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1.
Proc Natl Acad Sci U S A ; 119(17): e2120557119, 2022 04 26.
Artigo em Inglês | MEDLINE | ID: mdl-35439052

RESUMO

The sun (∼6,000 K) and outer space (∼3 K) are two significant renewable thermodynamic resources for human beings on Earth. The solar thermal conversion by photothermal (PT) and harvesting the coldness of outer space by radiative cooling (RC) have already attracted tremendous interest. However, most of the PT and RC approaches are static and monofunctional, which can only provide heating or cooling respectively under sunlight or darkness. Herein, a spectrally self-adaptive absorber/emitter (SSA/E) with strong solar absorption and switchable emissivity within the atmospheric window (i.e., 8 to 13 µm) was developed for the dynamic combination of PT and RC, corresponding to continuously efficient energy harvesting from the sun and rejecting energy to the universe. The as-fabricated SSA/E not only can be heated to ∼170 °C above ambient temperature under sunshine but also be cooled to 20 °C below ambient temperature, and thermal modeling captures the high energy harvesting efficiency of the SSA/E, enabling new technological capabilities.

2.
Small ; : e2403020, 2024 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-38804864

RESUMO

Energy conversion from the environment into electricity is the most direct and effective electricity source to sustainably power off-grid electronics, once the electricity requirement exceeds the capability of traditional centralized power supply systems. Normally photovoltaic cells have enabled distributed power generation during the day, but do not work at night. Thus, efficient electricity generation technologies for a sustainable all-day power supply with no necessity for energy storage remain a challenge. Herein, an innovative all-day power generation strategy is reported, which self-adaptively integrates the diurnal photothermal and nocturnal radiative cooling processes into the thermoelectric generator (TEG) via the spectrally dynamic modulated coating, to continuously harvest the energy from the hot sun and the cold universe for power generation. Synergistic with the optimized latent heat phase change material, the electricity generation performance of the TEG is dramatically enhanced, with a maximum power density exceeding 1000 mW m-2 during the daytime and up to 25 mW m-2 during the nighttime, corresponding to an improvement of 123.1% and 249.1%, compared with the conventional strategy. This work maximizes the utilization of ambient energy resources to provide an environmentally friendly and uninterrupted power generation strategy. This opens up new possibilities for sustained power generation both daytime and nighttime.

3.
Nano Lett ; 23(16): 7297-7302, 2023 Aug 23.
Artigo em Inglês | MEDLINE | ID: mdl-37104700

RESUMO

Mass storage and removal in solids always play a vital role in technological applications such as modern batteries and neuronal computations. However, they were kinetically limited by the slow diffusional process in the lattice, which made it challenging to fabricate applicable conductors with high electronic and ionic conductivities at room temperature. Here, we proposed an acid solution/WO3/ITO sandwich structure and achieved ultrafast H transport in the WO3 layer by interfacial job-sharing diffusion, which means the spatially separated transport of the H+ and e- in different layers. From the color change of WO3, the effective diffusion coefficient (Deff) was estimated, dramatically increasing ≤106 times and overwhelming values from previous reports. The experiments and simulations also revealed the universality of extending this approach to other atoms and oxides, which could stimulate systematic studies of ultrafast mixed conductors in the future.

4.
J Am Chem Soc ; 142(9): 4136-4140, 2020 Mar 04.
Artigo em Inglês | MEDLINE | ID: mdl-32081005

RESUMO

Hydrogen doping of metal oxide semiconductors is promising for manipulation of their properties toward various applications. Yet it is quite challenging because it requires harsh reaction conditions and expensive metal catalysts. Meanwhile, acids as a cheap source of protons have long been unappreciated. Here, we develop a sophisticated acid-metal treatment for tunable hydrogenation of metal oxides at ambient conditions. Using first-principles simulations, we first show that, with proper work function difference between the metal and metal oxide, H-diffusion into negatively charged metal oxide can be well controlled, resulting in tunable H-doping of metal oxides with quasi-metal characteristics. This has been verified by proof-of-concept experiments that achieved the controllable hydrogenation of WO3 using Cu and hydrochloric acid at ambient conditions. Further, H-doping of other metal oxides (TiO2/Nb2O5/MoO3) has been achieved by metal-acid treatment and induced a change in properties. Our work provides a promising way to tailor metal oxides via tunable H-doping.

