Electrical conduction in thin thermally nitrided SiO2 (nitroxide)

Nitridation-enhanced conduction in thin nitroxide films has been examined in detail. Significant increase of high field current is attributed both to the enhanced Fowler-Nordheim (FN) tunneling injection and the Poole-Frenkel (PF) emission; the latter is confirmed by the linear dependence of log(I_PF) on E and the existence of a self-consistent dynamic dielectric constant. It is found that the enhancement of electron FN tunneling arises mainly from the piling up of nitrogen at the surface, but the PF component originates from the traps which are related to the nitrogen concentration in the bulk of nitroxide.     

SiO2的赝晶化及AlN/SiO2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不同SiO₂层厚度的AlN/SiO₂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SiO₂层在多层膜中的晶化现象及其对多层膜生长方式及力学性能的影响. 结果表明，由于受AlN六方晶体结构的模板作用，溅射条件下以非晶态存在的SiO₂层在其厚度小于0.6 nm时被强制晶化为与AlN相同的六方结构赝晶体并与AlN形成共格外延生长. 由于不同模量的两调制层存在晶格错配度，多层膜中产生了拉、压交变的应力场，使得多层膜产生硬度升高的超硬效应. SiO₂随层厚的进一步增加又转变为以非晶态生长，多层膜的外延生长结构受到破坏，其硬度也随之降低. 关键词： 2纳米多层膜')" href="#">AlN/SiO₂纳米多层膜 赝晶化 应力场 超硬效应     

Pentacene islands grown on ultra-thin SiO2

Ultra-thin oxide (UTO) films were grown on Si(1 1 1) in ultrahigh vacuum at room temperature and characterized by scanning tunneling microscopy. The ultra-thin oxide films were then used as substrates for room temperature growth of pentacene. The apparent height of the first layer is 1.57 ± 0.05 nm, indicating “standing up” pentacene grains in the thin film phase were formed. Pentacene is molecularly resolved in the second and subsequent molecular layers. The measured in-plane unit cell for the pentacene (0 0 1) plane (ab plane) is a = 0.76 ± 0.01 nm, b = 0.59 ± 0.01 nm, and γ = 87.5 ± 0.4°. The films are unperturbed by the UTO’s short-range spatial variation in tunneling probability, and reduce its corresponding effective roughness and correlation exponent with increasing thickness. The pentacene surface morphology follows that of the UTO substrate, preserving step structure, the long range surface rms roughness of ∼0.1 nm, and the structural correlation exponent of ∼1.     

Monte Carlo analysis of electron heating in Si/SiO2 superlattices

In this work, we investigate the transport properties of Si/SiO₂ superlattices with a multiband one-particle Monte Carlo simulator. Using the envelope function approximation, we solve the Krönig–Penney potential along the growth direction z using a tight-binding-like analytical form; we also consider parabolic dispersion along the xy plane. The scattering mechanisms introduced in the simulator are confined optical phonons, both polar and nonpolar.Owing to the very flat shape of the bands along the growth direction, very low drift velocities are found for vertical transport. However, the simulation shows that, for oblique fields, the transport properties along the vertical direction are strongly influenced by the in-plane component of the electric field: in this way higher vertical drift velocities can be obtained. The results point out that in-plane carrier heating and multiband properties are responsible for this behavior.     

Influence of the doping level on the charge distribution among the inequivalent CuO2 layers in Tl2Ba2Ca2Cu3O10−δ : a NMR study

and NMR measurements in the normal and superconducting states of Tl₂Ba₂Ca₂Cu₃O_10−δ with different δ are reported. In the overdoped Tl2223 sample with T_c=117 K (T_c^opt=123 K) and δ₁<δ^opt different temperature dependencies of the Knight shift are revealed for inequivalent CuO₂ layers. For the inner CuO₂ layer with the square oxygen coordination of Cu the decrease of with temperature is more gradual. In going towards the underdoped Tl2223 with T_c=104 K and δ₂>δ^opt the changes of with temperature are found to be the same for both types of copper layers. The quadrupole coupling constants for copper and oxygen from different CuO₂ layers were obtained. From the variations with doping of the valence contribution to the electric field gradient at copper sites, we estimate both the hole numbers at Cu and oxygen sites and the real concentration of mobile hole carriers n_h in each of inequivalent CuO₂ layers. In the overdoped Tl2223 sample the charge density in the inner layer differs from the one in the outer plane (with five-fold oxygen coordination for Cu). Our results show that the inhomogeneity of the charge distribution disappears in the underdoped regime. The results are compared with calculations of the charge distribution among the CuO₂ planes in multilayered cuprates reported by Haines and Tallon [E.M. Haines, J.L. Tallon, Phys. Rev. B 45 (1992) 3127].     

