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1.
Opt Express ; 27(20): A1467-A1480, 2019 Sep 30.
Artigo em Inglês | MEDLINE | ID: mdl-31684499

RESUMO

Optical concentration can improve the efficiency and reduce the cost of photovoltaic power but has traditionally been too bulky, massive, and unreliable for use in space. Here, we explore a new ultra-compact and low-mass microcell concentrating photovoltaic (µCPV) paradigm for space based on the monolithic integration of transfer-printed microscale solar cells and molded microconcentrator optics. We derive basic bounds on the compactness as a function of geometric concentration ratio and angular acceptance, and show that a simple reflective parabolic concentrator provides the best combination of specific power, angular acceptance, and overall fabrication simplicity. This architecture is simulated in detail and validated experimentally with a µCPV prototype that is less than 1.7 mm thick and operates with six, 650 µm square triple-junction microcells at a geometric concentration ratio of 18.4×. In outdoor testing, the system achieves a terrestrial power conversion efficiency of 25.8 ± 0.2% over a ±9.5° angular range, resulting in a specific power of approximately 111 W/kg. These results lay the groundwork for future space µCPV systems and establish a realistic path to exceed 350 W/kg specific power at >33% power conversion efficiency by scaling down to even smaller microcells.

2.
Adv Mater ; 31(42): e1902739, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31489737

RESUMO

Transient forms of electronics, systems that disintegrate, dissolve, resorb, or sublime in a controlled manner after a well-defined operating lifetime, are of interest for applications in hardware secure technologies, temporary biomedical implants, "green" consumer devices and other areas that cannot be addressed with conventional approaches. Broad sets of materials now exist for a range of transient electronic components, including transistors, diodes, antennas, sensors, and even batteries. This work reports the first examples of transient light-emitting diodes (LEDs) that can completely dissolve in aqueous solutions to biologically and environmentally benign end products. Thin films of highly textured ZnO and polycrystalline Mo serve as semiconductors for light generation and conductors for transparent electrodes, respectively. The emitted light spans a range of visible wavelengths, where nanomembranes of monocrystalline silicon can serve as transient filters to yield red, green, and blue LEDs. Detailed characterization of the material chemistries and morphologies of the constituent layers, assessments of their performance properties, and studies of their dissolution processes define the underlying aspects. These results establish an electroluminescent light source technology for unique classes of optoelectronic systems that vanish into benign forms when exposed to aqueous conditions in the environment or in living organisms.


Assuntos
Semicondutores , Molibdênio/química , Fenômenos Ópticos , Solubilidade , Água/química , Óxido de Zinco/química
3.
Proc Natl Acad Sci U S A ; 116(31): 15398-15406, 2019 07 30.
Artigo em Inglês | MEDLINE | ID: mdl-31308234

RESUMO

Flexible biocompatible electronic systems that leverage key materials and manufacturing techniques associated with the consumer electronics industry have potential for broad applications in biomedicine and biological research. This study reports scalable approaches to technologies of this type, where thin microscale device components integrate onto flexible polymer substrates in interconnected arrays to provide multimodal, high performance operational capabilities as intimately coupled biointerfaces. Specificially, the material options and engineering schemes summarized here serve as foundations for diverse, heterogeneously integrated systems. Scaled examples incorporate >32,000 silicon microdie and inorganic microscale light-emitting diodes derived from wafer sources distributed at variable pitch spacings and fill factors across large areas on polymer films, at full organ-scale dimensions such as human brain, over ∼150 cm2 In vitro studies and accelerated testing in simulated biofluids, together with theoretical simulations of underlying processes, yield quantitative insights into the key materials aspects. The results suggest an ability of these systems to operate in a biologically safe, stable fashion with projected lifetimes of several decades without leakage currents or reductions in performance. The versatility of these combined concepts suggests applicability to many classes of biointegrated semiconductor devices.

