Synthesis,formation mechanism and electric property of hollow InP nanospheres

The present work reports on novel four-layer thermally driven piezoresistive cantilevers implemented in one- and two-dimensional arrays for parallel proximity scanning. There, the heater (metallic meander), the piezoresistive deflection sensor, and the metal actuation film with significantly higher thermal expansion coefficient make up separate layers. Actuation efficiency and cross-talk of the novel cantilever design are studied and compared with two recent designs: thin metallic film and ion-implanted heater. The novel actuator, integrated on a 240 μm long and 3 μm thick silicon cantilever and supplied by V _dc=1 V enables deflections up to 5 μm of the AFM-tip with an actuation efficiency of about 170 nm/mW and suppressed cross-talk between actuator and sensor.     

Scanning probe oxidation of Si3N4 masks for nanoscale lithography,micromachining, and selective epitaxial growth on silicon

For studying the physical, chemical, and electronic properties of ultrasmall man-made structures, the major challenge is to fabricate highly uniform structures and control their positions on the nanometer length scale. Local oxidation of metals and semiconductors using a conductive-probe atomic force microscope (AFM) or other scanning probe microscopes in air at room temperature has emerged as a simple and universal method for this purpose. Here the uses of scanning probe oxidation of Si₃N₄ masks for performing nanolithography, nanomachining, and nanoscale epitaxial growth on silicon are reviewed. The three most unique features of this approach are presented: (1) exceptionally fast oxidation kinetics using silicon nitride masks (∼30 μm/s at 10 V for a ∼5-nm-thick film); (2) selective-area anisotropic etching of Si using a Si₃N₄ etch mask; and (3) selective-area chemical vapor deposition of Si using a SiO₂/Si₃N₄ bilayer growth mask.     

Ti-Si-N复合膜的界面相研究

为了揭示Ti_Si_N复合膜中Si₃N₄界面相的存在方式及其对薄膜力学 性能的影响 ，采用x射线衍射仪、高分辨透射电子显微镜、俄歇电子能谱仪和显微硬度仪对比研究了磁 控溅射Ti_Si_N复合膜和TiN/Si₃N₄多层膜的微结构和力学性能. 实 验结果表明 ，Ti_Si_N复合膜均形成了Si₃N₄界面相包裹TiN纳米晶粒的微结构. 其中低Si 含量的Ti_Si_N复合膜中Si₃N₄界面相的厚度小于1nm，且以晶体态 存在，薄膜 呈现高硬度. 而高Si含量的Ti_Si_N复合膜中的Si₃N₄界面相以非晶 态存在，薄 膜的硬度也相应降低. 显然，Ti_Si_N复合膜中Si₃N₄界面相以晶体 态形式存在 是薄膜获得高硬度的重要微结构特征，其强化机制可能与多层膜的超硬效应是相同的. 关键词： Ti－Si－N复合膜 界面相 微结构 超硬效应     

氮化硅薄膜的微结构

利用TEM,STM和PDS显微光度计研究了ECR-PECVD技术制备的Si₃N₄薄膜的微结构.结果表明：在较低沉积温度下，ECR-PECVD制备的Si₃N₄薄膜是一种纳米α-Si₃N₄薄膜，其晶粒粒度在14—29nm间，而且这种薄膜具有较好的表面平整度.初步分析了ECR-PECVD制备的Si₃N₄在较低沉积温度下形成晶态薄膜的机理. 关键词：     

