Free-standing paper-like or foil-like materials are an integral part of our technological society. Their uses include protective layers, chemical filters, components of electrical batteries or supercapacitors, adhesive layers, electronic or optoelectronic components, and molecular storage. Inorganic 'paper-like' materials based on nanoscale components such as exfoliated vermiculite or mica platelets have been intensively studied and commercialized as protective coatings, high-temperature binders, dielectric barriers and gas-impermeable membranes. Carbon-based flexible graphite foils composed of stacked platelets of expanded graphite have long been used in packing and gasketing applications because of their chemical resistivity against most media, superior sealability over a wide temperature range, and impermeability to fluids. The discovery of carbon nanotubes brought about bucky paper, which displays excellent mechanical and electrical properties that make it potentially suitable for fuel cell and structural composite applications. Here we report the preparation and characterization of graphene oxide paper, a free-standing carbon-based membrane material made by flow-directed assembly of individual graphene oxide sheets. This new material outperforms many other paper-like materials in stiffness and strength. Its combination of macroscopic flexibility and stiffness is a result of a unique interlocking-tile arrangement of the nanoscale graphene oxide sheets.

Transparent and electrically conductive composite silica films were fabricated on glass and hydrophilic SiOx/silicon substrates by incorporation of individual graphene oxide sheets into silica sols followed by spin-coating, chemical reduction, and thermal curing. The resulting films were characterized by SEM, AFM, TEM, low-angle X-ray reflectivity, XPS, UV-vis spectroscopy, and electrical conductivity measurements. The electrical conductivity of the films compared favorably to those of composite thin films of carbon nanotubes in silica.

This contribution describes an organosiloxane cross-linking approach to robust, efficient, adherent hole-transport layers (HTLs) for polymer light-emitting diodes (PLEDs). An example is 4,4'-bis[(p-trichlorosilylpropylphenyl)phenylamino]biphenyl (TPDSi(2)), which combines the hole-transporting efficiency of N,N-diphenyl-N,N-bis(3-methylphenyl)-1,1-biphenyl)-4,4-diamine) (TPD, prototypical small-molecule HTL material) and the strong cross-linking/densification tendencies of organosilanol groups. Covalent chemical bonding of TPDSi(2) to PLED anodes (e.g., indium tin oxide, ITO) and its self-cross-linking enable fabrication of three generations of insoluble PLED HTLs: (1) self-assembled monolayers (SAMs) of TPDSi(2) on ITO; (2) cross-linked blend networks consisting of TPDSi(2) + a hole transporting polymer (e.g., poly(9,9-dioctylfluorene-co-N-(4-(3-methylpropyl))diphenylamine), TFB) on ITO; (3) TPDSi(2) + TFB blends on ITO substrates precoated with a conventional PLED HTL, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS). PLED devices fabricated using these new HTLs exhibit comparable or superior performance vs comparable devices based on PEDOT-PSS alone. With these new HTLs, current efficiencies as high as approximately 17 cd/A and luminances as high as approximately 140,000 cd/m(2) have been achieved. Further experiments demonstrate that not only do these HTLs enhance PLED anode hole injection but they also exhibit significantly greater electron-blocking capacity than PEDOT-PSS. The present organosiloxane HTL approach offers many other attractions such as convenience of fabrication, flexibility in choosing HTL components, and reduced HTL-induced luminescence quenching, and can be applied as a general strategy to enhance PLED performance.

Layer-by-layer assembly of two palladium coordination-based multilayers on silicon and glass substrates is presented. The new assemblies consist of rigid-rod chromophores connected by terminal pyridine moieties to palladium centers. Both colloidal palladium and PdCl2(PhCN)2 were used in order to determine the effect of the metal complex precursor on multilayer structure and optical properties. The multilayers were formed by an iterative wet-chemical deposition process at room temperature in air on a siloxane-based template layer. Twelve consecutive deposition steps have been demonstrated resulting in structurally regular assemblies with an equal amount of chromophore and palladium added in each molecular bilayer. The optical intensity characteristics of the metal-organic films are clearly a function of the palladium precursor employed. The colloid-based system has a UV-vis absorption maximum an order of magnitude stronger than that of the PdCl2-based multilayer. The absorption maximum of the PdCl2-based film exhibits a significant red shift of 23 nm with the addition of 12 layers. Remarkably, the structure and physiochemical properties of the submicron scale PdCl2-based structures are determined by the configuration of the approximately 15 angstroms thick template layer. The refractive index of the PdCl2-based film was determined by spectroscopic ellipsometry. Well-defined three-dimensional structures, with a dimension of 5 microm, were obtained using photopatterned template monolayers. The properties and microstructure of the films were studied by UV-vis spectroscopy, spectroscopic ellipsometry, atomic force microscopy (AFM), X-ray reflectivity (XRR), scanning electron microscopy (SEM), and aqueous contact angle measurements (CA).

Accelerated growth of a molecular-based material that is an active participant in its continuing self-propagated assembly has been demonstrated. This nonlinear growth process involves diffusion of palladium into a network consisting of metal-based chromophores linked via palladium.

