Significant Enhancement Of Photoconductivity Research Articles

Dosimetric investigation of a new quantum dots/nanocomposite (CdTe QDs/PVK) sensor for real-time gamma radiation detection

The design of organic/inorganic polymer nanoparticles-based hybrids is promising for gamma ray sensor systems. Here, we design semiconducting nanocomposite system for efficient gamma ray harvesting system where cadmium telluride (CdTe) quantum dots act as dopant and poly(N-vinyl carbazole) (PVK) polymer acts as host. Highly crystalline 1-dodecanethiol (1-DDT) decorated CdTe quantum dots with average diameter of ~ 3 nm were synthesized and characterized with high-resolution transmission electron microscopy (HR-TEM) analysis. Nearly monodispersed CdTe/PVK nanocomposite was subsequently prepared by addition of CdTe quantum dots (QDs) in poly(N-vinyl carbazole) matrix. The photophysical interactions between polymer host and QDs have been investigated by preparing an ohmic contact detector using a conductive cell with two gold-coated walls. Gamma detecting properties of the CdTe QDs/PVK nanocomposite such as sensitivity, repeatability, and the linearity of dose rate response were assessed. Significant enhancement in photoconductivity induced by the gamma radiation in CdTe QDs/PVK nanocomposite has been demonstrated.

Electropolymerized highly photoconductive thin films of cyclopalladated and cycloplatinated complexes.

The complete characterization of novel electropolymerizable organometallic complexes is presented. These are newly synthesized cyclometalated complexes of general formula (PPy)M(O ∧ N)(n) (H(PPy) = 2-phenylpyridine, M = Pd(II) or Pt(II), H(O ∧ N)(n) = Schiff base). Polymeric thin films have been obtained from these complexes by electropolymerization of the triphenylamino group grafted onto the H(O ∧ N)(n) ancillary ligand. The redox behavior and the photoconductivity of both of the monomers (PPy)M(O ∧ N)(n) and the electropolymerized species have been investigated. The polymeric films of (PPy)M(O ∧ N)(n) have shown a very significant enhancement of photoconductivity when compared to their monomeric amorphous counterparts. The high stability of the obtained films strongly suggests that electropolymerization of cyclometalated complexes represents a viable deposition technique of quality thin films with improved photoconduction properties, hence opening the door to a new class of materials with suitable properties for optoelectronic applications.

Growth Mechanism and Characteristics of Semiconductor Nanowires for Photonic Devices

An overview on the growth mechanism of nanowire, fabrication and performance of selenide nanowires devices is presented. Binary, ternary and quaternary selenides have relatively low optical absorption coefficient and have wide transparency range. This combination of properties of selenides makes them very important materials for detector applications. Lead selenide (PbSe) nano particles and nanowires were grown by the physical vapor transport (PVT) method and zinc selenide (ZnSe) nanowire was grown by chemical vapor transport (CVT) methods. Observations on the growth of PbSe indicate that oriented attachment of nanocrystal building blocks produces nanowires. On silicon (111) substrates binding was observed to be on (001) and (111) faces. Zinc selenide nanowires were fabricated into nano Avalanche Photodiodes (Nano-APDs) structure. Experimental results on the fabricated devices of zinc selenide show significant enhancement in photoconductivity. Growth of nanowire and fabrication of devices has progressed significantly and has shown significant improvements in the performance, but fabrication still remains a big challenge.

Photoconduction and the electronic structure of silica nanowires embedded with gold nanoparticles

Silica nanowires (SiO${}_{x}$-NWs) embedded with Au peapods have been studied by energy-filtered scanning transmission electron microscopy (EFTEM), O $K$- and Au ${L}_{3}$-edge x-ray absorption near-edge structure (XANES), and extended x-ray absorption fine structure (EXAFS), x-ray emission spectroscopy (XES) and scanning photoelectron microscopy. XANES and XES data show that band gaps of Au-peapod-embedded and pure SiO${}_{x}$-NWs were 6.8 eV. In additional, XANES and EXAFS results indicate illumination-induced electron transfer from Au peapod to SiO${}_{x}$-NWs and does not show any feature attributable to the formation of Au-Si bonding in the Au peapod embedded in SiO${}_{x}$-NWs with or without illumination. Photoresponse and EFTEM measurements show that green light has more significant enhancement of photoconductivity than red and blue light due to surface plasmon resonance and suggest that transport of electrons across SiO${}_{x}$-NWs is via Mott-variable-range hopping mechanism through localized or defect states.

