Nm For Films Research Articles

Effect of Annealing Temperature on the Optical Spectra of CdS Thin Films Deposited at Low Solution Concentrations by Chemical Bath Deposition (CBD) Technique

Two different concentrations of CdCl2 and (NH2)2CS were used to prepare CdS thin films, to be deposited on glass substrate by chemical bath deposition (CBD) technique. CdCl2 (0.000312 M and 0.000625 M) was employed as a source of Cd2+ while (NH2)2CS (0.00125 M and 0.000625 M) for S2− at a constant bath temperature of 70 °C. Adhesion of the deposited films was found to be very good for all the solution concentrations of both reagents. The films were air-annealed at a temperature between 200 °C to 360 °C for one hour. The minimum thickness was observed to be 33.6 nm for film annealed at 320 °C. XRD analyses reveal that the films were cubic along with peaks of hexagonal phase for all film samples. The crystallite size of the films decreased from 41.4 nm to 7.4 nm with the increase of annealing temperature for the CdCl2 (0.000312 M). Optical energy band gap (Eg), Urbach energy (Eu) and absorption coefficient (α) have been calculated from the transmission spectral data. These parameters have been discussed as a function of annealing temperature and solution concentration. The best transmission (about 97%) was obtained for the air-annealed films at higher temperature at CdCl2 (0.000312 M).

Two novel propylenedioxythiophene-based copolymers with donor–acceptor structures for organic solar cell materials

Two novel conjugated copolymers consisting of alternating electron-rich propylenedioxythiophene and electron-deficient 2,3-diphenyltheno[3,4-b]pyrazine or 6,7-diphenyl[1,2,5]thiadiazole units have been synthesized through palladium catalyzed Sonogashira triple-bond coupling reaction. The structures and properties of the two copolymers, P 1 , P 2 , were characterized by FT-IR, NMR, UV–Vis absorbance (Abs), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), and cyclic voltammetry (CV). UV–Vis absorption spectra of the polymers show two absorption bands both in CHCl3 solution and films. The absorption peak maxima of P 1 , P 2 are 600 nm, 766 nm in solution and 627 nm, 823 nm in films, respectively. Thermal gravimetric analysis demonstrates that the two polymers are stable below 300 °C. Cyclic voltammetry studies reveal that the band gaps of P 1 , P 2 are 1.62 eV and 1.50 eV, suggesting their potential for applications as organic solar cell materials.

High-mobility low-bandgap conjugated copolymers based on indacenodithiophene and thiadiazolo[3,4-c]pyridine units for thin film transistor and photovoltaic applications

Two new semiconducting polymers based on indacenodithiophene and thiadiazolo[3,4-c]pyridine units were synthesized viaStille coupling polymerization. The polymers, PIDTPyT and PIDTDTPyT, exhibited main absorption bands in the range of 550–800 nm while their absorption maxima were located at around 700 nm in films. With two additional thiophene spacers, PIDTDTPyT showed a broader absorption band but a 20 nm blue-shifted maximum peak compared to that of PIDTPyT. Both of the polymers possess low bandgaps (∼1.6 eV) and deep energy levels for both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). Organic field-effect transistors (OFETs) device measurements indicate that PIDTPyT and PIDTDTPyT have high hole carrier mobilities of 0.066 and 0.045 cm2 V−1s−1, respectively, with the on/off ratio on the order of 106. Bulk heterojunction photovoltaic devices consisting of the copolymers and PC71BM gave power conversion efficiencies (PCE) as high as 3.91% with broadband photo-response in the range of 300–800 nm. The relationships between the photovoltaic performance and film morphology, energy levels, hole mobilities are discussed.

