Iodine doping of amorphous diamond-like carbon films

Amorphous diamond-like carbon (a:DLC) films have been doped by incorporation of iodine during the films deposition. XPS and AES analysis shows the existence of iodine atoms with constant concentration of 0.9% along the iodine doped DLC film (a:I-DLC). The optical and electronic properties of the doped films were studied. Optical measurements in the visible light show that iodine affects the interband absorption of the a:DLC films. Iodine causes decreasing of the optical energy gap, from 1.07 to 0.78 eV and affects the density of states at the conducting band. Like the optical measurements, electrical measurements show that iodine also decreases the activation energy of the films from 0.34 to 0.22 eV. This shows that although both gaps decrease, the optical energy gap remains different from that of electrical gap, also after doping.     

Relation between physical structure and electrical properties of diamond-like carbon thin films

Diamond-like carbon (DLC) belongs to very interesting materials used for a number of practical applications. Its properties strongly depend on the method of deposition and on the deposition parameters. In particular, the electrical properties of DLC films obtained by RF PCVD discharge depend substantially on the preparation conditions. Influence of deposition conditions on the physical structure and chemical content is discussed. Both the drift mobility of charge carriers and the electrical conductivity of DLC films strongly depend on deposition conditions. The electrical conductivity results are explained in terms of hopping mechanism. At the temperatures below 260 K, the hopping among states in a narrow band of states dominates; at the higher temperatures, the band-to-band transitions are suggested to occur. A model of the forbidden gap explaining the observed electrical properties of DLC films is proposed. Experimental results concerning the electrical conduction of DLC/Si heterostructures are also presented and discussed. The difference in the properties of DLC/n-Si and DLC/p-Si structures may suggest that the electron transport via localised states dominate in the investigated DLC films. Recombination lifetime of charge carriers in DLC films is measured using both dielectric spectroscopy and detection of decay of photocurrents. The lifetime is found to be of the order of 0.3–0.4 ms, which is quite long in comparison with classical doped silicon semiconductors.     

Optical and electrical characterization of (PEO+methyl violet) polymer electrolytes

Optical properties and electrical conductivity of polyethylene oxide (PEO) with methyl violet dopant film have studied. The complexation of the methyl violet dopant with PEO was confirmed by X‐ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopic studies. The microstructure morphology have been analyzed by scanning electron microscope (SEM) for pure and dopant films. The UV‐absorption studies were made in the wavelength range 190–1100 nm for pure and doped films. The dc electrical conductivity data was collected using two probe technique in the temperature range 303–333 K. The UV–visible spectra showed the absorption band at 190 nm for pure PEO and doped from 208–224 nm region with different absorption intensities. The absorption edge, direct and indirect band gap were estimated using Mott and Davis Model. The optical activation energy can be determined using the Urbach rule, for pure PEO it was found 2.38 eV and 1.28–4.08 eV for doped films. The absorption band was shifted toward the higher frequency, the direct and indirect band gap decreases with increasing of dopant concentration, corresponds to the allowed inter band transition of electron. The dc electrical conductivity results shows that it increases with increasing dopant weight percentage and temperature which corresponds to the enhancement of charge mobility in these dye doped polymers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Optical,electrical and morphological properties of transparent binary doped polyaniline thin films synthesized by in situ chemical bath deposition

The development of polymeric thin films has attracted attention in the optoelectronics field due to their transparency. The aim of the research presented was to obtain transparent polyaniline thin films by easy in situ oxidative polymerization of aniline with ammonium persulfate in the presence of a binary doping agent–poly(vinyl alcohol) mixture. Poly(acrylic acid), 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid or sodium dodecylsulfate were mixed with hydrochloric acid to form the binary doping agents. Polyaniline thin films were produced during aniline polymerization on Corning glass slides immersed in the mixture in order to study their optical, electrical and morphological properties. The optical absorption coefficient and the energy band gap were evaluated by optical transmission of the films in the UV‐visible spectral region. The optical absorption coefficient of all polyaniline films was of the order of 10⁴ cm^?1 with a maximum transmittance up to 80% at 550 nm. In order to investigate the effect of the mixture on the surface morphology and roughness of the films, atomic force microscopy was used. In general, surface roughness was reduced threefold by adding a mixture and optical transmission was increased by 20–30% without significantly affecting the absorption coefficient and the band gap of polyaniline. Islands and needle‐like structures on the film surfaces were obtained from various mixtures affecting the conductivity; for example, 0.17 S cm^?1 was obtained from needle‐like morphology, while 1.9 × 10^?4 S cm^?1 was obtained from island morphology. Raman spectroscopy studies confirmed the presence of poly(vinyl alcohol) in the thin films. Copyright © 2011 Society of Chemical Industry     

