Surface-Modified Graphene for Mid-Infrared Detection

In this chapter, morphology variation and electronic structure in a surface-modified graphene are demonstrated by both calculation and experimental results. The results indicate that the band structure and morphology of modified graphene sheets are altered because of changing in the type of hybridization of carbon atoms in the graphene sheet. Accordingly, the band gap of graphene can be tuned by surface modification using organic molecules. Then, modified graphene is used for fabrication of infrared detectors. The properties of unmodified graphene photodetectors were also measured so as to compare with modified graphene photodetectors. The results demonstrate that modification of graphene using organic ligands improved the detection parameters such as fast response time, electrical stability and low dark current. Moreover, the sensitivity of photodetectors based on modified graphene was significantly improved

Trap engineering in solution processed PbSe quantum dots for high-speed MID-infrared photodetectors

The ongoing quest to find methods to control the trap states in solution processed nanostructures (trap engineering) will revolutionise the applications of nanomaterials for optoelectronic purposes. In this paper, we present a new combined experimental/theoretical approach (molecular orbital theory) allowing a new view on trap engineering of nanostructures for applications in photodetectors. PbSe quantum dots (QDs) of about 30 nm diameter were prepared in a solution-based process from lead iodide (PbI2) and chloride (PbCl2), while using lead acetate (PbOAc2) reliably gave particles of about 200 nm in size under the same conditions. Comparison of the dangling acetate (OAc-) versus the spherical monoatomic surface ligands chloride (Cl-) and iodide (I-) and varying the covalent/ionic character of the particle-surface ligand (ionic: OAc- > Cl- > I-: covalent) bond allowed an interesting insight into what governs the trap states. Density functional theory (DFT) calculations are used to study band structures and density of states and show trap states localised within the bandgap moving to the conduction or valence band upon interaction of surface metal atoms with the surface ligands. Infrared detectors based on these materials are fabricated and allowed high-speed mid-infrared photo-detection with 100 ns rise and 110 ns fall response times

UV/IR Dual-Wavelength Photodetector Design Based on ZnO/PMMA/PbSe Nanocomposites

A UV/IR dual-wavelength photodetector based on a ZnO/PMMA/PbSe nanocomposite [PMMA = poly(methyl methacrylate)] for simultaneous detection of 365 nm UV and 4 mu m IR radiation is presented. For UV detection spherical nanoparticles of boron-doped ZnO were synthesized and stabilized using hexamethylenetetramine. The absorption intensity in the UV-vis range is increased upon B doping and discrete Fourier transform calculations confirm the results. Responsivity of the fabricated UV detector is 7.8 AW(-1) and the detector gain is 26.49 at a 365 nm input wavelength. For the synthesis of IR detecting PbSe a new method was worked out, including the stabilization of the particles with thioacetamide. The performance of the PbSe based IR detector turns out to be superior to previously reported PbSe based detectors synthesized by established methods. The responsivity and gain of the detector is 8 AW(-1) and 3.31, respectively for 4 mu m incident wavelength. The sensitivity is 30 for IR detection and overall this sensitivity is excellent for sensing in the mid-IR range. All three chemical factors, the B-doping, the synthesis conditions for nanoparticles, and the surface modification have contributed to the excellent optoelectronic performance of these new photodetector devices, while the polymethyl methacrylate layer turned out to be very effectively reducing the noise for IR detection

Transparent Display using a quasi-array of Si-SiO2 Core-Shell Nanoparticles

Abstract A novel type of transparent monitor with high-resolution images based on Si-SiO2 core-shell nanoparticles is presented in this contribution. In this monitor, a quasi-array of nanoparticles was used to obtain a very sharp scattering profile. For this purpose, the Si-SiO2 nanoparticles were synthesized and with controlling the size of particles, the dominant emission wavelength was controlled. For the fabrication of a blue color transparent monitor the solution processed Si-SiO2 nanoparticles were dispersed in polystyrene and then coated on a transparent glass surface. After drying the film, the typical features representing a transparent monitor were studied. A video projector was used and text and pictures were sent on the monitor. This monitor reveals very attractive features such as simplicity, wide viewing angle, scalability to larger sizes and low cost. Importantly, the texts and pictures can be well presented on both sides of the fabricated monitor. The composite thin film can be also separated from the glass and can be used as a flexible display. To shed light on the impact of the structure on the optical properties Si-SiO2 and Ag nanomaterials representing perfect arrays of nanoparticles, quasi-arrays and randomly oriented nanoparticles were calculated/simulated using the finite-difference time-domain (FDTD) method. The results were compared to the experimental data and show a high accordance

High-efficiency upconversion process in cobalt and neodymium doped graphene QDs for biomedical applications

Abstract Multiphoton absorbing upconversion nanoparticles are emerging as bioimaging materials but are limited by the low quantum yield of their visible fluorescence. This article contains colloids of graphene quantum dots (GQDs), Neodymium, and Cobalt doped Graphene Quantum dots (Co-GQDs and Nd-GQDs) surrounded by carboxylic acids are synthesized which especially are suitable for bio applications; in this way, carboxylic acid groups exchanged by Amoxicillin as an antibiotic with bactericidal activity. The XRD diffraction method, TEM microscope, UV–Vis, and photoluminescence spectroscopies characterize the synthesized materials. The synthesized Quantum dots (QDs) exhibit upconversion properties and their emission is centered at 480 nm, but a red shift was observed with the increase of the excitation wavelength. In the emission spectra of synthesized QDs that can be related to the defect levels introduced by passivation of the QDs in the structure, the results show that with the interaction of the surface QDs with more carboxylic groups, the redshift is not observed. As the results indicate an increase in the intensity of upconversion emission is recorded for Co-GQDs and Nd-GQDs. The absolute quantum efficiency (QY) for Co-GQDs and Nd-GQDs were determined to be 41% and 100% more than GQDs respectively. DFT calculations indicate a strong bond between graphene and cobalt and Neodymium atoms. In doped materials, there are trap levels between the band gap of the GQDs which are responsible for increasing the intensity of the upconversion phenomenon