| 51. |
- Chen, Junsheng, et al.
(författare)
-
Cation-Dependent Hot Carrier Cooling in Halide Perovskite Nanocrystals
- 2019
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 141:8, s. 3532-3540
-
Tidskriftsartikel (refereegranskat)abstract
- Lead halide perovskites (LHPs) nanocrystals (NCs), owing to their outstanding photophysical properties, have recently emerged as a promising material not only for solar cells but also for lighting and display applications. The photophysical properties of these materials can be further improved by chemical engineering such as cation exchange. Hot carrier (HC) cooling, as one of the key photophysical processes in LHPs, can strongly influence performance of LHPs NCs based devices. Here, we study HC relaxation dynamics in LHP NCs with cesium (Cs), methylammonium (MA, CH 3 NH 3 + ), and formamidinium (FA, CH(NH 2 ) 2 + ) cations by using femtosecond transient absorption spectroscopy. The LHP NCs show excitation intensity and excitation energy-dependent HC cooling. We investigate the details of HC cooling in CsPbBr 3 , MAPbBr 3 , and FAPbBr 3 at three different excitation energies with low excitation intensity. It takes longer time for the HCs at high energy to relax (cool) to the band edge, compared to the HCs generated by low excitation energy. At the same excitation energy (350 nm, 3.54 eV), all the three LHP NCs show fast HC relaxation (<0.4 ps) with the cooling time and rate in the following order: CsPbBr 3 (0.39 ps, 2.9 meV/fs) > MAPbBr 3 (0.27 ps, 4.6 meV/fs) > FAPbBr 3 (0.21 ps, 5.8 meV/fs). The cation dependence can be explained by stronger interaction between the organic cations with the Pb-Br frameworks compared to the Cs. The revealed cation-dependent HC relaxation process is important for providing cation engineering strategies for developing high performance LHP devices.
|
|
| 52. |
- Chen, Junsheng, et al.
(författare)
-
Enhanced Size Selection in Two-Photon Excitation for CsPbBr3 Perovskite Nanocrystals
- 2017
-
Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 8:20, s. 5119-5124
-
Tidskriftsartikel (refereegranskat)abstract
- Cesium lead bromide (CsPbBr3) perovskite nanocrystals (NCs), with large two-photon absorption (TPA) cross-section and bright photoluminescence (PL), have been demonstrated as stable two-photon-pumped lasing medium. With two-photon excitation, red-shifted PL spectrum and increased PL lifetime is observed compared with one-photon excitation. We have investigated the origin of such difference using time-resolved laser spectroscopies. We ascribe the difference to the enhanced size selection of NCs by two-photon excitation. Because of inherent nonlinearity, the size dependence of absorption cross-section under TPA is stronger. Consequently, larger size NCs are preferably excited, leading to longer excited-state lifetime and red-shifted PL emission. In a broad view, the enhanced size selection in two-photon excitation of CsPbBr3 NCs is likely a general feature of the perovskite NCs and can be tuned via NC size distribution to influence their performance within NC-based nonlinear optical materials and devices.
|
|
| 53. |
- Chen, Junsheng, et al.
(författare)
-
Size-And Wavelength-Dependent Two-Photon Absorption Cross-Section of CsPbBr3 Perovskite Quantum Dots
- 2017
-
Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 8:10, s. 2316-2321
-
Tidskriftsartikel (refereegranskat)abstract
- All-inorganic colloidal perovskite quantum dots (QDs) based on cesium, lead, and halide have recently emerged as promising light emitting materials. CsPbBr3 QDs have also been demonstrated as stable two-photon-pumped lasing medium. However, the reported two photon absorption (TPA) cross sections for these QDs differ by an order of magnitude. Here we present an in-depth study of the TPA properties of CsPbBr3 QDs with mean size ranging from 4.6 to 11.4 nm. By using femtosecond transient absorption (TA) spectroscopy we found that TPA cross section is proportional to the linear one photon absorption. The TPA cross section follows a power law dependence on QDs size with exponent 3.3 ± 0.2. The empirically obtained power-law dependence suggests that the TPA process through a virtual state populates exciton band states. The revealed power-law dependence and the understanding of TPA process are important for developing high performance nonlinear optical devices based on CsPbBr3 nanocrystals.
|
|
| 54. |
- Chen, Ruiyun, et al.
