X射线光电子能谱

X射线光电子能谱（X-ray photoelectron spectroscopy，XPS）技术也被称作用于化学分析的电子能谱（electron spectroscopy for chemical analysis，ESCA）．XPS属表面分析法，它可以给出固体样品表面所含的元素种类、化学组成以及有关的电子结构重要信息，在各种固体材料的基础研究和实际应用中起着重要的作用．文章简要介绍了XPS仪器的工作原理和分析方法，并给出了XPS在科学研究工作中的应用实例．     

X射线光电子能谱

X射线光电子能谱（X-ray photoelectron spectroscopy, XPS）技术也被称作用于化学分析的电子能谱（electron spectroscopy for chemical analysis,ESCA）.XPS属表面分析法,它可以给出固体样品表面所含的元素种类、化学组成以及有关的电子结构重要信息,在各种固体材料的基础研究和实际应用中起着重要的作用.文章简要介绍了XPS仪器的工作原理和分析方法,并给出了XPS在科学研究工作中的应用实例.     

Secondary electron emission of sputtered alumina films

Secondary electron emission yieldδ was measured for thin films of alumina prepared byrf sputtering technique. Single pulse method was used along with 4-gridleed optics system to determineδ. Maximum value of 4·3 was obtained at primary energy of 350 eV. The Dionne’s theory was used to analyse the results and the emission probability escape depth and absorption coefficient of secondaries were also estimated. Fairly good correlation is observed between experimental and theoretical values ofδ for beam energies upto 1 keV.     

On line shape analysis in X-ray photoelectron spectroscopy

Any solid state X-ray photoelectron spectrum (XPS) contains contributions due to multiple inelastic scattering in the bulk, surface excitations, energy losses originating from the screening of the final state hole (intrinsic losses), and, for non-monochromatized incident radiation, ghost lines originating from the X-ray satellites. In the present paper it is shown how all these contributions can be consecutively removed from an experimental spectrum employing a single general deconvolution procedure. Application of this method is possible whenever the contributions mentioned above are uncorrelated. It is shown that this is usually true in XPS to a good approximation. The method is illustrated on experimental non-monochromatized MgK spectra of Au acquired at different detection angles but for the same angle of incidence of the X-rays.     

Secondary electron emission data of cesiated oxygen free high conductivity copper

Because of its relevance for negative hydrogen ion sources, the change in secondary electron emission with the adsorption of Cs on Cu was studied. Properly prepared disks of oxygen free high conductivity (OFHC) copper yielded a maximum secondary electron emission δ_max=1.54±3%. The deposition of ≈0.5 monolayer of Cs resulted in δ_max=3.40±3%.     

金纳米结构表面二次电子发射特性

使用低气压蒸发工艺制备了金纳米结构,研究了金纳米结构的二次电子发射特性及其对表面形貌的依赖规律,表征了金纳米结构表面出射二次电子能量分布.实验结果表明:蒸发气压升高时,金纳米结构孔隙率增大,表面电子出射产额降低;能量分布表明金纳米结构仅对低能真二次电子有明显抑制作用,对背散射电子的作用效果则依赖于表面形貌.使用由半球和沟槽构成的复合结构,并结合二次电子发射唯象概率模型,对金纳米结构进行模型等效及电子发射特性仿真,模拟结果表明:纳米结构中的半球状纳米颗粒对两种电子产额均有增强作用;沟槽对真二次电子产额有强抑制作用,而对背散射电子产额仅有微弱抑制作用.本工作深入研究了金纳米结构表面电子发射机理,对于开发空间微波系统中纳米级低电子产额表面有重要参考价值.     

