多孔硅的分形结构及其荧光特性

用扫描电子显微镜(SEM)对多孔硅的结构进行了分析.结果显示多孔硅具有分形特性,同计算机模拟结果一致;用荧光光谱仪,研究了多孔硅的荧光特性与激发波长的依赖关系.激发光谱测量结果发现,当激发波长从650 nm变到340 nm时,荧光谱峰位从红端780 nm连续蓝移到500 nm.综合分析说明：正是由于多孔硅的分形微结构以及量子限制效应,导致了多孔硅的荧光特性随激发波长改变的物理现象.     

Correlation of excitation-wavelength dependent photoluminescence with the fractal microstructures of porous silicon

The correlation of the excitation-wavelength dependent photoluminescence with the fractal microstructures of porous silicon has been investigated. As the excitation wavelength increases from 340 to 650 nm, the photoluminescence of porous silicon redshifts from 500 to 780 nm. The excitation-wavelength dependent photoluminescence suggests the existence of a size distribution for the large number of silicon nanocrystallites in porous silicon. Using scanning electron microscopy and computer simulation, we have investigated the fractal features of the microstructures of porous silicon. Our results have demonstrated that the fractal features in the microstructures of porous silicon indicate the existence of a size distribution for the silicon nanocrystallites in porous silicon. The recorded excitation-wavelength dependent photoluminescence of porous silicon can be interpreted in terms of the bond-order-length-strength correlation theory.     

Photoluminescence of porous silicon saturated with tungsten-tellurite glass with rare-earth metal impurities

It has been shown that the presence of silicon nanoparticles in a layer of porous silicon saturated with tungsten-tellurite glass causes an increase in the photoluminescence quantum efficiency of erbium (1530 nm) by an order of magnitude in the case of long-wavelength excitation and an enhancement of the ytterbium photoluminescence (980 nm) by almost 50 times and erbium photoluminescence by 25 times in the case of short-wavelength pumping. This luminescence enhancement is explained by the formation of additional channels of transfer of external excitation by silicon nanocrystallites in porous silicon to impurity ytterbium and erbium ions in tungsten-tellurite glass.     

Porous silicon bandgap broadening at natural oxidation

Emission and excitation photoluminescence spectra of porous silicon thin layers have been investigated at natural oxidation. The shift of both types of spectra to high-energy region with time has been shown. Analysis of excitation spectra points out the indirect behavior of electron transitions responsible for visible photoluminescence, which remains unaltered at natural oxidation. The value of optical bandgap is estimated in each case. It is shown that the optical bandgap broadens during oxidation due to size reduction of silicon nanocrystallites.     

Comparative investigation of photoluminescence of silicon wire structures and silicon oxide films

Photoluminescence spectra and their dependence on temperature as well as Raman scattering spectra and Atomic Force Microscopy investigations have been used to study the peculiarities of the red photoluminescence band in low-dimensional Si structures, such as porous silicon and silicon oxide films. It has been shown that the red photoluminescence band of porous silicon is complex and can be decomposed into two elementary bands. It was discovered that elementary band intensities depend very much on surface morphology of porous silicon. The same positions of the photoluminescence bands are also observed in silicon oxide films for different oxide composition. Comparative investigation of the PL temperature dependences in porous silicon and silicon oxide films indicates that silicon-oxide defect related mechanisms of some elementary photoluminescence bands are involved.     

Luminescence centers in porous silicon

Photoluminescence studies on porous silicon show that there are luminescence centers present in the surface states. By taking photoluminescence spectra of porous silicon with respect to temperature, a distinct peak can be observed in the temperature range 100–150 K. Both linear and nonlinear relationships were observed between excitation laser power and the photoluminescence intensity within this temperature range. In addition, there was a tendency for the photoluminescence peak to red shift at low temperature as well as at low excitation power. This is interpreted as indicating that the lower energy transition becomes dominant at low temperature and excitation power. The presence of these luminescence centers can be explained in terms of porous silicon as a mixture of silicon clusters and wires in which quantum confinement along with surface passivation would cause a mixing of andX band structure between the surface states and the bulk. This mixing would allow the formation of luminescence centers.     

Luminescence of porous silicon films with an europium-containing complex

We obtained porous silicon films modified at room temperature by an Eu³⁺-containing polymer complex. The most intense photoluminescence of Eu³⁺ implanted in the porous silicon was observed at the wavelengths of 611, 618, 691, and 704 nm. In this case, the intensity of the intrinsic photoluminescence of strongly irradiated specimens of porous silicon decreased, while the intensity of weakly emitting films multiply increased. An investigation of the photoexcitation spectra made it possible to establish the effect of Eu³⁺-containing complexes on the mechanism underlying the excitation of photoluminescence of porous silicon. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 499–501, July–August, 1997.     

