| 1. |
- Alcorn, J, et al.
(författare)
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Basic instrumentation for Hall A at Jefferson Lab
- 2004
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 522:3, s. 294-346
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Tidskriftsartikel (refereegranskat)abstract
- The instrumentation in Hall A at the Thomas Jefferson National Accelerator Facility was designed to study electro-and photo-induced reactions at very high luminosity and good momentum and angular resolution for at least one of the reaction products. The central components of Hall A are two identical high resolution spectrometers, which allow the vertical drift chambers in the focal plane to provide a momentum resolution of better than 2 x 10(-4). A variety of Cherenkov counters, scintillators and lead-glass calorimeters provide excellent particle identification. The facility has been operated successfully at a luminosity well in excess of 10(38) CM-2 s(-1). The research program is aimed at a variety of subjects, including nucleon structure functions, nucleon form factors and properties of the nuclear medium. (C) 2003 Elsevier B.V. All rights reserved.
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| 2. |
- Darakchieva, Vanya, et al.
(författare)
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Free electron behavior in InN : On the role of dislocations and surface electron accumulation
- 2009
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 94:2, s. 022109-
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Tidskriftsartikel (refereegranskat)abstract
- The free electron behavior in InN is studied on the basis of decoupled bulk and surface accumulation electron densities in InN films measured by contactless optical Hall effect. It is shown that the variation in the bulk electron density with film thickness does not follow the models of free electrons generated by dislocation-associated nitrogen vacancies. This finding, further supported by transmission electron microscopy results, indicates the existence of a different thickness-dependent doping mechanism. Furthermore, we observe a noticeable dependence of the surface electron density on the bulk density, which can be exploited for tuning the surface charge in future InN based devices.
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| 3. |
- Darakchieva, Vanya, et al.
(författare)
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Role of impurities and dislocations for the unintentional n-type conductivity in InN
- 2009
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Ingår i: PHYSICA B-CONDENSED MATTER. - : Elsevier BV. - 0921-4526. ; 404:22, s. 4476-4481
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Tidskriftsartikel (refereegranskat)abstract
- We present a study on the role of dislocations and impurities for the unintentional n-type conductivity in high-quality InN grown by molecular beam epitaxy. The dislocation densities and H profiles in films with free electron concentrations in the low 10(17) cm(-1) and mid 10(18) cm(-3) range are measured, and analyzed in a comparative manner. It is shown that dislocations alone could not account for the free electron behavior in the InN films. On the other hand, large concentrations of H sufficient to explain, but exceeding substantially, the observed free electron densities are found. Furthermore, enhanced concentrations of H are revealed at the film surfaces, resembling the free electron behavior with surface electron accumulation. The low-conductive film was found to contain C and it is suggested that C passivates the H donors or acts as an acceptor, producing compensated material in this case. Therefore, it is concluded that the unintentional impurities play an important role for the unintentional n-type conductivity in InN. We suggest a scenario of H incorporation in InN that may reconcile the previously reported observations for the different role of impurities and dislocations for the unintentional n-type conductivity in InN.
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| 4. |
- Darakchieva, Vanya, et al.
(författare)
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Unravelling the free electron behavior in InN
- 2008
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Ingår i: Optoelectronic and Microelectronic Materials and Devices, 2008. - : IEEE. - 9781424427161 ; , s. 90-97
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Konferensbidrag (refereegranskat)abstract
- Precise measurement of the optical Hall effect in InN using magneto-optical generalized ellipsometry at IR and THz wavelengths, allows us to decouple the surface accumulation and bulk electron densities in InN films by non-contact optical means and further to precisely measure the effective mass and mobilities for polarizations parallel and perpendicular to the optical axis. Studies of InN films with different thicknesses, free electron densities and surface orientations enable an intricate picture of InN free electron properties to emerge. Striking findings on the scaling factors of the bulk electron densities with film thickness further supported by transmission electron microscopy point to an additional thickness dependent doping mechanism unrelated to dislocations. Surface electron accumulation is observed to occur not only at polar but also at non-polar and semi-polar wurtzite InN, and zinc blende InN surfaces. The persistent surface electron density shows a complex behavior with bulk density and surface orientation. This behavior might be exploited for tuning the surface charge in InN.
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| 5. |
- Emmanuel, Max, et al.
(författare)
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Fracture Energy Measurement of Prismatic Plane and Σ2 Boundary in Cemented Carbide
- 2021
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Ingår i: JOM. - : Springer Science and Business Media LLC. - 1047-4838 .- 1543-1851. ; 73:6, s. 1589-1596
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Tidskriftsartikel (refereegranskat)abstract
- The grain boundary network of WC in WC-Co is important, as cracks often travel intergranularly. This motivates the present work, where we experimentally measure the fracture energy of Σ2 twist grain boundaries between WC crystals using a double cantilever beam opened with a wedge under displacement control in a WC-10wt%Co sample. The fracture energy of this boundary type was compared with cleaving {10 1 ¯ 0 } prismatic planes in a WC single crystal. Fracture energies of 7.04 ± 0.36 Jm−2 and 3.57 ± 0.28 Jm−2 were measured for {10 1 ¯ 0 } plane and Σ2 twist boundaries, respectively.
