To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Bendable p-type NiO and n-type In2O3 thin films were epitaxially grown on synthetic mica using mist chemical vapor deposition. It was found that at a growth temperature of 400 °C, epitaxially grown cubic (111) NiO thin films developed twin rotational domains, and the epitaxial relationship between each domain and the substrate was (111) NiO [1-10] or [10-1] || (001) synthetic mica . In the visible light region, the epitaxial NiO thin films showed high transparencies, and their cut-offs appeared in the UV region. Additionally, at a growth temperature of 500 °C, cubic (111) In2O3 thin films with and without Sn doping were epitaxially grown on synthetic mica. As a result of the plasma oscillation of free carriers, Sn-doped In2O3 thin films exhibited reflection characteristics in the infrared region, while maintaining their visible light transmission characteristics. Furthermore, compared with non-doped In2O3, Sn doping decreased the sheet resistance by two digits.
Al-doped ZnO (AZO) is a promising earth-abundant alternative to Sn-doped In2O3 (ITO) as an n-type transparent conductor for electronic and photovoltaic devices. We have deposited AZO films with resistivities as low as 1.1 × 10−3 Ω·cm by atomic layer deposition (ALD) using trimethylaluminum (TMA), diethylzinc (DEZ), and water at 200 °C. The work functions of the films were measured using a scanning Kelvin probe (sKP) to investigate the role of aluminum concentration. The work function of AZO films prepared by two different ALD recipes were compared: a “Al-terminated” recipe and a “ZnO-terminated” recipe. As aluminum doping increases, the Al-terminated recipe produces films with a consistently higher work function than the ZnO-terminated recipe. The resistivity of the Al-terminated recipe films shows a minimum at a 1:16 Al:Zn atomic ratio and using a ZnO-terminated recipe, minimum resistivity was seen at 1:19. The film thicknesses were characterized by ellipsometry, chemical composition by EDX, and resistivity by a four-point probe.
Sn2Nb2O7 and SnNb2O6 are promising candidates for wide-gap p-type conducting oxides with high mobility, because their valence-band maximum are composed of Sn 5s orbital with large spatial spreading and isotropic nature. Though hole carriers were generated by Sn4+ substitutional defects on Nb5+ site (Sn’Nb) in the substructure of Nb2O6 octahedra in both tin niobates, the generation efficiency of hole carriers in SnNb2O6 was larger than that of Sn2Nb2O7. From the variation in bond length of Nb-O in the Nb2O6 octahedra calculated by Rietveld analysis, the difference in carrier generation efficiency of two tin niobates was examined. The bond length of Nb-O in p-type Sn2Nb2O7 with large amounts of Sn’Nb was smaller than that of n-type Sn2Nb2O7 with small amounts of Sn’Nb. The holes generated by Sn’Nb were considered to be captured by the negative charge of oxygen anions consisting of the Nb2O6 octahedra, resulting in low carrier generation efficiency. In SnNb2O6 showing higher efficiency, Nb-O was 8.6 % larger than that of p-type Sn2Nb2O7. It is considered that the large Nb-O bond length provide the preferred environment for the generation of positive holes, resulting in the higher carrier generation efficiency.
Indium oxide (InOx) and indium tin oxide (ITO) thin films were deposited on glass substrates by plasma enhanced reactive thermal evaporation (PERTE) at different substrate temperatures. The films were then submitted to two etching solutions with different chemical reactivity: i) HNO3 (6%), at room temperature; ii) HCl (35%): (40 °Bé) FeCl3 (1:1), at 40 °C. The dependence of the etchability of the films on the structural and deposition conditions is discussed. Previously to etching, structural characterization was made. X-ray diffraction showed the appearance of a peak around 2θ=31° as the deposition temperature increases from room temperature to 190 °C, both for ITO and InOx. AFM surface topography and SEM micrographs of the deposited films are consistent with the structural properties suggested by X-ray spectra: as the deposition temperature increases, the surface changes from a finely grained structure to a material with a larger-sized grain or/and agglomerate structure of the order of 250-300 nm. The roughness Rq varies from 0.74 nm for the amorphous tissue to a maximum of 10.83 nm for the sample with the biggest crystalline grains. Raman spectra are also presented.
We report first principles spin-polarized density functional theory calculations to study the electronic structure of pure and Magnesium doped (replacing Al) CuAlO2 and AgAlO2 transparent conducting oxides in the hexagonal 2H structural phase. Hole effective masses are obtained from the band structure. Additionally, the complex dielectric function is obtained. A discussion of the effects of Mg-doping on the optical properties and its effectiveness in reducing hole effective masses and increasing conductivity is also presented.
