Homogeneous Amorphous Films Research Articles

Enhanced diffusion in thin-film Cu-Zr nanoglasses

Tracer measurements with both radioactive, 55Fe, as well as natural, mainly 56Fe, isotopes are used to investigate Fe diffusion in a Cu-Zr nanoglass in comparison to their diffusion rates in a homogeneous amorphous counterpart. The columnar-structured nanoglass and the homogeneous amorphous films are synthesized using radio-frequency magnetron sputtering. Ion beam sputtering (with the 55Fe radioisotope) and time-of-flight secondary ion mass spectroscopy (with natural Fe) are used for the diffusion experiments. Remarkably, faster Fe diffusion is observed in the columnar nanoglasses, supporting the concept of glass–glass interfaces. The relative diffusion enhancement is explained within the excess free volume concept that is supported by structural investigations using transmission electron microscopy. For the first time, the relaxation dynamics in a nanoglass as well as in a homogeneous thin-film glass of identical composition are evaluated via time-dependent diffusion measurements.

Achieving non-doped deep-blue OLEDs by applying bipolar imidazole derivatives

Abstract In this work, we designed and synthesized two novel bipolar deep-blue emitting materials, 2-(4'-(9H-carbazol-9-yl)-[1,1′-biphenyl]-4-yl)-1 (4(tri-fluoromethyl) phenyl)-1H-phenanthro[9,10-d] imidazole (CzB-FMPPI) and 9-(4'-(4,5-diphenyl-1 (4-(trifluoromethyl) phenyl)-1H-imidazole-2-yl)-[1,1′-biphenyl]-4-yl)-9H-carbazole (CzB-FMPIM). Among them, carbazole and phenanthroimidazole are bridged linkage by the biphenyl ring and act as electron-donating part. The CF3-substituted phenyl ring applies as strong electron-withdrawing moiety. The exhibit highly twisted molecular configuration of two compounds efficiently shorten π-conjugation and inhibit intermolecular interaction, resulting in superior thermal stability and deep blue emission. High decomposition temperature of 431 °C and 414 °C, glass transition temperature of 150 °C and 135 °C for CzB-FMPPI and CzB-FMPIM, respectively, had been achieved. As a consequence of breaking the conjugation of phenanthroimidazole chromophore, CzB-FMPIM achieves an 8 nm blue-shifted emission compared with CzB-FMPPI. CzB-FMPPI exhibits a higher relative fluorescence quantum yield of 92.5% than 83.3% of CzB-FMPIM. Moreover, bipolar property was observed in both compound and homogeneous amorphous films were deposited and applied in the non-doped deep-blue OLEDs. The devices based on two emitters showed maximum luminance of 6667 cd/m2 and 3084 cd/m2, maximum EQE of 4.10% and 3.17%, respectively. Commission International de l'Eclairage (CIE) coordinates of CzB-FMPIM based device achieved (0.15, 0.07) which is extremely close to the NTSC standard blue CIE (0.14, 0.08).

Characterization of Ge15Sb85 phase change material grown by pulsed laser deposition

The phase change material eutectic binary compound Ge15Sb85 thin films were prepared, for the first time, by pulsed laser deposition technique. Various parameters were changed to obtain amorphous thin films in very good quality. X-ray diffraction, scanning electron microscope and electrical measurements were used to test the quality of the deposited films. The parameters that were changed are: chamber atmosphere (from vacuum to 4 × 10−4 mbar argon gas pressure), target–substrate distance (from 6 to 8 cm), deposition frequency (from 5 to 20 Hz) and laser energy (from 130 to 210 mJ). Our results showed that the influence of the plume on the temperature of the substrate is very critical. Less is the temperature of the substrate better is the quality of the film and more amorphous it is. The increase in the substrate temperature increases the chance of forming small crystallites within the deposited film as was shown in most of the samples. Best results were obtained using the following deposition conditions: laser energy of 130 mJ, frequency of 10 Hz, distance of 6 cm and vacuum chamber (no argon gas was present). Under these conditions, completely homogeneous amorphous films with very close stoichiometry to the source target (Ge∼16Sb∼84), a phase transition temperature of around 215 °C and an energy band gap of 0.6 eV were obtained.

