Enhanced Ultraviolet Photoresponse Characteristics of Indium Gallium Zinc Oxide Photo-Thin-Film Transistors Enabled by Surface Functionalization of Biomaterials for Real-Time Ultraviolet Monitoring.

Indium gallium zinc oxide (IGZO) is one of the most promising materials for diverse optoelectronic applications based on thin-film transistors (TFTs) including ultraviolet (UV) photodetectors. In particular, the monitoring of UV-A (320-400 nm) exposure is very useful for healthcare applications because it can be used to prevent various human skin and eye-related diseases. However, the relatively weak optical absorption in the UV-A range and the persistent photoconductivity (PPC) arising from the oxygen vacancy-related states of IGZO thin films limit efficient UV monitoring. In this paper, we report the enhancement of the UV photoresponse characteristics of IGZO photo-TFTs by the surface functionalization of biomolecules on an IGZO channel. The biomaterial/IGZO interface plays a crucial role in enhancing UV-A absorption and suppressing PPC under negative gate bias, resulting in not only increased photoresponsivity and specific detectivity but also a fast and repeatable UV photoresponse. In addition, turning off the device without external bias completely eliminates PPC due to the internal electric field induced by the surface functionalization of biomaterials. Such a volatile feature of PPC enables the fast and repeatable UV photoresponse. These results suggest the potential of IGZO photo-TFTs combined with biomaterials for real-time UV monitoring.

PEGylated Indium Nanoparticles: A Metallic Contrast Agent for Multiwavelength Photoacoustic Imaging and Second Near-Infrared Photothermal Therapy.

Indium, a low melting point metal, is well-known for constructing eutectic gallium-indium liquid metal. However, unlike liquid metal nanoparticles, the biomedical applications of metallic indium nanoparticles (In NPs) remain in their infancy. Herein, an ultrasound-assisted liquid-reduction synthesis strategy was developed to prepare PEGylated In NPs, which were then used as a high-performance contrast agent for enhancing multiwavelength photoacoustic imaging and second near-infrared (NIR-II) photothermal therapy of the 4T1 breast tumor. The obtained In NPs depicted remarkable optical absorption from the first near-infrared (NIR-I) to NIR-II region and a high photothermal conversion efficiency of 41.3% at 1064 nm, higher than the majority of conventional NIR-II photothermal agents. Upon injection into the tumor, the photoacoustic intensities of the tumor section post-injection were obviously increased by 2.59-, 2.62-, and 4.27-fold of those of pre-injection by using excitation wavelengths of 750, 808, and 970 nm, respectively, depicting an excellent multiwavelength contrast capability of photoacoustic imaging. In addition, efficient ablation of the 4T1 tumor was achieved through the photothermal performance of PEGylated In NPs under NIR-II laser irradiation. Importantly, as the widely used element in the clinic, In NPs were highly biocompatible in vitro and in vivo. Therefore, this work pioneered the biomedical applications of PEGylated In NPs for cancer diagnosis and treatment.

Cathode-Anode Spatial Division Photoelectrochemical Platform Based on a One-Step DNA Walker for Monitoring of miRNA-21.

Photoelectrochemical (PEC) biosensors carried out the whole reaction process in the same solution, which would limit the sensitivity and selectivity of detection in the sensing system. Herein, we reported a promising new cathode-anode spatial division PEC platform based on the two-electrode synergistic enhancement strategy. With the photoanode and photocathode integrated in the same current circuit, the platform exhibited an increased photocurrent response, as well as an improved anti-interference ability led by separating the two electrodes spatially. In this proposal, red light-driven AgInS2 nanoparticles (NPs) served as the photoanode to build biometric steps and amplify the signal, whereas p-type PbS quantum dots were selected as the photocathode to increase the signal. With the participation of alkaline phosphatase (ALP) labeled on Au NPs-DNA, ascorbic acid 2-phosphate was catalyzed to produce ascorbic acid as an electron donor, resulting in the enhancement of the PEC signal. Interestingly, in the presence of miRNA-21 and T7 Exo, the one-step DNA walker amplification can be triggered to reduce the PEC signal by releasing ALP-Au NP-DNA. The constructed PEC biosensor exhibited a detection limit of as low as 3.4 fM for miRNA-21, which was expected to be applied to early clinical diagnosis. Also, we believe that the proposed cathode-anode spatial division PEC platform can open up a new view for the establishment of other types of PEC biosensors.

