中子辐照Al2O3的缺陷及退火恢复研究

用剂量为5.74×1018 cm-2的中子对Al2O3晶体进行了辐照,利用吸收光谱等手段观测了中子辐照引起的损伤及其恢复.中子辐照产生了大量的阴离子单空位(F和F+)、阴离子双空位(F2)及其它更高阶的缺陷.通过等时退火,发现低阶的阴离子单空位缺陷在较低温度下即可恢复,而高阶的缺陷则会在退火过程中得到加强,新的吸收峰(更高阶的缺陷)也会在退火过程中出现,在1000℃退火温度下,所有缺陷全部恢复.     

快中子辐照硅中双空位的退火行为研究

本文利用傅立叶变换红外光谱技术(FTIR)及正电子湮没谱技术(PAS)对快中子辐照硅中的双空位(V2)的退火行为作了详细研究.研究发现区熔硅中双空位在250 ℃热处理会通过相互连接形成链状而在红外光谱中消失,提高退火温度到350～450 ℃,它们将进一步结合形成具有三维结构的四空位型缺陷;而在直拉硅中双空位主要通过捕获间隙氧或A中心(VO)形成V3O复合体而消失.     

超高能量电子辐照氮掺杂金刚石的光致发光研究

利用低温光致发光光谱研究了MeV超高能量电子辐照氮掺杂金刚石,结果表明,辐照缺陷以氮-空位缺陷(NV)和中性单空位缺陷(GR1)为主;辐照电子经1.2 mm铝箔遮挡后,其能量大幅度衰减,金刚石中只剩余了NV缺陷,这表明此时辐照产生的空位都被氮杂质所束缚而以NV缺陷形式存在;经800℃高温退火后,空位扩散到晶体表面以下约15μm处而被氮杂质束缚,进而使得GR1信号减弱而NV信号增强.     

低温热处理对电子辐照直拉硅中V-O缺陷的影响

采用能量为1.5 MeV、辐照温度为100℃、辐照剂量为1.8 × 1018e/cm2电子辐照直拉单晶硅;然后对电子辐照样品进行不同温度和时间的低温(200～600℃)热处理.通过辐照样品的Fourier变换红外光谱研究了热处理后样品中的空位-氧相关缺陷的转化情况.结果表明:未经热处理的电子辐照的硅样品中出现了空位-双...     

中子辐照掺氮6H-SiC晶体的电学性能及退火的影响

在60～80℃用剂量为1.67×1020n/cm2的全能谱中子对掺氮6H-SiC晶体进行了辐照,对辐照样品从室温至1600℃进行了等时退火,研究了辐照和退火对样品电学性能的影响.大剂量中子辐照在晶体内产生了大量缺陷和损伤,并引起样品的电学性能发生变化,使电阻率升高、介电常数和介电损耗减小.测试表明:在辐照缺陷及其电学性能的退火演化过程中,存在约为1 000和1400℃两个特征温度.当退火温度低于1 000℃时,随着退火温度的升高,电阻率小幅增加,而介电常数和介电损耗亦下降;在退火温度高于1 000℃时,电阻率开始下降.在退火温度高于1 400℃时,电阻率急剧地下降,而介电常数和介电损耗快速地增加.以间隙原子和空位为缺陷的主要形式作为辐照损伤的模型,对上述现象做了定性解释.测试还表明,掺氮6H-SiC的介电常数高达3.5 x 104,这一奇特的物性主要来源于电子的长程迁移极化.     

中子辐照剂量对直拉硅中VO退火行为的影响

本文通过红外吸收光谱技术研究了不同剂量快中子辐照直拉硅中空位氧缺陷(A中心)的退火行为.实验发现,经200℃热处理后样品中均会出现V2O (840 cm-1)和VO2 (919.6 cm-1)的红外吸收峰;当退火温度升高到400至450℃之间,在低剂量辐照样品(SL)的红外吸收光谱中会有较强的VO2 (889 cm-1)的吸收峰,而在高剂量辐照样品(SH)中则会有较强的V2O2(825 cm-1)和VO2(919.6 cm-1)的吸收峰.分析认为,在低剂量辐照样品中VO主要是通过与Oi结合形成稳定的VO2而消失;而在高剂量辐照条件下VO则是通过相互结合形成V2O2或与Oi结合形成VO2而消失.     

快中子辐照直拉硅中的空位型缺陷

利用正电子湮没谱(PAS)及Fourier变换红外吸收光谱(FTIR)技术研究了快中子辐照直拉硅(CZSi)中辐照缺陷.研究发现,经快中子辐照后的硅中会有大量的单空位型缺陷VO及多空位型缺陷V2和V2O;经200～450℃热处理后,FTIR光谱中出现的720和919.6 cm-1红外吸收峰为单空位型缺陷,其正电子寿命与VO的寿命接近,约为290 ps;经450～600℃热处理后,随单空位型缺陷VO消失,V4型缺陷浓度迅速增加,600℃热处理后其浓度达到最大(相对浓度约为70％).     

