Electronic Properties Of Films Research Articles

Field-Effect Transistor Based on 2D Microcrystalline MoS2 Film Grown by Sulfurization of Atomically Layer Deposited MoO3.

Atomically thin molybdenum disulfide (MoS2) is a promising channel material for next-generation thin-body field-effect transistors (FETs), which makes the development of methods allowing for its controllable synthesis over a large area an essential task. Currently, one of the cost-effective ways of its synthesis is the sulfurization of preliminary grown oxide- or metallic film. However, despite apparent progress in this field, the electronic quality of the obtained MoS2 is inferior to that of exfoliated samples, making the detailed investigation of the sulfurized films’ properties of great interest. In this work, we synthesized continuous MoS2 films with a thickness of ≈2.2 nm via the sulfurization of an atomic-layer-deposited MoO3 layer. X-ray photoelectron spectroscopy, transmission electron microscopy, and Raman spectroscopy indicated the appropriate chemical composition and microcrystalline structure of the obtained MoS2 films. The semiconductor quality of the synthesized films was confirmed by the fabrication of a field-effect transistor (FET) with an Ion/Ioff ratio of ≈40, which was limited primarily by the high contact resistance. The Schottky barrier height at the Au/MoS2 interface was found to be ≈1.2 eV indicating the necessity of careful contact engineering. Due to its simplicity and cost-effectiveness, such a technique of MoS2 synthesis still appears to be highly attractive for its applications in next-generation microelectronics. Therefore, further research of the electronic properties of films obtained via this technique is required.

Orientation-dependent stabilization of MgCr2O4 spinel thin films

$A{B}_{2}{\mathrm{O}}_{4}$ normal spinels with a magnetic $B$ site can host a variety of magnetic and orbital frustrations leading to spin-liquid phases and field-induced phase transitions. Here, we report the epitaxial growth of (111)-oriented $\mathrm{Mg}{\mathrm{Cr}}_{2}{\mathrm{O}}_{4}$ thin films. By characterizing the structural and electronic properties of films grown along the (001) and (111) directions, the influence of growth orientation has been studied. Despite distinctly different growth modes observed during deposition, the comprehensive characterization reveals no measurable disorder in the cation distribution nor multivalency issue for Cr ions in either orientation. Contrary to a naive expectation, the (111) stabilized films exhibit a smoother surface and a higher degree of crystallinity than (001)-oriented films. The preference in growth orientation is explained within the framework of heteroepitaxial stabilization in connection to a significantly lower (111) surface energy. These findings open broad opportunities in the fabrication of two-dimensional kagome-triangular heterostructures with emergent magnetic behavior inaccessible in bulk crystals.

Electronic properties of the passive films formed on CoCrFeNi and CoCrFeNiAl high entropy alloys in sodium chloride solution

In the present work, the electronic properties of the passive films formed on equiatomic CoCrFeNi and CoCrFeNiAl high-entropy alloys were investigated in sodium chloride solution. The point defect model (PDM) was employed to study the effect of aluminum addition on the transport of p-type or n-type dopants through the passive films. The crystalline structure of the alloys was determined by X-ray diffraction. CoCrFeNi alloy was comprised of one single face-centered cubic crystalline phase. Aluminum addition promoted the formation of a mixed B2 and BCC structure. X-ray photoelectron spectroscopy (XPS) analysis allowed the examination of the correlation between passive film composition and their electronic properties. The major species in the passive film of the CoCrFeNi alloy were Cr2O3 and Cr(OH)3 while Al2O3 and Al(OH)3 were the predominant species in that of the Al-containing alloy. Electrochemical impedance spectroscopy (EIS) was employed to evaluate the corrosion resistance of the alloys. Aluminum addition promoted the formation of a thicker and more defective passive film. The pitting corrosion susceptibility of the HEAs was dependent on the passive film composition and increased with Al addition. The predominance of n-type defects in the passive film of the CoCrFeNiAl alloy was enhanced upon Al addition. Interaction between passive film composition and the electronic properties of the film played a central role in the corrosion resistance of the high entropy alloys.

