Laser Engineering Nanocarbon Phases within Diamond for Science and Electronics.

Diamond, as the densest allotrope of carbon, displays a range of exemplary material properties that are attractive from a device perspective. Despite diamond displaying high carbon-carbon bond strength, ultrashort (femtosecond) pulse laser radiation can provide sufficient energy for highly localized internal breakdown of the diamond lattice. The less-dense carbon structures generated on lattice breakdown are subject to significant pressure from the surrounding diamond matrix, leading to highly unusual formation conditions. By tailoring the laser dose delivered to the diamond, it is shown that it is possible to create continuously modified internal tracks with varying electrical conduction properties. In addition to the widely reported conducting tracks, conditions leading to semiconducting and insulating written tracks have been identified. High-resolution transmission electron microscopy (HRTEM) is used to visualize the structural transformations taking place and provide insight into the different conduction regimes. The HRTEM reveals a highly diverse range of nanocarbon structures are generated by the laser irradiation, including many signatures for different so-called diaphite complexes, which have been seen in meteorite samples and seem to mediate the laser-induced breakdown of the diamond. This work offers insight into possible formation methods for the diamond and related nanocarbon phases found in meteorites.

Diamond for Electronics: Materials, Processing and Devices.

Progress in power electronic devices is currently accepted through the use of wide bandgap materials (WBG). Among them, diamond is the material with the most promising characteristics in terms of breakdown voltage, on-resistance, thermal conductance, or carrier mobility. However, it is also the one with the greatest difficulties in carrying out the device technology as a result of its very high mechanical hardness and smaller size of substrates. As a result, diamond is still not considered a reference material for power electronic devices despite its superior Baliga's figure of merit with respect to other WBG materials. This review paper will give a brief overview of some scientific and technological aspects related to the current state of the main diamond technology aspects. It will report the recent key issues related to crystal growth, characterization techniques, and, in particular, the importance of surface states aspects, fabrication processes, and device fabrication. Finally, the advantages and disadvantages of diamond devices with respect to other WBG materials are also discussed.

Improved Field Electron Emission Properties of Phosphorus and Nitrogen Co-Doped Nanocrystalline Diamond Films.

Nanocrystalline diamond (NCD) field emitters have attracted significant interest for vacuum microelectronics applications. This work presents an approach to enhance the field electron emission (FEE) properties of NCD films by co-doping phosphorus (P) and nitrogen (N) using microwave plasma-enhanced chemical vapor deposition. While the methane (CH4) and P concentrations are kept constant, the N2 concentration is varied from 0.2% to 2% and supplemented by H2. The composition of the gas mixture is tracked in situ by optical emission spectroscopy. Scanning electron microscopy, atomic force microscopy (AFM), transmission electron microscopy, and Raman spectroscopy are used to provide evidence of the changes in crystal morphology, surface roughness, microstructure, and crystalline quality of the different NCD samples. The FEE results display that the 2% N2 concentration sample had the best FEE properties, viz. the lowest turn-on field value of 14.3 V/µm and the highest current value of 2.7 µA at an applied field of 73.0 V/µm. Conductive AFM studies reveal that the 2% N2 concentration NCD sample showed more emission sites, both from the diamond grains and the grain boundaries surrounding them. While phosphorus doping increased the electrical conductivity of the diamond grains, the incorporation of N2 during growth facilitated the formation of nano-graphitic grain boundary phases that provide conducting pathways for the electrons, thereby improving the FEE properties for the 2% N2 concentrated NCD films.

Crystalline Defects Induced during MPCVD Lateral Homoepitaxial Diamond Growth.