We present the optical and electrical properties of ITO and AZO films fabricated directly on silicon substrates under several growth and annealing temperatures, as well as their potential performance when used as low emissivity coatings in hybrid photovoltaic-thermal systems. We use broadband spectroscopic ellipsometry measurements (from 300 nm to 20 μm) to obtain a consistent model for the permittivity of each of the films. The best performance is found using the properties of the ITO film grown at 250 °C, with a state of the art resistivity of 0.2 mΩ-cm and an optimized thickness of 75 nm which leads to an estimated 50% increase in the extracted power compared to a standard diffused silicon solar cell. The Hall mobility and resistivity measurements of all the films are also provided, complementing and supporting the observed optical properties.
We employed ultrasonic spray deposition method for production of high quality FTO
thin film TCOs to be employed in a silver embedded grid type and monolithic type
dye sensitized solar modules. Produced films exhibited dense and crystalline
structure with homogeneous coverage on solar glass substrates. Obtained
resistivity and light transmission values of FTO are comparable to commercially
available FTO coated glasses used widely in the industry. After optimization of
the chemistry and deposition conditions, 10x10 cm sized glass substrates could
be produced for large area photovoltaic modules. Produced FTO films were used to
construct monolithic type and parallel type dye sensitized solar modules.
Monolithic modules yielded 1.61% active area efficiency value. In order to
enhance the active area of the parallel type modules, silver grid lines were
embedded in glass substrate and FTO coating was deposited on the lines. Due to
this effective design, we achieved 2.42% efficiency on the total area of the
55x55 mm sized module compared to 2.90% active area efficiency, proving that
this design is suitable for enhancing efficiency values of parallel type dye
sensitized solar modules.
The cross-plane thermal conductivities of InGaZnO (IGZO) thin films in different morphologies were measured on three occasions within 19 months, using the 3ω method at room temperature 300 K. Amorphous (a-), semi-crystalline (semi-c-) and crystalline (c-) IGZO films were grown by pulsed laser deposition (PLD), followed by X-ray diffraction (XRD) for evaluation of film quality and crystallinity. Semi-c-IGZO shows the highest thermal conductivity, even higher than the most ordered crystal-like phase. After being stored in dry low-oxygen environment for months, a drastic decrease of semi-c-IGZO thermal conductivity was observed, while the thermal conductivity slightly reduced in c-IGZO and remained unchanged in a-IGZO. This change in thermal conductivity with storage time can be attributed to film structural relaxation and vacancy diffusion to grain boundaries.
Wrinkle-less graphene films are obtained through roll-to-roll microwave plasma chemical vapor deposition by using flexible copper/polyimide (Cu/PI) webs. Raman spectra suggests that the average domain size of the obtained graphene on the flexible Cu/PI is almost the same compared to the graphene on a Cu web that includes wrinkles. Also, by utilizing the flexible Cu/PI webs, the compressive strains decreased. The sheet resistances of graphene deposited on the Cu/PI are (1∼5)×104Ω, which is two orders of magnitude lower than those of graphene deposited on the Cu webs. Our results suggest that the controlling the expansion of web material an important technology to improve graphene transparent conductive properties.
In this work, we have reported the interface characterization of rf sputtered ZnO/HfO2 in thin film transistor structure by dc current-voltage and admittance spectroscopy. The interface state density (Dit) of 1013 eV−1cm−2 was extracted from the Gp/ω vs ω plot was comparable to value obtained from the subthreshold behavior. The grain boundary trap density (NGB) of 9.12×1012 cm−2 was estimated using Levinson’s model. The interface state density distribution below the conduction band edge shows a decreasing trend with energy below the conduction band edge. We also studied the impact of introducing MgO interfacial layer between ZnO and HfO2 interface as an approach towards decreasing the interface state density.
Transparent conducting thin-films of SnO2: F were grown on preheated glass, Al2O3 coated glass, and quartz substrates by Streaming Process for Electrodeless Electrochemical Deposition (SPEED). Stannic chloride (SnCl4) and ammonium fluoride (NH4F) dissolved in a mixture of deionized water and organic solvents were used as precursors. The preheated substrate temperature was varied between 440 and 500 °C. High quality SnO2:F films were grown at all the substrate temperatures studied. The resulting typical film thickness was 250 nm. X-ray diffraction shows that the grown films are polycrystalline SnO2 with a tetragonal crystal structure. The average optical transmission of the films was around 93% throughout the wavelength range 400 to 1000 nm. The lowest electrical resistivity achieved was 6 × 10-4 Ω-cm. The Hall measurements showed that the film is an n-type semiconductor, with carrier mobility of 8.3 cm2/V-s, and carrier concentration of 1 × 1021 cm-3. The direct bandgap was determined to be 4.0 eV from the transmittance spectrum.