4.
Nat Biomed Eng ; 3(1): 37-46, 2019 01.
Artigo em Inglês | MEDLINE | ID: mdl-30932064

RESUMO

Pressures in the intracranial, intraocular and intravascular spaces are clinically useful for the diagnosis and management of traumatic brain injury, glaucoma and hypertension, respectively. Conventional devices for measuring these pressures require surgical extraction after a relevant operational time frame. Bioresorbable sensors, by contrast, eliminate this requirement, thereby minimizing the risk of infection, decreasing the costs of care and reducing distress and pain for the patient. However, the operational lifetimes of bioresorbable pressure sensors available at present fall short of many clinical needs. Here, we present materials, device structures and fabrication procedures for bioresorbable pressure sensors with lifetimes exceeding those of previous reports by at least tenfold. We demonstrate measurement accuracies that compare favourably to those of the most sophisticated clinical standards for non-resorbable devices by monitoring intracranial pressures in rats for 25 days. Assessments of the biodistribution of the constituent materials, complete blood counts, blood chemistry and magnetic resonance imaging compatibility confirm the biodegradability and clinical utility of the device. Our findings establish routes for the design and fabrication of bioresorbable pressure monitors that meet requirements for clinical use.


Assuntos
Implantes Absorvíveis , Doença Crônica , Pressão Intracraniana , Monitorização Fisiológica/instrumentação , Dióxido de Silício/química , Temperatura , Cicatrização , Animais , Feminino , Cinética , Imagem por Ressonância Magnética , Masculino , Camundongos , Ratos Endogâmicos Lew , Distribuição Tecidual
5.
ACS Nano ; 12(10): 10317-10326, 2018 10 23.
Artigo em Inglês | MEDLINE | ID: mdl-30281278

RESUMO

Biomedical implants that incorporate active electronics and offer the ability to operate in a safe, stable fashion for long periods of time must incorporate defect-free layers as barriers to biofluid penetration. This paper reports an engineered material approach to this challenge that combines ultrathin, physically transferred films of silicon dioxide (t-SiO2) thermally grown on silicon wafers, with layers of hafnium oxide (HfO2) formed by atomic layer deposition and coatings of parylene (Parylene C) created by chemical vapor deposition, as a dual-sided encapsulation structure for flexible bioelectronic systems. Accelerated aging tests on passive/active components in platforms that incorporate active, silicon-based transistors suggest that this trilayer construct can serve as a robust, long-lived, defect-free barrier to phosphate-buffered saline (PBS) solution at a physiological pH of 7.4. Reactive diffusion modeling and systematic immersion experiments highlight fundamental aspects of water diffusion and hydrolysis behaviors, with results that suggest lifetimes of many decades at physiological conditions. A combination of ion-diffusion tests under continuous electrical bias, measurements of elemental concentration profiles, and temperature-dependent simulations reveals that this encapsulation strategy can also block transport of ions that would otherwise degrade the performance of the underlying electronics. These findings suggest broad utility of this trilayer assembly as a reliable encapsulation strategy for the most demanding applications in chronic biomedical implants and high-performance flexible bioelectronic systems.


Assuntos
Técnicas Biossensoriais , Háfnio/química , Óxidos/química , Polímeros/química , Dióxido de Silício/química , Água/química , Xilenos/química , Técnicas Biossensoriais/instrumentação , Eletrônica , Íons/química , Volatilização
6.
ACS Nano ; 12(10): 9721-9732, 2018 10 23.
Artigo em Inglês | MEDLINE | ID: mdl-30160102

RESUMO

Foundry-compatible materials and processing approaches serve as the foundations for advanced, active implantable microsystems that can dissolve in biofluids into biocompatible reaction products, with broad potential applications in biomedicine. The results reported here include in vitro studies of the dissolution kinetics and nanoscale bioresorption behaviors of device-grade thin films of Si, SiN x, SiO2, and W in the presence of dynamic cell cultures via atomic force microscopy and X-ray photoemission spectroscopy. In situ investigations of cell-extracellular mechanotransduction induced by cellular traction provide insights into the cytotoxicity of these same materials and of microcomponents formed with them using foundry-compatible processes, indicating potential cytotoxicity elicited by W at concentrations greater than 6 mM. The findings are of central relevance to the biocompatibility of modern Si-based electronics technologies as active, bioresorbable microsystems that interface with living tissues.