Electrical and optical properties of diamond-like carbon films deposited by pulsed laser ablation

Pulsed laser ablation of a graphite target was carried out by ArF excimer laser deposition at a laser wavelength of 193 nm and fluences of 10 and 20 J/cm² to produce diamond-like carbon (DLC) films. DLC films were deposited on silicon and quartz substrates under 1 × 10^? 6 Torr pressure at different temperatures from room temperature to 250 °C. The effect of temperature on the electrical and optical properties of the DLC films was studied. Laser Raman Spectroscopy (LRS) showed that the DLC band showed a slight increase to higher frequency with increasing film deposition temperature. Spectroscopic ellipsometry (SE) and ultraviolet–visible absorption spectroscopy showed that the optical band gap of the DLC films was 0.8–2 eV and decreased with increasing substrate temperature. These results were consistent with the electrical resistivity results, which gave values for the films in the range 1.0 × 10⁴–2.8 × 10⁵ Ω cm and which also decreased with deposition temperature. We conclude that at higher substrate deposition temperatures, DLC films show increasing graphitic characteristics yielding lower electrical resistivity and a smaller optical band gap.     

Diamond-like carbon by pulsed laser deposition from a camphoric carbon target: effect of phosphorus incorporation

DLC thin films were grown by XeCl excimer pulsed-laser deposition (PLD) at room temperature using a camphoric carbon (CC) target. To carry out doping, CC soot was mixed with varying amounts (1–7% by mass) of phosphorus (P) powder. The resistivity was observed to increase initially for the films deposited from a target containing 1% P. The resistivity then decreased sharply at first, and gradually thereafter, for the films deposited from targets with a higher P content. Raman, optical gap and the electrical resistivity studies suggest that the P incorporation in carbon films results in controlled doping for the films deposited from targets containing up to 5% P, and a higher P content induces graphitization by narrowing the optical gap.     

Nitrogen incorporated diamond-like carbon films by microwave surface wave plasma CVD

Nitrogen incorporated diamond like carbon films have been deposited by microwave surface wave plasma chemical vapor deposition (MW-SWP-CVD), using methane (CH₄) as the source of carbon and with different nitrogen flow rates (N₂ / CH₄ flow ratios between 0 and 3). The influence of the nitrogen incorporation on the optical, structural properties and surface morphology of the carbon films were investigated using different spectroscopic techniques. The nitrogen has been incorporated into DLC:N films which was confirmed by the X-ray photoelectron spectroscopy (XPS) measurement. Moreover, the nitrogen incorporation was accompanied by a variation in the optical gap, which was attributed to the removal or creation of band tail states.     

Vibrational properties of nitrogen-doped ultrananocrystalline diamond films grown by microwave plasma CVD

Ultrananocrystalline diamond (UNCD) films grown in an argon-rich Ar/CH₄/H₂ microwave plasma with nitrogen gas added in amounts of 0%–20% were studied by Raman spectroscopy with multiple excitation wavelengths in the range of 244–647 nm and by optical absorption in UV–visible. The Raman spectra have demonstrated the presence of diamond, amorphous carbon and polyacetylene in the UNCD films. Analysis of vibrational and optical properties of amorphous carbon phase proves that nitrogen stimulates the transition from amorphous carbon into an ordered graphite-like structure with narrowed optical band gap, which is supposed to be responsible for the high electrical conductivity of the N-doped UNCD.     

