Dielectric resonance effect with negative permittivity in a La1.5Sr0.5NiO4+δ ceramic

Tran Dang Thanh,Nguyen Van Dang,Le Van Hong,The-Long Phan,Seong-Cho Yu 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.10

A polycrystalline sample of La1.5Sr0.5NiO4+δ was prepared by using a solid-state reaction. Xraydiffraction proved the sample to be a single phase with a tetragonal structure (space group:I4/mmm). By using an iodometric titration method to determine the non-stoichiometric oxygenconcentration (δ) in La1.5Sr0.5NiO4+δ, we found δ = −0.017, which corresponds to a doping level ofnh = x + 2δ = 0.466. Also, a strong increase of the magnetization in theM(T) curve at temperaturesbelow the spin-ordering temperature (TSO 100 K) was observed. The M(H) curves show verysmall magnetic moments, which proves the weak ferromagnetic nature of La1.5Sr0.5NiO4+δ. Thedependences of the dielectric constant on the frequency and the temperature, "(!, T) = "0(!, T) +i"00(!, T), was investigated in the frequency range of 1 − 13 MHz. At temperatures around roomtemperature, the maximum of the real part ("0) was higher than 105. Particularly, an abnormaldependence of the permittivity on frequency was observed. Depending on temperature, a dielectricresonance was observed at about 500 kHz or 8 MHz. Interestingly, we observed the dielectricresonanceeffect with a negative permittivity. Such a feature is very similar to that observed inleft-handed materials. The fitting of the experimental data for the dielectric constant at frequenciesaround the resonance frequency to the equations associated with an equivalent RLC series circuitproves that La1.5Sr0.5NiO4+δ belongs to the class of multiferroic materials.

Unipolar Resistance Switching Characteristics in a Thick ZnO/Cu/ZnO Multilayer Structure

Tran Le,Hoang Cao Son Tran,Van Hieu Le,Tuan Tran,Cao Vinh Tran,Thanh Tan Vo,Mau Chien Dang,김상섭,이재찬,Bach Thang Phan 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.7

The resistance switching mechanism and the electrical conduction of thick Cu/ZnO/Cu/ZnO/Cu structures were investigated for various ZnO thicknesses (40, 80, 160, and 320 nm) when the thickness of the middle Cu layer was 2 nm. The ZnO films had a microstructure with columnar grains normal to the substrate. The switching voltages (VSET and VRESET) varied with the thickness of the ZnO layer. A symmetric electrode structure exhibited a unipolar resistance switching. The electrical transport of both high-resistance state (HRS) and low-resistance state (LRS) was Ohmic conduction, and the resistance switching mechanism was driven by the formation and the rupture of Cu conducting paths.

Transfer-free graphene electrodes for super-flexible and semi-transparent perovskite solar cells fabricated under ambient air

Tran, Van-Dang,Pammi, S.V.N.,Park, Byeong-Ju,Han, Yire,Jeon, Cheolho,Yoon, Soon-Gil Elsevier 2019 Nano energy Vol.65 No.-

<P><B>Abstract</B></P> <P>Graphene has shown many advantages over the metal oxide transparent materials that serve as conventional electrodes in solar cells because graphene is more transparent, has greater stability, and is more mechanically flexible. Flexibility and semi-transparency of the perovskite solar cells are challenged to integrate with the flexible electronic devices since the perovskite solar cells have discovered. Herein, we provide the first report of transfer-free, large-scale monolayer graphene employed as a transparent and flexible bottom electrode. High-quality graphene without transfer process was directly synthesized at 150 °C on a polymer substrate <I>via</I> plasma assisted thermal chemical vapor deposition (PATCVD). Additionally, a highly transparent AZO/Ag/AZO (AAA) multilayer was utilized as a top counter electrode to create semi-transparent perovskite solar cells with a remarkable degree of mechanical flexibility. The 300 nm-thick perovskite solar cells with PATCVD-Graphene revealed a high transmittance of ~26% at a wavelength of 700 nm. The highest level of power conversion efficiency (PCE) (~14.2%) was recorded by an illumination from the bottom graphene side. After 1000 bending cycles under a tensile strain of 1.5%, the graphene-based devices maintained a level of PCE that was more than 90% greater than the initial reading. This superior bending robustness highlights the potential for non-transfer, graphene-based, perovskite photovoltaic material to establish a tandem structure for a foldable solar cell.</P> <P><B>Highlights</B></P> <P> <UL> <LI> High-quality graphene without transfer process was directly synthesized at 150 °C on a polymer substrate as transparent electrode. </LI> <LI> The smooth surface with grain size upon 700 nm of MAPbI<SUB>3</SUB> perovskite has been obtained by CVD process. </LI> <LI> Solar-cell devices with PATCVD-graphene electrodes demonstrated a PCE of 14.2% with a transmittance ~26% at a wavelength of 700 nm. </LI> <LI> PSC devices demonstrated a great flexibility, maintaining 90% of the original PCE value after 1000 bending cycles under a tensile strain of 1.5%. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Chemical vapor deposition in fabrication of robust and highly efficient perovskite solar cells based on single-walled carbon nanotubes counter electrodes