Radiation-tolerant materials, sensors and electronics can enable lightweight space subsystems with reduced packaging requirements and increased operation lifetimes. Such technology can be used within extreme harsh environments related to space exploration, radiation medicine and power generation (combustion and nuclear). Gallium nitride (GaN), a ceramic semiconductor material, is a candidate material due to its stability within high-radiation, high-temperature and chemically corrosive environments. In addition, the wide bandgap of GaN (3.4 eV) can be leveraged for ultraviolet (UV) wavelength photodetection. In metal-semiconductor-metal (MSM) photodetector architectures using Schottky contacts, transparent electrodes (e.g., graphene) can increase sensitivity and improve overall device response. Here we present fabrication and characterization of GaN-based UV photodetectors using graphene electrodes irradiated up to 200 krad total ionizing dose (TID) then tested under UV light and dark conditions. For current-voltage measurements taken at 90, 120 and 200 krad TID, the current-voltage response does not vary significantly. From 90 to 120 krad TID, the responsivity shifts by 2% before dropping off at 200 krad TID. These initial findings suggest that graphene/GaN MSM UV photodetectors can provide robust operation within extreme harsh environments.
The polyaniline (PANI) and regioregular poly(3-hexylthiophene) (P3HTr) are polymers synthesized easily, can be deposited as a film by various techniques, are materials that exhibit a variety of colors to go through oxidation processes and reduction by applying an external potential, both polymers have an immediate response rate of color. The electrochemical behavior of the PANI and P3HTr is complementary, that is, if a positive potential to the device is applied, the PANI film is oxidized while the P3HTr film is reduced, on the other hand, if a negative potential is applied, the PANI film is reduced while the P3HTr film is oxidized. Both films in its redox process are clarified and obscured at the same time, this color change provides a significant difference in optical transmittance on a dual electrochromic device (DED's).
In this research, regioregular poly(3-hexylthiophene) was synthesized and characterized, films were deposited by spin-coating and dip-coating techniques. Polyaniline films were deposited by chemical bath and spin-coating techniques. Dual electrochromic devices based on P3HTr and PANI were prepared. The devices were studied by UV-vis spectroscopy at three different voltages: 1.4 V, 0 V and -1.4 V, optical kinetic tests were also performed at 550 nm applying a positive potential (1.4 V) and negative (-1.4 V). The results indicated the wavelength where both (PANI and P3HT) reach the greatest difference in transmittance. The influence of deposit type of polymer films on electrochromic response was determined.
Rutile TiO2 is well known for its ability to “trap” photoinduced electrons at Ti4+ ions and form Ti3+ ions with an unpaired d1 electron. This has been shown experimentally to result in a large family of similar, yet slightly different, Ti3+-related centers that include both intrinsic small polarons and donor-bound small polarons. In these latter centers, the Ti3+ ion is located next to an oxygen vacancy or an impurity such as fluorine, lithium, or hydrogen. These small polarons are easily formed in commercially available bulk single crystals of rutile TiO2 by illuminating oxidized (and nominally undoped) samples at temperatures between 5 and 30 K with sub-band-gap laser light (e.g., 442 nm) or by slight reducing treatments (in the case of hydrogen). Once formed, the ground states of the defects are readily studied at low temperature with magnetic resonance (EPR and ENDOR). Single crystals of rutile TiO2 provide complete sets of angular dependence data, and thus allow detailed information about the ground-state models of the electron traps to be extracted in the form of g matrices and hyperfine matrices. In this review, the differences and similarities of the various Ti3+-related trapped electron centers are described.
In recent years, the emerging areas of nanophotonics and, in particular, plasmonics and metamaterials, have seen an explosion of novel ideas. However, transforming revolutionary designs into practical devices requires a significant amount of effort. The constituent materials in plasmonic structures and metamaterials play a crucial role in realizing useful and efficient devices. Similar to the way silicon shaped the nanoelectronics field, finding the best set of materials for plasmonic and metamaterial devices could revolutionize the field of nanophotonics. As a potential solution, alternative plasmonic materials have recently gained significant attention. Metals, despite being essential components of plasmonic and metamaterial devices, pose many technological challenges toward the realization of practical devices—primarily due to their high optical loss, integration, and fabrication limitations. Hence, searching for an alternative is vital to the success of future nanophotonic devices. Several classes of materials, including doped semiconductor oxides and ceramics, are discussed as potential alternatives to metals that could lead to devices with drastically improved performance and new functionalities by providing low intrinsic loss, tunability, and compatibility with standard semiconductor fabrication processes.
