| 1. |
- Apaydin, Dogukan, 1991, et al.
(författare)
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Optically Pumped UVC Photonic Crystal Surface-Emitting Laser
- 2023
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Photonic crystal surface-emitting lasers (PCSELs) are a new type of semiconductor lasers that offer a high optical output power while maintaining single-mode operation and a low divergence angle. Such devices rely upon the in-plane optical feedback from a two-dimensional photonic crystal and feature out-of-plane emission of the modes with zero group velocity at the photonic band edges by diffraction. Since the demonstration of the first PCSEL [1], the concept has been implemented in standard semiconductor materials with the demonstration of highperforming infrared and blue-emitting lasers [2, 3]. Extending the laser operation to shorter emission wavelengths would be a major breakthrough as such lasers would be of high interest for disinfection, material processing, curing, and medical treatments.
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| 2. |
- Apaydin, Dogukan, 1991, et al.
(författare)
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UVC photonic crystal surface-emitting lasers with low-divergent far-fields
- 2023
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Photonic crystal surface-emitting lasers (PCSEL) emitting in the ultraviolet (UV) C spectral range are exciting devices due to their low divergence and single-mode emission capable of high output powers as already demonstrated in the infrared [1] and blue spectral range [2]. This is due to their unique design, which incorporates a photonic crystal leading to a large optical gain area. PCSELs are based upon in-plane feedback from the photonic crystal and out-of-plane emission by the diffraction of the modes with zero group velocity at the photonic band edges. We recently demonstrated, to the best of our knowledge, the first UVC PCSEL with an emission at 279 nm. The device structure consists of 3 x 2 nm AlGaN quantum wells (QW) in a 60 nm Al0.70Ga0.30N waveguide and AlN cladding layers. The 140x140 μm large photonic crystal is dry etched into the top AlN cladding layer with a hexagonal lattice consisting of circular holes with a lattice constant of 140 nm and an etch depth of 65 nm, leaving 65 nm between the bottom of the photonic crystals and the first quantum well. Lasing in these PCSELs was achieved by resonant pumping of the QWs by a 266 nm pulsed laser with a spot size of 82 μm at room temperature. The devices exhibit threshold pump power densities from 25 down to 13 MW/cm2 showing a spectral narrowing down to 25 pm. Far-field patterns and band structures were investigated for a range of filling factors (fraction of the surface that is etched) between 10% to 26%, and the far-fields contain emission bands that were not yet reported in PCSELs at longer wavelengths. Changing the filling factor affects the photonic crystal band structure and thereby the optical mode at the Γ-point that will reach threshold first. This feature enables us to intentionally select the lasing mode with the desired far-field pattern. By a proper choice of filling factor, the intensity in the angular emission bands is diminished, resulting in a far-field with a narrow beam divergence of <1°.
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| 3. |
- Chalangar, Ebrahim, PhD student, 1984-, et al.
(författare)
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Synthesis of Vertically Aligned ZnO Nanorods Using Sol-gel Seeding and Colloidal Lithography Patterning
- 2021
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Ingår i: Nanoscale Research Letters. - Heidelberg : Springer Science and Business Media LLC. - 1931-7573 .- 1556-276X. ; 16:1
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Tidskriftsartikel (refereegranskat)abstract
- Different ZnO nanostructures can be grown using low-cost chemical bath deposition. Although this technique is cost-efficient and flexible, the final structures are usually randomly oriented and hardly controllable in terms of homogeneity and surface density. In this work, we use colloidal lithography to pattern (100) silicon substrates to fully control the nanorods' morphology and density. Moreover, a sol-gel prepared ZnO seed layer was employed to compensate for the lattice mismatch between the silicon substrate and ZnO nanorods. The results show a successful growth of vertically aligned ZnO nanorods with controllable diameter and density in the designated openings in the patterned resist mask deposited on the seed layer. Our method can be used to fabricate optimized devices where vertically ordered ZnO nanorods of high crystalline quality are crucial for the device performance.
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| 4. |
- Jafari Jam, R., et al.
(författare)
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Embedded sacrificial AlAs segments in GaAs nanowires for substrate reuse
- 2020
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Ingår i: Nanotechnology. - Bristol : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 31:20
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Tidskriftsartikel (refereegranskat)abstract
- We report on the use of a sacrificial AlAs segment to enable substrate reuse for nanowire synthesis. A silicon nitride template was deposited on a p-type GaAs substrate. Then a pattern was transferred to the substrate by nanoimprint lithography and reactive ion etching. Thermal evaporation was used to define Au seed particles. Metalorganic vapour phase epitaxy was used to grow AlAs-GaAs NWs in the vapour-liquid-solid growth mode. The yield of synthesised nanowires, compared to the number expected from the patterned template, was more than 80%. After growth, the nanowires were embedded in a polymer and mechanically removed from the parent substrate. The parent substrate was then immersed in an HCl:H2O (1:1) mixture to dissolve the remaining stub of the sacrificial AlAs segment. The pattern fidelity was preserved after peeling off the nanowires and cleaning, and the semiconductor surface was flat and ready for reuse. Au seed particles were then deposited on the substrate by use of pulse electrodeposition, which was selective to the openings in the growth template, and then nanowires were regrown. The yield of regrowth was less optimal compared to the first growth but the pattern was preserved. Our results show a promising approach to reduce the final cost of III-V nanowire based solar cells. © 2020 The Author(s). Published by IOP Publishing Ltd.
