⇦Chinese Physics Letters, 2018, Vol. 35, No. 2, Article code 026501 Effect of Nickel Distributions Embedded in Amorphous Carbon Films on Transport Properties Vali Dalouji1**, Dariush Mehrparvar1, Shahram Solaymani2, Sahar Rezaee3 Affiliations 1Department of Physics, Faculty of Science, Malayer University, Malayer, Iran 2Department of Physics, Science and Research Branch, Islamic Azad University, Tehran, Iran 3Department of Physics, Kermanshah Branch, Islamic Azad University, Kermanshah, Iran Received 26 September 2017 **Corresponding author. Email: dalouji@yahoo.com Citation Text: Dalouji V, Mehrparvar D, Solaymani S and Rezaee S 2018 Chin. Phys. Lett. 35 026501 Abstract Electrical properties of C/Ni films are studied using four mosaic targets made of pure graphite and stripes of nickel with the surface areas of 1.78, 3.21, 3.92 and 4.64%. The conductivity data in the temperature range of 400–500 K shows the extended state conduction. The conductivity data in the temperature range of 150–300 K shows the multi-phonon hopping conduction. The Berthelot-type conduction dominates in the temperature range of 50–150 K. The conductivity of the films in the temperature range about $T < 50$ K is described in terms of variable-range hopping conduction. In low temperatures, the localized density of state around Fermi level $N(E_{\rm F})$ for the film deposition with 3.92% nickel has a maximum value of about $56.2\times10^{17}$ cm$^{-3}$eV$^{-1}$ with the minimum average hopping distance of about $3.43\times10^{-6}$ cm. DOI:10.1088/0256-307X/35/2/026501 PACS:65.80.-g, 66.30.Pa, 68.47.Fg © 2018 Chinese Physics Society Article Text Recently, nanomaterials have found a wide range of applications in several technological fields as reported by several researchers.[1-11] A combination of pure amorphous carbon films and metallic nanoparticles can enhance certain physical properties in carbon-based composite films.[12] The position of the Fermi energy in the band gap of the films can be affected by doping metal into the matrix.[13] Due to slight variation in their composition, embedded metal nanoparticles in carbon films, as electronic materials, will affect their conductivity behavior and change their properties from dielectric to metallic.[14] Various categories of theories have been applied to explain the conductivity transition in these systems. The percolation mechanism has been applied to inhomogeneous mixtures at the macroscopic scale and the quantum theories of localization by various models such as Anderson localization, variable range hopping, and the scaling theory of localization of non-interacting electrons have been developed.[15] The tunneling and percolation mechanism in metallic–nonmetallic materials with 2–5 mm thicknesses was investigated by Toker et al.[16] The films were synthesized at room temperature with non-wet chemical deposition which is the required conditions for their applications in optical and electronic devices.[17] Nickel is more important than other metal nanoparticles, because Ni has high catalyst effect and it can transform matrix amorphous-like carbon to graphene-like carbon.[18] In addition, the enhanced magnetic properties of Ni nanoparticles have been exploited in the field of data storage devices and in ferrofluids.[19] In our previous reports, we have studied the effect of deposition time and annealing temperature on morphology, optical and electrical properties of carbon films embedded by nickel nanoparticles in nondegenerating and homogenous semiconductors.[20-25] Adding Ni nanoparticles as impurities into films will make localized states. We have given that deposition time and annealing temperature have a strong effect on these semiconductors. It was also found that electrical transports in these films are governed by amorphous-like carbon (ALC). In the present work, we investigate the effect of Ni content and Ni distribution on the conduction mechanism of these films with more details. Ni-embedded amorphous carbon films were deposited on glass substrates using different targets by the rf magnetron sputtering method. Firstly, the substrates were ultrasonically cleaned with ethanol for 20 min followed by deionized water. Prior to the film deposition, the mosaic targets were pre-sputtered with Ar$^{+}$ plasma to remove oxide layers and adsorbed impurities on the surfaces of films. Stripes of Ni are attached to the pure graphite target with a length about of 40 mm. The Ni content in the deposited films was controlled by the number of the Ni stripes on the graphite target. The numbers of these attached stripes were 10, 18, 22 and 26, corresponding to 1.78, 3.21, 3.92 and 4.64% of nickel surface area, respectively. The background pressure of the sputtering chamber and the operation pressure were $2\times10^{-5}$ and $2\times10^{-2}$ mbar, respectively. The deposition process was carried out at 3 min with the constant rf power regime 400 W. The angle of incident ions through the surface of the target was 90$^{\circ}$, and the substrate-target distance was set to be 60 mm. Atomic forces microscopic (AFM) analysis on non-contact mode was used to obtain surface morphology properties. The field emission scanning electronic microscopy (FESEM) images were used for studying the morphological characterization. Energy dispersive x-ray studies (EDAX) were carried out with an AMETEK EDAX analyzer. Using the four-point contact method, the direct current electrical conductivity was measured by cooling the samples with a continuous He flow in cryogenic units (optical low temperature model CCS 450 USA) at the thermostatic chamber in the temperature range of 15–500 K. The high voltage power supply (ORTEC 456, USA, 0–3 kV), Metrix VX102A and Keithley 196 system DMM electrometers were used for voltage and current measurements, accordingly.
