Micro and Nanostructures最新文献

Microelectromechanical systems (MEMS) that utilize graphene-based materials have gained significant attention for gas-sensing applications owing to their unique properties. Graphene is a two-dimensional sheet of carbon atoms arranged in a hexagonal lattice that exhibits exceptional mechanical strength, high electrical conductivity, and large surface area. These properties make graphene an ideal candidate for gas sensing applications. In this study, we examined the fundamental characteristics of graphene, with emphasis on its practical use in sensors. We explored the latest techniques for synthesizing graphene, highlighting the importance of continual advancements in these manufacturing processes which are crucial for bringing graphene-based products to the market. We present various examples of how graphene is employed in MEMS for mass/gas sensing applications and discuss the advantages and challenges associated with devices using these materials. For successful incorporation of these materials into MEMS systems, it is essential to establish effective designs and integration processes that yield high results. Additionally, this analysis delves into the latest developments in graphene-based solid-state and movable MEMS devices, highlighting their promising gas-sensing applications.

In this work, we propose a promising source engineered Double - Gate (DG) Tunnel Field Effect Transistor (TFET) device capable of providing remarkably low value of Subthreshold Swing (SS) with sufficiently high drive current. Using Sentaurus TCAD simulations, we demonstrate that counter-doped horizontal pockets (doping of pocket is kept opposite to that of source) when placed in the source region introduces a built-in band bending at the source-pocket junction. This lowers the minima of Conduction Band (CB) in pocket region thereby reducing the barrier width as the pocket CB moves closer to source Valence Band (VB). As a result, stronger electric field is observed thereby reducing the threshold voltage (onset of band-to-band tunneling (BTBT)) and subsequent reduction in subthreshold swing. To boost the ON-current and suppress ambipolarity, high-k dielectric material along with low work-function gate material is introduced at source side and low-k gate dielectric along with high work-function gate material is introduced at drain side. Compared to point tunneling in conventional TFETs, the gate overlapped pockets in the proposed structure result in an increase in cross-section area available for BTBT thereby leading to line tunneling of carriers from the source to the pocket, resulting in higher ON-current. In this work, we discuss the role of source engineering in boosting the performance of Hetero-Dielectric (HD) Dual-Metal-Double-Gate (DMDG) TFET. We provide design guidelines to achieve steeper subthreshold swing while considering pocket doping and pocket thickness as the key parameters. A comparative study of conventional DG-TFET and HD-DG-TFET with the proposed Gate-over-Pockets (GoP) HD-DMDG-TFET structure is done. When compared to the conventional DG-TFET with same geometrical parameters, the proposed structure provides $\sim 33\times$ steeper SS, more than two order improved ON-current, two order lower ambipolar current and 133 folds better I_on/I_off thus becomes the perfect choice for low power applications.

The discovery of effective photocatalytic substances is crucial in reducing energy shortages and ecological contamination. This research involves creating SiC/PtSe₂ van der Waals heterostructure with both SiC and PtSe₂ monolayers, employing first-principles calculations for comprehensive theoretical analysis of their structural stability, electronic characteristics, optical features, Bader charge, and solar-to-hydrogen (STH) efficiency. Findings indicate that the SiC/PtSe₂ heterostructure is a semiconductor with an indirect bandgap of 1.52 eV and a direct Z-scheme charge transfer path, facilitating more efficient segregation of photogenerated electron-hole pairs. The Bader charge indicates that the SiC layer accumulates positive charges and the PtSe₂ layer accumulates negative charges, constituting a built-in electric field pointing from the SiC side to the PtSe₂ side at the interface region, which can impede the complexation of the photogenerated electron-hole pairs. Furthermore, the SiC/PtSe₂ heterostructure exhibits excellent optical absorption properties across both the ultraviolet and visible spectra, coupled with an exceptionally high STH efficiency of 34.7 %, significantly enhancing solar energy utilization. Ultimately, the Gibbs free energy calculations reveal the significant catalytic efficiency of the SiC/PtSe₂ heterostructure for redox reactions. Based on these results, the SiC/PtSe₂ heterostructure is a direct Z-scheme photocatalyst for overall water splitting.

