flexible photodetectors based on hybrid structure of surface modified few layer antimonene exhibited excellent performance.

Jiang T., Yin K., Wang C., You J., Ouyang H., Miao R., Zhang C., Wei K., Li H., Chen H., Zhang R., Zheng X., Xu Z., Cheng X., Zhang H.

The year 2019 marks the 10th anniversary of the first report of ultrafast fiber laser mode-locked by graphene. This result has had an important impact on ultrafast laser optics and continues to offer new horizons. Herein, we mainly review the linear and nonlinear photonic properties of two-dimensional (2D) materials, as well as their nonlinear applications in efficient passive mode-locking devices and ultrafast fiber lasers. Initial works and significant progress in this field, as well as new insights and challenges of 2D materials for ultrafast fiber lasers, are reviewed and analyzed.

Zhang B., Liu J., Wang C., Yang K., Lee C., Zhang H., He J.

Ilyas M., Khan M.A., Xiong L., Zhang L., Lauqman M., Abbas M., Zohaib H.M., Manurkar N., Li H.

A chiral cobalt coordination complex {[Co(GMP)(BPE)(H2O)3]·9H2O}n (1) has been studied and characterized by X-ray single crystal and powder diffraction.

Zhao X., Wang H., Zhou J.

Light‐induced topological phase transition and electric current generation have been receiving tremendous attention recently. In the current work, first‐principles calculations are used to investigate an experimentally fabricated material family, 1T′ Janus transition metal dichalcogenide monolayers. It is shown that under time‐periodic light field pump, these materials could exhibit twice of topological phase transition, yielding quantum anomalous Hall states with Chern number of ±2 under an intermediate light intensity. Furthermore, such a pump light could simultaneously generate a static direct current that flows in the plane. Under such a transient phase transition, the dielectric function shows contrasting behaviors. It is also suggested that such topological phase transitions can be detected using a weak probe light to generate bulk photovoltaic effect. This is a second‐order nonlinear optical response, and both intrinsic shift current and extrinsic injection current would emerge, which can be separated depending on their flow direction. With these theoretical and computational results, an all‐optical strategy to control and detect the ultrafast quantum anomalous Hall transitions is predicted.

Stefanucci G., Perfetto E.

The ultrafast conversion of coherent excitons into incoherent excitons, as well as the subsequent exciton diffusion and thermalization, are central topics in current scientific research due to their relevance in optoelectronics, photovoltaics and photocatalysis. Current approaches to the exciton dynamics rely on model Hamiltonians that depend on already screened electron-electron and electron-phonon couplings. In this work, we subject the state-of-the-art methods to scrutiny using the ab initio Hamiltonian for electrons and phonons. We offer a rigorous and intuitive proof demonstrating that the exciton dynamics governed by model Hamiltonians is affected by an overscreening of the electron-phonon interaction. The introduction of an auxiliary exciton species, termed the irreducible exciton, enables us to formulate a theory free from overscreening and derive the excitonic Bloch equations. These equations describe the time-evolution of coherent, irreducible, and incoherent excitons during and after the optical excitation. They are applicable beyond the linear regime, and predict that the total number of excitons is preserved when the external fields are switched off.

Hidding J., Cordero-Silis C.A., Vaquero D., Rompotis K.P., Quereda J., Guimarães M.H.

Zhang B., Wu J., Wang Q., Wang S., Zhou P., Han L.

Kumar R., Khera M., Garg S., Goel N.

Sirohi S., Narayanan S., Bisht P.B.

Hu L., Gao C., Du S., Guo Y., Li J., Yang C., Zhang X., Yin Z., Zhang L., Gu C.

Qin L., Tian H., Li C., Xie Z., Wei Y., Li Y., He J., Yue Y., Ren T.

AbstractWith field effect transistor (FET) sustained to downscale to sub‐10 nm nodes, performance degradation originates from short channel effects (SCEs) degradation and power consumption increment attributed to inhibition of supply voltage (VDD) scaling down proportionally caused by thermionic limit subthreshold swing (SS) (60 mV dec−1) pose substantial challenges for today's semiconductor industry. To further sustain the Moore's law life, incorporation of new device concepts or new materials are imperative. 2D materials are predicted to be able to combat SCEs by virtue of high carrier mobility maintainability regardless of thickness thinning down, dangling bonds free surface and atomic thickness, which contributes to super gate electrostatic controllability. To overcome increasing power dissipation problem, new device structures including negative capacitance FET (NCFET), tunnel FET (TFET), dirac source FET (DSFET) and the like, which show superiority in decreasing VDD by lowering SS below thermionic limit of 60 mV dec−1 have been brought out. The combination of 2D materials and ultralow steep slope device structures holds great promise for low power‐dissipation electronics, which encompass both suppressed SCEs and reduced VDD simultaneously, leading to improved device performance and lowered power dissipation.

Song S., Rahaman M., Jariwala D.

Suk S.H., Seo S.B., Cho Y.S., Wang J., Sim S.

