电子束蒸发氧化锆薄膜的粗糙度和光散射特性

利用电子束蒸发工艺，以Ag层为衬底，沉积了中心波长为632．8nm的氧化锆（ZrO2）薄膜，膜层厚度在80-480nm范围内变化．研究了不同厚度样品的粗糙度变化规律和表面散射特性．结果发现，随着膜层厚度的逐渐增加．其表面均方根（RMS）粗糙度和总积分散射（TIS）均呈现出先减小后增大的趋势．利用非相关表面粗糙度的散射模型对样品的TIS特性进行了理论计算，所得结果与测量结果相一致．

A physico-chemical comparative study on extracellular carbohydrate polymers from five desert algae

Hydrodynamic properties of five newly isolated algal extracellular polysaccharides with putative adhesive properties are described, using a combination of size exclusion chromatography, total or 'multi-angle' laser light scattering and analytical ultracentrifugation. The respective polysaccharides had been extracted from four filamentous cyanobacteria: Microcoleus vaginatus, Scytonema javanicum, Phormidium tenue and Nostoc sp. and a coccoid single-cell green. algae Desmococcus olivaceus that had been separated from desert algal crusts of the Chinese Tegger Desert. SEC/MALLS experiments showed that the saccharides had, diverse-weight average molecular weights ranging from 4000 to 250,000 g/mol and all five showed either bi-modal or tri-modal molecular weight distribution profiles. Use of the Mark-Houwink-Kuhn-Sakurada (MHKS) scaling relationship between sedimentation coefficient and (weight average) molecular weight for the five samples, assuming a homologous conformation series revealed an MHKS b exponent of (0.33 +/- 0.04), suggesting a conformation between that of a stiff rod (b similar to 0.18) and a random coil (b similar to 0.4-0.5), i.e. a 'flexible rod' or 'stiff coil'. (C) 2003 Elsevier Ltd. All rights reserved.

Micro-Raman study on hydrogenated protocrystalline silicon films

Good quality hydrogenated protocrystalline silicon films were successfully prepared by radio frequency plasma enhanced chemical vapor deposition (PECVD) with various hydrogen dilution ratios (R = ([H-2]/[SiH4]) from 10 to 100). The photosensitivity of the films is up to 10(6) under the light intensity of 50mW.cm(-2). The microstructure of the films was studied by micro-region Raman scattering spectra at room temperature. The deconvolution of the Raman spectra by Gaussion functions shows that the films deposited under low hydrogen dilution ratios (R < 33) exhibit typical amorphous properties, while the films deposited under high hydrogen dilution ratios (R > 50) possess a diphasic structure, with increasing crystalline volume fraction with R. The size of the crystallites in the diphasic films is about 2.4 mm, which was deduced from the phonon confinement model. The intermediate range order of the silicon film increases with increasing hydrogen dilution ratio.

Effect of defects on optical phonon Raman spectra in SiC nanorods

Fabricated one-dimensional (1D) materials often have abundant structural defects. Experimental observation and numerical calculation indicate that the broken translation symmetry due to structural defects may play a more important role than the quantum confinement effect in the Raman features of optical phonons in polar semiconductor quantum wires such as SiC nanorods, (C) 1999 Elsevier Science Ltd. All rights reserved.

Observation of defects in GaN epilayers

GaN epilayers grown on sapphire substrates nitridated for various lengthy periods were investigated by light scattering tomography (LST) and Raman scattering. In the LST images of the plane-view epilayers, the light scattering defects distribute in [<11(2)over bar 0>] directions. The defect density is lower in epilayer grown on substrate nitridated for a longer period. The defects are believed to be straight threading edge dislocations on {<1(1)over bar 00>} planes. The Raman shift of E-2 mode is larger in the sample grown on substrate nitridated for a longer period. Our results show that the stress is higher in the sample with fewer dislocations.

