Browsing by Author "Liu, Can"

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Complete structural characterization of single carbon nanotubes by Rayleigh scattering circular dichroism
(2021-10) Yao, Fengrui; Yu, Wentao; Liu, Can; Su, Yingze; You, Yilong; Ma, He; Qiao, Ruixi; Wu, Chunchun; Ma, Chaojie; Gao, Peng; Xiao, Fajun; Zhao, Jianlin; Bai, Xuedong; Sun, Zhipei; Maruyama, Shigeo; Wang, Feng; Zhang, Jin; Liu, Kaihui
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Non-invasive, high-throughput spectroscopic techniques can identify chiral indices (n,m) of carbon nanotubes down to the single-tube level1–6. Yet, for complete characterization and to unlock full functionality, the handedness, the structural property associated with mirror symmetry breaking, also needs to be identified accurately and efficiently7–14. So far, optical methods fail in the handedness characterization of single nanotubes because of the extremely weak chiroptical signals (roughly 10−7) compared with the excitation light15,16. Here we demonstrate the complete structure identification of single nanotubes in terms of both chiral indices and handedness by Rayleigh scattering circular dichroism. Our method is based on the background-free feature of Rayleigh scattering collected at an oblique angle, which enhances the nanotube’s chiroptical signal by three to four orders of magnitude compared with conventional absorption circular dichroism. We measured a total of 30 single-walled carbon nanotubes including both semiconducting and metallic nanotubes and found that their absolute chiroptical signals show a distinct structure dependence, which can be qualitatively understood through tight-binding calculations. Our strategy enables the exploration of handedness-related functionality of single nanotubes and provides a facile platform for chiral discrimination and chiral device exploration at the level of individual nanomaterials.
Forgetting of passwords: Ecological theory and data
(2018) Gao, Xianyi; Yang, Yulong; Liu, Can; Mitropoulos, Christos; Lindqvist, Janne; Oulasvirta, Antti
A4 Artikkeli konferenssijulkaisussa
It is well known that text-based passwords are hard to remember and that users prefer simple (and non-secure) passwords. However, despite extensive research on the topic, no principled account exists for explaining when a password will be forgotten. This paper contributes new data and a set of analyses building on the ecological theory of memory and forgetting. We propose that human memory naturally adapts according to an estimate of how often a password will be needed, such that often used, important passwords are less likely to be forgotten. We derive models for login duration and odds of recall as a function of rate of use and number of uses thus far. The models achieved a root-mean-square error (RMSE) of 1.8 seconds for login duration and 0.09 for recall odds for data collected in a month-long field experiment where frequency of password use was controlled. The theory and data shed new light on password management, account usage, password security and memorability.
Giant enhancement of optical nonlinearity in two-dimensional materials by multiphoton-excitation resonance energy transfer from quantum dots
(2021-07) Hong, Hao; Wu, Chunchun; Zhao, Zixun; Zuo, Yonggang; Wang, Jinhuan; Liu, Can; Zhang, Jin; Wang, Fangfang; Feng, Jiangang; Shen, Huaibin; Yin, Jianbo; Wu, Yuchen; Zhao, Yun; Liu, Kehai; Gao, Peng; Meng, Sheng; Wu, Shiwei; Sun, Zhipei; Liu, Kaihui; Xiong, Jie
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Colloidal quantum dots are promising photoactive materials that enable plentiful photonic and optoelectronic applications ranging from lasers, displays and photodetectors to solar cells1–9. However, these applications mainly utilize the linear optical properties of quantum dots, and their great potential in the broad nonlinear optical regime is still waiting for full exploration10–12. Here, we demonstrate that a simple coating of a sub-200-nm-thick quantum dot film on two-dimensional materials can significantly enhance their nonlinear optical responses (second, third and fourth harmonic generation) by more than three orders of magnitude. Systematic experimental results indicate that this enhancement is driven by a non-trivial mechanism of multiphoton-excitation resonance energy transfer, where the quantum dots directly deliver their strongly absorbed multiphoton energy to the adjacent two-dimensional materials by a remote dipole–dipole coupling. Our findings could expand the applications of quantum dots in many exciting areas beyond linear optics, such as nonlinear optical signal processing, multiphoton imaging and ultracompact nonlinear optical elements.
Graphene photonic crystal fibre with strong and tunable light–matter interaction
(2019-08-12) Chen, Ke; Zhou, Xu; Cheng, Xu; Qiao, Ruixi; Cheng, Yi; Liu, Can; Xie, Yadian; Yu, Wentao; Yao, Fengrui; Sun, Zhipei; Wang, Feng; Liu, Kaihui; Liu, Zhongfan
Letter
The integration of photonic crystal fibre (PCF) with various functional materials has greatly expanded the application regimes of optical fibre1–12. The emergence of graphene (Gr) has stimulated new opportunities when combined with PCF, allowing for electrical tunability, a broadband optical response and all-fibre integration ability13–18. However, previous demonstrations have typically been limited to micrometre-sized samples, far behind the requirements of real applications at the metre-scale level. Here, we demonstrate a new hybrid material, Gr–PCF, with length up to half a metre, produced using a chemical vapour deposition method. The Gr–PCF shows a strong light–matter interaction with ~8 dB cm−1 attenuation. In addition, the Gr–PCF-based electro-optic modulator demonstrates a broadband response (1,150–1,600 nm) and large modulation depth (~20 dB cm−1 at 1,550 nm) under a low gate voltage of ~2 V. Our results could enable industrial-level graphene applications based on this Gr–PCF and suggest an attractive platform for two-dimensional material-PCF.