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| 6. |
- Flink, Axel, et al.
(författare)
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Microstructural characterization of the tool-chip interface enabled by focused ion beam and analytical electron microscopy
- 2009
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Ingår i: WEAR. - : Elsevier BV. - 0043-1648. ; 266:11-12, s. 1237-1240
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Tidskriftsartikel (refereegranskat)abstract
- A method based on focused ion beam milling and analytical electron microscopy to investigate the nature of the tool-chip interface is presented. It is employed to study tool-chip interfaces of the rake face of a (Ti0.83Si0.17)N coated PCBN insert after turning of case-hardened steel. Analytical electron microscopy shows the presence of a smeared adhered layer on the coating, which consists of steel elements from the work-piece, oxygen, and Si and N, most likely originating from the coating.
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| 7. |
- Gangaprasad Rao, Smita, et al.
(författare)
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Thin film growth and mechanical properties of CrFeCoNi/TiNbZrTa multilayers
- 2022
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Ingår i: Materials & design. - : Elsevier Science Ltd. - 0264-1275 .- 1873-4197. ; 224
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Tidskriftsartikel (refereegranskat)abstract
- Multilayers of high entropy alloys (HEA) are picking up interest due to the possibility of altering material properties by tuning crystallinity, thickness, and interfaces of the layers. This study investigates the growth mechanism and mechanical properties of CrFeCoNi/TiNbZrTa multilayers grown by magnetron sputtering. Multilayers of bilayer thickness (A) from 5 nm to 50 nm were grown on Si(1 0 0) substrates. Images taken by transmission electron microscopy and energy-dispersive X-ray spectroscopy mapping revealed that the layers were well defined with no occurrence of elemental mixing. Multilayers with A < 20 nm exhibited an amorphous structure. As A increased, the CrFeCoNi layer displayed a higher crystallinity in comparison to the amorphous TiNbZrTa layer. The mechanical properties were influenced by the crystallinity of the layers and stresses in the film. The film with A = 20 nm had the highest hardness of approximately 12.5 GPa owing grain refinement of the CrFeCoNi layer. An increase of A >= 30 nm resulted in a drop in the hardness due to the increase in crystal domains of the CrFeCoNi layer. Micropillar compression induced shear in the material rather than fracture, along with elemental intermixing in the core of the deformed region of the compressed micropillar.
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| 8. |
- Wilhelmsson, Ola, et al.
(författare)
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Intrusion-type deformation in epitaxial Ti3SiC2/TiC0.67 nanolaminates
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:12, s. 123124-
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the deformation of epitaxial Ti3SiC2(0001)/TiCx(111) (x~0.67) nanolaminates deposited by magnetron sputtering. Nanoindentation and transmission electron microscopy show that the Ti3SiC2 layers deform via basal plane slip and intrusion into the TiC layers, suppressing kink-band and pile-up deformation behaviors analogous with monolithic Ti3SiC2. This remarkable response to indentation is due to persistent slip in the TiC layers and prevention of gross slip throughout the nanolaminate by the interleaving Ti3SiC2 layers. Hardness and Young's modulus were measured as ~15 and ~240 GPa, respectively.
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| 9. |
- Willmann, Herbert, et al.
(författare)
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Single-crystal growth of NaCl-structure Al-Cr-N thin films on MgO(0 0 1) by magnetron sputter epitaxy
- 2007
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 57:12, s. 1089-1092
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Tidskriftsartikel (refereegranskat)abstract
- Single-crystal NaCl-structure Al0.68Cr0.32N thin films were deposited onto MgO(0 0 1) substrates. The films exhibit cube-on-cube epitaxial growth with an initial pseudomorphic strained layer before complete relaxation into an isotropic lattice parameter of 4.119 Å as shown by symmetric high-resolution X-ray diffraction and asymmetric reciprocal space maps. The relaxation proceeds via a threading dislocation network as revealed by transmission electron microscopy. Films of 900 nm thickness have a hardness of 32.4 ± 0.5 GPa, an elastic modulus of 460.8 ± 5 GPa, and a room-temperature resistivity of 2.7 × 103 O cm as determined by nanoindentation and four-point probe measurements, respectively. © 2007 Acta Materialia Inc.
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| 10. |
- Yazdi, Gholamreza, et al.
(författare)
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Freestanding AlN single crystals enabled by self-organization of 2H-SiC pyramids on 4H-SiC substrates
- 2009
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Ingår i: APPLIED PHYSICS LETTERS. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 94:8, s. 082109-
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Tidskriftsartikel (refereegranskat)abstract
- A sublimation-recondensation process is presented for high quality AlN (0001) crystals at a high growth rate by employing 4H-SiC substrates with a predeposited epilayer. It is based on the coalescence of well oriented AlN microrods, which evolve from the apex of 2H-SiC pyramids grown out of hexagonal pits formed by thermal etching of the substrate during a temperature ramp up. This process yields stress-free 120-mu m-thick AlN single crystals with a dislocation density as low as 2x10(6) cm(-2).
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