γ射线辐照及其后退火MgAl2O4透明陶瓷中缺陷运动行为的研究

用不同剂量的γ射线辐照镁铝尖晶石透明陶瓷，并对辐照后的样品进行等时退火，UV－VIS和FT－IR，PAT测试表明，辐照前3360cm^-1处有吸收峰，它是由VOH^-心吸收引起的，通过γ射线辐照，样品在370nm处产生吸收带，它是由辐照产生的V型色心吸收引起的，通过退火可以使V型色心吸收带消除。结果表明：对陶瓷γ射线辐照及退火，将使样品中的空位团发生分裂和空位聚集。较低剂量的γ射线辐照能降低陶瓷紫外到红外透过率，大剂量的γ射线辐照能在陶瓷中产生局域退火效应，它能阻止可见和紫外透过率随剂量增加而下降并能增加陶瓷红外透过率。     

中子辐照6H-SiC晶体的光学性质及缺陷分析

利用透射电子显微镜、紫外--可见--近红外光谱和Raman光谱,对剂量为1.67×1020 n/cm2中子辐照的n型半导体6H-SiC晶体进行了微观结构、光学性质及退火过程的研究。结果显示,辐照并没有造成样品的完全非晶化,辐照缺陷主要是点缺陷及其聚集体。辐照后的样品的光吸收明显增加,带隙变小,Urbach能量变大,且在1 178、1 410和1 710nm处出现新的吸收峰。1 178和1 410nm峰的出现归因于辐照产生的Si空位VSi。对辐照样品进行了室温至1600℃退火,发现800℃是退火过程的转折点。低于800℃退火时,样品中的Frankel对、间隙原子和C空位VC消失;高于800℃退火时,含Si空位VSi缔合缺陷及复杂缺陷团分解湮灭。为了解释与VSi有关的多个光谱峰,建立了SiC中硅空位的"类铍原子模型"。     

电子束辐照致VO2(A)薄膜光电特性改变

以能量为1.0MeV,剂量为1.2×1013～1.2×105/cm2电子束辐照VO2(A)薄膜.利用X射线衍射仪、扫描电镜、电阻温度测试仪和Fourier中红外光谱仪对电子辐照前后的薄膜进行测试,研究了辐照剂量对薄膜结构、光电特性的影响.结果表明:剂量为1.2×1013/cm2时,辐照主要是在薄膜中引入点缺陷:剂量为1.2×1015/cm2时.辐照在薄膜中产生明显的退火效应.辐照剂量增加会引起薄膜相变过程中电阻温度系数增加,使相变温度点发生变化,热滞回线宽度最大可增加89.1%,相变前后薄膜电阻值变化的数量级增大,晶粒尺寸经历了31.8nm→21.3nm→20.3nm→33.5nm的变化.半导体相薄膜的透过率受缺陷影响较大,金属相时主要受晶粒尺寸的影响.     

Direct observation of freeze-thaw instability of latex coatings via high pressure freezing and cryogenic SEM

Despite its industrial importance, the subject of freeze-thaw (F/T) stability of latex coatings has not been studied extensively. There is also a lack of fundamental understanding about the process and the mechanisms through which a coating becomes destabilized. High pressure (2100 bar) freezing fixes the state of water-suspended particles of polymer binder and inorganic pigments without the growth of ice crystals during freezing that produce artifacts in direct imaging scanning electron microscopy (SEM) of fracture surfaces of frozen coatings. We show that by incorporating copolymerizable functional monomers, it is possible to achieve F/T stability in polymer latexes and in low-VOC paints, as judged by the microstructures revealed by the cryogenic SEM technique. Particle coalescence as well as pigment segregation in F/T unstable systems are visualized. In order to achieve F/T stability in paints, latex particles must not flocculate and should provide protection to inorganic pigment and extender particles. Because of the unique capabilities of the cryogenic SEM, we are able to separate the effects of freezing and thawing, and study the influence of the rate of freezing and thawing on F/T stability. Destabilization can be caused by either freezing or thawing. A slow freezing process is more detrimental to F/T stability than a fast freezing process; the latter actually preserves suspension stability during freezing. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004 in Chicago, IL. Tied for first place in The John A. Gordon Best Paper Competition.     

Insect antifeedant properties of anthranoids from the genusVismia

Vismiones and ferruginins, representatives of a new class of lypophilic anthranoids from the genusVismia were found to inhibit feeding in larvae of species ofSpodoptera, Heliothis, and inLocusta migratoria.     