Correlation between Electrical Properties of the Passive Film on Carbon Steel and Inhibition Efficiency by Phosphate and Nitrite Ions

The electronic properties of passive films grown at open circuit potential for 24 h and 7 days in pore simulating solutions are correlated to the inhibiting effect of nitrite and phosphate ions in chloride-rich alkaline solutions. Electrochemical impedance and Mott-Schottky plots were used to investigate the electronic properties of the films grown. Changes in composition were analyzed by X-ray photoelectron spectroscopy. Both anions are excellent inhibitors. However, the donor density (ND) decreases when nitrites are incorporated and remains constant when phosphates are added. ND increases with ageing time. These differences are interpreted in terms of the composition of each surface layer.

All-Inorganic Nanocrystal Thin Films Fabricated By Low-Voltage Electrophoretic Deposition

The solution processability of colloidal nanocrystals (NCs) offers prospective next-generation solar cells significantly reduced fabrication costs, yet methods for scalable deposition of conductive, well-adhered NC films have yet to be realized. Electrophoretic deposition (EPD), a low-waste, high-throughput technique used commercially in other fields, is proposed for depositing solution-processed absorbing layers for solar cells. Here we share methods for fabricating all-inorganic semiconductor-NC films through low-voltage EPD. Through light scattering, absorbance spectroscopy and electric measurements, the fundamental electrochemical reactions and transport processes that occur during EPD are studied. Special emphasis is applied to elucidate the requirements for low-voltage EPD of semiconductor NCs. Through insights gleaned from this study, choice of NC-ligand-solvent combinations and reactor design, film electronic properties and morphology improvements are realized. Low-voltage EPD is demonstrated using both continuous flow and batch reactors in this study.

Density functional study of BiSbTeSe2 topological insulator thin films

In this work, using density functional theory calculations, we have investigated the band topology of bulk BiSbTeSe2 and its thin film electronic properties in several thicknesses. It is one member of the quaternary compounds Bi2–xSbxTe3–ySey (BSTS) with the best intrinsic bulk insulating behavior. Based on our calculations we have found that a band inversion at Γ‐point is induced when spin–orbit coupling is turned on, with an energy gap of about 0.318 eV. The film thickness has an effect on the surface states such that a gap opens at Dirac point in 6 quintuple‐layers film and with decrease in thickness, the magnitude of the gap increases. The atomic contributions have been mapped out for the first few layers of thin films to demonstrate the surface states. The relative charge density has been calculated layer‐wise and the penetration depth of the surface states into the bulk region is found to be about 2.5–3.5 quintuple layers, depending on the termination species of thin films.

TCNQ Grown on Cu (001): Its Atomic and Electronic Structure Determination

In this paper we have resolved by means of “in situ” X-ray diffraction studies the atomic structure of the TCNQ films from 0.4 to 17 ML thickness grown on Cu(001) substrate. The film grown at low temperature, is a well crystallized and well oriented single phase. The TCNQ film has a (020) orientation. The electronic properties of the film have been studied by means of XPS and UPS spectroscopies. The measured electronic density has been compared to the theoretical ab-inito calculations. In this paper we have studied the structural and electronic properties of relatively thick films of TCNQ on Cu(100). Our results demonstrate that the strong charge transfer between the metallic substrate and the first layer of TCNQ molecules have important consequences for the film electronic and structural properties of films even as thick as 17 ML. From the structural point of view, the films grow with a well-defined (020) orientation that matches the modified molecular structure of the first layer. This first monolayer s...

Intercorrelation of Electronic, Structural, and Morphological Properties in Nanorods of 2,3,9,10-Tetrafluoropentacene.

We evidence the intercorrelation of electronic, structural, and morphological properties in nanorods of a substituted fluorine-based pentacene, 2,3,9,10-tetrafluoropentacene, deposited on gold single crystals by using photoemission and X-ray absorption spectroscopy investigations. Our investigations show changes in the XPS spectroscopy lines, and NEXAFS features correlate with the specific structure of the assemblies and their morphology. Consequently, the chemical structure affects not only the molecular electronic structure and the way the molecules assemble in a film but also the film morphology leading to specific thin film electronic properties.