Remarkably high miscibility of octa-substituted POSS with commodity conjugated polymers and molecular fillers for the improvement of homogeneities of polymer matrices

This manuscript describes the extremely high affinities of polyhedral oligomeric silsesquioxane (POSS) with conjugated polymers. Polymer films of polyfluorene (PF) and poly(3-hexylthiophene) (P3HT) containing a series of octa-substituted POSS at variable concentrations were prepared. The relationships between the thermal and optical properties of commodity-conjugated polymers and the chemical structures of the substituents in POSS were evaluated by a series of experiments. It was shown that the POSS fillers with relatively longer alkyl substituents can enhance the thermal stabilities of the polymer matrices, even though most of the POSS fillers reduced the decomposition temperatures. The UV−Vis absorption measurements showed that the narrower absorption bands were obtained from the POSS-containing film with PF. It was suggested that the aggregation of the polymer chains could be suppressed by the POSS filler, leading to highly homogeneous states in the films. Moreover, for the P3HT films, the extension of the main-chain conjugation was induced by the POSS fillers with shorter alkyl substituents via the suppression of intermolecular interactions among the polymer chains. These data mean that the POSS fillers can have a significant role in the improvement of the homogeneity in the polymer films due to their high affinity to the conjugated systems. Cubic silsesquioxanes (POSS) with various alkyl substituents were loaded onto commodity-conjugated polymers such as polyfluorene and poly(3-hexylthiophene-2,5-diyl) to investigate structure-property relationships between the substituents of POSS fillers and properties of the polymer films. It was found that the series of POSS fillers can be introduced into conjugated polymer films with high concentrations. Owing to high miscibility, it was demonstrated that POSS can work as a superior molecular filler for realizing homogeneous amorphous films with high thermal stability based on conjugated polymers.

OPTIMUM COMPROMISE BETWEEN OPTICAL ABSORPTION AND ELECTRICAL PROPERTY OF THE PLANAR MULTI-HETEROJUNCTION ORGANIC SOLAR CELLS BASED WITH NEW THIAZOL DERIVATIVE, THE (2-THIOXO-3-N-(2-METHOXYPHENYL) THIAZOLIDIN-4-ONE), AS ELECTRON DONOR

The synthesis of a new thiazol derivative, the (2-thioxo-3-N-(2-methoxyphenyl) thiazolidin-4-one) (called TH-2) is described. After characterization of the TH-2, the cyclic voltammetry study coupled with optical absorbance measurements show that its LUMO and HOMO are −3.5 and −5.5 respectively. Then the TH-2 is used as electron donor (ED) in organic solar cells (OSCs). The anode buffer layer being CuI the devices are based on the planar heterojunction TH-2/fullerene. Homogeneous amorphous films of TH-2 are obtained when it is deposited onto CuI. For an optimum TH-2 thickness of 20 nm, a power conversion efficiency of 0.42% is obtained. Then, in order to broaden the absorption range of the OSCs, it is coupled with the tetraphenyl-dibenzoperiflanthene, whose band structure matches the band structure of TH-2. Such new multilayer structure allows achieving a power conversion efficiency of 0.49%.

Preparation and properties of thin amorphous tantalum films formed by small e-beam evaporators

Large area (A = 6 cm2), thin tantalum films (5 nm < d < 100 nm) are accomplished by evaporation from tantalum rods using small pocket e-beam evaporators. Using a sample to source distance of ≈20 cm, homogeneous amorphous films with a small surface roughness (<1 nm) can be prepared on glass. Films are characterized by scanning electron microscope images, atomic force microscopy, electrochemical oxidation and resistivity measurements as a function of film thickness. The samples show high resistivities of 200–2000 µΩ cm. The temperature coefficient of the resistivity (TCR) is negative, as characteristic for highly disordered metals. A theoretical description of the thickness distribution (evaporation from plane and hemispherical sources on plane targets) is given in the appendix.

Radiative transitions of Eu 3+ in non-crystalline alkali–alkaline–titanate film

Non-crystalline Eu 3+-doped alkali–alkaline–titanate films have been fabricated by sol–gel route under low-temperature heating, and bright red emissions have been observed under UV radiation. Refractive index and thickness of the films calculated from the transmittance spectrum are 1.481 and 377 nm, respectively. Based on Judd–Ofelt theory, the optical intensity parameters Ω 2 and Ω 4 derived from the emission spectrum were 6.92×10 −20 and 1.84×10 −20 cm 2, respectively. The calculated radiative lifetime of 5D 0 level (3.67 ms) was estimated to be much longer than those in phosphate and fluorophosphates glasses, which is beneficial for achieving visible laser radiations. The homogeneous amorphous films with intense red emissions are promising candidates to develop illuminant, display, light conversion and optical waveguide devices.

