A scalable, flexible and transparent GaN based heterojunction piezoelectric nanogenerator for bending, air-flow and vibration energy harvesting

Johar, Muhammad Ali,Kang, Jin-Ho,Hassan, Mostafa Afifi,Ryu, Sang-Wan Elsevier 2018 APPLIED ENERGY Vol.222 No.-

<P><B>Abstract</B></P> <P>Flexible functional devices are extremely suitable for malleable, sustainable, and portable applications such as smart clothing, flexible electronics and medical applications. Here, we present a scalable, transparent, and flexible piezoelectric nanogenerator (STF PNG) fabricated by forming a p-n NiO/GaN heterojunction using an electrochemical lift-off process to transfer GaN onto a flexible substrate. Several actuation sources such as air-flow, finger forces for bending, vibrations with a frequency of 20 Hz, and cyclic stretching-releasing agitation by a linear motor were applied to generate piezoelectric bias. Peak piezoelectric output voltage and current of 30 V and 1.43 µA, respectively, were measured. Such high piezoelectric bias was generated by suppressing free carrier screening and junction screening; the former was achieved due to removal of compressive stresses from GaN after the lift-off process, while the latter was achieved by the deposition of a highly resistive p-type NiO layer on transferred GaN and a sandwiched Polydimethylsiloxane resulting in a very high junction resistivity of the p-n NiO/GaN heterojunction STF PNG. As a result, our approach provides a new strategy for novel and highly efficient design of semiconductor-based flexible PNGs for a wide variety of applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A novel fabrication of GaN based heterojunction flexible piezoelectric generator. </LI> <LI> Piezoelectricity from vibrations, finger force, air-flow, and cyclic agitation. </LI> <LI> High electrical energy generation from ambient vibrations. </LI> <LI> High output voltages by suppressing internal screening and junction screening. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Facile growth of high aspect ratio c-axis GaN nanowires and their application as flexible p-n NiO/GaN piezoelectric nanogenerators

Johar, Muhammad Ali,Waseem, Aadil,Hassan, Mostafa Afifi,Kang, Jin-Ho,Ha, Jun-Seok,Lee, June Key,Ryu, Sang-Wan Elsevier 2018 Acta materialia Vol.161 No.-

<P><B>Abstract</B></P> <P>Piezoelectric nanogenerators (PNGs) have attracted great interest as energy sources to power-up smart clothing, micro/nano systems, and portable electronic gadgets. Due to non-centrosymmetric crystal structure, bio-compatibility, and mechanical robustness of GaN, it is a promising candidate to fabricate PNGs. In this study, c-axis GaN nanowires were grown by MOCVD, then were embedded inside polydimethylsiloxane and flipped on to the flexible substrate, followed by the deposition of p-type NiO to form heterojunction. The fabrication of GaN nanowires based heterojunction PNG on flexible substrate is the first report to the best of our knowledge. The piezoelectric properties of PNGs were investigated as a function of the GaN nanowire length. A maximum piezoelectric output potential of 20.8 V and current of 253 nA were measured. The stability of the device was also evaluated and found stable even after 20,000 cycles. This high piezoelectric output was attributed to the suppression of free carrier screening and junction screening. Moreover, the underlying reasons for the high stability are the malleability of the device and high aspect ratio of the GaN nanowires. The design and stability of our device make it a promising candidate for applications in self-powered systems for environment monitoring and low power electronics.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Controlled conductivity of p-type Cu_xO/GaN piezoelectric generator to harvest very high piezoelectric potential

Johar, Muhammad Ali,Kang, Jin-Ho,Ha, Jun-Seok,Lee, June Key,Ryu, Sang-Wan ELSEVIER SCIENCE 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.726 No.-

