磁控溅射制备SiC薄膜的高温热稳定性

采用磁控溅射方法在Si基底上制备SiC薄膜,研究了SiC薄膜经不同温度和气氛条件高温退火前后结构、成份的变化.结果表明,薄膜主要以非晶为主,由Si-C键,C-C键和少量Si的氧化物杂质组成;在真空条件下经高温退火后,薄膜C-C键的含量减少,而Si-C键的含量增加,真空退火有利于SiC的形成;在800℃空气中退火后,薄膜表面生成一层致密的SiO2薄层,阻止了氧气与薄膜内部深层的接触,有效保护了内部的SiC.在空气条件下,SiC薄膜在800℃具有较好的热稳定性.     

周期性梯度富硅SiNx薄膜的微结构与发光特性

采用磁控共溅射结合快速光热退火技术在单晶硅和石英衬底上制备了含硅量子点的周期性梯度富硅SiN_x薄膜(梯度薄膜)和单层富硅SiN_x薄膜(单层薄膜)。采用Raman光谱、掠入射X射线衍射(GIXRD)、透射电子显微镜(TEM)、傅里叶变换红外(FTIR)光谱和光致发光(PL)光谱分析了薄膜的结构特性、键合特性和发光特性。Raman光谱、GIXRD和TEM结果表明, 梯度薄膜和单层薄膜中的硅量子点晶化率分别为41.7%和39.2%; 梯度薄膜的硅量子点密度是单层薄膜的5.4倍。FTIR光谱结果显示两种薄膜均为富硅氮化硅薄膜, 梯度薄膜的硅含量小于单层薄膜。PL光谱结果表明梯度薄膜中的辐射复合缺陷少于单层薄膜。     

磁控溅射非晶CNx薄膜的热稳定性研究

为了研究非晶CNx薄膜的热稳定性,采用射频磁控溅射方法沉积了非晶CNx薄膜样品,并在真空中退火至900℃,利用FTIR,Raman和XPS谱探讨了高温退火对CNx薄膜化学成分及键合结构的影响.研究表明:CNx薄膜样品中N原子分别与sp、sp2和sp3杂化状态的C原子相结合,退火处理极大地影响了CN键合结构的稳定性;当退火温度低于600℃时,膜内N含量的损失较少,CNx薄膜的热稳定性较好,退火温度超过600℃时,将导致CNx膜中大多数C、N间的键合分离,造成N大量损失,膜的热稳定性下降;退火可促使膜内sp3型键向sp2型键转变,在膜中形成大量的sp2型C键,导致CNx膜的石墨化.     

磁控溅射技术制备硅纳米晶多层膜及微观结构表征

在室温下,分别利用常规磁控溅射和反应磁控溅射技术交替沉积Si薄膜和Si1-xNx薄膜在单晶硅基体上制备了Si/Si1-xNx纳米多层膜。接下来,在高温下对Si/Si1-xNx多层膜进行退火诱发各层中形成硅纳米晶。研究了Si1-xNx层厚度和N2流量沉积对Si/Si1-xNx多层膜中Si量子点形成的影响。TEM检测结果表明,N2流量为2.5mL/min时沉积的多层膜退火后形成了尺寸为20～30nm的等轴Si3N4纳米晶;N2流量为5.0mL/min时沉积的多层膜退火后在Si层和Si1-xNx多层中均形成了硅纳米晶,而在7.5mL/min N2流量下沉积的Si/Si1-xNx多层膜退火后仅在Si层中形成了硅纳米晶。     

SiNx薄膜中硅纳米粒子的制备及表征

通过等离子增强化学气相沉积(PECVD)法, 以氨气和硅烷为反应气体, P型单晶硅和石英为衬底, 低温下(200℃)制备了含硅纳米粒子的非化学计量比氮化硅(SiN_x)薄膜. 经高温(范围500~950℃)退火处理优化了薄膜结构. 室温下测试了不同温度退火后含硅纳米粒子SiN_x薄膜的拉曼(Raman)光谱、光致发光(PL)光谱及傅立叶变换红外吸收(FTIR)光谱, 对薄膜材料的结构特性、发光特性及其键合特性进行了分析. Raman光谱表明. SiN_x薄膜内的硅纳米粒子为非晶结构. PL光谱显示两条与硅纳米粒子相关的光谱带, 随退火温度的升高此两光谱带峰位移动方向相同. 当退火温度低于800℃时, PL光谱峰位随退火温度的升高而蓝移. 当退火温度高于800℃时, PL光谱峰位随退火温度的升高而红移. 通过SiNx薄膜的三种光谱分析发现薄膜的光致发光源于硅纳米粒子的量子限制效应. 这些结果对硅纳米粒子制备工艺优化和硅纳米粒子光电器件的应用有重要意义.     

