Oxide Film Thickness Research Articles

Designing of screen-printed stannous oxide (SnO2) thick film sensors modified by cobalt and nitrogen elements for sensing some toxic gases and volatile organic compounds

The present research deals with fabrication of undoped SnO2, Co2+ doped SnO2 and nitrogen doped SnO2 nanostructures. These three materials were prepared by cost effective co-precipitation method. While the thick film sensors of the prepared materials was design by screen printing photolithography technique. The fabricated materials were characterized by several techniques. The structural properties of the screen-printed thick films measured by X-ray diffractometer (XRD), which confirms the formation of tetragonal SnO2 nanoparticles with average particle size between 15 and 17 ​nm. The morphological properties of fabricated thick of SnO2 were studied by scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HR-TEM) to get surface and lattice characteristics of prepared material. The EDS technique was utilized to get the elemental composition of the prepared thick film sensors. While the UV-DRS technique was used to get the band gap energy of undoped SnO2 and modified SnO2 sensors. Additionally, the materials were investigated by means of Brunauer-Emmett-Teller (BET) study, and from BET results the cobalt modified SnO2 has found to be higher surface area. These all-prepared sensors were applied for gas sensing results of NO2, LPG, CO and volatile organic compounds (VOC’S). The modified sensors found to be very effective at NO2 and VOC gas vapors with 80.23% and 69.13% gas response for cobalt modified SnO2 was observed. The tested gases NO2 and VOC found to be very selective modified sensors. Reusability and recycling results demonstrate that Co2+ doped SnO2 is very efficient, long time stable and reproducible sensor at NO2 and VOC gases at minimum gas concentration and moderate temperature.

Effect of azelaic acid on microstructure evolution and electrical properties of anodic aluminum foil for electrolytic capacitor

The effect of azelaic acid on microstructure evolution and electrical properties of anodic aluminum foil for electrolytic capacitor is studied quantitatively. The azelaic acid is selected as formation solution in the multi-step anodization process, and boric acid is applied for comparison. The field-emission scanning electron microscopy and X-ray diffractometer technologies are used for observation of microstructure and detection of crystallinity, respectively. The electrical properties are tested by LCR meter and T–V tester. The microstructure observation shows that the ‘corn-flake’ structures are taken place by ‘cotton-ball’ ones gradually along with the preparation process, and such phenomenon is more obvious when azelaic acid is used. The pores area of anodic aluminum foil formed in azelaic acid is larger because of the stronger acidity. The formation with azelaic acid induces smaller thickness of oxide film, promotes the formation of crystalline oxide, therefore, a barrier film with higher crystallinity and larger grain size is obtained. The barrier film formed in azelaic acid shows larger specific capacitance, lower withstand voltage and larger leakage current, which needs the multi-step anodization for performance improvement.

Designing of Screen-Printed Stannous Oxide Thick Film Sensors Modified by Cobalt and Nitrogen for Sensing Some Toxic Gases and Volatile Organic Compounds

The present deals with fabrication of undoped SnO2, transition metal Co2+ doped SnO2 and non-metal nitrogen doped SnO2 nanostructures. These three materials were prepared by cost effective co-precipitation method. While the thick film sensor was design by screen printing photolithography technique. The fabricated materials were characterized by several techniques. The structural properties of the screen-printed thick films measured by X-ray diffractometer (XRD), which confirms the formation of tetragonal SnO2 nanoparticles with average particle size between 15 -17 nm. The morphological properties of fabricated thick of SnO2 were studied by scanning electron microscopy (SEM), and HR-TEM to get surface and lattice characteristics of prepared material. The EDS technique was utilized to get the elemental composition of the prepared thick film sensors. While the UV-DRS technique was used to get the band gap energy of undoped SnO2 and modified SnO2 sensors. Since, the sensors effectively work over the surface, hence the prepared sensors were investigated by BET) study, from BET results the cobalt modified SnO2 found to be higher surface area. These all-prepared sensors were applied for gas sensing results of NO2, LPG, CO and volatile organic compounds (VOC’S). The modified sensors found to be very effective at NO2 and VOC gas vapours with 80.23 % and 69.13% gas response for cobalt modified SnO2 was observed. The tested gases NO2 and VOC found to be very selective modified sensors. Reusability and recycling results demonstrate that Co2+ doped SnO2 is very efficient, long time stable and reproducible sensor at NO2 and VOC gases.