The development of new power devices taking full advantage of the potential of diamond has prompted the design of innovative 3D structures. This implies the overgrowth towards various crystallographic orientations. To understand the consequences of such growth geometries on the defects generation, a Transmission Electron Microscopy (TEM) study of overgrown, mesa-patterned, homoepitaxial, microwave-plasma-enhanced, chemical vapor deposition (MPCVD) diamond is presented. Samples have been grown under quite different conditions of doping and methane concentration in order to identify and distinguish the factors involved in the defects generation. TEM is used to reveal threading dislocations and planar defects. Sources of dislocation generation have been evidenced: (i) doping level versus growth plane, and (ii) methane concentration. The first source of dislocations was shown to generate <110> Burgers vector dislocations above a critical boron concentration, while the second induces <112> type Burgers vector above a critical methane/hydrogen molar ratio. The latter is attributed to partial dislocations whose origin is related to the dissociation of perfect ones by a Shockley process. This dissociation generated stacking faults that likely resulted in penetration twins, which were also observed on these samples. Lateral growth performed at low methane and boron content did not exhibit any dislocation.

Control of the Alumina Microstructure to Reduce Gate Leaks in Diamond MOSFETs.

In contrast to Si technology, amorphous alumina cannot act as a barrier for a carrier at diamond MOSFET gates due to their comparable bandgap. Indeed, gate leaks are generally observed in diamond/alumina gates. A control of the alumina crystallinity and its lattice matching to diamond is here demonstrated to avoid such leaks. Transmission electron microscopy analysis shows that high temperature atomic layer deposition, followed by annealing, generates monocrystalline reconstruction of the gate layer with an optimum lattice orientation with respect to the underneath diamond lattice. Despite the generation of γ-alumina, such lattice control is shown to prohibit the carrier transfer at interfaces and across the oxide.

Boron-Doping Proximity Effects on Dislocation Generation during Non-Planar MPCVD Homoepitaxial Diamond Growth.

Epitaxial lateral growth will be required if complex diamond-based device architecture, such as, for example, Metal-oxide-semiconductor Field-effect transistors (MOSFETs) or epitaxial lateral overgrowth (ELO) substrates, need to be developed for high-power applications. To this end, undoped and doped non-planar homoepitaxial diamond were overgrown on (001)-oriented diamond-patterned substrates. Defects induced by both the heavy boron doping and three-dimensional (3D) growth were studied by transmission electron microscopy (TEM). At high methane and boron concentrations, threading dislocations with Burgers vectors b = 1/6 ⟨211⟩, b = 1/2 ⟨110⟩, or both were observed. Their generation mechanisms were established, revealing boron proximity effects as precursors of dislocations generated in boron-doped samples and providing clues as to the different Burgers vectors. The concentration ranges of boron and methane resulting in good crystalline quality depended on the plane of growth. The microwave plasma-enhanced chemical vapour deposition (MPCVD) growth conditions and the maximum boron concentration versus plane orientation yielding a dislocation-free diamond epitaxial layer were determined.

Microwave Permittivity of Trace sp2 Carbon Impurities in Sub-Micron Diamond Powders.

Microwave dielectric loss tangent measurements are demonstrated as a method for quantifying trace sp2-hybridized carbon impurities in sub-micron diamond powders. Appropriate test samples are prepared by vacuum annealing at temperatures from 600 to 1200 °C to vary the sp2/sp3 carbon ratio through partial surface graphitization. Microwave permittivity measurements are compared with those obtained using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and electron energy loss spectroscopy (EELS). The average particle size remains constant (verified by scanning electron microscopy) to decouple any geometric dielectric effects from the microwave measurements. After annealing, a small increase in sp2 carbon was identified from the XPS C 1s and Auger spectra, the EELS σ* peak in the C 1s spectra, and the D and G bands in Raman spectroscopy, although a quantifiable diamond to G-band peak ratio was unobtainable. Surface hydrogenation was also evidenced in the Raman and XPS O 1s data. Microwave cavity perturbation measurements show that the dielectric loss tangent increases with increasing sp2 bonding, with the most pertinent finding being that these values correlate with other measurements and that trace concentrations of sp2 carbon as small as 5% can be detected.

