Improved remnant polarization of Zr-doped HfO2 ferroelectric film by CF4/O2 plasma passivation.

In this work, the impact of fluorine (CF4) and oxygen (O2) plasma passivation on HfZrOx (HZO) based ferroelectric capacitor was investigated. By the fluorine passivation, the surface trap density and oxygen vacancies in the HZO-based Metal-ferroelectric-insulator-semiconductor (MFIS) capacitors were suppressed, resulting in the increased pristine remnant polarization (2Pr). The pristine value (2Pr) of baseline samples annealed at 500 °C and 600 °C were 11.4 µC/cm2 and 24.4 µC/cm2, respectively. However, with the F-passivation, the 2Pr values were increased to 30.8 µC/cm2 and 48.2 µC/cm2 for 500 °C and 600 °C, respectively. The amount of surface defects and oxygen vacancies are quantitatively confirmed by the conductance method and XPS analysis. However, due to the incorporation of fluorine atoms into the ferroelectric-insulator films, undesirable degradation on endurance characteristics were observed.

Oligoimide-Mediated Graphene Oxide-Epoxy Nanocomposites with Enhanced Thermal Conductivity and Mechanical Properties.

The current study reports the preparation of thermally conductive polymeric nanocomposites. For this purpose, two epoxy-based nanocomposites were prepared by dispersing a different type of functionalized graphene oxide (GO) nanofiller in each series. Both these GO nanofillers were functionalized by covalently bonding oligoimide chains on their surfaces. In one series, these oligoimide chains were prepared by reaction of 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) with a diamine 4,4'-methylenedianiline (MDA). While in the other case, BTDA was reacted with N,N'-[((propane-2,2-diylbis(4,1-phenylene))bis(oxy))bis(4,1-phenylene)]bis(4-aminobenzamide) (BDM) to mount oligoimide chains on the surface of GO. Both types of oligoimide chains have amino groups as chain-end functional groups. These modified GO nanofillers were added to the epoxy matrices separately to prepare their respective nanocomposites (MDA-B-GO-epoxy nanocomposites and BDM-B-GO-epoxy nanocomposites). The chain-end amino groups of oligoimide chains reacted with the epoxy ring developing a covalent bonding between oligoimide chains of GO and the epoxy matrix. Moreover, these oligoimide chains prevented the agglomeration of GO by acting as spacer groups leading to the uniform dispersion of GO in the epoxy matrix. Various analytical techniques were used to examine the attachment of oligoimide chains to the GO surface, and to examine the morphology, curing potential, mechanical strength, thermal stability, and thermal conductivity of the prepared nanocomposites. We demonstrated that the thermal conductivity of MDA-B-GO-epoxy nanocomposites increased by 52% and an increase of 56% was observed in BDM-B-GO-epoxy nanocomposites. Similarly, a significant improvement was observed in the mechanical strength and thermal stability of both types of nanocomposites.

Impact of Chamber/Annealing Temperature on the Endurance Characteristic of Zr:HfO2 Ferroelectric Capacitor.

The endurance characteristic of Zr-doped HfO2 (HZO)-based metal-ferroelectric-metal (MFM) capacitors fabricated under various deposition/annealing temperatures in the atomic layer deposition (ALD) process was investigated. The chamber temperature in the ALD process was set to 120 °C, 200 °C, or 250 °C, and the annealing temperature was set to 400 °C, 500 °C, 600 °C, or 700 °C. For the given annealing temperature of 700 °C, the remnant polarization (2Pr) was 17.21 µC/cm2, 26.37 µC/cm2, and 31.8 µC/cm2 at the chamber temperatures of 120 °C, 200 °C, and 250 °C, respectively. For the given/identical annealing temperature, the largest remnant polarization (Pr) was achieved when using the chamber temperature of 250 °C. At a higher annealing temperature, the grain size in the HZO layer becomes smaller, and thereby, it enables to boost up Pr. It was observed that the endurance characteristics for the capacitors fabricated under various annealing/chamber temperatures were quite different. The different endurance characteristics are due to the oxygen and oxygen vacancies in ferroelectric films, which affects the wakeup/fatigue behaviors. However, in common, all the capacitors showed no breakdown for an externally applied pulse (up to 108 cycles of the pulse).

Thermomechanical Behavior of Poly(3-hexylthiophene) Thin Films on the Water Surface.