提高砷化镓二次电子发射系数的探讨

介绍了延长负电子亲和势二次电子发射材料砷化镓的逸出深度的设计,并给出了经过特殊设计的这种砷化镓的能级示意图,然后对通常的砷化镓和经过特殊设计的砷化镓的二次电子发射系数的理论值进行了比较,得出:当原电子入射能量较低（小于10 keV）时,两种砷化镓的二次电子发射系数差值较小;当原电子入射能量较高（大于20 keV）时,经过特殊设计的砷化镓的二次电子发射系数比普通砷化镓的二次电子发射系数大,而且随着原电子入射能量的升高,两种砷化镓的二次电子发射系数差值也在增大。     

X-ray photoelectron spectroscopy study of Pd oxidation by RF discharge in oxygen

The low-temperature oxidation of polycrystalline palladium by RF oxygen plasma was studied via X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Detailed information about the electronic states of palladium and oxygen was obtained based on the XPS curve fitting analysis of Pd3d and Pd3p + O1s lines. The results showed that Pd oxidation by oxygen plasma was different from Pd oxidation in pure O₂ at high temperature. SEM shows well-structured submicron PdO particles result from oxidation in pure O₂, whereas plasma oxidation results in the predominant formation of two-dimensional PdO structures covering the initial crystallites of the Pd foil. Further oxidation to a three-dimensional PdO phase occurs under prolonged treatment with oxygen plasma. The formation of a PdO_x (x > 1) species, characterized by a E_b(Pd3d_5/2) = 338.0–338.2 eV value that is close to the Pd⁴⁺ oxidation state, was also observed. This PdO_x species was found to have low thermal stability (T < 400 K). It is proposed that the PdO_x species can be localized within the boundaries of crystallites.     

Near surface composition of some alloys by X-ray photoelectron spectroscopy

Chemical compositions of the alloys of CuNi (Cu_0.10Ni_0.90, Cu_0.30Ni_0.70, Cu_0.70Ni_0.30) and BiSb (Bi_0.80Sb_0.20, Bi_0.64Sb_0.34, Bi_0.55Sb_0.45) are determined by X-ray photoelectron spectroscopy. The stoichiometries are determined and are compared with the bulk compositions. Possible sources of systematic errors contributing to the results are discussed. Errors arising out of preferential etching in these alloys have been investigated. It has been inferred from such studies that the preferential etching does not enrich the surface composition with a particular component for the two systems reported here. Quantitative results of CuNi system indicate that the surface regions of the Cu_0.70Ni_0.30 alloy is Cu-rich, although no such evidence is observed in case of BiSb system.     

Secondary electron yield enhancement by MgO capping layers

The yield of secondary electrons emitted from an epitaxial three monolayer (3 ML) NiO(1 0 0)/Ag(1 0 0) film excited by soft X-ray linearly polarized synchrotron radiation at the Ni L_2,3 absorption threshold has been measured for different values of the thickness of a MgO(1 0 0) capping layer. Compared with the as grown 3 ML NiO(1 0 0)/Ag(1 0 0) film, we observe a significant enhancement by about a factor 1.2 of the secondary electron emission for the capped 8 ML MgO(1 0 0)/3 ML NiO(1 0 0)/Ag(1 0 0) sample. A further substantial yield enhancement by a factor 1.6 with respect to the uncapped NiO sample is observed after deposition of an additional 8 ML MgO(1 0 0) film, for a total capping layer thickness of 16 ML. The observed secondary electron yield enhancement is discussed in terms of modified electronic structure, surface work function changes, and characteristic electron propagation lengths.     

绝缘体二次电子发射系数测量装置的研制

 成功研制了测量绝缘体二次电子发射系数的测量装置，该装置主要由栅控电子枪系统、真空系统和电子采集系统组成，测量装置产生的原电子流的能量范围为0.8~60 keV。采用单脉冲电子枪法，测量了原电子能量范围为0.8~45 keV的多晶MgO的二次电子发射系数。测量中，收集极(偏置盒)离材料表面设置为约35 mm，偏置电压设置为 45 V。测量得到：用磁控溅射法制备的MgO的二次电子发射系数最大值约为2.83，处于 2~26范围内，其对应的原电子能量约为980 eV。这表明该装置测量的绝缘体二次电子发射系数是可信的，但用磁控溅射法制备的MgO的二次电子发射系数较低，这可能是制备MgO时引入了过多的杂质在MgO二次电子发射体里面所引起的。     