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| 5. |
- Palo-Nieto, Carlos, 1985-, et al.
(författare)
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Functionalization of cellulose nanofibrils to develop novel ROS-sensitive biomaterials
- 2023
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Ingår i: Materials Advances. - : Royal Society of Chemistry. - 2633-5409. ; 4:6, s. 1555-1565
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Tidskriftsartikel (refereegranskat)abstract
- Wood derived cellulose nanofibrils (CNFs) have emerged as an interesting material for biomedical applications. Functionalization of the nanofibrils with bioactive molecules is a potent tool to tailor CNF materials for specific applications in biomedicine. The present work proposes the functionalization of CNFs with a reactive oxygen species (ROS)-sensitive oligopeptide to develop a novel CNF-based material for the treatment of medical conditions associated with high levels of ROS such as chronic wounds. Oligoproline peptides of two different lengths (5 and 10 proline units) were covalently incorporated onto the CNF surface, several water-based chemical approaches were explored and the reaction conditions to maximize peptide substitution and the degree of fibre crosslinking were optimized. The chemical structure, degree of peptide substitution, degree of fibre crosslinking, surface morphology and ROS-sensitivity of the oligoproline–CNF materials were characterized. Double-crosslinked CNF hydrogels (Ca2+–oligoproline–CNF) were further prepared and the ability of the hydrogels to protect cells from an oxidative environment was investigated in vitro with human dermal fibroblasts, as a first evaluation of the potential of the novel CNF material to be used in chronic wound therapies. Optimization of the reaction conditions resulted in a degree of peptide substitution of 102 ± 10 μmol g−1 CNF irrespective of the oligoproline length and a degree of crosslinking of 55–80% depending on the number of proline units. The results showed that the oligoproline covalently attached to CNFs via carbodiimide chemistry maintained its ability to respond to ROS and that the responsiveness in terms of viscoelastic properties depended on the length of the oligopeptide, with the hydrogel being more responsive when functionalized with 10 proline units compared with 5 proline units. Furthermore, the double crosslinked Ca2+–oligoproline–CNF hydrogels promoted the survival of human dermal fibroblasts exposed to high levels of ROS. This study is the first one to provide an insight into the development of ROS-sensitive materials based on CNFs and opens up possibilities for further investigation on the use of these novel materials in chronic wound care.
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| 6. |
- Sedrpooshan, Mehran, et al.
(författare)
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Template-free generation and integration of functional 1D magnetic nanostructures
- 2023
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Ingår i: Nanoscale. - : Royal Society of Chemistry. - 2040-3372 .- 2040-3364.
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Tidskriftsartikel (refereegranskat)abstract
- The direct integration of 1D magnetic nanostructures into electronic circuits is crucial for realizing their great potential as components in magnetic storage, logical devices, and spintronic applications. Here, we present a novel template-free technique for producing magnetic nanochains and nanowires using directed self-assembly of gas-phase-generated metallic nanoparticles. The 1D nanostructures can be self-assembled along most substrate surfaces and can be freely suspended over micrometer distances, allowing for direct incorporation into different device architectures. The latter is demonstrated by a one-step integration of nanochains onto a pre-patterned Si chip and the fabrication of devices exhibiting magnetoresistance. Moreover, fusing the nanochains into nanowires by post-annealing significantly enhances the magnetic properties, with a 35% increase in the coercivity. Using magnetometry, X-ray microscopy, and micromagnetic simulations, we demonstrate how variations in the orientation of the magnetocrystalline anisotropy and the presence of larger multi-domain particles along the nanochains play a key role in the domain formation and magnetization reversal. Furthermore, it is shown that the increased coercivity in the nanowires can be attributed to the formation of a uniform magnetocrystalline anisotropy along the wires and the onset of exchange interactions.
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| 7. |
- Sun, Rui, et al.
(författare)
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Highly Porous Amorphous Calcium Phosphate for Drug Delivery and Bio-Medical Applications
- 2020
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Ingår i: Nanomaterials. - : MDPI. - 2079-4991. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous calcium phosphate (ACP) has shown significant effects on the biomineralization and promising applications in bio-medicine. However, the limited stability and porosity of ACP material restrict its practical applications. A storage stable highly porous ACP with Brunauer–Emmett–Teller surface area of over 400 m2/g was synthesized by introducing phosphoric acid to a methanol suspension containing amorphous calcium carbonate nanoparticles. Electron microscopy revealed that the porous ACP was constructed with aggregated ACP nanoparticles with dimensions of several nanometers. Large angle X-ray scattering revealed a short-range atomic order of <20 Å in the ACP nanoparticles. The synthesized ACP demonstrated long-term stability and did not crystallize even after storage for over 14 months in air. The stability of the ACP in water and an α-MEM cell culture medium were also examined. The stability of ACP could be tuned by adjusting its chemical composition. The ACP synthesized in this work was cytocompatible and acted as drug carriers for the bisphosphonate drug alendronate (AL) in vitro. AL-loaded ACP released 25% of the loaded AL in the first 22 days. These properties make ACP a promising candidate material for potential application in biomedical fields such as drug delivery and bone healing.