Optical properties from SRSO/SiO2 multilayers in planar microcavities

We report on the fabrication and characterization of an efficient and CMOS compatible Si-based light source. Silicon-rich silicon oxide (SRSO)/SiO₂ superlattices-doped planar optical microcavities have been grown by reactive magnetron sputtering. The devices were studied using reflectance and photoluminescence measurements. The reflectivity of the resonator is above 99.9% and the quality factor is reaching a value of 100. Modification of silicon nanocrystals emission is clearly observed in the visible and reveals narrow, intense and highly directional emission properties.     

TiO2/SiO2多层膜的带隙结构及光催化性能

利用传输矩阵法设计了由SiO2、TiO2组成的多层膜高透射率光子晶体结构,并分析了其透射谱特性,根据等效层原理改变多层膜一维光子晶体的自身结构来提高通带内特征波长附近的透射率,获得了最佳结构参数。研究结果表明,当晶格参数为150nm,填充比为0.346,周期数为6时,400nm波长附近吸收带处的透射率最低也可达96.5%,并且不论是TM模式还是TE模式,入射角在0°～45°范围内仍保持高的透射率,该结构可望用于空气净化装置以提高SiO2、TiO2光催化剂的光催化效率。     

Proton conduction in (NH4)3 H(SO4)2 single crystals

D.C. electrical conductivity, DTA and coulometric studies on (NH₄)₃ H(SO₄)₂ single crystals are made. Conductivity is markedly anisotropic with maximum along c¹ direction. A sudden jump in the conductivity plot along c¹ direction at 413 K is supported by a large endothermic peak in DTA, confirming the presence of transition at this temperature. The values of activation energy calculated from conductivity measurements indicated that the charge carriers are protons. This was further confirmed by coulometric experiment where the gas evolved was hydrogen, as established by a gas chromatograph and the volume of H₂ released agreed with that expected from electrolysis. The mechanism of protonic conduction in this crystal is discussed.     

A potential green-emitting phosphor Ca8Mg(SiO4)4Cl2:Eu for white light emitting diodes prepared by sol-gel method

A potential green emitting phosphor Ca₈Mg(SiO₄)₄Cl₂:Eu²⁺ was prepared by modified sol-gel method. The factors those affect the photoluminescence intensity including heating temperature, the usage of the chlorine source CaCl₂ and the concentration of dopant Eu²⁺ were also investigated in detail. As comparison, the phosphor prepared by solid-state reaction was also prepared. The phosphors show intense absorption in the range of 375-450 nm, which makes it a potential candidate of green emitting phosphor used for near-UV or blue light excited white LEDs.     

Si基Si3N4/SiO2双层膜驻极体的电荷储存与输运

利用等温表面电位衰减及热刺激放电(thermally stimulated discharge,TSD)方法探讨了恒栅压电晕充电经常压化学气相沉积(APCVD)的Si基Si3N4和热生长SiO₂双层薄膜驻极体电荷的存储特性.结果表明:在常温环境中,300℃高温下,以及95%相对湿度时的60℃条件下,所有试样表现出极好的电荷储存稳定性.对于负电晕充电试样,其电荷输运受慢再捕获效应(slow retrapping effect)控制;用热离子发射模型来描述了正电晕充电Si₃N₄/SiO₂驻极体的正电荷输运特性. 关键词： 驻极体 薄膜 电荷储存 热离子发射     

Synthesis and properties of magnetic and luminescent Fe3O4/SiO2/Dye/SiO2 nanoparticles

A simple and reproducible method was developed to synthesize a novel class of Fe₃O₄/SiO₂/dye/SiO₂ composite nanoparticles. As promising candidates for use in bioassays, the obtained nanoparticles have an average diameter of 30 nm, and the thickness of the outer shell of silica could be tuned by changing the concentration of the silicon precursor tetraethyl orthosilicate during the synthesis. These multifunctional nanoparticles were found to be highly luminescent, photostable and superparamagnetic. The luminescence intensity of the nanoparticles was increased as the dye concentration was increased in the preparation process. The color of the luminescence was successfully tuned by incorporating different dyes into the nanoparticles. The measurements of the emission spectra indicated that relative to the dye molecules dissolved in ethanol, the emission of the dye-doped nanoparticles exhibited either a red shift or a blue shift, to which a tentative explanation was given.     