<P><B>Abstract</B></P> <P>Typically, semiconductor piezoelectric-generators (PGs) exhibit low output potential because of the rapid screening by mobile carriers, and the output potential drops within fractions of a second. The reduction of internal carrier screening has been attempted by several groups, but complete suppression has not yet been reported. In this paper, a novel method for the fabrication of high-power PGs is presented. The detrimental screening issue was solved by fabricating a p–n heterojunction of p-type Cu<SUB>x</SUB>O (x = 1, 2) and GaN. This was found to be an effective structure for decreasing the internal screening, while the suppression of screening was directly proportional to the resistivity of the p-type layer. The resistivity of the p-type thin film was controlled by optimizing the oxygen content in the environment during deposition. From X-ray diffraction analysis, the crystal structure of copper oxide changed by varying the oxygen incorporation, which primarily controlled the p-type conductivity. The optimized device exhibited output voltage of 26 V with a current density of 11.40 μA cm<SUP>−2</SUP> under a pressure of 5 MPa. This study provides an effective approach for generating high electrical power, and it would be advantageous to construct flexible GaN PGs, which are essential devices for self-powered sensor networks.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Controlled conductivity of p-type Cu<SUB>x</SUB>O for Cu<SUB>x</SUB>O/GaN PG was fabricated. </LI> <LI> Junction screening was addressed to enhance piezoelectric output. </LI> <LI> Piezoelectric output of PG was 26 V and 11.4 μA cm<SUP>−2</SUP> with an efficiency of 2.6%. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Controlled carrier screening in p-n NiO/GaN piezoelectric generators by an Al₂O₃ insertion layer

Johar, Muhammad Ali,Jeong, Dae Kyung,Hassan, Mostafa Afifi,Kang, Jin-Ho,Ha, Jun-Seok,Lee, June Key,Ryu, Sang-Wan IOP 2017 Journal of Physics. D, Applied Physics Vol.50 No.48

<P>The performance of a piezoelectric generator (PG) depends significantly on the internal screening process inside the device. As piezoelectric charges appear on both ends of the piezoelectric crystal, internal screening starts to decrease the piezoelectric bias. Therefore, the piezoelectric energy generated by external stress is not fully utilized by external circuit, which is the most challenging aspect of high-efficiency PGs. In this work, the internal screening effect of a NiO/GaN p-n PG was analyzed and controlled with an Al<SUB>2</SUB>O<SUB>3</SUB> insertion layer. Internal screening in the p-n diode PG was categorized into free-carrier screening in neutral regions and junction screening due to charge drift across the junction. It was observed that junction screening could be significantly suppressed by inserting an Al<SUB>2</SUB>O<SUB>3</SUB> layer and that effect was dominant in a leaky diode PG. With this implementation, the piezoelectric bias of the NiO/GaN PG was improved by a factor of ~100 for high-leakage diodes and a factor of ~1.6 for low-leakage diodes. Consequently, NiO/Al<SUB>2</SUB>O<SUB>3</SUB>/GaN PGs under a stress of 5 MPa provided a piezoelectric bias of 12.1 V and a current density of 2.25 <I>µ</I>A cm<SUP>−2</SUP>. The incorporation of a highly resistive Al<SUB>2</SUB>O<SUB>3</SUB> layer between p-NiO and n-GaN layers in NiO/GaN heterojunctions provides an efficient means of improving the piezoelectric performance by controlling the internal screening of the piezoelectric field.</P>

Factors Associated with Early Breastfeeding Initiation among Women Who Underwent Cesarean Delivery at Tertiary Hospitals in Kelantan, Malaysia

Nazirah Johar,Noraini Mohamad,Norkhafizah Saddki,Tengku Alina Tengku Ismail,Zaharah Sulaiman 대한가정의학회 2021 Korean Journal of Family Medicine Vol.42 No.2

Background: Cesarean delivery is linked with lower rates of early breastfeeding initiation. This study aimed to determine the prevalence and associated factors of early initiation of breastfeeding among women admitted for elective cesarean delivery in Kelantan, Malaysia. Methods: A total of 171 women admitted for elective cesarean delivery at two tertiary hospitals in Kelantan, Malaysia, participated in this study. On day two after cesarean delivery, face-to-face interviews were conducted with the mothers to get information on feeding practice. Descriptive statistics, including simple and multiple logistic regressions, were used for data analysis. Results: Seventy-three percent of mothers initiated breastfeeding within 1 hour of birth. Approximately 15.8% and 10.5% of mothers initiated breastfeeding within 24 hours and ≥24 hours, respectively. Skin-to-skin contact between mothers and their infants occurred in 77.8% of cases after cesarean delivery. Breastfeeding initiation was significantly associated with skin-to-skin contact (odds ratio [OR], 14.42; 95% confidence interval [CI], 3.58–58.06), mothers who exclusively breastfed during hospitalization (OR, 36.37; 95% CI, 5.60–236.24), and infants who were not sleepy during attempts at breastfeeding (OR, 5.17; 95% CI, 1.32–20.21). Conclusion: Based on our results, it is possible to increase the proportion of mothers initiating breastfeeding within 1 hour among women who undergo elective cesarean delivery. Therefore, it is important that health practitioners educate women beginning in the antenatal period who plan to undergo cesarean delivery by emphasizing the importance of early initiation of breastfeeding.

