Sergio Manuel de sousa Pereira

University of Aveiro | UA · CICECO - Centre for Research in Ceramics and Composite Materials

Surface plasmon enhanced GaN and InGaN quantum wells (QWs) show promise for use as room-temperature light emitters. The effectiveness of the plasmon enhancement, however, is limited by the strong electron/hole and longitudinal optical phonon coupling found in the III-V nitrides. The electron-phonon coupling within semiconductor QWs has been modifie...

The light enhancement phenomena in InGaN/GaN multi-quantum wells (MQWs) infiltrated with metal nanoparticles (NPs) are studied using resonant and off-resonant localized plasmon interactions. The emission and recombination characteristics of carriers in InGaN/GaN MQW structures with inverted hexagonal pits (IHPs) are modified distinctly depending on...

Currently, it is understood that the carrier recombination rate in semiconductors can be modified by metals due to pure electrodynamic interactions through surface plasmons. We propose here an electrostatic mechanism for carrier-metallic nanoparticle interaction comparable in effect to plasmonic interactions. Arising from Coulomb attraction of elec...

We investigate interactions between Mott-Wannier MW and Frenkel excitons in a family of hybrid struc-tures consisting of thin organic polyfluorene films placed in close proximity systematically adjusted by GaN cap layer thickness to single inorganic Ga, InN/GaN quantum wells QWs. Characterization of the QW structures using Rutherford backscattering...

Using a top-down approach, we report a theoretical investigation of the melting temperature at the nanoscale, T(m) for different shapes of "free-standing" nanostructures. To easily calculate the nanoscale melting temperature for a wide range of metals and semiconductors, a convenient shape parameter called alpha(shape) is defined. Considering this...

Four different methods for measuring the compositions of epitaxial Scx Ga1−x N films were assessed and compared to determine which was the most reliable and accurate. The compositions of epitaxial Scx Ga1−x N films with 0 ≤ x ≤ 0.26 were measured directly using Rutherford backscattering (RBS) and x-ray photoelectron spectroscopy (XPS), and indirect...

Four different methods for measuring the compositions of epitaxial ScxGa1-xN films were assessed and compared to determine which was the most reliable and accurate. The compositions of epitaxial ScxGa1-xN films with 0 ≤ x ≤ 0.26 were measured directly using Rutherford backscattering (RBS) and x-ray photoelectron spectroscopy (XPS), and indirectly u...

Four different methods for measuring the compositions of epitaxial Sc x Ga1−x N films were assessed and compared to determine which was the most reliable and accurate. The compositions of epitaxial Sc x Ga1−x N films with 0 ≤ x ≤ 0.26 were measured directly using Rutherford backscattering (RBS) and x-ray photoelectron spectroscopy (XPS), and indire...

Gold/soap nanostructures were prepared by a green methodology using saponified household sunflower oil, as reducing and organic dispersing agent of auric acid. The incorporation of hydrophobic molecules on the novel water-soluble gold nanoparticles was followed by fluorescence lifetime imaging microscopy, using as model hydrophobic compound 5,10,15...

Epitaxial ScxGa1−xN films with 0 ≤ x ≤ 0.50 were grown using molecular beam epitaxy under metal-rich conditions. The ScxGa1−xN growth rate increased with increasing Sc flux despite the use of metal-rich growth conditions, which is attributed to the catalytic decomposition of N2 induced by the presence of Sc. Microstructural analysis showed that pha...

Optical transmittance measurements on epitaxial, phase-pure, wurtzite-structure ScxGa1xN films with 0 x 0.26 showed that their direct optical band gaps increased from 3.33 eV to 3.89 eV with increasing x, in agreement with theory. These films contained I1- and I2-type stacking faults. However, the direct optical band gaps decreased from 3.37 eV to...

In this work, we investigate the impact of minute amounts of pure nitrogen addition into conventional methane/hydrogen mixtures on the growth characteristics of nanocrystalline diamond (NCD) films by microwave plasma assisted chemical vapour deposition (MPCVD), under high power conditions. The NCD films were produced from a gas mixture of 4% CH4/H2...

Four nominally Al0.85In0.15N thin films with different strains were grown simultaneously on Al1−y Gay N (y = 1, 0.93, 0.87 and 0.69) templates by metal organic chemical vapour deposition. The nominal InN content of ~15% was chosen to achieve close lattice matching of Al1−x Inx N with the templates of intermediate GaN molar fractions, a small tensil...