Toward High-Efficiency Scalable GaAs and GaAsxP1-X Photoelectrodes Grown Via Vapor Transport from a Solid Source

GaAs and related III-V semiconductors are attractive materials for high-efficiency water-splitting photoelectrodes, but their implementation is limited in part by the high cost of metal-organic chemical vapor deposition, which employs toxic and pyrophoric gas-phase precursors. We report the study of GaAs and GaAsxP1-x grown by close-space vapor transport (CSVT), which uses solid GaAs as a source and water vapor as a transport agent as an alternative low-cost technique for depositing GaAs films and microstructures. The free carrier type and density (1016 – 1019 cm-3) in the films was adjusted by addition of Te or Zn powder to the GaAs source powder. The electronic properties of films grown under a variety of conditions are evaluated and correlated with the film structure and impurity content. We show using photoelectrochemical and electron beam-induced current analyses that the minority carrier diffusion lengths of the n- and p-GaAs epitaxial films reached 2-3 µm and 5-7 µm, respectively. Hall mobilities approach those achieved for GaAs grown by metal organic chemical vapor deposition, 500 - 4,000 cm2 V-1 s-1 for n-GaAs and 50-240 cm2 V-1 s-1 for p-GaAs depending on carrier concentration. Related efforts to control carrier collection through surface texture as well as the growth of GaAs on Si as an inexpensive high-efficiency tandem photoelectrode will also be discussed. Ritenour, A. J.; Boucher, J. W.; DeLancey, R.; Greenaway, A. L.; Aloni, S.; Boettcher, S. W. Doping and Electronic Properties of GaAs Grown by Close-Spaced Vapor Transport from Powder Sources for Scalable III-V Photovoltaics. Energy Environ. Sci. Accepted, 2014. Ritenour, A. J.; Levinrad, S.; Bradley, C.; Cramer, R. C.; Boettcher, S. W. Electrochemical Nanostructuring of n-GaAs Photoanodes. ACS Nano, 2013, 7 (8), 6840–6849. Ritenour, A. J.; Cramer, R. C.; Levinrad, S.; Boettcher, S. W. Efficient n-GaAs Photoelectrodes Grown by Close-Spaced Vapor Transport from a Solid Source. ACS Appl. Mater. Interfaces 2012, 4, 69-73.

Modeling Electronic Properties of the Passive Films on Carbon Steel in Simulated Concrete Pore Solutions

The performance of five existing models for predicting the electronic properties of passive oxide films on carbon steel that are exposed to synthetic alkaline media representing concrete pore solutions was investigated. It was found that the two donor band model, which is based on the presence of two discrete donor bands each with a Gaussian distribution of energy states for an n-type semiconductor, most accurately predicts experimental measurements. The model supports the experimental data that show an increase in the deep donor density and width of the deep donor band with increasing passivation time. A comparison of films formed in different passivating solutions revealed the potential of this model to predict the passive film electronic properties in environments not yet studied experimentally.

Insulating FerromagneticLaCoO3−δFilms: A Phase Induced by Ordering of Oxygen Vacancies

The origin of ferromagnetism in strained epitaxial ${\mathrm{LaCoO}}_{3}$ films has been a long-standing mystery. Here, we combine atomically resolved $Z$-contrast imaging, electron-energy-loss spectroscopy, and density-functional calculations to demonstrate that, in epitaxial ${\mathrm{LaCoO}}_{3}$ films, oxygen-vacancy superstructures release strain, control the film's electronic properties, and produce the observed ferromagnetism via the excess electrons in the Co $d$ states. Although oxygen vacancies typically dope a material $n$-type, we find that ordered vacancies induce Peierls-like minigaps which, combined with strain relaxation, trigger a nonlinear rupture of the energy bands, resulting in insulating behavior.

