Effects of Gamma-Ray Irradiation on Dielectric Surface Breakdown of Polybutylene Naphthalate and

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环氧树脂对伽马射线的屏蔽分析及耐辐照效应

环氧树脂对伽马射线的屏蔽分析及耐辐照效应董梦格;薛向欣;杨合;李哲夫【摘要】Taking the epoxy resin as the research object in thispaper ,shielding property of epoxy resin was analyzed in the energy of0.001‐100 MeV ,and shielding test was carried by 60Co gammaray .Besides ,the irradiation for epoxy resin was treated by 93.5 kGy gamma ray , w hile the density , macro photograph , mechanicalproperty , micro morphology ,temperature resistance and infrared spectra of epoxy resin before and after irradiation were analyzed .The results show that the attenuation of the gamma ray by epoxy resin is mainly related to the photoelectric absorption in the low energy (E<0.01 MeV) ,is mainly related to the incoherent scattering in the intermediate energy (0.01 MeV < E< 10 MeV ) ,is mainly related to the incoherent scattering and pair production in nuclear field in the high energy (10MeV< E<100 MeV) ,and the shiel‐ding property of epoxy resin by 60 Co gamma ray is general .T he irradiation of 93.5 kGy gamma ray results in the aging phenomenon of epoxy resin ,the decrease of density and the highest heat resistant temperature , the increase of mechanical property and the low ness of destruction level ,w hich show s the irradiation resistance of epoxy resin for 93.5 kGy gamma ray .%本文以环氧树脂为研究对象，分析了环氧树脂对能量范围在0.001～100 M eV的伽马射线的屏蔽性能，测试了环氧树脂对60 Co伽马射线的屏蔽性能，并对其进行了总剂量为93.5 kGy的伽马射线辐照处理，对辐照前后环氧树脂的密度、光学照片、力学性能、断面微观形貌、耐热性能和红外光谱进行了分析。

食品中丙烯酰胺减量措施研究进展

食品中丙烯酰胺减量措施研究进展王　萌，王　蓓（江苏旅游职业学院，江苏扬州 225000）摘　要：丙烯酰胺是一种食品在高温加工条件下产生的有害物质。

本文简要介绍了丙烯酰胺的发现历史，阐述了丙烯酰胺的形成机制，并对近年来食品中丙烯酰胺减量措施研究进展进行综述，以期为食物中有害物质控制以及产品品质提升提供理论依据。

关键词：丙烯酰胺；形成机制；减量措施Research Progress on Measures to Reduce Acrylamide in FoodWANG Meng, WANG Bei(Jiangsu College of Tourism, Yangzhou 225000, China)Abstract: Acrylamide is a harmful substance produced in food under high temperature processing conditions. This paper brieﬂy introduces the discovery history of acrylamide, describes the formation mechanism of acrylamide, and summarizes the research progress of acrylamide reduction measures in food in recent years, with a view to providing theoretical basis for the control of hazardous substances in food as well as the improvement of product quality.Keywords: acrylamide; formation mechanism; reduction measures随着生活水平的不断提高，人们对食物的评价不再停留在种类多样，而是更注重其风味多样以及营养与健康。

刘勇 - 哈尔滨工业大学材料学院

材料科学与工程学院刘勇工学博士副教授\硕士生导师+86-451-86413920转8109liuy@主要研究方向固体润滑材料及其空间摩擦学行为、润滑油脂及其空间环境润滑行为、空间原子氧模拟技术、表面改性材料及其空间环境效应社会兼职主要学术成果1.Y.Liu,D.Z.Yang,W.L.Wu,S.Q.Yang.Dry Sliding Wear Behavior of Ti-6Al-4V Alloy in Air.Journal of Harbin Institute of Technology(New Series).2002,19(1):67∼712.刘勇，杨德庄，何世禹，武万良.Ti-6Al-4V合金在真空中的干滑动磨损行为.金属学报.2003,9(7):711∼7143.刘勇，杨德庄，何世禹，武万良.Ti-6Al-4V合金表面的热氧化/真空扩散处理.中国有色金属学报.2003,13(1):177∼1804.Liu Yong，Yang De-Zhuang，He Shi-Yu，Wu parisons of dry sliding wear of the Ti-6Al-4V alloy under condition of air and vacuum.Transactions of Nonferrous Metals Society of China.2003,13(5):1137∼11405.Y.L iu,D.Z.Yang,S.Y.He,W.L.Wu.Microstructure developed in surface layer of Ti-6Al-4V alloy after sliding wear in vacuum.Materials Characterization.2003.50:275∼2796.Yong Liu,Zhuyu Ye,Dezhuang Yang,Shiyu He.Effect of temperature on friction and wear of titanium alloy in vacuum.7th International Conference on“Protection of Materials and Structures from Space Environment”,Toronto-Canada,May10-13,2004,72∼747.刘勇，杨德庄，何世禹，武万良.TC4合金的磨损率及磨损表面层的显微组织变化.稀有金属材料与工程.2005,34(1):128∼1318.刘勇，叶铸玉，杨德庄，何世禹.TC4合金在真空低温下的摩擦磨损行为.哈尔滨工业大学学报.2006.38:335∼3399.刘勇，罗崇泰，叶铸玉，杨剑群，杨德庄.MoS2/石墨溅射涂层在真空中不同载荷下的摩擦磨损行为研究.润滑与密封.2007.32(11): 131∼13210.Yong Liu,Chongtai Luo,Zhuyu Ye,Jianqun Yang,and Dezhuang Yang.Study on Tribological Properties of MoS2+Graphite Sputtering Composite Coating under Various Environment Pressures.9th International Conference on“Protection of Materials and Structures from Space Environment”,Toronto-Canada,May22-24,2007,11.Yong Liu,Zhongtai Luo,Zhuyu Ye,Xingdong Yuan,Dezhuang Yang.Study on Friction and Wear Properties in Vacuum forγ-Ray Irradiated PTFE Coatings.9th International Conference on“Protection of Materials and Structures from Space Environment”,Toronto-Canada,May22-24,2007,12.Yong Liu,Zhuyu Ye,Dezhuang Yang,Shiyu He.Thermal Oxidized Coating on Surface of Titanium Alloy for Improvement of Tribological Properties in Vacuum.第五届摩擦学国际会议CIST2008.13.Yong Liu,Zhuyu Ye,Xingdong Yuan,Dezhuang Yang.Study on Friction and Wear Properties in Vacuum forγ-Ray Irradiated PTFE Coatings.第五届摩擦学国际会议CIST2008.14.孙荣禄，刘勇，杨德庄，钛合金表面激光熔覆NiCrBSi-TiC复合涂层的组织和摩擦磨损性能.中国激光.2003.30(7):659∼66215.孙荣禄，刘勇，杨德庄.TC4合金及其表面TiC p/Ni基合金及光荣浮沉的摩擦磨损性能.摩擦学学报.2003.23(6):457∼46216.W.L.Wu,Y.Liu,D.Z.Yang,W.R.Huang.Microstructure of TiC dendrites reinforced titanium matrix composite layer by laser cladding. Journal of Materials Science Letters.2003.22(16):1169∼117117.杨剑群，刘勇，杨德庄，袁兴栋，叶铸玉.MoS2/Graphite涂层真空环境下摩擦学行为研究.哈尔滨工业大学学报.2006.38:358∼360.18.袁兴栋，刘勇，杨德庄，杨剑群，叶铸玉.聚四氟乙烯涂层真空中的摩擦磨损性能研究.哈尔滨工业大学学报.2006.38:363∼366.19.Yu Gao,Song He,Dezhuang Yang,Yong Liu,Zhi-jun Li.Effect of vacuum thermo-cycling on physical properties of unidirectionalM40J/POSITES PART B-ENGINEERING.2005,36:351∼35820.Gao Yu,Sheng-ling,Yang Dezhuang,Liu Yong,Li Zhi-jun.A study on damage effect of vacuum thermo-cycling on M40J-Epoxy composites. Journal of Reinforced plastics and Composites.2005,24(16):1705∼171121.WANG Gang,MA Xinxin,TANG Guangze,LIU Y ong,YANG Dezhuang,and HE Shiyu.Effect of sliding velocity in vacuum on tribological behavior of nitrided2Cr13steel.Rare metals(s)20071422.Jianqun Yang,Yong Liu,Ye Zhuyu,Yang dezhuang,He Shiyu.Wear Behavior of Plasma-nitrided2Cr13Martensitic Stainless Steel under Air and Vacuum.第五届摩擦学国际会议CIST2008.23.Jianqun Yang,Yong Liu,Ye Zhuyu,Yang dezhuang,He Shiyu.Effect of Gamma Irradiation on Friction and Wear Behavior of MoS2/graphite coatings in Vacuum.第五届摩擦学国际会议CIST2008.24.Xinxin Ma,Gang Wang,Guangze Tang,Yong Liu,Shiyu He and Dezhuang Yang.Tribological Behaviors at High Load of MoS2Films in Vacuum.第五届摩擦学国际会议CIST2008.25.高禹，董尚利，杨德庄，刘勇，李志君.在120keV质子辐照下环氧树脂的质损效应.高分子材料科学与工程.2008.(9)24:72∼7526.Jianqun Yang,Yong Liu,Zhuyu Ye,Dezhuang Yang,Shiyu He,Microstructure and tribological characteristics of nitrided layer on martensitic stainless steel in air and vacuum,Surf.Coat.&Tech.2009,204:705∼712。