Intramolecular Photoelectrochemical System Using Tyrosine-Modified Antibody-Targeted Peptide as Electron Donor for Detection of Biomarkers.

An intramolecular photoelectrochemical (PEC) system is designed from the novel electron donor YYYHWRGWV (Y3-H) peptide ligand for the first time. The bifunctional nonapeptide cannot only rely on the HWRGWV sequence as a site-oriented immobilizer to recognize the crystallizable fragment (Fc) domains of the antibody but also acts as electron donors for PEC generation via three tyrosine (Y) of the N-terminal. The Bi2WO6/AgInS2 heterojunction with a significant visible-light absorption is utilized as a photoelectric generator, and the motivation is ascribed to a proven proposition, namely, that short-wavelength illuminant radiates proteins, causing a decline in bioactivity of immune protein. An innovative biosensor is fabricated using the above strategies for the detection of CYFRA21-1, a biomarker of squamous cell lung carcinoma. This sort of PEC-based sensing platform shows convincing experimental data and could be an effective candidate for clinical application in the future due to their extremely skillful conception.

Photoelectrochemical aptasensor for thrombin based on Au-rGO-CuS as signal amplification elements.

A photoelectrochemical platform for thrombin determination was developed based on Au-rGO-CuS as multiple signal amplification elements. CuInS2 QDs was used to sensitize burr-shape TiO2 (b-TiO2) to obtain a strong photocurrent. Under the specific recognition between aptamer and thrombin, a sandwichlike structure was formed and the Au-rGO-CuS-labeled aptamer (S2@Au-rGO-CuS) was immobilized on the electrode surface. This induced a sharp decrease in photocurrent. The phenomenon is mainly due to the fact that CuS NPs can competitively consume the light energy and electron donor with CuInS2/b-TiO2. The rGO can increase the amount of CuS NPs and the Au NPs can accelerate charge transferring which depress the recombination of photogenerated electrons and holes in CuS to further enhance the competitive capacity of CuS. The sandwichlike structure has a steric hindrance effect. Therefore, the S2@Au-rGO-CuS has a multiple signal amplification function for thrombin determination. Under optimal conditions, the PEC aptasensor exhibited a wide linear concentration range from 0.1 pM to 10 nM with a low detection limit of 30 fM (S/N = 3) for thrombin. Besides, the designed aptasensor performed well in the assay of human serum sample, indicating good potential for the determination of thrombin in real samples. Graphical abstract.

Direct Z-scheme 1D/2D WO2.72/ZnIn2S4 hybrid photocatalysts with highly-efficient visible-light-driven photodegradation towards tetracycline hydrochloride removal.

There are increasing environmental concerns of serious pollution from emission of antibiotic wastewater. Herein, a series of direct Z-scheme WO2.72/ZnIn2S4 (WOZIS) hybrid photocatalysts composed of one-dimensional (1D) WO2.72 (WO) nanorods and two-dimensional (2D) ZnIn2S4 (ZIS) nanosheets have been designed and constructed for tetracycline hydrochloride (TCH) degradation without presence of solid-state electron mediators. The crystalline phase, chemical composition, morphology, optical properties and photocatalytic activity of the as-prepared samples were characterized by the XRD, XPS, SEM, HRTEM, BET, UV-vis DRS, and PL. Obviously, all the WOZIS hybrid photocatalysts exhibited significantly enhanced photocatalytic activity towards TCH degradation. Meanwhile, WOZIS-1 sample with WO/ZIS molar ratio of 1:1 showed the highest photocatalytic activity. The significantly enhanced photoactivity of WOZIS hybrid photocatalyst was due to Z-scheme charge separation mechanism based on the build of tight interfacial contacts between WO nanorods and ZIS nanosheets, thereby driving efficient charge separation. Moreover, the high photocatalytic stability of as-prepared WOZIS-1 hybrid sample was revealed through seven successive cycling reactions.