Efficient Solution-Processed Blue Electrophosphorescent Devices Based on a Novel Small-Molecule Host

Efficient blue small molecular phosphorescent light-emitting diodes with a blue phosphorescent dye bis(3,5- difluoro-2-(2-pyridyl)-phenyl-(2-carboxypride) iridium (III) (FIrpic) doped into a novel small-molecule host 9,9- bis[4-(3,6-di-tert-butylcarbazol-9-yl)phenyl] fluorene (TBCPF) as the light-emitting layer have been fabricated by spin-coating. The host TBCPF can form homogeneous amorphous films by spin-coating and has triplet energy higher than that of the blue phosphorescent dye FIrpic. All the devices with different FIrpic concentration in the emitting layer give emission from FIrpic indicating complete energy transfer from TBCPF to FIrpic. The device shows the best performance with a peak brightness of 8050 cd/m2 at 10.2 V and the maximum current efficiency up to 3.52 cd/A, when the FIrpic doped concentration is as high as 16%.

Morphological transformations of vanadium oxide films during low-temperature reduction in hydrogen electron cyclotron resonance plasma

Morphological transformations of amorphous vanadium oxide films obtained by the sol-gel method and polycrystalline V2O5 films are studied during their low-temperature (295–623 K) reduction in a hydrogen electron cyclotron resonance plasma. The morphology of films is analyzed using atomic force microscopy and high-resolution electron microscopy. It is found that a homogeneous amorphous film during the reduction process transforms to an island film and then bulk amorphous islands of a regular shape appear. These islands resemble microcrystals, and their concentration depends on the temperature and the reduction time. The low-temperature reduction of polycrystalline V2O5 films leads to their amorphization; however, the microcrystals in the polycrystalline film do not change their shape in this process. A mechanism of the reduction process is proposed. This mechanism explains the regularities of morphological transformations in amorphous sol-gel films of vanadium oxides based on the suggestion of a competition between the ion-stimulated nucleation and growth of nuclei of the crystalline phase and the amorphization of the growing nuclei.

Preparation and characterization of germanium oxysulfide glassy films for optics

Homogeneous amorphous films in the GeS 2–GeO 2 system have been deposited by a rf sputtering technique. Optical characterizations have shown that the cut-off wavelength and the linear indices increase with an increase in the S/O ratio. Raman spectroscopy indicates the presence of new modes that can be assigned to intermediate germanium oxysulfide structural units. Photo-sensitivity of the oxysulfide films has been demonstrated for irradiation near the band-gap. Diffraction gratings inscribed using 488 nm exposure displayed a limited diffraction efficiency (≤3%) that weakens with a corresponding decrease in the glass S/O ratio.

Dendrimer Complexes Based on Fine-Controlled Metal Assembling

Abstract A series of novel dendrimers composed of dendritic phenylazomethines (DPAs) were synthesized with several types of functional cores. The metal assembling to the DPAs is stepwise by the layers, therefore, they can be used as a scaffold for the precise hybridization between metal ions and organic macromolecules. Because of uniform structure of the dendrimer, there is no structural dispersion in the macromolecule–metal hybrid of the DPAs. Also, the number of metal ions loaded in one dendrimer should have no statistical distribution in principle due to the precise metal assembling. A rigid π-conjugating backbone structure contributes not only to the stepwise metal assembly, but also to the solid-state stability under high temperature. Development of this property without any reduction in solubility in organic media enabled the easy preparation of homogeneous amorphous films in which the metal and macromolecule are precisely hybridized. As a result, the thin solid of the metal-assembling dendrimer acts as an excellent organic semiconductor in the hole-transport layer of a light-emitting diode. Metal-assembling DPAs also enhance the electron-transfer reaction as a protein-like catalyst. The DPA having a cobalt porphyrin core-could catalyze the CO2 reduction at an applied overpotential 1.1 V lower than that needed for the catalysis by a model compound of the porphyrin core (CoTPP). Reversible encapsulation/release of multiple irons is also demonstrated as a mimic of the iron storage protein (Ferritin). The switching between these two coordinating states can be completely controlled by the redox states of the iron (FeII/FeIII). The finding of these unique dendritic ligands will afford new insight into molecular design for finely controlled macromolecule–metal hybrid materials.

