In the next generation wireless communication systems operating at near terahertz frequencies, dielectric substrates with the lowest possible permittivity and loss factor are becoming essential. In this work, highly p...In the next generation wireless communication systems operating at near terahertz frequencies, dielectric substrates with the lowest possible permittivity and loss factor are becoming essential. In this work, highly porous (98.9% ± 0.1%) and lightweight silica foams (0.025 ± 0.005 g/cm3), that have extremely low relative permittivity (εr = 1.018 ± 0.003 at 300 GHz) and corresponding loss factor (tan δ< 3 × 10−4 at 300 GHz) are synthetized by a template-assisted sol-gel method. After dip-coating the slabs of foams with a thin film of cellulose nanofibers, sufficiently smooth surfaces are obtained, on which it is convenient to deposit electrically conductive planar thin films of metals important for applications in electronics and telecommunication devices. Here, micropatterns of Ag thin films are sputtered on the substrates through a shadow mask to demonstrate double split-ring resonator metamaterial structures as radio frequency filters operating in the sub-THz band.展开更多
Metal halide perovskites have emerged as novel and promising photocatalysts for hydrogen generation.Currently,their stability in water is a vital and urgent research question.In this paper a novel approach to stabiliz...Metal halide perovskites have emerged as novel and promising photocatalysts for hydrogen generation.Currently,their stability in water is a vital and urgent research question.In this paper a novel approach to stabilize a bismuth halide perovskite[(CH_(3))_(2)NH_(2)]_(3)[Bil_(6)](DA_(3)Bil_(6))in water using dimethylammonium iodide(DAI)without the assistance of acids or coatings is reported.The DA3Bil6 powder exhibits good stability in DAI solutions for at least two weeks.The concentration of DAI is found as a critical parameter,where the I^(-)ions play the key role in the stabilization.The stability of DA3Bil6 in water is realized via a surface dissolution-recrystallization process.Stabilized DA3Bil6 demonstrates constant photocatalytic properties for visible light-induced photo-oxidation of I^(-)ions and with PtCI4 as a co-catalyst(Pt-DA_(3)Bil_(6)),photocatalytic H2 evolution with a rate of 5.7μmol·h^(-1)from HI in DAI solution,obtaining an apparent quantum efficiency of 0.83%at 535 nm.This study provides new insights on the stabilization of metal halide perovskites for photocatalysis in aqueous solution.展开更多
Owing to their higher intrinsic electrical conductivity and chemical stability with respect to their oxide counterparts, nanostructured metal sulfides are expected to revive materials for resistive chemical sensor app...Owing to their higher intrinsic electrical conductivity and chemical stability with respect to their oxide counterparts, nanostructured metal sulfides are expected to revive materials for resistive chemical sensor applications. Herein, we explore the gas sensing behavior of WS2 nanowire-nanoflake hybrid materials and demonstrate their excellent sensitivity （0.043 ppm-1） as well as high selectivity towards H2S relative to CO, NH~, H2, and NO （with corresponding sensitivities of 0.002, 0.0074, 0.0002, and 0.0046 pprn-1, respectively）. Gas response measurements, complemented with the results of X-ray photoelectron spectroscopy analysis and first-principles calculations based on density functional theory, suggest that the intrinsic electronic properties of pristine WS2 alone are not sufficient to explain the observed high sensitivity towards H2S. A major role in this behavior is also played by O doping in the S sites of the WS2 lattice. The results of the present study open up new avenues for the use of transition metal disulfide nanomaterials as effective alternatives to metal oxides in future applications for industrial process control, security, and health and environmental safety.展开更多
Ability of epitaxial perovskite oxide ferroelectric films to maintain a poled polarization state on a long-term scale is crucial for advanced devices employing such films.Here polarization relaxation with time,or agin...Ability of epitaxial perovskite oxide ferroelectric films to maintain a poled polarization state on a long-term scale is crucial for advanced devices employing such films.Here polarization relaxation with time,or aging,is experimentally studied in epitaxial capacitor heterostructures of PbTiO3 sandwiched between SrRuO_(3)and Pt electrodes.The relaxation obeys logarithmic time-decay for the time 10^(2)–10^(5)s after poling pulses.The decay is by factor10 slower than that reported for polycrystalline films.Our experimental results show that existing models are insufficient for epitaxial films.展开更多
