Isotope Engineered Fluorinated Single and Bilayer Graphene: Insights into Fluorination Selectivity, Stability, and Defect Passivation.

Tailoring the physicochemical properties of graphene through functionalization remains a major interest for next-generation technological applications. However, defect formation due to functionalization greatly endangers the intrinsic properties of graphene, which remains a serious concern. Despite numerous attempts to address this issue, a comprehensive analysis has not been conducted. This work reports a two-step fluorination process to stabilize the fluorinated graphene and obtain control over the fluorination-induced defects in graphene layers. The structural, electronic and isotope-mass-sensitive spectroscopic characterization unveils several not-yet-resolved facts, such as fluorination sites and CF bond stability in partially-fluorinated graphene (F-SLG). The stability of fluorine has been correlated to fluorine co-shared between two graphene layers in fluorinated-bilayer-graphene (F-BLG). The desorption energy of co-shared fluorine is an order of magnitude higher than the CF bond energy in F-SLG due to the electrostatic interaction and the inhibition of defluorination in the F-BLG. Additionally, F-BLG exhibits enhanced light-matter interaction, which has been utilized to design a proof-of-concept field-effect phototransistor that produces high photocurrent response at a time <200 µs. Thus, the study paves a new avenue for the in-depth understanding and practical utilization of fluorinated graphenic carbon.

Highly sensitive broadband binary photoresponse in gateless epitaxial graphene on 4H-SiC.

Due to weak light-matter interaction, standard chemical vapor deposition (CVD)/exfoliated single-layer graphene-based photodetectors show low photoresponsivity (on the order of mA/W). However, epitaxial graphene (EG) offers a more viable approach for obtaining devices with good photoresponsivity. EG on 4H-SiC also hosts an interfacial buffer layer (IBL), which is the source of electron carriers applicable to quantum optoelectronic devices. We utilize these properties to demonstrate a gate-free, planar EG/4H-SiC-based device that enables us to observe the positive photoresponse for (405-532) nm and negative photoresponse for (632-980) nm laser excitation. The broadband binary photoresponse mainly originates from the energy band alignment of the IBL/EG interface and the highly sensitive work function of the EG. We find that the photoresponsivity of the device is > 10 A/W under 405 nm of power density 7.96 mW/cm2 at 1 V applied bias, which is three orders of magnitude greater than the obtained values of CVD/exfoliated graphene and higher than the required value for practical applications. These results path the way for selective light-triggered logic devices based on EG and can open a new window for broadband photodetection.

Graphene-Templated Achiral Hybrid Perovskite for Circularly Polarized Light Sensing.

This study points out the importance of the templating effect in hybrid organic-inorganic perovskite semiconductors grown on graphene. By combining two achiral materials, we report the formation of a chiral composite heterostructure with electronic band splitting. The effect is observed through circularly polarized light emission and detection in a graphene/α-CH(NH2)2PbI3 perovskite composite, at ambient temperature and without a magnetic field. We exploit the spin-charge conversion by introducing an unbalanced spin population through polarized light that gives rise to a spin photoconductive effect rationalized by Rashba-type coupling. The prepared composite heterostructure exhibits a circularly polarized photoluminescence anisotropy gCPL of ∼0.35 at ∼2.54 × 103 W cm-2 confocal power density of 532 nm excitation. A carefully engineered interface between the graphene and the perovskite thin film enhances the Rashba field and generates the built-in electric field responsible for photocurrent, yielding a photoresponsivity of ∼105 A W-1 under ∼0.08 µW cm-2 fluence of visible light photons. The maximum photocurrent anisotropy factor gph is ∼0.51 under ∼0.16 µW cm-2 irradiance. The work sheds light on the photophysical properties of graphene/perovskite composite heterostructures, finding them to be a promising candidate for developing miniaturized spin-photonic devices.

Polarization-Resolved Position-Sensitive Self-Powered Binary Photodetection in Multilayer Janus CrSBr.

Recent progress in polarization-resolved photodetection based on low-symmetry 2D materials has formed the basis of cutting-edge optoelectronic devices, including quantum optical communication, 3D image processing, and sensing applications. Here, we report an optical polarization-resolving photodetector (PD) fabricated from multilayer semiconducting CrSBr single crystals with high structural anisotropy. We have demonstrated self-powered photodetection due to the formation of Schottky junctions at the Au-CrSBr interfaces, which also caused the photocurrent to display a position-sensitive and binary nature. The self-biased CrSBr PD showed a photoresponsivity of ∼0.26 mA/W with a detectivity of 3.4 × 108 Jones at 514 nm excitation of fluency (0.42 mW/cm2) under ambient conditions. The optical polarization-induced photoresponse exhibits a large dichroic ratio of 3.4, while the polarization is set along the a- and the b-axes of single-crystalline CrSBr. The PD also showed excellent stability, retaining >95% of the initial photoresponsivity in ambient conditions for more than five months without encapsulation. Thus, we demonstrate CrSBr as a fascinating material for ultralow-powered optical polarization-resolving optoelectronic devices for cutting-edge technology.

Microplasma-Enabled Graphene Quantum Dot-Wrapped Gold Nanoparticles with Synergistic Enhancement for Broad Band Photodetection.

