Effect of nitrogen gas in the agglomeration and photoluminescence of Zn-ZnO nanowires after high-temperature annealing

The effect of anti-agglomeration and enhanced photoluminescence after high-temperature annealing of Zn-ZnO nanowires in nitrogen at-mosphere is reported. The Zn-ZnO nanowires were deposited by the hot filament chemical vapor deposition technique and subsequentlyannealed at 1100±C in oxygen or nitrogen atmospheres. It was found that under both annealing atmospheres, the structure of the nanowireswas completely oxidized. Morphological studies suggest that annealing under oxygen-rich atmosphere, grain growth occurs, resulting in acontinuous surface with a micrograin-shaped structure. However, it seems that nitrogen-rich annealing partially prevents complete agglom-eration and longitudinal structures composed by nanometric grains were observed. Although photoluminescence properties of the annealednanowires are improved in both annealing atmospheres, it was observed that the PL spectrum of nanowires annealed in nitrogen showed astronger UV emission than that of the oxygen annealed nanowires

Synthesis and Luminescent Properties of Silicon Nanocrystals

Nowadays, study of silicon-based visible light-emitting devices has increased due to large-scale microelectronic integration. Since then different physical and chemical processes have been performed to convert bulk silicon (Si) into a light-emitting material. From discovery of Photoluminescence (PL) in porous Silicon by Canham, a new field of research was opened in optical properties of the Si nanocrystals (Si-NCs) embedded in a dielectric matrix, such as SRO (silicon-rich oxide) and SRN (silicon-rich nitride). In this respect, SRO films obtained by sputtering technique have proved to be an option for light-emitting capacitors (LECs). For the synthesis of SRO films, growth parameters should be considered; Si-excess, growth temperature and annealing temperature. Such parameters affect generation of radiative defects, distribution of Si-NCs and luminescent properties. In this chapter, we report synthesis, structural and luminescent properties of SRO monolayers and SRO/SiO2 multilayers (MLs) obtained by sputtering technique modifying Si-excess, thickness and thermal treatments

Luminescent Devices Based on Silicon-Rich Dielectric Materials

Luminescent silicon‐rich dielectric materials have been under intensive research due to their potential applications in optoelectronic devices. Silicon‐rich nitride (SRN) and silicon‐rich oxide (SRO) films have been mostly studied because of their high luminescence and compatibility with the silicon-based technology. In this chapter, the luminescent characteristics of SRN and SRO films deposited by low‐pressure chemical vapor deposition are reviewed and discussed. SRN and SRO films, which exhibit the strongest photoluminescence (PL), were chosen to analyze their electrical and electroluminescent (EL) properties, including SRN/SRO bilayers. Light emitting capacitors (LECs) were fabricated with the SRN, SRO, and SRN/SRO films as the dielectric layer. SRN‐LECs emit broad EL spectra where the maximum emission peak blueshifts when the polarity is changed. On the other hand, SRO‐LECs with low silicon content (~39 at.%) exhibit a resistive switching (RS) behavior from a high conduction state to a low conduction state, which produce a long spectrum blueshift (~227 nm) between the EL and PL emission. When the silicon content increases, red emission is observed at both EL and PL spectra. The RS behavior is also observed in all SRN/SRO‐LECs enhancing an intense ultraviolet EL. The carrier transport in all LECs is analyzed to understand their EL mechanism

Structural Properties of Zn-ZnO Core-Shell Microspheres Grown by Hot-Filament CVD Technique

We report the hot-filament chemical vapor deposition (HFCVD) growth of Zn-ZnO core-shell microspheres in the temperature range of 350–650°C only using ZnO pellets as raw material. The samples were characterized by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) techniques. SEM micrographs showed the presence of solid microspheres and a Zn-ZnO layer in all samples. The observed heterogeneous morphology on each sample suggested two different growth mechanisms. On the one hand, solid microspheres were formed by means of gas phase nucleation of Zn atoms. The Zn-ZnO layer was formed on the substrate as result of surface reactions. It is possible that Zn microspheres condensed during the natural cooling of the HFCVD reactor as they were observed on the Zn-ZnO layer

Optical and Structural Properties of Silicon Nanocrystals Embedded in SiOx Matrix Obtained by HWCVD

The interest in developing optoelectronic devices integrated in the same silicon chip has motivated the study of Silicon nanocrystals (Si-ncs) embedded in SiOx (nonstoichiometric silicon oxides) films. In this work, Si-ncs in SiOx films were obtained by Hot Wire Chemical Vapor Deposition (HWCVD) at 800, 900, and 1000°C. The vibration modes of SiOx films were determined by FTIR measurements. Additionally, FTIR and EDAX were related to get the proper composition of the films. Micro-Raman studies in the microstructure of SiOx films reveal a transition from amorphous-to-nanocrystalline phase when the growth temperature increases; thus, Si-ncs are detected. Photoluminescence (PL) measurement shows a broad emission from 400 to 1100 nm. This emission was related with both Si-ncs and interfacial defects present in SiOx films. The existence of Si-ncs between 3 and 6 nm was confirmed by HRTEM

Fast Formation of Surface Oxidized Zn Nanorods and Urchin-Like Microclusters

Entangled Zn-ZnO nanorods and urchin-like microstructures were synthesized by the hot filament chemical vapor deposition technique at 825 and 1015°C, respectively. X-ray diffraction results showed a mixture of ZnO and Zn phases in both nanorods and urchin-like structures. The presence of Zn confirms the chemical dissociation of the ZnO solid source. The Z-ZnO nanorods with diameter of about 100 nm showed dispersed-like morphology. The urchin-like structures with micrometer diameters exhibited porous and rough morphology with epitaxial formation of nanorods

In Situ Growth of ZnO inside a Porous Silicon Matrix Obtained by Electrochemical Etching with a Hydrofluoric Acid-Formaldehyde Solution

We present zinc oxide (ZnO) particles obtained inside a porous silicon matrix in the same electrolytic process using a p-type silicon wafer in a hydrofluoric acid (HF) solution containing formaldehyde (CH2O) and hydrated zinc sulfate as additives. The X-ray diffraction pattern of the sample confirmed the presence of ZnO with a hexagonal-type wurtzite structure. Photoluminescence (PL) spectra of the samples, before and after the functionalization process, were measured to observe the effect of ZnO inside the porous silicon. The PL measurements of porous silicon functionalized with ZnO (ZnO/PS) revealed infrared, red, blue, and ultraviolet emission bands. The ultraviolet region corresponds to the band-band emission of ZnO, and the visible emission is attributed to defects. The results of the nitrogen adsorption/desorption isotherms of the PS and ZnO/PS samples revealed larger BET surface areas and pore diameters for the ZnO/PS sample. We conclude that ZnO/PS can be obtained in a one-step electrolytic process. These types of samples can be used in gas sensors and photocatalysis