Successful application of two-dimensional transition metal dichalcogenides in optoelectronic,catalytic,or sensing devices heavily relies on the materials’quality,that is,the thickness uniformity,presence of grain bou...Successful application of two-dimensional transition metal dichalcogenides in optoelectronic,catalytic,or sensing devices heavily relies on the materials’quality,that is,the thickness uniformity,presence of grain boundaries,and the types and concentrations of point defects.Raman spectroscopy is a powerful and nondestructive tool to probe these factors but the interpretation of the spectra,especially the separation of different contributions,is not straightforward.Comparison to simulated spectra is beneficial,but for defective systems first-principles simulations are often computationally too expensive due to the large sizes of the systems involved.Here,we present a combined first-principles and empirical potential method for simulating Raman spectra of defective materials and apply it to monolayer MoS_(2) with random distributions of Mo and S vacancies.We study to what extent the types of vacancies can be distinguished and provide insight into the origin of different evolutions of Raman spectra upon increasing defect concentration.We apply to our simulated spectra the phonon confinement model used in previous experiments to assess defect concentrations,and show that the simplest form of the model is insufficient to fully capture peak shapes,but a good match is obtained when the type of phonon confinement and the full phonon dispersion relation are accounted for.展开更多
New strategies for spatially controlled growth of human neurons may provide viable solutions to treat and recover peripheral or spinal cord injuries.While topography cues are known to promote attachment and direct pro...New strategies for spatially controlled growth of human neurons may provide viable solutions to treat and recover peripheral or spinal cord injuries.While topography cues are known to promote attachment and direct proliferation of many cell types,guided outgrowth of human neurites has been found difficult to achieve so far.Here,three-dimensional(3D)micropatterned carbon nanotube(CNT)templates are used to effectively direct human neurite stem cell growth.By exploiting the mechanical flexibility,electrically conductivity and texture of the 3D CNT micropillars,a perfect environment is created to achieve specific guidance of human neurites,which may lead to enhanced therapeutic effects within the injured spinal cord or peripheral nerves.It is found that the 3D CNT micropillars grant excellent anchoring for adjacent neurites to form seamless neuronal networks that can be grown to any arbitrary shape and size.Apart from clear practical relevance in regenerative medicine,these results using the CNT based templates on Si chips also can pave the road for new types of microelectrode arrays to study cell network electrophysiology.展开更多
基金The authors thank Kai Metsäkoivu for the technical assistance and Henrikki Liimatainen for providing us with nanocellulose materialsThe financial support received partly from EU Interreg Nord-Lapin liitto(project Transparent,conducting and flexible films for electrodes),Academy of Finland(6Genesis Flagship under Grant 318927)+1 种基金University of Oulu(projects Entity and PoC:Ultra-low permittivity and loss porous nanocomposites for future 6G telecommunication),Hungarian National Research,Development and Innovation Office through the projects GINOP-2.3.2-15-2016-00013 and GINOP-2.3.3-15-2016-00010the Ministry of Human Capacities,Hungary,grant 20391-3/2018/FEKUSTRAT is acknowledged.D.S.is thankful for the János Bolyai Research Scholarship of the Hungarian Academy of Sciences.
文摘In the next generation wireless communication systems operating at near terahertz frequencies, dielectric substrates with the lowest possible permittivity and loss factor are becoming essential. In this work, highly porous (98.9% ± 0.1%) and lightweight silica foams (0.025 ± 0.005 g/cm3), that have extremely low relative permittivity (εr = 1.018 ± 0.003 at 300 GHz) and corresponding loss factor (tan δ< 3 × 10−4 at 300 GHz) are synthetized by a template-assisted sol-gel method. After dip-coating the slabs of foams with a thin film of cellulose nanofibers, sufficiently smooth surfaces are obtained, on which it is convenient to deposit electrically conductive planar thin films of metals important for applications in electronics and telecommunication devices. Here, micropatterns of Ag thin films are sputtered on the substrates through a shadow mask to demonstrate double split-ring resonator metamaterial structures as radio frequency filters operating in the sub-THz band.
基金the Kvantum Institute Em erging Project at the University of Oulu and Academy of Finland ELECTRA-project(No.2430291511).We thank Raija Oilunkaniemi and idarkus Riihimaki for the help with XRD and ATR characterization,respectively.We are grateful to the staff from Centre for Material Analysis(University of Oulu)for the characterization.ELI-ALPS is supported by the European Union and co-flnanced by the European Regional Development Fund(No.GINOP-2.3.6-15-2015-00001).M.U.K.also acknow ledgesfundingfrom PaNOSC Europeanproject.
文摘Metal halide perovskites have emerged as novel and promising photocatalysts for hydrogen generation.Currently,their stability in water is a vital and urgent research question.In this paper a novel approach to stabilize a bismuth halide perovskite[(CH_(3))_(2)NH_(2)]_(3)[Bil_(6)](DA_(3)Bil_(6))in water using dimethylammonium iodide(DAI)without the assistance of acids or coatings is reported.The DA3Bil6 powder exhibits good stability in DAI solutions for at least two weeks.The concentration of DAI is found as a critical parameter,where the I^(-)ions play the key role in the stabilization.The stability of DA3Bil6 in water is realized via a surface dissolution-recrystallization process.Stabilized DA3Bil6 demonstrates constant photocatalytic properties for visible light-induced photo-oxidation of I^(-)ions and with PtCI4 as a co-catalyst(Pt-DA_(3)Bil_(6)),photocatalytic H2 evolution with a rate of 5.7μmol·h^(-1)from HI in DAI solution,obtaining an apparent quantum efficiency of 0.83%at 535 nm.This study provides new insights on the stabilization of metal halide perovskites for photocatalysis in aqueous solution.
