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This paper explores the possibility of applying reverse engineering to flexible coupling spare parts through additive manufacturing. Although couplings’ simplicity makes them go unnoticed, they connect elements that transmit power between two shafts, thus being an essential component for most of the machinery currently used in the industry. In this study, flexible couplings with different infill density (60% and 80%) were 3D printed by the fused filament fabrication technique. The original and the additive manufactured couplings were modelled to compare their compressive response and energy-absorbing characteristics, and experimental tests were performed to validate finite element analysis. To derive an optimal material distribution within coupling structure, a generative design approach was conducted through nTopology software. With this novel simulation-driven design, it is possible to reduce the weight of the redesigned part up to 15.8% by defining the wall thickness of the internal structure based on the results of finite element simulation, while maintaining its functionality. Moreover, an economic-environmental study was carried out. Results ensure that the 3D printed prototypes are suitable for replacing the original one under its current operating conditions. Additionally, the economic study shows that the redesigned couplings allow companies to save more than €2700 per coupling in relation to CO2 emission payments.

In the new transformation of ‘Industry 4.0’, additive manufacturing technologies have become one of the fastest developed industries, with polylactic acid (PLA) playing a significant role. However, there is an increasing amount of garbage generated during the printing process and after prototypes or end-of-life parts. Re-3D printing is one way to recycle PLA waste from fused filament fabrication. To do this process successfully, the properties of the waste mixture should be known. Previous studies have found that PLA degrades hydrolytically, but the time at which this process occurs for 3D printed products is not specified. This work aims to establish the baseline of the degradation kinetics of 3D printed PLA products to predict the service time until which these properties are retained. To achieve this, 3D printed specimens were thermally and hydrothermally aged during several time intervals. Thermal and mechanical properties were also determined. This study reveals that tensile strength decreases after 1344 h of hydrothermal ageing, simulating 1.5–2.5 years of real service time. PLA therefore has the same thermo-mechanical properties before reaching 1.5-years of age, so it could be recycled.

This paper studies the thermal, morphological, and mechanical properties of 3D-printed polylactic acid (PLA) blends of virgin and recycled material in the following proportions: 100/0, 25/75, 50/50, and 75/25, respectively. Real waste, used as recycled content, was shredded and sorted by size without a washing step. Regular dog-bone specimens were 3D printed from filaments, manufactured in a single screw extruder. Thermogravimetric analysis indicated that adding PLA debris to raw material did not significantly impact the thermal stability of the 3D-printed samples and showed that virgin and recycled PLA degraded at almost the same temperature. Differential scanning calorimetry revealed a significant reduction in crystallinity with increasing recycled content. Scanning electron microscopy showed a more homogenous structure for specimens from 100% pure PLA, as well as a more heterogeneous one for PLA blends. The tensile strength of the PLA blends increased by adding more recycled material, from 44.20 ± 2.18 MPa for primary PLA to 52.61 ± 2.28 MPa for the blend with the highest secondary PLA content. However, this study suggests that the mechanical properties of the reprocessed parts and their basic association are unique compared with those made up of virgin material.

The influence of the neighbouring atomic-columns in determining the composition at atomic column scale of quaternary semiconductor compounds, using simulated HAADF-STEM images is evaluated. The InAlAsSb alloy, a promising material in the photovoltaic field, is considered. We find that the so called 'crosstalk' effect plays an important role for the aimed compositional determination. The intensity transfer is larger from neighbouring atomic columns with higher average Z, and towards atomic columns with smaller Z. Our results show that in order to obtain precise information on the column composition, the HAADF-STEM intensities of both columns need to be taken into account simultaneously.

The purpose of this work is to achieve the improvement of mechanical properties of polyamide 12 through dispersion of graphene-like nanofillers, for its use in Powder Bed Fusion. Nanocomposites have been prepared by conventional injection moulding in order to determine the mechanical and electrical behaviour of the different systems as a previous step for the design of new materials for Powder Bed Fusion. Structural characterisation and mechanical and electrical properties assessments were performed, showing the improvement of stiffness and mechanical strength for the prepared nanocomposites, compared to pristine polyamide. Electrical conductivity has been introduced as well in some of them. This enhancement of properties, together with the first tests carried out on nanocomposites prepared with Powder Bed Fusion, makes this study a starting point to obtain commercially interesting materials for this additive manufacturing technique.

