The presence of a direct optical bandgap in the transition metal dichalcogenide (TMD) layers leads to promising applications in optoelectronic devices such as phototransistors and photodetectors. These devices are commonly fabricated using few-layer and monolayer MoS2 sheets obtained using mechanical exfoliation or chemical vapor deposition techniques. The hybrid structure of quantum dots (QDs) and 2D materials has been investigated to provide outstanding properties for various applications. Herein we report the fabrication of a hybrid QDs/MoS2 photodetector consisting of graphene quantum dots (GQDs) and multilayer MoS2 sheets. The hybrid GQDs and MoS2 films are characterized by atomic force microscopy (AFM); additionally, the I-V characteristics are measured by two-point probe station.

The actual incorporation of dopant species into the ZnS Quantum Dots (QDs) host lattice will induce structural defects evidenced by a red shift in the corresponding exciton. The doping should create new intermediate energetic levels between the valence and conduction bands of the ZnS and affect the electron-hole recombination. These trap states would favour the energy transfer processes involved with the generation of cytotoxic radicals, so-called Reactive Oxygen Species, opening the possibility to apply these nanomaterials in cancer research. Any synthesis approach should consider the direct formation of the QDs in biocompatible medium. Accordingly, the present work addresses the microwave-assisted aqueous synthesis of pure and doped ZnS QDs. As-synthesized quantum dots were fully characterized on a structural, morphological and optical viewpoint. UV-Vis analyzes evidenced the excitonic peaks at approximately 310 nm, 314 nm and 315 nm for ZnS, Cu-ZnS and Mn-ZnS, respectively, Cu/Zn and Mn/Zn molar ratio was 0.05%. This indicates the actual incorporation of the dopant species into the host lattice. In addition, the Photoluminescence spectrum of non-doped ZnS nanoparticles showed a high emission peak that was red shifted when Mn2+ or Cu2+ were added during the synthesis process. The main emission peak of non-doped ZnS, Cu-doped ZnS and Mn-doped ZnS were observed at 438 nm, 487 nm and 521 nm, respectively. Forthcoming work will address the capacity of pure and Cu-, Mn-ZnS quantum dots to generate cytotoxic Reactive Oxygen Species for cancer treatment applications.

A significant drawback of enzyme use in industrial applications is its lack of stability. Graphene oxide (GO) has previously been investigated for enzyme immobilization and enhancement of enzymatic catalysis. Microbial transglutaminase (MTG) is an enzyme that is used to modify food proteins, increase durability of textiles, and crosslink hydrogels for drug delivery. We tested the effects of adding GO and partially reduced GO (pRGO) to water solutions of gelatin and then crosslinking it with MTG, measuring both the resulting gelatin modulus and then the time it took for the onset of gelation. We found that the presence of pRGO in a gelatin-MTG-water mixture (when using 0.75 g MTG in 10 ml of gelatin solution) significantly increases the modulus by 60% more than the control. Using this same concentration of MTG, we measured the onset of gelation time and found that pRGO in gelatin solution reduces the onset of gelation time by nearly 50% while inducing a very large increase in viscosity by three orders of magnitude, whereas the addition of GO increases the onset of gelation time by 33% and decreases the viscosity of the gel by more than one order of magnitude. The very large enhancement by pRGO of the viscosity may be due to pRGO’s electron withdrawing ability and/or may also be due to adsorption of gelatin to the pRGO platelets which effectively increases the crosslinking density through non-enzymatic processes assisting the enzymatic activity.

Defined chemical reactions in a physiological environment are a prerequisite for the in situ synthesis of implant materials potentially serving as matrix for drug delivery systems, tissue fillers or surgical glues. ‘Click’ reactions like thiol Michael-type reactions have been successfully employed as bioorthogonal reaction. However, due to the individual stereo-electronic and physical properties of specific substrates, an exact understanding their chemical reactivity is required if they are to be used for in-situ biomaterial synthesis. The chiral (S)-2-mercapto-carboxylic acid analogues of L-phenylalanine (SH-Phe) and L-leucine (SH-Leu) which are subunits of certain collagenase sensitive synthetic peptides, were explored for their potential for in-situ biomaterial formation via the thiol Michael-type reaction.