PS-b-PEO嵌段共聚物薄膜的结晶与微相分离

半结晶性嵌段共聚物中，嵌段间的不相容性导致的微相分离与结晶嵌段的结晶行为之间存在相互竞争与协同作用。现阶段的大部分工作主要集中于半结晶性嵌段共聚物相分离发生后的结晶行为的结晶动力学和内部链折叠，而对于结晶与微相分离同时发生时的结晶与微相分离行为的研究还较少。 本论文以半结晶性的聚苯乙烯和聚环氧乙烷的二嵌段共聚物（PS-b-PEO）薄膜为研究对象，研究其破坏性（break out）结晶行为，以及研究方形片晶与微相分离结构的关系。 首先，本论文研究了不同相分离取向对结晶行为的影响。我们通过控制膜厚得到垂直基底和平行基底的微相分离薄膜。在溶剂蒸汽中，微相分离取向垂直基底时，仅仅是有序度增加，片晶协同生成。退火时间增加，结晶成核控制生长向扩散控制生长转变，导致片晶周围树枝晶生长。微相分离结构为平行基底取向时，焓主要用于取向转变和有序度增加，体系没有片晶生成，仅边缘效应使树枝晶产生。在结晶取向方面，研究了溶剂蒸汽氛围内界面作用改变使分子链轴垂直基底（flat-on）结晶向分子链轴平行基底（edge-on）结晶的转变。随着溶剂分子扩散到基底界面，结晶嵌段PEO与基底相互作用从强变弱，是发生这种转变的决定因素。 其次，从片晶与微相分离相互转变和片晶上微相分离刷的形成两方面研究片晶与微相分离的竞争与协同关系。退火溶剂的选择性影响片晶与微相分离的竞争。在PEO不良溶剂蒸汽环己烷中发生以下转变：片晶生成，逐渐被微相分离破坏，片晶重新生成；PEO良溶剂水中仅存在结晶到微相分离的转变。即晶体溶解，与PS发生微相分离以获得能量上的有利状态。可溶解嵌段的自由体积增加和结晶嵌段的低溶胀性分别是微相分离和结晶发生的关键因素。片晶与微相分离协同关系研究上，通过调控二嵌段共聚物片晶上聚合物刷的密度（小于14.3大于3.8），获得具有微相分离结构的聚合物刷。PS-PS刷的弱相互作用以及PS与PEO（连接PEO片层结构未结晶的PEO链）之间的强不相容性对片层上微相分离刷的形成起来决定作用。

溶剂诱导嵌段共聚物薄膜的微观相分离

通过研究发现薄膜厚度、溶剂对不同链段的选择性以及溶剂蒸汽处理时间对嵌段共聚物薄膜表面形态的演变有重要影响。对于对称双嵌段共聚物（PS-b-PMMA）薄膜在薄膜厚度小于0.5L_o时，在PMMA的选择性溶剂中处理不同时间时，除了得到垂直的lamellae形态外，还得到了有序纳米孔洞以及有序纳米孔洞和片层共存的新形态。同时其表面组成发生了变化，由最初PS位于表面层而转变为PMMA位于表面层。更进一步，得到的纳米结构图案化的薄膜具有环境敏感性。当将其置于对PS嵌段具有选择性的溶剂蒸汽中时，表面形貌发生了反转。另外研究发现，二元双嵌段共聚物共混体系，即小分子量的PS-b-PMMA和大分子量的PS-b-PMA共混，在硅基底上发生自组装形成具有有序孔洞结构的薄膜。这种结构完全不同于某一组分单独存在时所形成的微相结构。根本原因在于PMA和PMMA嵌段化学结构上的相似性，使PMMA链部分嵌入能量上优先吸附于极性基底的PMA嵌段中，形成了两种分子中的PS相容在一起构成的连续相围绕着塌陷的PMMA相的形态。