微波等离子体化学气相沉积法生长非晶碳化硅薄膜

利用SiH4(80%Ar稀释)和CH4作为源气体,通过改变源气体流量比、基片温度、沉积气压等参量,使用微波电子回旋共振化学气相沉积法生长非晶碳化硅薄膜。实验结果表明碳化硅薄膜沉积速率随气体流量比R(CH4/(CH4+SiH4))的增加而减小、随基片温度的升高明显减小、随沉积气压的增加先增大后减小。红外结构表明:在较低流量比R下,薄膜主要由硅团簇和非晶碳化硅两相组成,而当R>0.5时,薄膜的结构主要由非晶碳化硅组成,薄膜中键合的H主要是Si和C的封端原子。同时,沉积温度的升高使碳化硅薄膜中Si-H,C-C和C-H键的含量减少,而薄膜中Si-C含量明显增加且峰位发生了红移。薄膜相结构的转变是薄膜光学带隙变化的原因。     

Ta上生长的硅薄膜退火的微晶化研究

对射频溅射功率80W条件下Ta缓冲层上生长的硅薄膜进行退火并用Raman散射和X射线衍射技术对样品的微观结构进行检测,系统研究了退火温度和退火时间对硅薄膜结晶性的影响.分析结果表明,在560℃退火2h或680℃退火1h之后,硅薄膜开始晶化,并且随着退火温度的增加或退火时间延长,薄膜逐渐由非晶向微晶转变.获得了可用于太阳能电池的微晶硅薄膜的最佳晶化参数.     

电子束蒸发玻璃薄膜中间层的阳极键合研究

介绍了一种用电子束蒸发Schott 8329玻璃薄膜作为中间层,实现硅-硅以及硅-SOI阳极键合的方法.调整蒸发时的工艺并且450℃退火,沉积了粗糙度9.62 nm、初始应力139 MPa、喷点较少的薄膜,从而获得了＞95%的键合面积.键合电压20 V,温度300℃～500℃下硅-硅的键合强度可达1.47 J/m2,同时分析了键合电流特性.400℃,40V下键合了Si和SIMOX SOI硅片,用TMAH溶液进行基底减薄,获得了厚介质层薄顶层硅结构,这为一些MEMS器件的制作奠定了基础.     

利用非晶SiC在硬质合金上原位生长石墨烯

针对空间钻探中硬质合金钻具部件的减摩润滑问题,提出一种在硬质合金基底上原位生长石墨烯的方法。在硬质合金基底上磁控溅射沉积非晶碳化硅(SiC)薄膜,利用合金中的粘结相Co在真空退火条件下催化非晶SiC,实现原位生长石墨烯。研究了在硬质合金基底表面磁控溅射沉积非晶SiC薄膜,在真空退火条件下,退火温度、退火时间和C/Si原子比对金属Co催化非晶SiC在硬质合金上原位生长石墨烯的影响,分析了金属Co在催化非晶SiC制备石墨烯过程中的反应机理,为石墨烯在真空钻探刀具润滑材料的应用提供了一定的理论基础。     

PECVD SiC薄膜的AES研究

本文介绍用俄歇电子能谱对等离子增强化学气相淀积非晶碳化硅薄膜进行组分的定量分析、深度剖析和元素的化学状态分析;不同制备条件下非晶碳化硅薄膜的一些淀积规律和工艺中的问题,并利用SiLVV和C KLL俄歇谱探讨非晶碳化硅的特征和硅、碳的化学状态。     

Investigation of bonding characteristics between Si quantum dots and a SiO2 matrix

In order to understand and control the properties of Si quantum dot (QD) superlattice structures (SLS), it is necessary to investigate the bonding between the dots and their matrix and also the structures' crystallinities. In this study, a SiOx matrix system was investigated and analyzed for potential use as an all-silicon multi-junction solar cell. Si QD SLS were prepared by alternating deposition of Si rich SiOx (x = 0.8) and SiO2 layers using RF magnetron co-sputtering and subsequent annealing at temperatures between 800 and 1,100 degrees C under nitrogen ambient. Annealing temperatures and times affected the formation of Si QDs in the SRO film. Raman and FTIR spectra revealed that nanocrystalline Si QDs started to precipitate after annealing at 1,100 degrees C for 1 hour. TEM images clearly showed SRO/SiO2 SLS and Si QDs formation in SRO layers after annealing at 1,100 degrees C for 2 hours. XPS analysis showed that Si-Si and Si-O bonding changes occurred above 1,100 degrees C. XPS analysis also revealed that Si QD SLSs started stabilizing after 2 hours' annealing and approached completion after 3 hours'. The systematic investigation of Si QDs in SiO2 matrices and their properties for solar cell application are presented.     