(författare)
-
Creation and Annihilation of Nonradiative Recombination Centers in Polycrystalline Metal Halide Perovskites by Alternating Electric Field and Light
- 2020
-
Ingår i: Advanced Optical Materials. - : Wiley. - 2195-1071. ; 8:4
-
Tidskriftsartikel (refereegranskat)abstract
- Metal halide perovskites are promising optoelectronic materials. Their electronic properties however are rather unstable which is often assigned to ion migration. Ion migration can be readily influenced by an electric field (EF). Here, the response of photoluminescence (PL) of individual MAPbX3 (MA = CH3NH3, X = I, Br) sub-micrometer-sized polycrystals to EF is studied. Alternating EF with frequency higher than 10 Hz is found to reversibly quench PL. It is proposed that an alternating EF when applied together with light increases ion migration. This leads to a shift in the equilibrium between creation and annihilation of defects toward higher concentration of nonradiative recombination centers. The PL quenching is found to increase with increasing frequency of the field. This can be rationalized by the frequency dependence of the dielectric constant, leading to stronger internal fields for high modulation frequencies compared to, e.g., a constant EF with the same external amplitude. PL quenching and enhancement observed under constant EF are hypothesized to be due to a reconfiguration of already existing nonradiative recombination centers situated on grain boundaries. The control of perovskite PL by alternating EF reported here can find applications in optoelectronic devices.
|
|
| 55. |
- Davidsson, Sabina, 1972-, et al.
(författare)
-
Androgen deprivation therapy in men with prostate cancer is not associated with COVID-2019 infection
- 2023
-
Ingår i: The Prostate. - : Alan R. Liss Inc.. - 0270-4137 .- 1097-0045. ; 83:6, s. 555-562
-
Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Androgens may play a role in severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection and host responses as the virus is dependent on the androgen-regulated protein transmembrane serine protease 2 for cell entry. Studies have indicated that prostate cancer patients receiving androgen deprivation therapy (ADT) are at reduced risk of SARS-CoV-2 infection and serious complications compared with patients without ADT, but data are inconsistent.METHODS: A total of 655 prostate cancer patients who were under surveillance at two urology departments in Sweden on April 1, 2020 were included in the study as well as 240 patients with benign prostatic hyperplasia (BPH). At follow-up early in 2021, the participants completed a questionnaire containing information about symptoms compatible with coronavirus disease 2019 (COVID-19). Blood samples were also collected for the assessment of SARS-CoV-2 IgG antibodies (SARS-CoV-2 Total; Siemens). We used multivariable logistic regression models to calculate odds ratios (ORs) and 95% confidence intervals (CIs) for the association between ADT and the risk of SARS-CoV-2 infection.RESULTS: The cumulative incidence of SARS-CoV-2 seropositivity was 13.4% among patients receiving ADT and 10.4% among patients without ADT. After adjusting for potential confounders, we observed no differences in symptoms or risk of SARS-CoV-2 infection between patients with and without ADT (OR: 0.98; 95% CI: 0.52-1.85). Higher body mass index, Type 1 diabetes, and prostate cancer severity, defined by high Gleason score (8-10; OR: 2.06; 95% CI: 1.04-4.09) or elevated levels of prostate-specific antigen (>20 µg/l; OR: 2.15; 95% CI: 1.13-4.07) were associated with increased risk of SARS-CoV-2 infection. Overall, the risk of SARS-CoV-2 infection was not higher among men with prostate cancer than among men with BPH.CONCLUSIONS: Our results do not support the hypothesis that ADT use in prostate cancer patients reduces the risk or symptom severity of SARS-CoV-2 infection or that prostate cancer patients are at increased risk of COVID-19 compared with men without prostate cancer.
|
|
| 56. |
- Deppert, Knut, et al.
(författare)
-
Magnetic-field directed self-assembly and chain formation of functional aerosol nanoparticles
- 2020
-
Konferensbidrag (refereegranskat)abstract
- Self-assembly of nanoparticles into vertical structures or larger ensembles can be a powerful method to achieve a strong collective behavior while still obtaining many of the same properties of the individual nanoparticles. In this study, we achieve directed self-assembly of magnetic nanoparticles into nanochains when depositing in a combined magnetic and electric field (M-ESP). We show that the Co nanoparticles are spontaneously magnetized in the aerosol phase, and that the role of the external magnetic field is mainly to guide the deposition in a certain direction.Lastly, we will present chain formation of mixed materials. Here, we combine a strong magnetic material, with other elements to achieve the same chain structure, but with a desired surface functionalization. Nanoparticle chains can therefore be formed with different functionalities, depending on the mixing material. This opens up for further combination to tune the functionalization of the nanoparticle chain structure.
|
|
| 57. |
- Deppert, Knut, et al.
