Influence of dopants on the performance of a fiber optic surface plasmon resonance sensor

In this paper, a theoretical analysis is carried out to estimate the sensitivity and the signal-to-noise ratio (SNR) of a fiber optic surface plasmon resonance (SPR) sensor when fibers with different dopants and different doping concentrations are used. The dopants considered are germanium oxide (GeO₂), boron oxide (B₂O₃), and phosphorus pentoxide (P₂O₅) in a pure silica fiber. The variation of the dispersion relation with different dopants and doping concentrations are taken into account for the analysis. It is shown that the doping of B₂O₃ increases the sensitivity of the sensor while the effect of dopant on SNR is negligible. The analysis is extended to fiber optic SPR sensor with bimetallic layers.     

Electronic structures and magnetic couplings of B-, C-, and N-doped BeO

The electronic structures and magnetic properties of B-, C-, and N-doped BeO supercells are investigated by means of ab initio calculations using density functional theory. The magnetic exchange constants of C-doped BeO at different doping levels are also calculated. A phenomenological band structure model based on p-d exchange-like p-p level repulsion between the dopants is proposed to explain the magnetic ground states in B-, C-, and N-doped BeO systems. The evolution from the antiferromagnetic phase to the ferromagnetic phase of C-doped BeO supercell with C concentration decreasing can also be well explained using this model. The findings in this study provide a simple guide for the design of band structure for a magnetic sp-electron semiconductor.     

The study on microstructure and microwave-absorbing properties of lithium zinc ferrites doped with magnesium and copper

Lithium zinc ferrites doped with magnesium and copper were prepared by means of a combination of sol-gel method and subsequent calcination. The crystalline phase and microstructure of different doped lithium zinc ferrites were measured by X-ray powder diffraction and scanning electronic microscopy analysis. The results indicate that there are no remarkable differences in phase composition between pure lithium zinc ferrite and the as-doped lithium zinc ferrites. The effects of magnesium and copper dopants on microwave absorption in low-frequency region were investigated by the transmission/reflection coaxial line method. It was found from the present work that doping with copper improved microwave-absorbing properties, while doping with magnesium had little effect on microwave absorption of pure lithium zinc ferrite.     

弛豫铁电体的键能与配位数模型

基于一定浓度的杂质会在钛酸钡型铁电体中导致键能与配位数的高斯型分布原理,利用键能与配位数起伏模型导出了介电峰温与测量频率的关系.当键能和配位数的相对起伏接近时,其关系呈现出一般弛豫铁电体所普遍具有的Vogel-Fulcher函数形式,且冻结温度仅与键能的相对起伏和激活能有关.并由此解释了低掺杂浓度下杂质均匀分布导致弥散性的机理和超过临界浓度时的弛豫铁电性的机理.同时提出,杂质替代对畴的形成和生长所产生的强烈抑制作用及微畴化是实现键能起伏与配位数起伏一致的来源.     

不同掺杂顺序的磷光OLED器件发光性能的研究

绿色GIr1和红色R-4B磷光染料,采用红绿红、绿红、红绿、绿红绿等顺序,与主体材料CBP共蒸,制备了四种红绿磷光器件,并结合TCTA和BCP对载流子和激子的阻挡作用,研究了发光层掺杂顺序对器件性能的影响。结果表明,四种器件光谱、光效、亮度和发光颜色均有较大差异,且BCP和CBP界面附近是主要的激子复合区。在电压为5v,红绿红掺杂型器件,亮度、电流效率和色坐标分别为40.12 cd·m-2,7.68 cd·A-1 和(0.630 1,0.365 4);而绿红绿掺杂型器件为104 cd·m-2,19.75cd·A-1和(0.371 7,0.576 8)。分析认为：CBP与GIr1,R-4B,BCP,TCTA有较大的LUMO能级差异,发光层中电子的主要传输方式为掺杂分子上的俘获和分子间跳跃,不同掺杂顺序会形成不同能级势垒分布,发光层内电荷累积形成的空间电场分布不同。     

Photoconductivity, dielectric and thermal investigations of pure, benzophenone- and iodine-doped benzoyl glycine NLO single crystals

Physical properties such as photoconductivity, dielectric and thermal stability have been investigated for pure benzoyl glycine (BG) crystals. In addition to this, the influence of dopants (benzophenone and iodine) of these properties on BG crystals has been studied. Photoconductivity studies on pure BG, benzophenone-and iodine-doped BG revealed the positive photoconducting nature. The dielectric responses of the samples have been studied in the frequency range 100 Hz-500 KHz at room temperature and the results are discussed in detail. The thermogravimetric studies of pure and doped BG crystals indicate that the presence of dopants has slightly increased the decomposition temperature of pure BG samples, thereby enhancing thermal stability to the doped ones.     