Synthesis and characterization of solution-processable highly branched iridium (III) complex cored dendrimer based on tetraphenylsilane dendron for host-free green phosphorescent organic light emitting diodes

Solution processable highly branched iridium(III) complex fac-tris(2-phenylpyridyl)iridium-cored dendrimer based on tetraphenylsilane dendron and 2-ethylhexyloxy surface groups was prepared. The structure of dendrimer was confirmed by nuclear magnetic resonance, mass and infrared studies. Thermogravimetric analysis and differential scanning calorimetry studies show the thermal stability (∆T 5%) of 625 K with high glass transition temperature of 423 K. Photoluminescence studies of dendrimer showed the core emission at 516 nm in solution and at 521 nm in film, indicating the highly branched non-conjugated tetrahedral tetraphenylsilane dendrons around the core highly inhibit the intermolecular interactions between the cores in the film. The solution processed green emitting phosphorescent organic light emitting diodes based on dendrimer were fabricated and characterized. The device using host free dendrimer as emitter showed the external quantum efficiency of 0.4%. The results show the potential of this new type of dendritic emitting structure in highly efficient solution processed host-free green phosphorescent organic light emitting diodes.

Properties of fluorinated silica glass deposited at low temperature by atmospheric plasma-enhanced chemical vapor deposition

The atmospheric pressure plasma-enhanced chemical vapor deposition of fluorinated silica glass was demonstrated at a temperature of 120 °C. The process was carried out by simultaneously feeding tetramethylcyclotetrasiloxane (TMCTS) and triethoxyfluorosilane (TEOFS) into the afterglow of helium and oxygen plasma. The effect of the flow rate of the fluorinated precursor on the growth rate, composition, and optical properties was examined. The ratio of atomic fluorine to atomic silicon increased up to 10% at a TEOFS/TMCTS atomic Si feed ratio of 1.3 and then leveled off. Coatings made from pure TMCTS and both precursors showed higher surface roughness and porosity, and more hydroxyl content compared to coatings made from pure TEOFS. The refractive indices at 633 nm of films produced using pure TMCTS, a TEOFS/TMCTS atomic Si feed ratio of 1.3 and pure TEOFS were 1.457, 1.449, and 1.411, respectively.

Synthesis and Spectroscopy of Poly(9,9-dioctylfluorene-2,7-diyl-co-2,8-dihexyldibenzothiophene-S,S-dioxide-3,7-diyl)s: Solution-Processable, Deep-Blue Emitters with a High Triplet Energy

Poly(9,9-dioctylfluorene-2,7-diyl-co-2,8-dihexyldibenzothiophene-S,S-dioxide-3,7-diyl) copolymers (pF-S6 8−10) of varying composition have been synthesized by Suzuki−Miyaura polymerization. The hexyl substituents on the dibenzothiophene-S,S-dioxide (S) units improve the solubility of the copolymers and increase the dihedral angles in the backbone; this shifts the emission deep into the blue (λmax 420 nm for films of 10) and increases the photoluminescence quantum yield compared with previous pF-S copolymers containing non-alkylated S units. The backbone twist restricts formation of the intramolecular charge transfer (ICT) state for low incorporation ratios of S6 units. The triplet energy of these new copolymers increases as the percentage of the S6 unit increases (i.e., 15, 30, 50%: 8 → 9 → 10). The alternating copolymer 10 has a sufficiently high triplet energy (ET 2.46 eV for onset of phosphorescence) to host a green phosphorescent iridium guest emitter, as demonstrated in electroluminescence studies wh...

Growth and characterization of (Pb,La)(Zr,Ti)O 3 thin film epilayers on SrTiO 3-buffered Si(001)