The Effect of Growth Parameters on Electrophysical and Memristive Properties of Vanadium Oxide Thin Films.

We have experimentally studied the influence of pulsed laser deposition parameters on the morphological and electrophysical parameters of vanadium oxide films. It is shown that an increase in the number of laser pulses from 10,000 to 60,000 and an oxygen pressure from 3 × 10−4 Torr to 3 × 10−2 Torr makes it possible to form vanadium oxide films with a thickness from 22.3 ± 4.4 nm to 131.7 ± 14.4 nm, a surface roughness from 7.8 ± 1.1 nm to 37.1 ± 11.2 nm, electron concentration from (0.32 ± 0.07) × 1017 cm−3 to (42.64 ± 4.46) × 1017 cm−3, electron mobility from 0.25 ± 0.03 cm2/(V·s) to 7.12 ± 1.32 cm2/(V·s), and resistivity from 6.32 ± 2.21 Ω·cm to 723.74 ± 89.21 Ω·cm. The regimes at which vanadium oxide films with a thickness of 22.3 ± 4.4 nm, a roughness of 7.8 ± 1.1 nm, and a resistivity of 6.32 ± 2.21 Ω·cm are obtained for their potential use in the fabrication of ReRAM neuromorphic systems. It is shown that a 22.3 ± 4.4 nm thick vanadium oxide film has the bipolar effect of resistive switching. The resistance in the high state was (89.42 ± 32.37) × 106 Ω, the resistance in the low state was equal to (6.34 ± 2.34) × 103 Ω, and the ratio RHRS/RLRS was about 14,104. The results can be used in the manufacture of a new generation of micro- and nanoelectronics elements to create ReRAM of neuromorphic systems based on vanadium oxide thin films.

Corrosion inhibition of Mg90 alloy by mixtures based on sodium oleate. Influence of oxide film thickness

Corrosion inhibition of Mg90 alloy by mixtures based on sodium oleate. Influence of oxide film thickness

Effect of fluoride on the thickness, surface roughness and corrosion resistance of titanium anodic oxide films formed in a phosphate buffer solution at different applied potentials

The anodizing process and anions type present in the electrolyte during anodic oxidation are important parameters to improve oxide biocompatibility. From these parameters, it is possible to control the thickness and surface roughness of the oxide film. This control is of major importance, once blood clots can be avoided when the oxide film on the metal substrate has a small surface roughness (Ra ≤ 50 nm). In this paper, the thickness, surface roughness, and corrosion resistance of the anodized titanium film were studied in a phosphate buffer solution containing fluoride anions (0.6 w.t % NaF), at 20 V, 40 V, 60 V, and 80 V, using atomic force microscopy (AFM), spectroscopic ellipsometry (SE), and electrochemical impedance spectroscopy (EIS) techniques. It was observed that thickness and roughness tend to increase as the applied potential rises. For oxides grown in the solution without NaF, the growth rate is roughly 1.3 ± 0.2 nm/V. Surface roughness generally presents the same behaviour. Moreover, EIS and SE thickness measurements agree at 20 V and 60 V but disagree at 80 V. This may be associated with a possible dielectric breakdown at 80 V. The oxide film formed at 60 V showed the best corrosion resistance in relation to the other studied potentials. Globular structures were also observed using AFM on surfaces at 40 V, 60 V, and 80 V, which suggests oxide film nucleation. Oxide films formed in solution with NaF presented lower thickness, excellent corrosion resistance, and low surface roughness (Ra ≤ 50 nm).