cpl-35-2-026501-fig1.png
Fig. 1. Typical FESEM images of films deposited at (a) 3.92% and (b) 4.64%, (c) variation of Ni concentration of films versus different Ni surface areas, and AFM images of films deposited at (d) 3.92% and (e) 4.64%.
Figures 1(a) and 1(b) show the FESEM images of deposited films with 3.92% and 4.64% Ni surface areas. The nanoparticle sizes of the deposited films with 1.78%, 3.21%, 3.92 and 4.64% Ni surface areas were estimated to be about 70, 50, 30 and 100 nm, respectively, which show that the sizes of nanoparticles were decreased by changing the Ni surface areas from 1.78 to 3.92%, and then increased from 3.92 to 4.64%. Figure 1(c) shows the variation of Ni concentration of films with different Ni surface areas on the mosaic target. Figure 1(c) shows that with increasing Ni surface areas from 1.78 to 4.64%, Ni concentrations of films increase. Due to the metaling paths in films deposited at 3.92%, the resistivity of film decreases. The decreasing resistivity of the film can cause a transition from nonmetal to metal, which is consistent with the decreasing activation energies $E_{\rm a}$ of films at 3.92%. In spite of increasing metal concentrations of films deposited at 4.64%, due to the disappearance of metaling paths on surface of these films, the film resistivity increases. The increasing resistivity of the film can cause a transition from metal to nonmetal, which is consistent with the increasing activation energies $E_{\rm a}$ of films at 4.64%. The films in regions 1 and 3 have a nonmetal behavior, while the films in region 2 have a metal behavior. As shown in Fig. 1(c), films deposited at 1.78 and 3.21% are in region 1, films deposited at 3.92% are in region 2 and films deposited at 4.64% are in region 3. These values are 59.68, 86.47, 89.91 and 92.89 wt.%, corresponding to Ni surface areas 1.78, 3.21, 3.92 and 4.64%, respectively. Figure 1(d) shows the AFM images of films deposited with Ni surface area 3.92% where Ni nanoparticles are connected to each other. Figure 1(e) shows the AFM images of films deposited with Ni surface area 4.64% where Ni nanoparticles are disconnected from each other.
cpl-35-2-026501-fig2.png
Fig. 2. The variation of $\ln\sigma (T)$ of films versus $1/T$ in the temperature range of 15–500 K. Inset: the best fits of these plots in the temperature range of 400–500 K.
cpl-35-2-026501-fig3.png
Fig. 3. Variation of activation energy $E_{\rm a}$ of films with different Ni surface areas versus temperature.