Hole transporting materials are widely used in multilayer organic and polymer light-emitting diodes (OLEDs, PLEDs, respectively) and are indispensable if device electroluminescent response and durability are to be truly optimized. This contribution analyzes the relative effects of tin-doped indium oxide (ITO) anode-hole transporting layer (HTL) contact versus the intrinsic HTL materials properties on OLED performance. Two siloxane-based HTL materials, N,N'-bis(p-trichlorosilylpropyl)-naphthalen-1-yl)-N,N'-diphenyl-biphenyl-4,4'-diamine (NPB-Si(2)) and 4,4'-bis[(p-trichlorosilylpropylphenyl)phenylamino]biphenyl (TPD-Si(2)), are designed and synthesized. They have the same hole transporting triarylamine cores as conventional HTL materials such as 1,4-bis(1-naphthylphenylamino)biphenyl (NPB) and N,N-diphenyl-N,N-bis(3-methylphenyl)-1,1-biphenyl)-4,4-diamine (TPD), respectively. However, they covalently bind to the ITO anode, forming anode-HTL contacts that are intrinsically different from those of the anode to TPD and NPB. Applied to archetypical tris(8-hydroxyquinolato)aluminum(III) (Alq)-based OLEDs as (1) the sole HTLs or (2) anode-NPB HTL interlayers, NPB-Si(2) and TPD-Si(2) enhance device electroluminescent response significantly versus comparable devices based on NPB alone. In the first case, OLEDs with 36 000 cd/m(2) luminance, 1.6% forward external quantum efficiency (eta(ext)), and 5 V turn-on voltages are achieved, affording a 250% increase in luminance and approximately 50% reduction in turn-on voltage, as compared to NPB-based devices. In the second case, even more dramatic enhancement is observed (64 000 cd/m(2) luminance; 2.3% eta(ext); turn-on voltages as low as 3.5 V). The importance of the anode-HTL material contact is further explored by replacing NPB with saturated hydrocarbon siloxane monolayers that covalently bind to the anode, without sacrificing device performance (30 000 cd/m(2) luminance; 2.0% eta(ext); 4.0 V turn-on voltage). These results suggest new strategies for developing OLED hole transporting structures.

Structural investigation in systems of anionic polyelectrolytes and dodecyl-(DPC) and cetylpyridinium chlorides (CPC) were performed at various surfactant to polyelectrolyte (S/P) ratios using synchrotron X-ray scattering. The polyelectrolytes used were sodium poly(styrenesulfonate) (NaPSS), poly(acrylate) (NaPA), and poly(methacrylate) (NaPMA). From the Bragg peaks emerging in the scattering curves, different types of organization of the surfactant in conjunction with the polyion are proposed. They depend on the surfactant chain length, on the polyelectrolyte chemistry, and on the S/P value: (1) NaPSS/DPC (all S/P values), NaPSS/CPC (S/P < 1), and NaPA(NaPMA)/DPC (S/P < 1) complexes produced a micellelike organization of the surfactant along the polyion chain. The NaPSS-induced micelle is smaller in size than the ordinary one because of the inclusion of the aromatic rings on the PSS chain into the hydrophobic interior of the micelle. The size of the ordered elements in complexes with the hydrophilic NaPA and NaPMA corresponds to the radius of an ordinary globular micelle together with the thickness of the polyelectrolyte chain that surrounds it. (2) In NaPSS/CPC precipitate (S/P g 1), a hexagonal phase is observed with a unit cell parameter equal to 39.5 Å. (3) The multiple reflections in the scattering curves of NaPA(NaPMA)/DPC complexes with S/P g 1 and of NaPA(NaPMA)/CPC ones for all S/P values point to some cubic structure. The cell constants of these mesophases correspond approximately to 2.5 diameters of a globular surfactant micelle. (4) In addition to a cubic phase, a well-pronounced hexagonal phase with a unit cell parameter of 40.5 Å develops in the NaPA/CPC case with S/P g 1.

The integrity of anode/organic interfacial contact is shown to be crucial to the performance and stability of archetypical small molecule organic light-emitting diodes (OLEDs). In this contribution, vapor-deposited lipophilic, hole-transporting 1,4-bis(phenyl-m-tolylamino)biphenyl (TPD) and 1,4-bis(1-naphthylphenylamino)biphenyl (NPB) thin films are shown to undergo decohesion on ITO anode surfaces under mild heating. An effective approach to ameliorate such interfacial decohesion is introduction, via self-assembly or spin-coating, of covalently bound N(p-C6H4CH2CH2CH2SiCl3)3 (TAA)- and 4,4‘-bis[(p-trichlorosilylpropylphenyl)phenylamino]biphenyl (TPD-Si2)-derived adhesion/injection layers at the anode/hole transport layer interface. The resulting angstrom-scale hole transport layers prevent decohesion of vapor-deposited hole transport layers and significantly enhance OLED hole injection fluence. OLEDs fabricated with these modified interfaces exhibit appreciably reduced turn-on voltages, considerably higher luminous intensities, and enhanced thermal robustness versus bare ITO-based control devices. Spin-coated, cross-linked TPD-Si2 films, in particular, prove to be superior to conventional ITO functionalization interlayers, including copper phthalocyanine, in this regard. The present ITO-functionalized devices achieve maximum external forward quantum efficiencies as high as 1.2% and a luminous level of 15 000 cd/m2 in simple ITO/interlayer/HTL/Alq/Al heterostructures. We also show that Cu(Pc) interlayers actually suppress, rather than enhance, hole injection and template crystallization of vapor-deposited TPD and NPB at modest temperatures, resulting in poor OLED thermal stability.