Electronic Structure of Molybdenum Oxide Oxidized at Different Pressures

Electronic structure of molybdenum oxides obtained by the oxidation of molybdenum at an oxygen pressure of 1 Torr (thin film) and air (thick film) was studied. It was shown that a thick oxide film is formed from MoO3 oxide, and a thin film from a mixture of MoO3 and MoO2 oxides, which is reflected in the form of valence band spectra. Oxygen on the surface belongs both in molybdenum oxide and in the hydroxyl group, which is associated with dissociative adsorption of water during the oxidation of molybdenum in air for a thick film.

Galvanic Corrosion Behavior between Aluminum and Iron in Chloride Solutions at Near-Neutral pH and Corrosion Prevention By Anodizing

The joints between steels and aluminum alloys are expected to be used as multi-material structures due to their low cost, high stiffness, and high corrosion resistance. When aluminum alloys are connected to steels, galvanic corrosion is expected to occur because the corrosion potentials of aluminum alloys are lower than those of iron and steels. In the case of the galvanic corrosion in chloride solutions at near-neutral pH, the anodic reaction on aluminum alloys are oxide film formation and/or pitting. For pure Al and aluminum alloys, the generation of localized corrosion is evaluated by the critical potential for localized corrosion, such as pitting potential. In this study, the electrode potential under galvanic coupling and pitting potential were compared. Surface modification is effective methods for improvement on corrosion resistance of aluminum alloys. However, there is little research related to the galvanic corrosion between steels and aluminum alloys. In this research, the galvanic corrosion behavior of pure aluminum coupled to pure iron in chloride containing near-neutral pH solutions and the effect of anodizing on galvanic corrosion were investigated.Pure iron and pure aluminum were prepared as specimens in this research. The specimen surface of aluminum was polished down to 0.25 µm with a diamond paste. The iron surface was also polished down to 1 µm with a diamond paste. Diluted synthetic seawater (200 mg/L Cl-, pH 8.2) was used as the electrolyte for electrochemical measurements. The electrode area was ca. 10 mm2. Ag/AgCl (3.33 M KCl) was used as the reference electrode. Galvanic currents and electrode potentials were measured. The distance between iron and aluminum electrodes was kept at 10 mm. A zero resistance ammeter was used to measure the galvanic currents. The electrode potential of pure aluminum was also measured. Additionally, anodizing in sulfuric acid was conducted to pure aluminum in various voltages and times. Galvanic current measurements were carried out between these anodized specimens and pure iron to evaluate the effect of anodizing on galvanic corrosion prevention.The galvanic currents and electrode potentials of pure aluminum coupled to pure iron were measured. The galvanic currents were anodic currents. The oscillations of galvanic currents and electrode potentials were generated during the measurements. Filiform corrosion was observed on pure aluminum after the measurements. The generation of filiform corrosion was caused by higher electrode potentials of pure aluminum coupled to pure iron compared with the initiate potential for filiform corrosion.The time variation of galvanic currents and electrode potentials of anodized aluminum coupled to pure iron were also measured in the diluted synthetic seawater (pH 8.2). Pure aluminum specimens were anodized at 4, 8 and 16 V at 18 s. The oscillations were observed in the galvanic currents of anodized aluminum (4 and 8V); however, no oscillation was measured on the specimen anodized at 16 V. After the measurements, pitting was observed on anodized aluminum (4 and 8V). However, no pitting was observed on the specimen anodized at 16 V. The thickness of anodic oxide film was measured. It was confirmed that the thickness of the oxide film increased with anodizing voltage. Consequently, it was indicated that the galvanic corrosion resistance of pure aluminum for galvanic corrosion was enhanced by the increase of the thickness of the oxide film.

