Rapid laser nanomanufacturing and direct patterning of 2D materials on flexible substrates-2DFlex.

Direct synthesis, large-scale integration, and patterning of two-dimensional (2D) quantum materials (e.g. MoS2, WSe2) on flexible and transparent substrates are of high interest for flexible and conformal device applications. However, the growth temperatures (e.g. 850 °C) of the emerging 2D materials in the common gas-phase synthesis methods are well beyond the tolerances limit of flexible substrates, such as polydimethylsiloxane (PDMS). In addition, random nucleation and growth process in most growth systems limits the predicted integration and patterning freedoms. Here, we report a rapid direct laser crystallization and mask-free large-scale patterning of MoS2 and WSe2 crystals on PDMS substrates. A thin layer of stoichiometric amorphous 2D film is first laser-deposited via pulsed laser deposition (PLD) system onto the flexible substrates followed by a controlled crystallization and direct writing process using a tunable nanosecond laser (1064 nm). The influences of pulse duration, number of pulses, and the thickness of the deposited amorphous 2D layer on the crystallization of 2D materials are discussed. Optical spectroscopy and electrical characterizations are performed to confirm the quality of crystallized 2D materials on flexible substrates. This novel method opens up a new opportunity for the crystallization of complex patterns directly from computer-aided design models for the future 2D materials-based wearable, transparent, and flexible devices.

Effects of TiS2 on Inhibiting Candida albicans Biofilm Formation and Its Compatibility with Human Gingival Fibroblasts in Titanium Implants.

Titanium is widely used in medical devices, such as dental and orthopedic implants, due to its excellent mechanical properties, low toxicity, and biocompatibility. However, the titanium surface has the risk of microbial biofilm formation, which results in infections from species such as Candida albicans (C. albicans). This kind of biofilm prevents antifungal therapy and complicates the treatment of infectious diseases associated with implanted devices. It is critical to developing a feasible surface to decrease microbial growth while not interfering with the growth of the host cells. This study reports the influence of titanium surface modification to titanium disulfide (TiS2) on inhibiting C. albicans biofilm formation while allowing the attachment of human gingival fibroblasts (HGFs) on their surface. The surface of titanium parts is directly converted to structured titanium and TiS2 using direct laser processing and crystal growth methods. C. albicans adhesion and colonization are then investigated on these surfaces by the colony counting assay and reactive oxygen species (ROS) assay, using 2',7'-dichlorofluorescin diacetate (DCFH-DA) and microscopy images. Also, the viability and adhesion of HGFs on these surfaces are investigated to show their adhesion and biocompatibility. Titanium samples with the TiS2 surface show both C. albicans biofilm inhibition and HGF attachment. This study provides insight into designing and manufacturing titanium biomedical implants.

Wafer-Scale Synthesis of 2D Materials by an Amorphous Phase-Mediated Crystallization Approach.

The interest in the wafer-scale growth of two-dimensional (2D) materials, including transition metal dichalcogenides (TMDCs), has been rising for transitioning from lab-scale devices to commercial-scale systems. Among various synthesis techniques, physical vapor deposition, such as pulsed laser deposition (PLD), has shown promise for the wafer-scale growth of 2D materials. However, due to the high volatility of chalcogen atoms (e.g., S and Se), films deposited by PLD usually suffer from a lack of stoichiometry and chalcogen deficiency. To mitigate this issue, excess chalcogen is necessary during the deposition, which results in problems like uniformity or not being repeatable. This study demonstrates a condensed-phase or amorphous phase-mediated crystallization (APMC) approach for the wafer-scale synthesis of 2D materials. This method uses a room-temperature PLD process for the deposition and formation of amorphous precursors with controlled thicknesses, followed by a post-deposition crystallization process to convert the amorphous materials to crystalline structures. This approach maintains the stoichiometry of the deposited materials throughout the deposition and crystallization process and enables the large-scale synthesis of crystalline 2D materials (e.g., MoS2 and WSe2) on Si/SiO2 substrates, which is critical for future wafer-scale electronics. We show that the thickness of the layers can be digitally controlled by the number of laser pulses during the PLD phase. Optical spectroscopy is used to monitor the crystallization dynamics of amorphous layers as a function of annealing temperature. The crystalline quality, domain sizes, and the number of layers were explored using nanoscale and atomistic characterization (e.g., AFM, STEM, and EDS) along with electrical characterization to explore process-structure-performance relationships. This growth technique is a promising method that could potentially be adopted in conventional semiconductor industries for wafer-scale manufacturing of next-generation electronic and optoelectronic devices.

Two-Dimensional-Material-Based Field-Effect Transistor Biosensor for Detecting COVID-19 Virus (SARS-CoV-2).

The emergence of rapidly expanding infectious diseases such as coronavirus (COVID-19) demands effective biosensors that can promptly detect and recognize the pathogens. Field-effect transistors based on semiconducting two-dimensional (2D) materials (2D-FETs) have been identified as potential candidates for rapid and label-free sensing applications. This is because any perturbation of such atomically thin 2D channels can significantly impact their electronic transport properties. Here, we report the use of FET based on semiconducting transition metal dichalcogenide (TMDC) WSe2 as a promising biosensor for the rapid and sensitive detection of SARS-CoV-2 in vitro. The sensor is created by functionalizing the WSe2 monolayers with a monoclonal antibody against the SARS-CoV-2 spike protein and exhibits a detection limit of down to 25 fg/µL in 0.01X phosphate-buffered saline (PBS). Comprehensive theoretical and experimental studies, including density functional theory, atomic force microscopy, Raman and photoluminescence spectroscopies, and electronic transport properties, were performed to characterize and explain the device performance. The results demonstrate that TMDC-based 2D-FETs can potentially serve as sensitive and selective biosensors for the rapid detection of infectious diseases.

Phase-Selective and Localized TiO2 Coating on Additive and Wrought Titanium by a Direct Laser Surface Modification Approach.

Titanium has been the material of interest in biological implant applications due to its unique mechanical properties and biocompatibility. Their design is now growing rapidly due to the advent of additive manufacturing technology that enables the fabrication of complex and patient-customized parts. Titanium dioxides (TiO2) coatings with different phases (e.g., anatase, rutile) and morphologies have shown to be effective in enhancing osteointegration and antibacterial behavior. This enhanced antibacterial behavior stems from the photocatalytic activity generated from crystalline TiO2 coatings. Anatase has commonly been shown to be a more photocatalytic oxide phase compared to rutile despite its larger band gap. However, more recent studies have suggested that a synergistic effect leading to increased photocatalytic activity may be produced with a combination of oxides containing both anatase and rutile phases. Here, we demonstrate the selective and localized formation of TiO2 nanostructures on additive and wrought titanium parts with anatase, rutile, and mixed phases by a laser-induced transformation approach. Compared to conventional coating processes, this technique produces desired TiO2 phases simply by controlled laser irradiation of titanium parts in an oxygen environment, where needed. The effects of processing conditions such as laser power, scanning speed, laser pulse duration, frequency, and gas flow on the selective transformation were studied. The morphological and structural evolutions were investigated using various characterization techniques. This method is specifically of significant interest in creating phase-selective TiO2 surfaces on titanium-based bioimplants, including those fabricated by additive manufacturing technologies.