Conduction in non-crystalline systems V. Conductivity, optical absorption and photoconductivity in amorphous semiconductors

Davis, E. A.; Mott, N. F.

doi:10.1080/14786437008221061

Cited by 3,683 publications

(707 citation statements)

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“…Using the method developed by Tauc et al 38 to determine the value of an optical bandgap, a function of the product of the absorbance (α) and the photon energy (E) may be plotted as a function of photon energy and the x-intercept of a fit of the linear region gives the value of the optical band gap (Figure 3f). Because slightly different treatments of the density of states and matrix elements gives rise to different functional forms to be plotted on the ordinate, 39 we have used the square root of the product of the absorbance and the photon energy, (αE) 1/2 , as it is appropriate for the electrical states of a-C and hydrogenated amorphous carbon (a-C:H) 22 and fits the data reported here well. This optical gap is associated with π to π* band transitions in the aromatic domains, and we report values of 0.68 eV in anthracite and 1.8 eV in hvAb films.…”

Section: * S Supporting Informationmentioning

confidence: 99%

Rethinking Coal: Thin Films of Solution Processed Natural Carbon Nanoparticles for Electronic Devices

2016

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Disordered carbon materials, both amorphous and with long-range order, have been used in a variety of applications, from conductive additives and contact materials to transistors and photovoltaics. Here we show a flexible solution-based method of preparing thin films with tunable electrical properties from suspensions of ball-milled coals following centrifugation. The as-prepared films retain the rich carbon chemistry of the starting coals with conductivities ranging over orders of magnitude, and thermal treatment of the resulting films further tunes the electrical conductivity in excess of 7 orders of magnitude. Optical absorption measurements demonstrate tunable optical gaps from 0 to 1.8 eV. Through low-temperature conductivity measurements and Raman spectroscopy, we demonstrate that variable range hopping controls the electrical properties in as-prepared and thermally treated films and that annealing increases the sp 2 content, localization length, and disorder. The measured hopping energies demonstrate electronic properties similar to amorphous carbon materials and reduced graphene oxide. Finally, Joule heating devices were fabricated from coal-based films, and temperatures as high as 285°C with excellent stability were achieved. KEYWORDS: Coal, amorphous carbon, organic semiconductors, thin films, solution processing C arbon has long been known as one of the most chemically versatile elements. As a result, carbonaceous materials have been of technological interest for their wide range of electronic propertiesresulting in materials ranging from low cost conducting materials such as graphite and carbon black, to semiconducting fullerenes and carbon nanotubes, and to insulating diamond and diamond-like carbon. Specifically, carbon black, carbon filaments, and other carbon materials are used in electrodes, conductivity additives, and electromagnetic reflectors. 1 Graphitic materials 2 and amorphous carbon (a-C) 3,4 are the leading and a promising candidate, respectively, for anode materials in lithium ion batteries. Amorphous carbon has also been used in the manufacturing of transistors 5,6 and photovoltaic devices, 7,8 and nanostructured graphitic materials (such as graphene and reduced graphene oxide) have gained significant attention for applications including in photovoltaics, 9−11 transparent conductive membranes, 12−16 and Joule heating devices. 17−19 Despite decades of research on synthetically processed carbon materials, facile, tunable, 20 low-temperature, solution processing methods remain elusive. Carbon black synthesis requires temperatures as high as 2000°C, 21 and a-C is typically deposited by plasma-enhanced chemical vapor deposition (CVD) 22,23 although aerosol-assisted CVD has recently been demonstrated. 8 While extensive research has been conducted to develop solution-based methods of graphene deposition, rGO films remain several orders of magnitude less conductive than CVD graphene. 16,24,25 In contrast to the widely studied world of synthetic carbonaceous materials, the optical...

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Section: * S Supporting Informationmentioning

confidence: 99%

Rethinking Coal: Thin Films of Solution Processed Natural Carbon Nanoparticles for Electronic Devices

2016

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“…It is clear that these values vary largely with composition in an irregular trend, within the range from 0.16 to 0.73 eV for PVPGdCl 3 films and in the range from 0.09 to 0.52 eV for PVP-HoCl 3 films. Thus, a model based on the electronic transition between localized states suggests that some tail states are generated in the systems under investigation 33 in which the dopant concentration has an important role in morphological and microstructural changes occurring in the polymer matrix. [33][34][35] Figure 6 Representative plots of (a) (ahu) 2 vs hu for pure PVP, PVP+10 wt% GdCl 3 and PVP+10 wt% HoCl 3 films, and (b) (ahu) 1/2 vs hu for pure PVP, PVP+10 wt% GdCl 3 and PVP+10 wt% HoCl 3 films.…”