Observation of two-step excitation of photoluminescence in silicon nanostructures

Efficient visible-range photoluminescence with photon energy higher than the photon energy of the exciting radiation is observed in nanostructures of porous silicon subjected to heat treatment in vacuum. The photoluminescence intensity is found to be virtually identical for cw and femtosecond excitation by Ti:sapphire laser radiation with the same average power. The results can be explained by a two-step cascade photoluminescence excitation process in which optical passivation of defects of the dangling silicon bond type occurs. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 10, 732–736 (25 November 1998)     

Photoluminescence of porous silicon surfaces stabilized through Lewis acid mediated hydrosilylation

Lewis acid mediated hydrosilylation on porous silicon surfaces permits facile incorporation of a wide variety of functionalities through stable silicon–carbon bonds. The surfaces demonstrate high chemical stability with respect to hydrofluoric acid and aqueous base. The effects of the covalently bound surface groups on photoluminescence have been investigated and it was noted that alkyl and alkenyl termination induced only small decreases in photoluminescence efficiency. Aromatic substituents conjugated through a vinyl group, however, bring about almost complete quenching of the observed photoluminescence, regardless of substitution with either electron withdrawing (chloride) or donating (methyl) functionalities. The photoluminescence fatigue of dodecyl terminated surfaces in air for 12–16 h periods has been monitored and compared to unfunctionalized porous silicon. In air, the photoluminescence of dodecyl terminated surfaces degrades faster than the unfunctionalized porous silicon but under inert atmosphere (nitrogen), the rate of photoluminescence fatigue is slow in both cases and approximately equivalent.     

二氧化硫监测的光纤传感方法研究

提出一种用于监测二氧化硫的光纤传感方法,该方法以光化学氧化的n型多孔硅作为传感材料和蓝光发光二激管作为激发光源,通过微型光纤光谱仪测量二氧化硫气氛中多孔硅的光致发光猝灭程度,从而获取二氧化硫含量信息;依据半导体电化学和固体光谱学理论分别讨论n型多孔硅形成和二氧化硫传感的基本原理,采用红外光谱仪研究光化学氧化的n型多孔硅化学组成,并进一步开展二氧化硫光纤传感实验,证明光化学氧化的n型多孔硅在传感过程中稳定性高、可逆性好,其光致发光峰强度随二氧化硫浓度增加而减小,多孔硅荧光峰强度对二氧化硫浓度的线性响应范围为10×10－6～10 000×10－6,检测限为10×10－6;可形成一种便携、全固态的二氧化硫光纤传感器.     

多孔硅的后处理及其发光特性

采用一种新颖而简便的方法,改善多孔硅的发光特性。该方法包括酸处理和阴极还原两步。实验证明通过对多孔硅进行酸处理,能有效提高多孔硅的发光强度;通过对多孔硅进行阴极还原处理,能明显改善多孔硅的发光稳定性,而且发光强度也得到了提高。综合酸处理和阴极还原两技术的特点,对所制备的多孔硅立即先进行酸处理,然后再对其进行阴极还原处理,结果表明该方法能较好地提高多孔硅的发光效率和发光稳定性。而且还对其发光机制进行了探讨。     

532 nm纳秒激光辐照下的单晶硅表面微结构及荧光特性

采用Nd:YAG纳秒脉冲激光对单晶硅在空气中进行辐照,研究了表面微结构在不同能量密度和扫描速度下的演化情况。扫描电子显微镜测量表明,激光在相对较低能量密度下辐照硅表面诱导出鱼鳞状波纹结构,激光能量密度相对较大时,诱导出絮状多孔的不规则微结构。光致荧光谱（PL）表明,激光扫描区域在710 nm附近有荧光发射。用氢氟酸腐蚀掉样品表面的SiOx后,荧光峰的强度显著降低,说明SiOx在光致发光增强上起重要作用。能量色散X射线谱（EDS）表明氧元素的含量随激光能量密度的增大而增加。研究表明:纳秒激光的能量密度和扫描速度对微结构形成起着决定性作用,改变了硅材料表面微结构尺寸,增大了光吸收面积; 氧元素在光致发光增强上起重要作用,微构造硅和SiOx对光致荧光的发射都有贡献。     

X-ray luminescence of disperse SiO2 and porous silicon

We carry out a comparison between the luminescence spectra (photo-and x-ray luminescence) of porous silicon and disperse SiO₂, which by its physical characteristics is most similar to oxide films on porous silicon. The photoluminescence of porous silicon was also investigated using fluorescence (excitation by a nitrogen laser) and metallographic microscopes. We found that the natures of the luminescence centers of porous silicon and disperse SiO₂ are identical. A porous layer on single-crystal silicon ensures the creation of a highly branched surface of oxide film. Luminescence centers are located on its inner (as viewed from the porous silicon) surface. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 247–251, March–April, 1998.     

Effects of selenium treatment on composition and photoluminescence properties of porous silicon

In this work, an ultrasonically enhanced anodic electrochemical etching is developed to fabricate light-emitting porous silicon material. Porous silicon layer is fabricated in n-type (1 0 0) oriented silicon using HF solution and treated in selenious acid to increase the photoluminescence intensity. It is found that the increase of photoluminescence intensity after selenious acid treatment is higher in the intact zones and lower in the detached zones of ultrasonic excitation. The photoluminescence appears as a non-monotonous function of time exposure of selenious acid treatment. Surface chemical composition analysis by X-ray photoelectron spectroscopy shows formation of Si-Se_x and Si-Se_x-O_y on the surface of porous silicon treated with the selenious acid.     