Ferroelectric Pb 0.92La 0.08Zr 0.4Ti 0.6O 3 (PLZT) thin films were deposited on SrTiO 3-buffered Si(001) substrate by on-axis radio frequency magnetron sputtering. X-ray diffraction analysis revealed epitaxial growth of monocrystalline PLZT films, with an (001) rocking curve full width at half maximum of ∼ 0.3°. φ-scans showed 45° in-plane orientation of the perovskite unit cell relative to that of silicon. The elemental composition of the thin film heterostructure was examined by Auger sputter depth profiling measurements. The recorded profiles suggest that the SrTiO 3 buffer layer serves not only as a template for epitaxial growth, but also as a barrier suppressing Pb–Si interdiffusion between the PLZT layer and the Si substrate. The surface roughness of the PLZT layer was measured at ∼ 4 nm for films with ∼ 500 nm thickness. Wavelength dispersions for the refractive index ( n) and the extinction coefficient ( k) were obtained from spectroscopic ellipsometry measurements, with n ∼ 2.48 at the main communication wavelength λ = 1550 nm and k < 0.001 for λ > 650 nm. Recorded polarization vs. electric field loops for the PLZT epilayer, with a SrRuO 3 electrode layer interposed between PLZT and SrTiO 3, showed a remnant polarization P r ≈ 40 µC/cm 2 and coercive field E c ≈ 100 kV/cm. These findings suggest that the sputter-deposited PLZT thin films retain the functional properties critical to ferroelectric and electro-optic device applications, also when integrated on a semiconductor substrate.

Correlation between microstructure and residual stress of nanocrystalline silicon films

AbstractThe nanocrystalline silicon films have been prepared using very high frequency PECVD technique. The deposition power density and hydrogen dilution of Silane were varied. The sizes of the grains varies from 6 nm to 32 nm for films deposited under different conditions. The stress of the nanocrystalline films have been estimated from (220) line. It is observed that compressive stress decreases and become tensile stress as Xc of the films increases with increase in power density. Whereas compressive stress increases as crystalline volume fraction increases with increase in hydrogen dilution. Maximum tensile stress and compressive stress obtained are 0.23 GPa and 5.1 GPa respectively. It is also observed that compressive stress in the film increases as grain size increases. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

New electrochromic polymeric pyridinium salts

A series of new anode-cathode conjugated electrochromic polymeric pyridinium salts containing mainchain triphenylamine units and demonstrating multicolor electrochromism has been synthesized. All of the polymers exhibit intense UV absorption with maxima of absorption and fluorescence at 340–343 and 336–338 nm in DMF solutions and 460–461 and 410–438 nm in films. The electrochromic properties of the films are investigated by electrochemical and spectroelectrochemical methods. Reversible redox signals with stable electrochromic characteristics are found in cyclic voltamperograms. The electrochromic properties of the polymers remain highly stable after 50 cycles in the range 0–1.2 V.

Fabrication and electrical characteristics of ultrathin (HfO 2) x(SiO 2) 1−x films by surface sol–gel method and reaction-anneal treatment

Hafnium oxide (HfO 2) films were deposited on Si substrates with a pre-grown oxide layer using hafnium chloride (HfCl 4) source by surface sol–gel process, then ultrathin (HfO 2) x (SiO 2) 1− x films were fabricated due to the reaction of SiO 2 layer with HfO 2 under the appropriate reaction-anneal treatment. The observation of high-resolution transmission electron microscopy indicates that the ultrathin films show amorphous nature. X-ray photoelectron spectroscopy analyses reveal that surface sol–gel derived ultrathin films are Hf–Si–O alloy instead of HfO 2 and pre-grown SiO 2 layer, and the composition was Hf 0.52Si 0.48O 2 under 500 °C reaction-anneal. The lowest equivalent oxide thickness (EOT) value of 0.9 nm of film annealed at 500 °C has been obtained with small flatband voltage of −0.31 V. The experimental results indicate that a simple and feasible solution route to fabricate (HfO 2) x (SiO 2) 1− x composite films has been developed by means of combination of surface sol–gel and reaction-anneal treatment.

