| 1. |
- Adnan, Safdar, et al.
(author)
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Evaluation of microstructural development in electron beam melted Ti-6Al-4V
- 2012
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In: Materials Characterization. - : Elsevier BV. - 1044-5803 .- 1873-4189. ; 65, s. 8-15
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Journal article (peer-reviewed)abstract
- In the current work an investigation of the microstructures of EBM built Ti-6Al-4V test bars has been performed using OM, SEM, TEM and XRD. It has been found that the prior beta phase, that formed during the initial solidification, possesses a column shaped morphology with growing direction parallel to built direction. Typical (alpha+beta) structures namely Widmanstatten alpha platelets with rod-like beta phase formed on the interfaces of the fine alpha grains, have been observed in the columnar prior beta grains. Grain boundary alpha phase was found to be formed around the boundaries of the columnar prior beta grains. Different phases present in the parts, especially the BCC beta phases have been characterized. The TEWEDX results indicate very high V composition in the beta phase. Results of TEWSAED and XRD also revealed that a superlattice structure could be present in the beta phase. Phase transformation sequence is discussed according to the processing history and the microstructures observed.
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| 2. |
- Fu, Yifeng, 1984, et al.
(author)
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Templated Growth of Covalently Bonded Three-Dimensional Carbon Nanotube Networks Originated from Graphene
- 2012
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In: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 24:12, s. 1576-1581
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Journal article (peer-reviewed)abstract
- A template-assisted method that enables the growth of covalently bonded three-dimensional carbon nanotubes (CNTs) originating from graphene at a large scale is demonstrated. Atomic force microscopy-based mechanical tests show that the covalently bonded CNT structure can effectively distribute external loading throughout the network to improve the mechanical strength of the material.
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| 3. |
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| 4. |
- Song, Yuxin, 1981, et al.
(author)
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Effects of doping and grading slope on surface and structure of metamorphic InGaAs buffers on GaAs substrates
- 2009
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 106:12, s. 123531-
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Journal article (peer-reviewed)abstract
- We investigate the effects of doping and grading slope on the surface and structure of linearly alloy graded InGaAs buffers. It is found that the Be doping can improve material properties, resulting in smaller surface roughness and a lower threading dislocation density, while the Si doping has an opposite effect. The effect is strongly dependent on the grading slope. A moderate In grading slope is preferable for the strain relaxation and the minimization of the negative effect of Si doping. Physical mechanisms are proposed to explain the experimental observations. Since doping is essential for many types of optoelectronic devices, these results are valuable for improving the material properties and performance of metamorphic devices.
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| 5. |
- Song, Yuxin, 1981, et al.
(author)
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Enhancement of optical quality in metamorphic quantum wells using dilute nitride buffers
- 2010
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 97:9, s. 091903-
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Journal article (peer-reviewed)abstract
- Strong enhancement of optical quality in quantum wells by incorporating nitrogen in metamorphic InGaAs buffers grown on GaAs substrates is demonstrated. This has resulted in 3.7 or 5.4 times enhancement of photoluminescence intensity from the metamorphic quantum wells when using dilute nitride superlattice alone or adding nitrogen in a strain compensated GaAs/In0.3Al0.7As superlattice, respectively. This study shows great potentials by incorporating N in metamorphic buffers to further improve the quality of metamorphic optoelectronic devices.
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| 6. |
- Tångring, Ivar, 1978, et al.
(author)
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A study of the doping influence on strain relaxation of graded composition InGaAs layers grown by molecular beam epitaxy
- 2009
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In: Journal of Crystal Growth. - 0022-0248. ; 311, s. 1684-
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Journal article (peer-reviewed)abstract
- We investigate the role of p- and n-type doping in strain relaxation of graded composition InGaAs layers grown by molecular beam epitaxy. It is found that p-type Be-doping can improve material properties, resulting in smaller surface roughness and lower threading dislocation density, while n-type Si-doping has an opposite effect. The effect is strongly dependent on the grading profile, with linear grading showing small differences, while there is a significant difference when an exponential grading is used. Since doping is essential for many types of devices, these results are useful for improving the material properties and performance of metamorphic devices.
