Biofunctional polymer coatings via initiated chemical vapor deposition

Scope and Method of Study:Surface modification is of essential importance in bioengineering. Polymer thin coatings offer various functionalities and biocompatibility to the interface of biomaterials and biosystems. While conventional solution-based polymer coating techniques are fully capable of providing uniform thin coatings on flat surfaces, they have limitations in coating nano- and micro-structured substrates. Vapor-based polymer coatings have also been investigated mainly by plasma-assisted processes, which encounter difficulties in retaining the delicate functional groups and controlling stoichiometric chemistry. We employed initiated chemical vapor deposition (iCVD) to conformally coat micro- and nano-structured materials with different biofunctional polymer films. The introduction of the initiator allows complete retention of the monomer functionality, while the vaporbased approach permits the excellent preservation of the original morphology of the substrates.Findings and Conclusions:Using iCVD technique, we achieved successful surface modification in three different applications of bioengineering. In CHAPTER II, we demonstrate the creation of durable antibacterial coatings on textile and catheter. Bacterial killing efficacy of more than 99% was achieved on both substrates. The bactericidal effect was durable against continuous washing for up to 10 hours. CHAPTER III, IV, and V presented another important application of iCVD functionalization of vertically aligned carbon nanotubes, which is difficult to achieve using conventional methods. We demonstrated both non-covalent and covalent functionalization of aligned carbon nanotubes with different chemistry. The epoxy chemistry enabled significantly enhanced mechanical properties and wetting stability to the multi-walled carbon nanotube arrays. The covalent functionalization tuned electronic properties of the single walled carbon nanotube arrays. Hydrogel chemistry offered pH-responsiveness and substantially improved wettability to the low-site-density carbon nanotube arrays. In CHAPTER VI, we presented thermo-responsive hydrogel coatings on nanoporous membranes to fabricate smart nanovalves. The tunable transportation of biomolecules through the nanovalves was successfully triggered by the adjustment of temperatures

Optical Diode Based on Two-Dimensional Photonic Crystal

The integrated optical diodes have been a thriving research theme due to their potential on-chip applications in photonic circuits for all-optical computing and information processing. Analogous to electronic counterparts, the unidirectional light propagation is characterized by the high contrast between forward and backward transmissions. In this chapter, we demonstrate the proposed schemes and designs for reciprocal and nonreciprocal optical diodes based on two-dimensional (2D) photonic crystal (PhC). The reciprocal devices are built by linear and passive PhC, and the spatial asymmetric mode conversion is utilized to achieve the unidirectionality. The presented nonreciprocal optical diodes rely on the optical nonlinearity of cavity. New 2D PhC optical diodes with high contrast ratio, low insertion loss, large operational bandwidth, small device footprint, and ease of fabrication are highly desirable and still pursued

Inducing and Manipulating Heteroelectronic States in a Single MoS2 Thin Flake

By dual gating a few-layer MoS2 flake, we induce spatially separated electronic states showing superconductivity and Shubnikov–de Haas (SdH) oscillations. While the highly confined superconductivity forms at the K/K′ valleys of the topmost layer, the SdH oscillations are contributed by the electrons residing in the Q/Q′ valleys of the rest of the bottom layers, which is confirmed by the extracted Landau level degeneracy of 3, electron effective mass of 0.6me, and carrier density of 5×10^12  cm^−2. Mimicking conventional heterostructures, the interaction between the heteroelectronic states can be electrically manipulated, which enables “bipolarlike” superconducting transistor operation. The off-on-off switching pattern can be continuously accessed at low temperatures by a field effect depletion of carriers with a negative back gate bias and the proximity effect between the top superconducting layer and the bottom metallic layers that quenches the superconductivity at a positive back gate bias

