Archimedean Tilings and Hierarchical Lamellar Morphology Formed by Semicrystalline Miktoarm Star Terpolymer Thin Films.

3-Miktoarm star terpolymer architecture provides a window of opportunity in the design of complex "three-colored" patterns at the nanometer scale. Here, the directed self-assembly (DSA) of 3-miktoarm star terpolymer (poly(1,1-dimethyl silacyclobutane)-arm-polystyrene-arm-poly(d,l-lactide acid)) (PDMSB-arm-PS-arm-PLA, noted hereafter 3 µ-DSL) into a hierarchical lamellar morphology is described. Excellent orientational order has been achieved by templating the asymmetric hierarchical lamellar morphology with topographical substrates. Increasing the PLA volume fraction leads to the formation of a hexagonal [6.6.6] Archimedean tiling which coexists with a metastable square symmetry [4.8.8] tiling stabilized by the step between terraces. Stability of the [6.6.6] tiling over the [4.8.8] one is also demonstrated with GISAXS measurements.

Laterally Ordered Sub-10 nm Features Obtained From Directed Self-Assembly of Si-Containing Block Copolymer Thin Films.

Laterally ordered sub-10 nm features are produced from the directed self-assembly of poly(1,1-dimethyl silacyclo-butane)-block-poly(methyl methacrylate) (PDMSB-b-PMMA) thin films on sinusoidal azobenzene-containing patterns. The use of sinusoidal surface relief grating enables the formation of very large grain areas (over several µm(2) ) consisting of out-of-plane PMMA cylinders.

Clues to the electrical switching mechanism of carbazole-containing polyimide thin films.

The mechanism behind electrical memory behavior of carbazole-containing polyimides (PIs) in nanoscale thin films was investigated. For this investigation, a series of poly(3,3'-dihydroxy-4,4'-biphenylene-co-3,3'-bis(N-ethylenyloxycarbazole)-4,4'-biphenylene hexafluoro-isopropylidenedi-phthalimide)s (6F-HAB-HABCZn PIs) with various compositions was synthesized as a model carbazole-containing polymer system. The thermal properties, band gaps, and molecular orbital levels of the PIs were determined. Furthermore, the chemical compositions, as well as the nanoscale thin film morphologies and electron densities, were analyzed, providing detailed information on the population and positional distribution of carbazole moieties in thin films of the PIs. PI Devices were fabricated with aluminum electrodes and tested electrically. The PI thin film layers in the devices exhibited electrically permanent memory behavior, which was driven by trap-limited space-charge limited conduction and ohmic conduction. The permanent memory characteristics were found to be attributed to the incorporated carbazole moieties rather than from the other chemical components. Furthermore, the memory characteristics depended significantly on the population and positional distribution of carbazole moieties in the PI layer, as well as the film thickness. Considering that the backbone is not conjugated, the present results collectively indicate that the electrical switching behavior of the PI films is driven by the carbazole moieties acting as charge traps and a hopping process using the carbazole charge-trap sites as stepping-stones.

Programmable bipolar and unipolar nonvolatile memory devices based on poly(2-(N-carbazolyl)ethyl methacrylate) end-capped with fullerene.

A novel polymer, poly(2-(N -carbazolyl)ethyl methacrylate) end-capped with fullerene (PCzMA-C(60) ), has been synthesized via living anionic polymerization. Electrically programmable flash memory devices were easily fabricated with this polymer by using solution coating and metal deposition. This polymer was found in these devices to exhibit bipolar and unipolar switching behaviors with a high ON/OFF current ratio, a long retention time, high reliability, and low power consumption. The excellent properties and easy processability of this polymer open up the possibility of the mass production of high performance nonvolatile memory devices at low cost.

Molecular layer-by-layer self-assembly and mercury sensing characteristics of novel brush polymers bearing thymine moieties.