Many Drugs of Abuse May Be Acutely Transformed to Dopamine,Norepinephrine and Epinephrine In Vivo

It is well established that a wide range of drugs of abuse acutely boost the signaling of the sympathetic nervous system and the hypothalamic–pituitary–adrenal (HPA) axis, where norepinephrine and epinephrine are major output molecules. This stimulatory effect is accompanied by such symptoms as elevated heart rate and blood pressure, more rapid breathing, increased body temperature and sweating, and pupillary dilation, as well as the intoxicating or euphoric subjective properties of the drug. While many drugs of abuse are thought to achieve their intoxicating effects by modulating the monoaminergic neurotransmitter systems (i.e., serotonin, norepinephrine, dopamine) by binding to these receptors or otherwise affecting their synaptic signaling, this paper puts forth the hypothesis that many of these drugs are actually acutely converted to catecholamines (dopamine, norepinephrine, epinephrine) in vivo, in addition to transformation to their known metabolites. In this manner, a range of stimulants, opioids, and psychedelics (as well as alcohol) may partially achieve their intoxicating properties, as well as side effects, due to this putative transformation to catecholamines. If this hypothesis is correct, it would alter our understanding of the basic biosynthetic pathways for generating these important signaling molecules, while also modifying our view of the neural substrates underlying substance abuse and dependence, including psychological stress-induced relapse. Importantly, there is a direct way to test the overarching hypothesis: administer (either centrally or peripherally) stable isotope versions of these drugs to model organisms such as rodents (or even to humans) and then use liquid chromatography-mass spectrometry to determine if the labeled drug is converted to labeled catecholamines in brain, blood plasma, or urine samples.     

Ethanol and (−)-α-Pinene: Attractant Kairomones for Bark and Ambrosia Beetles in the Southeastern US

In 2002–2004, we examined the flight responses of 49 species of native and exotic bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae) to traps baited with ethanol and/or (−)-α-pinene in the southeastern US. Eight field trials were conducted in mature pine stands in Alabama, Florida, Georgia, North Carolina, and South Carolina. Funnel traps baited with ethanol lures (release rate, about 0.6 g/day at 25–28°C) were attractive to ten species of ambrosia beetles (Ambrosiodmus tachygraphus, Anisandrus sayi, Dryoxylon onoharaensum, Monarthrum mali, Xyleborinus saxesenii, Xyleborus affinis, Xyleborus ferrugineus, Xylosandrus compactus, Xylosandrus crassiusculus, and Xylosandrus germanus) and two species of bark beetles (Cryptocarenus heveae and Hypothenemus sp.). Traps baited with (−)-α-pinene lures (release rate, 2–6 g/day at 25–28°C) were attractive to five bark beetle species (Dendroctonus terebrans, Hylastes porculus, Hylastes salebrosus, Hylastes tenuis, and Ips grandicollis) and one platypodid ambrosia beetle species (Myoplatypus flavicornis). Ethanol enhanced responses of some species (Xyleborus pubescens, H. porculus, H. salebrosus, H. tenuis, and Pityophthorus cariniceps) to traps baited with (−)-α-pinene in some locations. (−)-α-Pinene interrupted the response of some ambrosia beetle species to traps baited with ethanol, but only the response of D. onoharaensum was interrupted consistently at most locations. Of 23 species of ambrosia beetles captured in our field trials, nine were exotic and accounted for 70–97% of total catches of ambrosia beetles. Our results provide support for the continued use of separate traps baited with ethanol alone and ethanol with (−)-α-pinene to detect and monitor common bark and ambrosia beetles from the southeastern region of the US.     

Novel polyurethane coating technology through glycidyl carbamate chemistry

Glycidyl carbamate chemistry combines the excellent properties of polyurethanes with the crosslinking chemistry of epoxy resins. Glycidyl carbamate functional oligomers were synthesized by the reaction of polyfunctional isocyanate oligomers and glycidol. The oligomers were formulated into coatings with several amine functional crosslinkers at varying stoichiometric ratios and cured at different temperatures. Properties such as solvent resistance, hardness, and impact resistance were dependent on the composition and cure conditions. Most coatings had an excellent combination of properties. Studies were carried out to determine the kinetics of the curing reaction of the glycidyl carbamate functional oligomers with multifunctional and model amines. Detailed kinetic analysis of the curing reactions was also undertaken. The results indicated that the glycidyl carbamate functional group is more reactive than a glycidyl ether group. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, on October 27–29, 2004, in Chicago, IL.     

Highly moisture-proof polysilsesquioxane coating prepared via facile sol-gel process

A highly moisture-proof polysilsesquioxane coating was obtained from a new bis-silylated precursor, which was synthesized from 3-aminopropyltriethoxysilane (APTES) and m-xylylene diisocyanate (m-XDI) in tetrahydrofuran (THF) and verified by ¹H MAS NMR. For direct comparison purposes, an SiO₂ coating was also prepared by the Stöber method using tetraethoxysilane (TEOS) as the reactant. Interestingly, the coating obtained from the polysilsesquioxane sol exhibited a much higher moisture resistance capability than its counterpart, which was attributed to its more compact feature between nanoparticles as characterized by N₂ absorption experiment and transmission electron microscopy (TEM). Furthermore, its high transparency of about 92% showed potential for application in the protection of optical crystals.