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
Glass series with general formula 25Li2O-（75-x）B2O3-xNd2O3 was prepared by conventional melt quench technique. Electrical and optical characterizations of these glasses were carried out. It was observed that conduct...Glass series with general formula 25Li2O-（75-x）B2O3-xNd2O3 was prepared by conventional melt quench technique. Electrical and optical characterizations of these glasses were carried out. It was observed that conductivity of glasses decreased and activation energy in- creased with the addition of Nd2O3. The density and refractive index of the glasses increased while optical band gap and radiation length de- creased due to structural changes.展开更多
Terbium-picrate triethylene glycol（EO3-Tb-Pic） complex was prepared in thin film and single layer device structure of ITO/EO3-Tb-Pic/Al, using spin coating technique. The UV-Vis absorption spectroscopy analysis was ...Terbium-picrate triethylene glycol（EO3-Tb-Pic） complex was prepared in thin film and single layer device structure of ITO/EO3-Tb-Pic/Al, using spin coating technique. The UV-Vis absorption spectroscopy analysis was performed to evaluate the electronic molecular transition of the complex. The optical band gap, Eg estimated from the Tauc model revealed that EO3-Tb-Pic thin film exhibited a direct transition with Eg of 2.70 eV. The electronic parameters of the ITO/EO3-Tb-Pic/Al device such as the ideality factor n, barrier height Φb, saturation current Io, and series resistance Rs, were extracted from the conventional lnI-V, Cheung＇s functions and Norde＇s method. It was found that the evaluated parameters calculated from Norde＇s and Cheung＇s methods were consistent with those calculated from the conventional I-V method. In the double logarithmic I-V plot, three distinct regions based on the slope were identified, and the conduction mechanisms were discussed and explained. The mobility, μ value was estimated from SCLC region as 2.58×10^–7 cm2/（V·s）. This newly obtained lanthanide complex may be potentially utilized in electronic devices.展开更多
Over the recent years, the global increase of electronic wastes from electrical and electronic devices (e-wastes) has been on an alarming trend in quantity and toxicity and e-waste<span style="font-family:Verd...Over the recent years, the global increase of electronic wastes from electrical and electronic devices (e-wastes) has been on an alarming trend in quantity and toxicity and e-waste<span style="font-family:Verdana;">s</span><span style="font-family:""><span style="font-family:Verdana;"> are non-biodegradable resulting in its cumulative increase over time. Changes in technology and unrestricted regional movement of electrical devices have facilitated the generation of more e-wastes leading to high levels of air, soil and water pollution. To address these challenges, biodegradable organic components such as chitosan have been used to replace their inorganic counterparts for optoelectronic device applications. However, in-depth knowledge on how such materials can be used to tune the optical properties of their hybrid semiconductors is unrivaled. Thus, systematic studies of the interplay between the preparation methods and optical </span><span style="font-family:Verdana;">band gap and Urbach energy of such organic components are vital. This study has thus been dedicated to map out the effect of acid concentrations</span><span style="font-family:Verdana;"> during chitosan extraction on the corresponding optical band gap and Urbach energy with a view to improving its applications in optoelectronic devices. The,</span></span><span style="font-family:""> </span><span style="font-family:Verdana;">1.0 to 2.5 molar hydrochloric acid (HCl) was used for 12 hours at room temperature during demineralization and 2.0 molar sodium hydroxide (NaOH) during deprotonation processes. The absorbance spectrum of the samples was collected by UV-Vis spectrophotometer and band gap energies were analyzed by performing Tauc’s plot. This study revealed that the energy band gap of chitosan extracted from 1 M HCl, 1.5 M HCl, 2.0 M HCl and 2.5 M HCl were 3.72 eV, 3.50 eV</span><span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> 3.45 eV and 3.36 eV respectively. Furthermore, the Urbach energy of chitosan extracted from 1 M HCl, 1.5 M HCl, 2.0 M HCl and 2.5 M HCl were 0.60496 eV, 0.5292 eV, 4724 eV and 0.2257 eV, respectively.</span>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Glass series with general formula 25Li2O-（75-x）B2O3-xNd2O3 was prepared by conventional melt quench technique. Electrical and optical characterizations of these glasses were carried out. It was observed that conductivity of glasses decreased and activation energy in- creased with the addition of Nd2O3. The density and refractive index of the glasses increased while optical band gap and radiation length de- creased due to structural changes.
基金Project supported by University Malaya and Ministry of Higher Education Malaysia under grant(KPT 1059-2012)Science Fund(SF019-2013)Fundamental Research Grant Scheme(FP033-2013B)
文摘Terbium-picrate triethylene glycol（EO3-Tb-Pic） complex was prepared in thin film and single layer device structure of ITO/EO3-Tb-Pic/Al, using spin coating technique. The UV-Vis absorption spectroscopy analysis was performed to evaluate the electronic molecular transition of the complex. The optical band gap, Eg estimated from the Tauc model revealed that EO3-Tb-Pic thin film exhibited a direct transition with Eg of 2.70 eV. The electronic parameters of the ITO/EO3-Tb-Pic/Al device such as the ideality factor n, barrier height Φb, saturation current Io, and series resistance Rs, were extracted from the conventional lnI-V, Cheung＇s functions and Norde＇s method. It was found that the evaluated parameters calculated from Norde＇s and Cheung＇s methods were consistent with those calculated from the conventional I-V method. In the double logarithmic I-V plot, three distinct regions based on the slope were identified, and the conduction mechanisms were discussed and explained. The mobility, μ value was estimated from SCLC region as 2.58×10^–7 cm2/（V·s）. This newly obtained lanthanide complex may be potentially utilized in electronic devices.
文摘Over the recent years, the global increase of electronic wastes from electrical and electronic devices (e-wastes) has been on an alarming trend in quantity and toxicity and e-waste<span style="font-family:Verdana;">s</span><span style="font-family:""><span style="font-family:Verdana;"> are non-biodegradable resulting in its cumulative increase over time. Changes in technology and unrestricted regional movement of electrical devices have facilitated the generation of more e-wastes leading to high levels of air, soil and water pollution. To address these challenges, biodegradable organic components such as chitosan have been used to replace their inorganic counterparts for optoelectronic device applications. However, in-depth knowledge on how such materials can be used to tune the optical properties of their hybrid semiconductors is unrivaled. Thus, systematic studies of the interplay between the preparation methods and optical </span><span style="font-family:Verdana;">band gap and Urbach energy of such organic components are vital. This study has thus been dedicated to map out the effect of acid concentrations</span><span style="font-family:Verdana;"> during chitosan extraction on the corresponding optical band gap and Urbach energy with a view to improving its applications in optoelectronic devices. The,</span></span><span style="font-family:""> </span><span style="font-family:Verdana;">1.0 to 2.5 molar hydrochloric acid (HCl) was used for 12 hours at room temperature during demineralization and 2.0 molar sodium hydroxide (NaOH) during deprotonation processes. The absorbance spectrum of the samples was collected by UV-Vis spectrophotometer and band gap energies were analyzed by performing Tauc’s plot. This study revealed that the energy band gap of chitosan extracted from 1 M HCl, 1.5 M HCl, 2.0 M HCl and 2.5 M HCl were 3.72 eV, 3.50 eV</span><span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> 3.45 eV and 3.36 eV respectively. Furthermore, the Urbach energy of chitosan extracted from 1 M HCl, 1.5 M HCl, 2.0 M HCl and 2.5 M HCl were 0.60496 eV, 0.5292 eV, 4724 eV and 0.2257 eV, respectively.</span>