聚苯乙烯-聚丁二烯嵌段共聚物反转相行为的研究

本论文以聚苯乙烯（PS）一聚丁二烯（PB）三嵌段和二嵌段共聚物体系为研究对象，利用聚合物的软有序化，控制聚合物分子链的取向和聚集条件，系统地考察了嵌段共聚物在由溶液成膜的过程中动力学效应和墒效应对其相结构和相转变行为的影响。并探讨了不同相结构和其力学性能之间的构效关系。设计了聚苯乙烯（PS）一聚丁二烯（PB）（PS≈30wt％）／非选择性溶剂体系，通过改变溶剂的挥发速率，控制了嵌段共聚物薄膜相结构形成的动力学过程。在快速挥发的条件下，在嵌段共聚物中观察到了特殊的反转相结构，即共聚物中含量多的组分（PB）形成了分散相，而当溶剂挥发很慢的条件下，得到的是热力学较稳定的正常相的结构。对不同分子量的一系列嵌段共聚物的研究表明，反转相的形成和分子量相关，与聚合物的链段数目无关，只有在低于临界分子量 （Mw=70-100 KDa）的嵌段共聚物中，成膜过程的动力学过程才影响嵌段共聚物薄膜的最终相态，即形成反转相。这种依赖于分子量的相转变行为，揭示了分子链运动速度与环境变化速率的匹配对嵌段共聚物薄膜有序相结构形成的重要作用，即动力学效应对聚合物软有序化的重要作用。利用冷冻干燥的方法，进一步研究了嵌段共聚物在极慢的溶剂挥发下，由溶液膜变成固体膜的过程中，随着溶液浓度的增加，不同聚合物分子链在溶液中自组织形成有序结构的过程。结果表明反转相是由稀溶液向亚浓溶液转变的过程中形成的。通过选取具有代表性的不同亲和性的溶剂：苯和环己烷及其混合溶剂，研究了溶剂对不同链段亲和性的差异对反转相形成的影响。由聚合物一溶剂相互作用参数判断，苯是体系的良溶剂，环己烷是体系的。溶剂，而苯对PS链段有较好的亲和性，与之相反环己烷对PB链段有较好的亲和性，通过对聚苯乙烯（PS）一聚丁二烯印B）二嵌段共聚物在苯和环己烷极其混合溶剂中的相转变行为的研究发现，随着溶剂对含量少的PS链段亲和性的降低，反转相不再出现。这是由于苯与PS．链段、环己烷与PB链段有更好的亲和性，嵌段共聚物在稀溶液中，在耗尽吸引的（depletion attraction）作用下，与溶剂亲和性弱的链段，在溶液中优先发生聚集，而有序聚集后导致的混合熵的损失会被更多的因有序聚集后小分子自由体积增加引起的平移嫡的增量所补偿，因此导致了嫡驱动的软有序化。最后，通过原子力显微镜纳米压印法，分别对反转相和正常相结构的纳米力学性能进行了对比研究，讨论了不同相结构间模量的差异，结果表明软段（PB）形成分散相结构时薄膜的模量总是小于硬段（PS）形成分散相结构时薄膜的模量，这主要是由嵌段共聚物不同组分的相对含量及形成的相的结构决定的。

Microstructure of the silicon film prepared near the phase transition regime from amorphous to nanocrystalline

A kind of hydrogenated diphasic silicon films has been prepared by a new regime of plasma enhanced chemical vapor deposition (PECVD) near the phase transition regime from amorphous to nanocrystalline. The microstructural properties of the films have been investigated by the micro-Raman and Fourier transformed Infrared (FT-IR) spectra and atom force microscopy (AFM). The obtained Raman spectra show not only the existence of nanoscaled crystallites, but also a notable improvement in the medium-range order of the diphasic films. For the FT-IR spectra of this kind of films, it notes that there is a blueshift in the Si-H stretching mode and a redshift in the Si-H wagging mode in respect to that of typical amorphous silicon film. We discussed the reasons responsible for these phenomena by means of the phase transition, which lead to the formation of a diatomic hydrogen complex, H-2* and their congeries.

Observation of defects in GaN epilayers

GaN epilayers grown on sapphire substrates nitridated for various lengthy periods were investigated by light scattering tomography (LST) and Raman scattering. In the LST images of the plane-view epilayers, the light scattering defects distribute in [<11(2)over bar 0>] directions. The defect density is lower in epilayer grown on substrate nitridated for a longer period. The defects are believed to be straight threading edge dislocations on {<1(1)over bar 00>} planes. The Raman shift of E-2 mode is larger in the sample grown on substrate nitridated for a longer period. Our results show that the stress is higher in the sample with fewer dislocations.

流体力学半径对估算胶体微球聚集速率常数的影响

胶体粒子聚集速率常数实验值远低于理论值一直是被普遍关注的问题.聚集速率常数的理论推导是基于粒子的几何半径来考虑的,但决定粒子扩散速率及聚集速率的应该是粒子的流体力学半径(大于几何半径),因而它是使聚集速率常数实验值低于理论值的因素之一.影响流体力学半径的因素很多,其中,带电粒子在溶液中因表面存在双电层,会明显增大流体力学半径,造成聚集速率减慢.而双电层的厚度又随溶液中离子强度的不同而改变.本工作在聚集速率的公式中引入了修正因子,即几何半径与其流体力学半径之比,以修正由于用几何半径代替流体力学半径带来的误差.其中几何半径和流体力学半径可以分别用扫描电镜(SEM)和动态光散射(DLS)来测定.以两种粒径的聚苯乙烯带电微球为例,考察了在不同离子强度下,该误差的大小.结果发现,对于半径为30 nm的微球,用流体力学半径计算的慢聚集速率常数比理论值偏低约8%.该误差随离子强度增加而减少.对于快聚集情况,流体力学半径对聚集速率基本没有影响.