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A Novel Model for Implementation of GammaRadiation Effects in GaAs HBTs Jincan Zhang,Yuming Zhang,Senior Member,IEEE,Hongliang Lu,Member,IEEE,Yimen Zhang,Senior Member,IEEE,and Min LiuAbstract—For predicting the effects of gamma radiation on gal-lium–arsenide(GaAs)heterojunction bipolar transistors(HBTs), a novel model is presented in this paper,considering the radiation effects.Based on the analysis of radiation-induced degradation in forward base current and cutoff frequency,three semiempirical models to describe the variation of three sensitive model parame-ters are used for simulating the radiation effects within the frame-work of a simpliﬁed vertical bipolar inter-company model.Its va-lidity was demonstrated by analysis of the experimental results of GaAs HBTs before and after gamma radiation.Index Terms—Cutoff frequency,forward base current,gamma radiation effects,heterojunction bipolar transistor(HBT),semi-conductor device modeling,vertical bipolar inter-company (VBIC).I.I NTRODUCTIONG ALLIUM–ARSENIDE(GaAs)heterojunction bipolartransistors(HBTs),due to their superior performance, are widely used in space radiation environments,and the recent boost of wireless and other high-end communications continue to draw more and more attention to its reliable long-term per-formance under radiation.Earlier studies on radiation effects on GaAs HBT have shown that GaAs HBTs are very attractive candidates for applications in space-based communication sys-tems[1],[2].In this case,many integrated circuits(ICs)have been designed with a GaAs HBT process[3]–[5].However, to improve the radiation hardness of HBT ICs,designers need electrical models taking account for the degradation induced by radiation.However,most of the radiation studies on GaAs HBTs re-ported thus far have mainly focused on the radiation induced changes from the experimental results with the measured elec-trical characteristics of the devices(e.g.,excess base current, cutoff frequency,etc.)[1],[2],[6],[7].To our knowledge,there is not much published information on modeling the electrical characteristics of HBTs subjected to high-energy radiations[8]. The work of modeling the effects of gamma radiation on the dc characteristics of GaAs HBTs has been studied in our pre-vious work[9].However,the complexity of the radiation-in-Manuscript received May03,2012;revised September16,2012;accepted September20,2012.This work was supported by the National Basic Research Program of China under Grant2010CB327505,the Advance Research Project of China under Grant51308030306,and the Advance Research Foundation of China under Grant9140A08030511DZ111.The authors are with the Microelectronics Institute,Xidian University,Xi’an, Shaanxi710071,China(e-mail:zjc850126@).Digital Object Identiﬁer10.1109/TMTT.2012.2221137duced degradation processes makes it difﬁcult to develop a de-tailed physical model of the device after radiation.An alter-native semiempirical approach is to develop an improved ver-tical bipolar inter-company(VBIC)model to describe electrical characteristics of the device before and after irradiation.One can use the extracted model parameters to describe the degra-dation of sensitive model parameters as a function of radiation dose,and then assemble the device model.We believe that such an approach is very useful to predict the degradation effects of devices.There were reports for simulating radiation-induced degradation of dc characteristics in bipolar transistors of silicon based on the semiempirical approach[10],[11].However,very little progress has been made in modeling the degradation of ac characteristics as a function of radiation dose in bipolar transis-tors based on the semiempirical approach,which is now studied in this work.In this paper,a novel model for implementation of gamma ra-diation effects in GaAs HBTs is developed.This paper is orga-nized as follows.The novel model based on a simpliﬁed VBIC model is presented in Section II.To validate the validity of the model,the experimental results of GaAs HBTs under gamma radiation are shown in Section III.The modeled results are com-pared with the measured results in Section IV and conclusions are presented in Section V.II.M ODELThe VBIC model was deﬁned by a group of representa-tives from IC and computer-aided design(CAD)industries to overcome the shortcomings of the Spice Gummel Poon(SGP) model.The equivalent network of VBIC is given in[12].There are several improvements comparing with the SGP model, such as temperature-dependence modeling,quasi-saturation modeling,and decoupling of base and collector currents. However,special characteristics of HBTs make it possible to consider a simpliﬁed VBIC model,as shown in Fig.1.In this simpliﬁed VBIC model,the following assumptions are consid-ered.1)There is no parasitic pnp transistor in npn HBTs[13];there-fore,the parameters to describe the parasitic transistor can be eliminated.2)The extrinsic base–emitter current and chargecan be neglected compared to the intrinsic base–emitter current and charge,respectively.3)Since de-embedding the parasitic parameters has beendone,base–collector small-signal capacitance and base–emitter small-signal capacitance can be ig-nored.0018-9480/$31.00©2012IEEEFig.1.Simpliﬁed VBIC model.4)In HBTs,both early voltages and knee currents for the for-ward and reverse operations can be considered to be inﬁ-nite[14],therefore the normalized base charge tends to be1.The validity of the model to describe HBTs characteristics has been veriﬁed in our earlier work[15].Unfortunately,the simpliﬁed VBIC model also has not taken account of the par-ticular effects of radiation on the electrical behavior of devices. However,HBTs are signiﬁcantly degraded when exposed to ra-diation.Forward base current and cutoff frequency are mainly affected.A.Forward Base CurrentIn the measurement of forward-mode Gummel plot,the base current is measured when isﬁxed at zero while the base–emitter junction is in forward bias.The presence of the relatively large valence band discontinuity at the base–emitter heterointerface leads to effective suppression of the hole current injected from the base region into the emitter.Thus,the base current is mostly determined by the recombination of:1)in the bulk and along the periphery of the base–emitter space-charge region(BE-SCR)and2)in the bulk and at the surface of the neutral base region(NBR).In the simpliﬁed VBIC model,the total forward base current for low-level injection where voltage drop across parasitic re-sistances can be neglected is followed by(1) where is the thermal voltage.As can be seen from (1),the base current includes a component,formed by the NBR recombination modeled with saturation current and ideality factor,and a component,caused by the BE-SCR recombination modeled with saturation currentand ideality factor.Radiation-induced degradation in the forward base current of HBTs is attributed to excess carrier recombination including ra-diation-induced traps in the BE-SCR[9],whereas excess base current deﬁned as the difference between the post-radi-ation and pre-radiation base current can be experimentally ex-tracted by the variations of and with radiation dose. In this case,(1)will be improved as(2),in which radiation-in-duced excess saturation current and excess ideal factor are included.