Si3N4的晶体化和ZrN/Si3N4纳米多层膜的超硬效应

研究了Si₃N₄层在ZrN/Si₃N₄纳米多层膜中的晶化现象及其对多层膜微结构与力学性能的影响. 一系列不同Si₃N₄层厚度的ZrN/Si₃N₄纳米多层膜通过反应磁控溅射法制备. 利用X射线衍射仪、高分辨透射电子显微镜和微力学探针表征了多层膜的微结构和力学性能. 结果表明，由于受到ZrN调制层晶体结构的模板作用，溅射条件下以非晶态存在的Si₃N₄层在其厚度小于0.9 nm时被强制晶化为NaCl结构的赝晶体，ZrN/Si₃N₄纳米多层膜形成共格外延生长的柱状晶，并相应地产生硬度升高的超硬效应. Si₃N₄随层厚的进一步增加又转变为非晶态，多层膜的共格生长结构因而受到破坏，其硬度也随之降低.     

Crystallization of amorphous Si3N4 and superhardness effect in HfC/Si3N4 nanomultilayers

HfC/Si₃N₄ nanomultilayers with various thicknesses of Si₃N₄ layer have been prepared by reactive magnetron sputtering. Microstructure and mechanical properties of the multilayers have been investigated. The results show that amorphous Si₃N₄ is forced to crystallize and grow coherently with HfC when the Si₃N₄ layer thickness is less than 0.95 nm, correspondingly the multilayers exhibit strong columnar structure and achieve a significantly enhanced hardness with the maximum of 38.2 GPa. Further increasing Si₃N₄ layer thickness leads to the formation of amorphous Si₃N₄, which blocks the coherent growth of multilayer, and thus the hardness of multilayer decreases quickly.     

Si3N4在h-AlN上的晶体化与AlN/Si3N4纳米多层膜的超硬效应

采用反应磁控溅射法制备了一系列具有不同Si₃N₄层厚度的AlN/Si₃N₄纳米多层膜,利用X射线衍射仪、高分辨透射电子显微镜和微力学探针表征了多层膜的微结构和力学性能.研究了Si₃N₄层在AlN/Si₃N₄纳米多层膜中的晶化现象及其对多层膜生长结构与力学性能的影响.结果表明,在六方纤锌矿结构的晶体AlN调制层的模板作用下,通常溅射条件下以非晶态存在的Si₃N₄层在其厚度小于约1nm时被强制晶化为结构与AlN相同的赝形晶体,AlN/Si₃N₄纳米多层膜形成共格外延生长的结构,相应地,多层膜产生硬度升高的超硬效应.Si₃N₄随层厚的进一步增加又转变为非晶态,多层膜的共格生长结构因而受到破坏,其硬度也随之降低.分析认为,AlN/Si₃N₄纳米多层膜超硬效应的产生与多层膜共格外延生长所形成的拉压交变应力场导致的两调制层模量差的增大有关. 关键词： 3N₄纳米多层膜')" href="#">AlN/Si₃N₄纳米多层膜 外延生长 赝晶体 超硬效应     

Theoretical investigation on the electronic structure, elastic properties, and intrinsic hardness of Si2N2O

According to the density functional theory we systematically study the electronic structure, the mechanical prop- erties and the intrinsic hardness of Si2N2O polymorphs using the first-principles method. The elastic constants of four Si2N2O structures are obtained using the stress-strain method. The mechanical moduli (bulk modulus, Young’s mod- ulus, and shear modulus) are evaluated using the Voigt-Reuss-Hill approach. It is found that the tetragonal Si2N2O exhibits a larger mechanical modulus than the other phases. Some empirical methods are used to calculate the Vickers hardnesses of the Si2N2O structures. We further estimate the Vickers hardnesses of the four Si2N2O crystal structures, suggesting all Si2N2O phases are not the superhard compounds. The results imply that the tetragonal Si2N2O is the hardest phase. The hardness of tetragonal Si2N2O is 31.52 GPa which is close to values of β-Si3N4 and γ-Si3N4.     

Vapour phase formation of amino functionalised Si3N4 surfaces

Self-assembled monolayer (SAM) formation of silanes on SiO₂ surfaces has been extensively studied. However, SAMs formed on silicon nitride (Si₃N₄) substrates have not been explored to the same level as SiO₂, even though they are of technological interest with a view to the chemical modification of microelectromechanical systems (MEMS). Therefore, this article presents the formation and characterisation of 3-aminopropyltrimethoxysilane (APTMS) SAMs on Si₃N₄ substrates from solution phase and vapour phase, compared to the well characterised APTMS SAMs formed on SiO₂ surfaces. Contact angle, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and ellipsometric data indicate the formation of APTMS SAMs (0.55 nm ellipsometric thickness) after 60 min immersion of either SiO₂ or Si₃N₄ substrates in APTMS solution (0.5 mM in EtOH). By comparison Si₃N₄ substrates exposed to APTMS vapour, at 168 mbar for 60 min, result in the formation of the equivalent of a bi or trilayer of APTMS.     