Effect of strain-rate and moisture content on the mechanical properties of adhesively bonded joints

M. Johar,K. J. Wong,S. A. Rashidi,M. N. Tamin 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.5

Mechanical performance of polymer-based adhesive joints is susceptible to moisture absorption. In this respect, this study establishes a validated methodology for predicting the mechanical responses of adhesively bonded joints under strain rate-dependent and moisture conditions. For this purpose, adhesively bonded lap-joint specimens were tested under the opening (Mode I) and in-plane shear (Mode II) loadings at machine crosshead displacement rates up to 500 mm/min. The mechanics response of the adhesively bonded joint is predicted using the extended cohesive zone model to capture the strain rate- and absorbed moisture-dependent effects. Good correlation of the predicted and measured flexural responses are demonstrated for the independent case of the mixed-mode flexure (MMF) test configuration. The corresponding failure processes of the adhesively bonded joint are described in terms of the characteristic interface damage and stress evolution.

U.S. Campaigns of Knowledge in the Philippines and Japan and Their Afterlives Today

Malini Johar Schueller(말리니 슈엘러) 경북대학교 인문학술원 2018 동서인문 Vol.0 No.10

미국이 일본을 점령하고 필리핀을 식민화하면서 사용해온 주요 생정치 기술은 인종적 성격이 매우 강한 교육 프로젝트를 통해 적절한 교육 내용을 만들어내는 작업이었다. 하지만 인종적 정체성을 부여하는 작업은 결코 간단하지 않았다. 그것은 헤게모니가 대개 그러하듯이 끊임없는 수정과 점검, 변호의 과정을 거쳐야 하는 일이었다. 이 글에서는 필리핀 공립학교의 영어교육과 일본의 문자개혁 같은 언어개혁에 반영된 인종담론의 정당화와 함께 인종 프로젝트로서 생겨난 일본의 브라이즈 학교를 살펴본다. 또한 강제성을 띠면서도 끊임없이 변화하는 인종담론이 일본과 필리핀에서 독특하게 나타나는 다양한 인종들의 혼합에서 비롯된 산물임을 밝히고자 한다. 미국은 필리핀을 식민화하고 일본을 점령하면서 매우 상이한 오리엔탈리즘적 인종관리 프로젝트를 추진했다. 이 글에서는 필리핀에 관한 1902년 상원 청문회와 〈일본에 대한 미국교육 선교 보고서〉, 브라이즈 학교의 교재를 분석하면서 다음 두 가지 사실을 보여주고자 한다. 먼저는 필리핀의 인종 고양과 일본의 탈문화를 보여주고, 다음으로 군국주의화에서 미국 내의 동화로 바뀐, 일본의 교육 지침에 나타난 인종화의 성격 전환을 보여준다. 이 글에서는 헤게모니적이면서도 상황에 따라 바뀌는 식민지의 주체적인 인종담론 수용 과정과 식민지 인종주의의 다원성, 오늘날 미 제국주의로까지 이어지는 지식 캠페인의 중요성을 부각시킨다. The creation of a suitable pedagogical subject through highly racialized educational projects has been a major biopolitical technology of U.S. colonization and occupation. Yet this racialization was never simply available but like all hegemony, had to be constantly renewed, affirmed, and defended. This talk examines the racialized justifications offered for language reform-the institution of English in public schools in the Philippines and script reform in Japan- and then Brides’ schools in Japan as racial projects and points to the regulatory, yet ever-shifting discourses of race as they emerge from the intersection of domestic racial categories, the specificities of conditions in the Philippines and Japan. Colonizing the Philippines and occupying Japan involved contrasting projects of Orientalist racial management. By analyzing the 1902 Senate Hearings on the Philippines, the Report of the United States Educational Mission to Japan and two Brides School manuals I demonstrate, first, the contrast between Filipino racial uplift and Japanese deculturation and then the shift in Japanese racialization as pedagogical imperative changed from re-education from militarization to assimilation within America. My talk emphasizes the hegemonic, yet contingent process of colonial racial subjectification, the pluralism of colonial racial formation, and the continued importance of campaigns of knowledge to U.S. imperialism today.