5.
Angew Chem Int Ed Engl ; 58(39): 13711-13716, 2019 Sep 23.
Artigo em Inglês | MEDLINE | ID: mdl-31332923

RESUMO

Charge doping is an effective way to induce the metal-insulator transition (MIT) in correlated materials for many important utilizations, which is however practically limited by problem of low stability. An electron-proton co-doping mechanism is used to achieve pronounced phase modulation of monoclinic vanadium dioxide (VO2 ) at room temperature. Using l-ascorbic acid (AA) solution to treat VO2 , the ionized AA- species donate electrons to the adsorbed VO2 surface. Charges then electrostatically attract surrounding protons to penetrate, and eventually results in stable hydrogen-doped metallic VO2 . The variations of electronic structures, especially the electron occupancy of V 3d/O 2p hybrid orbitals, were examined by synchrotron characterizations and first-principle theoretical simulations. The adsorbed molecules protect hydrogen dopants from escaping out of lattice and thereby stabilize the metallic phase for VO2 .

6.
Phys Chem Chem Phys ; 16(33): 17705-14, 2014 Sep 07.
Artigo em Inglês | MEDLINE | ID: mdl-25031088

RESUMO

The mechanism for the decreasing critical temperature (T(C)) of the metal-insulator transition (MIT) in vanadium dioxide (VO2) by tungsten (W) doping is a matter of debate. Here, to clarify the correlation between W doping and T(C), the electronic and geometrical structures around W and V atoms in W(x)V(1-x)O2 samples are systematically investigated by X-ray absorption fine structure (XAFS) spectroscopy. The evidence of electron doping of W(6+) ions in VO2 is obtained from the reduction of V(4+) to V(3+) ions. This kind of electron doping has been considered to favor the MIT process. Moreover, from the XAFS results, the local rutile structure around W dopants is identified even at low doping, and acts as the structure-guided domain to facilitate the MIT in VO2. Considering the electronic band structures of W(x)V(1-x)O2 samples, the internal stresses induced by W(6+) doping yield the detwisting of the nearby monoclinic VO2 lattice. This lattice detwisting will drive the downward shift of the π* electron band and a smaller separation between antibonding and bonding d∥ orbitals in the band structure of VO2, which induces the decreased band gaps of W(x)V(1-x)O2 samples. As a consequence, the potential energy barrier for phase transition is lowered and the reduced T(C) is observed.

7.
Small Methods ; 8(2): e2300175, 2024 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-37317014

RESUMO

GaN's outstanding physical characteristics allow for a wide range of applications in numerous industries. Although individual GaN-based ultraviolet (UV) photodetectors are the subject of in-depth research in recent decades, the demand for photodetectors array is rising as a result of advances in optoelectronic integration technology. However, as a prerequisite for constructing GaN-based photodetectors array, large-area, patterned synthesis of GaN thin films remains a certain challenge. This work presents a facile technique for pattern growing high-quality GaN thin films for the assembly of an array of high-performance UV photodetectors. This technique uses UV lithography, which is not only very compatible with common semiconductor manufacturing techniques, but also enables precise patterning modification. A typical detector has impressive photo-response performance under 365 nm irradiation, with an extremely low dark current of 40 pA, a high Ilight /Idark ratio over 105 , a high responsivity of 4.23 AW-1 , and a decent specific detectivity of 1.76 × 1012 Jones. Additional optoelectronic studies demonstrate the strong homogeneity and repeatability of the photodetectors array, enabling it to serve as a reliable UV image sensor with enough spatial resolution. These outcomes highlight the proposed patterning technique's enormous potential.

8.
ACS Appl Mater Interfaces ; 16(31): 41072-41079, 2024 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-39046366

RESUMO

As the fields of photonics and information technology develop, a lot of novel applications based on VO2 material, such as optoelectronic computing and information encryption, have been developed. While the performance of these devices was not only closely associated with the VO2 phase transition properties but also depended on their dimensional characteristics. In the current study, we conducted the dimension-controlled vanadium dioxide (VO2) film growth, resulting in the epitaxial 2-dimensional (2D) VO2 film and well-distributed 3-dimensional (3D) VO2 crystal film deposition, respectively. It was revealed that, unlike the 2D film, the pronounced localized surface plasmon resonance dominated the near-infrared spectrum across the phase transition for the 3D VO2 film due to the naturally formed meta-surface structure, which showed a transmittance valley in the infrared spectrum after metallization. Based on this distinct infrared spectrum feature in the 3D VO2 film, we proposed an optoelectronic logic gate controlled by the input voltage and the probing Vis/IR light. By detecting the transmittance states of the probing light with different wavelengths, we achieved multistate encoding functions and demonstrated the information encryption application. This new conception device also showed great potential for some other applications such as optoelectronic coupled computing, information encryption, and optical near-field sensing computing.