(2)B.Cutoff FrequencyPhysically,can be expressed as(3)(4)(5) where is the base–emitter junction capacitor charge time,is the base–collector junction capacitor charge time,is the base transit time,and is the base–collector space-charge region delay time.It has been shown that capacitance and resistance are slightly or even not degraded under radiation for HBTs in our previous works[16],Therefore,the degradation of is mainly caused by the increase of the transit time,which is just the sum of the variations of and in the compact model[17].In the simpliﬁed VBIC model,the transit time is modeled as(6) where is the forward transit time,is the variation of with basewidth modulation,is the coefﬁcient of bias dependence,is the coefﬁcient of dependence on, is the coefﬁcient of dependence on,and is the forward collector current.Inserting a parameter related to the variation of due to radiation effect,the equation of the transit time can be im-proved as(7) where radiation-induced excess forward transit time is used to predict the increase of,in turn to describe the degra-dation of.III.E XPERIMENTSIn order to determine the regulations of,,and with radiation dose,and verify the validity of the presented model,the following radiation experiment has been performed.ZHANG et al.:NOVEL MODEL FOR IMPLEMENTATION OF GAMMA RADIATION EFFECTS IN GaAs HBTs3Fig.2.Radiation-induced degradation of base current for different total dose levels.The devices applied in the experiment are GaAs HBTs with a single fabrication batch from the WIN Semiconductors Corpo-ration,Tao Yuan Shien,Taiwan(type Q1H201B1).The width and length of each emitter mesa for Q1H201B1are1and20 m,respectively.Radiation of devices,without bias,was im-plemented in a“Gamma-Cell”with a Co source providing a dose rate of about50rd(Si)/s rd Si rd GaAs, and radiation time of5.5,16.5,38.5,and55h,equivalent to a gamma total dose of1,3,7,and10Mrd(Si),respectively.In order to get enough accurate test data,there were four test sam-ples under every radiation total dose mentioned above.Before the experiment,the samples were carefully selected to ensure the differences of performances among the16tested HBTs to be less than3%and the spread of the measured data for the four devices at each radiation to be within0.1%.All of samples were measured at room temperature K before and after radiation.On-chip forward dc Gummel characteristic measure-ments were made with an HP4142Semiconductor Analyzer. Scattering parameters(-parameters)were measured using an HP8510C vector network analyzer from100MHz to40GHz, and in a wide bias current range based on circuit applications.A.Forward Base CurrentFig.2shows the plot of measured versus with the base–collector junction shorted for different total dose radiation, while the collector current remains approximately unchanged. As can be seen from thisﬁgure,at low current levels,the curve shows signiﬁcant change after radiation.In the high current regime,almost has no change.The increase rate of base current,deﬁned as the ratio of excess base current to pre-radiation base current,is plotted with incremental dose values,as shown in Fig.3.The increase rate increases with the total dose,and reaches620%at V after a gamma total dose of10Mrd(Si).However,as can be seen from Fig.3,the increase rate of base current versus decreases.In the regime of V,the increase rate becomes close to0.Fig.4shows the effect of the total dose on the excess base current for different total dose levels.The results presented are limited in the low injection current region where the excess base current remains signiﬁcant compared with thevalue of the total base current.The excess basecurrent is approximately linear throughout the biasrange with a slope of the idea factor Fig.3.Increase rate of forward base current.Fig.4.Radiation-induced excess base current.Fig.5.versus collector current for different total dose levels..These results indicate that radiation-induced recombi-nation mechanism in the BE-SCR is more dominant in the ex-cess base current.Thus,it is reasonable that only the and parameters associated with the BE-SCR are improved in the novel model,as shown in(2).There are two possible recombination mechanisms in the BE-SCR to be consistent with the measured base current ide-ality factor[18].One is trap-assisted tunneling due to gamma radiation induced traps.The second possible mecha-nism is the recombination from a nonuniform distribution of Shockley–Read–Hall centers within the BE-SCR.B.Cutoff FrequencyThe cutoff frequency was extracted using-parameters measurements in the common-emitter conﬁguration by extrap-olating.Fig.5shows measured versus collector current for different total dose levels.In general,relatively obvious degradation is observed for the GaAs HBT after10-Mrd(Si)ra-diation.4IEEE TRANSACTIONS ON MICROWA VE THEORY ANDTECHNIQUESing ﬂy-backing ﬂy-back measurement.The emitter series resistance was measured with the ﬂy-back technique in which the emitter is grounded and current is forced into the base.The open circuit collector voltage was measured.The emitter resistance is taken as the slope of the linear segment of the curve.Fig.6shows the comparison of from ﬂy-back measurement curves before and after 10-Mrd(Si)radiation.As can be seen from this ﬁgure,there is almost no change in .In the simpli ﬁed VBIC model,includes the extrinsic col-lector resistance and intrinsic collector resistance .Fig.7shows from ﬂy-back measurement curves to be similar to measurement.The value of is equal to the slope of the linear segment of the curve,and has no change after radiation.can be determined by optimizing the ﬁtting to quasi-saturation region data of common-emitter char-acteristics.It can then be obtained that there is almost no change in .The possible reason for almost unchanged and after radiation is that the doped concentration in HBT devices is high,which makes radiation induced a little reduction of carrier con-centration causing no obvious increment in and .Fig.8shows the comparison of the capacitances for the GaAs HBT.The curves nearly coincide,suggesting that even after 10-Mrd(Si)total dose gamma radiation,the capacitances almost do not change.According to the measured results,it can be concluded that the degradation of is only due to the change of ,which validates the correctness of the discussion in Section II-B.IV .A NALYSIS AND D ISCUSSIONTo predict the electrical behavior of ICs for a given radiation total dose,designers usually need an ef ﬁcient evaluation oftheFig.8.Capacitances (and )for GaAs HBT.TABLE I V ALUES OF,,,AND P ARAMETERS FOR P RE -R ADIATIONAND P OST -R ADIATION OF D IFFERENT R ADIATION L EVELSradiation parameters embedded in sensitive device model pa-rameters to determine the degradation of these parameters with dose.Such an approach permits an easy implementation for ra-diation-induced degradation in the electrical simulator,such as the Advanced Design System (ADS),by means of symbolically de ﬁned device (SDD),which is an equation-based module to en-able designer to quickly and easily de ﬁne custom and nonlinear components.Furthermore,this approach,which allows reason-able computation time,is generally preferred for the applica-tions of complex physics with large numbers of parameters.A.Forward Base CurrentTo extract the forward Gummel base current parameters,theand parameters can be determined from the inter-cept and the slope of the plot in the region of low .The values of and are then easily obtained by ﬁtting the curve in the high injection region.The obtained ,,,and parameter values are listed in Table I for pre-radiation and post-radiation of different radiation levels.The extracted curves for and versus total dose are plotted in Fig.9(a)and (b),respectively.A saturation effect is exhibited for high total doses.The objective functions for ﬁtting and are shown in (8)and (9),respec-tively,where Dose represents the gamma radiation total dose [in Mrd(Si)]and ,,,,,and are ﬁtting parametersDose (8)Dose(9)As can be seen from Fig.9(a)and (b),the ﬁtting curves of the ﬁrst four dose levels (ﬁrst four modeled)nearly coincide with that of all the ﬁve dose levels (modeled).The values of and at Dose Mrd(Si)obtained from the ﬁrst four modeled,modeled,and measured are shown in Table II.ThereZHANG et al.:NOVEL MODEL FOR IMPLEMENTATION OF GAMMA RADIATION EFFECTS IN GaAs HBTs5(a)(b)Fig.9.