Micro-Clearance Oil Film Temperature Field Characteristics of High Speed and Heavy Type Hydrostatic Thrust Bearing under Extreme Operating Conditions

To explore the micro-clearance oil film temperature field characteristics of hydrostatic thrust bearings under operating conditions of high speed and heavy load, a mathematical model of micro-clearance oil film is established. According to the principle of computational fluid dynamics, the relationship between load capacity and rotational speed is calculated, and the model is solved using the finite volume method. The micro-clearance oil film temperature field is also investigated and tested to verify the theoretical analysis. The results show that the rotational speed is coupled with the load-carrying capacity of hydrostatic thrust bearings. When the extreme operating conditions are between 0t-228.9r/min and 4t-214.9r/min, the oil film maximum temperature increases slowly with the load increase and rotational speed decrease, and the average temperature decreases slowly. On the other hand, when the extreme operating conditions are between 4t-214.9r/min and 32t-78.9r/min, the maximum temperature and the average temperature slowly decrease as the load increases and the rotational speed decreases; the influence of rotational speed is greater than that of load, and the temperature rise of the upstream side is sharper than that of the downstream side

Ultrafast and Sensitive Self-Powered Photodetector Featuring Self-Limited Depletion Region and Fully Depleted Channel with van der Waals Contacts

Self-powered photodetectors with great potential for implanted medical diagnosis and smart communications have been severely hindered by the difficulty of simultaneously achieving high sensitivity and fast response speed. Here, we report an ultrafast and highly sensitive self-powered photodetector based on two-dimensional (2D) InSe, which is achieved by applying a device architecture design and generating ideal Schottky or ohmic contacts on 2D layered semiconductors, which are difficult to realize in the conventional semiconductors owing to their surface Fermi-level pinning. The as-fabricated InSe photodiode features a maximal lateral self-limited depletion region and a vertical fully depleted channel. It exhibits a high detectivity of 1.26 × 1013 Jones and an ultrafast response speed of ∼200 ns, which breaks the response speed limit of reported self-powered photodetectors based on 2D semiconductors. The high sensitivity is achieved by an ultralow dark current noise generated from the robust van der Waals (vdW) Schottky junction and a high photoresponsivity due to the formation of a maximal lateral self-limited depletion region. The ultrafast response time is dominated by the fast carrier drift driven by a strong built-in electric field in the vertical fully depleted channel. This device architecture can help us to design high-performance photodetectors utilizing vdW layered semiconductors

The effects of online social networking on retail consumer dynamics in the attractions industry: The case of ‘E-da’ theme park, Taiwan

Purpose of this study is to examine the trends in retail consumers’ consumption dynamics and patterns of purchase behavior within this new-technology-mediated environment. A behavioral purchase model was developed and tested to understand the ways social networks influence the decision making of individuals planning to visit a theme park. In particular, the proposed model delineates how online social networking (OSN) experience factors affect actual use (AU) of social media for purchasing of theme park services through an assessment of perceived usefulness (PU) and perceived ease of use (PEOU). An electronic survey was conducted with members of a theme park’s brand fan page on the Facebook social media site namely, the E-da World Theme park in the southern Taiwanese city of Kaohsiung. Smart PLS 3, a partial least squares analysis, was employed to examine a series of eleven research hypotheses. The findings revealed a series of statistically significant influences from five exogenous variables on PU and PEOU, as well as the mediating role of PU on the PEOU – AU relationship. The results also provide important practical implications both for academics and practitioners by shedding light on the way social media works to encourage and support online purchasing of amusement services.

Hollow multi-shell structured SnO2 with enhanced performance for ultraviolet photodetectors

We fabricated a photodetector using hollow multi-shell structured (HoMSs) SnO2 as an active material, which exhibits enhanced ultraviolet responsivity and detectivity compared to SnO2 nanoparticles. This is because the internal cavity within the HoMSs helps to trap light and enhance light absorption. With an increase in the number of shells, the photodetector performance is improved

Ultra-broadband SnSe-based photothermoelectric detector for mid-infrared gas spectroscopy

