| 1. |
- Arndt, Tina, et al.
(författare)
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Spidroin N-terminal domain forms amyloid-like fibril based hydrogels and provides a protein immobilization platform
- 2022
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- Recombinant spider silk proteins (spidroins) have multiple potential applications in development of novel biomaterials, but their multimodal and aggregation-prone nature have complicated production and straightforward applications. Here, we report that recombinant miniature spidroins, and importantly also the N-terminal domain (NT) on its own, rapidly form self-supporting and transparent hydrogels at 37 °C. The gelation is caused by NT α-helix to β-sheet conversion and formation of amyloid-like fibrils, and fusion proteins composed of NT and green fluorescent protein or purine nucleoside phosphorylase form hydrogels with intact functions of the fusion moieties. Our findings demonstrate that recombinant NT and fusion proteins give high expression yields and bestow attractive properties to hydrogels, e.g., transparency, cross-linker free gelation and straightforward immobilization of active proteins at high density.
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| 2. |
- Ha Ryu, Jae, et al.
(författare)
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Beam stability of buried-heterostructure quantum cascade lasers employing HVPE regrowth
- 2021
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Ingår i: Optics Express. - : The Optical Society. - 1094-4087. ; 29:2, s. 2819-2826
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of beam stability for mid-infrared (IR)-emitting quantum cascade lasers (QCLs) are important for applications that require the beam to travel through air to remote targets, such as free-space communication links. We report beam-quality measurement results of narrow-ridge, 4.6 mu m-emitting buried-heterostructure (BH) QCLs fabricated using ICP etching and HVPE regrowth. Beam-quality measurements under QCW operation exhibit M-2 < 1.2 up to 1 W for similar to 5 mu m-wide ridges. 5 mu m-wide devices display some small degree of centroid motion with increasing output power (< 0.125 mrad), which corresponds to a targeting error of similar to 1.25 cm over a distance of 100 m.
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| 3. |
- Manavaimaran, Balaji, et al.
(författare)
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Investigation of OP-GaP Grown on OP-GaAs Templates Using Nondestructive Reciprocal Space Mapping
- 2023
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Ingår i: Crystals. - : MDPI AG. - 2073-4352. ; 13:2, s. 168-
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Tidskriftsartikel (refereegranskat)abstract
- Orientation-patterned gallium phosphide (OP-GaP) has been grown heteroepitaxially on OP gallium arsenide (GaAs) templates using hydride vapor phase epitaxy (HVPE). The effect of OP-GaAs template fabrication methods of epitaxial-inversion and wafer bonding on the heteroepitaxial OP-GaP growth has been investigated. OP-GaP layers with a growth rate of up to 35 mu m/h and excellent domain fidelity were obtained. The growth rate and the domain fidelity have been revealed/studied by scanning electron microscope (SEM). In addition, we demonstrate that the crystalline quality of the individual domains, namely, the substrate-oriented domains (ODs) and the inverted domains (IDs), can be investigated by high-resolution x-ray diffraction reciprocal space mapping (HRXRDRSM), which can also indicate the domain fidelity. Attempts to increase the growth rate and improve the domain fidelity by increasing the III and V group precursors resulted in either an increase in the growth rate in the OP-GaP layers grown on epitaxial inversion OP-GaAs template at the expense of the domain crystalline quality and fidelity or an improvement in the crystalline quality of the domains at the expense of the growth rate in the OP-GaP layers grown on wafer-bonded OP-GaAs templates. In the case of OP-GaP grown on OP-GaAs templates prepared by epitaxial inversion, the crystalline quality of the ODs is better than that of the IDs, but it shows that the quality of the inverted layer in the template influences the quality and fidelity of the grown domains. To the authors' knowledge, exploitation of HRXRDRSM studies on OP-GaP to establish the crystalline quality of its individual domains (ODs and IDs) is the first of its kind. OP-ZnSe grown on OP-GaAs templates has also been included in this study to further emphasize the potential of this method. We propose from this study that once the growth rate is optimized from SEM studies, HRXRDRSM analysis alone can be used to assess the structural quality and to infer the domain fidelity of the OP structures.
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| 4. |
- Oberhausen, Wolfhard, et al.