Terrestrial Gamma Radiation Dose and its Relationship with Soil Ph Level in Seri Gading Industrial Area, Batu Pahat District, Malaysia

Saffuwan Mohamed Johar,Zaidi Embong 한국토양비료학회 2014 한국토양비료학회 학술발표회 초록집 Vol.2014 No.6

Effect of crystal orientation of GaN/V₂O₅ core-shell nanowires on piezoelectric nanogenerators

Waseem, Aadil,Johar, Muhammad Ali,Hassan, Mostafa Afifi,Bagal, Indrajit V.,Ha, Jun-Seok,Lee, June Key,Ryu, Sang-Wan Elsevier 2019 Nano energy Vol.60 No.-

<P><B>Abstract</B></P> <P>GaN/V<SUB>2</SUB>O<SUB>5</SUB> core-shell nanowire (NW) piezoelectric generators of controlled crystallographic orientations were fabricated, and the device performance was characterized. Catalyst-assisted c- and m-axis GaN NWs were grown on a c-plane GaN thin film by varying the NH<SUB>3</SUB> flow rate and reactor pressure. The grown NWs were then utilized to fabricate the flexible piezoelectric nanogenerators (PNGs) to practically investigate the impact of the c- and m-axis GaN NWs on the piezoelectric response. The c-axis GaN NWs exhibited a higher piezoelectric output than m-axis GaN NWs. Furthermore, the GaN/V<SUB>2</SUB>O<SUB>5</SUB> core-shell structure was utilized in the NWs to suppress the internal carrier screening that degrades the piezoelectric output. The maximum output voltage (27 V) exhibited by core-shell c-axis NWs was thrice the voltage exhibited by pristine c-axis GaN NWs (9 V). A stability test was performed for one hour to verify the feasibility of using flexible PNGs for real applications. The high stability of PNGs was attributed to the flexibility and high crystallinity of the NWs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> C- & m-axis GaN NWs are grown by MOCVD for piezoelectric generators. </LI> <LI> The piezoelectric output for pristine c-axis NWs is twice the output of m-axis NWs. </LI> <LI> The piezoelectric output of the GaN/V<SUB>2</SUB>O<SUB>5</SUB> core-shell NWs is three times of pristine NWs. </LI> <LI> PNGs exhibited long-term stability due to excellent mechanical properties of NWs. </LI> <LI> GaN/V<SUB>2</SUB>O<SUB>5</SUB> heterojunction suppressed the junction current screening effect. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>GaN/V<SUB>2</SUB>O<SUB>5</SUB> core-shell nanowire (NW) piezoelectric generators of controlled crystallographic orientations are reported. Catalyst-assisted c- and m-axis GaN NWs grown by MOCVD are utilized to fabricate the flexible piezoelectric nanogenerators to investigate the impact of the c- and m-axis GaN NWs on the piezoelectric response. The c-axis GaN NWs exhibited the higher piezoelectric output than m-axis GaN NWs. The GaN/V<SUB>2</SUB>O<SUB>5</SUB> core-shell structure is utilized in the NWs which further enhanced the output voltage to 27 V and output current to 590 nA.</P> <P>[DISPLAY OMISSION]</P>

Type-II ZnO/ZnS core-shell nanowires: Earth-abundant photoanode for solar-driven photoelectrochemical water splitting

Hassan, Mostafa Afifi,Johar, Muhammad Ali,Waseem, Aadil,Bagal, Indrajit V.,Ha, Jun-Seok,Ryu, Sang-Wan The Optical Society 2019 Optics express Vol.27 No.4