The photovoltaic behaviors of PPV- and PPE-type conjugated polymers featured with diketopyrrolopyrrole (DPP) units

The photovoltaic behaviors of diketopyrrolopyrrole (DPP) embedded poly(phenylenevinylene) (C8-DPP-PPV) and poly(phenyleneethynylene) (C10-DPP-PPE) were investigated. The two polymers exhibited good solubility in common organic solvents, high thermal stability and broad UV/visible absorption ranging from 300 to 600 nm in films. Their optical band gaps were found to be 1.94 eV for C8-DPP-PPV and 2.05 eV for C10-DPP-PPE. Moreover, their HOMO energy levels were relatively low at around −5.6 to −5.8 eV as estimated by electrochemical measurements. The polymer/PCBM bulk heterojunction solar cells exhibited a power conversion efficiency of 0.16% for C10-DPP-PPE. In addition, all-polymer solar cells consisting of C10-DPP-PPE/P3HT were also fabricated in view of the potential of C10-DPP-PPE as a polymeric acceptor, revealing an efficiency of 0.01%.

Synthesis of a soluble conjugated copolymer based on dialkyl-substituted dithienothiophene and its application in photovoltaic cells

A soluble conjugated alternating 3,5-didecanyldithieno[3,2-b:2′,3′-d]thiophene–thiophene copolymer was synthesized by palladium(0)-catalyzed Stille coupling reaction. The thermal, absorption, emission, electrochemical, and photovoltaic properties of the polymer were examined. A weight-average molecular weight around 6.2 × 104 and a polydispersity index of 1.8 was estimated for the polymer using gel permeation chromatography. The polymer exhibits good thermal stability with decomposition temperature of 340 °C and glass-transition temperature of 136 °C. The polymer shows strong absorption peaked at 505 nm in diluted solution and 518 nm in thin film with an optical band gap 2.0 eV. The polymer exhibits intense emission located at 550 nm in solution and 603 nm in film. The HOMO and LUMO energies of the polymer were estimated to be −5.4 and −3.4 eV, respectively, by cyclic voltammetry. Polymer solar cells were fabricated based on the blend of the polymer and methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM). The power conversion efficiency of 0.7% was achieved under AM 1.5, 100 mW/cm2 using polymer:PCBM (1:4, w/w) as active layer.

Soluble dithienothiophene polymers: Effect of link pattern

AbstractSoluble conjugated polymers based on 3,5‐didecanyldithieno[3,2‐b:2′,3′‐d]thiophene—single‐bond (1), double‐bond (2), and triple‐bond linked (3)—were synthesized by palladium(0)‐catalyzed Stille coupling reaction and oxidation polymerization. The thermal, absorption, emission, and electrochemical properties of these polymers were examined; the effect of the link pattern was studied. All polymers exhibit decomposition temperatures over 295 °C and glass‐transition temperatures in the range of 137–202 °C. The absorption spectra of 1, 2, and 3 in thin films exhibit absorption maxima at 381, 584, and 444 nm, respectively. Polymer 1 exhibits intense green emission located at 510 nm in film, whereas polymers 2 and 3 are nonemissive both in solution and in film due to H‐aggregate. Cyclic voltammograms of polymers 1, 2, and 3 display irreversible oxidation waves with onset oxidation potentials at 1.73, 0.78, and 1.03 V versus Ag+/Ag, respectively. Theory calculation on model compounds suggests that the dihedral angle decreases in the order of 1 &gt; 3 &gt; 2. On reducing the dihedral angle, the polymer exhibits a longer absorption maximum, a smaller bandgap, a less oxidizing potential and fluorescence quench, due to more coplanar and more π‐electron delocalized backbone structure. Polymer solar cells were fabricated based on the blend of polymer 2 and methanofullerene [6,6]‐phenyl C61‐butyric acid methyl ester (PCBM). The power conversion efficiency of 0.45% was achieved under AM 1.5, 100 mW cm−2 using polymer 2:PCBM (1:2, w/w) as active layer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2843–2852, 2009

Supramolecular π−π Stacking Pyrene-Functioned Fluorenes: Toward Efficient Solution-Processable Small Molecule Blue and White Organic Light Emitting Diodes