Nanoscale phase change films of (MoTe₂)_xSb_1-x were prepared using magnetron sputtering technique. The investigation focused on the influence of the presence of MoTe₂ on the phase change characteristics of Sb materials as well as the electrical properties of devices. (MoTe₂)_xSb_1-x phase change films showed good thermal stability, especially for (MoTe₂)_0.08Sb_0.92 films. (MoTe₂)_xSb_1-x films had higher phase change temperature (∼185 °C), larger crystallization activation energy (∼4.0 eV), smaller resistance drift index (∼0.03582), and wider band gap (0.629 eV) than pure Sb films, indicating better thermal stability. According to X-Ray Diffraction and Atomic Force Microscope, it could be found that doping MoTe₂ in Sb could inhibit the grain growth and make the surface of Sb film flatter. According to the outcomes stemming from X-ray photoelectron spectroscopy, some bonds involving Mo–Te and Sb–Sb underwent breakage and actively contributed to the formation process of other chemical bonds at the interface. The formation of small Sb₂Te₃ and Sb grains in the as-deposited state played a role in inducing crystallization and accelerating phase transition. The band gap in (MoTe₂)_xSb_1-x films augmented with the increase of MoTe₂ content. The power consumption of the (MoTe₂)_0.08Sb_0.92-based phase-change memory device was considerably reduced compared to GST film and could achieve ultra-fast resistance transition within 10 ns. The results showed that (MoTe₂)_xSb_1-x phase change films have the advantages of high stability, low power consumption, and rapid speed, which is a potential choice for phase change memory.

In this study, we utilize Nextnano device simulation software to systematically investigate the dependence of 2-DEG (two-dimensional electron gas) density on the barrier and spacer Layers in InAlN/GaN high electron mobility transistors (HEMTs). By simulating a range of barrier thicknesses, In mole fractions, and spacer layer thicknesses, we reveal the intricate ways in which these parameters influence device performance. Our simulations demonstrate that precise control of the InAlN barrier thickness and In mole fraction, along with the AlN spacer thickness, is crucial for optimizing 2DEG density and, consequently, the overall electrical properties of the HEMTs. Notably, our results highlight that an InAlN barrier thickness below 12 nm, coupled with an optimized In mole fraction and a finely tuned AlN spacer thickness close to 1 nm, significantly enhances 2DEG density without compromising mobility. These insights provide a detailed understanding of the material and structural dependencies critical for the design and development of high-performance InAlN/GaN HEMTs. Our study includes detailed calculations of the device's I–V characteristics. Notably, the highest peak output current is observed at a 1 nm AlN spacer thickness, reaching 0.91 A/mm. Our findings highlight a noteworthy agreement between the results derived from our computational simulations and experimental measurements.

A double hexagonal single ‘S’ metamaterial (DHSSM), exhibiting plasmon-induced transparency (PIT) in its spectral response is studied in this paper. Amplitude modulation of the PIT window is achieved by varying the azimuth angle of substructure ‘S’. Theoretical investigations into the PIT effect are conducted through numerical simulations. Moreover, an equivalent coupling circuit and Lorentz model are constructed to elucidate the PIT modulation mechanism. The results reveal that the PIT physical mechanism of the DHSSM has originated in destructive interference between bright-bright modes, which is directly excited by terahertz waves on the double hexagonal split rings and the ‘S’ substructure. For slow optical propagation performance, the structure has a high group delay (up to 41.92 ps) while allowing for the adjustment of the transparency window amplitude. The proposed metamaterial holds promising prospects for applications in slow light devices, switches, and filters within the terahertz frequency range.