IdM@ti network members concurred in the diagnosis of the difficulties and opportunities arising from Bologna process implementation and teaching methodologies improvement in Materials Science and Engineering (MSE) teaching. This network has been created with the aim of improving efficiency of underway and future collaborations.The main objectives are related to MSE resources sharing (course programs, exercises, lab scripts, projects, PBL and case studies, etc.). The network will allow classifying those educational resources already individually implemented by each University, monitoring their statewide and promote the creation of new resources. In order to promote discussion and sharing of experiences, achievements and challenges, a workshop is annually organized, arose from the convenience of joining forces on the axes of innovation and improving the quality of teaching in MSE field.

In this work, we have characterized by transmission electron microscopy techniques the structural properties of InAlAsSb/InGaAs/InP heterostructures, with target applications in high efficiency solar cells. Previous photoluminescence (PL) 1 analysis suggested the existence of compositional fluctuations in the active layer of these heterostructures. 220 bright field (BF) 2 diffraction contrast micrographs have revealed strong strain contrast in the InGaAs buffer layer, related to the existence of these compositional fluctuations. The effect of a decomposed buffer on the growth of the InAlAsSb layer has been analyzed through the simulation of the strain fields in the heterostructure using the finite elements method (FEM). 3 These simulations have shown that the strain in the buffer layer due to the compositional fluctuations only affects the first few nm of the InAlAsSb layer. The analysis by aberration corrected high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) 4 and electron energy loss spectroscopy (EELS) 5 of the composition of the InAlAsSb layer reveals that any compositional fluctuation is only observed as an average effect, rather than in the form of clustering or atomically sharp transitions. The limitations of these techniques for the detection of small 3D compositional fluctuations are discussed.

The effect of a post-growth thermal treatment in two different heterostructures with InAlAsSb as the top layer grown by molecular beam epitaxy lattice-matched to InP, have been studied by diffraction contrast transmission electron microscopy (TEM). 1 This novel top cell layer material with application in ultra-high efficiency solar cells were grown on (001) InP substrate with or without an InGaAs buffer layer. Initial photoluminescence (PL) 2 measurements revealed deviations from their predicted bandgap, suggesting non-random atomic distribution of the quaternary layer. Then, a thermal annealing was performed at different temperatures and times. The effect on the structure of the InAlAsSb active layer caused by the new arrangement of layers and the post-growth annealing treatments has been reported. Our results show that the small compositional fluctuations of the as-grown heterostructures disappear after being annealed, and the bandgap energy correspondingly increases towards the predicted value.

The Bi content in GaAs/GaAs1 − xBi x /GaAs heterostructures grown by molecular beam epitaxy at a substrate temperature close to 340 °C is investigated by aberration-corrected high-angle annular dark-field techniques. The analysis at low magnification of high-angle annular dark-field scanning transmission electron microscopy images, corroborated by EDX analysis, revealed planar defect-free layers and a non-homogeneous Bi distribution at the interfaces and within the GaAsBi layer. At high magnification, the qHAADF analysis confirmed the inhomogeneous distribution and Bi segregation at the GaAsBi/GaAs interface at low Bi flux and distorted dumbbell shape in areas with higher Bi content. At higher Bi flux, the size of the Bi gathering increases leading to roughly equiaxial Bi-rich particles faceted along zinc blende {111} and uniformly dispersed around the matrix and interfaces. FFT analysis checks the coexistence of two phases in some clusters: a rhombohedral pure Bi (rh-Bi) one surrounded by a zinc blende GaAs1 − xBi x matrix. Clusters may be affecting to the local lattice relaxation and leading to a partially relaxed GaAsBi/GaAs system, in good agreement with XRD analysis.

This article investigates nanostructures by means of scanning transmission electron microscopy. The electron microscope is uniquely suited to the study of individual nanostructures, allowing differentiation of different structures and properties that is difficult or impossible to do with techniques that provide a spatial average. The present generation of aberration correctors, which correct all aberrations up to third order, makes it possible to obtain sufficient sensitivity to image and spectroscopically analyze single atoms. This article begins with a brief overview of the correction of lens aberration in electron microscopy, followed by several examples of insights into nanomaterials and the atomic origins of their functionality. In particular, it considers semiconductor nanocrystals, semiconductor quantum wires, and nanocatalysts. It also discusses magnetism in gold and silver nanoclusters as well as charge ordering in manganites.