Tran, Van-Dang,Pammi, S.V.N.,Dao, Van-Duong,Choi, Ho-Suk,Yoon, Soon-Gil Elsevier 2018 JOURNAL OF ALLOYS AND COMPOUNDS Vol.747 No.-

<P><B>Abstract</B></P> <P>This study presents a strategy of fabricating a perovskite layer through chemical vapor deposition (CVD) method and applying it as an efficient absorber in PSCs based on SWCNT counter electrode. As the results, the CVD method produced smooth and void-free perovskite films, which reduced the moisture absorption at the grain boundaries then delayed the degradation of the organic/inorganic composition. Furthermore, the smooth surface of the dye layer enhances charge collection at the interface with counter electrodes. Thus, the efficiency of cell fabricated by CVD method was 7.9%, which is improved by 29.5% as compared with cells using the conventional spin-coating method. Furthermore, the cell fabricated by CVD method gave an excellent stability. Accordingly, the efficiency was lost only 17% after 500 h performances. This approach could pave the way to develop low-cost PSCs with long-term stability.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Smooth surface with grain size upon 2 μm of MAPbI<SUB>3</SUB> via CVD. </LI> <LI> Degradation of MAPbI<SUB>3</SUB> films by moisture absorption depends on surface morphology. </LI> <LI> Single-wall carbon nanotube for hybrid hole-transporter and counter electrode. </LI> <LI> A small linear efficiency loss of SWCNT-based devices under illumination of 500 h. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Utilization of AZO/Au/AZO multilayer electrodes instead of FTO for perovskite solar cells

Dang, Tran-Van,Pammi, S.V.N.,Choi, Jihoon,Yoon, Soon-Gil Elsevier 2017 Solar energy materials and solar cells Vol.163 No.-

<P><B>Abstract</B></P> <P>Aluminum (3at%)-doped ZnO (AZO)/Au/AZO multilayer films with low resistivity and high transmittance are in situ deposited at room temperature via facing-target sputtering for AZO and direct current (DC) sputtering for Au. The optical and electrical properties of multilayer films are compared with conventionally (<I>on</I>-axis) sputtered and facing-target sputtered (FTS) AZO films. The FTS samples show better crystallinity than that of <I>on</I>-axis sputtered samples, and the lowest value for resistivity is 7.9×10<SUP>−5</SUP> Ω-cm at an Au layer thickness of 8nm, which is compared with that of a conventional FTO electrode. The photo-conversion efficiencies (PCE) of the perovskite solar cells based on the AZO multilayer electrodes deposited via FTS and <I>on</I>-axis sputtering are 9.5% and 8.2%, respectively. Although the PCE of AZO multilayer-based-solar cells exhibit a lower efficiency than that of the FTO based-devices (~12.3%), the perovskite solar cell performance based on the FTS AZO multilayer electrodes is very attractive for applications to flexible planar-structured solar cells.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Utilization of the AZO/Au/AZO multilayer electrodes for perovskite solar cells. </LI> <LI> Low resistivity and high transmittance of AZO/Au/AZO deposited at room temperature via FTS. </LI> <LI> Damage-free FTS method from the plasma for multilayer electrodes. </LI> <LI> Achievement of high photo-conversion efficiency (~9.5%) using multilayer electrodes deposited via FTS. </LI> </UL> </P>