In this work, we study the growth habit of nanocrystalline diamond (NCD) films by exploring the very high power regime, up to 4 kW, in a 5 kW microwave plasma chemical vapour deposition (MPCVD) reactor, through addition of a small amount of nitrogen and oxygen (0.24%) into 4% CH4 in H2 plasma. The coupled effect of high microwave power and substrat...

DOI:https://doi.org/10.1103/PhysRevB.87.239902

X-ray Reciprocal Space Mapping (RSM) is a powerful tool to explore the structure of semiconductor materials. However, conventional lab-based RSMs are usually measured in two dimensions (2D) ignoring the third di-mension of diffraction-space volume. We report the use of a combination of X-ray microfocusing and state-of-the-art 2D area detectors to s...

We report a general method for the synthesis of metal oxide colloidal nanocrystals in sunflower oil using single-source precursors. In this research, iron oxide nanocrystals have been synthesized and characterized though this method can be extended to the synthesis of other common metal oxides such as ZnO and also to other types of vegetable oils a...

Ultrafast differential transmission spectroscopy was employed to study the carrier dynamics in InGaN/GaN multiple quantum wells with high inverted hexagonal pits density due to threading dislocation. By monitoring the temporal evolution of the excitonic absorption spectrum, a reduction of the quantum-confinement Stark shift was observed due to the...

The aim of the present study is to synthesize new mannosylated dextran derivative that can be labeled with Tc-99m for potential use in sentinel lymph node detection (SLND). The compound was designed to have a dextran with molecular weight of 10 kDa as a backbone, mannose for binding to mannose receptors of the lymph node and S-derivatized cysteine...

We report a study of InGaN and InAlN epilayers grown on GaN/Sapphire substrates by microfocused three-dimensional X-ray Reciprocal Space Mapping (RSM). The analysis of the full volume of reciprocal space, while probing samples on the microscale with a focused X-ray beam, allows us to gain uniquely valuable information about the microstructure of II...

We report the use of microfocused three-dimensional x-ray reciprocal space mapping to study InGaN epilayers with average InN content similar to 20%-22%. Analysis of the full volume of reciprocal space, while probing samples on the microscale with a focused x-ray beam, allowed us to gain valuable information about the nanostructure of InN-rich InGaN...

We demonstrate the modification of coherent zone-folded longitudinal acoustic phonons (ZFLAPs) oscillations in InGaN/GaN multiple quantum wells by the inclusion of metal nanoparticles (Au and Ag) via self-assembled inverted hexagonal pits. Blueshift and redshift have been observed in photoluminescence spectra due to the effect of electrostatic char...

Advances in nanophotonics are beginning to allow for the creation of nano-scale light emitting devices. Improving the quality of these next-generation emitters requires similarly advanced methods for characterization. These techniques need to be capable of imaging operational prototypes with nanometric resolution. We demonstrate here a new method f...

The strained semiconductor multiple quantum wells have the capability to generate acoustic terahertz emission via coherent acoustic phonon oscillations. The frequency of the THz emission is usually limited by the periodicity of the quantum wells or superlattice structures. We propose a novel technique to modify the frequency and amplitude of THz os...

We report a new mechanism of enhancement of light emission from InGaN/GaN quantum wells (QW). This mechanism is due to electrostatic attraction of the carriers to gold nanoparticles (NP) imbedded within a QW. Metal equally attracts electrons and holes, causing the carriers to concentrate near its surface. Since the probability of e-h recombination...

Despite being widely used in the clinical setting for sentinel lymph node detection (SLND), (99m)Tc-based colloids (e.g., (99m)Tc-human serum albumin colloids) present a set of properties that are far from ideal. Aiming to design novel compounds with improved biological properties, we describe herein the first class of fully characterized (99m)Tc(C...

High quality Al(1-x)In(x)N/GaN bilayers, grown by metal organic chemical vapor deposition (MOCVD), were characterized using structural and optical techniques. Compositional analysis was performed using Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA). The InN molar fraction x decreased approximately linearly...

We present a rigorous analysis of the thermal conductivity of bulk silicon (Si) and Si nanowires (Si NWs) which takes into account the exact physical nature of the various acoustic and optical phonon mechanisms. Following the Callaway solution for the Boltzmann equation, where resistive and nonresistive phonon mechanisms are discriminated, we deriv...

The potential-energy surface PES for Sr adsorption on Si111-7 7 is calculated within density-functional theory. The main diffusion paths and corresponding energy barriers are determined for a Sr atom on recon-structed Si111 surface. Comparison of simulated and experimental scanning tunneling microscopy STM images of apparently noisy patches in halv...