9.
ACS Appl Mater Interfaces ; 16(11): 13997-14005, 2024 Mar 20.
Artigo em Inglês | MEDLINE | ID: mdl-38447142

RESUMO

The efficient generation and active modulation of terahertz (THz) waves are strongly required for the development of various THz applications such as THz imaging/spectroscopy and THz communication. In addition, due to the increasing degree of integration for the THz optoelectronic devices, miniaturizing the complex THz system into a compact unit is also important and necessary. Today, integrating the THz source with the modulator to develop a powerful, easy-to-adjust, and scalable or on-chip THz emitter is still a challenge. As a new type of THz emitter, a spintronic THz emitter has attracted a great deal of attention due to its advantages of high efficiency, ultrawide band, low cost, and easy integration. In this study, we have proposed a multifield-modulated spintronic THz emitter based on the VO2/Ni/Pt multilayer film structure with a wide band region of 0-3 THz. Because of the pronounced phase transition of the integrated VO2 layer, the fabricated THz emitter can be efficiently modulated via thermal or electric stimuli with a modulation depth of about one order of magnitude; the modulation depths under thermal stimulation and electrical stimulation were 91.8% and 97.3%, respectively. It is believed that this multifield modulated spintronic THz emitter will provide various possibilities for the integration of next-generation on-chip THz sources and THz modulators.

10.
Adv Mater ; 36(16): e2308871, 2024 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-38183328

RESUMO

Redox gating, a novel approach distinct from conventional electrolyte gating, combines reversible redox functionalities with common ionic electrolyte moieties to engineer charge transport, enabling power-efficient electronic phase control. This study achieves a colossal sheet carrier density modulation beyond 1016 cm-2, sustainable over thousands of cycles, all within the sub-volt regime for functional oxide thin films. The key advantage of this method lies in the controlled injection of a large quantity of carriers from the electrolyte into the channel material without the deleterious effects associated with traditional electrolyte gating processes such as the production of ionic defects or intercalated species. The redox gating approach offers a simple and practical means of decoupling electrical and structural phase transitions, enabling the isostructural metal-insulator transition and improved device endurance. The versatility of redox gating extends across multiple materials, irrespective of their crystallinity, crystallographic orientation, or carrier type (n- or p-type). This inclusivity encompasses functional heterostructures and low-dimensional quantum materials composed of sustainable elements, highlighting the broad applicability and potential of the technique in electronic devices.

11.
ACS Appl Mater Interfaces ; 15(10): 13517-13525, 2023 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-36856296

RESUMO

Vanadium dioxide (VO2) is widely employed in developing tunable optoelectronic devices due to its significant changes in optical and electric properties upon phase transition. To fabricate the VO2-based functional devices down to the micro/nanoscale, a high-resolution processing technique is in demand. Scanning probe lithography (SPL) on the basis of a tip-induced electric field provides a promising approach for prototyping. Here, we demonstrated a precise VO2 etching strategy by direct writing on a VO2 film with a negative tip bias and subsequent sonication removal of the written area. The effects of bias voltage, sonication, and thermal treatment as well as the mechanical difference between the tip-modulated area and the pristine VO2 film were investigated systematically. The results show that VO2 can be etched layer by layer via alternately repeating tip modulation and sonication, and arbitrary patterns can be written. Based on this route, we designed a kind of metasurface by arranging VO2-gold nanoblocks with different sizes and heights for spectrally selective tunable reflectivity in near- and mid-infrared. This electric-field SPL method demonstrates the prominent advantages of high resolution down to several tens of nanometers, quasi-3D patterning, and resist-free maskless direct writing, which should be applicable for prototyping other micro/nanodevices.

12.
Adv Sci (Weinh) ; 10(21): e2300908, 2023 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-37114834

RESUMO

In the information explosion society, information security is highly demanded in the practical application, which raised a surge of interest in designing secure and reliable information transmission channels based on the inherent properties of emerging devices. Here, an innovative strategy to achieve the data encryption and reading during the data confidential transmission based on VO2 device is proposed. Owing to the specific insulator-to-metal transition property of VO2 , the phase transitions between the insulator and metallic states are modulated by the combination of electric field, temperature, and light radiation. These external stimulus-induced phase diagram is directly associated with the defined VO2 device, which are applicable for control the "0" or "1" electrical logic state for the information encryption. A prototype device is fabricated on an epitaxial VO2 film, which displayed a unique data encryption function with excellent stability. The current study not only demonstrated a multiphysical field-modulated VO2 device for information encryption, but also supplied some clues for functional devices applications in other correlated oxide materials.