Inclusion of spatial incoherence has been shown to give quantitative agreement between non-aberration-corrected high-angle annular dark-field scanning transmission electron microscopy images and theoretical simulations. Here we show that, using the same approach, a significant improvement in the correlation between calculated and experimental normalized integrated intensities is obtained in the InAsP ternary semiconductor alloy, but residual discrepancies remain. We have demonstrated, in good agreement with experimental intensities obtained in calibrated samples, that normalized integrated intensities show a low dependence on the sample thickness over a wide range of thickness values. This behaviour does not occur in conventional (non-aberration-corrected) images and constitutes a powerful tool for straightforward interpretation of high-resolution images in terms of atomic column-resolved compositional maps.

5 páginas, 3 fiugras, 1 tabla.-- PACS: 81.70.Jb; 61.16.Bg, A phenomenological method is developed to determine the composition of materials, with atomic column resolution, by analysis of integrated intensities of aberration-corrected Z-contrast scanning transmission electron microscopy images. The method is exemplified for InAsxP1−x alloys using epitaxial thin films with calibrated compositions as standards. Using this approach we have determined the composition of the two-dimensional wetting layer formed between self-assembled InAs quantum wires on InP(0 0 1) substrates., This work was supported by the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, US DOE (MVandSJP),the SANDiE European Network of Excellence (Contract No NMP4-CT-2004-500101),the Spanish MEC (TEC2005-05781-C03-01y02,NAN2004-09109-C04-01,Consoli- der-Ingenio2010CSD2006-00019),the CAM(S0505ESP0200) and the Junta de Andalucia(PAI research groups TEP-120 and TIC- 145;project No PAI05-TEP-00383).

The influence of post-growth annealing on the microstructure and photoluminescence (PL) of GaAsBi alloys grown on (3 1 1)B GaAs is analyzed. Conventional transmission electron microscopy (TEM) performed on as-grown samples evidence the presence of structural defects and a mosaic structure in the GaAsBi layer. A sequence of stacking faults at regions close to the GaAs/GaAsBi interface are observed in high resolution TEM images. After annealing at 473 K during 3 h the mosaic structure disappears, the presence of defects is reduced and the PL peak intensely enhances. © 2010 Elsevier B.V. All rights reserved.

3 páginas, 3 figuras.-- Progress in Applied Surface, Interface and Thin Film Science - SURFINT SREN II.-- PACS codes: 68.37.Lp; 81.05.Ea; 81.15.Hi, The compositional distribution of InAs quantum dots grown by molecular beam epitaxy on GaAs capped InAs quantum dots has been studied in this work. Upper quantum dots are nucleated preferentially on top of the quantum dots underneath, which have been nucleated by droplet epitaxy. The growth process of these nanostructures, which are usually called as quantum dots molecules, has been explained. In order to understand this growth process, the analysis of the strain has been carried out from a 3D model of the nanostructure built from transmission electron microscopy images sensitive to the composition., This work was supported by the Spanish MCI (TEC2008-06756-C03-02/TEC), CONSOLIDER CSD2009-00013, and the Junta de Andalucia (PAI research groups TEP-120 and TIC-145, project P08-TEP-03516).

In this work, photomodulated transmittance (PT) has been applied to investigate the energy gap of GaBiAs layers grown on (001) and (311)B GaAs substrates. In PT spectra, a clear resonance has been observed below the GaAs edge. This resonance has been attributed to the energy gap-related absorption in GaBiAs. The energy and broadening of PT resonances have been determined using a standard approach in electromodulation spectroscopy. It has been found that the crystallographic orientation of GaAs substrate influences on the incorporation of Bi atoms into GaAs and quality of GaBiAs layers. The Bi-related energy gap reduction has been determined to be ~90meV per percent of Bi. In addition to PT spectra, common transmittance spectra have been measured and the energy gap of GaBiAs has been determined from the square of the absorption coefficient α2 around the band-gap edge. It has been found that the tail of density of states is significant for GaBiAs and influences the accuracy of energy gap determination from the α2 plot. In the case of PT spectra, the energy gap is determined unambiguously since this technique is directly sensitive to singularities in the density of states.