An CuInS2 photocathode for the sensitive photoelectrochemical determination of microRNA-21 based on DNA-protein interaction and exonuclease III assisted target recycling amplification.

A photocathode is described for the determination of microRNA-21 by using CuInS2 as an active photocathode material. Exonuclease III assisted target recycling amplification was employed to enhance the detection sensitivity. The TATA-binding protein (TBP) was applied to enhance steric hindrance which decreases the photoelectrochemical intensity. This strategy is designed by combining the anti-interference photocathode material, enzyme assisted target recycling amplification and TBP induced signal off, showing remarkable amplification efficiency. Under the optimized conditions, the detection limit for microRNA-21 is as low as 0.47 fM, and a linear range was got from 1.0 × 10-15 M to 1.0 × 10-6 M. Graphical abstract Schematic representation of sensitive photoelectrochemical detection of microRNA-21.CuInS2 is used as an active photocathode material. Combined Exonuclease III assisted target recycling amplification and TATA-binding protein decreased of photoelectrochemical intensity, the detection limit was 0.47 fM with good selectivity. (miR-21: microRNA-21; CS: chitosan).

Three-dimensional biogenic C-doped Bi2MoO6/In2O3-ZnO Z-scheme heterojunctions derived from a layered precursor.

Novel 3D biogenic C-doped Bi2MoO6/In2O3-ZnO Z-scheme heterojunctions were synthesized for the first time, using cotton fiber as template. The as-prepared samples showed excellent adsorption and photodegradation performance toward the hazardous antibiotic doxycycline under simulated sunlight irradiation. The morphology, phase composition and in situ carbon doping could be precisely controlled by adjusting processing parameters. The carbon doping in Bi2MoO6/In2O3-ZnO was derived from the cotton template, and the carbon content could be varied in the range 0.9-4.4 wt.% via controlling the heat treatment temperature. The sample with Bi2MoO6/In2O3-ZnO molar ratio of 1:2 and carbon content of 1.1 wt.% exhibited the highest photocatalytic activity toward doxycycline degradation, which was 3.6 and 4.3 times higher than those of pure Bi2MoO6 and ZnInAl-CLDH (calcined layered double hydroxides), respectively. It is believed that the Z-scheme heterojunction with C-doping, the 3D hierarchically micro-meso-macro porous structure, as well as the high adsorption capacity, contributed significantly to the enhanced photocatalytic activity.

Photoluminescence Detection of Surface Oxidation Processes on InGaN/GaN Nanowire Arrays.

InGaN/GaN nanowire arrays (NWA) exhibit efficient photoluminescence (PL) in the green spectral range, which extends to temperatures well beyond 200 °C. Previous work has shown that their PL is effectively quenched when oxidizing gas species such as O2, NO2, and O3 abound in the ambient air. In the present work we extend our investigations to reducing gas species, in particular to alcohols and aliphatic hydrocarbons with C1 to C3 chain lengths. We find that these species give rise to an enhancing PL response which can only be observed when the NWAs are operated at elevated temperature and in reactive synthetic air backgrounds. Hardly any response can be observed when the NWAs are operated in inert N2 backgrounds, neither at room temperature nor at elevated temperature. We attribute such enhancing PL response to the removal of quenching oxygen and the formation of enhancing water adsorbates as hydrocarbons interact with oxygen species coadsorbed on the heated InGaN surfaces.

One-step in situ hydrothermal fabrication of octahedral CdS/SnIn4S8 nano-heterojunction for highly efficient photocatalytic treatment of nitrophenol and real pharmaceutical wastewater.