(författare)
-
One-step Gas-phase Synthesis of Core-shell Nanoparticles via Surface Segregation.
- 2019
-
Konferensbidrag (refereegranskat)abstract
- A great amount of research effort has been devoted to theproduction of core-shell nanoparticles for applications in variousfields including biomedical imaging, catalysis, and plasmonics.Such attention to core-shell nanoparticles arise from the fact thatthey can exhibit enhanced physical and/or chemical properties.Furthermore, core-shell particles with distinctly new propertiescompared to those of the constituent materials can be designedby tuning, for example, their size, shell thickness, and structure [1,2].Although chemical synthesis techniques are currently the mostpopular methods for fabricating core-shell nanoparticles,interface and surface contaminations are often an unavoidableissue in the solution-based approaches. Aerosol based methodsare cleaner alternatives and have been used to produce core-shellnanoparticles [3-6]. Here we present aerosol core-shellnanoparticles generated via spark discharge generation (SDG) [7].Cu-Ag core shell nanoparticles were fabricated via surfacesegregation using SDG accompanied by sintering directly in thegas phase. The surface segregation employed in this methodrefers to the phenomenon of the enrichment of one componentof a mixture in the surface region and is attributed to theinterplay between the atomic radii, cohesive energy, and surfaceenergy of the core and shell materials [8].Depending on the sintering temperature, the SDG-generatednanoparticles form Janus-like or core-shell structures. Themorphology, crystallinity, and composition of the SDG-generatedbimetallic nanoparticles were investigated by scanning electronmicroscopy, high-resolution transmission electron microscopy,and energy-dispersive X-ray spectroscopy. Molecular dynamicssimulations were carried out to investigate the structuralevolution of Cu-Ag nanoparticles during heating and coolingprocesses corresponding to the sintering. This appealingly simpleone-step gas-phase synthesis method presented here can beemployed for other bimetallic systems.
|
|
| 58. |
- Deppert, Knut, et al.
(författare)
-
Predicted trends of core-shell preferences for bimetallic nanoparticles by molecular dynamics
- 2020
-
Konferensbidrag (refereegranskat)abstract
- We present predicted trends of core-shell preferences obtained by molecular dynamics (MD) simulations for 28 bimetallic nanoparticle systems (approximately 4 nm in diameter) composed of 8 metals; Ag, Cu, Au, Pd, Fe, Co, Ni, and Pt. The two single-element FCC crystals were heated up to the melting temperature to form a bimetallic system and subsequently cooled to a room temperature. The core-shell preferences were quantified by identifying surface atoms in the MD results using a method based on the alpha-shapes method. Three different types of structures were observed in the solidified bimetallic systems; a) mixed b) core-shell c) Janus-like. Our MD simulations were carried out for significantly larger nanoparticles than the previous DFT calculations. It also provided more detailed information on the core-shell preferences and clearly distinguished Janus-like from core-shell structures. The deciding factors in core-shell preferences are investigated from the general trends found in this study.
|
|
| 59. |
- Dick Thelander, Kimberly, et al.
(författare)
-
Control of III-V nanowire crystal structure by growth parameter tuning
- 2010
-
Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 25:2
-
Tidskriftsartikel (refereegranskat)abstract
- In this work we investigate the variation of the crystal structure of gold-seeded III-V nanowires with growth parameters, in order to gain a cohesive understanding of these effects. We investigate six III-V materials: GaAs, InAs, GaP, InP, GaSb and InSb, over a variation of growth conditions. All six of these materials exhibit a cubic zinc blende structure in bulk, but twin planes and stacking faults, as well as a hexagonal wurtzite structure, are commonly observed in nanowires. Parameters which may affect the crystal structure include growth temperature and pressure, precursor molar fraction and V/III ratio, nanowire diameter and surface density, and impurity atoms. We will focus on temperature, precursor molar fraction and V/III ratio. Our observations are compared to previous reports in the literature of the III-V nanowire crystal structure, and interpreted in terms of existing models. We propose that changes in the crystal structure with growth parameters are directly related to changes in the stable side facets.
|
|
| 60. |
|
|