The effect of growth interruption time on the structural properties of InAs/GaAs self-assembled quantum dots grown by molecular beam epitaxy on (3 1 1)B GaAs substrates is studied. Changes both in the density and the size of the dots in comparison with a sample without growth interruption are presented. The trends of both parameters with the interruption time are closely related to red shift and increased photoluminescence intensity observed in the set of samples. Growth interruption allows larger dots; however there is a limit after which dots exceed a critical size and become defective.

The structure and composition of single GaAsBi/GaAs epilayers grown by molecular beam epitaxy were investigated by optical and transmission electron microscopy techniques. Firstly, the GaAsBi layers exhibit two distinct regions and a varying Bi composition profile in the growth direction. In the lower (25 nm) region, the Bi content decays exponentially from an initial maximum value, while the upper region comprises an almost constant Bi content until the end of the layer. Secondly, despite the relatively low Bi content, CuPtB-type ordering was observed both in electron diffraction patterns and in fast Fourier transform reconstructions from high-resolution transmission electron microscopy images. The estimation of the long-range ordering parameter and the development of ordering maps by using geometrical phase algorithms indicate a direct connection between the solubility of Bi and the amount of ordering. The occurrence of both phase separation and atomic ordering has a significant effect on the optical properties of these layers. PACS: 78.55.Cr III-V semiconductors; 68.55.Nq composition and phase identification; 68.55.Ln defects and impurities: doping, implantation, distribution, concentration, etc; 64.75.St phase separation and segregation in.

In this chapter, we review results obtained by conventional and advanced electron microscopy related techniques of complex 1-D nanostructures such as spontaneous core–shell AlxGa 1−x N/GaN (0001) nanowires, ZnO/Si(111) nanorods, ZnO/CdTe (111) nanowires, and InAsxP1−x/InP(001) quantum wires.

The use of GaAsSbN capping layers on InAs/GaAs quantum dots (QDs) has recently been proposed for micro- and optoelectronic applications for their ability to independently tailor electron and hole confinement potentials. However, there is a lack of knowledge about the structural and compositional changes associated with the process of simultaneous Sb and N incorporation. In the present work, we have characterized using transmission electron microscopy techniques the effects of adding N in the GaAsSb/InAs/GaAs QD system. Firstly, strain maps of the regions away from the InAs QDs had revealed a huge reduction of the strain fields with the N incorporation but a higher inhomogeneity, which points to a composition modulation enhancement with the presence of Sb-rich and Sb-poor regions in the range of a few nanometers. On the other hand, the average strain in the QDs and surroundings is also similar in both cases. It could be explained by the accumulation of Sb above the QDs, compensating the tensile strain induced by the N incorporation together with an In-Ga intermixing inhibition. Indeed, compositional maps of column resolution from aberration-corrected Z-contrast images confirmed that the addition of N enhances the preferential deposition of Sb above the InAs QD, giving rise to an undulation of the growth front. As an outcome, the strong redshift in the photoluminescence spectrum of the GaAsSbN sample cannot be attributed only to the N-related reduction of the conduction band offset but also to an enhancement of the effect of Sb on the QD band structure.

This chapter briefly describes the fundamentals of high-resolution electron microscopy techniques. In particular, the Peak Pairs approach for strain mapping with atomic column resolution, and a quantitative procedure to extract atomic column compositional information from Z-contrast high-resolution images are presented. It also reviews the structural, compositional, and strain results obtained by conventional and advanced transmission electron microscopy methods on a number of III–V semiconductor nanostructures and heterostructures.

The photoluminescence efficiency of GaAsSb-capped InAs/GaAs type II quantum dots (QDs) can be greatly enhanced by rapid thermal annealing while preserving long radiative lifetimes which are ∿20 times larger than in standard GaAs-capped InAs/GaAs QDs. Despite the reduced electron-hole wavefunction overlap, the type-II samples are more efficient than the type-I counterparts in terms of luminescence, showing a great potential for device applications. Strain-driven In-Ga intermixing during annealing is found to modify the QD shape and composition, while As-Sb exchange is inhibited, allowing to keep the type-II structure. Sb is only redistributed within the capping layer giving rise to a more homogeneous composition. © 2012 American Institute of Physics., This work has been supported by Spanish MICINN (Project No. MAT2010-15206), MEC (Project No. TEC2011-29120-C05-04), and CAM (Project No. P2009/ESP-1503). J. M. Ulloa was supported by MICINN through the “Ramón y Cajal” program.