First-principles study of plasmons in doped graphene nanostructures

The operating frequencies of surface plasmons in pristine graphene lie in the terahertz and infrared spectral range,which limits their utilization. Here, the high-frequency plasmons in doped graphene nanostructures are studied by the timedependent density functional theory. The doping atoms include boron, nitrogen, aluminum, silicon, phosphorus, and sulfur atoms. The influences of the position and concentration of nitrogen dopants on the collective stimulation are investigated,and the effects of different types of doping atoms on the plasmonic stimulation are discussed. For different positions of nitrogen dopants, it is found that a higher degree of symmetry destruction is correlated with weaker optical absorption. In contrast, a higher concentration of nitrogen dopants is not correlated with a stronger absorption. Regarding different doping atoms, atoms similar to carbon atom in size, such as boron atom and nitrogen atom, result in less spectral attenuation. In systems with other doping atoms, the absorption is significantly weakened compared with the absorption of the pristine graphene nanostructure. Plasmon energy resonance dots of doped graphene lie in the visible and ultraviolet spectral range.The doped graphene nanostructure presents a promising material for nanoscaled plasmonic devices with effective absorption in the visible and ultraviolet range.     

Influence of optical-damage-resistant dopants on the nonlinear optical properties of lithium niobate

Using the chemical-bond method, nonlinear optical properties of lithium niobate containing different dopants are calculated. In crystals with stoichiometric composition the second order nonlinear susceptibility decreases approximately linearly with increasing dopant concentration. Among the dopants studied – Mg, Zn and In – this behaviour is most highly expressed for In doping. In contrast to that, congruently grown crystals show a different behaviour; only a weak dependence on the dopant concentration is found for, for example, Mg-doped material. Received: 24 October 2000 / Published online: 21 March 2001     

Atomistic simulation of Mn-site substitution in multiferroic h-YMnO3

Atomistic simulation has been performed to systematically investigate the Mn-site doping of h-YMnO(3) (hexagonal yttrium manganese oxide). It is found that tetravalent dopants are the most energetically favorable for incorporation into a crystal lattice. For divalent dopants, hole compensation is the more likely charge compensation mechanism, whereas for dopants with mixed valence, the divalent state is the energetically preferred form. Structural and local polarization changes caused by Mn-site doping are also investigated. The tilting angle of the MnO(5) trigonal bipyramid is suppressed for all of the dopants investigated, with the reduction dependent on the dopant ion radius, while the influence on buckling is closely related to the valence of the dopants. Our results reveal that both electrostatic and size effects play important roles in the ferroelectric polarization of h-YMnO(3).     

Secondary ion mass spectrometry measurements of deuterium penetration into silicon by low pressure RF glow discharges

Abstract

Using secondary ion mass spectrometry (SIMS) the penetration of deuterium into Si(100) substrates as a result of exposure to deuterium low pressure rf discharges has been determined as a function of exposure time, thermal contact of the Si wafers to the substrate electrode, substrate doping, and discharge pressure. For undoped (100) single crystal Si exposed without intentional heating to a 25 m torr D₂ plasma for 1 min the deuterium concentration in the near-surface region (0—30 nm) approaches 10²¹ at.cm^?3. It drops off with depth, but is still greater than 10¹⁷ at.cm.^?3 at a silicon depth of 200 nm. The large penetration depth, the observation that lowering the substrate temperature decreases the rate of deuterium uptake, and the dependence of deuterium penetration on the substrate doping type indicate that hydrogen diffusion is of primary importance. The presence of a 50 nm thick oxide layer on the Si substrate during plasma exposure lowers the deuterium near-surface concentration in the Si substrate by about three orders of magnitude, while the presence of 10 nm of thermal oxide reduces the deuterium uptake only insignificantly. Heavily B and As doped polycrystalline Si show less deuterium penetration, while undoped polycrystalline Si shows more deuterium uptake than undoped single crystal Si for the same plasma treatment.     