(a)Comparison of the measured and modeled.(b)Comparisonof the measured and modeled.TABLE IIVALUES OFANDP ARAMETERS AT DoseMrd(Si)parison of the measured and ﬁrst four modeled excess base cur-rent for 10-Mrd(Si)gamma radiation.are little deviations between the measured values and the ﬁrstfour modeled values.The error between the measured excess base current and the excess base current based on ﬁrst four modeled is less than 5%for the ﬁfth total dose 10Mrd(Si),as depicted in Fig.10.Thus,it can be concluded that the novel model should be able to pre-dict accurately the radiation-induced degradation in excess base current even after more than 10-Mrd(Si)gammaradiation.The measured and modeled forward base current for dif-ferent total doses is drawn in Fig.11.The modeled results parison of the measured and modeled forward base current for different total dose levels.TABLE IIIV ALUES OF,,,,AND P ARAMETER FOR P RE -R ADIATION AND P OST -R ADIATION OF D IFFERENT R ADIATION L EVELSmatch the measured data reasonably well (the error within 2%)up to V.The difference between the measured and modeled increases up to 3%for the high injection current region because our model does not account for the degradation of the NBR.However,this mismatch is still not bad.B.Cutoff FrequencyIn order to extract the transit time parameters,the forward transit time is obtained from the intercept of against the curve.The ,,,and param-eters of the transit time are further estimated by optimization.Table III presents the extracted ,,,,and parameter values for pre-radiation and post-radiation of dif-ferent radiation levels.It seems that parameters do not change much between pre-radiation and post-radiation.Since the most susceptible transistor materials to be sensitive to the total dose effect are insulators,the SiN insulator instead of oxides in the GaAs HBTs does not show serious degradation to the total dose effect.To describe the decrease of ,the following objective func-tion is used to describe excess forward transit time :Dose(10)where ,,and are ﬁtting parameters.The measured and modeled versus total dose is pre-sented in Fig.12.The ﬁtting curve based on the ﬁrst four dose levels almost entirely coincides with that based on all ﬁve dose levels,suggesting that the novel model should be able to predict the degradation of cutoff frequency under more than 10-Mrd(Si)gamma radiation.The cutoff frequency versus is illustrated in Fig.13for different total dose levels with a maximum error less than 1%in the all-bias range.6IEEE TRANSACTIONS ON MICROWA VE THEORY ANDTECHNIQUESparison of the measured and modeled.parison of the measured and modeled cutoff frequency for dif-ferent total dose levels.V .C ONCLUSIONA novel model to include total dose effects for HBTs has been presented in this paper.To predict the behavior of ICs in space-like environments,semiempirical models for radiation parameters as a function of radiation total dose have been pro-posed.By incorporating the radiation parameters into sensitive model parameters,a novel model based on a simpli ﬁed VBIC model has been implemented to simulate accurately the radia-tion-induced degradation in forward base current and cutoff fre-quency at least 10-Mrd(Si)gamma total dose.Our analysis also shows that the model can possibly predict the electrical charac-teristics of HBTs even more than 10-Mrd(Si)gamma radiation;however,further experimental study is required to prove the de-duction.R EFERENCES[1]S.M.Zhang,G.F.Niu,J.D.Cressler,S.J.Mathew,U.Gogineni,S.D.Clark,P.Zampardi,and R.L.Pierson,“A comparison of the effects of gamma radiation on SiGe HBT and GaAs HBT technologies,”IEEE Trans.Nucl.Sci.,vol.47,no.6,pp.2521–2527,Dec.2000.[2]S.Vuppala,C.S.Li,P.Zwicknagl,and S.Subramanian,“Neutron,proton and electron radiation effects in InGaP/GaAs single hetero-junc-tion bipolar transistors,”IEEE Trans.Nucl.Sci.,vol.50,no.6,pp.1846–1851,Dec.2003.[3]U.Karthaus,D.Sukumaran,S.Tontisirin,S.Ahles,A.Elmaghraby,L.Schmidt,and H.Wagner,“Fully integrated 39dBm,3-stage doherty PA MMIC in a low-voltage GaAs HBT technology,”IEEE Microw.Wireless Compon.Lett.,vol.22,no.2,pp.94–96,Feb.2012.[4]N.G.Constantin,P.J.Zampardi,and M.N.El-Gamal,“Automatichardware recon ﬁguration for current reduction at low power in RFIC PAs,”IEEE Trans.Microw.Theory Techn.,vol.59,no.6,pp.1560–1570,Jun.2011.[5]K.Yamamoto,H.Kurusu,S.Suzuki,and M.Miyashita,“High-direc-tivity enhancement with passive and active bypass circuit techniques for GaAs MMIC microstrip directional couplers,”IEEE Trans.Mi-crow.Theory Techn.,vol.59,no.12,pp.3095–3107,Dec.2011.[6]E.P.Wilcox,S.D.Phillips,P.Cheng,T.Thrivikraman,A.Madan,J.D.Cressler,G.Vizkelethy,P.W.Marshall,C.Marshall,J.A.Babcock,K.Kruckmeyer,R.Eddy,G.Cestra,and B.Y.Zhang,“Single event transient hardness of a new complementary npn pnp SiGe HBT technology on thick-ﬁlm SOI,”IEEE Trans.Sci.,57,no.6,pp.3293–3297,Dec.2010.[7]S.Díez,M.Lozano,G.Pellegrini,F.Campabadal,I.Mandic,D.Knoll,B.Heinemann,and M.Ullán,“Proton radiation damage on SiGe:C HBTs and additivity of ionization and displacement effects,”IEEE Trans.Nucl.Sci.,vol.56,no.4,pp.1931–1936,Aug.2009.[8]M.V.Uffelen,S.Geboers,P.Leroux,and F.Berghmans,“Spice mod-elling of a discrete COTS SiGe HBT for digital applications up to MGy dose levels,”IEEE Trans.Nucl.Sci.,vol.53,no.4,pp.1945–1949,Aug.2006.[9]J.C.Zhang,Y.M.Zhang,H.L.Lu,Y.M.Zhang,and S.Yang,“Themodel parameter extraction and simulation for the effects of gamma ir-radiation on the DC characteristics of InGaP/GaAs single heterojunc-tion bipolar transistors,”Microelectron.Reliab.,Art.ID MR-D-11-00657,to be published.[10]X.Montagner,R.Briand,P.Fouillat,R.D.Schrimpf,A.Touboul,K.F.Galloway,M.C.Calvet,and P.Calve1,“Dose-rate and irradiation temperature dependence of BJT spice model rad-parameters,”IEEE Trans.Nucl.Sci.,vol.45,no.3,pp.1431–1437,Jun.1998.[11]X.Montagner,P.Fouillat,R.Briand,R.D.Schrimpf,A.Touboul,K.F.Galloway,M.C.Calvet,and P.Calvel,“Implementation of total dose effects in the bipolar junction transistor Gummel–Poon model,”IEEE Trans.Nucl.Sci.,vol.44,no.6,pp.1922–1929,Dec.1997.[12]C.C.McAndrew,J.A.Seitchik,D.F.Bowers,M.Dunn,M.Foisy,I.Getreu,M.McSwain,S.Moinian,J.Parker,D.J.Rouston,M.Schroter,P.van Wijnen,and L.F.Wagner,“VBIC95:The vertical bipolarinter-company model,”IEEE J.Solid-State Circuits ,vol.31,no.10,pp.1476–1483,Oct.1996.[13]S.V.Cherepko and J.C.M.Hwang,“VBIC model applicability andextraction procedure for InGaP/GaAs HBT,”in –Paci ﬁc Mi-crow.Conf.,2001,pp.716–721.[14]W.Liu,“Switching characteristics and spice models,”in Handbook ofIII–V Heterojunction Bipolar Transistors .New York:Wiley,1998,pp.1088–1090.[15]J.C.Zhang,Y.M.Zhang,H.L.Lu,Y.M.Zhang,S.Yang,and P.Yuan,“A simpli ﬁed VBIC model and SDD implementation for InP DHBT,”in IEEE Int.Electron Devices and Solid-State Circuits Conf.,Tianjin,China,2011,pp.1–2.[16]S.Yang,H.L.Lu,Y.M.Zhang,Y.M.Zhang,J.C.Zhang,and H.P.Zhang,“The effects of gamma irradiation on GaAs HBT,”in IEEE Int.Electron Devices and Solid-State Circuits Conf.,Tianjin,China,2011,pp.1–2.[17]J.Ge,Z.Jin,Y.B.Su,W.Cheng,X.T.Wang,G.P.Chen,and X.Y.Liu,“A physics-based charge-control model for InP DHBT including current-blocking effect,”Chinese Phys.Lett.,vol.26,no.7,pp.1–4,2009.[18]G.A.Schrantz et al.,“Neutron radiation effects on AlGaAs/GaAs het-erojunction bipolar transistors,”IEEE Trans.Nucl.Sci.,vol.35,no.6,pp.1657–1661,Dec.1988.Jincan Zhang,photograph and biography not available at time of publication.Yuming Zhang (M’01–SM’05),photograph and biography not available at time of publication.Hongliang Lu (M’07),photograph and biography not available at time of pub-lication.Yimen Zhang (SM’91),photograph and biography not available at time of pub-lication.Min Liu,photograph and biography not available at time of publication.。