Measurement of complex optical susceptibility for individual carbon nanotubes by elliptically polarized light excitation
(2018-12-01) Yao, Fengrui; Liu, Can; Chen, Cheng; Zhang, Shuchen; Zhao, Qiuchen; Xiao, Fajun; Wu, Muhong; Li, Jiaming; Gao, Peng; Zhao, Jianlin; Bai, Xuedong; Maruyama, Shigeo; Yu, Dapeng; Wang, Enge; Sun, Zhipei; Zhang, Jin; Wang, Feng; Liu, Kaihui
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The complex optical susceptibility is the most fundamental parameter characterizing light-matter interactions and determining optical applications in any material. In one-dimensional (1D) materials, all conventional techniques to measure the complex susceptibility become invalid. Here we report a methodology to measure the complex optical susceptibility of individual 1D materials by an elliptical-polarization-based optical homodyne detection. This method is based on the accurate manipulation of interference between incident left- (right-) handed elliptically polarized light and the scattering light, which results in the opposite (same) contribution of the real and imaginary susceptibility in two sets of spectra. We successfully demonstrate its application in determining complex susceptibility of individual chirality-defined carbon nanotubes in a broad optical spectral range (1.6–2.7 eV) and under different environments (suspended and in device). This full characterization of the complex optical responses should accelerate applications of various 1D nanomaterials in future photonic, optoelectronic, photovoltaic, and bio-imaging devices.
Optical fibres with embedded two-dimensional materials for ultrahigh nonlinearity
(2020-12) Zuo, Yonggang; Yu, Wentao; Liu, Can; Cheng, Xu; Qiao, Ruixi; Liang, Jing; Zhou, Xu; Wang, Jinhuan; Wu, Muhong; Zhao, Yun; Gao, Peng; Wu, Shiwei; Sun, Zhipei; Liu, Kaihui; Bai, Xuedong; Liu, Zhongfan
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Nonlinear optical fibres have been employed for a vast number of applications, including optical frequency conversion, ultrafast laser and optical communication1–4. In current manufacturing technologies, nonlinearity is realized by the injection of nonlinear materials into fibres5–7 or the fabrication of microstructured fibres8–10. Both strategies, however, suffer from either low optical nonlinearity or poor design flexibility. Here, we report the direct growth of MoS2, a highly nonlinear two-dimensional material11, onto the internal walls of a SiO2 optical fibre. This growth is realized via a two-step chemical vapour deposition method, where a solid precursor is pre-deposited to guarantee a homogeneous feedstock before achieving uniform two-dimensional material growth along the entire fibre walls. By using the as-fabricated 25-cm-long fibre, both second- and third-harmonic generation could be enhanced by ~300 times compared with monolayer MoS2/silica. Propagation losses remain at ~0.1 dB cm–1 for a wide frequency range. In addition, we demonstrate an all-fibre mode-locked laser (~6 mW output, ~500 fs pulse width and ~41 MHz repetition rate) by integrating the two-dimensional-material-embedded optical fibre as a saturable absorber. Initial tests show that our fabrication strategy is amenable to other transition metal dichalcogenides, making these embedded fibres versatile for several all-fibre nonlinear optics and optoelectronics applications.
Twist Phase Matching in Two-Dimensional Materials
(2023-12-08) Hong, Hao; Huang, Chen; Ma, Chenjun; Qi, Jiajie; Shi, Xuping; Liu, Can; Wu, Shiwei; Sun, Zhipei; Wang, Enge; Liu, Kaihui
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Optical phase matching involves establishing a proper phase relationship between the fundamental excitation and generated waves to enable efficient optical parametric processes. It is typically achieved through birefringence or periodic polarization. Here, we report that the interlayer twist angle in two-dimensional (2D) materials creates a nonlinear geometric phase that can compensate for the phase mismatch, and the vertical assembly of the 2D layers with a proper twist sequence generates a nontrivial "twist-phase-matching"(twist-PM) regime. The twist-PM model provides superior flexibility in the design of optical crystals, which can be applied for twisted layers with either periodic or random thickness distributions. The designed crystal from the twisted rhombohedral boron nitride films within a thickness of only 3.2 μm is capable of producing a second-harmonic generation with conversion efficiency of ∼8% and facile polarization controllability that is absent in conventional crystals. Our methodology establishes a platform for the rational design and atomic manufacturing of nonlinear optical crystals based on abundant 2D materials.