Incorporation of AsSe centers in ZnSe far from equilibrium

An experimental technique employing nuclear transmutation to probe the effects of arsenic doping in ZnSe is presented. ZnSe epitaxial layers are grown from elemental Zn and elemental Se that contains the ⁷⁵Se isotope. Arsenic dopants are incorporated in ZnSe through the decay of ⁷⁵Se to ⁷⁵As which proceeds via electron capture. The 118.5 day half-life of the decay allows ZnSe epitaxial layers to be deposited prior to significant arsenic formation so that As_Se dopants are incorporated after all crystal growth processes are complete. Also, the temperature at the time of dopant incorporation is under investigator control. Because the decay process produces nuclear recoils that are far too small to displace the arsenic dopants from their substitutional selenium sites, no post-growth thermal annealing is required. This experimental technique permits a limiting case of far-from-equilibrium doping, and the long half-life of ⁷⁵Se results in the gradual incorporation of As_Se so that time-resolved studies can be performed. In the experimental work reported here, As_Se centers are introduced in ZnSe homoepitaxial layers in concentrations greater than 1.5×10¹⁸ cm⁻³. Time-resolved low temperature photoluminescence is employed to observe the effects of As_Se doping of ZnSe.     

Electrical and optical investigation on doping of II–VI compounds using radioactive isotopes

Using radioactive isotopes of shallow dopants (Ag, As, Rb) as well as of native or isoelectronic elements (Se, Te, Cd, Sr) which were incorporated as host atoms and then transmuted into relevant dopants (transmutation doping) we investigated doping phenomena occurring in the wide band gap II–VI compounds CdTe, ZnTe, ZnSe and SrS by the classical methods of semiconductor physics: Hall effect, C–V and photoluminescence measurements. Thus, we could assign unambiguously defect features in electrical and photoluminescence measurements to extrinsic dopants by means of the half lives of radioactive decay. In As doped ZnSe samples we observed two states: a metastable effective mass like state and a deep state. The occurrence of the latter state is always linked with the high resistivity of As doped ZnSe crystals. The transmutation doping experiments reveal that the so-called self-compensation typical for wide band gab II–VI compounds can be overcome when the thermal treatment for dopant incorporation is time separated from its electrical activation, achieved using transmutation at room temperature. Under these conditions we found an almost one-to-one doping efficiency relative to the implanted dose. Thus, these investigations are a contribution to understanding compensation phenomena occurring due to interactions between dopants and native defects during conventional doping treatments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Abnormal oxidation in nickel silicide and nickel germanosilicide in sub-micro CMOS

After post-silicidation annealing at various temperatures for 30 min,abnormal oxidation and agglomeration in nickel silicide and nickel germanosilicide are investigated under different conditions of NiSi,with As-,In-,and Sb-doped Si substrates of nickel germanosilicide without any dopants.The NiSi thickness,dopant species,doping concentration,and silicide process conditions are dominant factors for abnormal oxidation and NiSi agglomeration.Larger dopants than Si,thinner NiSi thickness and SiGe substrates,and higher dopant concentrations promote abnormal oxidation and agglomeration.     

Anisotropic scattering rates and antiferromagnetic precursor effects in the t-t'-U Hubbard model

We have investigated the evolution of the electronic properties of the t-t'-U Hubbard model with hole doping and temperature. Due to the shape of the Fermi surface, scattering from short wavelength spin fluctuations leads to strongly anisotropic quasi-particle scattering rates at low temperatures near half-filling. As a consequence, significant variations with momenta near the Fermi surface emerge for the spectral functions and the corresponding ARPES signals. At low doping the inverse lifetime of quasiparticles on the Fermi surface is of order varying linearly in temperature from energies of order t down to a very low energy scale set by the spin fluctuation frequency while at intermediate doping a sub-linear T-dependence is observed. This behavior is possibly relevant for the interpretation of photoemission spectra in cuprate superconductors at different hole doping levels. Received 31 July 2000     

Conductivity in Nd+K doped ferroelectric lead germanate single crystals

Nd⁺³+K⁺ doped ferroelectric lead germanate (LG) single crystals were grown to study the influence of the double dopants on ferroelectric behavior of LG. The crystals were grown by controlled cooling of the melt. Temperature variation of d.c. conductivity of the grown samples was studied in temperature range of 40-400 °C. Room temperature conductivity was enhanced as a result of doping. The existence of two activation energies, one in the ferroelectric phase (0.61 eV) and another in the paraelectric phase (0.77 eV) in the results, were revealed. The increase in conductivity due to doping is attributed to the generation of charge carriers due to double doping and the existence of two activation energies is attributed to the structural changes taking place at the ferroelectric transition temperature.     

