Thermal buckling of cylindrical shell with temperature-dependent material properties : conventional theoretical solution and new numerical method

Even though the thermal buckling behavior of shells has been investigated for many years, until now the thermal buckling problem with temperature-dependent material properties still cannot be solved by the existing commercial finite element codes. Therefore, the conventional theoretical solution of the critical temperature rise of cylindrical shell with the temperature-dependent material properties is first derived in this work. Then, an innovative numerical approach is developed by introducing the bisection method and a user subroutine of ANSYS to overcome the shortcoming of existing finite element codes. The results prove that the temperature-dependent material properties have a great negative influence on the ability of the thermal buckling resistance of the cylindrical shell. As a result, the subroutine of ANSYS developed in this work provides a convenient design method for engineers to avoid the complicated theoretical calculation

Numerical simulation on transverse buckling behavior of submarine pipeline with defects

Local or overall initial geometric defects may inevitably occur in the manufacturing, laying and operation of submarine pipelines. To study the transverse buckling behavior of pipelines with defects laid on the seabed surface, the nonlinear numerical model for transverse thermal buckling of pipelines with 5 kinds of initial geometric defects was established firstly, and then the accuracy of the finite element model was verified. The influence of defect types and nonstraightness on the transverse buckling behavior of pipelines was emphatically analyzed. The results show that the transverse buckling deformation poses a great threat to the safe operation of submarine pipelines. The greater the nonstraightness, the smaller the critical temperature rise will be, and the more prone the pipelines will be to the transverse thermal buckling. Under the condition of the same nonstraightness, the smaller the absolute value of curvature at the center of the initial geometric defect of the pipeline, the stronger the transverse thermal buckling resistance will be. Finally, based on the dimensionless analysis method, the general expression was proposed for calculating the critical temperature rise of submarine pipelines with various common initial geometric defects, and it is anticipated to provide a reference for the thermal buckling design of submarine pipelines

Significant Improvement of SiO 2 /4H-SiC Interface Properties by Electron Cyclotron Resonance Nitrogen Plasma Irradiation