Solid-state NMR investigations of Si-29 and N-15 enriched silicon nitride

We compare ²⁹Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectra from the two modifications of silicon nitride, α-Si₃N₄ and β-Si₃N₄, with that of a fully (²⁹Si, ¹⁵N)-enriched sample ²⁹Si₃¹⁵N₄, as well as ¹⁵N NMR spectra of Si₃¹⁵N₄ (having ²⁹Si at natural abundance) and ²⁹Si₃¹⁵N₄. We show that the ¹⁵N NMR peak-widths from the latter are dominated by J(²⁹Si–¹⁵N) through-bond interactions, leading to significantly broader NMR signals compared to those of Si₃¹⁵N₄. By fitting calculated ²⁹Si NMR spectra to experimental ones, we obtained an estimated coupling constant J(²⁹Si–¹⁵N) of 20 Hz. We provide ²⁹Si spin-lattice (T₁) relaxation data for the ²⁹Si₃¹⁵N₄ sample and chemical shift anisotropy results for the ²⁹Si site of β-Si₃N₄. Various factors potentially contributing to the ²⁹Si and ¹⁵N NMR peak-widths of the various silicon nitride specimens are discussed. We also provide powder X-ray diffraction (XRD) and mass spectrometry data of the samples.     

ECR-PECVD制备Si3N4薄膜的光学特性研究

本文研究了ECR-PECVD制备的Si₃N₄薄膜的光学特性.得到的Si₃N₄薄膜具有光致发光效应,在280℃沉积制备的Si₃N₄薄膜的光致发光波长为400nm,具有较好的单色性.测试分析了Si₃N₄薄膜对可见光、红外光具有较高的透射性能,Si₃N₄薄膜可作为红外光的增速减反射膜.     

Electrical characteristics of metal-dielectric-semiconductor structures with silicon nitride prepared by reactive cathode atomization

The effect of the technology of preparation of silicon nitride in a low temperature gas discharge plasma upon the volt-ampere and volt-farad characteristics of metal-dielectricsemiconductor (MDS) structures (Al-Si₃N₄-Si-Al) is studied. It is shown that by using a heterogeneous Si₃N₄ formation reaction with ionic purification of the silicon surface, it is possible to obtain MDS structures with lower and more stable surface charge in comparison to similar structures in which the Si₃N₄ is grown by other methods (for example, gas transport reaction methods). The conductivity of the Si₃N₄ film is described approximately by the well known Frankel model, and its value is close to that of Si₃N₄ films prepared by other methods.     

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.     

Long silicon nitride nanowires synthesized in a simple route

Long silicon nitride (Si₃N₄) nanowires with high purity were synthesized by heating mixtures of SiO₂ powders and short carbon fibers at 1430°C for 2 h in a flowing N₂ atmosphere. The nanowires had the length of 1–2 millimeters and the diameters of 70–300 nm, and were mainly composed of ⍺-Si₃N₄, growing along the [001] direction. The vapor–solid (VS) mechanism was employed to interpret the nanowires growth.     

Radiation response of strained Si---SiO2 layered system

In the presented paper radiation effects in silicon-silicon dioxide systems in the presence of additional tensile and compressive stresses were investigated. These stresses were produced by placing additional layers of SiO₂ or Si₃N₄ on the back side of oxidized silicon wafers.The results obtained indicate that relaxation takes place in the oxide during irradiation and leads to the decrease of the compressive stress in the oxide film. Relaxation of strained bonds causes defect generation and the increase of the oxide charge density. This increase is larger for oxides with higher level of compressive stress. No significant changes of the density of surface states were observed since the additional coatings did not affect the strain gradient in the SiO₂.     

Fluoride-doped MWCNT/Si3N4 composite with improved mechanical and structural properties

The addition of carbon nanotubes (CNT) in ceramic composites has stimulated a substantial interest due to their high mechanical, thermal and electrical properties. This approach used fluoride additives (AlF₃ and MgF₂) to prepare multi-walled carbon nanotubes/silicon nitride (MWCNT/Si₃N₄) composite densified at 1700 °C for 1 h by hot press (HP) sintering. The microstructural analyses of MWCNT/Si₃N₄ composites indicate that the fluoride additives have substantially improved densification and the transformation of α-Si₃N₄ to β-Si₃N₄. As observed, the mechanical properties, i.e. flexural strength, fracture toughness, Young's modulus and hardness of MWCNT/Si₃N₄ composites are improved with an increasing concentration of MWCNT. These results attributed to the highly dense composites, strong interfacial interaction and the pull-out mechanism of MWCNT and β-Si₃N₄. The maximum values of fracture toughness flexural strength, Young's modulus, and hardness were 12.76 ± 1.15 MPa.m^0.5, 883 ±46 MPa, 260 ±9 GPa, and 26.4 ± 1.3 GPa, respectively. The improved mechanical properties also ascribed to the synergistic strengthening and toughening influence of MWCNT and β-Si₃N₄.     