非粮原料燃料乙醇发酵关键技术的研究

生物质燃料乙醇是一种高度清洁的交通液体燃料，是减少温室气体排放，缓解大气污染的最佳技术选择。以非粮原料生产燃料乙醇可以在进行能源生产的同时保证粮食安全，有利于产业的可持续发展。在众多的非粮原料中，甘薯是我国开发潜力最大的生物质能源作物之一。我国占世界甘薯种植总面积和产量的90％。同时，甘薯的单位面积燃料乙醇产量远大于玉米和小麦。其成本是目前酒精中最低廉的，因此利用甘薯生产乙醇是发展生物质燃料乙醇的首要选择。目前采用薯类全原料主要采用分批发酵生产乙醇，其技术水平低，发酵强度低，一般在0.7－2.5g/（L•h），乙醇浓度低，甘薯发酵乙醇为6－8％(v/v)，能耗高，环境负荷大，污染严重。针对上述问题，本文从菌株选育、原料预处理、中试放大、残糖成分分析等方面进行研究。 为了研究乙醇发酵生产规模扩大过程中，大型发酵罐底部高压条件下，CO2对酵母乙醇发酵的影响，我们通过CO2 加压的方法进行模拟试验，研究结果表明，发酵时间随压强的升高而逐渐延长，高压CO2 对乙醇发酵效率影响不大，在0.3 MPa 以下时，发酵效率均可达到90%以上。高压CO2 对发酵的抑制作用是高压和CO2 这两个因素联合作用的结果。高压CO2 条件下，酵母胞外酶和胞内重要酶类的酶活均表现出特征性。0.2 MPa 下，酶活性的变化趋势和0.1 MPa 条件下的较为一致。而0.3 MPa 下的酶活变化趋势与0.4 MPa 下的酶活更为接近。通过全基因表达分析发现在CO2 压力为0.3 MPa 下，乙醇发酵途径中多个基因表达量下调，同时海藻糖合成酶和热激蛋白基因表达量上调。 筛选耐高温的乙醇酵母菌株能够解决糖化温度和发酵温度不协调的矛盾，实现真正意义上的边糖化边发酵。高温发酵还能够降低发酵时的冷却成本，实现乙醇的周年生产。本研究筛选出一株高温发酵菌株Y-H1，进而我们对该菌株的胞外酶和胞内乙醇代谢重要酶类的酶活性进行了分析。结果表明Y-H1 能够在40 ℃条件下正常进行乙醇发酵，发酵33h，最终乙醇浓度达到10.7%（w/w），发酵效率达到90%以上。同时发酵液最终pH 在3.5 左右，显示菌株具有一定的耐酸性能力。同时观察到40 ℃下，菌株的胞外酶和胞内乙醇代谢重要酶类的酶活性发生了变化，乙醇发酵途径中关键酶基因表达下调，而海藻糖合成酶与热激蛋白基因表达量上调，这些结果为进一步研究酵母菌耐热调控机理提供了依据。 糖蜜是一种大规模工业生产乙醇的理想原料，本研究利用选育高浓度乙醇发酵菌株结合配套的发酵稳定剂，研究了糖蜜高浓度乙醇发酵情况。结果表明采用冷酸沉淀预处理糖蜜溶液，采用分批补料的发酵方式，乙醇浓度最高达到了10.26% (w/w)，发酵时间为42 h。同时观察到在糖蜜发酵中，乙醛含量与乙醇浓度存在一定的相关性。 快速乙醇发酵对于缩短乙醇生产周期、降低乙醇生产成本、减少原料腐烂损失具有重要意义。本研究诱变和筛选得到了一株快速乙醇发酵菌株10232B。在优化后的发酵条件下，采用10L 发酵罐进行分批乙醇发酵，经过18h,乙醇的最终浓度达到88.5g/L,发酵效率93.6%，平均乙醇生产速度达到4.92 g/L/h。此菌株在保持较高乙醇生产浓度的同时，拥有快速生产乙醇的能力，适合作为快速乙醇发酵生产菌种。 由于鲜甘薯具有粘度大的特点，传统液化糖化处理很难在短时间内充分糖化原料；高粘度的醪液也难以进行管道输送，容易堵塞管路；同时，也会降低后续的乙醇发酵效率。 本文采用了快速粘度分析法对鲜甘薯糊化粘度特性进行了分析，进而对预处理条件进行了研究，在最佳预处理条件下，糖化2h 后，醪液葡萄糖值最高可达99.3，粘度4.5×104 mPa.s，而采用传统糖化工艺，醪液DE 值仅为85.8，粘度大于1.0×105 mPa.s。 此预处理方法也可用于快速糖化不加水的醪液。后续的乙醇发酵试验表明，通过此预处理方法获得的糖化醪液对乙醇发酵无负面影响。 在前期已实现了实验室水平的鲜甘薯燃料乙醇快速乙醇发酵基础上，进一步将发酵规模扩大到500L，在中试水平上对甘薯乙醇发酵进行了研究。结果表明在500L 中试规模，采用边糖化边发酵（SSF）工艺，在料液比为3∶1，发酵醪液最高粘度为6×104mPa.s 条件下，发酵37h，乙醇浓度达到了12.7%（v/v），发酵效率91%，发酵强度为2.7 g/（L•h）。与目前国内的薯类乙醇发酵生产技术水平具有明显的优越性。 为研究甘薯、木薯乙醇发酵中残糖的组成，采用了高效液相色谱—蒸发光散射检测法，对乙醇发酵残糖进行了分析。结果表明，甘薯、木薯乙醇发酵残糖均为寡聚糖，主要由葡萄糖、木糖、半乳糖、阿拉伯糖和甘露糖构成。随着发酵时间延长，寡聚糖中的葡萄糖、半乳糖、甘露糖可被缓慢的水解释放。提高糖化酶量仅在一定程度上降低残糖，过量的糖化酶反而会导致残糖增加。同时发现3, 5-二硝基水杨酸法不能准确测定甘薯、木薯乙醇发酵中的残总糖含量。进一步筛选了两株残糖降解菌株，对甘薯乙醇发酵残糖的降解利用率均达到了40%以上，而且还能显著降低发酵醪液粘度。经形态学和rRNA ITS 序列分析，确定这两株菌分别属于为木霉属和曲霉属黑曲霉组。 通过对以甘薯原料为代表的非粮原料发酵技术研究开发，以期形成乙醇转化率高，能耗低，生产效率高、季节适应性好，原料适应性广，经济性强，符合清洁生产机制的燃料乙醇高效转化技术，为具有我国特色的燃料乙醇发展模式提供技术支持。 Sweet potato is one of the major feedstock for the fuel ethanol production in China. The planting area and the yield in China take 90% of the world. Sweet potato is an efficient kind of energy crops. The energy outcome per area is higher than corn or wheat. And the manufacture cost of ethanol is the lowest, compared with corn and wheat. So sweet potato is the favorable crop for the bioethanol production in China. However, the low-level fermentation technology restricts the development of ethanol production by sweet potato, including slow ethanol production rate, low ethanol concentration and high energy cost. To solve these problems, we conducted research on the strain breeding, pretreatment, pilot fermentation test and residual saccharides analysis. To study the impact of hyperbaric condition at bottom of the large fermentor on yeast