(författare)
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Phase-matching in terahertz quantum cascade laser sources based on Cherenkov difference-frequency mixing
- 2023
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Ingår i: APL Photonics. - : AIP Publishing. - 2378-0967. ; 8:9
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Tidskriftsartikel (refereegranskat)abstract
- Terahertz quantum cascade laser sources based on intra-cavity Cherenkov difference-frequency generation in dual-wavelength mid-infrared quantum cascade lasers are currently the only monolithic semiconductor laser technology that can deliver continuous-wave coherent terahertz output at room temperature. Because the Cherenkov difference-frequency generation process enables terahertz radiation generation and extraction across a wide range of frequencies, it is often assumed that phase-matching conditions for this process are automatically fulfilled. We theoretically analyze and experimentally demonstrate that phase-matching plays an important role in these devices, and significant improvements in terahertz power output can be achieved by adjusting the waveguide configuration of the quantum cascade lasers to provide better phase-matching.
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| 5. |
- Ryu, J. H., et al.
(författare)
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Beam stability of buried-heterostructure quantum cascade lasers formed by ICP-etching and HVPE regrowth
- 2021
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE-Intl Soc Optical Eng.
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Konferensbidrag (refereegranskat)abstract
- Scaling the coherent power of mid-infrared (IR)-emitting quantum cascade lasers (QCLs) to the multi-watt range remains an important objective for applications where the laser beam needs to travel through air to remote targets, such as freespace communication links. For such applications requiring long-range pointing accuracy, measurements of beam stability are also important. We present beam-quality measurement results of narrow-ridge (4-5 μm), 4.6 μm-emitting buriedheterostructure (BH) QCLs. A 40-stage, step-tapered active-region (STA) structure was grown by MOCVD, and ICP etching was used to make deep ridges. InP:Fe was preferentially regrown in the field regions by using an SiO2 mask for ridge etching and Hydride Vapor Phase Epitaxy (HVPE). The HVPE process is attractive for selective regrowth, since high growth rates (0.2-0.3 μm/min) can be utilized, and highly planar top surfaces can readily be obtained. HVPE regrowth has been previously employed for BH devices of MBE-grown QCL ridges, but beam-stability measurements were not reported. HR-coated, 7.5 mm-long devices were measured under QCW operation (100 μsec pulse width, 0.5%-10% duty cycle) - very good beam quality factors, M2 < 1.2, were observed for both 4 μm and 5 μm ridge widths, but the narrower ridge exhibited better pointing stability. Collimated 5 μm-wide BH devices displayed some small degree of centroid motion with increasing power (< 0.125 mrad). This corresponds to a targeting error of ∼1.25 cm over a distance of 100 m. Significantly improved lateral-beam stability was observed for narrower ridge width, although at the expense of reduced output power.
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| 6. |
- Ryu, Jae Ha, et al.
(författare)
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Reverse-Taper Mid-Infrared Quantum Cascade Lasers for Coherent Power Scaling
- 2022
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Ingår i: IEEE Photonics Journal. - : Institute of Electrical and Electronics Engineers (IEEE). - 1943-0655. ; 14:3
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Tidskriftsartikel (refereegranskat)abstract
- We present a reverse-taper quantum cascade laser (QCL) emitting at 4.6 mu m, a novel-geometry device that can scale the output power while maintaining good beam quality. Buried-ridge waveguides with tapered and straight regions were formed by ICP etching and HVPE regrowth - the tapered region scales the output power, while the emitting facet is located at the narrow-end taper section, which provides mode filtering by suppressing high-order spatial modes. Beam profiles were observed under quasi-continuous-wave (QCW)/CW operation and beam quality (M-2) measurements along with beam-stability measurements were performed - a small degree of collimated-beam centroid movement (<0.46 mrad, peak-to-peak) was observed, along with M-2 values close to 1 up to similar to 1 W QCW power. Devices of shorter cavity lengths were also investigated, indicating that the output power scales with the core-region volume but results in a small increase in angular deviation.
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| 7. |
- Ryu, Jae Ha, et al.
(författare)
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Reverse-Taper Mid-IR Quantum Cascade Lasers for Coherent Power Scaling
- 2021
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Ingår i: 2021 27th International Semiconductor Laser Conference (ISLC). - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- Novel-geometry, 4.6 mu m-emitting BH QCLs were fabricated, where a tapered region scales the output power and, ahead of the emitting aperture, a narrow section provides mode filtering for suppressing high-order spatial modes. Beam-stability measurements indicate a small degree of collimated-beam centroid motion (< 0.25 mrad).
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| 8. |
- Strömberg, Axel, et al.