Section: Ir Spectramentioning

confidence: 99%

“…33 The range of the validity of this equation is too small, and hence it becomes very difficult to determine the exact value of the exponent r. 34 In this study, the fits for all values of r were compared for different compositions of the PVP-GdCl 3 and PVP-HoCl 3 films. It was found that the values r¼2 and r¼½ gave a better fit to the experimental results than the other exponents, suggesting the existence of both direct and indirect types of optical transition.…”

Section: Ir Spectramentioning

confidence: 99%

Magnetic and optical studies on polyvinylpyrrolidone thin films doped with rare earth metal salts

Basha

2010

Polym J

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A casting technique was used to prepare new nanocomposite thin films of pure and GdCl 3 -or HoCl 3 -doped polyvinylpyrrolidone (PVP). Transmission electron microscopy (TEM) was used to study the particle size and dispersibility in the investigated nanocomposites. Magnetic measurements, using a vibrating sample magnetometer (VSM), were carried out at room temperature and applied magnetic fields up to 10 kO e . The appearance of hysteresis loops with small values of saturation flux density (B s ), remanent flux density (B r ), squareness ratio (SQR) and coercive field (H c ), along with permeability (l) values relatively higher than 1, may be taken, as a matter of experimentation, to consider the investigated composites as soft magnet materials. In this study, PVP-HoCl 3 films showed slightly better magnetic properties compared with PVP-GdCl 3 films. A comparative analysis of infrared (IR) and ultraviolet-visible spectra of the parent components and their composites indicated the effective role of dopant nature and concentration in morphological and microstructural changes occurring in the PVP matrix. Optical constants, such as the energy gap (E g ) and the Urbach tail (E e ), were determined and discussed in terms of a model based on the electronic transition between localized states in the band structure.

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“…However, it is to note that in most of the bulk glasses including the present one α seems to be in the order of 10 2 -10 3 cm -1 even if the thickness is reduced to a few tens of centimetres. The above equation (1) is still suitable to apply because the absorption edge in disordered materials is usually interpreted in terms of indirect transitions across the optical band gap [25]. Since this equation can be readjusted to represent the linearity between (αћω) 1/2 and (ћω -E opt ), following the procedure given by Dayanand et al [26], the E opt value is determined from the plot of (αћω) 1/2 versus ћω (eV).…”

Section: Resultsmentioning

confidence: 99%

“…The slow exponential rise of absorption is an indication of indirect transitions of electrons. Using the Tauc equation [24], optical band gap is calculated for these glasses, and absorption coefficient (α) from the expression (1) [25] (1) where C is constant and α expected to be > 10 4 cm -1 in the case of direct transitions. However, it is to note that in most of the bulk glasses including the present one α seems to be in the order of 10 2 -10 3 cm -1 even if the thickness is reduced to a few tens of centimetres.…”

Section: Resultsmentioning

confidence: 99%

Structural Investigations of Cr3+ Ions Doped Alkali Lead Zinc Phosphate Glasses

Sastry¹

2015

IJIRSET

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Lead zinc phosphate glasses containing 0.1% transition metal ion Cr 3+ were prepared by melt quenching technique and their amorphous nature confirmed by X-Ray diffraction. The covalent bond nature of Cr 3+ ions with octahedral symmetry in glass network was established through Electron Paramagnetic Resonance and optical absorption spectroscopic studies. Endothermic dip for glass transition temperature (T g ) at about 410 0 C and an exothermic peak subsisted from thermal studies were obtained. De-polymerization of host glass network due to addition of alkali content to the glass matrix, has turned as a strong candidate for nonlinear optical laser applications.

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Conduction in non-crystalline systems V. Conductivity, optical absorption and photoconductivity in amorphous semiconductors

Cited by 3,683 publications

References 36 publications

Rethinking Coal: Thin Films of Solution Processed Natural Carbon Nanoparticles for Electronic Devices

Rethinking Coal: Thin Films of Solution Processed Natural Carbon Nanoparticles for Electronic Devices

Magnetic and optical studies on polyvinylpyrrolidone thin films doped with rare earth metal salts

Structural Investigations of Cr3+ Ions Doped Alkali Lead Zinc Phosphate Glasses

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