Photorefractivity in a bi-functional polymer nanocomposites sensitized by CdS nanoparticle

We report an organic/inorganic hybridized nanocomposite consisting of a bi-functional poly(N-vinyl)-3-[p-nitrophenylazo]carbazolyl serves as a polymeric charge-transporting and second-order nonliner optical matrix, and CdS nanoparticles as photosensitizers to manifest photorefractive (PR) effect. The unpoled PVNPAK film exhibits a second harmonic generation (SHG) coefficient of 4.7 pm/V due to the possibility of self-alignment of the azo chromophore. Significant enhancement of photoconductivity is noticed with the increase of CdS nanoparticles concentration. The photorefractive property of the polymer nanocomposites were determined by two-beam coupling (TBC) experiment. The TBC gain and diffraction efficiency of 11.89 cm−1 and 3.2% were obtained for PVNPAK/CdS at zero electrical field.

Photorefractive effect in a CdS nanoparticles-sensitized polymer composite

The photorefractive (PR) performance of an organic/inorganic hybrid polymer composite sensitized by CdS nanoparticles, combining poly(N-vinylcarbazole) (PVK), the second-order optically nonlinear chromophore 1-n-butoxy-2-methyl-(4-p-nitropheylazo)benzene (BMNPAB) and 9-ethylcarbazole (ECZ) was studied. It was confirmed that the CdS colloidal particles had a nanoscale size and quantum confinement effect adopting transmission electron microscopy and UV-Vis absorption spectroscopy. The addition of CdS nanoparticles as a photosensitizer in PVK will be significant enhancement of photoconductivity because of the high photocharge generation quantum efficiency and high charge transport to conducting polymer. The polymer composite film exhibited PR effect with a method of two-beam coupling experiment. And an asymmetric two-beam coupling gain of 45.8 cm−1 without applied electric filed is obtained at 632.8 nm wavelength.

Synthesis and characterization of a novel poly( N-vinyl)-3-[ p-nitrophenylazo]carbazolyl-CdS nanocomposites through chemical hybridization

A novel bi-functional photorefractive (PR) poly( N-vinyl)-3-[ p-nitrophenylazo]carbazolyl with carbazolyl fragments and chromophoric azophenyl was synthesized by a post azo coupling reaction and characterized by 1H NMR, elemental analysis, UV–Vis absorption and FTIR spectroscopy. Then chemical hybridized poly( N-vinyl)-3-[ p-nitrophenylazo]carbazolyl-CdS nanocomposites with different molar ratio of CdS to poly( N-vinyl)-3-[ p-nitrophenylazo]carbazolyl were prepared. It was confirmed that the CdS particles had a nanoscale size and quantum confinement effect adopting transmission electron microscopy and UV–Vis absorption spectroscopy. The generation of photocurrent on illumination and photoconductive properties of the nanocomposites were studied. Significant enhancement in photoconductivity induced by the chemical doping of CdS in poly( N-vinyl)-3-[ p-nitrophenylazo]carbazolyl has also been demonstrated.

Significant enhancement of photoconductivity in truly two-component and chemically hybridized CdS-poly(N-vinylcarbazole) nanocomposites

Chemically hybridized CdS-poly(N-vinylcarbazole) (PVK) nanocomposites with different molar ratios of CdS to PVK were prepared. A variety of techniques including optical absorption, photoluminescence (PL), photocurrent spectroscopy, and time-resolved PL were employed to investigate the properties of CdS–PVK nanocomposites. A significant enhancement of photoconductivity was observed in CdS–PVK nanocomposites as compared to pure PVK and CdS/PVK nanoblends. We interpret this result as the improved interface quality between CdS and PVK in CdS–PVK nanocomposites, which facilitates fast interfacial carrier transfer and thus increases the charge generation efficiency.

Poly(N-vinylcarbazole) (PVK) Photoconductivity Enhancement Induced by Doping with CdS Nanocrystals through Chemical Hybridization

We have functionalized poly(N-vinyl carbazole) (PVK) by controlled sulfonation. CdS nanocystals of 3−20 nm across were synthesized in the sulfonated PVK matrix with the CdS molar fraction of ∼1−18%. The CdS nanoparticle size increased with the molar fraction of CdS. At high CdS molar fractions, the CdS nanocrystals exist in both cubic and hexagonal phases. Photoluminescence efficiency of PVK decreases when the molar fraction of CdS increases due to quenching through interfacial charge transfer. Photoluminescence attributable to the CdS nanocrystals can be observed only at low molar fractions of CdS. Significant enhancement in photoconductivity induced by the chemical doping of CdS in PVK has also been demonstrated.