Figure 2 shows the variation of $\ln\sigma$ with respect to reciprocal temperature of films according to the Arrhenius law given by[26] $$ \sigma (T)=\sigma_{0}\exp(-E_{\rm a}/k_{_{\rm B}}T),~~ \tag {1} $$ where $\sigma_{0}$ is a pre-exponential factor, $E_{\rm a}$ is the activation energy, and $k_{_{\rm B}}$ is the Boltzmann constant. The activation energies of these films were estimated from the slopes of the best fit lines of this equation at the range of 400–500 K. The activation energies of deposited films with 1.78, 3.21, 3.92 and 4.64% Ni surface areas were estimated to be 0.49, 0.25, 0.038, and 0.6 eV, respectively. These activation energies are in good agreement with the values of the optical band gap obtained in a previous report.[21] Due to the increase of the Ni content and hence the increase of the impurity energy levels of films from 1.78 to 3.92% the activation energies of films decrease. The increase of the activation energy of films from 3.92 to 4.64% is due to the increase of the distance between Ni nanoparticles into films. Figure 3 shows a numerical evaluation of the differential activation energies using $E_{\rm a}=-k_{_{\rm B}}\Delta\ln(\sigma (T))/\Delta(1/T)$ for successive points at the temperature range of 100–400 K in the Arrhenius plot of the data shown in Fig. 2. There is a fluctuation in the activation energies of deposited films with Ni surface areas 1.78, 3.21, 3.92 and 4.64%, which is decreased by increasing the Ni surface area.[27] It is found that a single activated term of the Arrhenius plot for films in range less than 400 K is therefore inappropriate. As shown in Fig. 3, the room-temperature activation energies $E_{\rm a}$ for deposited films with 1.78, 3.21, 3.92 and 4.64% Ni surface areas have no physical meaning. Therefore, in this temperature range, the conduction mechanism may be explained by the multi-phonon assisted mechanism, which is frequently observed in semiconducting oxides.[27,28] Therefore, in the temperature range of 400–500 K the variation of $\ln\sigma$ with respect to $1/T$ according to the Arrhenius law has the best fit lines, and the values of $-k_{_{\rm B}} \Delta\ln(\sigma (T))/\Delta(1/T)$ for successive points, which are equivalent to the activation energies, are single data. In the temperature range of 150–300 K consisting with room temperature, the values of $-k_{_{\rm B}} \Delta\ln(\sigma (T))/\Delta(1/T)$ for successive points, which are equivalent to the activation energies, are not single data and there are fluctuations in the activation energies of films. With characterization of other conductive mechanisms and measuring values of the activation energies, we find that the multi-phonon assisted mechanism is the best in this temperature range and the obtained parameters in this mechanism are consistent with the room-temperature conductivity. The electrical conductivity of films due to multi-phonon tunneling of localized carriers is expressed as[27,28] $$ \sigma=n_{\rm c}e^{2}R^{2}{\it \Gamma}/6k_{_{\rm B}}T,~~ \tag {2} $$ where ${\it \Gamma}=c\exp(-\gamma p)(k_{_{\rm B}}T/h\nu_{0})^{p}$ is the hopping rate of carriers, $e$ is the electron charge, $k_{_{\rm B}}$ is the Boltzmann constant, $c\approx\nu_{0}$ and $n_{\rm c}=R^{-3}$, $R$ is the hopping distance, and $\gamma=\ln({\it \Delta}/E_{\rm M})-1$. The parameter $E_{\rm M}$ or $\gamma$ is the measurement of the coupling strength between carrier and phonon, and $\nu_{0}$ is the frequency of the acoustical phonon which is most effective coupled to localized electrons. As is reported by Emin, ${\it \Delta}=2E_{\rm nn}$, where $E_{\rm nn}$ is defined as the average needed energy to hop to the nearest neighbor at a distance $r$.[29] The values of MPH parameters at room temperature for deposited films with 1.78, 3.21, 3.92 and 4.64% Ni surface areas are listed in Table 1.
Table 1. Different multi-phonon tunneling parameters of the films.
Sample Nickel surface area (%) $R$ (10$^{-6}$ cm) $p$ $\nu_0$ (10$^{12}$ Hz) $\gamma$ $\sigma_{\rm RT}$ ($\Omega^{-1}$cm$^{-1}$)
1 1.78 7 1.65 0.004 2.85 1.18$\times$10$^{-3}$
2 3.21 5 0.68 0.14 4.95 40.3
3 3.92 3 0 727
4 4.64 10 1.33 0.3 0.49 32.3
cpl-35-2-026501-fig4.png
Fig. 4. Variation of $\ln\sigma$ versus $\ln T$ of films in the temperature range of 15–500 K. Inset: the best fits of these plots in the temperature range of 150–300 K.
