Mengbing Huang

White light emission from amorphous silicon oxycarbide (a-SiCxOy) thin films: Role of composition and postdeposition annealing

The effects of carbon and postdeposition annealing on white luminescence are studied in amorphous silicon oxycarbide (a-SiCxOy) films grown by chemical vapor deposition. The films showed strong room-temperature luminescence in a broad spectral range from blue-violet to near infrared, depending on excitation energy. Photoluminescence (PL) intensity exhibited good correlation with SiOC bond concentration. At low C (<5%), matrix PL was completely quenched after annealing in O2 even at 500 °C. PL was unaffected by O2 annealing at higher C, and could be enhanced when excited by an ultraviolet laser. These findings are correlated to C- and Si-related O defect centers as luminescence sources in a-SiCxOy.

Comparative study of the effects of thermal treatment on the optical properties of hydrogenated amorphous silicon-oxycarbide

Findings are presented from a systematic study of the effects of postdeposition thermal treatment on the optical characteristics of hydrogenated amorphous silicon-oxycarbide (a-SiCxOyHz) materials. Three different classes of a-SiCxOyHz films: SiC-like (SiC1.08O0.07H0.21), Si-C-O (SiC0.50O1.20H0.22), and SiO2-like (SiC0.20O1.70H0.24), were deposited by thermal chemical vapor deposition. The effects of thermal annealing on the compositional and optical properties of the resulting films were characterized using Fourier-transform infrared spectroscopy, x-ray photoelectron spectroscopy, nuclear reaction analysis, and spectroscopic ultraviolet-visible ellipsometry. As the Si-C-O system evolved from a SiC-like to SiO2-like matrix, its refractive index and optical absorption strength decreased, while its optical band gap increased. Thermal annealing between 500 and 1100 °C resulted in hydrogen desorption from and densification of the a-SiCxOyHz films. Concurrently, thermally induced changes were also observed for...

Observation of crystallite formation in ferromagnetic Mn-implanted Si

Mn-implanted Si was investigated using transmission electron microscopy to gain insight into the structure of the implanted region. Diffraction contrast images, selected area diffraction patterns, and high resolution images of the samples were acquired before and after postimplant annealing at 800°C. The images of the annealed samples revealed the formation of nanometer size precipitates distributed throughout the implanted region. Analysis of the selected area diffraction pattern determined that the most prominent lattice spacing of the crystallites is 2.15A. This spacing indicates that the most probable phase of the crystallites is MnSi1.7 and this is consistent with the Mn:Si binary phase diagram. This phase is paramagnetic at room temperature with a Curie temperature of 47K and cannot readily account for the high Curie temperature of the material.Mn-implanted Si was investigated using transmission electron microscopy to gain insight into the structure of the implanted region. Diffraction contrast images, selected area diffraction patterns, and high resolution images of the samples were acquired before and after postimplant annealing at 800°C. The images of the annealed samples revealed the formation of nanometer size precipitates distributed throughout the implanted region. Analysis of the selected area diffraction pattern determined that the most prominent lattice spacing of the crystallites is 2.15A. This spacing indicates that the most probable phase of the crystallites is MnSi1.7 and this is consistent with the Mn:Si binary phase diagram. This phase is paramagnetic at room temperature with a Curie temperature of 47K and cannot readily account for the high Curie temperature of the material.

Efficient energy transfer from silicon oxycarbide matrix to Er ions via indirect excitation mechanisms

Efficient Er excitation was observed in Er-doped silicon oxycarbide with strong room-temperature photoluminescence of ∼1540nm within a broad (460–600nm) band. Er PL power dependence modeling yielded an effective Er excitation cross section of approximately four orders of magnitude higher than direct Er excitation. PL for undoped a-SiC0.5O1.0 extended from visible to near infrared (500–750nm), with intensity decreasing with Er doping. Er photoluminescence excitation overlapped with the Urbach edge in a-SiC0.5O1.0:Er absorption spectrum. Energy transfer from electron-hole recombination at band edges or/and defect levels in a-SiC0.5O1.0:Er may provide an efficient excitation route for Er ions via electron excitation from ground state (I15∕24) to 4f levels.

Thermal property of regioregular poly(3-hexylthiophene)/nanotube composites using modified single-walled carbon nanotubes via ion irradiation

The effects of radiation-induced modifications on the thermal stability and phase transition behaviour of composites made of 1% pristine or ion irradiated single-walled carbon nanotubes (SWNTs) and poly(3-hexylthiophene) (P3HT) are reported. Thermogravimetry analysis (TGA), differential scanning calorimetry (DSC), Raman spectroscopy and electron spin resonance (ESR) were used to investigate the radiation-induced functionalization of carbon nanotubes and to assess the effect of ionizing radiation on the adhesion between macromolecular polymer and carbon nanotubes. Irradiation was used to introduce defects in a controlled way solely within pristine nanotubes before composite synthesis. The addition of irradiated SWNTs to a polymer matrix was found to enhance thermo-oxidative stability and phase transition behaviour. Further, ESR studies demonstrate the electronic interaction through charge transfer between filler and matrix. These results could have immense applications in nanotube composite processing. Based on the experimental data, a model for the interaction between polymeric chains and carbon nanotubes is proposed.