Versión española del cuestionario de calidad de vida para niños y adolescentes con cardiopatías (PedsQL TM) / The spanish version of the health-related quality of life questionnaire for children and adolescents with heart disease (PedsQL TM)

Introducción y objetivos. Adaptar al español el cuestionario de calidad de vida Pediatric Quality of Life Inventory (PedsQLTM) (Módulo General y Módulo Cardiaco, versión 3.0). Métodos. Metodología de traducción directa e inversa. La entrevista cognitiva se utilizó para probar la versión previa al test. Se realizó la evaluación de las propiedades psicométricas de la versión española. Resultados. La nueva versión contiene algunos cambios de formato con intención de facilitar la lectura de los enunciados y la comprensión de las instrucciones de respuesta (versión para niños de 5-7 años). Se identificaron algunos problemas de «descontextualización» en relación con el desarrollo evolutivo de los niños en las versiones para los niños más pequeños y sus padres (2-4 y 5-7 años). El porcentaje de ítems sin respuesta osciló entre 0 y el 5,9%. Se encontraron efectos techo elevados, especialmente en el Módulo Cardiaco, donde osciló en un 19-48,6%. La consistencia interna fue > 0,7, excepto en la dimensión de Apariencia Física y Funcionamiento Escolar en los niños. Los grados de acuerdo entre la información dada por los niños y la dada por los padres fueron en general muy altos. Se observó una tendencia de descenso de las puntuaciones en todas las escalas en relación con la gravedad de la cardiopatía, pero sólo en algunas dimensiones las diferencias fueron estadísticamente significativas. Conclusiones. La versión española del PedsQLTM presenta algunas diferencias con la versión original, concretamente con las dimensiones de Funcionamiento Escolar y Apariencia Física, como se observó en las entrevistas cognitivas. Por otro lado, no se ha demostrado que tenga validez predictiva (AU)

Introduction and objectives. To adapt the Pediatric Quality of Life Inventory (PedsQLTM) (General Module and Cardiac Module, 3.0 version) into Spanish. Methods. Forward and back translation methodology. Cognitive interviewing was used to check the pre-test version. Psychometric properties were computed for the PedsQLTM Cardiac Module Scales. Cross-informant variance between children and parents was assessed. Results. The Spanish version has some format changes to make it easier to read and to clarify response choices (version for 5-7 years age group). Some semantically complex terms were replaced with synonyms and others illustrated with examples. Some "out of context" problems were identified with respect to some items (version for children 2-4 and 5-7 years). The percentage of missing item responses ranged from 0% to 5.9%. A high ceiling effect was found, especially in the Cardiac Module, which ranged from 19% to 48.6%. Internal consistency was higher than 0.7, except for Physical Appearance Scale and School Functioning in children. Agreement between information given by children and parents was generally very high. A decreasing trend in scores on all scales was observed in relation to the severity of heart disease, but the differences were only statistically significant in some dimensions. Conclusions. The Spanish version of the PedsQLTM differs somewhat from the original version, particularly on the School Functioning and Physical Appearance Scales, as observed in cognitive interviews. Predictive validity was not demonstrated (AU)

The Spanish version of the health-related quality of life questionnaire for children and adolescents with heart disease (PedsQL(TM)).

INTRODUCTION AND OBJECTIVES: To adapt the Pediatric Quality of Life Inventory (PedsQL(TM)) (General Module and Cardiac Module, 3.0 version) into Spanish. METHODS: Forward and back translation methodology. Cognitive interviewing was used to check the pre-test version. Psychometric properties were computed for the PedsQL(TM) Cardiac Module Scales. Cross-informant variance between children and parents was assessed. RESULTS: The Spanish version has some format changes to make it easier to read and to clarify response choices (version for 5-7 years age group). Some semantically complex terms were replaced with synonyms and others illustrated with examples. Some "out of context" problems were identified with respect to some items (version for children 2-4 and 5-7 years). The percentage of missing item responses ranged from 0% to 5.9%. A high ceiling effect was found, especially in the Cardiac Module, which ranged from 19% to 48.6%. Internal consistency was higher than 0.7, except for Physical Appearance Scale and School Functioning in children. Agreement between information given by children and parents was generally very high. A decreasing trend in scores on all scales was observed in relation to the severity of heart disease, but the differences were only statistically significant in some dimensions. CONCLUSIONS: The Spanish version of the PedsQL(TM) differs somewhat from the original version, particularly on the School Functioning and Physical Appearance Scales, as observed in cognitive interviews. Predictive validity was not demonstrated.