Quasi-ordering in spontaneously associated surface dipoles: an intrinsic interfacial factor for high-<i>k</i> polymer insulated organic field-effect transistors

Xu, Wentao,Wang, Feng,Rhee, Shi-Woo The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.4

<P>In this study, we report the observation of quasi-ordering in spontaneously associated highly polar surface functional groups (C&z.tbd;N) in the high-<I>k</I> polymer dielectric, cyanoethyl pullulan, and its impact on the organic field-effect transistor (OFET) characteristics. We find that the association originates from C&z.tbd;N⋯H–C–C&z.tbd;N hydrogen bonding as confirmed by XPS, NEXAFS experiments and molecular simulations. The quasi-ordered surface dipoles preferentially induce vertically well-stacked local semiconductor molecular clusters during the initial deposition process, which then promote large-area layer-by-layer growth. By maintaining sufficient quasi-ordering, high transistor performance (<I>μ</I>≈ 6.5 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP>, SS ≈ 0.062 V dec<SUP>−1</SUP>) is obtained under low driving voltages (−3 to −5 V), while breakup of the association at higher baking temperatures leads to a dramatic drop in <I>μ</I> by a factor of ∼10. Our results demonstrate that local quasi-ordering of polymeric surface dipoles, which has a significant effect on the initial semiconductor molecular growth, represents a novel and sensitive factor affecting OFET characteristics.</P> <P>Graphic Abstract</P><P>We demonstrate the quasi-ordering in spontaneously-associated high-k polymer surface dipoles via C–α–H⋯N&z.tbd;C hydrogen-bonding, its impact on the growth of semiconducting molecules and organic field-effect transistor characteristics. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1jm14398k'> </P>

“Knitting up” the inter-dipole gaps in dielectric surfaces: an efficient route for high performance organic field-effect transistors

Xu, Wentao,Guo, Chang,Rhee, Shi-Woo The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.14

<P>Suberoyl chloride (SCL) or ethylenediaminetetraacetic dianhydride (EDT) was added as crosslinking agents into the high-<I>k</I> cyanoethyl pullulan (CEP) polymer and the mixture was cured at temperatures of 90–120 °C. In the crosslinking reaction of the CEP polymer chain with SCL, ester groups were produced to knit up the gaps between the self-associated dipole clusters. Well-stacked pentacene molecular clusters were formed on the dipole clusters and 2-dimensional (2D) layer-by layer growth of the pentacene layer was observed. On the other hand, the dangling carboxylic acid (COOH) group in EDT-cured dielectrics disrupted the quasi-order by shielding the dipoles. This caused discontinuous 3D pentacene grains, which degraded the pentacene organic field effect transistor performance. A high field-effect mobility of ∼8.62 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP>, an on/off current ratio (<I>I</I><SUB>on</SUB>/<I>I</I><SUB>off</SUB>) of ∼10<SUP>5</SUP> and a steep subthreshold slope (SS) of 0.099 V dec<SUP>−1</SUP> were obtained using SCL as a cross-linking agent.</P> <P>Graphic Abstract</P><P>The inter-dipole gaps in the cyanoethyl pullulan dielectric surface can be knitted up by ester groups and this significantly improves the pentacene molecular stacking and transistor performance. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm15888d'> </P>

Low-operating voltage organic field-effect transistors with high-k cross-linked cyanoethylated pullulan polymer gate dielectrics

Xu, Wentao,Rhee, Shi-Woo Royal Society of Chemistry 2009 Journal of materials chemistry Vol.19 No.29

<P>The performance of organic field-effect transistors (OFETs) with high-k cross-linked cyanoethylated pullulan (CLCEP) polymer as a gate dielectric was studied. The optimized film spin-coated from the polymer blend showed high dielectric constant (13.4), high capacitance (53.4 nF cm<SUP>−2</SUP>, at 1 MHz), and negligible hysteresis enabling reliable and low-voltage OFET operations (−3V). With optimized cross-linking temperature, a field-effect mobility of 1.32 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP>, an on/off current ratio (I<SUB>on</SUB>/I<SUB>off</SUB>) of ∼10<SUP>5</SUP> and a threshold voltage (V<SUB>th</SUB>) as low as −1.05 V were obtained. Also a low inverse subthreshold slope (SS) of 89 mV dec<SUP>−1</SUP> was obtained which is close to the theoretical value of 57 mV dec<SUP>−1</SUP> at room temperature. The number of trap states was estimated from threshold voltage shift and SS values, and was confirmed to be related to the OH intensities measured via FT-IR. The morphology and microstructure of the pentacene layer grown on CLCEP dielectrics were also investigated and correlated with OFET device performance.</P> <P>Graphic Abstract</P><P>Organic field-effect transistors with cross-linked cyanoethylated pullulan gate dielectric were fabricated. A high dielectric constant (13.4) enables high capacitance, as well as reliable and low-voltage operations (−3 V). <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b905263a'> </P>