Influence of SiNx:H film properties according to gas mixture ratios for crystalline silicon solar cells

The Hydrogenated silicon nitride (SiN_x:H) using plasma enhanced chemical vapor deposition is widely used in photovoltaic industry as an antireflection coating and passivation layer. In the high temperature firing process, the SiN_x:H film should not change the properties for its use as high quality surface layer in crystalline silicon solar cells. For optimizing surface layer in crystalline silicon solar cells, by varying gas mixture ratios (SiH₄ + NH₃ + N₂, SiH₄ + NH₃, SiH₄ + N₂), the hydrogenated silicon nitride films were analyzed for its antireflection and surface passivation (electrical and chemical) properties. The film deposited with the gas mixture of SiH₄ + NH₃ + N₂ showed the best properties in before and after firing process conditions.The single crystalline silicon solar cells fabricated according to optimized gas mixture condition (SiH₄ + NH₃ + N₂) on large area substrate of size 156 mm × 156 mm (Pseudo square) was found to have the conversion efficiency as high as 17.2%. The reason for the high efficiency using SiH₄ + NH₃ + N₂ is because of the good optical transmittance and passivation properties. Optimized hydrogenated silicon nitride surface layer and high efficiency crystalline silicon solar cells fabrication sequence has also been explained in this study.     

Irradiation of amorphous Ta<Subscript>42</Subscript>Si<Subscript>13</Subscript>N<Subscript>45</Subscript> film with a femtosecond laser pulse

Films of 260 nm thickness, with atomic composition Ta₄₂Si₁₃N₄₅, on 4″ silicon wafers, have been irradiated in air with single laser pulses of 200 femtoseconds duration and 800 nm wave length. As sputter-deposited, the films are structurally amorphous. A laterally truncated Gaussian beam with a near-uniform fluence of ∼0.6 J/cm² incident normally on such a film ablates 23 nm of the film. Cross-sectional transmission electron micrographs show that the surface of the remaining film is smooth and flat on a long-range scale, but contains densely distributed sharp nanoprotrusions that sometimes surpass the height of the original surface. Dark field micrographs of the remaining material show no nanograins. Neither does glancing angle X-ray diffraction with a beam illuminating many diffraction spots. By all evidence, the remaining film remains amorphous after the pulsed femtosecond irradiation.     

Nanostructuring Si surface and Si/SiO2 interface using porous-alumina-on-Si template technology. Electrical characterization of Si/SiO2 interface

In this work, anodic porous alumina thin films with pores in the nanometer range are grown on silicon by electrochemistry and are used as masking material for the nanopatterning of the silicon substrate. The pore diameter and density are controlled by the electrochemical process. Through the pores of the alumina film chemical oxidation of the silicon substrate is performed, leading to the formation of regular arrays of well-separated stoichiometric silicon dioxide nanodots on silicon, with a density following the alumina pores density and a diameter adjustable by adjusting the chemical oxidation time. The alumina film is dissolved chemically after the SiO₂ nanodots growth, revealing the arrays of silicon dioxide dots on silicon. In a next step, the nanodots are also removed, leaving a nanopatterned bare silicon surface with regular arrays of nanopits at the footprint of each nanodot. This silicon surface structuring finds interesting applications in nanoelectronics. One such application is in silicon nanocrystals memories, where the structuring of the oxidized silicon surface leads to the growth of discrete silicon nanocrystals of uniform size. In this work, we examine the electrical quality of the Si/SiO₂ interface of a nanostructured oxidized silicon surface fabricated as above and we find that it is appropriate for electronic applications (an interface trap density below 1–3×10¹⁰ eV⁻¹ cm⁻² is obtained, indicative of the high quality of the thermal silicon oxide).     