Optical property of silicon quantum dots embedded in silicon nitride by thermal annealing

We present the effects on the thermal annealing of silicon quantum dots (Si QDs) embedded in silicon nitride. The improved photoluminescence (PL) intensities and the red-shifted PL spectra were obtained with annealing treatment in the range of 700 to 1000 °C. The shifts of PL spectra were attributed to the increase in the size of Si QDs. The improvement of the PL intensities was also attributed to the reduction of point defects at Si QD/silicon nitride interface and in the silicon nitride due to hydrogen passivation effects.     

退火条件对Sn量子点生长和红外光学性质的影响

首次采用固相外延生长技术在Si(001)表面直接生长Sn量子点,并应用原子力显微镜(AFM)、X射线衍射(XRD)和同步辐射傅里叶红外光谱(FTIR)研究了退火条件对量子点样品的表面形貌、结晶性和红外光学性质的影响.AFM结果表明,随着退火温度的升高和退火时间的延长,量子点的平均尺寸变大,面密度减小.XRD结果显示,外延得到的Sn量子点为四方结构的β-Sn,与衬底的相对取向为Sn(110)//Si(001).由于β-Sn量子点的尺寸仍较大,同步辐射FTIR谱中没有观察到量子点的特征吸收峰.     

Silicon quantum dot/crystalline silicon solar cells

Silicon (Si) quantum dot (QD) materials have been proposed for 'all-silicon' tandem solar cells. In this study, solar cells consisting of phosphorus-doped Si QDs in a SiO(2) matrix deposited on p-type crystalline Si substrates (c-Si) were fabricated. The Si QDs were formed by alternate deposition of SiO(2) and silicon-rich SiO(x) with magnetron co-sputtering, followed by high-temperature annealing. Current tunnelling through the QD layer was observed from the solar cells with a dot spacing of 2?nm or less. To get the required current densities through the devices, the dot spacing in the SiO(2) matrix had to be 2?nm or less. The open-circuit voltage was found to increase proportionally with reductions in QD size, which may relate to a bandgap widening effect in Si QDs or an improved heterojunction field allowing a greater split of the Fermi levels in the Si substrate. Successful fabrication of (n-type) Si QD/(p-type) c-Si photovoltaic devices is an encouraging step towards the realization of all-silicon tandem solar cells based on Si QD materials.     

Misfit-guided self-organization of anticorrelated ge quantum dot arrays on si nanowires

Misfit-strain guided growth of periodic quantum dot (QD) arrays in planar thin film epitaxy has been a popular nanostructure fabrication method. Engineering misfit-guided QD growth on a nanoscale substrate such as the small curvature surface of a nanowire represents a new approach to self-organized nanostructure preparation. Perhaps more profoundly, the periodic stress underlying each QD and the resulting modulation of electro-optical properties inside the nanowire backbone promise to provide a new platform for novel mechano-electronic, thermoelectronic, and optoelectronic devices. Herein, we report a first experimental demonstration of self-organized and self-limited growth of coherent, periodic Ge QDs on a one-dimensional Si nanowire substrate. Systematic characterizations reveal several distinctively different modes of Ge QD ordering on the Si nanowire substrate depending on the core diameter. In particular, Ge QD arrays on Si nanowires of around 20 nm diameter predominantly exhibit an anticorrelated pattern whose wavelength agrees with theoretical predictions. The correlated pattern can be attributed to propagation and correlation of misfit strain across the diameter of the thin nanowire substrate. The QD array growth is self-limited as the wavelength of the QDs remains unchanged even after prolonged Ge deposition. Furthermore, we demonstrate a direct kinetic transformation from a uniform Ge shell layer to discrete QD arrays by a postgrowth annealing process.     

Optimization of process parameter for synthesis of silicon quantum dots using low pressure chemical vapour deposition

Si quantum dots-based structures are studied recently for performance enhancement in electronic devices. This paper presents an attempt to get high density quantum dots (QDs) by low pressure chemical vapour deposition (LPCVD) on SiO ₂ substrate. Surface treatment, annealing and rapid thermal processing (RTP) are performed to study their effect on size and density of QDs. The samples are also studied using Fourier transformation infrared spectroscopy (FTIR), atomic force microscopy (AFM), scanning electron microscopy (SEM) and photoluminescence study (PL). The influence of Si–OH bonds formed due to surface treatment on the density of QDs is discussed. Present study also discusses the influence of surface treatment and annealing on QD formation.     