In this paper, we described a new category of solution-processible small molecule organic light emitting materials—the pyrene-functioned diarylfluorenes: 2PPPF and DPPPF. In solution, both of the materials show deep blue emission. In film, their emission largely red-shifted due to strong π−π stacking of pyrene groups. 2PPPF, which is quite rigid in molecular structure, bearing only one alkoxyl group, could form smooth film by spin-coating. From the photoluminescence and morphology study, we believe the strong π−π stacking enhanced the film forming ability. 2PPPF is an amorphous blue light emitter, with a Tg over 100 °C and Td over 430 °C. The good thermal stability is comparable to polymeric light emitting materials. The material shows strong aggregated emission with a broad structureless peak at about 460 nm in film. Electroluminescent devices by spin-coating were successfully fabricated. A single-layered device using 2PPPF as the active material shows a turn on voltage of 4.3 V, brightness over 3600 cd/...

Synthesis and characterization of a new ethynyl‐linked alternating anthracene/fluorene copolymer for organic thin film transistor

AbstractA new p‐type conjugated copolymer, poly(9,10‐diethynylanthracene‐alt‐9,9‐didodecylfluorene) (PDADF), which is composed of ethynyl‐linked alternating anthracene/fluorene, is synthesized via a palladium(II)‐catalyzed Sonogashira coupling reaction with 9,10‐diethynylanthracene and 2,7‐diiodo‐9,9‐didodecyl‐fluorene. The obtained polymer is confirmed by FTIR, 1H‐NMR, 13C‐NMR and elemental analysis. The PDADF had very good solubility in organic solvents such as chloroform and had a weight average molecular weight of 29,300 with a polydispersity index of 1.29. The PL maximum of the polymer was found at 533 and 568 nm for a solution and 608 nm for film, respectively. The highest occupied molecular orbital (HOMO) energy of the polymer is −5.62 eV as measured via cyclic voltammetry (CV). A solution‐processed thin film transistor device showed a carrier mobility value of 6.0 × 10−4 cm2/Vs with a threshold voltage of −17 V and a capacitance (Ci) of 10 nF/cm2. The out‐of‐plane and in‐plane GIXD pattern of spin‐coated polymer on SiO2 dielectric surfaces showed an amorphous halo near 2θ = 20°. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1609–1616, 2009

Structural and electrical properties of magnetron sputtered Ti(ON) thin films: The case of TiN doped in situ with oxygen

Incorporation of oxygen into TiN lattice results in formation of titanium oxynitrides, TiOxNy that have become particularly interesting for photocatalytic applications. Elaboration as well as characterization of TiN and in situ oxygen-doped thin films is the subject of this paper. Thin films, 250–320nm in thickness, have been deposited by dc-pulsed magnetron reactive sputtering from Ti target under controllable gas flows of Ar, N2 and O2. Optical monitoring of Ti plasma emission line at = 500nm has been implemented in order to stabilize the sputtering rate. Scanning electron microscopy (SEM), X-ray diffraction in grazing incidence (GIXRD), micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), optical spectrophotometry and four-point probe electrical resistivity measurements have been performed in order to follow evolution of film physical parameters as a function of the oxygen flow rate O2 at which the films were deposited. The relationship between O2 expressed in standard cubic centimetres per minute, sccm and the nitrogen/oxygen content in thin films has been established by means of the analysis of the XPS spectra. GIXRD studies indicate that incorporation of oxygen results in a progressive loss of preferential orientation in 111 direction, a change in the grain size from 16nm for TiN to about 3 nmfor films deposited at O2 = 1.32 sccm and a decrease in the lattice constant. A systematic shift of all X-ray diffraction (XRD) lines towards higher diffraction angles is consistent with substitution of oxygen for nitrogen. Micro-Raman investigations indicate amorphisation of thin films upon oxidation. Binding energies determined fromfitting of the XPS results concerning the N1s and Ti2p lines give evidence of the presence of TiOxNy compound. Red-shift of the plasma reflectance edge upon TiN oxidation is correlated with a decreased carrier concentration. Metal–semiconductor transition can be expected on the basis of the electrical conductivity decrease and development of the fundamental absorption across the forbidden band of TiO2 upon increase in the oxygen flow rate. Additional absorption feature in the visible range, being a consequence of coexistence of free-electron and interband absorption within almost the same spectral range ( = 400–600 nm) seems to be very promising for photocatalytic applications of titanium oxynitride thin films.