Two new brush polyoxyethylenes bearing thymine moieties at the bristle ends have been synthesized as model polymers in which the chemical loading of the thymine functional group into the polymer is maximized: poly(oxy(11-thyminoacetyloxyundecylthiomethyl)ethylene) (PECH(S)-T) and poly(oxy(11-thyminoacetyloxyundecylsulfonylmethyl)ethylene) (PECH(SO(2))-T). These brush polymers are thermally stable up to around 225 °C, and their glass transitions occur in the range 23-27 °C, but they have significantly different properties despite the similarity of their chemical structures. In particular, PECH(SO(2))-T films exhibit better performance in sensing mercury ions than PECH(S)-T films. These differences were found to originate in the differences between their morphological structures. The PECH(SO(2))-T film has a multi-bilayer structure without interdigitation, in which the layers stack along the out-of-plane of the film and provide a thymine-rich surface. In contrast, the PECH(S)-T film is amorphous with a relatively low population of thymine moieties at the surface. This study demonstrated that a thymine-rich surface is required for recyclable thymine-based polymers to provide highly improved sensitivity and selectivity as well as full reversibility in the sensing of mercury ions. A thymine-rich surface can be achieved with a brush polymer bearing thymine moieties that can self-assemble into a multi-bilayer structure. Because of the thymine-rich surface, the PECH(SO(2))-T thin films even in only 6 nm thickness demonstrate the detection of mercury ions in aqueous solutions with a detection limit of 10(-6) M.

Well-defined DNA-mimic brush polymers bearing adenine moieties: synthesis, layer-by-layer self-assembly, and biocompatibility.

Two new DNA-mimicking brush polymers were synthesized: poly[oxy(11-(3-(9-adeninyl)propionato)-undecanyl-1-thiomethyl)ethylene] (PECH-AP) and poly[oxy(11-(5-(9-adenylethyloxy)-4-oxopentanoato)undecanyl-1-thiomethyl)ethylene] (PECH-AS). These polymers were found to be thermally stable up to 220 °C and could be applied easily by conventional coating processes to produce good quality films. Interestingly, both brush polymers formed molecular multibilayer structures to provide an adenine-rich surface. Despite the structural similarities, PECH-AS surprisingly exhibited higher hydrophilicity and better water sorption properties than PECH-AP. These differences were attributed to the chemical structures in the bristles of the polymers. The adenine-rich surfaces of the polymer films demonstrated selective protein adsorption, suppressed bacterial adherence, facilitated HEp-2 cell adhesion, and exhibited good biocompatibility in mice. However, the high hydrophilicity and good water sorption characteristics of the PECH-AS film suggest that this brush polymer is better suited to applications requiring good biocompatibility and reduced chance of bacterial infection compared with the PECH-AP film.

High temperature polyimide containing anthracene moiety and its structure, interface, and nonvolatile memory behavior.

A high temperature polyimide bearing anthracene moieties, poly(3,3'-di(9-anthracenemethoxy)-4,4'-biphenylene hexafluoroisopropylidenediphthalimide) (6F-HAB-AM PI) was synthesized. The polymer exhibits excellent thermal stability up to around 410 °C. This polymer is amorphous but orients preferentially in the plane of nanoscale thin films. In device fabrications of its nanoscale thin films with metal top and bottom electrodes, no diffusion of the metal atoms or ions between the polymer and electrodes was found; however, the aluminum bottom electrode had somewhat undergone oxide layer (about 1.2 nm thick) formation at the surface during the post polymer layer formation process, which was confirmed to have no significant influence on the device performance. The polymer thin film exhibited excellent unipolar and bipolar switching behaviors over a very small voltage range, less than ±2 V. Further, the PI films show repeatable writing, reading, and erasing ability with long reliability and high ON/OFF current ratio (up to 10(7)) in air ambient conditions as well as even at temperatures up to 200 °C.

Electrical memory characteristics of a nondoped pi-conjugated polymer bearing carbazole moieties.

Poly[bis(9H-carbazole-9-ethyl)dipropargylmalonate] (PCzDPM) is a novel pi-conjugated polymer bearing carbazole moieties that has been synthesized by polymerization of bis(9H-carbazole-9-ethyl)dipropargylmalonate with the aid of molybdenum chloride solution as the catalyst. This polymer is thermally stable up to 255 degrees C under a nitrogen atmosphere and 230 degrees C in air ambient; its glass-transition temperature is 147 or 128 degrees C, depending on the polymer chain conformation (helical or planar structure). The charge-transport characteristics of PCzDPM in nanometer-scaled thin films were studied as a function of temperature and film thickness. PCzDPM films with a thickness of 15-30 nm were found to exhibit very stable dynamic random access memory (DRAM) characteristics without polarity. Furthermore, the polymer films retain DRAM characteristics up to 180 degrees C. The ON-state current is dominated by Ohmic conduction, and the OFF-state current appears to undergo a transition from Ohmic to space-charge-limited conduction with a shallow-trap distribution. The ON/OFF switching of the devices is mainly governed by filament formation. The filament formation mechanism for the switching process is supported by the metallic properties of the PCzDPM film, which result in the temperature dependence of the ON-state current. In addition, the structure of this pi-conjugated polymer was found to vary with its thermal history; this change in structure can affect filament formation in the polymer film.