7 páginas, 7 figuras., The compositional distribution in a self-assembled InAs(P) quantum wire grown by molecular beam epitaxy on an InP(001) substrate has been determined by electron energy loss spectrum imaging. We have determined the strain and stress fields generated in and around this wire capped with a 5 nm InP layer by finite element calculations using as input the compositional map experimentally obtained. Preferential sites for nucleation of wires grown on the surface of this InP capping layer are predicted, based on chemical potential minimization, from the determined strain and stress fields on this surface. The determined preferential sites for wire nucleation agree with their experimentally measured locations. The method used in this paper, which combines electron energy loss spectroscopy, high-resolution Z contrast imaging, and elastic theory finite element calculations, is believed to be a valuable technique of wide applicability for predicting the preferential nucleation sites of epitaxial self-assembled nano-objects., This work was supported by the SANDiE European Network of Excellence (Contract No NMP4-CT-2004-500101), the MEC NANOSELF II project (TEC2005-05781-C03), the CAM: S 0505ESP 0200 project, the Junta de Andalucia (PAI research group TEP-0120; project PAI05-TEP-00383) and by the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, US DOE, under contract DEAC05- 00OR22725 with ORNL, managed and operated by UTBattelle, LLC.

This article is distributed under the terms of the Creative Commons Attribution Noncommercial License.-- This article is part of the series 8th International Workshop on Epitaxial Semiconductors on Patterned Substrates and Novel Index Surfaces., In this work, we present results on the formation of vertical molecule structures formed by two vertically aligned InAs quantum dots (QD) in which a deliberate control of energy emission is achieved. The emission energy of the first layer of QD forming the molecule can be tuned by the deposition of controlled amounts of InAs at a nanohole template formed by GaAs droplet epitaxy. The QD of the second layer are formed directly on top of the buried ones by a strain-driven process. In this way, either symmetric or asymmetric vertically coupled structures can be obtained. As a characteristic when using a droplet epitaxy patterning process, the density of quantum dot molecules finally obtained is low enough (2 × 108 cm−2) to permit their integration as active elements in advanced photonic devices where spectroscopic studies at the single nanostructure level are required., The authors wish to acknowledge to Spanish MICINN through projects Consolider-Ingenio 2010 QOIT (CSD2006-0019) and IMAGINE (CSD2009-00013), NANINPHO-QD (TEC2008-06756-C03-01/03 and 02), the Junta de Andalucía (PAI research group TEP-120 and project P08-TEP-03516) and CAM 2010 Q&CLight (S2009ESP-1503).

Evolution of the size, shape and composition of self-assembled InAs/InP quantum wires through the Stranski–Krastanov transition has been determined by aberration-corrected Z-contrast imaging. High resolution compositional maps of the wires in the initial, intermediate and final formation stages are presented. (001) is the main facet at their very initial stage of formation, which is gradually reduced in favour of {114} or {118}, ending with the formation of mature quantum wires with {114} facets. Significant changes in wire dimensions are measured when varying slightly the amount of InAs deposited. These results are used as input parameters to build three-dimensional models that allow calculation of the strain energy during the quantum wire formation process. The observed morphological evolution is explained in terms of the calculated elastic energy changes at the growth front. Regions of the wetting layer close to the nanostructure perimeters have higher strain energy, causing migration of As atoms towards the quantum wire terraces, where the structure is partially relaxed; the thickness of the wetting layer is reduced in these zones and the island height increases until the (001) facet is removed., This work was supported by the Spanish MCI (TEC2008-06756-C03-02 and 03, Consolider-Ingenio 2010 IMAGINE CSD2009-00013 and QOIT CSD2006-0019), the Junta de Andalucia (PAI research groups TEP-120 and TIC-145; project P08-TEP-03516), the CAM (Q&CLight S2009ESP-1503) and the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, US DOE (MV and SJP).