The origin of white luminescence from silicon oxycarbide thin films

Silicon oxycarbide (SiCxOy) is a promising material for achieving strong room-temperature white luminescence. The present work investigated the mechanisms for light emission in the visible/ultraviolet range (1.5–4.0 eV) from chemical vapor deposited amorphous SiCxOy thin films, using a combination of optical characterizations and electron paramagnetic resonance (EPR) measurements. Photoluminescence (PL) and EPR studies of samples, with and without post-deposition passivation in an oxygen and forming gas (H2 5 at. % and N2 95 at. %) ambient, ruled out typical structural defects in oxides, e.g., Si-related neutral oxygen vacancies or non-bridging oxygen hole centers, as the dominant mechanism for white luminescence from SiCxOy. The observed intense white luminescence (red, green, and blue emission) is believed to arise from the generation of photo-carriers by optical absorption through C-Si-O related electronic transitions, and the recombination of such carriers between bands and/or at band tail states. Thi...

Photoluminescence in erbium doped amorphous silicon oxycarbide thin films

Photoluminescence (PL) in Er-doped amorphous silicon oxycarbide (a-SiCxOy:Er) thin films, synthesized via thermal chemical vapor deposition, was investigated for carbon and oxygen concentrations in the range of 0–1.63. Intense room-temperature PL was observed at 1540 nm, with the PL intensity being dependent on the carbon and oxygen content. The strongest PL intensity was detected for a-SiC0.53O0.99:Er when pumped at 496.5 nm, with ∼20 times intensity enhancement as compared to a-SiO2:Er. Broadband excitation in the visible was observed for a-SiC0.53O0.99:Er. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy analyses suggest that the formation of Si–C–O networks plays an important role in enhancing the Er optical activity in a-SiCxOy:Er films.

Ion-implantation-prepared catalyst nanoparticles for growth of carbon nanotubes

This letter demonstrates the use of catalyst nanoparticles prepared by ion implantation for growth of carbon nanotubes (CNTs) via chemical vapor deposition. Nickel ions of energy in 100keV were first implanted at room temperature into silicon dioxide to doses of 1015–1017cm−2. Postimplantation annealing was conducted to induce precipitation of implanted Ni atoms into nanoparticles. The samples were chemically etched to expose Ni nanoparticles on the surface. Finally, CNT growth on such prepared SiO2 substrates was achieved via chemical vapor deposition through decomposition of hydrocarbon. Our data show strong correlation in the size of resultant tube structures and preformed catalyst nanoparticles, with larger Ni nanoparticles resulting in larger tube diameters. This work may provide an effective way for seeding catalyst nanoparticles in high-aspect-ratio via/trench structures for growing CNTs for interconnect applications.

Stability of ion implanted single-walled carbon nanotubes: Thermogravimetric and Raman analysis

In this work, the effect of different ions (hydrogen, helium, and neon) implanted on single-walled carbon nanotube (SWNT) is being analyzed using thermogravimetric analysis (TGA), Raman scattering, and x-ray photoelectron spectroscopy (XPS). The TGA result shows that the temperature for maximum decomposition rate (Tmax) increases at relatively low doses, i.e., by about 30°C after hydrogen ion implantation (at the ion dose of 1015cm−2), 17°C after helium ion implantation (at the ion dose of 1013cm−2), and contributes no significant enhancement after neon implantation for all doses. The increase of Tmax indicates that small mass ion can be utilized to improve the thermal-oxidative stability of SWNTs. Raman scattering and XPS were used to monitor the lattice damage from ion implantation and chemical bonding states of the materials. The results indicated the material rigidity for low doses of hydrogen and helium, while the application of higher doses of neon caused the material to transform towards amorphous ...

Enhanced radiation hardness of photoluminescence from InAs quantum dots embedded in an AlAs/GaAs superlattice structure

Abstract We report a study of proton irradiation effects on the luminescence of self-assembled InAs quantum dots (QDs) embedded in an AlAs/GaAs short-period superlattice structure. As opposed to the QDs grown in a GaAs thin film, the QDs embedded in an AlAs/GaAs superlattice structure were found to exhibit much higher photoluminescence (PL) degradation resistance to proton irradiation. For example, at the highest dose (10 14 cm −2 ) used in this work, the PL intensity from the QDs in superlattice dropped by a factor of ∼4, while the PL intensity from the QDs in GaAs decreased by almost two orders of magnitude, relative to their respective as-grown samples. Effects of thermal annealing on the luminescence of irradiated QDs were also examined. Possible mechanisms leading to the enhanced PL radiation hardness for QDs in superlattice are discussed.