科技英语的翻译(汉译英)

科技英语的翻译

问题： those on chromosomes表示染色体的减少效应，而不是染色体上的基因的减少效应。我们要的是后者的意思。所以要写成those of genes。 Reduction effects是指粒重的减少效应，而不是 genes on chromosomes的减少效应，所以要加上on grain weight。改译为: The reduction effects of genes on chromosomes 1B and 2B on grain weight were obviously higher than those of genes on chromosomes 5A, 6B, 2D and 7D.

科技英语的翻译
例
2 The division frequency of protoplasts was lower in the liquid medium than that embedded in the medium containing agarose. 原生质体在液体培养基中的分裂频率低于包埋在含有琼脂糖的培养基中的分裂频率。
科技英语的翻译
例
2 Owing to these changes of basic equilibrium state, with the result that the basic characters of dynamics will be changed.
由于这些基本的平衡的变化，将导致动力学基
科技英语的翻译
问题：两句是主从关系句。改译为: The total area under natural protection reaches 19,330, which accounts for 2.1% of the total area of China.

Effects_of_gamma_irradiation_on_the_structure_and_mechanical_properties_of_wild_silkworms_and_Bombyx

Effects of Gamma Irradiation on The Structure and MechanicalProperties of Wild Silkworms and Bombyx Mori Silk Fibroin Films Siyong Xiong1,2, Yamei Xu1,Yuhong Jiao1,Lu Wang1, Mingzhong Li1,a1National Engineering Laboratory for Modern Silk, College of Textile and Clothing Engineering, Soochow University, No. 199 Ren’ai Road, Industrial Park, Suzhou 215123, China2Suzhou Institute of Scientific & Technical Information, No. 979 Renming Road, Suzhou 215002,Chinaa mzli@Keywords: Silk Fibroin; Film; Structure; Mechanical Properties;Gamma IrradiationAbstract: The structure and mechanical properties of A. yamamai, A. perny and B. mori silk fibroin films irradiated by gamma ray with various doses of 0, 25, 50, 100 and 200 kGy, respectively were determined by XRD, FT-IR, DSC and Instron 3365 equipment. Results showed that the aggregation structure and molecular conformation of A. yamamai, A. perny and B. mori silk fibroin films irradiated by gamma ray with those doses mentioned above were not significantly changed. However, with the increase of radiation intensity, the thermal stability of silk fibroin films declined slightly, and the breaking strength and extensibility reduced significantly, due to the breakdown of parts of secondary bonds and covalent bonds. These results suggested that, when these silk fibroin materials were sterilized by gamma irradiation, smaller radiation doses should be used, otherwise irreversible damages on these materials would be caused.IntroductionSilk fibroin produced from cultivated silkworms or wild silkworms has been famous for the outstanding mechanical properties, and silk fibroin materials had been studied for new biomedical applications due to its excellent biocompatibility, slow degradability and permeability to oxygen.Regenerated silk fibroin film is one of the important form of silk fibroin materials and it has been shown to support stem cell adhesion, proliferation and differentiation in vitro and promote tissue repair in vivo[1-4]. However, biomedical materials had to be sterilized for clinical application and there were various methods for sterilization[5-8]. Gamma radiation is one of the common sterilization methods, it is necessary to explore the effects of gamma radiation on the structure and properties of silk fibroin films, which could provide theoretical basis for medical applications in the future. Researchers had studied the changes in the fine structure of Bombyx mori (B. mori) silk fibroin fibers irradiated by gamma ray[9]. However, there were few papers studied about the changes in structure and properties of Antheraea yamamai (A. yamamai), Antheraea perny (A. perny) and B. mori silk fibroin films irradiated by gamma ray.In this paper, we mainly focused on the effects of gamma radiation on the structure and mechanical properties of A. yamamai, A. perny silk fibroin films. The changes in the structure and mechanical properties of B. mori silk fibroin films irradiated by gamma ray were taken as controls.Materials and methodsPreparation of regenerated A. yamamai, A. perny and B. mori silk fibroin solutionThe A. yamamai cocoons were treated three times with 0.35 wt % Na2CO3 solution at 98～100°C for 30 min to remove sericin. Degummed A. yamamai silk fibers were dissolved in the melting Calcium Nitrate solutions for 1 h at 90°C and the liquor ratio was 1:20. Then the mixed solution was dialyzed in the flowing distilled water for 96h. The A. yamamai silk fibroin solution withconcentration of about 3.0 wt % was obtained. The preparation of A. perny silk fibroin solution wasaqueous Natrium Carbonicum solutions (0.25 wt %), the liquor ratio (1:10), and the dissolving time (5 hours).According to the literature[10], the B. mori silks were treated three times with 0.05 wt % Na2CO3 solution at 98~100°C for 30 min to remove sericin, respectively. The pure silk fibroin fibers were dissolved in the triadic solvent CaCl2·CH3CH2OH·H2O (mole ratio=1:2:8) for 1 h at 78±2°C through stirring and the liquor ratio was 1:10. The prepared solution was purified by dialyzed for 96h. The regenerated B. mori silk fibroin solution with concentration of about 3.0 wt % was obtained. Preparation of silk fibroin films and gamma irradiationThe silk fibroin films were prepared by casting the same volume of silk fibroin solution (40mL) on a polyethylene dish and air-dried at 20°C. Then A. yamamai, A. perny and B. mori silk fibroin films were obtained. Each type of silk fibroin films was divided into five portion irradiated by gamma ray with 0, 25, 50, 100, 200kGy at room temperature, respectively. The irradiations were carried out by a 6.4×104 Curie 60Co irradiation facility located at Soochow University, China.MeasurementsXRD was performed by a Rigaku D/Max-3C diffractometer with Cu-Kα radiation (λ= 0.15418 nm). The X-ray source was operated at 40 kV and 40 mA. Diffraction intensity was measured in reflection mode at scanning rate of 2°/min for 2θ=5~45°.FT-IR spectra were obtained by a Nicolet Avatar-IR360 in the spectral region of 400~1800 cm-1.The DSC measurements were carried out under Nitrogen by a Perkin-Elmer Diamond DSC/TG instrument at a heating rate of 15 °C/min.The mechanical properties of silk fibroin films (15 mm × 2 mm) were determined on Instron 3365 equipment under relative humidity of 65% at 20 °C. The crosshead speed was 10mm/min. Results and discussionXRD（1）（2）Figure 1 XRD curves of silk fibroin films irradiated by gamma ray with various doses: (1) A. yamamai silk fibroin films;(2) B. mori silk fibroin films; a—silk fibroin films without gamma irradiation; b, c, d, e—silk fibroin films irradiated with25, 50, 100 and 200 kGy, respectively.In Figure 1(1), there are some apparent diffraction peaks around 11.8º and 22.0º in XRD curve (a) of A. yamamai silk fibroin films without gamma irradiation. It indicates that silk fibroin film mainly consists of α-helix structure, according to the studies on wild silkworms silk fibroin molecular conformation[11-18], and a certain amount of amorphous structure is possibly existed. In addition, with the increase of irradiation doses, these diffraction peaks around 11.8º and 22.0º in curve b to e almost have no changes, indicating that the crystal structure of A. yamamai silk fibroin films has no significant changes after gamma irradiation. XRD curves of A. perny silk fibroin films irradiated by gamma ray with various doses are similar to that of A. yamamai silk fibroin films, due to their approximate primary structure.In Figure 1(2), based on those previous studies of B. mori silk fibroin[10, 19], there are some apparent diffraction peaks around 9.1º (w) in XRD curve (a) of B. mori silk fibroin films withouthas no significant changes, indicating that the crystal structure of B. mori silk fibroin films has no visible changes.FTIR spectra（1）（2）Figure 2 FTIR spectra of silk fibroin films irradiated by gamma ray with various doses: (1) A. yamamai silk fibroin films;(2) B. mori silk fibroin films; a—silk fibroin films without gamma irradiation; b, c, d, e—silk fibroin films irradiated with25, 50, 100 and 200 kGy, respectively.In Figure 2(1), these bands at 1652cm-1 (amide I), 1540 cm-1 (amide II), 892 cm-1 (amide IV), 622 cm-1 (amide V) in FT-IR spectra (a-e) are attributed to α-helix structure[11-15], suggesting