In this work, the coupled effect of nitrogen addition into CH4/H2 mixtures and surface temperature on diamond growth ranging from large grained polycrystalline to fine-grained nanocrystalline were investigated. Moreover a new growth parameter window for simultaneous growth of nanocrystalline diamond (NCD) and {100} textured large-grained diamond fi...

Currently an extensive range of noble metal colloidal nanocrystals (NCs) can be readily produced by diverse chemical methods. These nanomaterials present novel physical properties and can be regarded as building blocks to the nanofabrication of smaller, energy efficient and faster devices. Moreover, when these NCs are deposited on the surface of lu...

We report the synthesis of morphological uniform composites using miniemulsions of poly(tert-butyl acrylate) or poly(styrene) containing organically capped gold nanocrystals (NCs). The optical features of such hybrid structures are dominated by plasmonic effects and depend critically on the morphology of the resulting nanocomposite. In particular,...

This study comprises a set of AlyInxGa1-x-yN thin films grown on GaN/sapphire substrate by MOVPE, with In content between 2 and 8% and Al between 21 and 38%. The thin films were optically characterized by means of UV-Visible total reflectance and μ-UV-Raman scattering, performed at room temperature. It is shown that the [Al]/[In] ration influences...

We present a calculation of the thermal conductance (TC) of the interface between aluminium nitride (AlN) and silicon (Si) and that between AlN and silicon carbide (SiC) with taking into account the detailed phonon spectra of the materials, as obtained from first principles calculations, and the interface conditions. On the basis of the results obt...

In this paper we report on the motion of individual Sr adatoms within the limits of Si(111)-7x7 half unit cells (HUCs). The fast movement of the atom at the Si surface produces sharp signal fluctuations in scanning tunneling microscopy (STM) images resulting into noiselike patches. It is found that the length of the observed image streaks is a func...

The directional dependence of AlN intrinsic complex dielectric function, the phonon lifetimes, and decay channels are investigated by means of polarized infrared reflectivity measurements on several facets of self-nucleated wurtzite AlN crystal of high crystalline quality. The measurement technique and the AlN single crystal used have been selected...

The effects of annealing temperature on nanocrystalline sputter-deposited Ni thin films (500 nm) deposited on WC–Co (4 wt.%) were investigated. Special attention was focused on quantitative evaluation of residual stress and Ni diffusion into the WC–Co, after heat treatment, from 873 to 1273 K. The estimated level of residual stress, as measured by...

We report on the magnetic and structural properties of two types of nanostructures doped with Co or Mn, namely, ZnO nanowires and colloidal ZnO nanocrystals. Electron paramagnetic resonance (EPR) spectra have been measured and analysed to extract information on the incorporation of the ions in the lattice. A detailed analysis by means of simulation...

We report the synthesis and characterization of high-quality highly 〈1 0 0〉 oriented nanocrystalline diamond (NCD) films consisting of {1 0 0} nano-facets with a high growth rate of 2.6 μm/h. The NCD samples were grown on large (1 0 0) silicon wafers of 5.08 cm in diameter by employing CH4/H2/O2/N2 chemistries without the aid of bias for orientatio...

Recently, [Oh Phys. Rev. B 77, 155430 (2008)] reported on an atomic model for the so-called Si(557)-reconstructed surface with regular triple steps. The atomic structure model proposed was developed on the basis of high-resolution scanning tunneling microscopy (STM) images and first-principles calculations performed to match such STM images. Here w...

One of the key parameters which is necessary to understand and to control in nanoscience and nanotechnology is stress. Stress appears during the formation of nanograins and thin films; and is called residual stress. The presence of stress in thin films might lead to various effects like curvature, detachment, fracture and therefore it affects direc...

Surface structures induced by submonolayer Sr adsorption on Si(111) surface were investigated by scanning tunneling microscopy (STM). Depending on the sample temperature and Sr coverage the following reconstructions on Si(111) surface could be directly resolved: 3×2 , n×1 (n=5,7,9) , 2 √ 3 × √ 13 , 4 √ 3 ×4 √ 3 , and √ 3 ×2 with increasing Sr cover...

Epitaxial layers of wurtzite-phase Al1-xInxN, similar to 120 nm thick with (0 0 0 1) orientation, were grown by metal organic chemical vapour deposition on GaN buffer layers at setpoint temperatures between 760 and 840 degrees C. For growth temperatures >= 800 degrees C, the AlInN layers grew with uniform composition, pseudomorphic with the underly...