Figure 4 shows the variation of $\ln\sigma$ versus $\ln T$ of the films deposited with 1.78, 3.21, 3.92 and 4.64% Ni surface areas in the temperature range of 150–300 K. From these fits, the number of phonons participating in transportation between hopping sites, given by $p={\it \Delta}/h\nu_{0}$, is obtained. The MPH process involves absorption and emission of phonons, which can be a non-integer number.[27] As shown in Fig. 4, there are fluctuations in electrical conductivity due to the multi-phonon tunneling of localized carriers with Ni surface areas in the temperature range of 150–300 K, which are in good agreement with the variation of the room temperature electrical conductivity $\sigma_{\rm RT}$ with Ni surface areas. With increasing Ni surface areas from 1.78 to 3.92% the room-temperature electrical conductivity $\sigma_{\rm RT}$ increases from $1.18\times10^{-3}$ to 727 $\Omega^{-1}$cm$^{-1}$ and then decreases to 32.3 $\Omega^{-1}$cm$^{-1}$ for films deposited at 4.64%. The increasing conductivity of films deposited from 1.78 to 3.92% can be attributed to the decreasing distance between Ni nanoparticles and hence overlapping electrons' wave functions and the decrease of the conductivity from 3.92 to 4.64% may be attributed to the increase of the distance between Ni nanoparticles. The values of $R$ given in Eq. (2) used here is in order of magnitude of the nickel nanoparticle size into the investigated films. In a disordered system, the carrier conduction at low temperatures may be assisted by variable range hopping given as[30] $$ \ln(I) \alpha n (T_{0}/T),~~ \tag {3} $$ where $n$ gives the information on the type of carrier conduction mechanism and depends on the grain sizes and the temperature region.[31] It is expected that for $n=-1$ the Berthelot-type conduction mechanism is observed, where $T_{0}$ is a constant and can be replaced by $T_{\rm B}$. The values of $n$ for films with 1.78, 3.21, 3.92 and 4.64% Ni surface area are estimated to be $-$0.77, $-$1, $-$1.3 and $-$1.13, respectively, which suggest the existence of the Berthelot-type conduction within the gap near the Fermi energy. As shown in the previous work,[30] the two absorption bands observed at about 510 cm$^{-1}$ and 436 cm$^{-1}$ correspond to the vibrations of tetrahedral and octahedral complexes, respectively.[32] The full expression for the transfer rate $\mathcal{R}$ in the vibration of barrier model is[33,34] $$ \mathcal{R}=c\exp(-2\alpha S_{\rm o})\exp(-U/k_{_{\rm B}}T)\exp(2\alpha^{2}k_{_{\rm B}}T/m\omega^{2}),~~ \tag {4} $$ where $\mathcal{R}$ is affected by the overlap term $\exp(-2\alpha S_{\rm o})$, the coincidence term $\exp(-U/k_{_{\rm B}}T)$, and the tunneling term $\exp(2\alpha^{2}k_{_{\rm B}}T/m\omega^{2}$. It is obvious that the increasing Ni concentration up to 392% will cause the decrease of the distance between the Ni ions. Figure 5 shows the dependency of current $I$ with temperature for the films with Ni surface area from 1.78 to 4.64%. In the temperature range of 50–150 K the films have the Berthelot-type conduction mechanism. Using data obtained from the slopes in the best line fit of Fig. 5, the Berthelot temperatures are estimated to be 34.4, 833, 909 and 175 for the films with 1.78, 3.21, 3.92, and 4.64% Ni surface areas, respectively. For the absorption band at 436 cm$^{-1}$, with increasing Ni surface areas from 1.78 to 3.92%, the distance between ions ($S_{\rm o}$) is decreased from $2.52\times10^{-7}$ to $0.49\times10^{-7}$ cm and then from 3.92 to 4.64% Ni surface area it increases to $1.11\times10^{-7}$ cm. Also, for the absorption band at 510 cm$^{-1}$, the values of $S_{\rm o}$ decrease from $2.15 \times10^{-7}$ to $0.41\times10^{-7}$ cm for 1.78 to 3.92% Ni surface area films, and increases to $0.95\times10^{-7}$ cm for the film with 4.64% Ni surface area. To observe the Berthelot-type hopping conduction experimentally, the localization length parameter $\alpha^{-1}$ and the average distance between the sites $S_{0}$ should be small. The extents of the carrier wave function from 1.78 to 3.92% increase from $1.73\times10^{-7}$ to $8.91\times10^{-7}$ cm and then decrease to $3.91\times10^{-7}$ cm from 3.92 to 4.64% in the absorption band 436 cm$^{-1}$. The extents of the carrier wave function from 1.78 to 3.92% increase from $1.48\times10^{-7}$ to $7.62\times10^{-7}$ cm and then decrease to $3.34\times10^{-7}$ cm in the absorption band 510 cm$^{-1}$. Therefore, it can be seen that the extent of the carrier wave function due to vibrations of Ni ions in tetrahedral is lower than octahedral complexes sites. These results are listed in Table 2. Therefore, in the temperature range of 50–150 K, lower than the room temperature range, the variation of $\ln\sigma$ respect to $\ln T$ is an increasing function and then the third term of the transfer rate $\exp(2\alpha^{2}k_{_{\rm B}}T/m\omega^{2}$, in the vibration of the barrier model is dominant. Therefore, the excitation of carriers to the transport band (high temperatures) and variable range hopping (low temperatures) cannot prevail. A fitting of the low temperature data in this temperature range yields the Berthelot-type conductivity, which is given by the expression $\exp(T/T_{\rm B})$, where $T_{\rm B}$ is the Berthelot temperature of the films.