3 páginas, 3 figuras., In this work we report on the ability to form low density Ga(As)Sb quantum ring-shaped nanostructures (Q-rings) on GaAs(001) substrates by the droplet epitaxy technique. The Q-rings are formed by crystallization of Ga droplets under antimony flux. After being capped by a GaAs layer, these nanostructures show surface mounding features that are correlated with the buried nanostructures, as demonstrated by TEM analysis, permitting an easy surface location of the optically active Q-rings., The authors gratefully acknowledge the financial support by the Spanish MEC (TEC-2005-05781-C03- 01/-03, NAN2004-09109-C04-01/-03, Consolider-QOIT CSD- 2006-0019), CAM (S-505/ESP/000200), JA (TEP383) and by the European Commission through SANDIE Network of Excellence (No. NMP4-CT-2004-500101). P.A.G. thanks the I3P program.

Erratum to: ‘‘Column-by-column compositional mapping by Z-contrast imaging’’ [Ultramicroscopy 109(2) (2009) 172–176] S.I. Molina a, , D.L. Sales , P.L. Galindo , D. Fuster , Y. Gonz alez , B. Al en , L. Gonz alez , M. Varela , S.J. Pennycook d a Departamento de Ciencia de los Materiales e I.M. y Q.I., Facultad de Ciencias, Universidad de C adiz, Campus Ŕio San Pedro, s/n, 11510 Puerto Real, C adiz, Spain b Departamento de Lenguajes y Sistemas Inform aticos, CASEM, Universidad de C adiz, Campus Ŕio San Pedro, s/n, 11510 Puerto Real, C adiz, Spain c Instituto de Microelectronica de Madrid (CNM, CSIC), Isaac Newton 8, 28760 Tres Cantos, Madrid, Spain d Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

5 páginas, 4 figuras., We determine the compositional distribution with atomic column resolution in a horizontal nanowire from the analysis of aberration-corrected high resolution Z-contrast images. The strain field in a layer capping the analysed nanowire is determined by anisotropic elastic theory from the resulting compositional map. The reported method allows preferential nucleation sites for epitaxial nanowires to be predicted with high spatial resolution, as required for accurate tuning of desired optical properties. The application of this method has been exemplified in this work for stacked InAs(P) horizontal nanowires grown on InP separated by 3 nm thick InP layers, but we propose it as a general method to be applied to other stacked nano-objects., This work was supported by the DOE Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, the SANDiE European Network of Excellence (Contract No NMP4-CT- 2004-500101), the Spanish MEC (TEC2005-05781-C03- 01 y 02, NAN2004-09109-C04-01, Consolider-Ingenio 2010 CSD2006-00019), the CAM (S 0505ESP 0200) and the Junta de Andalucia (PAI research groups TEP-120 and TIC-145; project PAI05-TEP-00383).

It is well known that there is intense interest in expanding the usable wavelength for electronic devices. Research efforts are dedicated to develop GaAs technology in order to achieve emission at 1.3 and 1.55 µm, so GaAs could be used for telecommunication applications [1]. Ga(As)Sb on InAs/GaAs quantum dots (QDs) is a promising nanostructure to be used in telecommunications. The introduction of antimony to these nanostructures is an effective solution to obtain redshift emission, even at room temperature [2].

One of the main requirements for the development of quantum computing is the ability of manufacturing single photon emitters. Self assembled semiconductor nanostructures are ones of the most reliable candidates for this application, once control of size and spatial location is achieved. The droplet epitaxy technique allows growth of low density distributions of nanostructures with good optical quality, constituting a promising method for single photon devices and quantum applications [1].

To manufacture improved nanostructures for telecommunication devices which respond to increasing requirements of data transmission speed and stability, the self-assembly process is an interesting approach to be followed. In this context, the control of the morphology, position, composition and strain of the nano-objects constituting these nanostructures is a crucial factor to improve their functionality [1]. It is well known that, during the growth of stacked layers, the upper nano-objects are strongly influenced by the distribution and intensity of the heterogeneous strain field caused by the ones underneath. Key aspects such as substrate temperature and spacer layer thickness between layers alter the strain field at the growth surface and therefore the nucleation sites of the stacked nano-objects.