TEM structural characterization of Sn–Te–O thin films on monocrystalline silicon wafers

The structural properties of Sn–Te–O thin films, deposited by co-evaporation of Sn and TeO 2 on monocrystalline Si substrates at room temperature are investigated by transmission electron microscopy analysis. Instead of homogeneous amorphous films, the obtained films are inhomogeneous multilayered structures, with clearly expressed polycrystalline and monocrystalline regions. Some exotic crystalline forms of Sn, Te and SnTe are detected in the layers. The composition and microstructure of the investigated films depend mainly on the Sn/Te ratio, the thickness of the layers and the substrate surface.

Unexpected nanoscale phase separation in sputterdeposited Ni-25 at.%Al thin films

Thin films of nominal composition Ni-25at.%Al, sputter deposited from a target of the intermetallic compound Ni 3 Al on unheated substrates, exhibit an unexpected phase separation, in contrast with other intermetallic-forming systems such as Ti-Al which are deposited as compositionally homogeneous amorphous films under similar conditions. Precipitates of a novel tetragonal phase, a few nanometres in size, were formed in the matrix consisting of a fcc Ni-rich Ni(Al) phase and a hcp Ni-rich Ni(Al) phase. Ni-Al films of the same composition deposited on heated substrates exhibited the formation of a single, chemically long-range-ordered Ni 3 Al phase with the L1 2 structure, the thermodynamically stable phase for this composition.

Raman characterization of amorphous carbon films

Amorphous carbon films, deposited with the LASER-ARC technique, have been characterized using Raman scattering experiments at an excitation wavelength of 633 nm provided by a He-Ne laser. To distinguish between the homogeneous amorphous film and incorporated particles area resolved measurements have been carried out due to the laser spot diameter of 1 μm. Typical diamondlike (DLC) films, grown near room temperature, show a broad Raman band between 1000 cm−1 and 1800 cm−1 fitted very well by two gaussian distributions. Films deposited at higher substrate temperatures reveal more graphitic features in the spectra. The spectra of particles consists of a graphite-like portion originated from the graphitic structure of the particle and a diamond-like portion caused by the covering DLC film. The degree of disorder and diamond-likeness in the film structure is quantified by the peak position, the full width at half maximum (FWHM) and intensity relation of the fitted “D”- and “G”-peaks.

Effect of surfactant on casting metalorganic films and writing copper metal patterns

A highly effective wetting agent and emulsifier, Triton X-100 detergent is introduced to metalorganic solutions. When applied to a substrate, this detergent/metalorganic solution promotes the formation of a uniform spin-on thin film with good adhesion. The precursor, copper formate film, was spin-deposited with a metalorganic solution prepared by a solvent mixture of methanol and Triton X-100 (50:1 by volume). KrF laser (248 nm) direct writing of high-purity copper patterns on glass and polyimide substrates has been achieved. When the laser beam is imaged through a slit device, periodic copper metal structures with a linewidth of ∼2.5 μm are observed, which may be attributed to result from Fraunhofer diffraction. A general process for casting homogeneous amorphous films on substrates from a solution of molecular or ionic metalorganics dissolved in the neutral or charged micelles is proposed.

Temperature effects on the formation of the Sb/InP(110) interface

The adsorption of Sb on UHV cleaved InP(110) surfaces was studied for substrate temperatures of 300 K (RT) and 100 K (LT) using high resolution soft X-ray photoemission spectroscopy. The In 4d, Sb4d core levels, and the valence band emission were monitored from submonolayer coverages of Sb up to around 20 monolayers. At LT Sb is found to form a homogeneous amorphous film rather than islands on an ordered first monolayer as observed at RT. Furthermore, Fermi level shifts were derived from energy shifts in the In 4d emission lines. Complementing the different overlayer growth modes the Fermi level shift gradually increases with Sb coverage at LT, whereas at RT a Sb coverage of 0.5 ML leads to a maximum shift which is diminished with the completion of the first ordered monolayer.