The thermomechanical behavior of a conjugated polymer (CP) in a thin film state has rarely been studied despite the importance of understanding the polymer morphologies and optimizing the thermal processes of organic semiconductors. Moreover, the seamless integration of multilayers without mechanical failures in CP-based electronic devices is crucial for determining their operational stability. Large differences in the coefficients of thermal expansion (CTEs) between the multilayers can cause serious degradation of devices under thermal stress. In this study, we measure the intrinsic thermomechanical properties of poly(3-hexylthiophene) (P3HT) thin films in a pseudo-freestanding state on the water surface. The as-cast P3HT thin films exhibited a large thermal shrinkage (-1001 ppm K-1) during heating on the water surface. Morphological analyses revealed that the thermal shrinkage of the polymer films was caused by the rearrangement of the polymer chain networks accompanied by crystallization, thus indicating that preheating the polymer films is essential for estimating their intrinsic CTE values. Moreover, the rigidity of the substrate significantly influences the thermomechanical behavior of the polymer films. The polymer films that were preheated on the glass substrate showed nonlinear thermal expansion due to the substrate constraint inhibiting sufficient relaxation of the polymer chains. In comparison, a linear expansion behavior is observed after preheating the films on the water surface, exhibiting a consistent CTE value (185 ppm K-1) regardless of the number of thermal strain measurements. Thus, this work provides a direct method for measuring in-plane CTE values and an in-depth understanding of the thermomechanical behaviors of CP thin films to design thermomechanically reliable organic semiconductors.

High-Performance, Flexible NO2 Chemiresistors Achieved by Design of Imine-Incorporated n-Type Conjugated Polymers.

Flexible and mechanically robust gas sensors are the key technologies for wearable and implantable electronics. Herein, the authors demonstrate the high-performance, flexible nitrogen dioxide (NO2 ) chemiresistors using a series of n-type conjugated polymers (CPs: PNDIT2/IM-x) and a polymer dopant (poly(ethyleneimine), PEI). Imine double bonds (C = N) are incorporated into the backbones of the CPs with different imine contents (x) to facilitate strong and selective interactions with NO2 . The PEI provides doping stability, enhanced electrical conductivity, and flexibility. As a result, the NO2 sensors with PNDIT2/IM-0.1 and PEI (1:1 by weight ratio) exhibit outstanding sensing performances, such as excellent sensitivity (ΔR/Rb = 240% @ 1 ppm), ultralow detection limit (0.1 ppm), high selectivity (ΔR/Rb < 8% @ 1 ppm of interfering analytes), and high stability, thereby outperforming other state-of-the-art CP-based chemiresistors. Furthermore, the thin film of PNDIT2/IM-0.1 and PEI blend is stretchable and mechanically robust, providing excellent flexibility to the NO2 sensors. Our study contributes to the rational design of high-performance flexible gas sensors.

The first report on genome sequence of high-level ciprofloxacin-resistant Salmonella enterica serovar Indiana ST17 in Korean livestock.

OBJECTIVES: Salmonella enterica Indiana ST17 strain (K16SI097), exclusively found in China, was first isolated in 2016 in Korea from a chicken carcass. This strain contains multidrug-resistant genes, and is particularly resistant to ciprofloxacin (64 µg/mL). In this study, we aimed to elucidate the genomic relationship and compare antimicrobial resistance factors between Korean chicken-derived and Chinese clones of S. Indiana ST17. METHODS: The genomic DNA of S. enterica Indiana K16SI097 was sequenced via the combined analysis of 20-kb PacBio SMRTbell library and PacBio RS II. Antimicrobial resistance genes were analysed by the Center for Genomic Epidemiology (http://www.genomicepidemiology.org/). Chromosomal and plasmid DNA of the Korean and Chinese strains were compared. RESULTS: The K16SI097 genome comprises two contiguous sequences (contigs) amounting to 4 731 335 base pairs with a 51.85% GC content. In total, 4574 protein-coding regions, 84 tRNA genes, and 22 rRNA genes were detected. Among the annotated contigs, 14 antimicrobial resistance genes were detected; DNA gyrase and topoisomerase IV contained mutations. Moreover, chromosomal DNA of K16SI097 and of the published Chinese strain displayed 99.9% similarity. Furthermore, plasmids displayed similar sizes, sequences, and structures. CONCLUSIONS: This is the first report on the complete genome sequence of the high-level ciprofloxacin-resistant S. enterica Indiana ST17 strain isolated in Korea. This genome sequence will help us understand the ST17 strain lineage and its features such as antimicrobial resistance.

Selective engineering of oxygen-containing functional groups using the alkyl ligand oleylamine for revealing the luminescence mechanism of graphene oxide quantum dots.

Oxygen-containing functional groups such as epoxy, hydroxyl, carboxylic, and carboxyl groups have a great influence on the luminescence properties of graphene oxide quantum dots (GOQDs). Understanding their roles is essential for the design and optimization of GOQD performance. Herein, we investigate the effect of epoxide functional groups in GOQDs on the luminescence mechanism through passivation of the epoxide functional groups using the alkyl ligand oleylamine. Luminescence in the as-synthesized GOQDs has two separate origins: intrinsic states derived from localized sp2 carbon subdomains and extrinsic states formed by oxygen-functional groups. When the oleylamine ligand is conjugated on the GOQDs, intrinsic PL emission from the localized sp2 carbon subdomains decreases. This is discussed in detail, based on optical characterization and first-principles density functional theory calculations, which reveal that the role of the epoxide functional groups is to form localized sp2 carbon subdomains emitting intrinsic PL. To the best of our knowledge, this is the first investigation of the role of epoxide functional groups on the luminescence mechanism in GOQDs.