Seebeck effect is one of the desirable pathways for developing advanced room-temperature (RT) broadband photothermoelectric (PTE) detectors, which are important for infrared spectroscopy applications. However, achieving high performance PTE detectors utilizing materials with high Seebeck coefficient remains a great challenge and further improvements are highly desired. Herein, we introduce a layered material SnSe with high Seebeck coefficient up to 507 ± 20 μV K−1 and further demonstrate an RT ultra-broadband PTE detector ranging from a visible region to a mid-infrared (MIR) region (0.532–13.2 μm). The detector yields a high responsivity of 0.47 V W−1 and a moderate response speed of 107 ms at an excitation wavelength of 8.1 μm at zero bias, which is comparable or higher than those parameters of the commercial products. Moreover, we have retrieved absorption fingerprints of molecular gases during MIR spectroscopy by using this detector owing to its wide response range, which illustrates great potential of this type of broadband high performance PTE detector toward advanced optoelectronics applications.Agency for Science, Technology and Research (A*STAR)National Research Foundation (NRF)Submitted/Accepted versionThis research was supported by the National Natural Science Foundation of China (NSFC, Grant Nos. 61922005 and U1930105) and the Beijing Natural Science Foundation (BNSF, Grant No. JQ20027). This research was also supported partially by the National Research Foundation Singapore programme (Nos. NRF-CRP19-2017-01 and NRF-CRP22-2019-0007) and A*STAR Grant Nos. A18A7b0058 and A2090b0144

Two-Dimensional van der Waals Materials with Aligned In-Plane Polarization and Large Piezoelectric Effect for Self-Powered Piezoelectric Sensors

Piezoelectric two-dimensional (2D) van der Waals (vdWs) materials are highly desirable for applications in miniaturized and flexible/wearable devices. However, the reverse-polarization between adjacent layers in current 2D layered materials results in decreasing their in-plane piezoelectric coefficients with layer number, which limits their practical applications. Here, we report a class of 2D layered materials with an identical orientation of in-plane polarization. Their piezoelectric coefficients (e22) increase with layer number, thereby allowing for the fabrication of flexible piezotronic devices with large piezoelectric responsivity and excellent mechanical durability. The piezoelectric outputs can reach up to 0.363 V for a 7-layer α-In2Se3 device, with a current responsivity of 598.1 pA for 1% strain, which is 1 order of magnitude higher than the values of the reported 2D piezoelectrics. The self-powered piezoelectric sensors made of these newly developed 2D layered materials have been successfully used for real-time health monitoring, proving their suitability for the fabrication of flexible piezotronic devices due to their large piezoelectric responses and excellent mechanical durability

On-chip mid-infrared photothermoelectric detectors for full-Stokes detection

On-chip polarimeters are highly desirable for the next-generation ultra-compact optical and optoelectronic systems. Polarization-sensitive photodetectors relying on anisotropic absorption of natural/artificial materials have emerged as a promising candidate for on-chip polarimeters owing to their filterless configurations. However, these photodetectors can only be applied for detection of either linearly or circularly polarized light, not applicable for full-Stokes detection. Here, we propose and demonstrate three-ports polarimeters comprising on-chip chiral plasmonic metamaterial-mediated mid-infrared photodetectors for full-Stokes detection. By manipulating the spatial distribution of chiral metamaterials, we could convert polarization-resolved absorptions to corresponding polarization-resolved photovoltages of three ports through the photothermoelectric effect. We utilize the developed polarimeter in an imaging demonstration showing reliable ability for polarization reconstruction. Our work provides an alternative strategy for developing polarization-resolved photodetectors with a bandgap-independent operation range in the mid-infrared.Agency for Science, Technology and Research (A*STAR)National Research Foundation (NRF)Published versionThis research was supported by National Research Foundation Singapore programme (NRF-CRP18-2017-02 (Q.J.W.) and NRF-CRP22-2019- 0007 (Q.J.W.)) and A*STAR grant number A18A7b0058 (Q.J.W.), A20E5c0095 (Y.L., Q.J.W.), and A2090b0144 (Q.J.W.