Examination of Conductive Properties of ZrO2 Film Formed By Self-Oxidation Method

By forming an oxide film on the surface of metallic zirconium, ZrO2 works as a corrosion resistant film and prevents the permeation of hydrogen. This material is expected to be utilized as a plasma facing material for fusion reactors, because zirconium and ZrO2 have excellent compatibility at high temperature under the redaction atmosphere. Vapor deposition methods such as electron beam vapor deposition and pulse laser vapor deposition are the main methods of forming oxide films on metallic zirconium surfaces. In this study, the self-oxidation method using water vapor was employed as a film forming method, because a dense film of zirconium oxide can be obtained on the surface of metallic zirconium by the heat treatment at 500 °C in water vapor. Although the self-oxidation method using water vapor is promising, the previous reports have been limited yet. An oxide film is formed on the surface of metal Zr by a self-oxidation method in a water vapor atmosphere, and its conductive properties due to the difference in the thickness of each layer of the film are examined.The fine structure of the preparing film was observed with a field emission Scanning Electron Microscope (SEM). The film thickness was determined as the average film thickness from the cross-sectional SEM image using image processing software Image Processing and Analysis in JAVA (Image J). The O/Zr ratio in the film was analyzed by line analysis of an Energy Dispersive X-ray analyzer (EDX). The Crystallinity and formed phase of the film were identified by Electron Back Scatter Diffraction (EBSD) analysis and "grazing incidence X-ray diffraction". impedance measurement was performed using SP-150 electrochemical measurement system of Bio-Logic Sciences Instruments. It was decided to separate the conductivity of each layer by measuring the oxide film prepared by adjusting the film thickness.In the previous studies, it was revealed from the SEM observation of the cross section of the oxide film that the oxide film was not a single layer but a laminated structure whose O/Zr ratio gradually decreases with increasing of the film depth. Therefore, by changing the X-ray incident angle (θ = 1 ~ 12 °) by XRD analysis, we analyzed the change of the formed phase in the thickness direction and found that each phase is not an amorphous phase but a crystalline phase. The sample formed by steam oxidation was subjected to EDS line analysis in the direction perpendicular to the oxide film cross section, and the O/Zr ratio of each layer was measured. It was observed that the atomic ratios of the three kinds of layer, bottom layer, second layer and top layer were observed to be 0.3-0.6, 0.6, and 1.5 or more, respectively. The samples with the various thickness of oxide film were prepared and the specific electrical resistances of each film were measured with the impedance measurements. The electrical conductive properties of each layer were investigated with the fitting of equation whose parameters are the thickness and the specific electrical resistance of each layer.

Oxidation Behavior of Additively Manufactured 316L in a Supercritical CO2 Environment

The general properties of additively manufactured (AM) metals have been fairly well characterized to this point with respect to mechanical behavior and even general corrosion response. However, as the fields of application of AM metals broadens, the need for unique/specialized evaluation is required. For instance, there remains a lack in understanding how AM metals behave under atmospheric corrosion exposure conditions where local heterogeneous environments govern the surface reactivity and susceptibility. Similarly, knowledge gaps exist in specialized environment, for example supercritical CO2 (sCO2). Materials and environment parameters such as composition, pressure, and temperature will influence corrosion susceptibility and/or oxidation properties. As AM metals often display vastly different microstructures from their wrought counterparts due to non-equilibrium cooling during processing, an understanding of their behavior in these environments is critical prior to possible application. Additionally, typical engineering design of oxy-combustion gas turbine systems used in these environments, results in atypical conditions, usually localized, that are well known to affect environmental performance of materials (such as crevices, welds, residual stresses, or galvanic coupling).Austenitic stainless steel, type 316L, specimens made by selectively laser melting (SLM) were exposed with their traditional wrought counterparts for comparison at 450°C and 7.6 MPa in pure sCO2 for one week. SLM samples were exposed in the as printed (a contour scan strategy was used) and the ground (ground to 1200 grit) state and compared to wrought samples ground to 1200 grit. Prior to exposure, samples were partially coated with a zirconia film to establish an initial true height to aid ellipsometry. Post exposure, oxide film thickness was measured with respect to the non-reactive coating height. Preliminary analysis of oxide film thickness measurements performed using ellipsometry showed a thinner oxide film grown on the in-process polished SLM samples (0.66 - 0.79 µm) versus the ground SLM (1.1 µm) or wrought samples (0.8 – 1.22 µm). Additional analysis was performed through scanning electron microscopy and focused ion beam combined with transmission electron microscopy to characterize the oxides formed and elucidate possible microstructural and/or morphological dependence of the film growth.SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. SAND2020-4568 A