纳米锗镶嵌二氧化硅薄膜的光学性质及其应用的研究

采用射频磁控溅射技术与热退火处理制备了纳米锗镶嵌二氧化硅(nc-Ge/SiO2)复合薄膜.对薄膜的光吸收谱进行分析,得到了纳米Ge晶粒的光学带隙.单光束Z-扫描的实验结果表明薄膜具有较强的可饱和吸收特性.将薄膜作为可饱和吸收体插入LD端面抽运的Nd:YVO4激光器内,分别实现1342 nm和1064 nm激光的被动调Q,得到脉宽分别为29 ns和22 ns的脉冲序列.理论分析认为,纳米Ge晶粒形成的界面态和缺陷态对1342 nm激光产生的饱和吸收作用,是导致被动调Q的主要原因.     

Effects of hydrogen plasma annealing on the luminescence from a-Si:H/SiO2 and nc-Si/SiO2 multilayers

Effects of post-hydrogen plasma annealing (HPA) on a-Si:H/SiO₂ and nc-Si/SiO₂ multilayers have been investigated and compared. It is found that photoluminescence (PL) from hydrogen-passivated samples was improved due to the reduction of non-radiative recombination defects. Some interesting difference is that during HPA, atomic hydrogen can directly passivate defects of a-Si:H/SiO₂, which results in the reappearance of luminescence band at 760 nm, while for nc-Si/SiO₂, hydrogen passivation requires additional thermal annealing after nc-Si/SiO₂ multilayer was treated by HPA. It is indicated that higher atomic mobility is needed to passivate defects at nc-Si/SiO₂ interface compared with a-Si:H/SiO₂ interface.     

合成温度和N2/O2流量比对碳纤维衬底上生长的SnO2纳米线形貌及场发射性能影响

采用化学气相沉积法系统研究了合成温度和N₂/O₂流量对生长在碳纤维衬底上的SnO₂纳米线形貌及场发射性能的影响规律. 利用扫描电镜(SEM)、透射电镜(TEM), X射线衍射(XRD)及能谱仪(EDS)对产物细致表征, 结果表明, SnO₂纳米线长径比随反应温度的升高而增大; 随N₂/O₂流量比值的增大先增大后变小, 场发射测试表明, 合成温度780 ℃, N₂/O₂流量比为300 : 3 时SnO₂纳米线阵列具有最佳的场发射性能, 开启电场为1.03 V/μm, 场强增加到1.68 V/μm时, 发射电流密度达0.66 mA/cm², 亮度约2300 cd/m².     

压力对纳米CoFe2O4/SiO2复合材料结构的影响

 采用溶胶-凝胶工艺和高温高压实验技术,制备了纳米CoFe₂O₄/SiO₂复合材料。利用X射线衍射仪、扫描电子显微镜和振动样品磁强计,对样品的结构、微观形貌和磁性进行了研究,并对CoFe₂O₄中阳离子的占位情况进行了讨论。结果表明,随着处理压力的升高,样品的晶粒尺寸增大,晶格常数减小,比饱和磁化强度增大。通过计算结果可以推断,压力的升高导致CoFe₂O₄中的部分Fe³⁺从A位移向了B位,而部分Co²⁺则从B位移向了A位。     

Observation of large magnetic resistance in weak magnetic fields using CuPt/SiO2/Si/SiO2/CuPt structure

The magnetoresistive effect of CuPt(8 nm)/SiO₂(5 nm)/Si(50,000 nm)/SiO₂(5 nm)/CuPt(8 nm) structure made by e-beam evaporation technique is studied in this work. Variation in magnetoresistance obtained by I-V measurements at 77 K and in the presence of less than 5 mT magnetic field applied in parallel to the surface is investigated. We have found that this structure exhibit large magnetoresistance in low magnetic fields (i.e. <5 mT). Our results also indicate that the variation in magnetoresistance in the presence of external magnetic field has oscillatory behavior and has the maximum value of 3295%. This structure due to its high sensitivity to low magnetic fields can also be used as an active element in magnetic field sensor devices.     

A facile synthesis of monodisperse CoFe2O4/SiO2 nanoparticles

Aminated-CoFe₂O₄/SiO₂ magnetic nanoparticles (NPs) were prepared from primary silica particles using modified StÖber method. By optimizing the preparation conditions, monodisperse CoFe₂O₄/SiO₂ NPs with high amino groups’ density were obtained, which is necessary for enzyme immobilization. TEM confirm that the sample is a core/shell structure. These aminated-CoFe₂O₄/SiO₂ NPs have narrow size distributions with a mean size of about 60 nm. Moreover, the aminated-CoFe₂O₄/SiO₂ NPs can be easily dispersed in aqueous medium. The experimental results also show that the NPs have superparamagnetism, indicating that the aminated-CoFe₂O₄/SiO₂ NPs can be used as an effective carrier for the enzyme immobilization.     