纳米晶ZrO2：Pr^3＋与ZrO2：Pr^3＋，Sm^3＋发光研究

采用化学共沉淀法制备了纳米晶ZrO2：pr^3＋粉体，所制备的纳米晶ZrO2：Pr^3＋粉体中Pr^3＋的强室温特征发射的两个主发射带为^1D2-^2H4和^3P0-^3H4跃迁。不同热处理温度下纳米晶ZrO2：Pr^3＋晶体结构不同，因此它们的发光不同；ZrO2基质向Pr^3＋有能量传递，在高温煅烧得到的单斜相配位场中能量传递较好。荧光强度与Pr^3＋浓度的关系研究表明：^3P0和^1D2功能级有不同的猝灭规律，由于[^1D2,^3H4]→[^1G4,^3F4]的交叉弛豫，使得^1D2-^3H4跃迁的猝灭浓度很低，在我们的实验中，掺0．1mol％Pr^3＋时^1D2-^3H4地跃迁发射最强，掺2mol％Pr^3＋时^3R0-^3H4跃迁发射最强。文章制备的纳米晶ZrO2：Pr^3＋，Sm^3＋中Sm^3＋的^4G（5-2）～^6H（7／2）跃迁荧光峰因Pr^3＋加入而增强，这除了两种离子某些能级相近产生荧光发射的叠加效应外，还存在Pr^3＋→Sm^3＋的能量传递。     

Photoluminescence in fluorescent 4H-SiC single crystal adjusted by B,Al,and N ternary dopants

This paper reports the sensitive effect of photoluminescence peak intensity and transmittance affected by B, Al, and N dopants in fluorescent 4H-SiC single crystals. The crystalline type, doping concentration, photoluminescence spectra,and transmission spectra were characterized at room temperature. It is found that the doped 4H-SiC single crystal emits a warm white light covering a wide range from 460 nm to 720 nm, and the transmittance increases from ~10% to ~60%with the fluctuation of B, Al, and N ternary dopants. With a parameter of C_(D-A), defined by B, Al, and N concentration, the photoluminescence and transmittance properties can be adjusted by optimal doping regulation.     

Trapping and retention of deuterium in plasma-irradiated carbonic materials

Trapping and retention of deuterium in the graphitized carbon composite CFC N11 and pyrolytic graphite PG99 under plasma irradiation were investigated using the technique of thermal desorption spectroscopy. In particular, it was shown that (1) deuterium is trapped even when the energy of irradiating ions approaches zero and in the case of electron irradiation’ (2) the doses being equal, trapping depends on irradiation duration’ and (3) the effect of temperature on trapping depends on the ion energy. Two mechanisms of deuterium trapping are considered. The observed regularities are explained by the peculiarities of their action in different conditions.     

UV absorption edge shift by doping alkali fluorides in fluoroaluminate glass

The effect on transmittance and reflectance in the vacuum ultraviolet (VUV) region by doping alkali fluorides (LiF, NaF and KF) has been investigated in a ternary fluoroaluminate (18BaF₂-37CaF₂-45AlF₃) glass. The absorption edge of the glass obeys the Urbach rule and was shifted monotonically towards higher energies by increasing the concentration of each alkali fluoride. The VUV reflection peak at 11.3 eV was not sensitive to the change of the concentration of dopants. The magnitude of the edge shift was 10-20 times larger than that expected from the additive law on the magnitude of absorption coefficients of the glass and alkali fluorides. An excitonic interaction similar to that observed in mixed crystals of alkali halides is suggested from the monotonic shift toward the absorption edges of the dopants. The weak sensitivity of the reflection peak upon doping supports that the excitonic state lies predominantly around the edge energies.     

Different substitutions lead to differences in the transport and recombination properties of group V doped SiCNTs

Silicon carbide nanotubes (SiCNTs) has attractive application prospects in the field of micro-nanodevices. Based on first-principle, we find that a shallow and a deep impurity levels appearing when a group-V element replaces a C, while only one deep impurity level appears when a group-V replaces a Si. This indicates that different electronic properties will be generated when group-V replace different sites of SiCNTs. Further numerical simulation results show that when dopant replaces C, the conductivity is about an order of magnitude higher than dopant replaces Si, and the conductivity increase with increasing temperature; the non-equilibrium minority carrier lifetime decrease with increasing temperature, when group-V replace the C, they are strong n-type, when replace the Si, they are in weak n-type and strong p-type. These results will help reveal the doping mechanism of SiC nanomaterials and the selection of dopants, and provide a theoretical basis for the preparation of micro-nanodevices.