Compromise of electrical leakage and capacitance density effects: a facile route for high mobility and sharp subthreshold slope in low-voltage operable organic field-effect transistors

Xu, Wentao,Rhee, Shi-Woo Royal Society of Chemistry 2011 Journal of materials chemistry Vol.21 No.4

<P>The effects of electrical leakage and capacitance density were investigated in the low-voltage operated organic field-effect transistors (OFETs) by using a gate dielectric with a bi-layer structure of atomic layer deposited alumina (ALD-Al<SUB>2</SUB>O<SUB>3</SUB>) and high-k polymeric cyanoethylated pullulan (CEP) layer. A significant improvement in the device performance was achieved by compromising the two effects, suppressing the leakage current with ALD-Al<SUB>2</SUB>O<SUB>3</SUB> dielectric and maintaining the high capacitance with high-k polymeric layer. With the optimized thickness of ∼5 nm alumina (<I>C</I><SUB>i,CEP/Al<SUB>2</SUB>O<SUB>3</SUB></SUB> ∼ 85 nF cm<SUP>−2</SUP>), a high mobility of ∼5 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> and sharp subthreshold slope (SS) of 0.066 V dec<SUP>−1</SUP> were obtained. The smoother surface of the polymeric dielectric surface enhanced the 2-dimensional vertical molecular layer growth and contributed to the better device performance.</P> <P>Graphic Abstract</P><P>A compromise of electrical leakage and capacitance density effects was found to be a facile route to obtain high mobility and steep subthreshold slope in low-voltage operated pentacene field-effect transistors <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0jm02401e'> </P>

Ultrasensitive artificial synapse based on conjugated polyelectrolyte

Xu, Wentao,Nguyen, Thanh Luan,Kim, Young-Tae,Wolf, Christoph,Pfattner, Raphael,Lopez, Jeffrey,Chae, Byeong-Gyu,Kim, Sung-Il,Lee, Moo Yeol,Shin, Eul-Yong,Noh, Yong-Young,Oh, Joon Hak,Hwang, Hyunsang,Pa Elsevier 2018 Nano energy Vol.48 No.-

<P><B>Abstract</B></P> <P>Emulating essential synaptic working principles using a single electronic device has been an important research field in recent years. However, achieving sensitivity and energy consumption comparable to biological synapses in these electronic devices is still a difficult challenge. Here, we report the fabrication of conjugated polyelectrolyte (CPE)-based artificial synapse, which emulates important synaptic functions such as paired-pulse facilitation (PPF), spike-timing dependent plasticity (STDP) and spiking rate dependent plasticity (SRDP). The device exhibits superior sensitivity to external stimuli andlow-energy consumption. Ultrahigh sensitivity and low-energy consumption are key requirements for building up brain-inspired artificial systems and efficient electronic-biological interface. The excellent synaptic performance originated from (i) a hybrid working mechanism that ensured the realization of both short-term and long-term plasticity in the same device, and (ii) the mobile-ion rich CPE thin film that mediate migration of abundant ions analogous to a synaptic cleft. Development of this type of artificial synapse is both scientifically and technologically important for construction of ultrasensitive highly-energy efficient and soft neuromorphic electronics.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Conjugated polyelectrolyte (CPE)-based artificial synapse was fabricated. </LI> <LI> Important working principles of a biological synapse are emulated. </LI> <LI> The artificial synapse potentially exhibited ultrahigh sensitivity and low energy consumption. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>An artificial synapse is fabricated to emulate biological functions with high sensitivity and low-energy consumption</P> <P>[DISPLAY OMISSION]</P>

N-doped graphene field-effect transistors with enhanced electron mobility and air-stability.

Xu, Wentao,Lim, Tae-Seok,Seo, Hong-Kyu,Min, Sung-Yong,Cho, Himchan,Park, Min-Ho,Kim, Young-Hoon,Lee, Tae-Woo Wiley-VCH 2014 Small Vol.10 No.10

<P>Although graphene can be easily p-doped by various adsorbates, developing stable n-doped graphene that is very useful for practical device applications is a difficult challenge. We investigated the doping effect of solution-processed (4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine (N-DMBI) on chemical-vapor-deposited (CVD) graphene. Strong n-type doping is confirmed by Raman spectroscopy and the electrical transport characteristics of graphene field-effect transistors. The strong n-type doping effect shifts the Dirac point to around -140 V. Appropriate annealing at a low temperature of 80 oC enables an enhanced electron mobility of 1150 cm(2) V(-1) s(-1). The work function and its uniformity on a large scale (1.2 mm 1.2 mm) of the doped surface are evaluated using ultraviolet photoelectron spectroscopy and Kelvin probe mapping. Stable electrical properties are observed in a device aged in air for more than one month.</P>