X-ray photoelectron spectroscopy and magnetism of Mn1−x Al x alloys

X-ray photoelectron spectroscopy (XPS), magnetization and magnetic susceptibility of Mn_1−x Al _x (x = 0.0, 0.2, 0.4, 0.5, 0.6, 0.7) alloys are reported. X-ray diffraction measurements showed that all investigated samples have the same crystallographic structure as the parent compound (AuCu₃-structure type). The alloys are disordered for x ≤ 0.5, but become almost crystallographically ordered for higher Al concentration. This change in the crystallographic order is reflected both in the magnetization and Curie temperature values. The exchange interaction is ferromagnetic between the pairs of the near-neighbour Mn-Ni and Ni-Ni magnetic moments and antiferromagnetic for Mn-Mn pairs. The last one is present only in the disordered alloys, which leads to smaller values of the magnetization of these alloys in comparison with the ordered ones. The Mn magnetic moment has the fully ordered value of 3.2 μB in all investigated alloys. The decrease of the Ni magnetic moment as the Al concentration increases may be explained by the hybridization of the Ni 3d and Al 3sp states, which leads to a partial filling of the Ni 3d band. The magnetic susceptibility measurements pointed out the existence of spin fluctuations on Ni sites.      

Heating-induced variations of secondary electron emission from ion-cleaned copper samples

Secondary electron (SE) emission due to electron impact depends strongly on surface conditions. The variations of SE yield and spectrum with the heating temperature of Ar-ion-cleaned oxygen-free copper samples are therefore measured in situ in a multifunctional ultrahigh vacuum system. The SE yield and the SE spectrum are observed to increase and to narrow, respectively, after sample heating. The maximum SE yield increases from 0.97 before heating to 1.25 after heating at ∼313 °C, and the corresponding full width at half maximum of SE spectrum decreases considerably from 9.3 to 5.5 eV. More CO₂ and Ar ions are shown to desorb at a higher heating temperature by residual gas analysis, indicating their contribution to the reduction in work function and surface potential barrier. Ar-ion desorption appears to affect the SE spectrum more than the SE yield. The obtained results provide a new insight into complicated surface influences on SE emission in thermal applications of scanning electron microscopy.     

颗粒膜厚度对表面传导电子发射的影响

制备了不同厚度下的C-Ti颗粒膜用作表面传导电子发射的阴极发射薄膜,研究了不同颗粒膜厚度对电子发射特性的影响。将所制备阴极器件加载不同电压幅值下的等幅三角波,对器件进行电形成,结果表明:颗粒膜厚度为69 nm的器件开启电压为32 V,在33 V时具有最大发射效率;颗粒膜厚度为855 nm的器件开启电压为15 V, 在23 V时发射效率最高;颗粒膜厚度为69 nm的器件所形成的电压范围和电子发射效率都明显高于颗粒膜厚度为855 nm的器件。     

Secondary electron emission yield from vertical graphene nanosheets by helicon plasma deposition

The secondary electron emission yields of materials depend on the geometries of their surface structures.In this paper,a method of depositing vertical graphene nanosheet(VGN)on the surface of the material is proposed,and the secondary electron emission(SEE)characteristics for the VGN structure are studied.The COMSOL simulation and the scanning electron microscope(SEM)image analysis are carried out to study the secondary electron yield(SEY).The effect of aspect ratio and packing density of VGN on SEY under normal incident condition are studied.The results show that the VGN structure has a good effect on suppressing SEE.     