Probing and Tuning the Spin Textures of the K and Q Valleys in Few-Layer MoS2

The strong spin-orbit coupling along with broken inversion symmetry in transition metal dichalcogenides (TMDs) results in spin polarized valleys, which are the origins of many interesting properties such as Ising superconductivity, circular dichroism, valley Hall effect, etc. Herein, it is shown that encapsulating few-layer MoS2 between hexagonal boron nitride (h-BN) and gating the electrical contacts by ionic liquid pronounce Shubnikov-de Haas (SdH) oscillations in magnetoresistance. Notably, the SdH oscillations remain unchanged in tilted magnetic fields, demonstrating that the spins of the Q/Q ' valleys are firmly locked to the out-of-plane direction; therefore, Zeeman energy is insensitive to the in-plane magnetic field. Ionic liquid gating induces superconductivity on the surface of unencapsulated MoS2. The spins of Cooper pairs are strongly pinned to the out-of-plane direction by the effective Zeeman field, hence are protected from being realigned by an in-plane magnetic field, namely, Ising protection. As a result, superconductivity persists in an in-plane magnetic field up to 14 T, in which T-c only decreases by approximate to 0.3 K from T-c0 as approximate to 7 K. By applying back gate, the strength of Ising protection can be effectively tuned, where an increase in 70% is observed when back gate changes from +90 to -90 V

Josephson coupled Ising pairing induced in suspended MoS2 bilayers by double-side ionic gating

Superconductivity in monolayer transition metal dichalcogenides is characterized by !sing-type pairing induced via a strong Zeeman-type spin-orbit coupling. When two transition metal dichalcogenides layers are coupled, more exotic superconducting phases emerge, which depend on the ratio of !sing-type protection and interlayer coupling strength. Here, we induce superconductivity in suspended MoS2 bilayers and unveil a coupled superconducting state with strong !sing-type spin-orbit coupling. Gating the bilayer symmetrically from both sides by ionic liquid gating varies the interlayer interaction and accesses electronic states with broken local inversion symmetry while maintaining the global inversion symmetry. We observe a strong suppression of the Ising protection that evidences a coupled superconducting state. The symmetric gating scheme not only induces superconductivity in both atomic sheets but also controls the Josephson coupling between the layers, which gives rise to a dimensional crossover in the bilayer.</p

Different healing characteristics of thiol-bearing molecules on CVD-grown MoS₂

Vacancies in atomically thin molybdenum disulphide play an essential role in controlling its optical and electronic properties, which are crucial for applications in sensorics, catalysis or electronics. For this reason, defect engineering employing thiol-terminated molecules is used to heal and/or functionalise defective nanosheets. In this work, chemical vapour deposition-grown MoS2 with different defect densities was functionalised with three molecules: 4-aminothiophenol (ATP), biphenyl-4-thiol (BPT) and 4-nitrothiophenol (NTP). The molecules’ efficacy in functionalising MoS2 was probed by x-ray photoelectron, Raman and photoluminescence (PL) spectroscopy. The results show that exposing a defective single layer of MoS2 to either ATP, BPT or NTP molecules heals the defects, however the chemical structure of these molecules affects the optical response and only for BPT the PL intensity increases.</p

High-performance piezoelectric nanogenerators based on Cs₂Ag_0.3Na_0.7InCl₆ double perovskites with high polarity induced by Zr/Te codoping

Piezoelectric nanogenerators (PENGs), which operate based on mechanical-to-electrical energy conversion, have been widely explored for exciting applications in modern devices such as wearable electronics, self-powered sensors, and energy harvesters. Herein, we report on high-performance PENGs based on Cs2Ag0.3Na0.7InCl6 double perovskite (CDP) within a polyvinylidene fluoride (PVDF) matrix, which exhibit enhanced polarity due to rationally designed Zr/Te codoping. As a proof of concept, the resultant PENGs based on Zr/Te codoped CDP@PVDF deliver an excellent piezoelectric output, with a maximum open-circuit voltage and short-circuit current density of 67 V and 18 μA·cm−2. This level of performance is ∼19 and ∼12 times higher than PVDF-based PENGs with no CDP, and ∼2 and ∼4 times higher than CDP@PVDF-based PENGs without doping or with single Te doping, and ∼1 and ∼2 times higher than CDP@PVDF-based PENGs with single Zr doping, respectively. Moreover, the as-assembled PENGs exhibit impressive potential in wearable energy harvesters, motion sensors, and DC-power devices with robust stability, underscoring their bright future toward practical applications.</p