Table 2. Electrical parameters of the Berthelot-type mechanism of the films.
Sample Nickel surface $T_{\rm B}$ $\omega_{1}$ $\alpha_{1}^{-1}$ $S_{01}$ $\omega_{2}$ $\alpha_{2}^{-1}$ $S_{02}$
area (%) (K) (10$^{13}$ S$^{-1}$) (10$^{-7}$ cm) (10$^{-7}$ cm) (10$^{13}$ S$^{-1}$) (10$^{-7}$ cm) (10$^{-7}$ cm)
1 1.78 34.4 8.21 1.73 2.52 9.6 1.48 2.15
2 3.21 833 8.21 8.53 0.51 9.6 7.29 0.43
3 3.92 909 8.21 8.91 0.49 9.6 7.62 0.41
4 4.64 175 8.21 3.91 1.11 9.6 3.34 0.95
cpl-35-2-026501-fig5.png
Fig. 5. Dependence of current $I$ of films versus temperature. Inset: the variation of $\ln I$ of films versus temperature in the temperature range of 50–150 K.
The variable range hopping (VRH) is generally valid at low temperatures.[2,35] The films deposited with 1.78, 3.21, 3.92 and 4.64% Ni surface areas are fitted in the temperature range of $T < 50$ K. The density of states at the Fermi level in this model is assumed to be a constant. According to Mott's VRH model, the conductivity is given by $$ \sigma=\sigma_{0}\exp[-(T_{0}/T)^{0.25}],~~ \tag {5} $$ where $T_{0}$, a characteristic temperature coefficient, depends on the density of states, $N(E_{\rm F})$, at the Fermi level in the form $T_{0}=[18\alpha^{3}/k_{_{\rm B}}N(E_{\rm F})]$, and $\sigma_{0}$ is given as $\sigma_{0}=3e^{2}\nu_{0}/(8\pi)^{1/2}[N(E_{\rm F})/\alpha T]^{1/2}$. Figure 6 shows $\ln(\sigma T^{1/2}$ versus $T^{-1/4}$ for all the films. A good fit of the measured data is essential but not sufficient criterion for applicability of Mott's variable range hopping (VHR) model. The hopping parameters should satisfy two conditions $W_{\rm hop}\alpha >1$ and $W_{\rm hop}>k_{_{\rm B}}T$, where $R_{\rm hop}$ and $W_{\rm hop}$ are the average hopping distance and the average hopping energy, respectively. These hopping parameters are given as $$\begin{align} R_{\rm hop}=\,&[9/(8\pi N(E_{\rm F}) \alpha k_{_{\rm B}}T)]^{1/4},\\ W_{\rm hop}=\,&3/(4\pi R_{\rm hop}^{3} N(E_{\rm F})).~~ \tag {6} \end{align} $$ These results are listed in Table 3. Table 3 lists the values of Mott's variable range hopping parameters of films deposited with Ni surface areas 1.78, 3.21, 3.92 and 4.64% calculated from the experimental data for the temperature 15 K. The increase of $T_{0}$ confirms the disorder in these films. The inverse localization length parameter increases with increasing the deposition processing from 1.78 to 3.92% and then decreases from 3.92 to 4.64%, which show that the inverse localization length parameter strongly depends on the nonmetal-metal transition. Therefore, the carrier wave function in the films deposited at 1.78% falls more sharply than other films. The localized density of states of the films around the Fermi level $N(E_{\rm F})$ increases with the increasing Ni surface area from 1.78 to 3.92%, and decreases at 3.92 to 4.64% Ni surface area films, which show that the localized density of states around the Fermi level, $N(E_{\rm F})$, also depends on the nonmetal–metal transition.
cpl-35-2-026501-fig6.png
Fig. 6. Variation of $\ln(\sigma T^{1/2}$ of films versus $T^{-1/4}$ in the temperature range of 15–500 K. Inset: the best fits of these plots in the temperature range of 15–50 K.