We report on the contribution of optical phonon decay into acoustic phonon to the thermal conductivity [k(T)] of semiconductors. We have considered this mechanism as an acoustic phonon generation rate within the full modified Callaway theory to accurately describe experimental data of k(T) for Ge as a function of isotopic composition. The proposed...

We present the highlights of a research programme on hybrid inorganic–organic light emitters. These devices combine recent developments in III–V nitride technology (including UV emitting micro-arrays and specifically tailored quantum wells) with conjugated polymers to access the entire visible spectrum. Two types of devices are studied, those based...

The thermal conductivity along two high-symmetry directions of several aluminum nitride (AlN) single crystals differing in their mass-fluctuation phonon-scattering parameter is described accurately in the full temperature range by taking into account the contribution of optical phonon decay into acoustic phonon. The accuracy of the proposed model s...

A series of chemically prepared Co(2+)-doped ZnO colloids has been surface modified either by growing shells of ZnSe or by the in situ encapsulation in poly(styrene). The surface modification effects using these two distinct chemical strategies on the magnetic properties of the nanocrystals were probed by electron paramagnetic resonance (EPR). Stru...

There is strong current interest in Forster resonant energy transfer (FRET) from a semiconductor quantum well (QW) to an overlayer of another luminescent material. The FRET process becomes efficient when the two materials are placed at interaction distance of a few nanometres. The additional requirement of large spectral overlap between the energy...

Spontaneously formed nano-pits are exploited to effectively control the incorporation of gold nanocrystals (NCs) at the surface of light emitting InGaN/GaN heterostructures. Nanoengineering either the NCs size, or pit size, allows the number of NCs incorporated in each pit to be controlled, thus enabling research of well-defined assemblies of few g...

We investigate the effect of simultaneous nitrogen and oxygen addition into conventional methane–hydrogen plasma on morphology and texture of diamond films produced in a high power high pressure 5 kW microwave plasma chemical vapor deposition (MPCVD) reactor. Diverse diamond films ranging from large-grained polycrystalline to nanocrystalline can be...

We report a theoretical investigation concerning the melting temperature, T m , of ZnO and Zn nanoparticles (NPs), nanowires (NWs) and nanotubes (NTs). The shapes considered here for the zinc oxide low dimensional structures include spherical NPs, NWs with circular, rectangular (nanobelts) and hexagonal sections and NTs with circular and hexagonal...

Synthetic ZnO nanocrystals have been intentionally doped with Eu3+ ions. Structural analysis performed on the nanocrystals showed wurtzite-ZnO as the only phase present in the samples. Photoluminescence in emission and excitation modes allows the assignment of the intra-4f(6) transitions for the Eu3+ ions. From the analysis of the optical data we a...

Synthetic ZnO nanocrystals have been intentionally doped with Eu3+ ions. Structural analysis performed on the nanocrystals showed wurtzite-ZnO as the only phase present in the samples. Photoluminescence in emission and excitation modes allows the assignment of the intra-4f6 transitions for the Eu3+ ions. From the analysis of the optical data we are...

Energy scalability of the excitation-emission spectra of InGaN epilayers, quantum wells and light-emitting diodes provided indirect evidence for a fundamental common cause of the remarkable optical properties of this commercially important semiconductor alloy. Phase segregation on the nanoscale ( accidental quantum dot formation) has generally been...

Pereira and co-workers report on p. 37 that nanoscale strain inhomogeneity plays a fundamental role in the spectral properties of InGaN/GaN epilayers. For layers grown above a certain critical thickness, a strong and spatially varying strain profile accompanies a nonplanar surface morphology (as shown on the cover), which is associated with a trans...

InGaN is the basis of a new generation of light-emitting devices, with enormous technological potential; it is currently one of the most intensively studied semiconductor materials. It is generally accepted that compositional fluctuations resulting from phase segregation are the origin of the high luminescence efficiency of InGaN. Evidence to show...

Photoluminescence (PL), photoluminescence excitation (PLE) and selective excitation (SE-PL) studies were performed in an attempt to identify the origin of the emission bands in a pseudomorphic In0.05Ga0.95N/GaN film. Besides the InGaN near-band-edge PL emission centred at 3.25 eV an additional blue band centred at 2.74 eV was observed. The lower en...

Comparative Ga and In K-edge extended x-ray absorption fine structure studies provide the first direct evidence of an inequality of mean In-Ga and Ga-In next-nearest neighbor separations in InGaN alloys. The degree of inequality increases with decreasing InN fraction x in the range accessible to extended x-ray absorption fine structure analysis of...