Conjugated Thiophene-Containing Polymer Zwitterions: Direct Synthesis and Thin Film Electronic Properties

We report a direct and facile synthesis of novel conjugated polymeric zwitterions (CPZs) as a simple route to electronically active homopolymers and copolymers containing dipole-inducing pendent zwitterions. Sulfobetaine-containing polythiophenes (PTSB-1 and PTSB-2) and alternating thiophene–benzothiadiazoles (PTBTSB-1 and PTBTSB-2) were prepared and characterized relative to alkylated polymer analogues (POT-a-T and POT-a-BT). The polar zwitterionic side chains make these polymers hydrophilic and salt-responsive, with interesting electronic properties that depend on zwitterion distance from the conjugated polymer backbone (tether length), as characterized by UV–vis absorption and ultraviolet photoelectron spectroscopy (UPS). Close proximity (CH2 spacer) of the sulfobetaine groups to the polymer backbone results in increased ionization potential and enlarged band gaps of 2.19 and 2.04 eV for PTSB-1 and PTBTSB-1, respectively. On Au and Ag surfaces, the zwitterionic pendent groups significantly alter the work function due to the presence of an interfacial dipole, with the largest interfacial dipoles measuring −1.29 eV (PTBTSB-1/Au) and −0.69 eV (PTBTSB-1/Ag).

Thin Film Electronic Properties of Ternary Topological Insulator

ABSTRACTUsing an ab initio density functional theory (DFT), we study thin film electronic properties of topological insulators (TIs) based on ternary compounds of Tl (thallium) and Bi (bismuth). We consider TlBiX2 (X=Se, Te) and Bi2X2Y (X, Y=Se, Te) compounds. Here we discuss the nature of surface states, their locations in the Brillouin Zone (BZ) and their interactions within the bulk region. Our calculations suggest a critical film thickness to maintain the Dirac cone which is smaller than that in binary Bi-based compounds. Atomic relaxations are found to affect the Dirac cone in some of these compounds. We discuss the penetration depth of surface states into the bulk region.

Structural, electronic, and optical properties of ITO thin films prepared at room temperature by pulsed laser deposition

In this work, indium tin oxide (ITO) thin films have been prepared by pulsed laser deposition (PLD) on quartz and silicon substrates at room temperature, starting from an ITO target with a Sn/In concentration ratio of 0.18. Structural, optical, and electronic properties of these films have been analyzed by means of X-ray photoemission and optical spectroscopy. By the analysis of the X-ray photoemission spectroscopy spectra in the In 3d5/2, Sn 3d5/2, and O 1s binding energy regions, carried out both for films and target, evidence of structural changes after the ablation process was found. It was deduced that the deposited films have an Sn/In ratio equal to 0.10, and are characterized by a predominantly amorphous structure. The optical properties in the visible and the near ultraviolet regions have been deduced by near normal incidence optical reflectivity and absorption measurements. A value of 3.7 eV for the optical band gap and an average refraction index of about 3.0 in the visible photon energy range have been obtained, in agreement with the results of other authors.

Pressure-induced phenomena in single-walled carbon nanotubes probed by infrared spectroscopy

The electronic properties of films of unoriented single-walled carbon nanotubes were studied by transmission measurements as a function of pressure. The energies of the optical transitions between the Van Hove singularities decrease with increasing pressure, which can be attributed to pressure-induced hybridization and symmetry-breaking effects. We observe an anomaly in the pressure-induced shift of the optical transitions at around 2 GPa due to a structural phase transition. The low-energy absorbance monotonically decreases with increasing pressure, suggesting an increasing carrier localization.

Hydrogen Plasma Annealing of ZnO Films Deposited by Magnetron Sputtering with Third Electrode

Al doped zinc oxide (AZO) films were deposited using a radio frequency (rf) magnetron sputtering apparatus with a mesh grid electrode. Improvement of crystalline uniformity was achieved by the use of an appropriate negative grid bias to effectively suppress the bombardment of high-energy charged particles onto the film surface. The uniformity of the film's electronic properties, such as resistivity, carrier concentration and Hall mobility, was also improved using the sputtering method. Hydrogen plasma annealing was investigated to further decrease the resistivity of the ZnO films and the carrier concentration was increased by 1-2×1020cm-3 without decrease in the Hall mobility.

