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RISS 인기검색어
- 검색키워드
- 저자 : Muhammad Zahir (검색결과 21 건)
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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>
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Numerical Investigation of Collection Efficiency of Virtual Impactor with Electro-Aerodynamic Lens
Muhammad Zeeshan Zahir,Se-Jin Yook(육세진) 한국기계가공학회 2019 한국기계가공학회지 Vol.18 No.7
An electro-aerodynamic lens for improving the performance of virtual impactor has been proposed in this study. ANSYS FLUENT Release 16.1 was used for numerical analysis of virtual impactor with and without the electro-aerodynamic lens, used to collimate the incoming aerosol particles into a particle beam before injecting the particles into the virtual impactor. Particles supplied to the electro-aerodynamic lens were assumed to be highly charged. By using an aerodynamic lens before the virtual impactor, without any electrostatic effect, it was found that the cut-off diameter of the virtual impactor was reduced from 4.2 ㎛ to 0.68 ㎛ and that the fine particle contamination problem became more serious. However, by employing the combined electrostatic and aerodynamic effects, that is, by applying electric voltage potential to the electro-aerodynamic lens, the cut-off diameter was found to be further reduced to 0.45 μm and the fine particle contamination was eliminated.
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Zahir, Muhammad Nauman,Jabbar, Adnan Abdul Asian Pacific Journal of Cancer Prevention 2015 Asian Pacific journal of cancer prevention Vol.16 No.14
Background: Pancreatic cancer is the fourth leading cause of cancer related death with median survival ranging from 3 to 6 months for metastatic disease. Palliative chemotherapy has been the backbone of treatment in advanced stage and has evolved over time. Data pertaining to the disease are scarce from our part of the world where treatment poses a significant challenge due to lack of resources. Materials and Methods: A retrospective chart review was performed for all patients presenting with stage IV pancreatic carcinoma at a tertiary care hospital in Karachi, Pakistan between January 2008 and December 2012. Data were collected using a pre-designed, coded questionnaire looking at patient characteristics, treatment given and outcome. Results: 101 patients were found to be eligible. Mean age was $56.7{\pm}12.8years$, the male to female ratio was 2:1 and most patients had a good performance status. More than half of the tumors were located in the head (57%, n=58) and almost all were adenocarcinomas (95%, n=96). Some 58% (n=59) received first line chemotherapy of which 49% (n=29) received gemcitabine-based regimens and 39% (n=23) received FOLFIRINOX. The median progression free survival for gemcitabine based treatment was 2.9 months (IQR=1.6-5.6) as opposed to 7.3 months (IQR=4.5-9.2) for FOLFIRINOX (P=0.02). Median overall survival was 4.9 months (IQR=2.3-9.5) for first line gemcitabine based treatment and 10.5 months (IQR=7.0-13.2) for first line FOLFIRINOX therapy (P=0.002). Patients on FOLFIRINOX had better survival across all subgroups. Inpatient admissions and dose reductions were more frequent with FOLFIRINOX but the difference between the two regimens was not statistically significant. FOLFIRINOX could be successfully administered as outpatient therapy to a number of patients. Conclusions: FOLFIRINOX remains a suitable first line option in patients with metastatic pancreatic cancer with good performance status even in a resource-poor country where diagnostic and supportive care facilities may be less than optimal and cost is a limitation.
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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>
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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>
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Iqbal Muhammad Zahir,Ullah Akhtar,Aziz Umer,Asif Muhammad,Wabaidur Saikh Mohammad,Ansari Mohd Zahid 한국물리학회 2023 Current Applied Physics Vol.52 No.-
Hybrid supercapacitors (SCs) have acquired astonishing features and being recognized as prospective energy storage devices for energy applications. Herein this work, we describe the hydrothermal synthesis of cobalt sulfide and the polymerization of aniline to prepare polyaniline (PANI). Initially, each electrode was tested in three electrode setup in which the CoS/PANI composite showed high electrochemical performance compared to pristine sample. Furthermore, CoS/PANI was studied along with activated carbon (AC) to explore the hybrid SCs application of the prepared composite. In two electrode arrangement, the hybrid device has achieved a remarkable Qs of 123.6 C g-1 at 0.2 A g-1, energy 29.2 Wh kg-1 as well as high specific power 1275 W kg-1. The hybrid SCs also displayed a maximum capacity retain value of 86.4% after 5000 GCD cycles. These results show that the CoS/PANI can be utilized as a best electrode material for the contemporary energy storage devices.
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Layer dependent electrical transport in exfoliated graphene FETs under UV illumination
Iqbal, Muhammad Zahir,Khan, Abbas,Sung, Dongchul,Eom, Jonghwa,Hong, Suklyun Elsevier 2019 APPLIED SURFACE SCIENCE - Vol.479 No.-
<P><B>Abstract</B></P> <P>Controlled tunability of charge carriers is an intriguing technique to modify the electrical behavior of graphene. In this article, we report the photo-induced oxidation and its reversibility in single, bi and tri-layer graphene (S-B-TLG) devices by employing deep ultraviolet (DUV) light treatment in O<SUB>2</SUB> and N<SUB>2</SUB> atmosphere, respectively. Oxygen molecules in the presence of DUV light show dissociative adsorption onto the surface resulting a p-type carrier modulation in S-B-TLG devices. Treated graphene samples are characterized by Raman spectroscopy where blue-shift in G and 2D-peak positions is observed by DUV/O<SUB>2</SUB> treatment without inclusion of any defect. The reverse effect of carrier modulation is observed when DUV/O<SUB>2</SUB> treated samples are further studied in DUV/N<SUB>2</SUB> atmosphere. The results of electrical measurements show the shift of Dirac point (DP) towards higher gate voltages (V<SUB>g</SUB> > 0) which confirms a p-type carrier modulation in graphene whereas restoration of DP towards pristine state indicates the de-modulation of carriers in S-B-TLG devices. In addition, UV irradiation induced charge transport mechanism on graphene surface is further interpreted by employing density functional theory calculation and Bader charge transfer analysis. Such experimental and computational insights enhance the probability to understand the defect-free and controlled carrier modulation process, intensifying its applicability in electronic and optoelectronic devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Optical sensitivity of graphene is studied by DUV irradiation under oxygen and nitrogen atmosphere. </LI> <LI> Reversible carrier tunability and its mechanism in single, bi- and tri-layer graphene has been presented. </LI> <LI> Computational analysis is carried out for further investigation of tunability mechanism. </LI> <LI> Device mobility is found to be sustainable without inducting defects in graphene. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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