13.
Sci Adv ; 9(40): eadg9376, 2023 Oct 06.
Artigo em Inglês | MEDLINE | ID: mdl-37792938

RESUMO

Neuromorphic computing has shown remarkable capabilities in silicon-based artificial intelligence, which can be optimized by using Mott materials for functional synaptic connections. However, the research efforts focus on two-terminal artificial synapses and envisioned the networks controlled by silicon-based circuits, which is difficult to develop and integrate. Here, we propose a dynamic network with laser-controlled conducting filaments based on electric field-induced local insulator-metal transition of vanadium dioxide. Quantum sensing is used to realize conductivity-sensitive imaging of conducting filament. We find that the location of filament formation is manipulated by focused laser, which is applicable to simulate the dynamical synaptic connections between the neurons. The ability to process signals with both long-term and short-term potentiation is further demonstrated with ~60 times on/off ratio while switching the pathways. This study opens the door to the development of dynamic network structures depending on easily controlled conduction pathways, mimicking the biological nervous systems.

14.
ACS Nano ; 17(10): 9501-9509, 2023 May 23.
Artigo em Inglês | MEDLINE | ID: mdl-37166276

RESUMO

Extensive use of renewable and clean energy is one of the promising ways to solve energy/environmental problems and promote the sustainable development of our society. As inexhaustible energy sources, the photothermal (PT) and radiative cooling (RC) energy from the sun and outer space have recently attracted tremendous interest. However, these two kinds of energy utilization have distinctly opposite spectral properties, especially in the infrared range, making it extremely difficult to integrate these two energy harvesting modes within a fixed device for continuous energy collection. Thus, in the current study, we have proposed a spectrally self-adaptive broadband absorber/emitter (SSBA/E) based on vanadium dioxide (VO2), a typical phase transition material, to achieve continuous energy harvesting via collecting solar thermal energy in PT mode during the day and obtaining cool energy in wide-band RC mode at night. Experimental results show that owing to the phase transition property of the VO2 layer, these two energy collection modes can be adaptively switched. Specifically, the VO2-based device shows a broadband infrared emissivity modulation from 0.21 to 0.75 and low critical temperatures (58.4 and 49.2 °C) during the phase transition, leading to continuous energy harvesting with high efficiency. Due to the broadband infrared emission, the RC maximum power of the SSBA/E device was estimated to be 58 W m-2. The proposed VO2 smart coatings are also applicable for many other applications such as thermal management of spacecraft, infrared camouflage, or adaptive optical devices.

15.
Phys Chem Chem Phys ; 14(43): 15021-8, 2012 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-23034581

RESUMO

The driving mechanism of the metal-insulator transition (MIT) in VO(2) has always attracted attention, in particular with regards to understanding if and how the doping mechanism may tune the MIT transition temperature. However, due to the lack of detailed local structural information, in this oxide the underlying MIT mechanism is still matter of debate. In this contribution on the V(1-x)W(x)O(2) system, we attempt to clarify the origin of the MIT induced by tungsten doping. Combining W L(3)-edge and V K-edge extended X-ray absorption fine-structure (EXAFS) spectroscopy, the local structures around both V and W have been obtained. The data point out the occurrence of internal stress along the V-V chains induced by doping. It reaches a critical value that remains constant during the transition. The main effect of the internal stress on the vanadium local structure has also been identified. Actually, upon increasing the dopant concentration, the tilt of the V-V pairs towards the apex oxygen atoms in the VO(6) octahedron decreases while the V-V bond lengths remain unchanged. The electronic structure has also been investigated by O K-edge X-ray absorption near-edge structure (XANES) spectroscopy. Actually, at high doping concentrations the interaction of O(2p) and the V d(∥) state increases, while the hybridization of O(2p) and V π* decreases. The O(2p)-V(3d) hybridization is therefore an essential parameter correlated with the decreasing transition temperature in the V(1-x)W(x)O(2) system.

16.
ACS Appl Mater Interfaces ; 14(28): 32253-32260, 2022 Jul 20.
Artigo em Inglês | MEDLINE | ID: mdl-35802381

RESUMO

The electrochromic WO3 smart window based on an aqueous electrolyte shows an excellent liquid/solid interface and thus can achieve a fast electrochromic response, while the aqueous electrolyte has a limited electrochemical window, which probably induces the H+ reduction and degrades the practical application. Here, we propose a strategy to modify the traditional Li+ acidic aqueous electrolyte by adding some selective inert metal ions, which not only improve the electrochromic performance but also avoid the possible production of hydrogen bubbles due to the broadened electrochemical window. Furthermore, reversible electroplating of inert metal ions will occur, leading to an enhanced optical transmission change of up to 77.5% at 500 nm and 70.4% at 700 nm. This combination of Li-ion insertion and metal electroplating in the ESW device makes it superior to all of the previous reports. The device also demonstrates high stability and high electrochromic efficiency after 1000 cycles. The current study not only emphasizes the rational design for aqueous electrolytes but also demonstrates a practical way to realize an excellent electrochromic window for practical applications.