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| 8. |
- Surendiran, Pradheebha, et al.
(författare)
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Solving Exact Cover Instances with Molecular-Motor-Powered Network-Based Biocomputation
- 2022
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Ingår i: ACS Nanoscience Au. - : American Chemical Society (ACS). - 2694-2496 .- 2694-2496.
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Tidskriftsartikel (refereegranskat)abstract
- Information processing by traditional, serial electronic processors consumes an ever-increasing part of the global electricity supply. An alternative, highly energy efficient, parallel computing paradigm is network-based biocomputation (NBC). In NBC a given combinatorial problem is encoded into a nanofabricated, modular network. Parallel exploration of the network by a very large number of independent molecular-motor-propelled protein filaments solves the encoded problem. Here we demonstrate a significant scale-up of this technology by solving four instances of Exact Cover, a nondeterministic polynomial time (NP) complete problem with applications in resource scheduling. The difficulty of the largest instances solved here is 128 times greater in comparison to the current state of the art for NBC.
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| 9. |
- Abbondanza, Giuseppe, 1991, et al.
(författare)
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Au-Pd Barcode Nanowires with Tailored Lattice Parameters and Segment Lengths for Catalytic Applications
- 2024
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Ingår i: ACS Applied Nano Materials. - 2574-0970. ; 7:4, s. 3861-3874
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we present a systematic investigation of the controlled fabrication of Au-Pd barcode nanowires within nanoporous anodic aluminum oxide (NP-AAO) templates. By using a combination of in situ X-ray diffraction (XRD), focused ion beam scanning electron microscopy (FIB-SEM), and transmission electron microscopy (TEM), we elucidate the influence of template preparation methods on the resulting nanowire properties. The template treatment, involving either pore widening or barrier layer thinning, significantly impacts nanowire growth. Through the analysis of the XRD data, we observe sequential deposition of Au and Pd segments with lattice parameter variations and strain effects. Particularly, the lattice parameters of Au and Pd segments display intricate temporal dependencies, influenced by interfacial effects and strain caused by growth under confinement. FIB-SEM imaging reveals uniform and reproducible nanowire lengths in the template treated with pore widening. Furthermore, TEM analysis confirms the presence of distinct Au and Pd segments, while scanning TEM-energy-dispersive X-ray spectroscopy revealed minor evidence of interdiffusion between the first and the second electrodeposited segments. Our findings emphasize the potential of the electrodeposition process within nanoporous templates for producing barcode nanowires with precise segmental properties. The combination of in situ XRD and electron microscopy offers valuable insights into the growth dynamics and structural characteristics of the fabricated Au-Pd barcode nanowires. This controlled fabrication strategy opens doors to tailoring nanowire properties for diverse applications, particularly in catalysis.
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| 10. |
- Abbondanza, Giuseppe
(författare)
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Ordered arrays of low-dimensional Au and Pd : synthesis and in situ observations
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electrodeposition of metals in templates of nano-porous anodic aluminum oxide (NP-AAO) is a versatile way of fabricating ordered arrays of metal nanowires. Thanks to the self-arranged long-range hexagonal order of the pores, electrodeposition in NP-AAO is an easily scalable bottom-up synthesis route and an attractive alternative to traditional top-down fabrication methods such as electron beam lithography.Since NP-AAO is a non-conductive medium and since it is potentially soluble in non-neutral pH solutions, the electrodeposition of metals in NP-AAO represents a challenge. These aspects are discussed in this thesis, aiming to establish a reproducible and reliable protocol for the electrodeposition of Au and Pd.By using ex situ x-ray diffraction, it has been found that the growth of Au and Pd in the confined environment of nano-pores leads (i) to a deformation of the crystalline structure, as the lattice constant is smaller along the nanowire radius and larger along the nanowire axis, compared to the bulk lattice constant, and (ii) to a crystallite size anisotropy: it is limited by the pore radius in the horizontal direction and it is larger in the direction of growth.The electrochemical growth of Au and Pd nanowires was followed in situ by x-ray scattering methods. In the case of Au nanowires, the time-resolved measurements revealed that the anisotropy of the lattice parameter progresses as a function of time, which suggests that the strain state of the nanomaterials can be artificially selected. This findings might be beneficial in the strain-engineering of Au nanoelectrode arrays for electrocatalysis. In the case of Pd nanowires, the measurements revealed strain variations, as well as phase transitions attributed to the existence of alpha- and beta-phase Pd hydride in the NP-AAO template, due to the exposure of Pd to hydrogen evolved at the working electrode. These findings suggest that Pd in NP-AAO has potential applications in the design of hydrogen storage devices.
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