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Optical Properties of GaAs in Si nano-trench grown by Gas Source Molecular Beam Epitaxay
No full text我們利用掃描式電子顯微鏡(SEM）、陰極螢光(CL)及拉曼(Raman)光譜量測以氣態源分子束磊晶法成長在平面矽基板及有圖樣的矽基板上的砷化鎵。
從SEM的觀測，我們可以看到300奈米厚的砷化鎵成長於平面矽基板時，呈現連續山狀的樣貌，並且有方向的小縫隙分佈其間，砷化鎵的覆蓋率超過95％。而成長於有圖樣的矽機板的砷化鎵，幾乎全部都長入矽奈米溝渠中，藉由氫等離子體的幫助，成功地達成選擇性成長，在溝渠寬度小於200奈米之後，才有眼形的小塊堆積在溝渠邊緣的二氧化矽上。
砷化鎵成長於平面矽基板及成長於奈米矽溝渠內的室溫(RT)和低溫(LT)的CL光譜也被量測。無論是成長於平面矽基板還是成長於奈米矽溝渠內，室溫陰極螢光的波峰相較於同質磊晶的砷化鎵皆呈現相同程度約三倍的變寬，以及30 meV左右的藍移。我們認為波峰變寬主要歸因於各個被拉張或擠壓的結晶為了達到費米能階一致而造成的能帶變形，以致於原有的能階數減少，在電子束產生大量載子的同時，也同時填滿能階到更高/低能階，造成放光時波峰的變寬。而大程度的藍移則歸咎於成長時的自動摻雜，或所謂的Burstein-Moss shift。成長於矽奈米溝渠內的砷化鎵LTCL光譜在溝渠寬度介於90奈米至140奈米間的波形呈現雙峰態。較低能量的波段被歸因於深層載子與碳受體的復合，而較高能量的波段則被歸因於施體與受體的復合。在溝渠寬度大於140奈米之後，其放光波形接近成長於平面矽機板的砷化鎵，藉由高斯(Gaussian)分佈擬合波峰，可以得到三至四個波峰。而溝渠邊緣的二氧化矽由於缺陷結構放光，共有三個波段。常溫時為1.9 eV的放光，歸因於非橋接氧電洞中心；2.2 eV的放光，歸因於氧空洞與空隙氧分子間電子電洞的復合；2.7 eV的放光，歸因於矽孤對電子與電洞的復合。在LTCL的觀察中，2.2 eV及2.7 eV這兩種放光會縮減，起因於降溫時對這兩種缺陷結構的消減。
常溫的拉曼光譜也觀察到不尋常的現象：在所有的試片中我們均量測到強烈的原本禁帶的橫向聲子模態。我們認為此一現象是源於晶體中大量的微雙晶缺陷，此種缺陷會把原本(001)面轉成{122}面。另一現象是在溝渠寬度小於100 nm以後，我們使用Lorentz分佈擬合的實驗值在橫向聲子與縱向聲子模態之間有多一「表面聲子」模態，起因於較大的表面積/體積比。We have utilized scanning electron microscopy (SEM), cathodoluminescence (CL) spectroscopy and Raman spectroscopy to investigate heteroepitaxial GaAs on planar Si and patterned Si wafer samples grown by gas source molecular beam epitaxy (GSMBE) system.
With the observation of SEM image of the sample top view, the hydrogen-plasma -assisted-grown-300-nm-thick-GaAs on Si planar substrate formed a successional mountain-like “perforated film”. This structure composed by GaAs covers more than 95% area of the planar Si substrate. The filling ratio of GaAs in the trenches is estimated to be nearly 100%. GaAs in the trenches break to become nanowires with lengths varying from hundreds nanometer to several micron. When the trench widths decrease less than 200 nm, the epi-GaAs overflow the trench onto the SiO2 sidewall and form eye-shaped islands whose dimension is about 500 nm.