Assuntos
Materiais Biocompatíveis/farmacologia , Mecanotransdução Celular/efeitos dos fármacos , Compostos de Silício/farmacologia , Tungstênio/farmacologia , Materiais Biocompatíveis/química , Sobrevivência Celular/efeitos dos fármacos , Células Cultivadas , Humanos , Cinética , Microscopia de Força Atômica/instrumentação , Espectroscopia Fotoeletrônica/instrumentação , Semicondutores , Compostos de Silício/química , Tungstênio/química
7.
ACS Nano ; 12(5): 4164-4171, 2018 05 22.
Artigo em Inglês | MEDLINE | ID: mdl-29641889

RESUMO

Recently developed approaches in deterministic assembly allow for controlled, geometric transformation of two-dimensional structures into complex, engineered three-dimensional layouts. Attractive features include applicability to wide ranging layout designs and dimensions along with the capacity to integrate planar thin film materials and device layouts. The work reported here establishes further capabilities for directly embedding high-performance electronic devices into the resultant 3D constructs based on silicon nanomembranes (Si NMs) as the active materials in custom devices or microscale components released from commercial wafer sources. Systematic experimental studies and theoretical analysis illustrate the key ideas through varied 3D architectures, from interconnected bridges and coils to extended chiral structures, each of which embed n-channel Si NM MOSFETs (nMOS), Si NM diodes, and p-channel silicon MOSFETs (pMOS). Examples in stretchable/deformable systems highlight additional features of these platforms. These strategies are immediately applicable to other wide-ranging classes of materials and device technologies that can be rendered in two-dimensional layouts, from systems for energy storage, to photovoltaics, optoelectronics, and others.


Assuntos
Eletrônica/instrumentação , Nanoestruturas/química , Silício/química , Análise de Elementos Finitos , Iluminação , Fenômenos Mecânicos , Metais/química , Óxidos/química , Dióxido de Silício
8.
Adv Mater ; 30(11)2018 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-29349821

RESUMO

Biodegradable electronic systems represent an emerging class of technology with unique application possibilities, from temporary biomedical implants to "green" consumer gadgets. This paper introduces materials and processing methods for 3D, heterogeneously integrated devices of this type, with various functional examples in sophisticated forms of silicon-based electronics. Specifically, techniques for performing multilayer assembly by transfer printing and for fabricating layer-to-layer vias and interconnects by lithographic procedures serve as routes to biodegradable, 3D integrated circuits composed of functional building blocks formed using specialized approaches or sourced from commercial semiconductor foundries. Demonstration examples range from logic gates and analog circuits that undergo functional transformation by transience to systems that integrate multilayer resistive sensors for in situ, continuous electrical monitoring of the processes of transience. The results significantly expand the scope of engineering options for biodegradable electronics and other types of transient microsystem technologies.


Assuntos
Implantes Absorvíveis , Impressão , Semicondutores , Silício
9.
Proc Natl Acad Sci U S A ; 114(28): E5522-E5529, 2017 07 11.
Artigo em Inglês | MEDLINE | ID: mdl-28652373