In model reactions were investigated the kinetics, the specificity and influence of stereochemistry of this reaction. We could show that only reactions involving SH-Leu yielded the expected thiol-Michael product. The inability of SH-Phe to react was attributed to the steric hindrance of the bulky phenyl group. In aqueous media, successful reaction using SH-Leu is thought to proceed via the sodium salt formed in-situ by the addition of NaOH solution, which was intented to aid the solubility of the mercapto-acid in water. Fast reaction rates and complete acrylate/maleimide conversion were only realized at pH 7.2 or higher suggesting the possible use of SH-Leu under physiological conditions for thiol Michael-type reactions. This method of in-situ formed alkali salts could be used as a fast approach to screen mercapto-acids for thio Michael-type reactions without the synthesis of their corresponding esters.

Lithium substituted magnesium ferrites (LixMg1-xFe2O4, where x = 0.1 to 0.5) were synthesized by solid state reaction method. Various characterization techniques viz. X - Ray Diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometry (VSM) and fourier transform infrared spectroscopy (FTIR) were used to study the effect of lithium substitution. Differences in particle size, crystallinity and magnetic parameters of the ferrites synthesized with difference in composition were observed. XRD patterns of the synthesized samples confirmed phase purity and showed that the lattice parameter decreases with increase in Li content in magnesium ferrite. Decrease in coercivity with increase in lithium concentration was observed from magnetic analysis (VSM). Through FTIR, it was observed that Li+ ions occupy B – sites. FTIR spectrum peaks obtained in the region 1620 – 1670 cm-1 supported water molecule dissociation. It is the required characteristic of the lithium substituted magnesium ferrite to be used in various applications like humidity sensor and hydroelectric cell.

Nb-doped TiO2 thin-films were prepared on fluorine-doped tin oxide (FTO) coated glass directly with niobium ethoxide and TiCl4 in water under the acidic conditions with several concentrations of HCl at 70-90 °C for 45 minutes or 1 hour followed by rinsing with water and annealing at 100 °C for 1 hour. Thin films of 0-1% Nb-doped TiO2 with rutile phase on FTO were obtained, which were confirmed through X-ray diffraction analyses and measurements of energy dispersive X-ray spectroscopy (EDS). Scanning electron microscopy observations equipped with EDS revealed that higher growth temperature over 90 °C is required for doping of Nb. While higher concentration of HCl resulted in much amount of Nb-doping. Band gap of rutile TiO2 gradually reduced from 3.3 eV to 3.23 eV through Nb-doping from 0% to 1%, which were estimated from uv-vis absorption spectroscopic analyses. Hall effect measurements by taking van der Pauw method confirmed that 2.26 times increase of the carrier density and 1.78 times enhancement of the conductivity have been achieved in the case of 1% Nb-doping.

The adsorption/degradation of caffeine and irgasan from aqueous artificial solutions by using.Lignocellulosic residues (LR) impregnated with TiO2 nanoparticles was studied. Three different LR were used: bamboo (Guadua angustifolia), laurel (Cordia allidora) and moringa (Moringa oleifera Lam.), each one with three nominal particle size ranges: 75–149, 45–75, and ≤45 μm. Commercially available TiO2 nanoparticles were added to these residues using the wet impregnation technique. The chemical composition of the LR was determined according to ASTM standards. FTIR spectroscopy and scanning electron microscopy were used to determine the functional groups and morphology of the modified materials, respectively. Adsorption/degradation tests were carried out in batch systems as a function of adsorbent concentration, contact time, nanoparticle content on the impregnated residues and light type influence. The maximum adsorption capacity was (37.1 mg. g-1/55.3 mg.g-1), using 40 wt.% nanoparticle-impregnated ≤45 μm laurel residues during 180 minutes, for a (7.0/0.7 g.L-1) concentration of (caffeine/irgasan). The caffeine adsorption isotherms were well described by the Langmuir and Freundlich models, while the Freundlich model describes irgasan adsorption. The use of UV radiation accelerated threefold the removal process.