Based on the effective mass approximation and the compact density matrix theory, the electronic states and optical absorption properties of intersubband transitions between the conduction-band energy levels in zinc blende InGaN/GaN/InGaN/GaN core-shell quantum dots (CSQDs) are investigated by using the finite difference method. The effects of hydrogen-like impurity and In component on the wave functions, transition energies, and optical absorption properties are discussed in detail. The results show that hydrogen-like impurity can cause the peak positions of optical absorption coefficients (OACs) and refractive index changes (RICs) to move to high energy area, and the peak values of OACs rise. Increasing In component of InGaN crystal in the core region of a CSQD has the same effect. But an opposite tendency will be found when increasing In component in the shell-well of a CSQD, i.e. optical absorption peaks move to low energy area and their values decrease. Comparing to the shell-well, the core region has more powerful confinement effect on electrons. So the better absorption properties are more likely to be obtained for this type of multi-layer InGaN/GaN CSQDs when In component in the core is larger than that in the shell-well.

Face–centered cubic–Bi₂O₃ (δ–phase), a high–ion conductor, is an essential solid electrolyte option, particularly for low–low–temperature SOFC applications. It is widely accepted that δ–Bi₂O₃ exhibits higher conductivity than the YSZ electrolytes typically utilized in HT–SOFC units. The present study investigates the structural, thermal, surface, and conductivity characteristics of the Bi₂O₃ electrolytes co–doped with Tb–Sm–Gd rare earth. The XRD data indicate that, except composition 20Tb20Sm20Gd, all compositions are stabilized with the cubic δ–phase at room temperature. The estimated lattice constants additionally suggest lattice contraction, confirming that the partial cation substitutes between host Bi³⁺ and rare earth cations are successful. The DTA curves do not have any endothermic or exothermic peaks, indicating a possible phase transition. Arrhenius plots prove that DC conductivity decreases as the dopant ratio increases, implying a drop in polarization power. The highest conductivity is found to be 0.131 S/cm for the composition 10Tb10Sm10Gd.

To avoid Shockley-Queisser limit in single p-n junctions, tandem solar cells were proposed. A new tandem cell is simulated here using the 1-dimensional SCAPS. The new cell combines two reported single solar cells together, aiming at achieving high performance by optimizing various layer characteristics. The bottom sub-cell is Mo/Si(p)/CZTSSe(p)/CdS(n)/ZnO(i)/ZnO(Al), where ZnO is an electrodeposited transparent-conductor oxide, with high UV transmittance, ZnO(i) is intrinsic layer, CZTSSe/Si is bi-absorber layer of p-CuZnSnSSe and p-Si, Mo is back contact. The optimized sub-cell exhibits a high fill factor of 85.18 % with overall efficiency 20 %. Based on literature, a perovskite CsPbI₂Br layer is included in the top sub-cell Cu₂O(HTL)/CsPbI₂Br)/TiO₂(ETL), where Cu₂O is a hole-transport layer and TiO₂ is electron-transport layer. The top sub-cell layers have been carefully selected for best alignment. Matching and optimizing various parameters in the two sub-cells is a simulation challenge. Therefore, layers in the two sub-cells have been studied separately, keeping in mind the proper combinations between various layers. With optimized layer thicknesses and band gaps, together with proper alignment of band edges, the proposed tandem solar cell exhibits high characteristics of 80 % fill factor and higher than 32 % overall efficiency.

Owing to the fact that the gate-all-around architecture is expected to prevail in the upcoming technology nodes, in this work we have taken up a simulation-based investigation on design of a gate-all-around junctionless transistor (GAA-JLT) based label-free gas sensor with conducting polymer (CP) gate. In the initial part of our work we have focused on the variation n device and sensor performance with initial work function of the CP, which depends upon its growth condition and primary doping. Interaction with various test gases modifies the CP characteristics, thereby changing its work function. Due to this a change in device characteristics is observed, which serves as the metric for assessing the GAA-JLT-based gas sensor performance. We have investigated the variation in device characteristics in the presence of different test gases. Further, the variation in sensor performance on interaction with the different test gases has been examined. The impact of operating conditions such as ambient temperature and partial pressure of the test gas on the sensing performance has been investigated. The impact of device dimension on the sensing performance has also been evaluated. Our computations reflect that tuning the initial work function of the CP by choosing the proper primary dopant concentration model along with proper tuning of the operating conditions can enhance the performance accuracy of the sensor.