AlN/Si3N4纳米多层膜的外延生长与力学性能

采用射频磁控溅射方法制备单层AlN, Si₃N₄薄膜和不同调制周期的AlN/Si₃N₄纳米多层膜.采用X射线衍射仪、高分辨透射电子显微镜和纳米压痕仪对薄膜进行表征.结果发现,多层膜中Si₃N₄层的晶体结构和多层膜的硬度依赖于Si₃N₄层的厚度.当AlN层厚度为4.0nm、 Si₃N₄层厚度 关键词： 3N₄纳米多层膜')" href="#">AlN/Si₃N₄纳米多层膜 外延生长 应力场 超硬效应     

Spectroscopic ellipsometric characterization of TiAlN/TiAlON/Si3N4 tandem absorber for solar selective applications

Sputter deposited TiAlN/TiAlON/Si₃N₄ tandem absorber has been characterized by spectroscopic ellipsometry in the wavelength range of 450-1200 nm. Each layer of the tandem absorber viz., TiAlN, TiAlON and Si₃N₄ has been deposited separately on copper substrate (Cu) and ellipsometric measurements have been carried out on each of these layers. The measured ellipsometric spectra were fitted with theoretically simulated spectra and the sample structure and wavelength dispersion of optical constants of each layers have been determined. The ellipsometric measurements have also been carried out on the three-layer tandem absorber deposited on Cu substrate. By analyzing the ellipsometric data, depth profiling of the tandem absorber has been carried out using the derived optical constants of the individual layers.     

Investigation of SiO2/Si3N4 films prepared on sapphire by r.f. magnetron reactive sputtering

Sapphire is a desired material for infrared-transmitting windows and domes because of its excellent optical and mechanical properties. However, its thermal shock resistance is limited by loss of compressive strength along the c-axis of the crystal with increasing temperature. In this paper, double layer films of SiO₂/Si₃N₄ were prepared on sapphire (α-Al₂O₃) by radio frequency magnetron reactive sputtering in order to increase both transmission and high temperature mechanical performance of infrared windows of sapphire. Composition and structure of each layer of the films were analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), respectively. Surface morphology and roughness of coated and uncoated sapphire have been measured using a talysurf. Flexural strengths of sapphire sample uncoated and coated with SiO₂/Si₃N₄ have been studied by 3-point bending tests at different temperatures. The results show that SiO₂/Si₃N₄ films can improve the surface morphology and reduce the surface roughness of sapphire substrate. In addition, the designed SiO₂/Si₃N₄ films can increase the transmission of sapphire in mid-wave infrared and strengthen sapphire at high temperatures. Results for 3-point bending tests indicated that the SiO₂/Si₃N₄ films increased the flexural strength of c-axis sapphire by a factor of about 1.4 at 800 °C.     

Preparation, characterization and luminescence properties of porous Si3N4 ceramics with Eu2O3 as sintering additive

Porous Si₃N₄ ceramics with photoluminescence properties were prepared by pressureless sintering using α-Si₃N₄ powder as raw material and Eu₂O₃ as sintering additive. Chemical composition, phase formation, microstructure and photoluminescence properties of porous Si₃N₄ ceramics were studied by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence measurements (PL/PLE). The results show that single Eu₂O₃ additive promotes α→β transformation but not significant densification. A broad band emission center at 570 nm assigned to Eu²⁺ is observed, Eu³⁺ in Eu₂O₃ is (partially) converted to Eu²⁺ by reaction with Si₃N₄, which results in a lower β aspect ratio and β-content compared to the other Ln (Ln=lanthanide) oxide additives.     

Examination of temperature distribution and the thermal effects on Si3N4 engineering ceramics during fibre laser surface treatment

The thermal effects of fibre laser surface treatment on a Si₃N₄ engineering ceramic were studied using a computational finite element analysis (FEA). Temperature increases on the surface of the Si₃N₄ during fibre laser processing were measured using an infra-red thermometer; temperature distributions in the bulk were measured with specifically located thermocouples. A computational model by using FEA was then developed to model the flow and the distribution of the radiated heat resulting from the fibre laser treatment of the Si₃N₄ ceramic. By utilising data obtained from a TG-DSC analysis the FEA model predictions of the temperature distribution were used to map phase transformations and significant events occurring during the fibre laser surface treatment of the Si₃N₄. The TG-DSC analysis also indicated that the fibre laser surface treatment generally resulted in a phase transformation of the Si₃N₄ from α-phase to β-phase modification as elongated rod-like grains were found.     