Outcomes of laparoscopic choledochotomy using cholangioscopy via percutaneous-choledochal tube for the treatment of hepatolithiasis and choledocholithiasis: A preliminary Vietnamese study

Loi Van Le,Quang Van Vu,Thanh Van Le,Hieu Trung Le,Khue Kim Dang,Tuan Ngoc Vu,Anh Hoang Ngoc Nguyen,Thang Manh Tran 한국간담췌외과학회 2024 Annals of hepato-biliary-pancreatic surgery Vol.28 No.1

Backgrounds/Aims: Hepatolithiasis and choledocholithiasis are frequent pathologies and unfortunately, with the current treatment strategies, the recurrence incidence is still high. This study aimed to assess the outcomes of laparoscopic choledochotomy using cholangioscopy via the percutaneous-choledochal tube for the treatment of hepatolithiasis and choledocholithiasis in Vietnamese patients. Methods: A cross-sectional study of patients with hepatolithiasis and/or choledocholithiasis who underwent laparoscopic choledochotomy using intraoperative cholangioscopy via percutaneous-choledochal tube at the Department of Hepatopancreatobiliary Surgery, 108 Military Central Hospital, from June 2017 to March 2020. Results: A total of 84 patients were analyzed. Most patients were females (56.0%) with a median age of 55.56 years. Among them, 41.8% of patients had previous abdominal operations, with 33.4% having choledochotomy. All patients underwent successful laparoscopic common bile duct exploration followed by T-tube drainage without needing to convert to open surgery. Most patients (64.3%) had both intrahepatic and extrahepatic stones. The rate of stones ≥ 10 mm in diameter was 64.3%. Biliary strictures were observed in 19.1% of patients during cholangioscopy. Complete removal of stones was achieved in 54.8% of patients. Intraoperative complications were encountered in two patients, but there was no need to change the strategy. The mean operating time was 121.85 ± 30.47 minutes. The early postoperative complication rate was 9.6%, and all patients were managed conservatively. The residual stones were removed through the T-tube tract by subsequent choledochoscopy in 34/38 patients, so the total success rate was 95.2%. Conclusions: Laparoscopic choledochotomy combined with cholangioscopy through the percutaneous-choledochal tube is a safe and effective strategy for hepatolithiasis and/or choledocholithiasis, even in patients with a previous choledochotomy.

Magnetocaloric Effect in La_0.7Ca_0.25Ba_0.05MnO₃ Nanocrystals Exhibiting the Crossover of First- and Second-Order Magnetic Phase Transformation

Thanh, Tran Dang,Linh, Dinh Chi,Van, Hoang Thanh,Ho, Thi Anh,Van Manh, Tien,Bau, Le Viet,Phan, The-Long,Yu, Seng-Cho The Japan Institute of Metals 2015 MATERIALS TRANSACTIONS Vol.56 No.9

Management of Antibiotic-Resistant Helicobacter pylori Infection: Perspectives from Vietnam

Vu Van Khien,Duong Minh Thang,Tran Manh Hai,Nguyen Quang Duat,Pham Hong Khanh,Dang Thuy Ha,Tran Thanh Binh,Ho Dang Quy Dung,Tran Thi Huyen Trang,Yoshio Yamaoka 거트앤리버 소화기연관학회협의회 2019 Gut and Liver Vol.13 No.5