文摘Owing to their higher intrinsic electrical conductivity and chemical stability with respect to their oxide counterparts, nanostructured metal sulfides are expected to revive materials for resistive chemical sensor applications. Herein, we explore the gas sensing behavior of WS2 nanowire-nanoflake hybrid materials and demonstrate their excellent sensitivity （0.043 ppm-1） as well as high selectivity towards H2S relative to CO, NH~, H2, and NO （with corresponding sensitivities of 0.002, 0.0074, 0.0002, and 0.0046 pprn-1, respectively）. Gas response measurements, complemented with the results of X-ray photoelectron spectroscopy analysis and first-principles calculations based on density functional theory, suggest that the intrinsic electronic properties of pristine WS2 alone are not sufficient to explain the observed high sensitivity towards H2S. A major role in this behavior is also played by O doping in the S sites of the WS2 lattice. The results of the present study open up new avenues for the use of transition metal disulfide nanomaterials as effective alternatives to metal oxides in future applications for industrial process control, security, and health and environmental safety.
基金the Finnish Funding Agency for Innovation(Grant No.400.31.2013).
文摘Ability of epitaxial perovskite oxide ferroelectric films to maintain a poled polarization state on a long-term scale is crucial for advanced devices employing such films.Here polarization relaxation with time,or aging,is experimentally studied in epitaxial capacitor heterostructures of PbTiO3 sandwiched between SrRuO_(3)and Pt electrodes.The relaxation obeys logarithmic time-decay for the time 10^(2)–10^(5)s after poling pulses.The decay is by factor10 slower than that reported for polycrystalline films.Our experimental results show that existing models are insufficient for epitaxial films.
基金We are grateful to the Academy of Finland for the support under Projects No.286279 and 311058.
文摘Successful application of two-dimensional transition metal dichalcogenides in optoelectronic,catalytic,or sensing devices heavily relies on the materials’quality,that is,the thickness uniformity,presence of grain boundaries,and the types and concentrations of point defects.Raman spectroscopy is a powerful and nondestructive tool to probe these factors but the interpretation of the spectra,especially the separation of different contributions,is not straightforward.Comparison to simulated spectra is beneficial,but for defective systems first-principles simulations are often computationally too expensive due to the large sizes of the systems involved.Here,we present a combined first-principles and empirical potential method for simulating Raman spectra of defective materials and apply it to monolayer MoS_(2) with random distributions of Mo and S vacancies.We study to what extent the types of vacancies can be distinguished and provide insight into the origin of different evolutions of Raman spectra upon increasing defect concentration.We apply to our simulated spectra the phonon confinement model used in previous experiments to assess defect concentrations,and show that the simplest form of the model is insufficient to fully capture peak shapes,but a good match is obtained when the type of phonon confinement and the full phonon dispersion relation are accounted for.
基金G.S.L.and L.Y-O.acknowledge the support from the Academy of Finland(Nos.320090,317437 and 286990,respectively)J.T.K.and T.J.acknowledge the support from the Finnish Cultural Foundation Pirkanmaa Regional Fund(No.50151501)+1 种基金the Central Fund(#00150312),respectively.S.N.,T.J.and M.K.acknowledge the support from the Academy of Finland(S.N.and T.J.No.312414 and M.K.No.312409)Business Finland(former Tekes,Human Spare Parts project).This work made use of the electron microscopy and clean-room facilities at the Centre of Microscopy and Nanotechnology,at the University of Oulu.The authors also acknowledge the Tampere Imaging Facility(TIF)and the Tampere CellTech Laboratories for their service.
文摘New strategies for spatially controlled growth of human neurons may provide viable solutions to treat and recover peripheral or spinal cord injuries.While topography cues are known to promote attachment and direct proliferation of many cell types,guided outgrowth of human neurites has been found difficult to achieve so far.Here,three-dimensional(3D)micropatterned carbon nanotube(CNT)templates are used to effectively direct human neurite stem cell growth.By exploiting the mechanical flexibility,electrically conductivity and texture of the 3D CNT micropillars,a perfect environment is created to achieve specific guidance of human neurites,which may lead to enhanced therapeutic effects within the injured spinal cord or peripheral nerves.It is found that the 3D CNT micropillars grant excellent anchoring for adjacent neurites to form seamless neuronal networks that can be grown to any arbitrary shape and size.Apart from clear practical relevance in regenerative medicine,these results using the CNT based templates on Si chips also can pave the road for new types of microelectrode arrays to study cell network electrophysiology.