Table 3. Different variable hopping rang (VRH) parameters of the films.
Sample Nickel surface $T_{\rm o}$ $R_{\rm hop}$ $\alpha$ $N(E_{\rm F})$ $\alpha_{\rm hop}$ $W_{\rm VRH}$
No. area (%) (K) ($\times$10$^{-6}$ cm) (cm$^{-1}$) ($\times$10$^{17}$ cm$^{-3}$eV$^{-1}$) (meV)
1 1.78 789.04 8.77 118682.2 3.93 1.04 0.89
2 3.21 4096 6.29 249614.8 7.04 1.57 1.36
3 3.92 1477.63 3.43 355183.5 56.2 1.21 1.05
4 4.64 5996.95 6.39 270572.3 6.13 1.72 1.49
In conclusion, it is observed that Ni surface areas on mosaic target play an important role in electrical properties of C/Ni films. It is shown that films deposited with Ni surface area 4.64% have the maximum activation energy of about 0.66 eV. In addition, the number of phonons in multi-phonon hopping conduction mechanism has the maximum value of 1.65 at 1.78%. Also, the extents of the carrier wave function of the metal at the tetrahedral site at 3.92% have maximum values of $8.91\times10^{-7}$ cm and $7.62\times10^{-7}$ cm in octahedral-metal stretching vibrations and intrinsic stretching vibrations, respectively. The average hopping distance $R_{\rm hop}$ of films deposited at 3.92% Ni surface area has the minimum value of $3.43\times10^{-6}$ cm. References Structural and optical characterization of ZnO and AZO thin films: the influence of post-annealingCarbon films embedded by nickel nanoparticles: fluctuation in hopping rate and variable-range hopping with respect to annealing temperatureNi nanoparticle catalyzed growth of MWCNTs on Cu NPs @ a-C:H substrateCatalysis effect of metal doping on wear properties of diamond-like carbon films deposited by a cathodic-arc activated deposition processLow-pressure, metastable growth of diamond and "diamondlike" phasesMicrostructure and micromorphology of Cu/Co nanoparticles: Surface texture analysisInfluence of annealing process on surface micromorphology of carbon–nickel composite thin filmsElectronic conduction in polymers, carbon nanotubes and grapheneReduced Graphene Oxides: Light-Weight and High-Efficiency Electromagnetic Interference Shielding at Elevated TemperaturesThe effects of temperature and frequency on the dielectric properties, electromagnetic interference shielding and microwave-absorption of short carbon fiber/silica compositesTemperature dependent microwave attenuation behavior for carbon-nanotube/silica compositesStructural, electrical and magnetic properties of carbon–nickel composite thin filmsTemperature dependence of conduction mechanism of ZnO and Co-doped ZnO thin filmsMetal–nonmetal transition in the copper–carbon nanocomposite filmsQuantum localization versus classical percolation and the metal-nonmetal transition in Hg-Xe filmsTunneling and percolation in metal-insulator composite materialsDeposition of amorphous carbon–silver compositesElectron‐beam fabrication of 80‐Å metal structuresEnhanced magnetization of nanostructured granular Ni/[Cu(II)–C–O] filmsPower spectral densities and polaron hopping conduction parameters in carbon films embedded by nickel nanoparticlesNonmetal–metal transition in carbon films embedded by nickel nanoparticles: absorption coefficients studies and Wemple–Didomenico dispersion parametersElectric Susceptibility and Energy Loss Functions of Carbon-Nickel Composite