Octahedral CdS/SnIn4S8 nano-heterojunctions were fabricated by a facile and simple one-step in situ hydrothermal method, and the molar ratio of CdS to SnIn4S8 was optimized. The optimal (0.5:1)CdS/SnIn4S8 heterojunctions exhibit the highest visible-light photocatalytic activity with 97.1% degradation efficiency of 2-nitrophenol in 120min, which is much higher than those of individual CdS and SnIn4S8. The enhanced photocatalytic performance could be attributed to the effective separation and transfer of photogenerated charges originating from the well-matched band gap structures. Of special significance is that (0.5:1)CdS/SnIn4S8 can effectively mineralize 2-nitrophenol and real pharmaceutical wastewater. Moreover, CdS/SnIn4S8 nano-heterojunctions show excellent reusability in five cycles due to the stable surface composition and chemical valence state.

MoS2 Nanosheet-Modified CuInS2 Photocatalyst for Visible-Light-Driven Hydrogen Production from Water.

Exploiting photocatalysts respond to visible light is of huge challenge for photocatalytic H2 production. Here, we synthesize a new composite material consisting of few-layer MoS2 nanosheets grown on CuInS2 surface as an efficient photocatalyst for solar H2 generation. The photocatalytic results demonstrate that the 3 wt % MoS2 /CuInS2 photocatalyst exhibits the highest H2 generation rate of 316 µmol h(-1) g(-1) under visible light irradiation, which is almost 28 times higher than that of CuInS2 . Importantly, the MoS2 /CuInS2 photocatalyst shows a much higher photocatalytic activity than that of Pt-loaded CuInS2 photocatalyst. The enhanced photocatalytic activities of MoS2 /CuInS2 photocatalysts can be attributed to the improved charge separation at the interface of MoS2 and CuInS2, which is demonstrated by the significant enhancement of photocurrent responses in MoS2 /CuInS2 photoelectrodes. This work presents a noble-metal-free photocatalyst that responds to visible light for solar H2 generation.

Nano-sized quaternary CuGa2In3S8 as an efficient photocatalyst for solar hydrogen production.

The synthesis of quaternary metal sulfide (QMS) nanocrystals is challenging because of the difficulty to control their stoichiometry and phase structure. Herein, quaternary CuGa2In3S8 photocatalysts with a primary particle size of ≈4 nm are synthesized using a facile hot-injection method by fine-tuning the sulfur source injection temperature and aging time. Characterization of the samples reveals that quaternary CuGa2In3S8 nanocrystals exhibit n-type semiconductor characteristics with a transition band gap of ≈1.8 eV. Their flatband potential is located at -0.56 V versus the standard hydrogen electrode at pH 6.0 and is shifted cathodically by 0.75 V in solutions with pH values greater than 12.0. Under optimized conditions, the 1.0 wt % Ru-loaded CuGa2In3S8 photocatalyst exhibits a photocatalytic H2 evolution response up to 700 nm and an apparent quantum efficiency of (6.9±0.5) % at 560 nm. These results indicate clearly that QMS nanocrystals have great potential as nano-photocatalysts for solar H2 production.

Adsorption and enhanced photocatalytic activity of the {0 0 0 1} faceted Sm-doped ZnIn2S4 microspheres.

In this study, the doping effect of samarium on the structure, morphology, adsorption and photocatalytic performance of hexagonal ZnIn2S4 microspheres was studied. The photocatalytic activity of Sm-doped ZnIn2S4 microspheres was evaluated for the photodegradation of Rhodamine B (RhB) and methyl orange (MO) under visible light irradiation. The samples were characterized by XRD, SEM, XPS, UV-vis, TEM, and N2 adsorption-desorption analysis. The results show that the hexagonal ZnIn2S4 microspheres are composed of nanoplates growing along c-axis with the predominant negative-charged S plane. Compared with the photodegadation of MO dye, the negative-charged {0 0 0 1} facets not only are beneficial for the adsorption of RhB by -N(Et)2 groups but also can accumulate the separation of photogenerated electrons and holes, enhancing photodegradation efficiency by direct-hole photocatalysis. Moreover, Sm is partially substituted for In in the crystal lattice for forming the doping energy level which promotes the separation of photoinduced electron-hole pairs and enhances absorption of visible light. Hexagonal 2% Sm-doped ZnIn2S4 microspheres with exposed {0 0 0 1} facets resulted in higher photodegradation efficiency of RhB under visible light irradiation.