Plasmonic nanostructure/semiconductor nanohybrids offer many opportunities for emerging electronic and optoelectronic device applications because of their unique geometries in the nanometer scale and material properties. However, the development of a simple and scalable synthesis of plasmonic nanostructure/semiconductor nanohybrids is still lacking. Here, we report a direct synthesis of colloidal gold nanoparticle/graphene quantum dot (Au@GQD) nanohybrids under ambient conditions using microplasmas and their application as photoabsorbers for broad band photodetectors (PDs). Due to the unique AuNP core and graphene shell nanostructures in the synthesized Au@GQD nanohybrids, the plasmonic absorption of the AuNP core extends the usable spectral range of the photodetectors. It is demonstrated that the Au@GQD-based visible light photodetector simultaneously possesses an extraordinary photoresponsivity of ∼103 A/W, ultrahigh detectivity of 1013 Jones, and fast response time in the millisecond scale (65 ms rise time and 53 ms fall time). We suggest that the synergistic effect can be attributed to the strong fluorescence quenching in Au@GQD coupled with the two-dimensional graphene layer in the device. This work provides knowledge of tailoring the optical absorption in GQDs with plasmonic AuNPs and the corresponding photophysics for broad band response in PD-related devices.

Optically coupled engineered upconversion nanoparticles and graphene for a high responsivity broadband photodetector.

A hybrid upconversion nanoparticle (UCNP)-graphene composite is demonstrated as a high-sensitivity and high-gain photodetector. The 980 nm multiphoton absorbing UCNPs are used as the photoabsorber, and optimized graphene is used as an efficient charge transporter. Although this device class is in its infancy, we show how critical engineering of the UCNPs, with a silica (SiO2) shell, helps to couple it optically with graphene to get a superior device. This initial report of UCNP-graphene optical coupling is expressed as fluorescence enhancement/quenching of the former in the presence of the latter. While the published literature relies mostly on fluorescence quenching in the UCNPs, our devices use both fluorescence quenching (using core UCNPs), and enhancement (using UCNP@SiO2) to significantly enhance the detector parameters. For example, the photoresponsivity of the core-UCNP device was ∼1.52 × 104 A W-1 which could be improved to ∼2.7 × 104 A W-1 (at 980 nm, power density of ∼31.84 µW cm-2, and under a 1.0 V bias) with the UCNP@SiO2 device. The responsivity, gain, and detectivity thus obtained are the highest reported so far for this class of composite photodetectors. The device could detect signals from domestic hand-held appliances such as laser pointers, cellphone flashlights, and air-conditioning remotes. This work will further the knowledge of device photophysics in this class of hybrids.

In Vivo and in Vitro Demonstration of Gold Nanorod Aided Photothermal Presoftening of B16F10 Melanoma for Efficient Chemotherapy Using Doxorubicin Loaded Graphene Oxide.

A combined photothermal therapy (PTT) and chemotherapy (chemo) were performed in vitro on B16F10 melanoma cells and in vivo using melanoma bearing C57BL/6 mice. The 785 nm (100 mW) irradiated gold nanorods (AuNRs) were used as the PT agent, and electrostatically conjugated Doxorubicin (Dox) to a nanocarrier graphene oxide (GO) worked as the chemotherapeutic. Selection of dosage was optimized from the individual viability studies, and finally a combined therapeutic (AuNR (100 ppm), GO (125, and 250 ppm), Dox (0.0058, and 0.00058 ppm)), was delivered in vitro. PTT, followed by chemo, sequentially, resulted in <10% viability, whereas simultaneous PTT with chemo resulted in a viability of ∼40% for the melanoma cells. Flow cytometry indicated optical inhomogeneity in the cells that internalized GO, and AuNR; however, the Dox amount was identical within the cells treated with or without PTT. Confocal microscopy revealed that GO+Dox was internalized, and Dox was distributed uniformly within the cells irrespective of the treatment protocol. In vivo results in melanoma bearing C57BL/6 mice resembled the in vitro data closely. The tumor growth inhibition index was highest at 0.78 for the group receiving sequential treatment, followed by 0.61 for those receiving simultaneous treatment, where the control group had a score of 0. For the sequential treatment, presoftening of the cells with PTT, followed by the chemo resulted in significantly improved toxicity of the treatment, whereas simultaneous PTT with chemo results were dominated by the Dox alone.

Evaluation of complementary diagnostic tools for bovine tuberculosis detection in dairy herds from India.

AIM: A cross-sectional study was undertaken to know the herd prevalence and evaluate the single intradermal tuberculin testing (SITT), culture isolation, and polymerase chain reaction (PCR) analysis for the diagnosis of bovine tuberculosis (TB). MATERIALS AND METHODS: A total of 541 cows of three dairy farms of Bareilly and Mukteshwar were screened by SITT followed by collection of pre-scapular lymph node (PSLN) aspirates (71), milk (54), and blood (71) samples from reactor animals. These clinical samples were processed for culture isolation and direct PCR-based identification and species differentiation. RESULTS: Out of 541 cows screened by SITT, 71 (13.12%) animals were found positive. Mycobacteria were isolated from 3 (4.22%) PSLN aspirate but not from any cultured milk and blood samples. 28 (39.43%) PSLN aspirate and 5 (9.25%) milk samples were positive for Mycobacterium TB (MTB) complex (MTC) by PCR amplification for the IS6110 insertion sequence; however, blood samples were found negative. For species differentiation, multiplex-PCR using 12.7 kb primers was conducted. Out of 28 PSLN aspirate, Mycobacterium bovis was detected in 18 (64.28%) and MTB in 8 (28.57%), whereas 2 aspirate samples (7.14%) were positive for both the species. All the five milk positive samples were positive for M. bovis. CONCLUSION: Direct detection of bovine TB by a molecular-based method in dairy animals after preliminary screening was appeared to be more sensitive and specific compared to the conventional method (i.e., culture isolation). Its application in form of serial testing methodology for the routine diagnosis and thereafter, culling of infected stock may be suggested for the control programs in dairy herds. The PSLN aspirate was found to be the most suitable specimen for culture isolation and PCR-based detection of Mycobacterium spp. among live infected animals.