Growth, coalescence, and electrical resistivity of thin Pt films grown by dc magnetron sputtering on SiO 2

Ultra thin platinum films were grown by dc magnetron sputtering on thermally oxidized Si (1 0 0) substrates. The electrical resistance of the films was monitored in situ during growth. The coalescence thickness was determined for various growth temperatures and found to increase from 1.1 nm for films grown at room temperature to 3.3 nm for films grown at 400 ° C. A continuous film was formed at a thickness of 2.9 nm at room temperature and 7.5 nm at 400 ° C. The room temperature electrical resistivity decreases with increased growth temperature, while the in-plain grain size and the surface roughness, measured with a scanning tunneling microscope (STM), increase. Furthermore, the temperature dependence of the film electrical resistance was explored at various stages during growth.

Polymeric like carbon films prepared from liquid gas and the effect of nitrogen

Polymeric like carbon (PLC) films are grown by a capacitance coupled RF-PECVD on the grounded electrode at room temperature from liquid gas (40% propane and 60% butane) in two regimes with nitrogen and without nitrogen gas. Films are characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), Fourier transform infrared (FTIR) absorption and Raman spectroscopy. The result of FTIR analyses indicates that more than 90% of hydrogen atoms are bonded to carbon with sp 3 hybridization. The abundance of CH 3 is more than that of CH 2 and this one is more than that of CH for carbon with sp 3 hybridization in these films. The C 1s line of the XPS spectra is deconvoluted to several peaks that are attributed to the CH 3, CH 2 and CH terminations. The result of this deconvolution is consistent with FTIR results. AFM images show that the mean nanoparticle size is reduced from about 100 nm for films without nitrogen to less than 80 nm for films with nitrogen. This is in agreement with our Raman results. By addition of nitrogen to the feed gas, no variation in the C–H stretching vibration mode is observed. The effect of N–H bonds is observable in both FTIR and XPS spectra and a very small trace of N–C bonds is present only in deconvolution of N 1s line of XPS spectra. These results indicate that by addition of nitrogen to feed gas, internal structure of a-C:H nanoparticles is not changed but particle size is decreased. We suggest that the internal stress reduction due to nitrogen addition in the feed gas for PLC films can be related to decreasing of the a-C:H particle size.

Metal–organic chemical vapor deposition of Bi 2Mn 4O 10 films on SrTiO 3 〈1 0 0〉

Bi 2Mn 4O 10 films were deposited on SrTiO 3 (1 0 0) substrates via metal–organic chemical vapor deposition (MOCVD) from the Bi(phenyl) 3 and Mn(tmhd) 3 (Htmhd = 2,2,6,6-tetramethyl-3,5-heptanedione) precursors. The films were deposited in the temperature range of 600–800 °C. The X-ray diffraction (XRD) characterization indicates that the Bi 2Mn 4O 10 phase is stable within the investigated range, but the temperature plays a crucial role in determining the out-of-plane orientation of the films. The SEM shows very homogeneous surfaces with a fiber texture morphology at the highest deposition temperature. The AFM data indicate a textured surface with a root mean square roughness of 77.67 nm for films deposited at 800 °C.

Electrical resistivity and morphology of ultra thin Pt films grown by dc magnetron sputtering on SiO2

.Ultra thin platinum films were grown by dc magnetron sputtering on thermally oxidized Si (100) substrates. The electrical resistance of the films was monitored in-situ during growth. The coalescence thickness was determined for various growth temperatures and found to increase from 1.3 nm for films grown at room temperature to 1.8 nm for films grown at 250°C, while a continuous film was formed at a thickness of 3.9 nm at room temperature and 3.5 nm at 250°C. The electrical resistivity increases with increased growth temperature, as well as the morphological grain size, and the surface roughness, measured with a scanning tunneling microscope (STM).