Fabrication of In2S3 nanoparticle decorated TiO2 nanotube arrays by successive ionic layer adsorption and reaction technique and their photocatalytic application.

In2S3 nanoparticle (NP) decorated self-organized TiO2 nanotube array (In2S3/TiO2 NT) hybrids were fabricated via simple successive ionic layer adsorption and reaction (SILAR) technique. The In2S3 NPs in a size of about 15 nm were found to deposit on the top surface of the highly oriented TiO2 NT while without clogging the tube entrances. The loading amount of In2S3 NPs on the TiO2 NT was controlled by the cycle number of SILAR deposition. Compared with the bare TiO2 NT, the In2S3/TiO2 NT hybrids showed stronger absorption in the visible light region and significantly enhanced photocurrent density. The photocatalytic activity of the In2S3/TiO2 NT photocatalyst far exceeds that of bare TiO2 NT in the degradation of typical herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) under simulated solar light. After 160-min irradiation, almost 100% 2,4-D removal is obtained on the 7-In2S3/TiO2 NT prepared through seven SILAR deposition cycles, much higher than 26% on the bare TiO2 NT. After 10 successive cycles of photocatalytic process with total 1,600 min of irradiation, In2S3/TiO2 NT maintained as high 2,4-D removal efficiency as 95.1% with good stability and easy recovery, which justifies the potential of the photocatalytic system in application for the photocatalytic removal of organic pollutants such as herbicides or pesticides from water.

Negative gate bias and light illumination-induced hump in amorphous InGaZnO thin film transistor.

While observing the transfer characteristics of a-IGZO TFTs, it was noticed that a hump occurred in the subthreshold regime after light and bias stress. This study analyzes the mechanism of the hump occurrence. It was determined that hump characteristics were related with parasitic TFTs which formed at the peripheral edges parallel with the channel direction. It seems that the negative shift of the transfer characteristics of parasitic TFTs was larger than that of the main TFT under light and bias stress. Therefore, the difference in the negative shift between the main TFT and the parasitic TFT was the origin of the hump occurrence. We investigated the instability of a-IGZO TFTs under negative gate bias with light illumination for various channel structures in order to verify the above mechanism.

Spectroscopic studies of In2O3 nanostructures; photovoltaic demonstration of In2O3/p-Si heterojunction.

The thermal oxidation process of the indium nitride (InN) nanorods (NRs) was studied. The SEM studies reveal that the cracked and burst mechanism for the formation of indium oxide (In2O3) nanostructures by oxidizing the InN NRs at higher temperatures. XRD results confirm the bcc crystal structure of the as prepared In2O3 nanostructures. Strong and broad photoluminescence spectrum located at the green to red region with maximum intensity at 566 nm along with a weak ultraviolet emission at 338 nm were observed due to oxygen vacancy levels and free excitonic transitions, respectively. The valence band onset energy of 2.1 eV was observed from the XPS valence band spectrum, clearly justifies the alignment of Fermi level to the donor level created due to the presence of oxygen vacancies which were observed in the PL spectrum. The elemental ratio In:O in as prepared In2O3 was found to be 42:58 which is in close agreement with the stoichiometric value of 40:60. A downward shift was observed in the Raman peak positions due to a possible phonon confinement effect in the nanoparticles formed in bursting mechanism. Such single junction devices exhibit promising photovoltaic performance with fill factor and conversion efficiency of 21% and 0.2%, respectively, under concentrated AM1.5 illumination.