Stable ultraviolet photoluminescence emission in n-type porous silicon

This very paper is focusing on the investigation of porous silicon preparation with n-type silicon wafer by means of electrochemical anodization in the dark and, particularly, on its stable ultraviolet photoluminescence emission. A lateral electrical potential was applied, for this purpose, on silicon wafers, driving the electrons away and letting holes appear on the surface of the silicon wafer to enhance the electrochemical etching process. Characterizations have been made with scanning electronic microscope, fluorescence spectrophotometer and Fourier transform infrared spectroscope. An ultraviolet photoluminescence emission of 370 nm is found in the as-prepared n-type porous silicon, which seems to be well associated with the formation of oxygen-related species (twofold coordinated silicon defect) during the anodic oxidation. The result characterized by photo-bleaching performance indicates that the ultraviolet photoluminescence emission is so stable—only 7% reduction within 3600 s. Meanwhile the morphology of as-prepared n-type porous silicon is investigated.     

Phonon confinement effects in Raman spectra of porous silicon at non‐resonant excitation condition

Light emitting porous silicon samples with different porosities, i.e. crystalline sizes, were produced from the low level doped p‐type silicon wafers by the anodization process. The effects of strong phonon confinement, redshift and broadening, were found on the O(Γ) phonon mode of the Raman spectra recorded at non‐resonant excitation condition using a near infrared 1064 nm laser excitation wavelength. Similarly, the blueshift of the photoluminescence peak was observed by reducing the crystalline sizes. Vibrational and optical findings were analysed within the existing models of confinement on the vibrational and electronic states of silicon nanocrystals. Since the energy of the photoluminescence peak of small nanocrystals also depends on the oxygen content on the surface of nanocrystals, the surface oxidation states were examined using infrared and energy dispersive spectroscopy. The partial coverage of the surface of nanocrystals was found due to the sample exposure to air. As a consequence, the photoluminescence energy did not increase as would be expected from the quantum confinement model. These results further indicate that the oxygen passivation along with the quantum confinement determines the electronic states of the silicon nanocrystals in porous silicon. Copyright © 2014 John Wiley & Sons, Ltd.     

Influence of successive electron and laser irradiation on the photoluminescence of porous silicon

The influence of electron irradiation on the light-emitting properties of p-and n-type porous silicon prepared by electrochemical etching is investigated. The dose and energy dependences of the electron-stimulated quenching of the photoluminescence (PL) are determined. It is shown that electron treatment of a porous silicon surface followed by prolonged storage in air can be used to stabilize the PL. The excitation of photoluminescence by a UV laser acting on sections of porous silicon samples subjected to preliminary electron treatment is discovered for the first time. The influence of the electron energy and the power of the laser beam on this process is investigated. The results presented are attributed to variation in the number of radiative recombination centers as a result of the dissociation and restoration of hydrogen-containing groups on the pore surface. Zh. Tekh. Fiz. 68, 58–63 (March 1998)     

Effects of light localization in photoluminescence and Raman scattering in silicon nanostructures

The effect of light localization in photoluminescence (PL) and Raman scattering (RS) in silicon nanowires with diameter of 100 nm was investigated. The optical excitation was done by CW radiation of a YAG:Nd laser at 1.064 μm. The PL an RS intensities were found to increase strongly for the samples with Si nanowires in comparison with corresponding values of c-Si substrate. The effect is explained by an increase of the lifetime of photons in silicon nanowire structures.     

Improvement of photoluminescence and electrical properties of porous silicon layer treated with lanthanum

The influence of surface treatment of porous silicon (PS) in lanthanum (La) containing solution during different times on its photoluminescence and electrical properties has been investigated. For this purpose, chemical composition, structural, vibrational, photoluminescence and electrical characteristics of the porous silicon layer with and without lanthanum were examined using X-ray diffractometry (XRD), energy dispersive X-ray (EDX) spectroscopy, Fourier transmission infrared (FTIR) spectroscopy, photoluminescence (PL) spectroscopy and current–voltage (I–V) measurements. The results indicate that porous silicon layers treated with lanthanum exhibit an enhancement of photoluminescence intensity and show an improvement current intensity compared to untreated porous silicon layer.     

Peculiarities of photoluminescence of porous silicon with luminescent liquid crystal fillers

Photoluminescence spectra of porous silicon filled by luminescent liquid crystals 5CB and H109 were investigated. It was observed that there were photoluminescence bands corresponding to both porous silicon and liquid crystal in experimental spectra. In addition, the band corresponding to porous silicon increases in comparison with photoluminescence of porous silicon without the filler. Experimental results are explained by the radiating and nonradiating energy transfer from liquid crystal to porous silicon.