that these A. yamamai silk fibroin films contain much α-helix structure. The bands at 1238 cm-1 (amide III), 966 cm-1(amide IV) indicated that it still contained a few β-sheet structure. With the increase of irradiation doses, the band at 660 cm-1 (amide V) assigned to random coil disappeared gradually and the bands shifted from 622 cm-1 (amide V) and 660 cm-1 (amide V) to 696 cm-1 (amide V). It indicates that the molecular conformation of silk fibroin films was very likely to transform from random coil or α-helix to β-sheet. And there is no obvious change in the molecular conformation of A. yamamai silk fibroin films with gamma irradiation compared with that of the control samples, which was closely consistent with the results of XRD profile. The FT-IR spectra of A. perny silk fibroin films irradiated by gamma ray with various doses are also similar to that of A. yamamai silk fibroin films.In Figure 2(2), the FT-IR spectra (a-e) of B. mori silk fibroin films irradiated by gamma ray with various doses are similar. The intense bands at 1660 cm-1 (amide I), 1652 cm-1 (amide I), 1540 cm-1 (amide II) and 1536 cm-1(amide III) are assigned to random coil[16-18], indicating that it mainly contained random coil in these silk fibroin films. The bands at 1652 cm-1 (amide I), 1520 cm-1 (amide II) and 700 cm-1 (amide V) show that both silk I and silk II existed. With the increase of irradiation doses, there is no obvious change in the molecular conformation of B. mori silk fibroin films.DSC（1）（2）Figure 3 DSC curves of silk fibroin films irradiated by gamma ray with various doses: (1) A. yamamai silk fibroin films;(2) B. mori silk fibroin films; a—silk fibroin films without gamma irradiation; b, c, d, e—silk fibroin films irradiated with25, 50, 100 and 200 kGy, respectively.In Figure 3(1), the A. yamamai silk fibroin films without gamma irradiation exhibited an endothermal to exothermal transition at around 230 °C, attributed to the pyrolysis of silk fibroin films[20]endothermic peak at about 354.80 °C is due to the thermal decomposition of silk fibroin molecules with unoriented β-sheet configuration[18]. With the increase of irradiation doses, the thermal decomposition temperature of silk fibroin films reduced gradually but slightly, which was also similar to the results of DSC curves of A. perny silk fibroin films irradiated by gamma ray.In Figure 3(2), the B. mori silk fibroin films exhibited visible endothermal to exothermal transition peak from 207°C to 231 °C in curves a to e, especially the exothermal peak at around 218 °C, which is attributed to the transition of silk fibroin from amorphous to silk II[10], suggesting that these silk fibroin films still contain lots of amorphous structure. The endothermic peak at around 282 °C was attributed to the thermal decomposition. With the increase of irradiation doses, the thermal decomposition temperature of B. mori silk fibroin films reduced slightly. That is because when silk fibroin films were irradiated by the high-energy electron produced by gamma ray, the silk fibroin molecules absorbed radiation energy and the original thermodynamic equilibrium in these films was broken. Then it was ionized and polarized to produce various kinds of active particles (such as ions, secondary electrons, free radicals, etc.), leading to the breakage of hydrogen bonds and covalent bonds between silk fibroin molecules, which was very likely to damage the molecular chains. Meanwhile, the thermal movement of the silk fibroin molecules in the amorphous and crystalline regions increased with the increase of irradiation doses, the molecular chains rearrange to disorder silk fibroin chains and weaken intermolecular force, resulting in the scission of peptide bonds in the amorphous regions, the decrease of molecular orientation, and then the thermal stability declined[9]. Mechanical properties（1）（2）（3）Figure 4 The relation curves between irradiation dose and breaking strength or elongation at break of silk fibroin films in dry state: (1) A. yamamai silk fibroin films; (2) A. perny silk fibroin films; (3) B. mori silk fibroin films.In Figure 4(1) to (3), with the increase of irradiation doses, the breaking strength and elongation at break of silk fibroin films in dry state show a significant downtrend, especially the breaking strength. The breaking strength and elongation at break of B. mori silk fibroin films present almost a linear downtrend. These results were consistent with the analyses stated above. When the silk fibroin films were irradiated by gamma ray with various doses, free radical formation, main chains breakage, and disordering of silk fibroin chains were caused due to the broken of hydrogen bonds and peptide bonds in amorphous region, consequently, the average molecular orientation declined. Therefore, the breaking strength and elongation at break of silk fibroin films decreased[9]. However, there were no significant changes in the molecular conformation and crystal structure of silk fibroin films irradiated by gamma ray within the dosage range in this paper, but the breaking strength and elongation at break of silk fibroin films decreased significantly.ConclusionsThe effects of gamma radiation on the changes of structure and mechanical properties of A. yamamai, A. perny silk fibroin films were studied in this paper. Meanwhile, the changes in the structure and mechanical properties of B. mori silk fibroin films irradiated by gamma ray were taken as controls. Compared with silk fibroin films without gamma irradiation, the crystal structure and molecular conformation of those silk fibroin films irradiated by gamma ray with 25, 50, 100 and 200 kGy had no significant changes. With the increase of irradiation doses, the thermal stability of silk fibroin filmssignificantly. Therefore, considering mechanical properties, when sterilizing silk fibroin biomaterials by gamma irradiation, it is suggested that small doses had better be used.AcknowledgementsThis work was financially supported by National Natural Science Foundation of China (No. 30970714), College Natural Science Research Project of Jiangsu Province (No. 07KJA43010) and Nature Science Foundation of Jiangsu Province (No. BK2010252).References[1] Y. Wang, H.J. Kim, G. Vunjak-Novakovic, D.L. Kaplan. Biomaterials, 2006, 27(36): 6064-6082.[2] U.J. Kim, J. Park, H.J. Kim, M. Wada, D.L. Kaplan. Biomaterials, 2005, 26(15): 2275-2285.[3] D.W. Hutmacher. Biomaterials, 2000, 21: 2529-2543.[4] B.D. Lawrence, J.K. Marchant, M.A. Pindrus, et al. Biomaterials, 2009, 30:1299-1308.[5] Y. Shamis, S. Patel, A. Taube, et al. Tissue Engineering Part C: Methods, 2009, 15(3):445-454.[6] L. Morejon-Alonso, R.G. Carrodeguas, et al. Materials Research, 2007, 10(1):15-20.[7] M.S. Jahan, D.E. Thomas, M.D. Ridley. Materials Science Forum, 2003, 426-432(4):3139-3144.[8] K. Filipczak, M. Wozniak, P. Ulanski, et al. Macromolecular Bioscience, 2006, 6(4):261-273.[9] T. Masuhiro, et al. Journal of Applied Polymer Science, 1994, 51(5):823-829.[10] M.Z. Li, S.Z. Lu, Z.Y. Wu, et al. Journal of Applied Polymer Science, 2001, 79:2185-2191.[11] K. Hirabayashi, Y. Kondo, Y.Go. Sen-i Gakkaishi, 1967, 23(5): 199-207.[12] M.Z. Li, W. Tao, et al. Polymers for advanced technologies, 2003, 14: 694-698.[13] Y. Kondo, K. Hirabayashi, E. Iizuka, Y. Go. Sen-i Gakkaishi1, 1967, 23(7):311-315.[14] K. Hirabayashi, M. Tsukada. Journal of Sericulture Science, Japan, 1976, 45(6): 473-478.[15] M. Tsukada. Journal of Polymer Science Part B: Polymer Physics, 1986, 24: 457-460.[16] H.Y. Kweon, Y. H. Park. Journal of Applied Polymer Science, 2001, 82:750-758.[17] H.Y. Kweon, I.C. Um, Y.H. Park. Polymer, 2000, 41:7361-7367.[18] M. Tsukada, et al. Journal of Polymer Science Part B: Polymer Physics, 1994, 32:1407-1412.[19] M.Z. Li, et al. Journal of Dong Hua University (Nature Science Edition), 2001, 27: 12-19.[20] H. Kweon, S.O. Woo, Y.H. Park. Journal of Applied Polymer Science, 2001, 81(9): 2271-2276.New and Advanced Materialsdoi:10.4028//AMR.197-198Effects of Gamma Irradiation on the Structure and Mechanical Properties of Wild Silkworms and Bombyx Mori Silk Fibroin Filmsdoi:10.4028//AMR.197-198.27。