Abstract Two-dimensional (2D) layered materials exhibit strong light-matter interactions, remarkable excitonic effects, and ultrafast optical response, making them promising for high-speed on-chip nanophotonics. Recently, significant attention has been directed towards anisotropic 2D materials (A2DMs) with low in-plane crystal symmetry. These materials present unique optical properties dependent on polarization and direction, offering additional degrees of freedom absent in conventional isotropic 2D materials. In this review, we discuss recent progress in understanding the fundamental aspects and ultrafast nanophotonic applications of A2DMs. We cover structural characteristics and anisotropic linear/nonlinear optical properties of A2DMs, including well-studied black phosphorus and rhenium dichalcogenides, as well as emerging quasi-one-dimensional materials. Then, we discuss fundamental ultrafast anisotropic phenomena occurring in A2DMs, such as polarization-dependent ultrafast dynamics of charge carriers and excitons, their direction-dependent spatiotemporal diffusion, photo-induced symmetry switching, and anisotropic coherent acoustic phonons. Furthermore, we review state-of-the-art ultrafast nanophotonic applications based on A2DMs, including polarization-driven active all-optical modulations and ultrafast pulse generations. This review concludes by offering perspectives on the challenges and future prospects of A2DMs in ultrafast nanophotonics.

Balaji V.R., Ibrar Jahan M.A., Sridarshini T., Geerthana S., Thirumurugan A., Hegde G., Sitharthan R., Sundar Dhanabalan S.

In this paper, a novel 2D Photonic Crystal (PC)-based cancer biosensor is proposed for the detection of different types of cancer cells HeLa, PC12, MDA, MCF, and Jurkat. The sensor is designed using Silicon-on-insulator (SOI) substrate in a triangular lattice with holes in the slab. The proposed design is optimized to provide a high-quality factor of 15,000, high sensitivity and a low detection limit that are highly effective in cancer detection. Proposed biosensor uses a series of resonant cavities that slice the resonant wavelength to a high peak resonant wavelength with a spectral linewidth of 0.1 nm. The integration of 2D PC biosensors with machine learning techniques for early and accurate cancer detection is optimized for the data set. The performance analysis of Multiple Linear Regression (MLR) and Support Vector Machine (SVM) is studied by repeating training, testing, and optimization of target values (Resonant Wavelength) with dependent and independent features of a 2D PC biosensor system. The SVM model provides an R squared value of 0.99 for the biosensor, and the MLR model gave an R squared value of 0.88. The SVM model provides excellent accuracy in predicting the target values with all the trained input features of a 2D PC biosensing system.

Mao M.X., Fang Y., Wei H., Huang Z., Xu H.

Abstract Multilayer graphene and black phosphorus films exhibit strong nonlinearity under voltage modulation. In this paper, according to the nonlinear characteristics of graphene and black phosphorus, the frequency doubling characteristics of graphene and black phosphorus are introduced, and the nonlinear SDD model of graphene is established in EDA, and the simulation results are basically consistent with the measured results. Under the regulation of DC bias voltage, the second harmonic output power of both graphene frequency doubler and black phosphorus frequency doubler is larger than their third harmonic output power when the operating frequency is 800–1100 MHz. The experimental results show that the minimum conversion loss of the black phosphorus multiplier is 24.22 dB when the input voltage is 0.9 V and the input power is 12 dBm, and the minimum conversion loss of the graphene multiplier is 32.15 dB when the input voltage is 1.6 V. The experimental results show that the conversion loss of the black phosphorus multiplier is better than that of the graphene multiplier, and the conversion efficiency is higher.

Kumar V., Mishra R.K., Jeon H., Kumar P., Ahuja R., Gwag J.S.

Anisotropic dielectric and optical properties of two-dimensional (2D) calcium and magnesium difluorides were investigated in the vacuum ultraviolet (VUV) region of the electromagnetic spectrum (EM) using the first principles density functional theory (DFT). The anisotropy between the in-plane and out-of-plane directions shows that these materials are uniaxial, exhibiting optical and dielectric anisotropy. The optical functions of these anisotropic materials-optical absorption, photoconductivity, refractive index, reflection and extinction coefficients, and electron energy loss (EEL) spectra-are calculated in the framework of DFT. The low refractive index values and relatively small extinction coefficient make these materials alternative low-index 2D materials for the long wavelengths in the VUV region of the EM spectrum. The reflection and transmission spectra indicate the antireflective property of these materials. The calculated EEL function shows less energy loss of fast-traveling electrons in the material's medium. The maxima in the EEL spectrum are the main feature of plasma oscillations. The dissipation in the incident light radiation energy propagating through the dielectric medium is estimated with the dielectric loss tangent (tanδ). The magnesium difluoride is identified as a less dielectric loss medium than calcium difluoride in the VUV region. The present results suggest that these 2D materials are promising in low refractive index, high reflective, and antireflective coating materials in optoelectronic device applications. Also, electronic studies revealed that these are excellent materials for gate insulators in field-effect transistors based on 2D electronic materials.

Shang W., Wang B., Wang Q.

The development of efficient optical limiters to protect the human eyes and optoelectronic sensors is of great importance. Under this context, optical limiting based on the third-order nonlinearity has become one promising strategy. This chapter reviews the representative two-dimensional (2D) materials such as graphene, transition metal sulfide and black phosphorus for laser protection. We start with the introduction of typical nonlinear optical limiting mechanism including reverse saturable absorption (RSA), two-photon absorption/multiphoton absorption (TPA/MPA), and free carrier absorption (FCA). Then, we give detailed examples of 2D materials for optical limiting. Besides graphene and analogs, the latest development of several novel 2D materials, as well as materials with new structures and optical limiting mechanisms like nonlinear photonic metamaterials, plasmonic effect-enhanced nonlinearity is emphasized. We provide our insights into the key scientific problems to be solved and future development trends for this intriguing field in the final part.