Radiation damage effects on power VDMOS devices with composite SiO2–Si3N4 films

Total dose effects and single event effects on radiation-hardened power vertical double-diffusion metal oxide semiconductor (VDMOS) devices with composite SiO₂-–Si₃N₄ film gate are investigated. The relationships among the important electrical parameters of the samples with different thickness SiO₂-–Si₃N₄ films, such as threshold voltage, breakdown voltage, and on-state resistance in accumulated dose, are discussed. The total dose experiment results show that the breakdown voltage and the on-state resistance barely change with the accumulated dose. However, the relationships between the threshold voltages of the samples and the accumulated dose are more complex, not only positive drift, but also negative drift. At the end of the total dose experiment, we select the group of samples which have the smaller threshold voltage shift to carry out the single event effect studies. We find that the samples with appropriate thickness ratio SiO₂-–Si₃N₄ films have a good radiation-hardening ability. This method may be useful in solving both the SEGR and the total dose problems with the composite SiO₂-–Si₃N₄ films.     

Observing the effect of water vapor on post-irradiated surface morphology of SiO2 and Si3N4 insulators by atomic force microscopy

In this work, we investigated the effect of water-vapor treatment on the surface morphology of SiO₂ and Si₃N₄ insulators before and after Co⁶⁰ gamma-ray irradiation by using the atomic force microscopy (AFM) operated under non-contact mode. Before irradiation, no apparent surface morphology change was found in SiO₂ samples even they were water vapor treated. However, bright spots were found on post-irradiated water-vapor-treated SiO₂ sample surfaces but not on those without water-vapor treatment. We attributed the bright spots to the negative charge accumulation in the oxide due to charge balancing between hydroxyl (OH⁻) ions adsorbed on SiO₂ surface and electron-hole pairs (ehps) generated during irradiation since they can be annealed out after low temperature annealing process. On the contrary, no bright spots were observed on post-irradiated Si₃N₄ samples with and without water-vapor treatment. This result confirms that Si₃N₄ is a better water-resist passivation layer than SiO₂ layer.     

Evaluation of fracture toughness of ZrO2 and Si3N4 engineering ceramics following CO2 and fibre laser surface treatment

The fracture toughness property (K_1C) of Si₃N₄ and ZrO₂ engineering ceramics was investigated by means of CO₂ and a fibre laser surface treatment. Near surface modifications in the hardness were investigated by employing the Vickers indentation method. Crack lengths and the crack geometry were then measured by using the optical microscopy. A co-ordinate measuring machine was used to investigate the diamond indentations and to measure the lengths of the cracks. Thereafter, computational and analytical methods were employed to determine the K_1C. An increase in the K_1C of both ceramics was found by the CO₂ and the fibre laser surface treatment in comparison to the as-received surfaces. The K_1C of the CO₂ laser radiated surface of the Si₃N₄ was over 3% higher in comparison to that of the fibre laser treated surface. This was by softening of the near surface layer of the Si₃N₄ which comprised of lowering of hardness, which in turn increased the crack resistance. The effects were not similar in ZrO₂ ceramic to that of the Si₃N₄ as the fibre laser radiation in this case had produced an increase of 34% compared to that of the CO₂ laser radiation. This occurred due to propagation of lower crack resulting from the Vickers indentation test during the fibre laser surface treatment which inherently affected the end K_1C through an induced compressive stress layer. The K_1C modification of the two ceramics treated by the CO₂ and the fibre laser was also believed to be influenced by the different laser wavelength and its absorption co-efficient, the beam delivery system as well as the differences in the brightness of the two lasers used.     

Evaluation of Si3N4/Si interface by UV Raman spectroscopy

The stresses at Si₃N₄/Si (1 0 0), (1 1 1) and (1 1 0) interfaces were measured by UV Raman spectroscopy with a 364 nm excitation laser whose penetration depth into the Si substrate was estimated to be 5 nm. The Si₃N₄ films were formed on Si (1 0 0), (1 1 1) and (1 1 0) using nitrogen-hydrogen (NH) radicals produced in microwave-excited high-density Xe/NH₃ mixture plasma. The localized stress detected from Raman peak shift was compressive at the (1 0 0) interface, and tensile at the (1 1 1) and (1 1 0) interfaces. The results showed that stress had strong correlation with the total density of subnitrides at the Si₃N₄/Si interface, and also with the full-width at half-maximum (FWHM) of Si the 2p_3/2 photoemission spectrum arising from the substrate. We believe that the localized stress affected subnitride formation because the amount of subnitride and the FWHM of Si 2p_3/2 decreased while the interface stress shifted in the tensile direction.     