fermentation, high pressure carbon dioxide (CO2) was adopted to simulate the situation. The results showed that the fermentation was prolonged with the increasing pressure. The pressure of CO2 had little impact on the ethanol yield which could reach 90% under the pressure below 0.3 MPa. The inhibition was combined by the high pressure and CO2. Under the high CO2 pressure, the extracellular and important intracellular enzyme activities were different from those under normal state. The changes under 0.1 MPa and 0.2 MPa were similar. The changes under 0.3 MPa were closer to those under 0.4 MPa. The application of thermotolerance yeast could solve the problem of the inconsistent temperature between fermentation and saccharificaton and fulfill the real simultaneous saccharification and fermentation. And it could reduce the cooling cost. A thermotolerance strain Y-H1 was isolated in our research. It gave high ethanol concentration of 10.7%（w/w）at 40 ℃ for 33 h. The ethanol yield efficiency was over 90%. At 40 ℃, the extracellular and important intracellular enzyme activities of Y-H1 showed the difference with normal state, which may indicate its physiological changes at the high temperature. Molasses is another feedstock for industrial ethanol production. By our ethanol-tolerance strain and the regulation reagents, the fermentation with high ethanol concentration was investigated. In fed-batch mode combined with cold acid deposition, the highest ethanol concentration was 10.26% (w/w) for 42h. The aldehyde concentration in fermentation was found to be related to ethanol concentration. The development of a rapid ethanol fermentation strain of Zymomonas mobilis is essential for reducing the cost of ethanol production and for the timely utilization of fresh material that is easily decayed in the Chinese bioethanol industry. A mutant Z. mobilis strain, 10232B, was generated by UV mutagenesis. Under these optimized conditions, fermentation of the mutant Z. mobilis 10232B strain was completed in just 18 h with a high ethanol production rate, at an average of 4.92 gL-1h-1 per batch. The final maximum ethanol concentration was 88.5 gL-1, with an ethanol yield efficiency of 93.6%. This result illustrated the potential use of the mutant Z. mobilis 10232B strain in rapid ethanol fermentation in order to help reduce the cost of industrial ethanol production. As fresh sweet potato syrup shows high viscosity, it is hard to be fully converted to glucose by enzymes in the traditional saccharification process. The high-viscosity syrup is difficult to be transmitted in pipes, which may be easily blocked. Meanwhile it could also reduce the later ethanol fermentation efficiency. To solve these problems, effects of the pretreatment conditions were investigated. The highest dextrose equivalent value of 99.3 and the lowest viscosity of 4.5×104 mPa.s were obtained by the most favorable pretreatment conditions, while those of 85.8 and over 1.0×105 mPa.s was produced by traditional treatment conditions. The pretreatment could also be applied on the material syrup without adding water. The later