Tin oxide is one of the popular metal oxide semiconductor used in solar cells, sensors, and catalysts. The surface modification by organic self assembled monolayer is one of the promising techniques to tune and to control the surface work function. In our study, we investigated the work function change of the SnO2 (110) surface which was modified with various benzoic acids derivatives using density functional theory (DFT). All calculations were carried out on Quantum Espresso program. Electron correlation and exchange parts were treated by local density (LDA), generalized gradient approximation (GGA) with Hubbard U term. To improve band structure calculation we used LDA+U method. The results of the calculation with LDA method indicated that the work functions of the pure and modified surface of SnO2 (110) with -C6H4-COOH molecule were calculated to be 7.40 eV and 6.18 eV, respectively. As the experimental value of work function of SnO2 (110) surface is about 7.74 eV, the results of the DFT calculation for pure SnO2 (110) surface modification by benzoic acid derivatives are in good agreement with the experimental.
Nb-doped TiO2 (TNO) films, Ga-doped ZnO (GZO) films and TNO/GZO layered films were fabricated on glass substrates and electrical properties of TNO/GZO layered films were investigated in terms of interaction between TNO and GZO layers. By a thermal annealing in vacuum, the observed resistivity of the TNO/GZO layered films was lower than that of the single layered films fabricated and annealed at the same conditions. The resistivity reduction observed in the layered structure is not explained by the parallel connection of the TNO and GZO layers, indicating that there exists an interaction between these two layers. The TNO/GZO films with low resistivity have still been transparent.
Interest in patterned polymer-based flexible nanodevices and sub-100 nm metal and transparent conducting nanostructured electrodes have led us to modify the traditional nanoimprint lithography technique to enable fabrication of an array of sub-100 nm diameter electrode structures. Transparent conducting electrodes (TCOs) are fabricated by coating one or multiple TCO layers of choice on top of a polymer nanostructured scaffold of appropriate dimension. By optimizing the thickness of each of these layers one may tune and optimize the trade-off between the conductivity and transparency of the sample. Incorporation of plasmonic materials such as Ag leads to interplay of localized and tunable surface plasmon resonances within the TCO structures. At plasmon resonance the reflection of the sample is minimized and absorption in the TCO structures dominates. Experimental and simulated reflection spectra of these structures are in good agreement, including the appearance of sharp spectral features that are absent in a simple planar analog. The simulated Brewster angle of the nanopillars decreases compared to the planar reference sample by up to 10-13 degrees depending on the height of the pillars and indicates a reduced effective refractive index. The depolarization factor obtained by ellipsometry is about 0.05, as anticipated for ellipsoidal pillars.
We investigated electrical and structural properties of Ta-doped SnO2 (TTO) films on anatase TiO2 seed layers with various growth parameters of pulsed laser deposition. We found that anatase TiO2 seed layers induced pseudo-epitaxial (100) growth of TTO films with enhanced mobility (μ) in a wide range of growth parameters. The highest μ of 83 cm2V-1s-1 [resistivity (ρ) of 2.8 × 10-4 Ωcm] and the lowest ρ of 1.8 × 10-4 Ωcm (μ of 60 cm2V-1s-1) were obtained at a substrate temperature of 600 °C. Amorphization and (101)-preferred growth competed with (100) growth on the TiO2 seed layer at low temperatures. Introducing sufficient process oxygen suppressed such unwanted film growth, resulting in improved transport properties.
Transparent conducting cadmium tin oxide (CTO) thin films were obtained from a mixture of CdO and SnO2 precursor solutions by the dip-coating sol-gel technique. The thin films studied in this work were made with 7 coats (∼200 nm) on corning glass and quartz substrates. Each coating was deposited at a withdrawal speed of 2 cm/min, dried at 100°C for 1 hour and then sintered at 550°C for 1 hour in air. In order to decrease the resistivity values of the films, these were annealed in a vacuum atmosphere and another set of films were annealed in an Ar/CdS atmosphere. The annealing temperatures (Ta) were 450°C, 500°C and 550°C, as well as 600°C and 650°C, when corning glass and quartz substrates were used, respectively. X-Ray diffraction (XRD) patterns of the films annealed in a vacuum showed that there is only the presence of CTO crystals for 450°C≤ Ta ≤ 600°C and CTO+SnO2 crystals for Ta=650°C. The films annealed in Ar/CdS atmosphere were only constituted of CTO crystals independent of the Ta. The minimum resistivity value obtained was ∼4 x 10-4 Ωcm (Rsheet= 20 Ω/□) for the films deposited on quartz and annealed at Ta=600°C under an Ar/CdS atmosphere. The films deposited on quartz showed the higher optical transmission (∼90%) with respect to the films deposited on corning glass substrates (∼85%) in the Uv-vis region. For their optical and electrical characteristics, these films are good candidates as transparent electrodes in solar cells.