Photoluminescence of (Ba1−xEux)Si6N8O (0.005≤x≤0.2) phosphors

Eu²⁺-doped BaSi₆N₈O phosphors (Ba_1−xEu_xSi₆N₈O, 0.005≤x≤0.2) were synthesized by gas-pressure sintering of the powder mixture of BaCO₃, Si₃N₄, and Eu₂O₃ at 1750 °C under 0.5 MPa N₂. The fired powder consists of a major BaSi₆N₈O phase and a trace amount of impurity phases. The structural result of the BaSi₆N₈O powder, refined by the Rietveld method, agrees well with that of single crystals. A wide blue luminescence band peaking at about 500 nm is observed in BaSi₆N₈O:Eu²⁺, upon excitation with the ultraviolet light of 310 nm. Although Eu is covalently bonded to six nearest neighbor nitrogen atoms, the luminescence of Eu²⁺ is not significantly redshifted but shows a very narrow excitation spectrum at high energies. The origin of the short-wavelength luminescence is mainly ascribed to a small crystal-field splitting as a result of extremely long distances between europium and nitrogen ligands in BaSi₆N₈O:Eu²⁺.     

Photon recycling in Fabry–Perot micro-cavities based on Si3N4 waveguides

We present a numerical analysis and preliminary experimental results on one-dimensional Fabry–Perot micro-cavities in Si₃N₄waveguides. The Fabry–Perot micro-cavities are formed by two distributed Bragg reflectors separated by a straight portion of a waveguide. The Bragg reflectors are composed of a few air slits produced within the Si₃N₄ waveguides. In order to increase the quality factor of the micro-cavities, we have minimized, with a multiparametric optimization tool, the insertion loss of the reflectors by varying the length of their first pairs (those facing the cavity). To explain the simulation results, the coupling of the fundamental waveguide mode with radiative modes in the Fabry–Perot micro-cavities is needed. This effect is described as a recycling of radiative modes in the waveguide. To support the modelling, preliminary experimental results of micro-cavities in Si₃N₄ waveguides realized with the focused ion beam technique are reported.     

Si3N4Si量子点电子结构的理论研究

采用经表面优化的对称球形团簇作Ｓｉ₃Ｎ₄，Ｓｉ晶态量子点的模型，利用紧束缚近似和ｒｅｃｕｒｓｉｏｎ方法研究了它们的电子结构，给出了导带底和价带顶位置随量子点尺寸的变化。得到了３２８原子Ｓｉ₃Ｎ₄量子点、３２３原子Ｓｉ量子点的中心原子局域态密度及平均态密度，并讨论了态密度和光谱结构的关系，中心原子局域态密度能较好地描述量子点的光谱，这一点得到了实验结果的证实。 关键词：     

High power photoconductive switches of 4H SiC with Si3N4 passivation and n -GaN subcontact

The effect of a Si₃N₄ passivation layer on the breakdown voltage in 4H SiC high power photoconductive semiconductor switching devices has been investigated. An n⁺-GaN epitaxial layer was also used for these devices as a subcontact layer, which was between the contact metal and the high resistivity SiC bulk, to improve the ohmic contact and mitigate current spreading: the GaN subcontact layer protects the contact from damage occurring at high power levels. The Si₃N₄ passivation layer was grown by ultrahigh vacuum plasma enhanced chemical vapor deposition. By using the Si₃N₄ passivation, the dark leakage current of the devices was suppressed effectively and decreased by one order of magnitude, and the breakdown voltage of the switching devices was improved significantly from 2.9 to 5 kV without degrading the high photocurrent.     

Si3N4/Si表面Si生长过程的扫描隧道显微镜研究

利用原位扫描隧道显微镜和低能电子衍射分析了Si的纳米颗粒在Si₃N₄/Si(111)和Si₃N₄/Si(100)表面生长过程的结构演变.在生长早期T为350—1075K范围内,Si在两种衬底表面上都形成高密度的三维纳米团簇,这些团簇的大小均在几个纳米范围内,并且在高温退火时保持相当稳定的形状而不相互融合.当生长继续时,Si的晶体小面开始显现.在晶态的Si₃N₄(0001)/S 关键词： 氮化硅 扫描隧道显微镜 纳米颗粒     

Intrinsic photoluminescence properties of amorphous Si3B3N7 ceramic

Amorphous Si₃B₃N₇ ceramic shows intrinsic photoluminescence. Three distinctive emission regions have been observed. Excitation with wavelengths between 254 and 330 nm stimulates intense blue emissions with peak maxima ranging from 447 to 479 nm. Exciting between 315 and 420 nm results in two broad emission peaks; the first in the range between 400 and 440 nm, and the second between 560 and 690 nm. Of these two latter emissions, the one in the violet region dominates in intensity over the other one in the red region, thus a violet color is perceived with the eye via excitation with 330 nm or higher wavelengths. The three distinct intrinsic emissions in the photoluminescence spectrum of amorphous Si₃B₃N₇ ceramic are related to defect centers in three topologically different regions in its structure. Dependence of emission on excitation wavelength is associated with the Red-Edge Effect and can be explained with a reabsorption mechanism at the red excitation edge.