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| 7. |
- Chukharkin Leonidovich, Maxim, 1980, et al.
(author)
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Noise properties of high-T-c superconducting flux transformers fabricated using chemical-mechanical polishing
- 2012
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 101:4, s. Article Number: 042602 -
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Journal article (peer-reviewed)abstract
- Reproducible high-temperature superconducting multilayer flux transformers were fabricated using chemical mechanical polishing. The measured magnetic field noise of the flip-chip magnetometer based on one such flux transformer with a 9 x 9 mm(2) pickup loop coupled to a bicrystal dc SQUID was 15 fT/Hz(1/2) above 2 kHz. We present an investigation of excess 1/f noise observed at low frequencies and its relationship with the microstructure of the interlayer connections within the flux transformer. The developed high-T-c SQUID magnetometers may be advantageous in ultra-low field magnetic resonance imaging and, with improved low frequency noise, magnetoencephalography applications.
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| 8. |
- Dochev, Dimitar Milkov, 1981, et al.
(author)
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Growth and characterization of epitaxial ultra-thin NbN films on 3C-SiC/Si substrate for terahertz applications
- 2011
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In: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 24:3, s. 035016 (6pp)-
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Journal article (peer-reviewed)abstract
- We report on electrical properties and microstructure of epitaxial thin NbN films grown on 3C-SiC/Si substrates by means of reactive magnetron sputtering. A complete epitaxial growth at the NbN/3C-SiC interface has been confirmed by means of high resolution transmission electron microscopy (HRTEM) along with x-ray diffractometry (XRD). Resistivitymeasurements of the films have shown that the superconducting transition onset temperature (TC) for the best specimen is 11.8 K. Using these epitaxial NbN films, we have fabricated submicron-size hot-electron bolometer (HEB) devices on 3C-SiC/Si substrate and performed their complete DC characterization. The observed critical temperature TC = 11.3 K and critical current density of about 2.5 MA cm−2 at 4.2 K of the submicron-size bridges were uniform across the sample. This suggests that the deposited NbN films possess the necessary homogeneity to sustain reliable hot-electron bolometer device fabrication for THz mixer applications.
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| 9. |
- Dochev, Dimitar Milkov, 1981, et al.
(author)
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The influence of aging and annealing on the properties of Nb/Al-AlOx/Nb tunnel junctions
- 2010
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In: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 234:4
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Conference paper (peer-reviewed)abstract
- This paper presents results of our studies on aging and annealing properties of Nb/Al-AlOx/Nb junctions. We performed a long room temperature aging with subsequent annealing at different temperatures up to 250°C. A distinct change of the junctions' normal-state resistance has been observed. Aging at room temperature results in a slight decrease of the normal-state resistance combined with improved junction quality, characterised by a better subgap-to-normal resistance ratio. Annealing at moderate temperatures in air increases the normal-state resistance and leads to improvement of the junction quality followed by degradation at higher annealing temperatures. The increase in the junction quality after long-term aging at room temperature is attributed to relaxation of the internal junction structure and interfaces, thus, resulting in a lower density of interface traps. The deterioration at higher annealing temperatures could be a consequence of diffusion processes at the Al/Nb interface. We observe a sufficiently clear difference between the behaviour of preliminary aged and newly fabricated junctions after annealing: for the aged high-quality junction, the degradation was negligible up to temperatures of 200°C, while non-aged junctions show a much faster and abrupt degradation at lower annealing temperatures.
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| 10. |
- Song, Yuxin, 1981, et al.
(author)
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Molecular beam epitaxy growth of InSb1-xBix thin films
- 2013
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In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 378, s. 323-328
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Journal article (peer-reviewed)abstract
- Molecular beam epitaxy growth for InSb1-xBix thin films on (100) GaAs substrates is reported. Successful Bi incorporation for 2% is achieved, and up to 70% of the incorporated Bi atoms are at substitutional sites. The effects of growth parameters on Bi incorporation and surface morphology are studied. Strong In and Ga inter-diffusion induced by Bi incorporation is observed and discussed.
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