Programmable permanent data storage characteristics of nanoscale thin films of a thermally stable aromatic polyimide.

We have synthesized a new thermally and dimensionally stable polyimide, poly(4,4'-amino(4-hydroxyphenyl)diphenylene hexafluoroisopropylidenediphthalimide) (6F-HTPA PI). 6F-HTPA PI is soluble in organic solvents and is thus easily processed with conventional solution coating techniques to produce good quality nanoscale thin films. Devices fabricated with nanoscale thin PI films with thicknesses less than 77 nm exhibit excellent unipolar write-once-read-many-times (WORM) memory behavior with a high ON/OFF current ratio of up to 10(6), a long retention time and low power consumption, less than +/-3.0 V. Furthermore, these WORM characteristics were found to persist even at high temperatures up to 150 degrees C. The WORM memory behavior was found to be governed by trap-limited space-charge limited conduction and local filament formation. The conduction processes are dominated by hole injection. Thus the hydroxytriphenylamine moieties of the PI polymer might play a key role as hole trapping sites in the observed WORM memory behavior. The properties of 6F-HTPA PI make it a promising material for high-density and very stable programmable permanent data storage devices with low power consumption.

Nonvolatile unipolar and bipolar bistable memory characteristics of a high temperature polyimide bearing diphenylaminobenzylidenylimine moieties.

This study reports the synthesis and properties (in particular, the electrical switching characteristics) of a new high-performance polyimide (PI), poly(3,3'-di(4-(diphenylamino)benzylidenyliminoethoxy)-4,4'-biphenylene hexafluoroisopropylidenediphthalimide) (6F-HAB-TPAIE PI). This PI polymer bears diphenylaminobenzylidenylimine moieties as side groups and is dimensionally stable up to 280 degrees C and thermally stable up to 440 degrees C. In devices fabricated with the PI polymer as an active memory layer, the active PI polymer was found to operate at less than +/-2 V in electrically bistable unipolar and bipolar switching modes by controlling the compliance current. The PI polymer layer exhibits repeatable writing-reading-erasing capability with high reliability in ambient air conditions as well as at high temperatures up to 130 degrees C. This PI polymer also exhibits a high ON/OFF current ratio up to 10(9). The observed nonvolatile memory behaviors are due to Schottky emission and local filament formation. This study has demonstrated that this thermally, dimensionally stable PI polymer is a promising material for mass production at low cost for high-performance, programmable, nonvolatile memory devices that can be operated with low power consumption in unipolar and bipolar switching modes.

Programmable digital memory devices based on nanoscale thin films of a thermally dimensionally stable polyimide.

We have fabricated electrically programmable memory devices with thermally and dimensionally stable poly(N-(N',N'-diphenyl-N'-1,4-phenyl)-N,N-4,4'-diphenylene hexafluoroisopropylidene-diphthalimide) (6F-2TPA PI) films and investigated their switching characteristics and reliability. 6F-2TPA PI films were found to reveal a conductivity of 1.0 x 10(-13)-1.0 x 10(-14) S cm(-1). The 6F-2TPA PI films exhibit versatile memory characteristics that depend on the film thickness. All the PI films are initially present in the OFF state. The PI films with a thickness of >15 to <100 nm exhibit excellent write-once-read-many-times (WORM) (i.e. fuse-type) memory characteristics with and without polarity depending on the thickness. The WORM memory devices are electrically stable, even in air ambient, for a very long time. The devices' ON/OFF current ratio is high, up to 10(10). Therefore, these WORM memory devices can provide an efficient, low-cost means of permanent data storage. On the other hand, the 100 nm thick PI films exhibit excellent dynamic random access memory (DRAM) characteristics with polarity. The ON/OFF current ratio of the DRAM devices is as high as 10(11). The observed electrical switching behaviors were found to be governed by trap-limited space-charge-limited conduction and local filament formation and further dependent on the differences between the highest occupied molecular orbital and the lowest unoccupied molecular orbital energy levels of the PI film and the work functions of the top and bottom electrodes as well as the PI film thickness. In summary, the excellent memory properties of 6F-2TPA PI make it a promising candidate material for the low-cost mass production of high density and very stable digital nonvolatile WORM and volatile DRAM memory devices.