Reactive epitaxy of Co on vicinal Si(111) surfaces is found to be a flexible and a convenient method for the preparation of dense arrays of Co silicide quantum dots. In the present work, submonolayer amounts of Co were deposited at 800 K on vicinal and flat Si surfaces, analyzing the resulting structures by scanning tunneling microscopy. On vicinal Si(111) surfaces with relatively narrow (~40–100 Å) terrace width, such reactive epitaxy leads to self-assembled arrays of CoSi2 quantum dots with a sharp size distribution function. In contrast, the growth of Co on flat Si(111) results in an inhomogeneous array of dots mixed with a variety of silicide phases, This work was supported by the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, US DOE (MFC, MV and SJP), the SANDiE European Network of Excellence (Contract No. NMP4-CT-2004-500101), the Spanish MEC (TEC2005-05781-C03-01 y 02, NAN2004-09109-C04-01, Consolider-Ingenio 2010 CSD2006-00019 and -0004), the CAM (S 0505ESP 0200), and the Junta de Andalucia (PAI research groups TEP-120 and TIC-145; Project No. PAI05-TEP-00383)

We report the growth by molecular beam epitaxy of Ga Bix As1-x epilayers on (311) B GaAs substrates. We use high-resolution x-ray diffraction (HRXRD), transmission electron microscopy, and Z -contrast imaging to characterize the structural properties of the as-grown material. We find that the incorporation of Bi into the GaBiAs alloy, as determined by HRXRD, is sizably larger in the (311) B epilayers than in (001) epilayers, giving rise to reduced band-gap energies as obtained by optical transmission spectroscopy. © 2007 American Institute of Physics.

Optical transitions in coupled $\mathrm{In}\mathrm{As}∕\mathrm{In}\mathrm{P}$ self-assembled quantum wires are studied within the single-band effective-mass approximation including effects due to strain. Both vertically and horizontally coupled quantum wires are investigated and the ground state, excited states, and the photoluminescence peak energies are calculated. Where possible, we compare with available photoluminescence data from which it was possible to determine the height of the quantum wires. An anticrossing of the energy of excited states is found for vertically coupled wires signaling a change of symmetry of the exciton wave function. This crossing is the signature of two different coupling regimes.

Type II emission optoelectronic devices using GaAsSb strain reduction layers (SRL) over InAs quantum dots (QDs) have aroused great interest. Recent studies have demonstrated an extraordinary increase in photoluminescence (PL) intensity maintaining type II emission after a rapid thermal anneal (RTA), but with an undesirable blueshift. In this work, we have characterized the effect of RTA on InAs/GaAs QDs embedded in a SRL of GaAsSb by transmission electron microscopy (TEM) and finite element simulations. We find that annealing alters both the distribution of Sb in the SRL as well as the exchange of cations (In and Ga) between the QDs and the SRL. First, annealing causes modifications in the capping layer, reducing its thickness but maintaining the maximum Sb content and improving its homogeneity. In addition, the formation of Sb-rich clusters with loop dislocations is noticed, which seems not to be an impediment for an increased PL intensity. Second, RTA produces flatter QDs with larger base diameter and induces a more homogeneous QD height distribution. The Sb is accumulated over the QDs and the RTA enlarges the Sb-rich region, but the Sb contents are very similar. This fact leaves the type II alignment without major changes. Atomic-scale strain analysis of the nanostructures reveal a strong intermixing of In/Ga between the QDs and the capping layer, which is the main responsible mechanism of the PL blueshift. The improvement of the crystalline quality of the capping layer together with higher homogeneity QD sizes could be the origin of the enhancement of the PL emission.

The optical and structural properties of GaAsBi bulk and quantum well (QW) samples grown under various conditions were studied by photoluminescence (PL), high resolution x-ray diffraction (HR-XRD) and transmission electron microscopy (TEM). At 10 K, the 90 nm bulk sample shows two PL peaks at 1.18 and 1.3 eV. The temperature and power dependent PL data suggest that both PL peaks originate from the GaAsBi layer which consists of two regions with different Bi concentrations. The TEM images verify that the Bi concentration decreases monotonically across the layer, showing a high Bi concentration (~0.053) close to the bottom interface which then reduces to ~0.02 for thicknesses >25 nm. Besides, the high Bi content region cannot be detected by HR-XRD due to a broad and weak diffraction intensity. For multiple QW samples, a similar Bi profile was also observed in which the first well has a significantly higher Bi content compared to the other wells. The energy separation between the PL peaks is 0.12 eV and is consistent with the energy difference observed for the bulk sample. However, two PL peaks were not observed in the other GaAsBi bulk sample which was grown under different conditions, showing the importance of growth optimizations.