RESUMO

Foundry-based routes to transient silicon electronic devices have the potential to serve as the manufacturing basis for "green" electronic devices, biodegradable implants, hardware secure data storage systems, and unrecoverable remote devices. This article introduces materials and processing approaches that enable state-of-the-art silicon complementary metal-oxide-semiconductor (CMOS) foundries to be leveraged for high-performance, water-soluble forms of electronics. The key elements are (i) collections of biodegradable electronic materials (e.g., silicon, tungsten, silicon nitride, silicon dioxide) and device architectures that are compatible with manufacturing procedures currently used in the integrated circuit industry, (ii) release schemes and transfer printing methods for integration of multiple ultrathin components formed in this way onto biodegradable polymer substrates, and (iii) planarization and metallization techniques to yield interconnected and fully functional systems. Various CMOS devices and circuit elements created in this fashion and detailed measurements of their electrical characteristics highlight the capabilities. Accelerated dissolution studies in aqueous environments reveal the chemical kinetics associated with the underlying transient behaviors. The results demonstrate the technical feasibility for using foundry-based routes to sophisticated forms of transient electronic devices, with functional capabilities and cost structures that could support diverse applications in the biomedical, military, industrial, and consumer industries.

10.
ACS Appl Mater Interfaces ; 8(38): 24989-93, 2016 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-27618510

RESUMO

The effects of femtosecond-laser-induced periodic surface structures (LIPSS) on an indium tin oxide (ITO) surface applied to an organic photovoltaic (OPV) system were investigated. The modifications of ITO induced by LIPPS in OPV devices result in more than 14% increase in power conversion efficiency (PCE) and short-circuit current density relative to those of the standard device. The basic mechanisms for the enhanced short-circuit current density are attributed to better light harvesting, increased scattering effects, and more efficient charge collection between the ITO and photoactive layers. Results show that higher PCEs would be achieved by laser-pulse-treated electrodes.

11.
Opt Express ; 24(2): A414-23, 2016 Jan 25.
Artigo em Inglês | MEDLINE | ID: mdl-26832593

RESUMO

In this work, we investigate blade-coated organic interlayers at the rear surface of hybrid organic-silicon photovoltaics based on two small molecules: Tris(8-hydroxyquinolinato) aluminium (Alq(3)) and 1,3-bis(2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl) benzene (OXD-7). In particular, soluble Alq(3) resulting in a uniform thin film with a root-mean-square roughness < 0.2nm is demonstrated for the first time. Both devices with the Alq(3) and OXD-7 interlayers show notable enhancement in the open-circuit voltage and fill-factor, leading to a net efficiency increase by over 2% from the reference, up to 11.8% and 12.5% respectively. The capacitance-voltage characteristics confirm the role of the small-molecule interlayers resembling a thin interfacial oxide layer for the Al-Si Schottky barrier to enhance the built-in potential and facilitate charge transport. Moreover, the Alq(3) interlayer in optimized devices exhibits isolated phases with a large surface roughness, in contrast to the OXD-7 which forms a continuous uniform thin film. The distinct morphological differences between the two interlayers further suggest different enhancement mechanisms and hence offer versatile functionalities to the advent of hybrid organic-silicon photovoltaics.

12.
ACS Appl Mater Interfaces ; 7(31): 17155-61, 2015 Aug 12.
Artigo em Inglês | MEDLINE | ID: mdl-26183173

RESUMO

To expand the applications of graphene in optoelectronics and microelectronics, simple and effective doping processes need to be developed. In this paper, we demonstrate an aqueous process that can simultaneously transfer chemical vapor deposition grown graphene from Cu to other substrates and produce stacked graphene/dopant intercalation films with tunable work functions, which differs significantly from conventional doping methods using vacuum evaporation or spin-coating processes. The work function of graphene layers can be tuned from 3.25 to 5.10 eV, which practically covers the wide range of the anode and cathode applications. Doped graphene films in intercalation structures also exhibit excellent transparency and low resistance. The polymer-based solar cells with either low work function graphene as cathodes or high work function graphene as anodes are demonstrated.