Synchronous Periodic Frequency Modulation Based on Interleaving Technique to Reduce PWM Vibration Noise

Wentao Zhang,Yongxiang Xu,Jingwei Ren,Jianyong Su,Jibin Zou 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.6

Ear-piercing high-frequency noise from electromagnetic vibrations in motors has become unacceptable in sensitive environments, due to the application of pulse width modulation (PWM) and in consideration of switching losses. This paper proposed a synchronous periodic frequency modulation (SPFM) method based on the interleaving technique for paralleled three-phase voltage source inverters (VSIs) to eliminate PWM vibration noise. The proposed SPFM technique is able to effectively remove unpleasant high-frequency vibration noise as well as acoustic noise more effectively than the conventional periodic carrier frequency modulation (PCFM) and interleaving technique. It completely eliminates the vibration noise near odd-order carrier frequencies and reduces the PWM vibration noise near even-order carrier frequencies depending on the switching frequency variation range. Furthermore, the SPFM method is simple to implement and does not employ additional circuits in the drive system. Finally, the effectiveness of the proposed method has been confirmed by detailed experimental results.

Transceiver Optimization for the Multi-Antenna Downlink in MIMO Cognitive System

( Wentao Zhu ),( Jingbo Yang ),( Tingting Jia ),( Xu Liu ) 한국인터넷정보학회 2015 KSII Transactions on Internet and Information Syst Vol.9 No.12

Transceiver optimization in multiple input multiple output (MIMO) cognitive systems is studied in this paper. The joint transceiver beamformer design is introduced to minimize the transmit power at secondary base station (SBS) while simultaneously controlling the interference to primary users (PUs) and satisfying the secondary users (SUs) signal-to-interference-plus-noise ratio (SINR) based on the convex optimization method. Due to the limited cooperation between SBS and PUs, the channel state information (CSI) usually cannot be obtained perfectly at the SBS in cognitive system. In this study, both perfect and imperfect CSI scenarios are considered in the beamformer design, and the proposed method is robust to CSI error. Numerical results validate the effectiveness of the proposed algorithm.

Synthesis of Novel Amphiphilic Diblock Copolymers Containing Polyhedral Oligomeric Silsesquioxane (POSS) Using Ring Opening Metathesis Copolymerization

권영환,( Wentao Xu ) 한국공업화학회 2006 한국공업화학회 연구논문 초록집 Vol.2006 No.-

Isolation and characterization of tick-borne Roseomonas haemaphysalidis sp. nov. and rodent-borne Roseomonas marmotae sp. nov.

Zhu Wentao,Zhou Juan,Lu Shan,Yang Jing,Lai Xin-He,Jin Dong,Pu Ji,Huang Yuyuan,Liu Liyun,Li Zhenjun,Xu Jianguo 한국미생물학회 2022 The journal of microbiology Vol.60 No.2

Four novel Gram-negative, mesophilic, aerobic, motile, and cocci-shaped strains were isolated from tick samples (strains 546T and 573) and respiratory tracts of marmots (strains 1318T and 1311). The 16S rRNA gene sequencing revealed that strains 546T and 573 were 97.8% identical to Roseomonas wenyumeiae Z23T, whereas strains 1311 and 1318T were 98.3% identical to Roseomonas ludipueritiae DSM 14915T. In addition, a 98.0% identity was observed between strains 546T and 1318T. Phylogenetic and phylogenomic analyses revealed that strains 546T and 573 clustered with R. wenyumeiae Z23T, whereas strains 1311 and 1318T grouped with R. ludipueritiae DSM 14915T. The average nucleotide identity between our isolates and members of the genus Roseomonas was below 95%. The genomic G+C content of strains 546T and 1318T was 70.9% and 69.3%, respectively. Diphosphatidylglycerol (DPG) and phosphatidylethanolamine (PE) were the major polar lipids, with Q-10 as the predominant respiratory quinone. According to all genotypic, phenotypic, phylogenetic, and phylogenomic analyses, the four strains represent two novel species of the genus Roseomonas, for which the names Roseomonas haemaphysalidis sp. nov. and Roseomonas marmotae sp. nov. are proposed, with 546T (= GDMCC 1.1780T = JCM 34187T) and 1318T (= GDMCC 1.1781T = JCM 34188T) as type strains, respectively.