In this paper we describe a methodology developed at the University of Cadiz (Spain) in the past few years for the extraction of quantitative information from electron microscopy images at the atomic level. This work is based on a coordinated and synergic activity of several research groups that have been working together over the last decade in two different and complementary fields: Materials Science and Computer Science. The aim of our joint research has been to develop innovative high-performance computing techniques and simulation methods in order to address computationally challenging problems in the analysis, modelling and simulation of materials at the atomic scale, providing significant advances with respect to existing techniques. The methodology involves several fundamental areas of research including the analysis of high resolution electron microscopy images, materials modelling, image simulation and 3D reconstruction using quantitative information from experimental images. These techniques for the analysis, modelling and simulation allow optimizing the control and functionality of devices developed using materials under study, and have been tested using data obtained from experimental samples.

This work analyses the Bi incorporation in InAs1-xBix/InAs(100) epilayers grown by MBE through advanced transmission electron microscopy techniques. Samples grown from 350–400 °C resulted in Bi contents

The distribution of bismuth in InAs1-xBix/GaAs quantum dots is analyzed by atomic-column resolution electron microscopy and imaging simulation techniques. A random Bi distribution is measured in the case of

The possibility of an independent tuning of the electron and hole confinement in InAs/GaAs quantum dots (QDs) by using a thin GaAsSbN capping layer (CL) is studied. By controlling the Sb and N contents in the quaternary alloy, the band structure of the QDs can be broadly tuned and converted from type-II in the valence band (high Sb contents) to type-I and to type-II in the conduction band (high N contents). Nevertheless, the simultaneous presence of Sb and N is found to induce strain and composition inhomogeneities in the CL and to degrade the photoluminescence of the structure.

Diluted nitride self-assembled In(Ga)AsN quantum dots (QDs) grown on GaAs substrates are potential candidates to emit in the windows of maximum transmittance for optical fibres (1.3-1.55 µm). In this paper, we analyse the effect of nitrogen addition on the indium desorption occurring during the capping process of InxGa1-xAs QDs (x=1 and 0.7). The samples have been grown by molecular beam epitaxy and studied through transmission electron microscopy (TEM) and photoluminescence techniques. The composition distribution inside the dots was determined by statistical moire analysis and measured by energy dispersive X-ray spectroscopy. First, the addition of nitrogen in In(Ga)As QDs gave rise to a strong redshift in the emission peak, together with a large loss of intensity and monochromaticity. Moreover, these samples showed changes in the QDs morphology as well as an increase in the density of defects. The statistical compositional analysis displayed a normal distribution in InAs QDs with an average In content of 0.7. Nevertheless, the addition of Ga and/or N leads to a bimodal distribution of the Indium content with two separated QD populations. We suggest that the nitrogen incorporation enhances the indium fixation inside the QDs where the indium/gallium ratio plays an important role in this process. The strong redshift observed in the PL should be explained not only by the N incorporation but also by the higher In content inside the QDs.

The distribution of Bi atoms in epitaxial GaAs(1−x)Bix is analyzed through aberration-corrected Z-contrast images. The relation between the atomic number and the intensity of the images allows quantifying the distribution of Bi atoms in this material. A bidimensional map of Bi atoms is extracted showing areas where nanoclustering is possible and evidencing the location of Bi at As-substitutional positions in the lattice. The distribution of Bi atoms differs from a random spatial pattern of Bi atoms in the material.

The effect of low N-alloying on the structure of capped InAs/GaAs quantum dots is analyzed by transmission electron microscopy related techniques. A statistical study of interplanar distances in InAsN quantum dots shows an increase in the lattice parameter compared to the InAs case. We suggest that the addition of nitrogen blocks the Ga/In exchange processes during the quantum dot capping process, leading to an In enrichment. The observed strong photoluminescence redshift of InAsN structures must therefore be attributed not only to the effect of nitrogen in the band gap, but also to a minor depletion of indium during the capping process.