A novel series of temperature stable Li3Mg2NbO6–xTiO2 ceramics were prepared by the conventional solid-state route. The effects of TiO2 addition on the sintering behavior, phase composition, microstructure and microwave dielectric properties were investigated systematically. The dense microstructure could be obtained in low TiO2 content (x=0.1) samples sintered at 1100 °C. The dielectric constant εr was attributed to the bulk density and TiO2 content. The variation in Q×f values is related to the bulk density, and improved values could be obtained for Li3Mg2NbO6–0.1TiO2 ceramics. The quality factor (Q×f) had a maximum for x=0.1 and the temperature coefficient of resonant frequency (τf) value shifted towards positive direction with the increase of TiO2 addition. Notably, Li3Mg2NbO6–0.1TiO2 ceramics sintered at 1100 °C possessed excellent microwave dielectric properties: εr=15, Q×f =74,000 GHz(9.93GHz), τf= −3.4 ppm/°C, which made the ceramics as promising low loss and temperature stable candidates for millimeter-wave applications.

Two benzodifuran (BDF) polymers, PBDF-C and PBDF-S, with alkyl and alkylthio substituted thiophene side-chains and benzodithiophene-4,8-dione (BDD) as the acceptor were designed and synthesized. Their optical, electrochemical properties and photovoltaic performances were systematically investigated. The polymer solar cells (PSCs) with a device structure of ITO/PEDOT:PSS/polymer:PC71BM/Ca/Al were fabricated. The PBDF-C based device showed a power conversion efficiency (PCE) of 3.01% after adding 1 vol% 1,8-diodooctane (DIO) as the solvent additive, and PBDF-S gave an enhanced PCE of 3.48% without any post-treatments. The enhancements were from the higher open-circuit voltage (Voc) and fill factor (FF). The thermal- and solvent-treatment-free processing is more favourable for the large area roll-to-roll manufacturing or printing technology for PSCs.

La3+ doped yttrium iron garnet films have been grown on (111) oriented gadolinium gallium garnet substrates via Liquid phase epitaxy technique as a basic material for ISHE device fabrication. Pt as a material with a large spin hall angle was used as a spin detection layer. We investigated the dependence of the spin pumping effect on the power and frequency of the excitation microwaves in La:YIG/Pt bilayers by measuring the ISHE voltage. We demonstrated that the area under the ISHE curve(SISHE) across a wide power range had a nearly linear correlation with the input microwave power (Pin). The parameter SISHE can be used to describe the spin current energy in a Pt layer which can be a useful parameter for a microwave rectifier.

Thin polythiophene films were prepared by electrodeposition, using two novel thiophene monomers containing a pyrene unit linked via a flexible spacer. The obtained polymers have a suitable architecture for the further preparation of polymer composites with graphene via π-π interactions. Physicochemical characterization of the precursor polymers demonstrated that the resulting films are made of homogeneous electroactive polythiophene with pendant pyrene units regularly located on the polymer surface. These compounds are highly emissive and easily form excimers as other high pyrene content polymers. The polymer emission can be drastically quenched by the interaction with graphene after dipping the film into an aqueous suspension of reduced graphite oxide. The presence of aggregated graphene onto pyrene rich content areas by non-covalent interactions has been confirmed by AFM analysis. This kind of polythiophene/pyrene thin films showed to be a good matrix for the elaboration of fluorescent polymer composites.