高入射能量下的金属二次电子发射模型

基于高入射能量电子产生二次电子发射的物理过程, 分别对高入射能量电子产生的真二次电子和背散射电子的概率进行理论分析与建模. 利用Bethe能量损失模型和内二次电子逸出概率分布, 推导出高入射能量电子产生有效真二次电子发射的系数与入射能量的关系式; 根据高入射能量电子在材料内部被吸收的规律, 推导出高入射能量电子产生背散射电子的系数与入射能量之间的关系式. 结合两者得到高入射能量下金属的二次电子发射模型. 利用该模型计算得到典型金属材料Au, Ag, Cu, Al的二次电子发射系数, 理论计算结果与采用Casino软件模拟金属内部散射过程得到的数值模拟结果相符. 关键词： 二次电子发射 高入射能量 金属表面 散射过程     

颗粒膜厚度对表面传导电子发射的影响

制备了不同厚度下的C-Ti颗粒膜用作表面传导电子发射的阴极发射薄膜,研究了不同颗粒膜厚度对电子发射特性的影响。将所制备阴极器件加载不同电压幅值下的等幅三角波,对器件进行电形成,结果表明:颗粒膜厚度为69 nm的器件开启电压为32 V,在33 V时具有最大发射效率;颗粒膜厚度为855 nm的器件开启电压为15 V, 在23 V时发射效率最高;颗粒膜厚度为69 nm的器件所形成的电压范围和电子发射效率都明显高于颗粒膜厚度为855 nm的器件。     

二次发射微波电子枪的倍增特性

 利用3DRun程序通过数值模拟计算，对二次发射微波电子枪的束流倍增特性作了研究。用1维模型计算了束流倍增与腔两极间距离以及腔中场强的关系，并详细给出了腔两极间距离为10mm,场强为5-4MV/m时出射电子纵向聚束及能量聚焦过程；利用3DRun程序研究了在高频场及粒子束本身空间电荷场的共同作用下，束流在3维运动过程中的倍增特性，计算了出射束流的发射度。通过计算表明：二次发射微波电子枪可以提供低发射度、高流强的电子束。     

The charging stability of different silica glasses studied by measuring the secondary electron emission yield

This paper reports that the charging properties of lead silica,Suprasil silica and Infrasil silica are investigated by measuring the secondary electron emission(SEE) yield.At a primary electron beam energy of 25 keV,the intrinsic SEE yields measured at very low injection dose are 0.54,0.29 and 0.35,respectively for lead silica,Suprasil and Infrasil silica glass.During the first e-beam irradiation at a high injection current density,the SEE yields of lead silica and Suprasil increase continuously and slowly from their initial values to a steady state.At the steady state,the SEE yields of lead silica and Suprasil are 0.94 and 0.93,respectively.In Infrasil,several charging and discharging processes are observed during the experiment.This shows that Infrasil does not reach its steady state.Two hours later,all samples are irradiated again in the same place as the first irradiation at a low current density and low dose.The SEE yields of lead silica,Suprasil and Infrasil are 0.69,0.76 and 0.55,respectively.Twenty hours later,the values are 0.62,0.64 and 0.33,respectively,for lead silica,Suprasil and Infrasil.These results show that Infrasil has poor charging stability.Comparatively,the charging stability of lead silica is better,and Suprasil has the best characteristics.     

Tracking hydroxyl adsorption on TiO2 (1 1 0) through secondary emission changes

In surface science, rutile TiO₂ continues to be one of the most studied surfaces and in the catalysis field numerous groups study how adsorbates interact with this surface. All groups face the difficult problem of reproducibility due to surface preparation unknowns like defect concentration and the continuous aging of the crystals. Recent studies, using STM imaging, showed that hydroxyl adsorption takes place even in very good vacuum conditions. Upon adsorption, the surface electric field is reduced and the work function decreases. We found that this change may be readily detected in the onset energy of the secondary electrons. By following the onset region of secondary electron emission it is possible to track hydroxyl adsorption in quantities well below the detection level of XPS and LEIS. With this knowledge, we show that the time elapsed after surface preparation and water partial pressure should be accounted in the study of TiO₂ surfaces.