Room temperature CL (RTCL) and low temperature CL (LTCL) are also performed at trenches whose widths vary from 50 nm to 500 nm. The RTCL GaAs peaks of all trenches are about 3 times broadened and the same blue shifted about 30 meV regardless of the trench width. Meanwhile, the energies of SiO2 peaks remain unchanged. This phenomenon indicates that the blue shift and the broadening are due to the same mechanism. We attribute the blue shift to the Burstein-Moss shift. The broadening is attributed to the Fermi-level-consistency of grains induced band banding. The LTCL GaAs peaks reveal a two-peak feature when trench width between 90 nm and 140 nm. The low energy band is attributed to deep level carrier to carbon acceptor and the high energy band is attributed to donor to acceptor recombination, respectively. When trench width is larger than 140 nm, the peak form is like GaAs on planar (001) Si. With the assistance of Gaussian fitting, there are three or four bands. The origins of three SiO2 RTCL peaks are also surveyed. The 1.9 eV peak is attributed to the NBOHC; the 2.2 eV peak is attributed to the (VO;(O2)i) structure and the 2.7 eV peak is attributed to E’ center. From the observation of LTCL, we find out that the elimination of 2.7 eV and 2.2 eV peaks, which represents the elimination of these defects
The RT Raman spectra of GaAs on planar Si (001) substrates are measured in z(XX)z’ and z(xx)z’ configurations. Regardless of the growth condition, all samples reveal a strong originally forbidden transverse optical (TO) phonon mode. The RT Raman spectra of GaAs in variant trench widths are measured in z(YY)z’ configuration. Each of the epi-GaAs in Si nanotrenches also reveals a strong TO phonon mode and the longitudinal optical (LO) phonon mode broadens. Furthermore, there is an additional peak between the TO and the LO peak while trench width is under 100 nm, which is attributed to the surface optical (SO) phonon mode. The SO mode is measured because of the large surface-to-volume ratio
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Establishment of Risk Decision Model for Motorcycle Riding Space Control
No full text根據交通部統計，2015年台灣機車占有率高達64%，然而三車道以上路段普遍劃設「禁行機車」，為了保障機車合理行駛空間，政府自民國98年起採個案檢討例外開放原則陸續取消外側第三車道禁行機車，但是目前並無對於取消外側第三車道禁行機車事前事後影響較為詳細之分析，因此本研究以交通安全的角度探討該措施對於台灣交通的影響。 首先蒐集目前台北市自民國100年至民國105年取消外側第三車道禁行機車之肇事資料，並以完全貝氏法建立兩個貝氏統計模型Hierarchical Poisson-Gamma model和Hierarchical Poisson-Lognormal model，可求得且分析各車道肇事影響因子，並以DIC值比較模型適合度，結果以Hierarchical Poisson-Gamma model表現較優。 接著計算所蒐集路段事前與事後之風險值，並應用於決策樹(CART)，定義比較事前事後之風險為惡化或改善，以此作為決策樹之目標變數，道路幾何特性與交通量特性則作為自變數，可以得到七條規則，並以隨機森林找出影響決策之重要變數；並比較所有因子、貝氏因子與隨機森林因子建構出之決策樹，以錯誤矩陣驗證經過篩選因子後貝氏因子與隨機森林因子之決策樹整體誤差僅19%，可作為未來政府取消外側第三車道禁行機車之參考。According to the statistics of the ministry of transportation and communications, the sharing rate of the motorcycle is 64% in 2015. However, in generally, the three-lane section’s inside lane is set to be “Forbidding-Motorcycles”. In order to protect the riding space of motorcycles, the government gradually cancelled the forbidding-motorcycles of the third lane based on the local conditions. Nevertheless, there is no detailed analysis of before and after of cancel the forbidding-motorcycles of the third lane. In this case, this study aims to find the influence of motorcycle policy in the safety of traffic measure. The study collects the accident data of forbidding-motorcycles of the third lane from 2011 to 2016 in Taipei. Using the Full Bayesian Method to build two Bayesian Statistical Models: Hierarchical Poisson-Gamma model and Hierarchical Poisson-Lognormal model. With the above models, the accident factors of each lane can be obtained. The DIC value can be applied to define the fitness degree of the model. The result shows that Hierarchical Poisson-Gamma model has better performance. Finally, analyzing the traffic characteristic and accident data which before and after the forbidding-motorcycles, and computing the risk of each road. This result is used in the CART to fine the difference of traffic situation because of the motorcycle policy. After setting the result to be the decision variable of CART, and the road geometric characteristics and traffic volume as the independent variable, the seven rules are gained. The random forests can be applied to find the key variables. Comparison of decision trees which construct by all factors, Bayesian factors and random forests factors. The results show the error is 19% of decision trees which construct by all factors, Bayesian factors and random forests factors, which is comparatively low. This CART can be the effecttive reference for the government to decide whether the forbidding-motorcycles policy of the third lane cancelled or not
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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