S. R. C. Pinto

Low-temperature fabrication of layered self- organized Ge clusters by RF-sputtering

In this article, we present an investigation of (Ge + SiO2)/SiO2 multilayers deposited by magnetron sputtering and subsequently annealed at different temperatures. The structural properties were investigated by transmission electron microscopy, grazing incidence small angles X-ray scattering, Rutherford backscattering spectrometry, Raman, and X-ray photoelectron spectroscopies. We show a formation of self-assembled Ge clusters during the deposition at 250°C. The clusters are ordered in a three-dimensional lattice, and they have very small sizes (about 3 nm) and narrow size distribution. The crystallization of the clusters was achieved at annealing temperature of 700°C.

Formation of void lattice after annealing of Ge quantum dot lattice in alumina matrix

We report on the formation of a regularly ordered void lattice with a void size of about 4 nm in an alumina matrix. The voids were formed by thermal treatment of a well-ordered three-dimensional Ge quantum dot lattice formed earlier by self-assembled growth in an alumina matrix during magnetron sputtering codeposition of Ge+Al2O3. During the subsequent annealing the germanium atoms were lost from the film and so voids were produced. The positions of the voids are ordered in the same way as the Ge quantum dots that were present before annealing, while their sizes can be controlled by the deposition parameters.

Size and spatial homogeneity of SiGe quantum dots in amorphous silica matrix

In this paper, we present a study of structural properties of SiGe quantum dots formed in amorphous silica matrix by magnetron sputtering technique. We investigate deposition conditions leading to the formation of dense and uniformly sized quantum dots, distributed homogeneously in the matrix. X-ray and Raman spectroscopy were used to estimate the Si content. A detailed analysis based on grazing incidence small angle x-ray scattering revealed the influence of the deposition conditions on quantum dot sizes, size distributions, spatial arrangement, and concentration of quantum dots in the matrix, as well as the Si:Ge content.

Influence of annealing conditions on the formation of regular lattices of voids and Ge quantum dots in an amorphous alumina matrix.

In this work, the influence of air pressure during the annealing of Ge quantum dot (QD) lattices embedded in an amorphous Al(2)O(3) matrix on the structural, morphological and compositional properties of the film is studied. The formation of a regularly ordered void lattice after performing a thermal annealing process is explored. Our results show that both the Ge desorption from the film and the regular ordering of the QDs are very sensitive to the annealing parameters. The conditions for the formation of a void lattice, a crystalline Ge QD lattice and a disordered QD lattice are presented. The observed effects are explained in terms of oxygen interaction with the Ge present in the film.

Investigation of photoelectrical properties of CdSe nanocrystals embedded in a SiO2 matrix

CdSe nanocrystals (NCs) embedded in SiO2 thin films were prepared using RF-magnetron co-sputtering. The average NC size was estimated to be 18 nm. The dark and photocurrent temporal dependences have been measured as a function of the magnitude of applied voltage (50?150 V). Annealing the samples seems to improve the photoconductivity (~10?12 ??1) that increases with the film thickness and slightly changes under the bias voltage. Furthermore, the photovoltage measurements showed that a concentration of CdSe in the range of 27 mol% leads to the generation of a photovoltaic signal up to 5 V at 400 ?W cm?2. These results demonstrate the potential of silica films with embedded CdSe NCs for photovoltaic applications.

Estimation of Ge nanocrystals size by Raman, X-rays, and HRTEM techniques

Ge NCs have attracted considerable attention because of their potential applications in nonvolatile memory and integrated optoelectronics. A number of groups have already proposed integrate flash memories based on Ge NCs embedded SiO 2 matrix. Since Al 2 O 3 presents a high dielectric constant comparatively to SiO 2 , it is a good candidate to replace silica in flash memory systems, and therefore improve their performances. Moreover, Al 2 O 3 presents good mechanical properties, and supports high temperature, which leads it to be an ideal material for Si processing conditions. However, a few studies have been reported on Ge NCs embedded in Al 2 O 3 matrix.

Ge nanocrystals in alumina matrix: A structural study

Germanium (Ge) nanocrystals (NCs) embedded in alumina thin films were produced by deposition on silicon (111) substrates using radio-frequency (RF) magnetron sputtering. By changing growth condition and annealing parameters samples with large and small Ge-NCs were produced. The average size of NCs in the sample with larger NCs was estimated to be 7.2, 30.0 and 7.6 nm, and 5.0, 7.0 and 4.8 nm for the sample with smaller NCs, according to X-ray diffraction (XRD), Raman and high resolution transmission electron microscopy (HRTEM) results, respectively. Both, XRD and Raman peak positions of the larger NCs are shifted to higher angles and larger wave numbers in relation to the Ge bulk values, whereas the Raman peak was red-shifted for the smaller NCs indicating phonon confinement. HRTEM shows twinned structures, which is an indication of relaxation. Strain evaluation of the bigger NCs gave values < 0.5 % which is within the estimated error of the evaluation technique.

Tuning the properties of Ge-quantum dots superlattices in amorphous silica matrix through deposition conditions

In this work, we investigate the structural properties of Ge quantum dot lattices in amorphous silica matrix, prepared by low-temperature magnetron sputtering deposition of (Ge+SiO{sub 2})/SiO{sub 2} multilayers. The dependence of quantum dot shape, size, separation, and arrangement type on the Ge-rich (Ge + SiO{sub 2}) layer thickness is studied. We show that the quantum dots are elongated along the growth direction, perpendicular to the multilayer surface. The size of the quantum dots and their separation along the growth direction can be tuned by changing the Ge-rich layer thickness. The average value of the quantum dots size along the lateral (in-plane) direction along with their lateral separation is not affected by the thickness of the Ge-rich layer. However, the thickness of the Ge-rich layer significantly affects the quantum dot ordering. In addition, we investigate the dependence of the multilayer average atomic composition and also the quantum dot crystalline quality on the deposition parameters.