Electric Resistance Measurements of Anodic Oxide Films on Titanium and Zirconium

Valve metals such as titanium and zirconium can be subjected to anodization to form a thick compact oxide film in fluoride-free electrolytes at room temperature, and the thickness and structure of the film can be controlled by anodization conditions. Although various studies on the formation, characterization and application of anodic titanium oxide film as well as zirconium oxide film have been carried out so far, the electrical resistivity of the anodic oxide films is quite limited. In the present work, we measured electric resistance of the anodic oxide films formed on titanium and zirconium under various anodization conditions, aiming at investigating effects of anodization on electrical resistivity of anodic oxide films.

Study of Supercapacitor Performance Degradation Depending on Oxide Layer of Aluminum Current Collector

Supercapacitor performance comparison depending on the various oxide film thickness of aluminum foil was studied. The study was focused on the anodic behavior of organic solvent based cylindrical supercapacitor.The study aimed to see correlation between the active material current collector interface changes and the performance of the supercapacitor such as capacitance, ESR or gas generation depending on varying Al current collector oxidation pre-treatment. The results of performance test showed that electrode degradation of the interface between active material coating layer and the Al current collector are influenced by the oxidation pre-treatment process. Furthermore, the supercapacitor performance test by using long time period stored Al foil as a current collector (which is naturally oxidized at room temperature) was conducted to see how long the Al foil for supercapacitor can be stored without notable performance degradation.

Bonding Mechanisms in Cold Spray: Influence of Surface Oxidation During Powder Storage

Cold spray is a solid-state process in which solid particles are subjected to severe plastic deformation to form a coating. The effect of naturally occurring oxides on bonding in the cold spray was investigated in this work. Deposition characteristics of copper powder with different surface oxide thicknesses on steel substrate were examined using a local pull-off test. This enables the investigation of individual particle/substrate interfaces. X-ray photoelectron spectroscopy was used to study thoroughly the powder surface chemistry and the oxide thickness as a function of exposure time. This study revealed that the oxide film thickness grew from 6 nm for the as-received powder to 11.6 nm after 2 months of exposure to atmospheric conditions. Scanning electron microscopy and x-ray energy dispersive spectroscopy were used to characterize the particle/substrate interfacial bonding. Adhesion test results show that the bond strength is highly influenced by the surface oxide thickness. Different bonding behaviors and a drop in coating deposition efficiency were observed as the oxide thickness increased. Finite element simulations supplemented our understanding of the particle adhesion dynamics as the oxide film thickness increases. They were also used to study the surface oxide cleanup and bonding mechanism for particles with different oxide film thicknesses.

Fabrication of layer-by-layer graphene oxide thin film on copper substrate by electrophoretic deposition

In this paper, we investigate the fabrication of graphene oxide (GO) films on copper substrates by means of an electrophoretic technique, with the aim of realizing conductive thin films that could be applied as reliable electrical contacts for use in various applications. Uniform films were fabricated, and the film thickness measured using atomic force microscopy. The graphene oxide film thickness is estimated to range from a few manometers to several tens of manometers, depending on the deposition time. Cross-sectional transmission electron microscopy images indicate that the films possess a multi-layered structure, and that the distance between layers is approximately 0.5 nm. Furthermore, the electrical contact resistance of the films was measured, using conductive probe atomic force microscopy. The prepared GO films exhibit electrical conductivity due to their layered structure, which affects their electrical properties.