伽马辐照对掺镱硅酸盐玻璃光学性能的影响

伽马辐照对掺镱硅酸盐玻璃光学性能的影响盛于邦;邢瑞先;栾怀训;刘自军;李进延;戴能利【摘要】A series of Yb-doped silicate glasses were prepared by a conventional melting method under normal processing conditions. The effects of gamma-ray (from a 60Co γ source) radiation on the absorption and emission properties of all glass samples were investigated. The radiation exposure leaded to the formation of color centers in glass samples. Such radiation-induced photodarkening caused a strong broad optical absorption band, which had a maximum wavelength centered at around 400 nm and the tail extended into the near infrared region. In addition, a minor part of the Yb3+ ions were converted into Yb2+ by trapping free electrons during irradiation based on the radiation induced absorption (RIA) spectra. The excitation energy could be transferred from Yb3+ ions to radiation-induced defects through cooperative upconversion or multiphoton absorption processes under 960 nm LD pumping. Such energy transfer processes resulted in a decrease of the upper state lifetime of Yb ion which was accompanied by an increase in oxygen deficient center ODC(Ⅱ) defect fluorescence at around 476 nm. Photobleaching effect was observed in irradiated Yb-doped glasses during the fluorescence measurement at room temperature.%采用传统的高温熔融法熔制了一系列掺镱硅酸盐玻璃,并测试了这些样品经总剂量为5 kGy的钴-60伽马射线辐射源辐照前后的吸收谱、荧光谱和上转换发光光谱.实验结果表明:辐致暗化效应导致玻璃样品在400 nm附近出现一个非常强的宽吸收带,其尾端可延伸至近红外区.经辐致损耗谱分析可知,部分Yb3+离子在辐照过程中通过俘获电离自由电子转变成了Yb2+离子,导致掺杂样品的辐致损耗明显比基质材料的要大.在960 nm LD泵浦下辐照过的样品荧光强度、上转换发光强度及荧光寿命均有所下降,且在476 nm附近出现了氧缺陷ODC(Ⅱ)的荧光.室温下辐照过的样品在荧光测试过程中温度明显升高并出现漂白现象.【期刊名称】《无机材料学报》【年(卷),期】2012(027)008【总页数】5页(P860-864)【关键词】掺镱硅酸盐玻璃;辐致损耗;价态转变;色心荧光【作者】盛于邦;邢瑞先;栾怀训;刘自军;李进延;戴能利【作者单位】华中科技大学武汉光电国家实验室,光电子科学与工程学院,武汉430074;华中科技大学武汉光电国家实验室,光电子科学与工程学院,武汉430074;华中科技大学武汉光电国家实验室,光电子科学与工程学院,武汉430074;华中科技大学武汉光电国家实验室,光电子科学与工程学院,武汉430074;华中科技大学武汉光电国家实验室,光电子科学与工程学院,武汉430074;华中科技大学武汉光电国家实验室,光电子科学与工程学院,武汉430074【正文语种】中文【中图分类】TQ171随着科技的发展, 掺镱光纤(YDF)已经被广泛用于光纤激光器和放大器中, 可产生非常高的激光功率和脉冲能量[1-3]. 由于 Yb3+离子的能级结构非常简单(只有基态2F5/2和激发态2F7/2两个能级), 不存在激发态吸收和浓度淬灭效应, 故掺镱光纤具有很高的能量转换效率和量子效率[4]. Yb3+离子还可以作为敏化剂, 吸收并将泵浦能量传递给其他发光离子, 比如 Er3+离子, 可以极大地提高后者的发光效率[5-6]. 此外, 较长的上能级寿命和较小量子缺陷等优势更使得掺镱光纤成为低功耗调Q激光器的理想材料[7].掺镱光纤激光器具有高可靠性、高效率、高光束质量、重量轻及体积小等优势, 可做为空间通信、地球观测和深空探测等系统中信息获取与传输的理想器件, 因此得到了世界各国众多航天机构的青睐.但是在太空中石英基有源光纤及其器件难免要受到恶劣的辐射环境影响. 地球轨道天然空间辐射带由范•艾伦(Van Allen)辐射带粒子和宇宙射线(包括太阳宇宙射线和银河宇宙射线)组成, 处于其中的光纤器件所受到的长时间、低剂量率的空间辐照是导致其性能降低甚至失效的主要因素[8-11]. 近几十年来, 辐照对无源及有源光纤的影响已得到各国科研人员的广泛研究. 一般认为光纤性能下降的主要原因在于辐照在基质材料中电离出的自由电子和空穴对被材料中的杂质或初始原子缺陷俘获形成了色心,从而导致在 400 nm附近出现一个非常强的宽吸收带, 其尾端可延伸至近红外区[8,12-14]. 实际上, 太空中辐照剂量率非常低, 即使经过长达十年的时间光纤所受到的总剂量也不超过 2 kGy, 这个剂量对普通光纤的性能影响并不严重.但是对掺镱光纤来说,为了改善光纤性能通常还会共掺一些其他元素, 如铝或磷, 这些共掺剂极大地提高了有源光纤的辐照敏感性[15]. 此外近红外光泵浦下镱离子通过离子间相互作用可以在 500 nm附近产生协同上转换发光[16], 这个波长恰好处在辐致损耗的强吸收范围内;同时由于Yb在硅酸盐玻璃中可以存在Yb2+和Yb3+两种价态, 因此在辐照过程中部分 Yb3+离子有可能俘获电离自由电子转变成Yb2+[17]. 所有这些因素使得辐照对掺镱光纤的影响变得非常复杂.截止目前, 关于掺镱光纤辐照特性的研究多集中在辐致损耗上, 因此有必要就高能辐照对掺镱玻璃材料光学性能的影响机理进行更深入地研究.考虑到辐照会导致玻璃材料在紫外光及可见光区出现新的吸收和荧光带, 实验中选择吸收谱和荧光谱测试作为研究辐照影响的两个主要手段[18]. 通过分析辐致损耗谱和荧光谱发现伽马射线辐照使得玻璃材料中形成了大量的色心, 这些色心具有新的能级结构, 使得基质对泵浦光的损耗明显增大. 实验还研究了960 nm LD泵浦下色心对Yb3+离子的发光特性影响, 并对其机理进行了讨论.1.1 玻璃样品的制备实验所有样品均采用传统高温熔融法制备所得.玻璃组成为 65SiO2-10Al2O3-25CaO-xYb2O3(x=0、0.2mol%、0.5mol%、1.0mol%、2.0mol%). 所用原料均为分析纯级, 其中 CaO以 CaCO3形式引入.按化学计量比准确称取所需的各原料, 然后放在玛瑙研钵中充分研磨均匀, 再装入刚玉坩埚, 整体放入用程序控制的电阻炉中. 在1580℃熔融2 h后, 将熔体浇铸在预热过的垫板上淬冷成型, 为了消除样品中存在的残余应力, 接着在退火炉中600℃退火2 h. 退火后的样品经切割和光学抛光后加工成尺寸为15 mm×15 mm×2 mm的玻璃片供测试.