A comprehensive study on the effects of alternative sulphur precursor on the material properties of chemical bath deposited CdS thin films

Chemical bath deposition (CBD) method was used to deposit CdS thin films on soda-lime glass substrates by using n-methylthiourea (NTU) as an alternative sulphur source and were compared to typical thiourea (TU) precursor. The sulphur source concentration was varied from 0.01 M to 0.1 M and the impact on the microstructural, surface morphology, optical and electrical properties of the grown films were studied. Increasing n-methylthiourea concentration in the precursor yielded thinner films that are less than 100 nm thickness, surface morphology with average surface roughness of 6.4 nm, larger granular structure, wider band gap at 2.3 eV–2.6 eV range. Raman spectroscopy revealed Raman peak at 303 cm-1. In contrast, an increase in thiourea concentration resulted in thinner amorphous films, less distinct granular structure, narrower energy band gap from 2.3 eV to 2.4 eV and a resonance Raman peak at 302 cm-1. CdS thin film deposited from n-methylthiourea precursor at higher precursor concentration of 0.1 M showed better electrical properties such as lower resistivity and higher carrier mobility compared to the thin film deposited from typical thiourea precursor.     

Synthesis of nitrogen incorporated diamond-like carbon thin films using microwave surface-wave plasma CVD

Nitrogenated diamond-like (DLC:N) carbon thin films have been deposited by microwave surface wave plasma chemical vapor deposition on silicon and quartz substrates, using argon gas, camphor dissolved in ethyl alcohol composition and nitrogen as plasma source. The deposited DLC:N films were characterized for their chemical, optical, structural and electrical properties through X-ray photoelectron spectroscopy, UV/VIS/NIR spectroscopy, Raman spectroscopy, atomic force microscope and current–voltage characteristics. Optical band gap decreased (2.7 to 2.4 eV) with increasing Ar gas flow rate. The photovoltaic measurements of DLC:N / p-Si structure show that the open-circuit voltage (V_oc) of 168.8 mV and a short-circuit current density (J_sc) of 8.4 μA/cm² under light illumination (AM 1.5 100 mW/cm²). The energy conversion efficiency and fill factor were found to be 3.4 × 10^{− 4}% and 0.238 respectively.     

Effects of potassium incorporation on the structural,optical, vibrational and electrical properties of NiO sprayed thin films for p-type optical windows

Nickel oxide thin films were deposited on glass substrates by a simple mini spray technique at 460 °C. Alternatively, some of the obtained films were doped with potassium at the molar rates of: 1, 2 and 3% (K). In addition to the classical structural investigations including XRD, the opto-thermal studies, Raman spectroscopy and photoluminescence measurements were investigated.First, structural study by means of X-ray diffraction shows that all K-doped NiO thin films crystallized in cubic space group with some noticeable changes in terms of [K]/[Ni] ratio. In the same line, Raman spectroscopy reveals the principal NiO vibration’s mode with the shift related to K incorporation in NiO matrix. Second, some optical parameters, such as optical band gap, Urbach energy, refractive indices extinction coefficients and dielectric constant were studied in terms of K doping level. For all NiO:K prepared thin films, PL measurements show three large bands located at 405, 420, 485 and 529 nm.Furthermore, electrical properties were performed using impedance spectroscopy technique in the frequency range 5 Hz–13 MHz at various temperatures. DC conductivity is thermally activated showing a semiconductor behavior of NiO:K sprayed thin films. This study shows that the electrical conductivity is thermally activated. The calculated values of the activation energy show semiconductor behavior of such films.On the other hand AC conductivity is investigated through Jonscher law. The imaginary part of the complex impedance has a maximum whose relaxation frequency increases with temperature according to Arrhenius law.     