experiments showed that the pretreated syrup had no negative effect on the ethanol fermentation and exhibited lower viscosity. The fuel ethanol rapid production from fresh sweet potato was enlarged in the 500L pilot scale after its fulfillment on the laboratory level. The optimal ratio of material to water was 3 to 1 in 500L fermentor. With low-temperature-cooking (85 ℃) using SSF, the Saccharomyces cerevisiae was able to produce ethanol 97.44 g/kg for 37h, which reached 92% of theoretical yield. The average ethanol production rate was 4.06 g/kg/h. And the maximum viscosity of syrup reached 6×104mPa.s. The results showed its superiority over current industrial ethanol fermentation. The compositions of the residual saccharides in the ethanol fermentation by sweet potato and cassava were analyzed by high performance liquid chromatography coupled with evaporative light-scattering detector. The results showed that all the residual saccharides were oligosaccharides, mainly composed of glucose, xylose, galactose, arabinose and mannose. The glucose, galactose and mannose could be slowly hydrolyzed from oligosaccharides in syrup during a long period. To increase the glucoamylase dosage could lower the residual saccharides to a certain extent. However, excess glucoamylase dosage led to more residual saccharides. And the method of 3, 5-dinitrosalicylic acid could not accurately quantify the residual total saccharides content. Two residual saccharides degrading strains were isolated, which could utilize 40% of total residual saccharide and lower the syrup viscosity. With the analysis of morphology and internal transcribed spacer sequence, they were finally identified as species of Trichoderma and Aspergillus niger.

Calibration of an audio-frequency ion trap mass spectrometer

A method for calibration of an audio-frequency (AF) ion trap mass spectrometer is described. The method is proposed to surmount the obstacle that there is a lack of a proper calibrant for mass spectrometers in the mass-to-charge ratio (m/z) range of 10(6) to 10(10). To calibrate such mass spectra, we determine the point of ejection, q(eject), on the stability diagram of the ion trap operated in a mass-selective axial instability mode. This is accomplished by measuring the radial secular frequencies (and therefore, the m/z value) of a single trapped particle using a light scattering method, followed by monitoring the action of particle ejection in real time to obtain the q(eject). A delayed ejection with q(eject) = 0.949 +/- 0.004 is found at a trap driving frequency of Ohm/2pi = 200-600Hz. Theoretical analysis for the origin of the delayed ejection indicates that the delay is predominantly resulted from the existence of multipole components in the fields due to trap imperfections. Inclusion of -3% of the octopole with respect to the basic quadrupole field can satisfactorily account for our observations. An m/z accuracy approaching 0.1% is attainable after proper calibration of the AF ion trap mass spectrometer. (Int J Mass Spectrom 214 (2002) 63-73) (C) 2002 Elsevier Science B.V. All rights reserved.