Effects of an AlN passivation layer on the microstructure and electronic properties of AlGaN/GaN heterostructures

Effects of an AlN passivation layer on the microstructure and electronic properties of AlGaN/GaN heterostructures were investigated by X-ray diffraction and Hall effect measurements. AlN passivation induced an additional compressive stress in an AlGaN barrier layer instead of an additional tensile stress induced by Si₃N₄ passivation. The change of strain after passivation contributes in a relatively small proportion to the variation of the carrier concentration in AlGaN/GaN heterostructures compared with the contribution from passivation of surface traps. The results from Hall effect measurements show that the AlN passivation layer has a better effect on passivation of deep levels than the Si₃N₄ film and also results in a remarkable increase in mobility of the two-dimensional electron gas. PACS 73.40.Kp; 71.55.Eq; 81.65.Rv; 81.05.Ea; 61.05.cp     

The impact of ultra thin silicon nitride buffer layer on GaN growth on Si (1 1 1) by RF-MBE

Ultra thin films of pure silicon nitride were grown on a Si (1 1 1) surface by exposing the surface to radio-frequency (RF) nitrogen plasma with a high content of nitrogen atoms. The effect of annealing of silicon nitride surface was investigated with core-level photoelectron spectroscopy. The Si 2p photoelectron spectra reveals a characteristic series of components for the Si species, not only in stoichiometric Si₃N₄ (Si⁴⁺) but also in the intermediate nitridation states with one (Si¹⁺) or three (Si³⁺) nitrogen nearest neighbors. The Si 2p core-level shifts for the Si¹⁺, Si³⁺, and Si⁴⁺ components are determined to be 0.64, 2.20, and 3.05 eV, respectively. In annealed sample it has been observed that the Si⁴⁺ component in the Si 2p spectra is significantly improved, which clearly indicates the crystalline nature of silicon nitride. The high resolution X-ray diffraction (HRXRD), scanning electron microscopy (SEM) and photoluminescence (PL) studies showed a significant improvement of the crystalline qualities and enhancement of the optical properties of GaN grown on the stoichiometric Si₃N₄ by molecular beam epitaxy (MBE).     

Improving the tribological performances of graphite-like carbon films on Si3N4 and SiC by using Si interlayers

Si interlayers were used to obtain the excellent tribological performances of graphite-like carbon (GLC) film on silicon nitride (Si₃N₄) and silicon carbide (SiC). The microstructure and mechanical characteristics of the as-prepared GLC films with Si interlayers were investigated by scanning electron microscopy, Raman spectroscopy, nanoindention and scratch test. The tribological behaviors of GLC-coated and uncoated Si₃N₄ and SiC were comparatively studied by a ball-on-disc tribo-meter in both dry and water environments. Results showed that the Si interlayers were dense and bonded well with both the substrates and GLC layers. The as-prepared GLC films exhibited excellent tribological performances in both dry and water environments. More importantly, the stably mild wear without any delamination was obtained in water by using Si interlayer. The mechanisms of friction reduction and anti-wear performances of GLC films on the two ceramics with Si interlayers under different environmental conditions were discussed, as well as the corresponding models were deduced.     

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.     

Improvement of solar cell efficiency by applying Si3N4 nanopattern on glass substrate

A cylindrical Si₃N₄ nanopattern whose heights was 200 nm was fabricated on a glass substrate, and an aluminum-doped zinc oxide (AZO) layer was grown on the nanopatterned glass substrate. The nanopattern was applied to an amorphous silicon solar cell in order to increase the light-scattering effect, thus enhancing the efficiency of the solar cell. The reflectance of the solar cell on the Si₃N₄ nanopattern decreased and its absorption increased. Compared to a flat substrate, the short-circuit current density (J_sc) and conversion efficiency of a solar cell on the Si₃N₄ nanopatterned substrate were improved by 17.9% and 24.2%, respectively, as determined from solar simulator measurements.