13.
Nano Lett ; 14(11): 6097-103, 2014 Nov 12.
Artigo em Inglês | MEDLINE | ID: mdl-25354234

RESUMO

The production of renewable solar fuel through CO2 photoreduction, namely artificial photosynthesis, has gained tremendous attention in recent times due to the limited availability of fossil-fuel resources and global climate change caused by rising anthropogenic CO2 in the atmosphere. In this study, graphene oxide (GO) decorated with copper nanoparticles (Cu-NPs), hereafter referred to as Cu/GO, has been used to enhance photocatalytic CO2 reduction under visible-light. A rapid one-pot microwave process was used to prepare the Cu/GO hybrids with various Cu contents. The attributes of metallic copper nanoparticles (∼4-5 nm in size) in the GO hybrid are shown to significantly enhance the photocatalytic activity of GO, primarily through the suppression of electron-hole pair recombination, further reduction of GO's bandgap, and modification of its work function. X-ray photoemission spectroscopy studies indicate a charge transfer from GO to Cu. A strong interaction is observed between the metal content of the Cu/GO hybrids and the rates of formation and selectivity of the products. A factor of greater than 60 times enhancement in CO2 to fuel catalytic efficiency has been demonstrated using Cu/GO-2 (10 wt % Cu) compared with that using pristine GO.


Assuntos
Grafite/química , Hidrocarbonetos/química , Nanopartículas Metálicas/química , Óxidos/química , Energia Solar , Catálise , Luz , Nanopartículas Metálicas/ultraestrutura , Oxirredução , Processos Fotoquímicos
14.
ACS Nano ; 8(8): 8582-90, 2014 Aug 26.
Artigo em Inglês | MEDLINE | ID: mdl-25094022

RESUMO

Monolayer molybdenum disulfide (MoS2) has become a promising building block in optoelectronics for its high photosensitivity. However, sulfur vacancies and other defects significantly affect the electrical and optoelectronic properties of monolayer MoS2 devices. Here, highly crystalline molybdenum diselenide (MoSe2) monolayers have been successfully synthesized by the chemical vapor deposition (CVD) method. Low-temperature photoluminescence comparison for MoS2 and MoSe2 monolayers reveals that the MoSe2 monolayer shows a much weaker bound exciton peak; hence, the phototransistor based on MoSe2 presents a much faster response time (<25 ms) than the corresponding 30 s for the CVD MoS2 monolayer at room temperature in ambient conditions. The images obtained from transmission electron microscopy indicate that the MoSe exhibits fewer defects than MoS2. This work provides the fundamental understanding for the differences in optoelectronic behaviors between MoSe2 and MoS2 and is useful for guiding future designs in 2D material-based optoelectronic devices.

15.
ACS Nano ; 8(8): 8317-22, 2014 Aug 26.
Artigo em Inglês | MEDLINE | ID: mdl-25046764

RESUMO

We realized photovoltaic operation in large-scale MoS2 monolayers by the formation of a type-II heterojunction with p-Si. The MoS2 monolayer introduces a built-in electric field near the interface between MoS2 and p-Si to help photogenerated carrier separation. Such a heterojunction photovoltaic device achieves a power conversion efficiency of 5.23%, which is the highest efficiency among all monolayer transition-metal dichalcogenide-based solar cells. The demonstrated results of monolayer MoS2/Si-based solar cells hold the promise for integration of 2D materials with commercially available Si-based electronics in highly efficient devices.

16.
ACS Nano ; 8(2): 1784-91, 2014 Feb 25.
Artigo em Inglês | MEDLINE | ID: mdl-24471977

RESUMO

We demonstrate a polymer-free method that can routinely transfer relatively large-area graphene to any substrate with advanced electrical properties and superior atomic and chemical structures as compared to the graphene sheets transferred with conventional polymer-assisted methods. The graphene films that are transferred with polymer-free method show high electrical conductance and excellent optical transmittance. Raman spectroscopy and X-ray/ultraviolet photoelectron spectroscopy also confirm the presence of high quality graphene sheets with little contamination after transfer. Atom-resolved images can be obtained using scanning tunneling microscope on as-transferred graphene sheets without additional cleaning process. The mobility of the polymer-free graphene monolayer is as high as 63,000 cm(2) V(-1) s(-1), which is 50% higher than the similar sample transferred with the conventional method. More importantly, this method allows us to place graphene directly on top of devices made of soft materials, such as organic and polymeric thin films, which widens the applications of graphene in soft electronics.