The effect of the insertion of a SiN film on the SiO 2 /4H-SiC interface properties was studied. The SiN interlayer was grown using electron cyclotron resonance (ECR) nitrogen plasma irradiation prior to the SiO 2 deposition. It was found that the insertion of a SiN interlayer led to a significant decrease in interface-state and fixed-charge densities in a SiO 2 /4H-SiC gate stack. This insertion also induced elimination of the near-interface traps in the oxide. It was clarified from X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry analyses that Si dangling bonds were terminated by nitrogen, and the SiN interlayer effectively suppressed the formation of carbon generated by the thermal reaction between SiC and O atoms. So far, 4H-SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) have still not been realized for commercial applications because of serious degradation of channel mobility, which is mainly attributed to the unacceptably high density of interfacial traps near the conduction-band edge (E C ) of 4H-SiC. Both experiments 1-9 and recent theoretical simulations 1-3 Unfortunately, these gases simultaneously introduce oxygen; consequently, a C-containing transition layer is inevitably formed near the SiO 2 /4H-SiC interface, 3 which limits the efficiency of N 2 O or NO passivation. Thus, the typical channel mobility of the 4H-SiC n-channel MOSFET is limited to a value of approximately 40 cm 2 /Vs despite N 2 O or NO passivation. 1, 2 Obviously this value is much lower than the bulk mobility and still insufficient for practical application. An effective way to suppress the interfacial transition layer formed during oxidation is the deposition of a gate dielectric on 4H-SiC. 7 As pointed out in the report by Noborio et al., Our group has established a method for growing a SiN layer on a Si substrate using electron cyclotron resonance (ECR) nitrogen plasma irradiation. 12 This method enables us to fabricate a near-stoichiometric SiN layer, which can be expected to have the potential to passivate a surface of 4H-SiC. In this work, ECR nitrogen plasma irradiation was employed for the formation of a SiN layer on 4H-SiC. A significant improvement of SiO 2 /4H-SiC interface properties was demonstrated by the insertion of a SiN interlayer (IL). The passivation mechanism of interfacial defects by nitrogen was clarified by low-temperature capacitance-voltage (C-V) measurements, X-ray photoelectron spectroscopy (XPS) analyses, and time-of-flight secondary ion mass spectrometry (TOF-SIMS). z E-mail: [email protected] Experimental The substrate used in this study was an n-type epitaxial wafer, which consisted of a 4 • off-axis 4H-SiC (0001) film with a thickness of 3.5 μm, a donor concentration of 1 × 10 16 cm −3 and a highly doped n-type 4H-SiC substrate. Metal-oxide-semiconductor (MOS) capacitors were fabricated using the following procedures. After a standard cleaning with a final 2% HF dip, the gate dielectric on 4H-SiC was fabricated through two steps without breaking the vacuum; namely, the ECR nitrogen plasma irradiation and subsequent ECR-SiO 2 sputter deposition at room temperature. A detailed description of the ECR system is given elsewhere. 13 ECR nitrogen plasma irradiation was performed for 30 min, resulting in the growth of a SiN film with a thickness of approximately 3 nm, which was confirmed from ellipsometry measurements. Here, the microwave power for ECR plasma generation was 250 W, and the Ar and N 2 flow rates were 10 and 15 sccm, respectively, which were the same as the optimal conditions for growing near-stoichiometric SiN film on a Si substrate. 12 Subsequently, a SiO 2 film with a thickness of approximately 50 nm was deposited on SiN-grown 4H-SiC, where the microwave and radio frequency powers were 300 W, and the Ar and O 2 flow rates were 16 and 8 sccm, respectively. Then, postdeposition annealing (PDA) was done at 1200 • C for 120 min in N 2 , which is required to improve the interface quality. • C for 4 h, resulting in a thickness of approximately 50 nm. Both types of gate dielectric were also treated by the same PDA like for the sample with a SiN interlayer. Finally, Al films were evaporated and patterned to form gate electrodes with a diameter of 600 μm, and an InGa alloy was rubbed onto the backside for ohmic contact formation. The structure and composition of gate dielectrics were analyzed by XPS and TOF-SIMS, and the electrical properties of MOS capacitors were evaluated by high-frequency (HF: 1 MHz) and quasistatic (QS) C-V measurements. Results and Discussion Electrical properties of 4H-SiC MOS capacitors without and with SiN IL.

An Omnidirectional Dual-Functional Metasurface with Ultrathin Thickness

Although metasurfaces have received enormous attention and are widely applied in various fields, the realization of multiple functions using a single metasurface is still rarely reported to date. In this work, we propose a novel dual-functional metasurface that can be applied as a mid-infrared narrowband thermal light source in optical gas sensing and a long-wave infrared broadband absorber in photodetection. By actively tailoring the structure and constituent materials of the metasurface, the device yields an absorptivity of over 90% from 8 µm to 14 µm, while it exhibits an emissivity of 97.4% at the center wavelength of 3.56 μm with a full width at half-maximum of 0.41 µm. Notably, the metasurface is insensitive to the incident angle under both TM- and TE-polarized light. The proposed dual-functional metasurface possesses many advantages, including a simple structure, thin thickness, angle and polarization insensitivity, and compatibility with optical devices, which are expected to simplify the existing imaging systems and improve the performance of photodetection equipment

Simultaneous field enhancement and loss inhibition based on surface plasmon polariton mode hybridization

In common plasmonic configurations, energy loss and field enhancement are mutually restricted. In a vast majority of cases, high confinement goes together with high loss, which is a serious limitation for some applications. In an attempt of breaking this rule, which holds true for surface plasmon polariton (SPP) resonators, a multilayer trench grating microstructure with an asymmetric waveguide is considered. It supports both Fabry-Perot (FP) and cavity modes, whose hybridization exhibits unusual properties. The electric field enhancement was modulated by regulating the corresponding absorption and radiation quality factors. At the same time, energy loss was reduced, which is fundamentally ascribed to the mutual recycling of radiation energy between FP and cavity resonators. The maximum total quality factor and strongest field enhancement were both observed at the vicinity of quasi-static limit, thereby signifying that the structure exhibited simultaneous optimizations of field enhancement and loss inhibition, which is crucial to the design of high-quality SPP-based devices