Films at Different Deposition TimesMicromorphology characterization of copper thin films by AFM and fractal analysisFERROMAGNETISM IN SEMICONDUCTOR C–Ni FILMS AT DIFFERENT ANNEALING TEMPERATURESolidCharge transport mechanism in high conductivity undoped tin oxide thin films deposited by reactive sputteringMultiphonon hopping of carriers in CuO thin filmsPhonon-Assisted Jump Rate in Noncrystalline SolidsMott and Efros-Shklovskii hopping conductions in porous silicon nanostructuresInfluence of Annealing Temperature on Berthelot-Type Hopping Conduction Mechanism in Carbon-Nickel Composite FilmsOverlapping large polaron tunneling conductivity and giant dielectric constant in Ni0.5Zn0.5Fe1.5Cr0.5O4 nanoparticles (NPs)Quantum tunnelling and the temperature dependent DC conduction in low-conductivity semiconductorsUnified model for the luminescence and transport data in self-supporting porous silicon
[1] Dejam L, Elahi S M, Nazari H H et al 2016 J. Mater. Sci.: Mater. Electron. 27 685
[2] Dalouji V, Elahi S M, Solaymani S et al 2016 Appl. Phys. A 122 541
[3] Ghodselahi T, Solaymani S, Akbarzadeh Pasha M et al 2012 Eur. Phys. J. D 66 299
[4] Chang Y Y, Wang D Y and Wu W 2002 Thin Solid Films 420 241
[5] Ţǎlu Ş Bramowicz M, Kulesza S et al 2016 J. Microsc. 264 143
[6] Ţǎlu Ş Bramowicz M, Kulesza S et al 2016 Electron. Mater. Lett. 12 580
[7] Ţǎlu Ş Bramowicz M, Kulesza S et al 2017 Opt. Quantum Electron. 49 204
[8] Kaiser A B and Skákalová V 2011 Chem. Soc. Rev. 40 3786
[9] Wen B, Cao M, Lu M et al 2014 Adv. Mater. 26 3484
[10] Cao M S, Song W L and Hou Z L 2010 Carbon 48 788
[11] Wen B, Cao M S and Hou Z L 2013 Carbon 65 124
[12] Sedlackova K, Lobotka P, Vavra I et al 2005 Carbon 43 2192
[13] Kumar R and Khare N 2008 Thin Solid Films 516 1302
[14] Ghodselahi T, Vesaghi M A, Shafiekhani A et al 2010 Physica B 405 3949
[15] Epstein K, Goldman A M and Kadin A M 1983 Phys. Rev. B 27 6685
[16] Toker D, Azulay D, Shimoni N et al 2003 Phys. Rev. B 68 041403
[17] Garcia-Zarco O, Rodil S E and Camacho-Lopez M A 2009 Thin Solid Films 518 1493
[18] Broers A N, Molzen W W, Cuomo J J et al 1976 Appl. Phys. Lett. 29 596
[19] Chow G M, Ding J and Zhang J 2002 Appl. Phys. Lett. 80 1028
[20] Dalouji V 2017 Optik 148 1
[21] Dalouji V and Asareh N 2017 Opt. Quantum Electron. 49 262
[22] Dalouji V, Elahi S M and Ahmadmarvili A 2017 Silicon 9 717
[23] Ţǎlu Ş Bramowicz M, Kulesza S et al 2016 Microsc. Res. Tech. 79 1208
[24] Dalouji V and Elahi S M 2016 Surf. Rev. Lett. 23 1650002
[25] Dalouji V 2016 Mater. Sci.-Poland 34 337
[26] Bansal S, Pandya D K and Kashyap S C 2012 Thin Solid Films 524 30
[27] Serin T, Yildiz A, Sahin S H et al 2011 Physica B 406 3551
[28]Singh J and Shimakawa K 2003 Advances in Amorphous Semiconductors (London: Taylor & Francis)
[29] Emin D 1974 Phys. Rev. Lett. 32 303
[30] Islam M N, Ram S K and Kumar S 2009 Physica E 41 1025
[31] Dalouji V, Elahi S M, Ghaderi A et al 2016 Chin. Phys. Lett. 33 057203
[32] Tan M, Köseoglu Y, Alan F et al 2011 J. Alloys Compd. 509 9399
[33] Hurd C M 1985 J. Phys. C: Solid State Phys. 18 1985 6487
[34] Mehra R M, Vivechana A, Vijay A S et al 1998 J. Appl. Phys. 83 2235
[35]Mott N F and Davis E A 1971 Electronic Processes in Non-Crystalline Materials (Oxford: Clarendon Press)