In this contribution, the optical and structural properties of InGaN/GaN layers grown by metal-organic chemical vapour deposition (MOCVD) are studied. The main focus of this investigation is on the difference between microstructural and luminescence characteristics, for layers grown below and above the critical layer thickness (CLT) for elastic str...

In recent years, there has been a resurgence in the interest in the use of ZnO (Eg � 3.37 eV) as a material for a wide range of optoemitter applications spanning visible and short wavelengths. Bulk, thin films and nanomaterials obtained using different synthesis methods have been investigated for optoelectronic and biotechnological device applicati...

In this work we investigated ZnO films grown on semi-insulating (100) GaAs substrates by pulsed laser deposition. Samples were studied using techniques including X-ray diffraction (XRD), scanning electron microscopy, atomic force microscopy, Raman spectroscopy, temperature dependent photoluminescence, C-V profiling and temperature dependent Hall me...

This paper concerns the structural and optical properties of the group III-IV semiconductor alloy, indium gallium nitride (InGaN). We focus on the reasons of interest to study InGaN. Recent advances regarding the basic understanding (ex. accurate composition determination) and some yet unclear issues (ex. phase separation) regarding this material s...

Photoluminescence, photoluminescence excitation and time-resolved photoluminescence studies were performed in a partially relaxed InGaN epilayer, and exhibiting a 3D growth mode at the surface. Two emission bands, a red (centred at ∼1.88 eV) and a blue (centred at ∼2.58 eV) were observed. In order to investigate their origin and their relation with...

This contribution is focused on Raman analysis of the InxGa1-xN alloy. It presents direct evidence that both strain and composition effects must be taken into account to interpret the Raman experimental results. Raman studies have been commonly discussed in view of composition inhomogeneity only, neglecting the possible existence of strain depth va...

The roughness in GaN/InGaN thin films and multilayers was studied with Rutherford backscattering (RBS). Quantitative data analysis, including the determination of the roughness parameters, was made through the application of models developed for specific kinds of roughness and/or intermixing. In a first step, the assumptions made in the development...

In this paper, we present a method to obtain symmetric and asymmetric reciprocal space maps (RSM) for group-III nitride multilayers on an absolute scale, regardless from the film or substrate lattice constants. The great benefits of full reciprocal space mapping for nitride alloys, in the case of a diffractometer incorporating a position sensitive...

The behavior of the A(1)(LO) phonon mode of relaxed and pseudomorphic InxGa1-xN epilayers, at the surface, is investigated by Raman spectroscopy. This study involves relaxed and pseudomorphic samples, with a compositional range of 0.12less than or equal tox<0.30 and 0.04<xless than or equal to0.20, respectively. Raman measurements were performed un...

This work reviews recent ellipsometric investigations of the infrared dielectric functions of binary, ternary, and quaternary group-III nitride films. Spectroscopic Ellipsometry in the mid-infrared range is employed for the first time to determine phonon and free-carrier properties of individual group-III nitride heterostructure components, includi...

Single crystalline InGaN epilayers with different In content were implanted with Er. fluences in the range of 1 x 10(13)-5 x 10(15) cm(-1) at room temperature. The structural changes and lattice site location were studied with emission channeling and RBS/channeling. Photoluminescence measurements were also performed to study the optical properties...

Reflectometry using a white light source has been applied to in situ monitoring of metal organic vapour phase epitaxy of InGaN alloy structures on GaN buffer layers. Both InGaN epilayers 60–350 nm in thickness and InGaN/GaN multi-quantum-well (MQW) structures with periods of order 10 nm were studied. The InGaN epilayers have indium mole fractions b...

All III–N visible light emitting devices contain ultrathin active layers of InGaN. Although this material has been widely studied during the last ten years or so, opinion is still divided as to its nature. Most researchers would agree with the proposition that III–nitride “alloys” are a mess, at least when compared with analogous III–As materials....

Nakamura and co-workers were first to report the observation of spontaneously formed In-rich clusters in InGaN quantum wells (QW), using transmission electron microscopy (TEM) [1,2]. Some of the present authors have argued that the exceptional optical efficiency of nitride devices is due to the presence of nearly pure InN QD which form accidentally...

We compare the structural and spectral properties of two multi quantum wells (MQWs), grown by metal organic chemical vapour deposition under the same nominal conditions, with a different number of periods. The MQWs, each with 20% InN and containing 8 and 18 wells, respectively, grew on-axis and coherent to GaN, as revealed by X-ray diffraction reci...