(författare)
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Direct Heteroepitaxy and Selective Area Growth of GaP and GaAs on Si by Hydride Vapor Phase Epitaxy
- 2021
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley-VCH Verlag. - 1862-6300 .- 1862-6319. ; 218:3
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Tidskriftsartikel (refereegranskat)abstract
- Direct heteroepitaxy and selective area growth (SAG) of GaP and GaAs on Si(100) and Si(111) are implemented by low-pressure hydride vapor phase epitaxy (LP-HVPE), which are facilitated by buffer layers grown at 410–490 °C with reactive gas mixing directly above Si substrates. High-density islands observed on GaP buffer layers on Si result in rough morphology and defect formation in the subsequent GaP layers grown at 715 °C. The impact of growth temperature of GaAs buffer layers on the crystal quality of GaAs/Si is studied. A decreased nucleation temperature significantly improves the morphology and crystalline quality of the overall GaAs growth on Si. It is observed that Si(111) substrates are favorable for both GaP and GaAs growths in comparison with Si(100). In SAGs of GaP/Si and GaAs/Si, the high selectivity innate to HVPE is maintained in the used unconventional growth regime. The spatially resolved photoluminescence mapping reveals the material quality of GaAs/Si is enhanced by defect filtering by SAG. The outcomes of this work will pave the way of III–V/Si integration realized by cost-effective HVPE for photonic device applications.
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| 9. |
- Strömberg, Axel, et al.
(författare)
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Direct Heteroepitaxy of Orientation-Patterned GaP on GaAs by Hydride Vapor Phase Epitaxy for Quasi-Phase-Matching Applications
- 2020
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Ingår i: Physica status solidi. A, Applied research. - : Wiley. - 0031-8965 .- 1521-396X. ; 217:3, s. 1900627-
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Tidskriftsartikel (refereegranskat)abstract
- Heteroepitaxial growth of orientation‐patterned (OP) GaP (OP‐GaP) on wafer‐bonded OP‐GaAs templates is investigated by low‐pressure hydride vapor phase epitaxy for exploiting the beneficial low two‐photon absorption properties of GaP with the matured processing technologies and higher‐quality substrates afforded by GaAs. First, GaP homoepitaxial selective area growth (SAG) is conducted to investigate the dependence of GaP SAG on precursor flows and temperatures toward achieving a high vertical growth rate and equal lateral growth rate in the [110] and [-110]‐oriented openings. Deteriorated domain fidelity is observed in the heteroepitaxial growth of OP‐GaP on OP‐GaAs due to the enhanced growth rate on domain boundaries by threading dislocations generated by 3.6% lattice matching in GaP/GaAs. The dependence of dislocation dynamics on heteroepitaxial growth conditions of OP‐GaP on OP‐GaAs is studied. High OP‐GaP domain fidelity associated with low threading dislocation density and a growth rate of 57 μm h−1 are obtained by increasing GaCl flow. The properties of heteroepitaxial GaP on semi‐insulating GaAs is studied by terahertz time‐domain spectroscopy in the terahertz range. The outcomes of this work will pave the way to exploit heteroepitaxial OP‐GaP growth on OP‐GaAs for frequency conversion by quasi‐phase‐matching in the mid‐infrared and terahertz regions.
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| 10. |
- Strömberg, Axel, et al.
(författare)
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Epitaxial Lateral Overgrowth of GaAsP for III-V/Si-Based Photovoltaics
- 2023
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 220:8
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Tidskriftsartikel (refereegranskat)abstract
- GaAsP/Si with high crystalline quality fabricated by cost-effective heteroepitaxial technology is a promising pathway for realizing low-cost Si-based tandem solar cell with efficiency higher than 30%. Herein, hydride vapor-phase epitaxy is used to perform selective area growth of GaAsP with high lateral coverage, referred to as epitaxial lateral overgrowth (ELOG). The ELOG is performed on GaAs-based substrates as a prestudy, followed by GaAs/Si and GaAsP/Si seed wafers employing chemical mechanical polishing to fabricate full 2 00 GaAsP/Si templates. These are subsequently used to grow and process GaAsP/Si pn-junction structures for electrical characterization. The ELOG GaAsP is studied by spatially resolved photoluminescence (PL) mapping and high-resolution X-ray diffraction measurements. PL analysis of the GaAsP/GaAs ELOG samples reveals an enhanced P-incorporation during lateral growth of GaAsP. This is also observed for the GaAsP/Si ELOG templates along with evidence of improved material quality, clearly distinguishing the laterally grown GaAsP from the planar growth directly above the Si substrate. Leakage pathways causing reduced electrical performance of the ELOG GaAsP/Si pn-junction structures are identified.
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