| 1. |
- Haas, Sylvio, et al.
(författare)
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Correlation of precipitate evolution with Vickers hardness in Haynes® 282® superalloy : In-situ high-energy SAXS/WAXS investigation
- 2018
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5107 .- 1873-4944 .- 0921-5093 .- 1873-4936. ; 11, s. 250-258
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this work is to characterize the precipitation kinetics in Haynes® 282® superalloys using in-situ high-energy Small Angle X-ray Scattering (SAXS) together with Wide Angle X-ray Scattering (WAXS). The phases identified by WAXS include γ (matrix), γ′ (hardening precipitates), MC (metallic carbides), and M23C6/M6C (secondary metallic carbides). The γ'-precipitates are spheroids with a diameter of several nanometres, depending on the temperature and ageing time. From the SAXS data, quantitative parameters such as volume fraction, number density and inter-particle distance were determined and correlated with ex-situ Vickers microhardness measurements. The strengthening components associated with precipitates and solid solutions are differentiated using the measured Vickers microhardness and SAXS model parameters. A square root dependence between strengthening attributable to the precipitates and the product of volume fraction and mean precipitate radius is found. The solid solution strengthening component correlates with the total volume fraction of precipitates.
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| 2. |
- Buyanova, Irina A., et al.
(författare)
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Optical properties of GaNAs/GaAs structures
- 2001
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Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 82:1-3, s. 143-147
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Tidskriftsartikel (refereegranskat)abstract
- We review our recent results on optical characterization of MBE-grown GaNAs/GaAs quantum structures with N content up to 4.5%, by employing photoluminescence (PL), PL excitation, and time-resolved PL spectroscopies. The dominant PL mechanism has been determined as recombination of excitons trapped by potential fluctuations of the band edge, due to composition disorder and strain nonuniformity of the alloy. The estimated value of the localization potential is around 60 meV for the low-temperature grown structures and can be reduced by increasing the growth temperature or using post-growth rapid thermal annealing (RTA). © 2001 Elsevier Science S.A.
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| 3. |
- Buyanova, Irina A., et al.
(författare)
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Photoluminescence characterization of defects created in electron-irradiated silicon at elevated temperatures
- 2000
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Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 72:2, s. 146-149
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Tidskriftsartikel (refereegranskat)abstract
- Photoluminescence (PL) spectroscopy is employed to investigate radiative defects created in Si during electron-irradiation at elevated temperatures. The use of high temperature during electron irradiation has been found to affect considerably the defect formation process. The effect critically depends on the temperature of the irradiation as well as doping of the samples. For carbon-lean Si wafers high temperature electron irradiation stimulates the formation of extended defects, such as dislocations and precipitates. For carbon-rich Si wafers the increase of irradiation temperature up to 300°C enhances the formation of the known carbon-related defects. In addition, several new excitonic PL lines were observed after electron irradiation at T = 450°C. The dominant new PL center gives rise to a BE PL emission at 0.961 eV. The electronic structure of the 0.961 eV defect is discussed based on temperature-dependent and magneto-optical studies.
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| 4. |
- Coomer, B.J., et al.
(författare)
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Vacancy-hydrogen complexes in germanium
- 1999
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Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 58:1-2, s. 36-38
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Tidskriftsartikel (refereegranskat)abstract
- Local-density-functional pseudopotential theory is used to investigate the structural, electronic and vibrational properties of vacancy-hydrogen complexes in germanium. The results are compared with recent infrared absorption data from proton and deuteron implanted Ge. The acceptor and donor levels of the VHn defects are derived semi-empirically from the relaxed structures
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| 5. |
- Du, Chun-Xia, et al.
(författare)
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Efficient 1.54 µm light emission from Si/SiGe/Si : Er
- 2001
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Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 81:1-3, s. 105-108
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Tidskriftsartikel (refereegranskat)abstract
- Si/SiGe/Si:Er:O-heterojunction bipolar transistor (HBT)-type light emitting devices with Er3+ ions incorporated in the collector region have been fabricated using layered structures prepared by differential molecular beam epitaxy (MBE). Intense light emission at 1.54 µm has been observed at room temperature by hot electron impact excitation at rather low injection current and applied voltage. Separate controls of the injection current and bias voltage make it possible to perform detailed electroluminescence (EL) studies that can not be done with conventional Si:Er light emitting diodes (LEDs). Saturation of the EL intensity occurs at very low current densities indicating a 100-fold increase of the effective excitation cross-section for Si/SiGe/Si:Er:O-HBTs compared with Si:Er-LEDs. © 2001 Elsevier Science B.V.
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| 6. |
- Fall, C.J., et al.
(författare)
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Electronic and vibrational properties of Mg- and O-related complexes in GaN
- 2001
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Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 82:1, s. 88-90
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Tidskriftsartikel (refereegranskat)abstract
- We investigate from first principles the energetic and vibrational properties of various candidate structures for the 3125 cm-1 local vibrational mode in GaN, known to be related to hydrogen passivated magnesium atoms. The orientation of the electric dipole of this mode has recently been measured with respect to the wurtzite c-axis, giving a result seemingly inconsistent with current atomic models for this defect. We study the possibility that complexes of magnesium, native impurities and hydrogen could give rise to the experimental observations. Furthermore, we consider a possible candidate giving rise to a 0.88-eV line in a variety of electron-irradiated GaN samples. We find evidence that a deep donor level including substitutional oxygen must result from a complex impurity.
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| 7. |
- Galeckas, A., et al.
(författare)
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Characterization of carrier lifetime and diffusivity in 4H-SiC using time-resolved imaging spectroscopy of electroluminescence
- 2003
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Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 102:03-jan, s. 304-307
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Tidskriftsartikel (refereegranskat)abstract
- We report on time- and spectrally resolved studies of recombination radiation in 4H-SiC by combining imaging spectroscopy and gated optical emission microscopy techniques. An insight into the basic characteristics of 3D carrier dynamics was attained by combining data of electroluminescence imaged from the backside and from the cross-sectional plane of a forward biased PN structures. We demonstrate the potential and efficiency of this method in mapping minority carrier lifetime and diffusivity parameters and also in locating and analysis of the structural defects in the active area. Finally, a detrimental impact of the intrinsic growth-related and long-term operation-induced defects on the carrier transport properties was directly revealed and quantified.
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| 8. |
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| 9. |
- Hai, P. N., et al.
(författare)
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Properties of GaAsN/GaAs quantum wells studied by optical detection of cyclotron resonance
- 2001
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Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 82:1-3, s. 218-220
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Tidskriftsartikel (refereegranskat)abstract
- Effective masses and carrier recombination in GaNAs/GaAs quantum wells (QWs) with nitrogen composition up to 4.5%, have been studied by optical detection of cyclotron resonance (ODCR). When monitoring the PL emissions under the conditions of above-GaAs barrier excitation, the ODCR spectrum is dominated by the electron CR in GaAs with an effective mass value 0.066m0. The ODCR mechanism is discussed in terms of hot carrier effects, resulting in a reduced carrier recombination in GaAs and an enhanced carrier trapping in the GaNAs QW. Under resonant excitation of the GaNAs QWs, only a broad ODCR signal can be observed, corresponding to an effective mass value of 0.12m0 and 0.19m0 when the N composition is about 1.2 and 2%, respectively. This is attributed to the electron CR in the GaNAs QW with a lower electron mobility. This sizeable increase in the electron effective mass is in agreement with earlier theoretical predictions. ⌐ 2001 Elsevier Science B.V.
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| 10. |
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