二氧化硅对稀土掺杂二氧化钛薄膜形貌与发光性能的影响

为提高稀土掺杂TiO₂薄膜的上转换效率,采用溶胶-凝胶法和旋涂镀膜工艺制备了Yb³⁺-Er³⁺共掺杂SiO₂/TiO₂上转换光致发光薄膜,研究了SiO₂对TiO₂薄膜形貌以及发光性能的影响。利用FE-SEM观察了薄膜的表面形貌,利用分光光度计测试了薄膜在近红外光区域的透射率的变化,并用荧光光谱仪测试了薄膜的上转换发光光谱。结果表明：SiO₂的掺杂导致TiO₂颗粒尺寸显著减小,TiO₂薄膜在近红外的透射率也有所下降。在980 nm红外光激发下,SiO₂/TiO₂薄膜在630~670 nm处获得了明显的上转换红光发射,在516~537 nm和537~570 nm处获得了较弱的上转换绿光发射。由上转换发光强度与激光泵浦功率的关系推知,绿色和红色上转换发光均为双光子吸收发射过程。     

基于Ni电极和ZrO_2/SiO_2/ZrO_2介质的MIM电容的导电机理研究

研究了基于Ni电极和原子层淀积的ZrO_2/SiO_2/ZrO_2对称叠层介质金属-绝缘体-金属(MIM)电容的电学性能.当叠层介质的厚度固定在14nm时,随着SiO_2层厚度从0增加到2nm,所得电容密度从13.1 fF/μm~2逐渐减小到9.3fF/μm~2,耗散因子从0.025逐渐减小到0.02.比较MIM电容的电流-电压(I-V)曲线,发现在高压下电流密度随着SiO_2厚度的增加而减小,在低压下电流密度的变化不明显,还观察到电容在正、负偏压下表现出完全不同的导电特性,在正偏压下表现出不同的高、低场I-V特性,而在负偏压下则以单一的I-V特性为主导.进一步对该电容在高、低场下以及电子顶部和底部注入时的导电机理进行了研究.结果表明,当电子从底部注入时,在高场和低场下分别表现出普尔-法兰克(PF)发射和陷阱辅助隧穿(TAT)的导电机理;当电子从顶部注入时,在高、低场下均表现出TAT导电机理.主要原因在于底电极Ni与ZrO_2之间存在镍的氧化层(NiO_x),且ZrO_2介质层中含有深浅两种能级陷阱(分别为0.9和2.3 eV),当电子注入的模式和外电场不同时,不同能级的陷阱对电子的传导产生作用.     

Nitric acid oxidation of Si (NAOS) method for low temperature fabrication of SiO2/Si and SiO2/SiC structures

We have developed low temperature formation methods of SiO₂/Si and SiO₂/SiC structures by use of nitric acid, i.e., nitric acid oxidation of Si (or SiC) (NAOS) methods. By use of the azeotropic NAOS method (i.e., immersion in 68 wt% HNO₃ aqueous solutions at 120 °C), an ultrathin (i.e., 1.3-1.4 nm) SiO₂ layer with a low leakage current density can be formed on Si. The leakage current density can be further decreased by post-metallization anneal (PMA) at 200 °C in hydrogen atmosphere, and consequently the leakage current density at the gate bias voltage of 1 V becomes 1/4-1/20 of that of an ultrathin (i.e., 1.5 nm) thermal oxide layer usually formed at temperatures between 800 and 900 °C. The low leakage current density is attributable to (i) low interface state density, (ii) low SiO₂ gap-state density, and (iii) high band discontinuity energy at the SiO₂/Si interface arising from the high atomic density of the NAOS SiO₂ layer.For the formation of a relatively thick (i.e., ≥10 nm) SiO₂ layer, we have developed the two-step NAOS method in which the initial and subsequent oxidation is performed by immersion in ∼40 wt% HNO₃ and azeotropic HNO₃ aqueous solutions, respectively. In this case, the SiO₂ formation rate does not depend on the Si surface orientation. Using the two-step NAOS method, a uniform thickness SiO₂ layer can be formed even on the rough surface of poly-crystalline Si thin films. The atomic density of the two-step NAOS SiO₂ layer is slightly higher than that for thermal oxide. When PMA at 250 °C in hydrogen is performed on the two-step NAOS SiO₂ layer, the current-voltage and capacitance-voltage characteristics become as good as those for thermal oxide formed at 900 °C.A relatively thick (i.e., ≥10 nm) SiO₂ layer can also be formed on SiC at 120 °C by use of the two-step NAOS method. With no treatment before the NAOS method, the leakage current density is very high, but by heat treatment at 400 °C in pure hydrogen, the leakage current density is decreased by approximately seven orders of magnitude. The hydrogen treatment greatly smoothens the SiC surface, and the subsequent NAOS method results in the formation of an atomically smooth SiO₂/SiC interface and a uniform thickness SiO₂.