Polymeric conjugated materials are very promising for developing future soft material-based semiconductors, conductors, electronic and optoelectronic devices due to their inherent advantages such as flexibility, low-cost, ease of processability, and decreased harmful waste. Like their inorganic counterparts, the addition of certain dopants can significantly alter the electronic and optoelectronic properties of the host conjugated polymers or composites allowing modification for a variety of electronic/optoelectronic applications. One way to improve device performance is through the process of thermal annealing. Annealing allows for polymer matrices to self-assemble into a lower energy state which typically leads to increased crystallinity and higher charge mobility. In this work, we plan to evaluate the effects of annealing on doped P3HT films to understand its effects on optoelectronic and electronic properties focusing solely on crystallinity and charge carriers. Further understanding of the connection between annealing and doping in polymeric conjugated materials and thermoelectric properties will allow for an increase net output from multi-function materials and devices.

Pristine poly(butylene adipate-co-terephthalate) (PBAT) is a biodegradable aliphatic-aromatic copolyester that shows no photoluminescent features. The radio induction of photoluminescence (PL) properties in PBAT, after exposure to high doses of gamma radiation, was firstly reported in 2014. These new PL properties have great potential for applications at “in vitro” imaging of human cancer, bio-imaging devices and radiation dosimetry. In this paper, we report the radio induction of photoluminescence (PL) properties in PBAT, after exposure to low energy UV irradiation. In this investigation, films of PBAT, produced by the wire-bar coating technique, were exposed to UV radiation for periods of time ranging from 50 to 500 hours. The PL emission analysis revealed that UV irradiation performed under O2 rich air atmosphere enhances the PL output when compared to irradiations performed in the air. FTIR data confirm that the mechanism behind the UV photo-induction of PL features are similar to the mechanism suggested for gamma radio-induction PL emission. The PL intensity x Spectral Irradiance relationship and RGB color components, the green (G) and blue (B) components, can be used to perform 2D UV dosimetry. The high quantum yield emission of UV-induced PL near 500 nm observed in PBAT is a very interesting finding because it involves the development of a new cheap biodegradable photoluminescent polymer that finds application in drug delivery, bio-imaging devices and also in 2D dosimetry.

It is well known the remarkable optical properties of both graphene and left handed materials, for which we study the optical properties of a multilayer system building by graphene-dielectric-left hand material. In this work, we show the transmission, reflection and absorption spectra for a different set of parameters of the left-handed material structure. It is important to highlight that the inclusion of graphene remarkably modifies the transmission and absorption spectra. The optical properties of the graphene-LHM can be modulated via the different parameters of system. We showed that the fill function do not change the line form of the spectra, however, modify their amplitudes. With respect to light polarization, it’s possible to observe that the spectra are widen for TM respect to TE polarization.

Wearable and bio-implantable health monitoring applications require flexible memory devices that can be used to locally store body vitals prior to transmission or to support local data processing in distributed smart systems. In recent years, non-volatile resistive random access memories composed of oxide-based insulators such as hafnium oxide and niobium pentoxide have attracted a great deal of interest. Unfortunately, hafnium and niobium are not low-cost materials and may also present health challenges. In this work, we have explored the alternative of using titanium dioxide as the insulating oxide using a low-cost solution-phase deposition process. Aqueous sol deposited thin films were deposited on standard RCA-cleaned commercial thermal silicon dioxide (500 nm) wafer (500 µm). Patterned bottom contacts Cr/Au (∼200/300 Å) using shadow masks were deposited on the substrate using successive DC sputtering, and thermal evaporation, respectively at 5 X 10-6 Torr. A sol was prepared using titanium (IV) butoxide as precursor hydrolysed under water and ethanol to form a colloidal solution (sol) at 50°C under constant stirring. Powder X-Ray Diffraction (PXRD) scans of calcined (from sol at 750°C) nanoparticles show a mixture of anatase and rutile phases, confirming the composition of the material. The sol was slowly cooled to room temperature before being spin coated at low rotational speeds on to the substrate in multiple steps involving several spin coating and drying steps to form a uniform film. Top contacts (Ag) of thickness (∼500 Å) were deposited on the sol-deposited thin films using thermal evaporation. The resulting devices were coated with a thick layer of polydimethylsiloxane (PDMS) using a 10:1 ratio of base elastomer and curing agent respectively. After drying the PDMS, resistance measurements were carried out. A high resistance state was detected prior to electroforming in the air at ∼5 MΩ which remains nearly unchanged (∼4.3 MΩ) when dipped in a ∼7.4 pH phosphate buffer solution (equivalent to human blood’s pH (reference average value ∼7.4 pH)). Unencapsulated devices (UM1) were further characterized in air using a Keithley 4200-SCS semiconductor parameter analyzer in dual sweep mode to observe repeatable hysteresis behavior with a large difference between trace and retrace R-V characteristics (∼50±3% over a pristine device), which compares favorably with recent data in the literature on high-performance sputtered TiO2 memristors. Unchanged retention ratio using biocompatible device materials and encapsulation suggests that these devices can be used for biomedical implantable sensor electronics.

