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Deep-ultraviolet-light-driven reversible doping of WS2 field-effect transistors.
Iqbal, Muhammad Waqas,Iqbal, Muhammad Zahir,Khan, Muhammad Farooq,Shehzad, Muhammad Arslan,Seo, Yongho,Eom, Jonghwa RSC Pub 2015 Nanoscale Vol.7 No.2
<P>Improvement of the electrical and photoelectric characteristics is essential to achieve an advanced performance of field-effect transistors and optoelectronic devices. Here we have developed a doping technique to drastically improve electrical and photoelectric characteristics of single-layered, bi-layered and multi-layered WS2 field-effect transistors (FET). After illuminating with deep ultraviolet (DUV) light in a nitrogen environment, WS2 FET shows an enhanced charge carrier density, mobility and photocurrent response. The threshold voltage of WS2 FET shifted toward the negative gate voltage, and the positions of E and A1g peaks in Raman spectra shifted toward lower wavenumbers, indicating the n-type doping effect of the WS2 FET. The doping effect is reversible. The pristine characteristics of WS2 FET can be restored by DUV light illumination in an oxygen environment. The DUV-driven doping technique in a gas environment provides a very stable, effective, easily applicable way to enhance the performance of WS2 FET.</P>
Modification of the structural and electrical properties of graphene layers by Pt adsorbates
Iqbal, M Waqas,Iqbal, M Zahir,Khan, M Farooq,Jin, Xiaozhan,Hwang, Chanyong,Eom, Jonghwa TaylorFrancis 2014 SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS Vol.15 No.5
<P>The properties of graphene are strongly affected by metal adsorbates and clusters on graphene. Here, we study the effect of a thin layer of platinum (Pt) metal on exfoliated single, bi- and trilayer graphene and on chemical vapor deposition-grown single-layer graphene by using Raman spectroscopy and transport measurements. The Raman spectra and transport measurements show that Pt affects the structure as well as the electronic properties of graphene. The shift of peak frequencies, intensities and widths of the Raman bands were analyzed after the deposition of Pt with different thicknesses (1, 3, 5 nm) on the graphene. The shifts in the G and 2D peak positions of the Raman spectra indicate the n-type doping effect by the Pt metal. The doping effect was also confirmed by gate-voltage dependent resistivity measurements. The doping effect by the Pt metal is stable under ambient conditions, and the doping intensity increases with the increasing Pt deposition without inducing a severe degradation of the charge carrier mobility.</P>
Edge Oxidation Effect of Chemical-Vapor-Deposition-Grown Graphene Nanoconstriction
Iqbal, Muhammad Waqas,Iqbal, Muhammad Zahir,Jin, Xiaozhan,Hwang, Chanyong,Eom, Jonghwa American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.6
<P>The edge oxidation effects of chemical-vapor-deposition-grown graphene devices with nanoconstrictions of different sizes are presented. The effects of edge oxidation on the doping level of a nanoconstriction graphene device were identified by Raman spectroscopy and using the back-gate-voltage-dependent resistance. Strong p-type doping was observed as the size of nanoconstriction decreased. The Dirac point of the graphene device shifted toward positive voltage, and the positions of the G and 2D peaks in Raman spectroscopy shifted toward a higher wave number, indicating the p-type doping effect of the graphene device. p-type doping was lifted by deep-ultraviolet light illumination under a nitrogen atmosphere at room temperature. p-type doping was restored by deep-ultraviolet light illumination under an oxygen atmosphere at room temperature. Edge oxidation in the narrow structures explains the origin of the p-type doping effect widely observed in graphene nanodevices.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-6/am405885c/production/images/medium/am-2013-05885c_0008.gif'></P>
Allergens of <i>Arachis hypogaea</i> and the effect of processing on their detection by ELISA
Iqbal, Amjad,Shah, Farooq,Hamayun, Muhammad,Ahmad, Ayaz,Hussain, Anwar,Waqas, Muhammad,Kang, Sang-Mo,Lee, In-Jung Co-Action Publishing 2016 Food & nutrition research Vol.60 No.-
<P>Food allergies are an emerging public health problem in industrialized areas of the world. They represent a considerable health problem in these areas because of the relatively high number of reported cases. Usually, food allergens are proteins or glycoproteins with a molecular mass ranging from 10 to 70 kDa. Among the food allergies, peanut is accounted to be responsible for more than 50% of the food allergy fatalities. Threshold doses for peanut allergenic reactions have been found to range from as low as 100 µg to 1 g of peanut protein, which equal to 400 µg to 4 g peanut meal. Allergens from peanut are mainly seed storage proteins that are composed of conglutin, vicilin, and glycinin families. Several peanut proteins have been identified to induce allergic reactions, particularly Ara h 1–11. This review is mainly focused on different classes of peanut allergens, the effect of thermal and chemical treatment of peanut allergens on the IgY binding and detectability of these allergens by enzyme linked immunosorbent assay (ELISA) to provide knowledge for food industry.</P>
Robust Face Recognition under Limited Training Sample Scenario using Linear Representation
( Omer Iqbal ),( Waqas Jadoon ),( Zia Ur Rehman ),( Fiaz Gul Khan ),( Babar Nazir ) 한국인터넷정보학회 2018 KSII Transactions on Internet and Information Syst Vol.12 No.7