Interfacial properties between CoO (100) andFe3O4(100)

Using molecular beam epitaxy 1\char21{}20 ML thick CoO (100) films were grown monolayer by monolayer on ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ (100) substrates. The stoichiometry of the films was verified by low-energy-electron diffraction and reflection-high-energy-electron diffraction patterns, as well as x-ray photoelectron spectroscopy. Auger measurements as a function of CoO film thickness indicated a layer-by-layer growth mode. Ultraviolet photoelectron spectroscopy (UPS) was used to monitor the thin film electronic properties. The evolution of the density of states in the $\mathrm{O}\phantom{\rule{0.2em}{0ex}}2p∕\mathrm{Fe}\phantom{\rule{0.2em}{0ex}}3d$ and $\mathrm{O}\phantom{\rule{0.2em}{0ex}}2p∕\mathrm{Co}\phantom{\rule{0.2em}{0ex}}3d$ bands exhibits a shift in the position of the CoO valence band for ultrathin films relative to bulklike thick films. The measured spectra (when aligned to cancel the band shift) are compared to models of the spectra that would be expected based on the bulk compounds, with and without additional interfacial electronic states. Electronic states at the ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}\text{\ensuremath{-}}\mathrm{Co}\mathrm{O}$ interface have been identified, and their UPS spectrum has been determined.

Optoelectronic properties of expanding thermal plasma deposited textured zinc oxide: Effect of aluminum doping

Aluminum-doped zinc oxide films exhibiting a rough surface morphology are deposited on glass substrates utilizing expanding thermal plasma. Spectroscopic ellipsometry is used to evaluate optical and electronic film properties. The presence of aluminum donors in doped films is confirmed by a shift in the zinc oxide bandgap energy from 3.32 to 3.65 eV. In combination with transmission reflection measurements in the visible and NIR ranges, charge carrier densities, optical mobilities, and film resistivities have been obtained from the free carrier absorption. Film resistivities are consistent with direct measurements, values as low as 6.0×10−4 ω cm have been obtained. The interdependence of electrical conductivity, film composition, and film morphology is addressed.

Electrochemical & optical characterisation of passive films on stainless steels

The formation and breakdown of the passive film are mainly controlled by ionic and electronic transport processes; processes that are in turn controlled by the electronic properties of the film. Consequently a comprehensive understanding of mechanisms behind passivity and localised corrosion require a detailed perception of the electronic properties of the passive films together with compositional and structural information. As a step towards this goal the passive film on austenitic stainless steel, AISI 316L, formed in borate solution was characterised by in situ Raman spectroscopy and photocurrent spectroscopy coupled with electrochemical measurements. The composition, structure and semiconductivity of the passive films depended on the potential; Fe rich n-type oxide and a Cr rich p-type oxide dominated at more positive potentials and more negative potentials respectively whilst n-type dual layered film formed at intermediate potentials. Analyses of the bandgap determined for these oxides suggested their structures to be Fe2O3 and a Fe-Cr spinel. This hypothesis was supported by the results of in situ Raman spectroscopy.

Synthesis and thin film electronic properties of two pyrene-substituted oligothiophene derivatives

The synthesis and the electric properties of two new pyrene end-substituted oligothiophene derivatives (Py-nT, n = 2,4) are described. The highest hole mobility (ca. 10−3 cm2 V−1 s−1) was obtained for vacuum evaporated thin films of Py-4T as the active layer in field effect transistors based on hexamethyldisilazane-treated SiO2/Si substrates. Moreover, Py-nT thin films were doped with molecular iodine, which led to a 106 fold increase of electric conductivity. In the case of Py-4T, a value of 1 S cm−1 was obtained after 21 minutes exposure to iodine vapor.