Surfactant-dependent photoluminescence of CdTe/CdS nanocrystals

ABSTRACT

The photoluminescence of aqueously synthesised core/shell CdTe/CdS quantum dots (QDs) was investigated. Two molar ratios (2.4 and 1.3) of thioglycolic acid (TGA) to Cd²⁺ were compared to determine the best synthesis conditions for high photoluminescent quantum yield (PLQY) and photostability. A difference in the PLQY of the CdTe/CdS QDs was observed when CdS shells were grown with different TGA/Cd²⁺ ratios. The difference in the observed PLQY was attributed to the quality of the passivation of the CdTe during the CdS shell growth. At TGA/Cd²⁺ ratio of 1.3, the CdS shell forms through homogeneous nucleation, which is limited by diffusion of growth material from the solution onto the QDs surface. Due to the lattice mismatch of CdTe and CdS, the core will experience coherence strain resulting in dislocation sites and surface defects between nucleation sites which can result in non-radiative trap states. When the TGA/Cd²⁺ ratio is 2.0, the CdS shell grows epitaxially, minimising the number of surface trap states. Finally, we observed that the fluorescence intermittency was supressed for CdTe QDs after UV light illumination, attributed to annealing of deep surface trap states by UV light.     

Optical encoding of microbeads based on silica particle encapsulated quantum dots and its applications

A novel method concerning the coding technology of polystyrene beads with Si encapsulated quantum dot (QD) particles (Si@QDs particles) is studied in this paper. In the reverse microemulsion system containing tetraethoxysilane (TEOS), water-soluble QDs (emission peak at 600?nm) were enveloped within the silica shell, forming Si@QDs particles. The Si@QDs particles were characterized by TEM, showing good uniform size, with an average diameter of about 167.0?nm. In comparison with the pure water-soluble QDs, the encapsulation of water-soluble QDs in the silica shell led to an enhancement in anti-photobleaching by providing inert barriers for the QDs. Images presented by SEM and confocal laser scanning microscopy demonstrated that the Si@QDs particles were equably coated on the surface of carboxyl functionalized polystyrene (PS) beads. Then, with the assistance of ethyl-3-(dimethyl aminopropyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS), human IgG could be successfully crosslinked to Si@QDs particle coated PS-COOH beads. Furthermore, the Si@QDs coated PS-COOH beads with human IgG were examined in immunoassay experiments, and the results indicated that these beads could be applied in the specific recognition of goat-anti-human IgG in solution. This investigation is expected to provide a new route to bead coding in the field of suspension microarrays, based on the use of QDs.     

Facile consecutive solvothermal growth of highly fluorescent InP/ZnS core/shell quantum dots using a safer phosphorus source

The work presents a facile, stepwise synthetic approach for the production of highly fluorescent InP/ZnS core/shell quantum dots (QDs) by using a safer phosphorus (P) precursor. First, InP quantum dots (QDs) were solvothermally prepared at 180?°C for 24 h by using a P source of P(N(CH(3))(2))(3). The as-grown InP QDs were consecutively placed in another solvothermal condition for ZnS shell overcoating. In contrast to the almost non-fluorescent InP QDs, due to their highly defective surface states, the ZnS-coated InP QDs were highly fluorescent as a result of effective surface passivation. After the shell growth, the resulting InP/ZnS core/shell QDs were subjected to a size-sorting processing, by which red- to green-emitting QDs with quantum yields (QYs) of 24-60% were produced. Solvothermal shell growth parameters such as the reaction time and Zn/In solution concentration ratio were varied and optimized toward the highest QYs of core/shell QDs.     

Highly luminescent blue emitting CdS/ZnS core/shell quantum dots via a single-molecular precursor for shell growth

Highly luminescent blue-emitting CdS/ZnS core/shell quantum dots (QDs) were synthesized in N-oleoylmorpholine by two facile steps: first, the CdS core QDs were prepared via a simple one-pot method involving a direct reaction of Cd precursor cadmium stearate and S precursor S powder in solvent N-oleoylmorpholine; second, ZnS shells were successively overcoated on CdS core through the decomposition of single molecular precursor zinc diethyldithiocarbamate. The thickness of shell was precisely tuned by controlling drip feed speed and amount of shell precursor. The obtained CdS/ZnS core/shell QDs showed the maximum photoluminescent quantum yield of 54.8% and narrow spectra bandwidth, exhibiting high monodispersity, good color purity and long fluorescent lifetimes. The CdS/ZnS core/shell QDs with tunable emission wavelength of 424–470 nm were obtained by controlling the thickness of ZnS shell overgrown on different-sized CdS QDs, which are promising materials for blue light-emitting devices.