17.
ACS Nano ; 7(12): 10780-7, 2013 Dec 23.
Artigo em Inglês | MEDLINE | ID: mdl-24224917

RESUMO

Interface carrier recombination currently hinders the performance of hybrid organic-silicon heterojunction solar cells for high-efficiency low-cost photovoltaics. Here, we introduce an intermediate 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) layer into hybrid heterojunction solar cells based on silicon nanowires (SiNWs) and conjugate polymer poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS). The highest power conversion efficiency reaches a record 13.01%, which is largely ascribed to the modified organic surface morphology and suppressed saturation current that boost the open-circuit voltage and fill factor. We show that the insertion of TAPC increases the minority carrier lifetime because of an energy offset at the heterojunction interface. Furthermore, X-ray photoemission spectroscopy reveals that TAPC can effectively block the strong oxidation reaction occurring between PEDOT:PSS and silicon, which improves the device characteristics and assurances for reliability. These learnings point toward future directions for versatile interface engineering techniques for the attainment of highly efficient hybrid photovoltaics.

18.
ACS Appl Mater Interfaces ; 5(21): 10614-22, 2013 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-24138603

RESUMO

We demonstrate high-efficiency small-molecule-based white phosphorescent organic light emitting diodes (PHOLEDs) by single-active-layer solution-based processes with the current efficiency of 17.3 cdA(-1) and maximum luminous efficiency of 8.86 lmW(-1) at a current density of 1 mA cm(-2). The small-molecule based emitting layers are codoped with blue and orange phosphorescent dyes. We show that the presence of CsF/Al at cathodes not only improves electron transport in oxadiazole-containing electron transport layers (ETLs), but also facilitates electron injection through the reacted oxadiazole moiety to reduce interface resistance, which results in the enhancement of current efficiency. By selecting oxadiazole-based materials as ETLs with proper electron injection layer (EIL)/cathode structures, the brightness and efficiency of white PHOLEDs are significantly improved.

19.
Small ; 9(18): 3169-82, 2013 Sep 23.
Artigo em Inglês | MEDLINE | ID: mdl-23650082

RESUMO

Photodegradation of organic pollutants in aqueous solution is a promising method for environmental purification. Photocatalysts capable of promoting this reaction are often composed of noble metal nanoparticles deposited on a semiconductor. Unfortunately, the separation of these semiconductor-metal nanopowders from the treated water is very difficult and energy consumptive, so their usefulness in practical applications is limited. Here, a precisely controlled synthesis of a large-scale and highly efficient photocatalyst composed of monolayered Au nanoparticles (AuNPs) chemically bound to vertically aligned ZnO nanorod arrays (ZNA) through a bifunctional surface molecular linker is demonstrated. Thioctic acid with sufficient steric stabilization is used as a molecular linker. High density unaggregated AuNPs bonding on entire surfaces of ZNA are successfully prepared on a conductive film/substrate, allowing easy recovery and reuse of the photocatalysts. Surprisingly, the ZNA-AuNPs heterostructures exhibit a photodegradation rate 8.1 times higher than that recorded for the bare ZNA under UV irradiation. High density AuNPs, dispersed perfectly on the ZNA surfaces, significantly improve the separation of the photogenerated electron-hole pairs, enlarge the reaction space, and consequently enhance the photocatalytic property for degradation of chemical pollutants. Photoelectron, photoluminescence and photoconductive measurements confirm the discussion on the charge carrier separation and photocatalytic experimental data. The demonstrated higher photodegradation rates demonstrated indicate that the ZNA-AuNPs heterostructures are candidates for the next-generation photocatalysts, replacing the conventional slurry photocatalysts.


Assuntos
Ouro/química , Nanopartículas Metálicas/química , Nanotubos/química , Óxido de Zinco/química , Catálise , Fotoquímica/métodos
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