Nanoscale 2D semi-conductors – Impact of structural properties on light propagation depth and photocatalytic performance

The performance of photocatalytic materials are largely dictated by the crystalline and optical properties of the semi-conductors. The density of photo-generated electron and hole pairs is greatly influenced by the light penetration in photocatalytic material, leading to specific degradation kinetics. In this work, the relationship between the metal oxide film thickness and the overall materials optical and photocatalytic performances are systematically established for the first time. Thin films of semiconductor metal oxides such as TiO2 and ZnO were prepared by atomic layer deposition (ALD) on stainless steel sputtered silicon wafers. The thickness of the metal oxide thin films was controlled by varying the number of deposition cycles (50–1000 cycles). The fabricated films were fully characterized to examine the change in morphology, roughness, crystallinity, optical and structural properties with varying thickness by several techniques such as Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-Ray Diffraction (XRD), Diffuse Reflectance Spectroscopy (DRS) and X-Ray Photo-electro Spectroscopy (XPS). The films were generated to yield very consistent crystallinity, roughness and light absorption properties. Critical thicknesses were observed when a plateau in photocatalytic efficiency was reached at the thickness of 31 nm in the case of the TiO2 and 89 nm thickness for ZnO films. The dependency of the thickness of nanometric ALD films on their photocatalytic efficiency results from the light diffusion and penetration within the material which was investigated through fundamentals and modelling of light-matter interaction in photocatalytic processes. This work establishes a new fundamental understanding of the operation and performance of photocatalysts for further development of advanced reactors and their scale-up.

Screen printed novel ZnO/MWCNTs nanocomposite thick films

Zinc oxide and multiwall carbon nanotubes (ZnO/MWCNT) nanocomposites thick films were prepared via sol-gel screen printing procedure and followed by sintering at 550 °C. Thus, the prepared films were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), Ultraviolet–visible (UV–vis), Photoluminescence (PL), Fourier transform infrared (FTIR), Raman spectroscopy and Two-probe method. XRD analysis revealed (101) orientation for both ZnO and ZnO/MWCNT thick films with wurtzite structure. SEM studies confirmed the porous nature of ZnO film while ZnO/MWCNT films showed ZnO particles trapped in the porous MWCNT network and free from cracks. Reflectance spectroscopy showed direct transition with decreasing band gap whereas refractive index and absorption index showed appreciable variation within the band gap regime related to the change in crystallite size. FTIR profile approved the Zn–O stretching and presence of carboxylic CDC group. The PL spectrum of ZnO and ZnO/MWCNT thick films shows red shift and exhibits UV, blue and green emissions confirmed from CIE diagram. Raman spectrum shows that Raman phonons are shifted and dominated due to doping of MWCNT in ZnO matrix. Electrical properties were investigated using 2-probe method and showed a reduction in resistance on MWCNT incorporation. The novelty of current-work is the fabrication of ZnO/MWCNT through a low-cost screen printing process for the first time and the results exhibits that the bandgap of the deposited film is decreased, which in turn, play a significant role in enhancement of conductivity and colour emission for fabrication of low cost optoelectronics devices (LEDs) as compared with the pure ZnO film.

Application of X-rays Diffraction for Identifying Thin Oxide Surface Layers on Zinc Coatings

Structural characterization of compound material coatings is usually achieved using time-consuming and destructive techniques such as optical and electrical microscopy, which require the use of grinding processes not always compatible with the material. This paper reports on the effective use of a theoretical model based on X-ray diffraction to calculate the thickness and composition of thin oxide films formed on the surface of zinc coatings. Zinc coatings are widely used in industrial application as protective layers against the atmospheric corrosion of steel substrates. The thickness of single- and multi-layer coatings is estimated using grazing incidence X-ray diffraction and various incidence angles. The coatings were grown using hot-dip, pack cementation and thermal spray techniques, and their experimental characteristics were compared to the theoretically predicted values of thickness and composition. The results indicate the formation of a thin zinc oxide film on top of each coating, which acts as an isolation layer and protects the surface of the sample against the environmental corrosion. Finally, the penetration depth of the X-rays into the zinc-based coatings for grazing incidence and Bragg–Brentano X-ray diffraction geometries were calculated using theoretical equations and experimentally confirmed.

