Vertically oriented single wall nanotubes (SWNTs) and few walled nanotubes (FWNTs) have been grown by electronic cyclotron resonance plasma enhanced chemical vapor deposition (PECVD) on silica flat substrates. The impact of the plasma parameters on SWNT and FWNT growth has been investigated using two different etching gas mixtures, namely, C2H2∕NH3 and C2H2∕H2 with various ratios and applied bias voltages. Kinetic studies are also proposed in order to describe the FWNT growth mechanism by plasma techniques. A key role played by the reactive gas (NH3 and H2) is observed in the PECVD process, contrary to multiwalled nanotube growth. It is demonstrated that the balance between FWNT growth versus FWNT etching can be widely modulated by varying the gas mixture and bias voltage. It is shown that the use of hydrogen for hydrocarbon gas dilution restricts the destruction of SWNT and FWNT by the plasma species (ions and radicals).
Abstract We have discovered a structural transition for the SrZnO alloy films from a wurtzite to a rock-salt structure, leading to a reduction in the (112̲0)/(0001) surface energy ratio. The films were grown by pulsed laser deposition using different SrO ratios, x. We have revealed that growth at a higher temperature, 750°C, resulted in a sharp 0002 peak at a low SrO content (5%), whereas growth at a higher SrO content (10%) resulted in a non-crystalline film with minute crystallites with a (112̲0) orientation. Generally the crystallinity decreased as the SrO content increased. No results obtained for the crystalline films showed any orientation of significant peaks besides the peak attributed to the (0001) plane, suggesting epitaxial growth. Optical measurements showed difference in transmission widows of alloys with different SrO percentage, and this was correlated to SrO influence on growth mode as indicated by scanning electron imaging. The studied SrZnO films, with SrO/(SrO + ZnO) ≤ 0.25, were grown by pulsed laser deposition using different SrO ratios, x. The effects of temperature and oxygen pressure during growth on the films’ structural properties were investigated. XRD results indicate that the film crystallinity was improved as the temperature and O 2 pressure increased up to 650°C and 0.5 Torr, respectively.
El nitruro de aluminio es un compuesto ceramico con multitud de aplicaciones tecnologicas en muchos campos,tales como la optica, la electronica y los dispositivos resonadores. La eficiencia del AlN es altamente dependientede las condiciones experimentales de deposicion. En este articulo se analiza el efecto de la presion de trabajo enel desarrollo de tensiones residuales en su estructura. Para ello, se depositaron peliculas delgadas de AlNmediante sputtering por magnetron DC en modo reactivo con presion de trabajo variable (3-6 mTorr) sobre Si(100). Estas muestras se caracterizaron mediante medicion de curvatura de la muestra, XRD (Difraccion de RayosX), HRTEM (Microscopia Electronica de Transmision de Alta Resolucion) y SAED (Difraccion de Electrones enArea Seleccionada). Los resultados muestran que la tension residual depende del espesor de la pelicula:compresiva a bajos valores, de traccion a altos valores. Ademas, la tension residual es dependiente de la presionde trabajo, luego a mas presion menos tension residual, inhibiendo el desarrollo de la textura en el plano (00·2),vital para las aplicaciones tecnologicas. Palabras clave: AlN, sputtering reactivo DC, microscopia electronica de transmision de alta resolucion, perfilde tensiones, difraccion de rayos X. Aluminum nitride is a ceramic compound with many technological applications in several fields: optics,electronics and resonators. AlN performance is highly dependent on experimental conditions during filmdeposition. This paper focuses on the effect of working pressure on residual stress development. Thus, AlN thinfilms have been deposited with reactive DC magnetron sputtering technique under different working pressures (3-6 mTorr) on Si (100) substrates. These samples were characterized by XRD (X-Ray Diffraction), HRTEM (HighResolution Transmission Electron Microscopy) and SAED (Selected Area Electron Diffraction) techniques.Results show that residual stress is dependent on film thickness: compressive at low thicknesses, tensile at highthicknesses. Moreover, residual stress changes with the working pressure and at high pressures this stress isreduced, hampering the (00·2) texture development, crucial in technological applications. Keywords: AlN, DC reactive sputtering, high resolution transmission electron microscopy, stress profile, X-raydiffraction.
Single-wall (SW-) and few-walled (FW-) carbon nanotubes (CNTs) were synthesized on aluminum/ cobalt coated silicon at temperatures as low as 450 degrees C by plasma enhanced chemical vapor deposition technique (PECVD). The SWCNTs and FWCNTs grow vertically oriented and well separated from each other. The cold field emission studies of as-grown SWCNTs and FWCNTs showed low turn-on field emission threshold voltages, strongly dependent of the nanotubes morphology. Current-voltage curves of individual CNTs, measured by conductive atomic force microscopy (CAFM), showed an electrical resistance of about 90 Komega, that is attributed mainly to the resistance of the contact between the CNTs and the conductive CAFM tip (Au and Pt).
In the paper, we aim to solve the thermal problems appearing in integrated silicon photonics by using high thermal conductivity Aluminium Nitride (ALN) as a thermal spreading layer located around the ridge of a hybrid III-V laser on silicon in comparison to the existing encapsulation material benzocyclobutene (BCB). Here, to facilitate the design of reliable hybrid semiconductor lasers, we first develop and implement a multiphysics electro-thermo-mechanical model within a finite element environment COMSOL. A phenomenological model of laser operation is used to numerically capture all the thermal and electrical characteristics of the lasers. In terms of the hybrid devices, the simulated thermal resistance agrees well with our device measurements presented in Part 1 of this work. We also demonstrate that the use of the ALN heat spreader can significantly reduce the thermal resistance. Moreover, a linear elastic model is employed for a mechanical analysis of the entire laser structure. The maximum allowable stress is estimated using the Christensen criterion. We find that the process-dependent residual stress dictates the device stress field. In the current design, the BCB encapsulation layer is at risk of failure around the InP waveguide. For AlN spreaders, lower film processing temperatures are key to reduce the stress in the deposited film. We further perform a parametric study on Tref to determine the maximum allowable deposition temperature of AlN/BCB. The simulations suggest that Tref should not exceed 59 °C and 69 °C for ALN and BCB respectively to avoid mechanical failure in the devices.
Hexagonal AlN thin films have been deposited by DC reactive magnetron sputtering at room temperature. For a first set of samples, sputtered AlN films were deposited on silicon Si (100) substrates. For a second set, AlN films were deposited on 200 nm (002) oriented AlN epitaxial layer obtained by Molecular Beam Epitaxy (MBE) on Si (111). X-ray Diffraction (XRD) and High Resolution Transmission Electron Microscopy (HRTEM) analysis of the synthesized films on Si (100) substrate have shown an amorphous phase close to the interface followed by a nano-crystalline layer exhibiting (100) and (002) orientations of the hexagonal AlN crystalline phase. Finally a relatively well crystallised layer with a single (002) orientation has been observed for the thickest films. This improvement of crystalline quality with film thickness has been consistent with a drastic decrease of the films stress from –1.2 GPa at 300 nm to no stress around 800 nm and even 0.3 GPa tensile stress for 1.5 μm thick film. This behaviour was different when epitaxial AlN was used as substrate. In fact, we have observed thanks to HRTEM images and Selected Area Electron Diffraction (SAED) patterns, that the AlN film deposited on such a substrate exhibits the same crystalline quality and have the same orientation as the AlN epitaxial layer during the first 500 nm of thickness. A further increase of film thickness has caused a decrease on the crystalline quality. The films became polycrystalline while preserving a (002) preferential orientation.