Effects of post-deposition annealing on different DLC films

Amorphous hydrogenated carbon films have been deposited by plasma-enhanced chemical vapour deposition at different process pressures and substrate temperatures, resulting in film properties ranging from polymer-like to diamond-like. The deposition parameter combinations were chosen by experimental design to enable the determination of both deposition pressure and deposition temperature effects on the annealing behaviour. The deposited films have then been annealed in vacuum at successively higher temperatures. Changes in optical band gap, internal stress, film thickness and infrared (IR) absorption spectra have been recorded to assess the influence of deposition parameters on the thermal stability of diamond-like carbon (DLC) and to identify temperature-induced modifications in the bonding structure. The results show a large variation in thermal stability between the different DLC films; samples deposited at low pressure display the greatest stability. The internal stress of the films starts decreasing at very low annealing temperature (<100 °C for the majority of samples), in most cases long before any decrease in the optical band gap can be detected. This is explained by a movement of hydrogen from sp² to sp³ sites as detected by IR measurements.     

The Structural,Optical and Electrical Properties of Spin Coated WO<Subscript><Emphasis Type="Bold">3</Emphasis></Subscript> Thin Films Using Organic Acids

Tungsten trioxide (WO₃) thin films were prepared incorporating various organic acid additives by the sol-gel spin coating technique. They were characterized by X-ray diffraction (XRD), UV-Visible analysis, scanning electron microscopy (SEM) and dc electrical conductivity. From XRD, the crystal phase, average grain size and structural parameters of WO₃ thin films were found to vary owing to different water dissolved organic acid additives. The variation of optical conductivity and band gap energy was calculated from the UV-Visible analysis. The SEM studies revealed that the organic acids influenced the surface morphology of the microsized plates of tungsten oxides. The electrical conductivity at various temperatures correlated with the average grain size of the nanocrystallites of WO₃ thin films.     

Influence of Substrate Temperature on the Properties of Cobalt Oxide Thin Films Prepared by Nebulizer Spray Pyrolysis (NSP) Technique

Cobalt oxide thin films are prepared by the nebulizer spray pyrolysis technique using cobalt chloride as the precursor material. The structural, optical, morphological and electrical properties are investigated as a function of substrate temperature (300–450 °C). The X-ray diffraction (XRD) analysis reveals that all the films are polycrystalline in nature, having cubic structure with preferential orientation along the (111) plane. The optical spectra show that the films are transparent (68 %) in the IR region. The optical band gap values are calculated for different substrate temperature. Photoluminescence (PL) spectra of the films indicate the presence of indigo, blue and green emission peaks with an ultraviolet emission peak centered around 368nm. SEM images reveals small sphere-like structures for the prepared Co3O4 films. The maximum conductivity obtained is 1.48 x 10?3 S/cm at 350 °C. The activation energy varies between 0.039 and 0.138 eV for the substrate temperature variation from 300-450 Q°C.     

Properties of Phosphorus‐Doped Silicon‐Rich Amorphous Silicon Carbide Film Prepared by a Solution Process

Using a polymeric precursor synthesized from a mixture of cyclopentasilane, white phosphorus, and 1‐hexyne, we deposited phosphorus‐doped silicon‐rich amorphous silicon carbide (a‐SiC) films via a solution‐based process. Unlike conventional polymeric precursors, this polymer requires neither catalysts nor oxidation for its synthesis and cross‐linkage. Therefore, the polymeric precursor is sufficiently pure for effective doping and fabricating semiconducting a‐SiC. This study presents the results of a detailed study of the effect of carbon and phosphorus concentrations on the structural, optical, and electrical properties of a‐SiC films. The lowest activation energy for these films is 0.39 eV, which leads to an optical gap and a dark conductivity of 2.1 eV and 10⁹ Ω cm, respectively. Moreover, these films satisfy the Meyer–Neldel rule for thermally activated conductivity, which indicates that white‐phosphorus doping of solution‐processed a‐SiC produces films with the same characteristics as phosphine‐doped vacuum‐processed a‐SiC.     

Piezoresistive,optical and electrical properties of diamond like carbon and carbon nitride films

In the present study diamond like carbon (DLC) and carbon nitride (a-CN_x:H) films were deposited by closed drift ion source from the acetylene and nitrogen gas mixture. The piezoresistive, electrical and optical properties of ion beam synthesized DLC films were investigated. Piezoresistive properties of the diamond like carbon and carbon nitride films were evaluated by four point bending test. The piezoresistors were fabricated on crystalline alumina substrates using Al-based interdigitated finger type electrodes. Effects of the nitrogen concentration on the piezoresistive gauge factor were investigated. The dependence of the resistance of the metal/a-CN_x:H/metal structures on temperature has been studied. Current–voltage (I–V) and capacitance–voltage characteristics were measured for a-CN_x:H/Si heterostructures. The main current transport mechanisms were analyzed. Optical parameters of the synthesized films such as optical bandgap and B parameter (slope of the linear part of the Tauc plot) were investigated to study possible correlation with the piezoresistive properties.     

