采用硅烷偶联剂对W型铁氧体类吸收剂和F型铁氧体类吸收剂进行复合改性,通过扫描电镜(SEM)研究偶联剂改性对吸收剂微观结构的影响,分析复合改性对吸波材料电磁性能的影响,并通过有效媒质理论(effective medium theory)讨论吸收剂电磁参...采用硅烷偶联剂对W型铁氧体类吸收剂和F型铁氧体类吸收剂进行复合改性,通过扫描电镜(SEM)研究偶联剂改性对吸收剂微观结构的影响,分析复合改性对吸波材料电磁性能的影响,并通过有效媒质理论(effective medium theory)讨论吸收剂电磁参数理论值与实际值的差异。结果表明:通过吸收剂复合改性可以实现复合吸波材料的电磁性能调整,实现材料宽带匹配,提高吸波材料吸收效率;改性后的吸波材料在8～18 GHz时反射率小于–10 dB,最小反射值可达–14.5 dB,附着力为6.32 MPa;耐热性能实验后,吸波材料外观和反射率无明显变化,说明复合改性后吸波材料耐环境性能优异。展开更多
Although there are numerous optical spectroscopy techniques and methods that have been used to extract the fundamental bandgap of a semiconductor,most of them belong to one of these three approaches:(1)the excitonic a...Although there are numerous optical spectroscopy techniques and methods that have been used to extract the fundamental bandgap of a semiconductor,most of them belong to one of these three approaches:(1)the excitonic absorption,(2)modulation spectroscopy,and(3)the most widely used Tauc-plot.The excitonic absorption is based on a many-particle theory,which is physically the most correct approach,but requires more stringent crystalline quality and appropriate sample preparation and experimental implementation.The Tauc-plot is based on a single-particle theo⁃ry that neglects the many-electron effects.Modulation spectroscopy analyzes the spectroscopy features in the derivative spectrum,typically,of the reflectance and transmission under an external perturbation.Empirically,the bandgap ener⁃gy derived from the three approaches follow the order of E_(ex)>E_(MS)>E_(TP),where three transition energies are from exci⁃tonic absorption,modulation spectroscopy,and Tauc-plot,respectively.In principle,defining E_(g) as the single-elec⁃tron bandgap,we expect E_(g)>E_(ex),thus,E_(g)>E_(TP).In the literature,E_(TP) is often interpreted as E_(g),which is conceptual⁃ly problematic.However,in many cases,because the excitonic peaks are not readily identifiable,the inconsistency be⁃tween E_(g) and E_(TP) becomes invisible.In this brief review,real world examples are used(1)to illustrate how excitonic absorption features depend sensitively on the sample and measurement conditions;(2)to demonstrate the differences between E_(ex),E_(MS),and E_(TP) when they can be extracted simultaneously for one sample;and(3)to show how the popular⁃ly adopted Tauc-plot could lead to misleading results.Finally,it is pointed out that if the excitonic absorption is not ob⁃servable,the modulation spectroscopy can often yield a more useful and reasonable bandgap than Tauc-plot.展开更多
掺钛蓝宝石晶体(简称“钛宝石晶体”,化学式为Ti∶Al_(2)O_(3))中的钛离子电子能级与周围氧化铝晶体晶格振动能级之间的电子-声子耦合作用非常激烈,致使钛宝石晶体基态和激发态能级的分布范围很宽,具有宽带吸收、宽带发射,以及高硬度、...掺钛蓝宝石晶体(简称“钛宝石晶体”,化学式为Ti∶Al_(2)O_(3))中的钛离子电子能级与周围氧化铝晶体晶格振动能级之间的电子-声子耦合作用非常激烈,致使钛宝石晶体基态和激发态能级的分布范围很宽,具有宽带吸收、宽带发射,以及高硬度、高热导等特点,广泛应用于工业、国防和科研等领域。国际上商用的钛宝石晶体主要由美国GT-Solar公司提供,在钛宝石晶体领域我国处于“卡脖子”状态。而美国GT-Solar公司提供的钛宝石晶体采用热交换法生长,尺寸偏小、钛离子浓度低、浓度均匀性差,且供货周期长。随着蓝光LD泵浦源、先进激光制造和十拍瓦-百拍瓦的高功率激光系统的发展,对高浓度、大口径(>∅150 mm)、高品质因数(figure of merit,FOM)的钛宝石晶体元件的需求将日益增大。展开更多
基金Supported by Bissell Distinguished Professor Endowment Fund at UNC-Charlotte。
文摘Although there are numerous optical spectroscopy techniques and methods that have been used to extract the fundamental bandgap of a semiconductor,most of them belong to one of these three approaches:(1)the excitonic absorption,(2)modulation spectroscopy,and(3)the most widely used Tauc-plot.The excitonic absorption is based on a many-particle theory,which is physically the most correct approach,but requires more stringent crystalline quality and appropriate sample preparation and experimental implementation.The Tauc-plot is based on a single-particle theo⁃ry that neglects the many-electron effects.Modulation spectroscopy analyzes the spectroscopy features in the derivative spectrum,typically,of the reflectance and transmission under an external perturbation.Empirically,the bandgap ener⁃gy derived from the three approaches follow the order of E_(ex)>E_(MS)>E_(TP),where three transition energies are from exci⁃tonic absorption,modulation spectroscopy,and Tauc-plot,respectively.In principle,defining E_(g) as the single-elec⁃tron bandgap,we expect E_(g)>E_(ex),thus,E_(g)>E_(TP).In the literature,E_(TP) is often interpreted as E_(g),which is conceptual⁃ly problematic.However,in many cases,because the excitonic peaks are not readily identifiable,the inconsistency be⁃tween E_(g) and E_(TP) becomes invisible.In this brief review,real world examples are used(1)to illustrate how excitonic absorption features depend sensitively on the sample and measurement conditions;(2)to demonstrate the differences between E_(ex),E_(MS),and E_(TP) when they can be extracted simultaneously for one sample;and(3)to show how the popular⁃ly adopted Tauc-plot could lead to misleading results.Finally,it is pointed out that if the excitonic absorption is not ob⁃servable,the modulation spectroscopy can often yield a more useful and reasonable bandgap than Tauc-plot.
文摘掺钛蓝宝石晶体(简称“钛宝石晶体”,化学式为Ti∶Al_(2)O_(3))中的钛离子电子能级与周围氧化铝晶体晶格振动能级之间的电子-声子耦合作用非常激烈,致使钛宝石晶体基态和激发态能级的分布范围很宽,具有宽带吸收、宽带发射,以及高硬度、高热导等特点,广泛应用于工业、国防和科研等领域。国际上商用的钛宝石晶体主要由美国GT-Solar公司提供,在钛宝石晶体领域我国处于“卡脖子”状态。而美国GT-Solar公司提供的钛宝石晶体采用热交换法生长,尺寸偏小、钛离子浓度低、浓度均匀性差,且供货周期长。随着蓝光LD泵浦源、先进激光制造和十拍瓦-百拍瓦的高功率激光系统的发展,对高浓度、大口径(>∅150 mm)、高品质因数(figure of merit,FOM)的钛宝石晶体元件的需求将日益增大。