Given the potential of Titanium Dioxide in diverse areas including alternative energy, drug delivery and protein adsorption, it is imperative that the underlying mechanism of surface-water interactions be thoroughly understood. Interaction lifetimes between the surface and the surface-adjacent water molecules have a major bearing on interfacial behaviour. Our study employs Molecular Dynamics simulations to understand interfacial interactions of water with a Titanium Dioxide surface, with focus on these interfacial interaction lifetimes. Two polymorphs of Titanium Dioxide, Anatase (101) and Rutile (110) are studied.

Carbon nanomaterials are consistently providing new excitement over their properties and potential applications, but many of these material have yet to fully live up to their expectations commercially. The barrier to adoption often exists as a result of complex processing, fragility of the as-produced material, or difficulty scaling beyond laboratory quantities. This work provides a new approach for utilizing fibrous carbon nanomaterials to advance the technology toward new applications and industrial utility. This is accomplished by creating tailored device architectures through in-situ integration of activated carbon powder using carbon nanofiber deposition. The resulting hybrid materials and components can serve in diverse applications, with each instance able to be fine-tuned through a combination of processing parameters. The applications of such materials are anticipated to directly serve current carbon-based technology in filtration, energy storage and delivery, and thermal management, but the concepts are not limited to current carbon applications.

Single-leg (p × n)-type transverse thermoelectrics (TTE) are reviewed as an alternative to conventional or “longitudinal” double-leg thermoelectrics for applications at room temperature and below. As the name suggests, this unique behavior of (p × n)-type transverse thermoelectrics results from choosing ambipolar anisotropic materials that have a Seebeck tensor with orthogonal p- and n-type Seebeck coefficients, leading to transverse relation between net heat and net electrical current. One feature of such materials is that they can operate near intrinsic doping and, therefore will not suffer from dopant freeze-out, opening the possibility of new cryogenic operation for solid state cooling. In this work, a Seebeck tensor analysis of thermoelectric materials is presented. To compare the performance of transverse thermoelectric materials, a transverse power factor PF⊥ is introduced. Materials searches based on these simple criteria reveal that over 1/4 of the database of about 48,000 inorganic materials could potentially function as (p × n)-type TTE’s, demonstrating the underappreciated prevalence of this class of materials.

Design approaches and achievements for the development of wrought TiAl alloys to be used for LPT and HPC blades are constructed. In case of Ti-Al-M1-M2 quaternary systems, conventional equivalency concept does not work for the alloy design, and a new thermodynamic database for phase diagram calculations in multi-component systems of the alloys is built by introducing the interaction parameters among four phases of β−Ti, α2−Ti3Al, α−Ti and γ−TiAl phases in the systems, in order to reproduce the experimentally determined phase diagrams. Based on the phase diagram calculations, the composition range of a unique phase transformation pathway of β+α→α→β+γ in the multi-component system can be identified, and thus model alloys with excellent hot workability even at higher strain rate and mechanical properties can be successfully proposed. It can be concluded that an introduction of bcc β phase and the morphology control through the phase transformation pathway make it possible to improve the room temperature ductility, creep and fatigue crack propagation resistance.