Antibiotic resistance is the most important factor leading to the failure of eradication regimens. This review focuses on the prevalence of Helicobacter pylori primary and secondary resistance to clarithromycin, metronidazole, amoxicillin, levofloxacin, tetracycline, and multidrug in Vietnam. We searched the PubMed, EMBASE, Vietnamese National Knowledge Infrastructure, and Vietnamese Biomedical databases from January 2000 to December 2016. The search terms included the following: H. pylori infection, antibiotic (including clarithromycin, metronidazole, amoxicillin, levofloxacin, tetracycline, and multidrug) resistance in Vietnam. The data were summarized in an extraction table and analyzed manually. Finally, Excel 2007 software was used to create charts. Ten studies (three studies in English and seven in Vietnamese) were included in this review. A total of 308, 412, 523, 408, 399, and 268 H. pylori strains were included in this review to evaluate the prevalence of H. pylori primary resistance to amoxicillin, clarithromycin, metronidazole, levofloxacin, tetracycline, and multidrug resistance, respectively. Overall, the primary resistance rates of amoxicillin, clarithromycin, metronidazole, levofloxacin, tetracycline, and multidrug resistance were 15.0%, 34.1%, 69.4%, 27.9%, 17.9% and 48.8%, respectively. Secondary resistance rates of amoxicillin, clarithromycin, metronidazole, levofloxacin, tetracycline, and multidrug resistance were 9.5%, 74.9%, 61.5%, 45.7%, 23.5% and 62.3%, respectively. In Vietnam, primary and secondary resistance to H. pylori is increasing over time and affects the effectiveness of H. pylori eradication.

Influence of Credit on the Income of Households Borrowing from Banks: Evidence from Vietnam Bank for Agriculture and Rural Development, Kien Giang Province

Quang Vang DANG(Quang Vang DANG ),Viet Thanh Truc TRAN(Viet Thanh Truc TRAN ),Hieu PHAM(Hieu PHAM ),Van Nam MAI(Van Nam MAI ),Quoc Duy VUONG(Quoc Duy VUONG ) 한국유통과학회 2023 The Journal of Asian Finance, Economics and Busine Vol.10 No.2

This paper investigates the determinants of credit accessibility and the effect of credit on the income of farm households borrowing from Vietnam Bank for Agriculture and Rural Development, Giong Rieng District Branch, Kien Giang Province. Based on the primary data of 200 farming households who are the customer of the bank, the study applied the Probit regression model to examine determinant factors of credit accessibility of farm households and employed the Propensity score matching method to investigate the impact of credit on households’ income. The findings of the Probit regression shown that three independent variables that significantly influence the access to credit of households are household size, income source, and farm size. Besides that, the Propensity score matching method results showed a difference of 23.799 million VND/year between the income of borrowing households and that of non-borrowing households at the significance level of 1%. The difference in the imcome from the interval and central matching methods are VND 24.700 million VND/year and VND 24.633 million VND/year, respectively. Given empirical findings suggetsted that several recommendations to increase the credit accessibility of farm households, thereby creating favorable conditions for improving their income.

Factors Affecting Logistics Capabilities for Logistics Service Providers: A Case Study in Vietnam

Dinh Dao DANG,Dieu Linh HA,Van Bao TRAN,Van Tuan NGUYEN,Thi Lien Huong NGUYEN,Thuy Hong DANG,Thi Thai Ha LE 한국유통과학회 2021 The Journal of Asian Finance, Economics and Busine Vol.8 No.5

This study aimed to investigate the factors affecting Logistics capabilities for Logistics Service Providers in Vietnam. Researchers inherited and developed based on previous research to focus on analyzing and evaluating dynamics, measuring Logistics capabilities, and the factors affecting Logistics capabilities for Logistics Service Providers. The logistics capabilities Model is used based on three factors: customer demand management capability, innovation capability, and information management capability. The empirical analysis used data from the survey data of l90 managers of Logistics Service Providers in Hai Phong, Ho Chi Minh City, Da Nang, Hue, Hanoi with reliable tools (SPSS 26.0 software). The data were analyzed by frequencies, percentages, means, Pearson’s Linear Correlation Coefficient, exploratory factor analysis, and multi-linear regression model based on the survey data. The research results identified the following factors affecting Logistics capabilities for Logistics Service Providers: innovation capability has the strongest impact on Logistics capabilities; customer demand management capability has the following strong effects on Logistics capabilities; and finally, information management capability that affects Logistics capabilities. There is also a positive relationship between all factors and Logistics capabilities. Several recommendations are further suggested to enhance to improve Logistics capabilities for Logistics Service Providers in Vietnam.