Influence of Process Parameters on the Aerosol Deposition (AD) of Yttria-Stabilized Zirconia Particles

Aerosol deposition (AD) is a novel deposition process for the fabrication of dense and rather thick oxide films at room temperature. The bonding of the deposited ceramic particles is based on a shock-loading consolidation, resulting from the impact of the ceramic particles on the substrate. However, the deposition mechanism is not fully understood. In addition, many technical challenges have been observed for achieving a successful deposition of the oxides with higher efficiency. In this work, the influence of different processing parameters on the properties of the deposited layer is studied. Proof of concept was done using 8 mol.% yttria-stabilized zirconia (8YSZ) powder as starting material. The window of deposition with respect to carrier gas flows for successful deposition was identified. The influence of this carrier gas flow, the substrate materials and the carrier gas species on the coating thickness, interface quality and coating microstructure was systematically investigated. The derived mechanical characteristics revealed an unexpected behavior related to a gradient microstructure. This study supports understanding of the mechanism of room-temperature impact consolidation and its effect on the mechanical properties of the deposited layer.

Adsorption and self-assembly of porphyrins on ultrathin CoO films on Ir(100).

Porphyrins represent a versatile class of molecules, the adsorption behavior of which on solid surfaces is of fundamental interest due to a variety of potential applications. We investigate here the molecule–molecule and molecule–substrate interaction of Co-5,15-diphenylporphyrin (Co-DPP) and 2H-tetrakis(p-cyanophenyl)porphyrin (2H-TCNP) on one bilayer (1BL) and two bilayer (2BL) thick cobalt oxide films on Ir(100) by scanning tunneling microscopy (STM) and density functional theory (DFT). The two substrates differ greatly with respect to their structural and potential-energy landscape corrugation with immediate consequences for adsorption and self-assembly of the molecules studied. On both films, an effective electronic decoupling from the metal substrate is achieved. However, on the 1BL film, Co-DPP molecules are sufficiently mobile at 300 K and coalesce to self-assembled molecular islands when cooled to 80 K despite their rather weak intermolecular interaction. In contrast, on the 2BL film, due to the rather flat potential landscape, molecular rotation is thermally activated, which effectively prevents self-assembly. The situation is different for 2H-TCNPP, which, due to the additional functional anchoring groups, does not self-assemble on the 1BL film but forms self-assembled compact islands on the 2BL film. The findings demonstrate the guiding effect of the cobalt oxide films of different thickness and the effect of functional surface anchoring.

The enhanced Coulomb interaction in three-dimensional indium tin oxide films

The Coulomb interaction effect in disordered conductors has long been a topic of fundamental importance and intense attention. Here, we systematically study the influence of this effect on the electrical transport of a series of ∼1 μm thick Sn-doped indium oxide (ITO) films grown at different oxygen partial pressures. We find that both the electrical conductivity σ and Hall coefficient RH vary linearly with T from ∼35 K down to ∼4 K. The extracted electron screening factor F~σ of each film is nearly in agreement with the corresponding theoretical value. Moreover, the F~σ values increase with decreasing carrier concentration in the ITO films, which originates from less screening effect of electrons and enhanced Coulomb interaction. These features are consistent with conventional three-dimensional Coulomb interaction theories. We explore the long-standing puzzle of the carrier concentration dependence of F~σ. Our results provide the fundamental physics to modulate the intensity of the Coulomb interaction effect, which may be useful to optimize the performance of electron transport for nanoscale electronic devices.