Observation of Near-Field Thermal Radiation between Coplanar Nanodevices with Subwavelength Dimensions.

With the continuous advancement of nanotechnology, nanodevices have become crucial components in computing, sensing, and energy conversion applications. The structures of nanodevices typically possess subwavelength dimensions and separations, which pose significant challenges for understanding energy transport phenomena in nanodevices. Here, on the basis of a judiciously designed thermal photonic nanodevice, we report the first measurement of near-field energy transport between two coplanar subwavelength structures over temperature bias up to ∼190 K. Our experimental results demonstrate a 20-fold enhancement in energy transfer beyond blackbody radiation. In contrast with the well-established near-field interactions between two semi-infinite bodies, the subwavelength confinements in nanodevices lead to increased polariton scattering and reduction of supporting photonic modes and, therefore, a lower energy flow at a given separation. Our work unveils exciting opportunities for the rational design of nanodevices, particularly for coplanar near-field energy transport, with important implications for the development of efficient nanodevices for energy harvesting and thermal management.

Nanoporous Silicon Thin Film-Based Hydrogen Sensor Using Metal-Assisted Chemical Etching with Annealed Palladium Nanoparticles.

This article reports a nanoporous silicon (Si) thin-film-based high-performance and low-power hydrogen (H2) sensor fabricated by metal-assisted chemical etching (MaCE). The nanoporous Si thin film treated with Pd-based MaCE showed improvement over a flat Si thin film sensor in H2 response (ΔI/I0 = 4.36% → 12.4% for 0.1% H2). Furthermore, it was verified that the combination of thermal annealing of Pd and subsequent MaCE on the Si thin film synergistically enhances the H2 sensitivity of the sensor by 65 times as compared to the flat Si thin film sensor (ΔI/I0 = 4.36% → 285% for 0.1% H2). This sensor also showed a very low operating power of 1.62 µW. After the thermal treatment, densely packed Pd nanoparticles agglomerate due to dewetting, which results in a higher surface-to-volume ratio by well-defined etched holes, leading to an increase in sensor response.

Buffered Oxide Etchant Post-Treatment of a Silicon Nanofilm for Low-Cost and Performance-Enhanced Chemical Sensors.

The high surface-to-volume ratio of nanostructured materials is the key factor for excellent performance when applied to chemical sensors. In order to achieve this by a facile and low-cost fabrication strategy, buffered oxide etchant (BOE) treatment of a silicon (Si)-based sensor was proposed. An n+-n--n+ Si nanofilm structure was treated with a BOE, and palladium nanoparticles (PdNPs) were coated on the n-type Si channel surface via short-time electron beam evaporation to enable a highly sensitive and selective sensing of hydrogen (H2) gas. The BOE treatment effect on lightly doped n-type Si was investigated, and the surface morphology of the etched Si was analyzed. Furthermore, the H2 sensing characterization of PdNP-decorated Si devices with various BOE treatment times was systematically evaluated at room temperature. The results revealed that the surface of n-type Si is roughened by BOE treatment, which can further enhance the H2-sensing performance of Pd-decorated Si. The elaborate study on the BOE-post-treated Si H2 sensor showed that the performance enhancement was stable. The BOE treatment strategy was also applied to the nanopatterned Si sensors, which induced a clear performance enhancement for the H2 sensing.

Half-Pipe Palladium Nanotube-Based Hydrogen Sensor Using a Suspended Nanofiber Scaffold.

A half-pipe palladium nanotube network (H-PdNTN) structure was developed for high-performance hydrogen (H2) sensor applications. To fabricate the sensor, suspended poly(vinyl alcohol) (PVA) nanofiber bundles were electrospun on a conductive substrate, followed by a palladium (Pd) deposition on top of the PVA nanofiber bundles. Then, Pd-deposited PVA nanofibers were transferred to a host substrate, and the PVA nanofiber templates were selectively removed. Various material analyses confirmed that the PVA nanofibers were successfully dissolved leaving a half-pipe-shaped Pd nanotube network. The fabricated Pd nanotube-based sensors were tested for H2 responses with different gas concentrations. The 4 nm thick sensor showed the highest response (Δ R/ R0) to H2 gas. Platinum (Pt) decoration of the sensor showed an improved response speed compared to that of the pristine sensor via the catalytic function of Pt. Additionally, the sensor exhibited good H2 selectivity against other interfering gases. The H-PdNTN H2 sensor provides a facile and cost-effective way to fabricate high-performance H2 sensors.

Mathematical analysis of the effects of valvular regurgitation on the pumping efficacy of continuous and pulsatile left ventricular assist devices.

BACKGROUND: A left ventricular assist device (LVAD) is normally contraindicated in significant aortic regurgitation (AR) and requires intraoperative valve repair or exclusion. Nevertheless, AR can coexist with an LVAD, so a valid question when asked might still be of clinical significance. The purpose of this study is to analyze the effects of valve regurgitation on the pumping efficacy of continuous and pulsatile LVADs with a computational method. METHODS: A cardiovascular model was developed based on the Windkessel model, which reflects the hemodynamic flow resistance and the blood wall elasticity. Using the Windkessel model, important cardiovascular components, such as the right atrium, right ventricle, pulmonary artery, pulmonary vein, left atrium (LA), left ventricle (LV), aorta, and branching blood vessels, were expressed. RESULTS: In the case of AR, continuous and pulsatile LVADs improved cardiac output and reduced mechanical load slightly. In the case of mitral regurgitation, the LVADs improved cardiac output (cardiac outputs were about 5 L/min regardless of the severity of regurgitation) and reduced afterload significantly. CONCLUSION: AR reduced both continuous and pulsatile LVAD function significantly while mitral regurgitation did not affect their pumping efficacy.