Red emissive CuInS2-based nanocrystals: a potential phosphor for warm white light-emitting diodes.

We here report the integration of red emissive CuInS(2) based nanocrysals as a potential red phosphor for warm light generation. By combining red emissive CuInS(2) based nanocrysals with commercial yellow emissive YAG:Ce and green emissive Eu(2+) doped silicate phosphors, we fabricated warm white light-emitting diodes with high color rendering index up to ~92, high luminous efficiency of 45~60 lm/W and color temperature less than 4000K.

Effect of non-vacuum thermal annealing on high indium content InGaN films deposited by pulsed laser deposition.

InGaN films with 33% and 60% indium contents were deposited by pulsed laser deposition (PLD) at a low growth temperature of 300 °C. The films were then annealed at 500-800 °C in the non-vacuum furnace for 15 min with an addition of N(2) atmosphere. X-ray diffraction results indicate that the indium contents in these two films were raised to 41% and 63%, respectively, after annealing in furnace. In(2)O(3) phase was formed on InGaN surface during the annealing process, which can be clearly observed by the measurements of auger electron spectroscopy, transmission electron microscopy and x-ray photoelectron spectroscopy. Due to the obstruction of indium out-diffusion by forming In(2)O(3) on surface, it leads to the efficient increment in indium content of InGaN layer. In addition, the surface roughness was greatly improved by removing In(2)O(3) with the etching treatment in HCl solution. Micro-photoluminescence measurement was performed to analyze the emission property of InGaN layer. For the as-grown InGaN with 33% indium content, the emission wavelength was gradually shifted from 552 to 618 nm with increasing the annealing temperature to 800 °C. It reveals the InGaN films have high potential in optoelectronic applications.

Electronic properties of GaAs, InAs and InP nanowires studied by terahertz spectroscopy.

We have performed a comparative study of ultrafast charge carrier dynamics in a range of III-V nanowires using optical pump-terahertz probe spectroscopy. This versatile technique allows measurement of important parameters for device applications, including carrier lifetimes, surface recombination velocities, carrier mobilities and donor doping levels. GaAs, InAs and InP nanowires of varying diameters were measured. For all samples, the electronic response was dominated by a pronounced surface plasmon mode. Of the three nanowire materials, InAs nanowires exhibited the highest electron mobilities of 6000 cm² V⁻¹ s⁻¹, which highlights their potential for high mobility applications, such as field effect transistors. InP nanowires exhibited the longest carrier lifetimes and the lowest surface recombination velocity of 170 cm s⁻¹. This very low surface recombination velocity makes InP nanowires suitable for applications where carrier lifetime is crucial, such as in photovoltaics. In contrast, the carrier lifetimes in GaAs nanowires were extremely short, of the order of picoseconds, due to the high surface recombination velocity, which was measured as 5.4 × 105 cm s⁻¹. These findings will assist in the choice of nanowires for different applications, and identify the challenges in producing nanowires suitable for future electronic and optoelectronic devices.

Large area photoconductive terahertz emitter for 1.55 µm excitation based on an InGaAs heterostructure.

We present scalable large area terahertz (THz) emitters based on a nanoscale multilayer InGaAs/InAlAs heterostructure and a microstructured electrode pattern. The emitters are designed for pump lasers working at the telecommunication wavelength of 1.55 µm. Electric THz fields of more than 2.5 V cm⁻¹ are reached with moderate pump powers of 80 mW, the corresponding spectrum extends up to 3 THz. The saturation characteristics have been investigated for different pump laser spot sizes. For small pump powers of less than 50 mW the emitted THz field is nearly independent of the spot size, for higher pump powers and small spot sizes a clear saturation of the generated THz pulse can be observed. Hence the use of scalable emitters is especially promising for high power fibre laser systems. The spectral content of the generated radiation is nearly independent of the parameters spot size, pump power, and bias voltage, which allows for stable operation in spectroscopic applications.