为研究辐照对掺镱硅酸盐玻璃的光学性能影响, 每种样品均用60Co γ辐射源进行了总剂量约为5 kGy的辐照处理.1.2 测试方法掺镱硅酸盐玻璃样品的吸收谱是用PYbkinElmYb-Lambda35紫外可见分光光度计测得,测量波长范围为200～1100 nm. 在960 nm LD泵浦下的荧光谱由ZOLIX SBP300光谱仪测得: 940～1140 nm范围的荧光由InGaAs探测器测得, 400～700 nm范围的由光电倍增管测得. 荧光寿命由 TRIAX550光谱仪测得.所有测试均在室温环境下进行.2.1 伽马辐照对掺镱硅酸盐玻璃吸收光谱的影响基质及Yb2O3掺杂浓度为1.0mol%的样品在伽马射线辐照前后的吸收系数谱如图1(a)所示.由图可知, 经 5 kGy剂量伽马射线辐照后, 所有样品在可见光范围内吸收系数都有明显地增大, 而 Yb3+离子本身的吸收峰值波长、半高宽和吸收系数在辐照前后却基本没有发生变化, 这说明镱离子的周围配位场环境基本没有受到影响, 伽马辐照只是在玻璃基质材料中产生了附加损耗.辐致损耗是衡量辐照对光学材料性能影响的一个关键指标[8,15], 能够反映出材料对高能辐照的敏感性.辐致损耗谱可通过相应各样品在辐照前后的吸收系数相减得到, 计算结果如图1(b)所示. 显然辐照后的样品在400 nm附近出现一个非常强的宽吸收带, 其尾端可延伸到近红外区. 前人的研究表明: 在高能辐射下玻璃材料电离出自由电子与空穴对, 被材料中缺陷俘获形成色心从而产生附加损耗. 这些辐致色心主要包括过氧连接(吸收峰为3.8 eV), DOS环(Dioxasilyrane Ring,～3 eV), 过氧基(2.3 eV)以及非桥氧空穴心(2.0 eV)[19-21].此外高能辐照还可以产生一些吸收带处在深紫外区的色心, 如氧空位ODC(Ⅰ)(7.6 eV), E'类心(5～6 eV),以及氧空位ODC(Ⅱ)(5.0 eV)等[18-20].有必要说明的是, 辐照后掺有 Yb元素的玻璃在可见光区的辐致损耗都要明显大于基质玻璃, 且其吸收强度随 Yb浓度增加而增大. 同时 Yb3+离子在980 nm附近的本征吸收则有所减小, 如图1(b)中插图所示．这可能是因为在辐照过程中材料电离出了自由电子和空穴对, 部分 Yb3+离子通过俘获自由电子而转变成了Yb2+离子, Yb2+离子的4f-5d跃迁引起的吸收带在 22000～55000 cm−1处, 且 f-d振子强度远远大于Yb3+离子的f-f振子强度(约数百倍)[17],故少量三价镱离子变成二价即可导致在紫外光至可见光区出现明显的附加吸收.2.2 伽马辐照对掺镱硅酸盐玻璃发光特性的影响图2为960 nm LD泵浦下, 不同Yb2O3掺杂浓度玻璃在辐照前后的荧光峰值强度. 从图中可知,玻璃的荧光强度随Yb2O3掺杂浓度增加先增大后减弱, 即出现了所谓的“浓度淬灭”现象. 虽然 Yb3+离子只有简单的两个能级, 但在高浓度掺杂时会出现团簇效应而形成 Yb3+离子对, 离子间相互作用可以导致镱离子激发态寿命淬灭, 从而影响样品的发光效率. 辐照后所有的掺镱硅酸盐玻璃荧光强度均明显下降, 且在较高Yb离子掺杂浓度样品中, 辐照后的荧光强度下降幅度较大. 从图 1(b)中可以看出,掺杂浓度越高的样品中, 辐照后 Yb3+离子的吸收下降幅度就越大, 即有越多的 Yb3+离子俘获了电离电子变成了 Yb2+离子. 虽然该过程能够减少辐致色心的数量, 但考虑到 Yb2+离子在 200～500 nm 范围内有较强的吸收, 因此高浓度掺杂样品总的辐致暗化效应就反而更加明显, 荧光强度下降幅度也就更大.但是所有样品荧光谱的峰值波长及半高宽都没有发生明显变化(未给出), 进一步说明了辐照并没有改变Yb3+离子的配位场环境.考虑到掺稀土玻璃在近红外激光泵浦下可能出现上转换现象, 产生位于500 nm附加的上转换荧光, 我们测试了辐照前后各样品在960 nm LD泵浦下的协同上转换荧光谱, 如图 3所示, 以深入研究伽马辐照对掺镱硅酸盐玻璃光学特性的影响.荧光谱在488和500 nm处有两个较明显的波峰, 荧光强度随 Yb2O3掺杂浓度增加而线性增大, 没有出现淬灭现象. 同近红外的荧光谱类似, 辐照后各样品协同上转换荧光强度也都有所减弱(Yb2O3浓度为2.0mol%的样品辐照后上转换荧光谱由于样品损坏没有给出). 协同发光是由两个处于激发态的近邻镱离子同时去激产生的, 荧光谱呈多峰值结构, 每个峰值分别对应两个能级对之间的跃迁:2F5/2(m)+2F5/2(m')→2F7/2(n)+2F7/2(n'), m, m'=1, 2, 3; n, n'=1, 2, 3,4.实际上, 掺镱硅酸盐玻璃协同上转换荧光谱还可以通过对其在近红外的荧光谱自卷积得到[16], 协同发光谱形函数F(E)与Yb3+的2F5/2→2F7/2跃迁自发辐射谱f(E)关系可由下式所示:Yb2O3掺杂浓度为 1.0mol%的样品未辐射上转换荧光谱计算结果如图 3中虚线所示. 由图可知,同测试结果一致计算所得上转换荧光谱也是在 488和500 nm附近有两个较明显的波峰, 只是后者荧光强度相对更大一些. 这或许跟测试荧光谱和上转换荧光谱时使用的探测器不同有关. 对比辐照后样品上转换荧光谱还可以发现, 500 nm附近的荧光强度下降幅度明显比488 nm处的要大一些, 这跟吸收测试中观察到的现象是矛盾的, 如图 1显示短波长处的辐致损耗相对更大, 可以猜测这可能跟某些能级结构之间的能量传递机制有关. 同时辐照过的样品在476 nm附近出现了一个新的荧光峰, 虽然在这个波长处有很强的辐致损耗, 该荧光峰强度仍高于未辐照的样品. 根据前人对辐致色心的研究, 此荧光峰应归结为ODC(Ⅱ)色心[22].该色心的吸收带在 5.0 eV(249 nm)处, 可以通过对协同上转换荧光进行双光子吸收激发, 在2.6 eV(478 nm)处产生一个荧光峰,当然具体的相关能量传递机理还需要后续进行更加深入的研究.结合辐致损耗谱可以看出, 镱离子的协同发光中心恰好处在辐致色心的强吸收带范围内, 因此推测泵浦光可经多光子吸收或协同上转换传递给了材料缺陷, 再经后者通过无辐射跃迁可转变成大量热能. 实际上辐照过的玻璃在测试过程中由于温度明显升高而出现漂白现象, 即在激光泵浦下辐致色心被还原而褪色. 这个过程不仅使掺镱硅酸盐玻璃的荧光强度下降, 同时还降低了样品的损伤阈值, 其中Yb2O3掺杂浓度为2.0mol%的样品由于测试过程中温度过高而被损坏. 为了研究 Yb3+离子与色心结构的能量传递, 本课题组还测试了 Yb2O3掺杂浓度为 0.5mol%的玻璃在辐照前后的荧光寿命. 如图 4所示, 样品的荧光寿命经5 kGy剂量伽马射线辐照后由1.33 ms减小为1.18 ms. 由于Yb3+离子只有两个能级, 且激发态2F5/2与基态2F7/2之间的能隙约为10000 cm−1, 无辐射多声子弛豫对激发态的影响可以忽略, 故激发态寿命基本不会受到声子环境变化的影响.因此导致 Yb3+离子的激发态寿命减小的最可能原因是能量从上能级转移给了辐致缺陷(包括Yb2+), 再经后者通过辐射跃迁或无辐射跃迁释放出来. 这种能量传递最终导致了辐照后掺镱硅酸盐玻璃的荧光强度下降.采用传统的高温熔融法熔制了一系列掺镱硅酸盐玻璃, 并测试了这些样品经5 kGy 伽马射线辐照前后的吸收、荧光和上转换发光光谱, 同时利用荧光谱计算 Yb3+离子的上转换发光光谱并与测试结果进行了对比. 实验结果表明高能辐照导致样品基质在400 nm附近出现一个非常强的宽吸收带, 其尾端可延伸至近红外区; 部分Yb3+离子在辐照过程中通过俘获电离自由电子变成 Yb2+离子. 辐照后, 样品在960 nm LD泵浦下荧光及上转换发光强度均有所下降, 且在476 nm附近出现ODC(Ⅱ)色心荧光峰,同时 Yb3+离子的激发态寿命也有所减小, 表明泵浦能量经过复杂的传递机理可从 Yb3+离子上能级传递给辐致色心. 部分泵浦能量最终经色心无辐射跃迁转换成了热能, 使得样品的温度明显升高并出现漂白现象.【相关文献】[1] Lu K, Dutta N K. 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