17.
Small Methods ; 6(12): e2200931, 2022 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-36287026

RESUMO

The utilization of clean hydrogen energy is becoming more feasible for the sustainable development of this society. Considering the safety issues in the hydrogen production, storage, and utilization, a sensitive hydrogen sensor for reliable detection is essential and highly important. Though various gas sensor devices are developed based on tin oxide, tungsten trioxide, or other oxides, the relatively high working temperature, unsatisfactory response time, and detection limitation still affect the extensive applications. In the current study, an amorphous tungsten trioxide (a-WO3 ) layer is deposited on a phase-change vanadium dioxide film to fabricate a phase transition controlled Pd/a-WO3 /VO2 hydrogen sensor for hydrogen detection. Results show that both the response time and sensitivity of the hydrogen sensor are improved greatly if increasing the working temperature over the transition temperature of VO2 . Theoretical calculations also reveal that the charge transfer at VO2 /a-WO3 interface becomes more pronounced once the VO2 layer transforms to the metal state, which will affect the migration barrier of H atoms in a-WO3 layer and thus improve the sensor performance. The current study not only realizes a hydrogen sensor with ultrahigh performance based on VO2 layer, but also provides some clues for designing other gas sensors with phase-change material.

18.
Nanotechnology ; 22(10): 105706, 2011 Mar 11.
Artigo em Inglês | MEDLINE | ID: mdl-21289405

RESUMO

Silver-doped zinc oxide (Ag:ZnO) nanostructures were prepared by a facile and efficient wet oxidation method. This method included two steps: metallic Zn thin films mixed with Ag atoms were prepared by magnetron sputtering as the precursors, and then the precursors were oxidized in an O(2) atmosphere with water vapour present to form Ag:ZnO nanostructures. By controlling the oxidation conditions, pure ZnO and Ag:ZnO nanobelts/nanowires with a thickness of ∼ 20 nm and length of up to several tens of microns were synthesized. Scanning electron microscopy, transmission electron microscopy, cathodoluminescence and low temperature photoluminescence (PL) measurements were adopted to characterize the microstructure and optical properties of the prepared samples. The results indicated that Ag doping during magnetron sputtering was a feasible method to tune the optical properties of ZnO nanostructures. For the Ag:ZnO nanostructures, the intensity of ultraviolet emission was increased up to three times compared with the pure ones. The detailed PL intensity variation with the increasing temperature is also discussed based on the ionization energy of acceptor in ZnO induced by Ag dopants.

19.
J Nanosci Nanotechnol ; 11(4): 3711-5, 2011 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-21776760

RESUMO

A simple two-steps method has been successfully developed to synthesize ZnO nanotubes. The alkaline etching process was investigated in detail using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The formation of ZnO nanotube structures was due to the preferential dissolution of the defect-rich top (polar) faces. Cathodoluminescence (CL) was performed on both top and side surfaces of the ZnO tubes. Only the near-band-edge UV emission was observed, implying that the as-grown ZnO nanotubes have a very low concentration of defects. This CL result also provides evidence for explanation of ZnO tubular structure growth.


Assuntos
Medições Luminescentes/métodos , Nanoestruturas/química , Nanoestruturas/ultraestrutura , Óxido de Zinco/química , Eletrodos , Medições Luminescentes/instrumentação , Substâncias Macromoleculares/química , Teste de Materiais , Microesferas , Conformação Molecular , Tamanho da Partícula , Propriedades de Superfície
20.
J Phys Chem Lett ; 12(39): 9579-9583, 2021 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-34582204

RESUMO

Oxygen vacancy is a common defect in metal oxides that causes appreciable damage to material properties and performance. Removing bulk defects of oxygen vacancy (VO) typically needs harsh conditions such as high-temperature annealing. Supported by first-principles simulations, we propose an effective strategy of removing VO bulk defects in metal oxides by evaporating hydrogen dopants. The hydrogen dopants not only lower the migration barrier of VO but also push VO away due to their repulsive interaction. The coevaporation mechanism was supported by a neural networks potential-based molecular dynamics simulation, which shows that the migration of hydrogen dopants from inside to surface at 400 K promotes the migration of VO as well. Our proof-of-concept study suggests an alternative and efficient way of modulating oxygen vacancies in metal oxides via reversible hydrogen doping.

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