Recently, several studies have shown that linear representation based approaches are very effective and efficient for image classification. One of these linear-representation-based approaches is the Collaborative representation (CR) method. The existing algorithms based on CR have two major problems that degrade their classification performance. First problem arises due to the limited number of available training samples. The large variations, caused by illumintion and expression changes, among query and training samples leads to poor classification performance. Second problem occurs when an image is partially noised (contiguous occlusion), as some part of the given image become corrupt the classification performance also degrades. We aim to extend the collaborative representation framework under limited training samples face recognition problem. Our proposed solution will generate virtual samples and intra-class variations from training data to model the variations effectively between query and training samples. For robust classification, the image patches have been utilized to compute representation to address partial occlusion as it leads to more accurate classification results. The proposed method computes representation based on local regions in the images as opposed to CR, which computes representation based on global solution involving entire images. Furthermore, the proposed solution also integrates the locality structure into CR, using Euclidian distance between the query and training samples. Intuitively, if the query sample can be represented by selecting its nearest neighbours, lie on a same linear subspace then the resulting representation will be more discriminate and accurately classify the query sample. Hence our proposed framework model the limited sample face recognition problem into sufficient training samples problem using virtual samples and intra-class variations, generated from training samples that will result in improved classification accuracy as evident from experimental results. Moreover, it compute representation based on local image patches for robust classification and is expected to greatly increase the classification performance for face recognition task.
Hussain, Sajjad,Iqbal, Muhmmad Waqas,Park, Jaehyun,Ahmad, Muneer,Singh, Jai,Eom, Jonghwa,Jung, Jongwan Springer 2014 NANOSCALE RESEARCH LETTERS Vol.9 No.1
<P>Hydrogen flow during low pressure chemical vapor deposition had significant effect not only on the physical properties but also on the electrical properties of graphene. Nucleation and grain growth of graphene increased at higher hydrogen flows. And, more oxygen-related functional groups like amorphous and oxidized carbon that probably contributed to defects or contamination of graphene remained on the graphene surface at low H<SUB>2</SUB> flow conditions. It is believed that at low hydrogen flow, those remained oxygen or other oxidizing impurities make the graphene films p-doped and result in decreasing the carrier mobility.</P>
Molecular n-doping of chemical vapor deposition grown graphene
Singh, Arun Kumar,Iqbal, Muhammad Waqas,Singh, Vivek Kumar,Iqbal, Muhammad Zahir,Lee, Jae Hong,Chun, Seung-Hyun,Shin, Koo,Eom, Jonghwa The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.30
<P>It is essential to tailor the electronic properties of graphene in order to apply graphene films for use in electrodes. Here we report the modification of the electronic properties of single layer chemical vapor deposition (CVD) grown graphene by molecular doping without degrading its transparency and electrical properties. Raman spectroscopy and transport measurements revealed that <I>p</I>-toluenesulfonic acid (PTSA) imposes n-doping on single layer CVD grown graphene. The shift of G and 2D peak wave numbers and the intensity ratio of D and G peaks are analyzed as a function of reaction time. In the gate voltage dependent resistivity measurement, it is found that the maximum resistivity corresponding to the Dirac point is shifted toward a more negative gate voltage with increasing reaction time, indicating an n-type doping effect. We have also made single layer graphene p–n junctions by chemical doping and investigated the current–voltage characteristics at the p–n junction.</P> <P>Graphic Abstract</P><P>It is essential to tailor the electronic properties of graphene in order to apply graphene films for use in electrodes. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm32716c'> </P>
Improving the electrical properties of graphene layers by chemical doping
Khan, Muhammad Farooq,Iqbal, Muhammad Zahir,Iqbal, Muhammad Waqas,Eom, Jonghwa TaylorFrancis 2014 SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS Vol.15 No.5
<P>Although the electronic properties of graphene layers can be modulated by various doping techniques, most of doping methods cost degradation of structural uniqueness or electrical mobility. It is matter of huge concern to develop a technique to improve the electrical properties of graphene while sustaining its superior properties. Here, we report the modification of electrical properties of single- bi- and trilayer graphene by chemical reaction with potassium nitrate (KNO<SUB>3</SUB>) solution. Raman spectroscopy and electrical transport measurements showed the n-doping effect of graphene by KNO<SUB>3</SUB>. The effect was most dominant in single layer graphene, and the mobility of single layer graphene was improved by the factor of more than 3. The chemical doping by using KNO<SUB>3</SUB> provides a facile approach to improve the electrical properties of graphene layers sustaining their unique characteristics.</P>