Preparation of diamond like carbon thin films above room temperature and their properties

Diamond like carbon (DLC) thin films were deposited on p-type silicon (p-Si), quartz and ITO substrates by microwave (MW) surface-wave plasma (SWP) chemical vapor deposition (CVD) at different substrate temperatures (RT ∼ 300 °C). Argon (Ar: 200 sccm) was used as carrier gas while acetylene (C₂H₂: 20 sccm) and nitrogen (N: 5 sccm) were used as plasma source. Analytical methods such as X-ray photoelectron spectroscopy (XPS), FT-IR and UV–visible spectroscopy were employed to investigate the structural and optical properties of the DLC thin films respectively. FT-IR spectra show the structural modification of the DLC thin films with substrate temperatures showing the distinct peak around 3350 cm^− 1 wave number; which may corresponds to the sp² C–H bond. Tauc optical gap and film thickness both decreased with increasing substrate temperature. The peaks of XPS core level C 1 s spectra of the DLC thin films shifted towards lower binding energy with substrate temperature. We also got the small photoconductivity action of the film deposited at 300 °C on ITO substrate.     

Electrical and optical properties of plasma polymerized eucalyptus oil films

Electrical and optical properties of the plasma polymerized eucalyptus oil (PPEo) films are discussed in this article. As part of our electrical studies, we have found that the conduction mechanism in the PPEo film is a Schottky type. We have also found that iodine doping can enhance the conductivity of the film. IR studies revealed that PPEo film is a highly crosslinked polymer, and UV‐vis‐NIR studies revealed the information that optical band gap energy of the PPEo film had been reduced as a result of iodine doping. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1102–1107, 2003     

Thiophene‐based copolymers synthesized by electropolymerization for application as hole transport layer in organic solar cells

Electrically conducting thiophene‐based copolymers were synthesized by electropolymerization. The potential range used has a strong influence on the film structure and properties. The extent of oxidation of the copolymers was determined from the ratio of the oxidation to reduction charge, Q_ox/Q_red. The use of wide potential range leads to reduced films, whereas the narrow range leads to partially oxidized films. The copolymers exhibit a characteristic band in UV–vis spectra at ～ 410 nm, which shifts to higher wavelengths for the more doped material. The electrical conductivity of the copolymers was correlated to their morphology and their structure. The copolymer with higher conductivity is partially reduced, has compact morphology and higher ratio of quinoid to benzenoid rings. The energy gap of the copolymers is reversely proportional to their electrical conductivity. The optical and electrical properties of the copolymers make them very well suited for use as hole transport layers (HTL) in organic opto‐electronic devices. We prepared polymer : fullerene solar cells with copolymer HTLs. The solar cell performance was tested with very encouraging initial results. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Ambient effects on the electrical conductivity of carbon nanotubes

We show that the electrical conductivity of single walled carbon nanotubes (SWCNT) networks is affected by oxygen and air humidity under ambient conditions by more than a magnitude. Later, we intentionally modified the electrical conductivity by functionalization with iodine and investigated the changes in the band structure by optical absorption spectroscopy.Measuring in parallel the tubes electrical conductivity and optical absorption spectra, we found that conduction mechanism in SWCNT is comparable to that of intrinsically conducting polymers. We identified, in analogy to conducting polymers, in the infrared spectra a new absorption band which is responsible for the increased conductivity, leading to a closing gap in semiconducting SWCNT.We could show that by different functionalizations of the same SWCNT starting material the properties like conductivity can be dramatically changed, leading to different imaginable applications. We investigated here, an ultraviolet sensor with weakly modified SWCNT.