Nano-optical engineering of anisotropic phonon resonances in a hyperbolic α-MoO₃ metamaterial

Low-dimensional α-phase molybdenum trioxide (α-MoO3), a layered van-der-Waals (vdW) semiconductor, has emerged as an attractive natural hyperbolic material supporting mid-infrared hyperbolic phonon polaritons (PhPs), which exhibit strong spatial confinement and low loss. With the advantages of strong in-plane optical anisotropy, many efforts have been devoted to investigating the properties of hyperbolic PhPs in α-MoO3 using scanning near-field optical microscopy. However, the studies of far-field controlling of hyperbolic PhPs in α-MoO3 have been quite limited so far. This work reports the first experimental demonstration of far-field excitation and manipulation of hyperbolic phonon resonances in metamaterial structures consisting of α-MoO3 nanodisks and slabs. The excited phonon resonances show a maximum spatial confinement factor (free space wavelength/period) of 32 and a quality factor of 76. It is shown that the in-plane phonon resonances in α-MoO3 can be selectively excited in the two Reststrahlen bands featuring hyperbolic dispersion relations along its two crystal directions, by simply controlling the incident polarization. In addition, the relative strength of resonances along different in-plane crystal directions and the resultant field distributions can be continuously reconfigured by varying the incident polarization angle. These findings pave the way for future development of novel nanophotonic devices based on hyperbolic PhPs in vdW materials.Agency for Science, Technology and Research (A*STAR)Ministry of Education (MOE)This work was partially supported by Singapore Ministry of Education Academic Research Fund Tier 2 under grant no. MOE2018-T2-1-176 and by A*STAR AME programmatic grant (grant no. A18A7b0058), AME IRG grant (Project No. A20E5c0095), and career development fund (grant no. C210112044)

Long-wave infrared photothermoelectric detectors with ultrahigh polarization sensitivity

Filter-free miniaturized polarization-sensitive photodetectors have important applications in the next-generation on-chip polarimeters. However, their polarization sensitivity is thus far limited by the intrinsic low diattenuation and inefficient photon-to-electron conversion. Here, we implement experimentally a miniaturized detector based on one-dimensional tellurium nanoribbon, which can significantly improve the photothermoelectric responses by translating the polarization-sensitive absorption into a large temperature gradient together with the finite-size effect of a perfect plasmonic absorber. Our devices exhibit a zero-bias responsivity of 410 V/W and an ultrahigh polarization ratio (2.5 × 104), as well as a peak polarization angle sensitivity of 7.10 V/W•degree, which is one order of magnitude higher than those reported in the literature. Full linear polarimetry detection is also achieved with the proposed device in a simple geometrical configuration. Polarization-coded communication and optical strain measurement are demonstrated showing the great potential of the proposed devices. Our work presents a feasible solution for miniaturized room-temperature infrared photodetectors with ultrahigh polarization sensitivity.Agency for Science, Technology and Research (A*STAR)National Medical Research Council (NMRC)National Research Foundation (NRF)Published versionThis research was supported by National Research Foundation Singapore programme (NRF-CRP22-2019-0007 (Q.J.W.)), National Research Foundation Singapore Competitive Research Program (NRF-CRP22- 2019-0006 (Y.L.)), A*STAR grant number A18A7b0058 (Q.J.W.), A20E5c0095 (Y.L., Q.J.W.) and A2090b0144 (Q.J.W.), and National Medical Research Council (NMRC) MOH-000927 (Q.J.W.)

Recent progress in 2D inorganic/organic charge transfer heterojunction photodetectors

2D materials possess superior optoelectronic properties, such as ultrahigh mobility and broadband photoresponse, making them one of the most vital platforms for diversified photodetectors. However, atomic thickness 2D materials usually suffer from intrinsic low absorption. To promote the photodetector performance, a feasible method is to integrate the 2D materials with low-cost, flexible, and tunable organics that form a charge transfer (CT) heterojunction. As results, in-depth multifunctional CT 2D-inorganic/organic detector exhibits extended functions such as low-power consumption, in-memory detection, and optical-bio synapse to meet the demand of contemporary photonic cell. Particularly, the progresses in wafer-scale monocrystal of both 2D and organic materials render vast potential applications with operation frequencies ranging from ultraviolet to terahertz. Here, the recent advances of 2D-inorganic/organic CT photodetectors are comprehensively reviewed by several classifications. Future developments and applications in optical biology, synapsis, and machine vision are also highlighted.Ministry of Education (MOE)National Research Foundation (NRF)Submitted/Accepted versionThe authors acknowledge financial support from National Science Funds for (Nos. 61922022, 62175026, 62171094 ̧ and 62104026), the Singapore Ministry of Education Academic Research Fund No. MOE-T2EP50120-0009 (S), by the National Research Foundation Singapore programme Nos. NRF-CRP18-2017-02 and NRF-CRP22-2019-0007. Also, thanks for China Scholarship Council