Surface Morphology Of Layers Research Articles

Fabrication, characterization and optimization of industrial alpha alumina powders based ceramic membrane supports and its applicative potential for CO2/N2 separation

In this investigation, an economically feasible strategy has been proposed for the fabrication of good quality membrane support by utilizing low-cost industrial-grade alumina powders, coded as A-16SG and CT-1200SG with an average particle size of 0.44 and 1.41 µm, respectively. Herein, the meticulous alteration of the processing parameters and the targeted utilization of industrial grade powders with distinctive particle morphologies have shown promising aspect towards governing the overall sintering and densification behavior, pore morphology and the microstructural facets of the sintered alumina compacts. More precisely, while connecting the structure-property relationship aspect, the broader particle size distribution and the higher quartile ratio of CT-1200SG powders lends to originate relatively higher average pore size and wider pore size distribution in the as-optimized sintered membrane support system in comparison to the narrow particle sized and low quartile ratio comprising A-16SG powder. Additionally, the near surface morphology of the intermediate layers deposited over the two distinctive membrane support systems via implementing differential colloidal chemistry of the respective sols have also been demonstrated for the precise understanding of the role of particle morphology on the progressive perseverance of pore characteristics of the overall asymmetric graded membrane substrate. Finally, the performance evaluation of the alumino-silicate membrane layer assembled on the tailor-made multilayered graded cost-competent alumina support system has been executed which revealed comparable CO2/N2 gas permeance of 46.44GPU and 534.25GPU along with the selectivity of 12.5 and 1.9 for the respective A-16SG and CT-1200SG powders based individual support systems under nearly identical flue gas separation conditions.

Surface kinetics in halide vapor phase epitaxial growth of GaN layers on GaN (0001) freestanding substrates

The effects of halide vapor phase epitaxial (HVPE) growth conditions such as input V/III ratio and substrate off-cut angle on the surface morphology of n-type GaN layers grown on GaN (0001) freestanding substrates were investigated to develop a model for growing smooth surfaces. The spiral hillock density increased with increasing input V/III ratio and/or decreasing off-cut angle. The critical off-cut angle between the spiral growth and the step-flow growth depended on the vapor supersaturation calculated by thermodynamic analysis. To understand the transition of the growth mode, we proposed a Burton–Cabrera–Frank-theory-based model considering the effect of spiral growth, which was utilized to explain the obtained experimental results. The developed growth model can be effective for predicting the HVPE growth mode between the spiral growth and the step-flow growth.

Development of 4-aminophenol sensor based on Co-MoS2 nanomaterials decorated on glassy carbon electrode using electrochemical technique

The present research discusses the incorporation of cobalt (7.5 and 10 wt%) in exfoliated MoS2 nanosheets via hydrothermal route. Phase purity and crystal structure of prepared Co doped MoS2 were confirmed with XRD. To observe the attached functional groups and presence of Mo-O characteristic peak, FTIR was used. Optical properties, surface morphology and agglomeration of layers were visualized through UV/Visible spectroscopy, FESEM and HR-TEM, respectively. In this study, sensitive 4-aminophenol (4-AP) sensor was fabricated with Co-MoS2 nanomaterials (NMs) decorated on glassy carbon electrode (GCE) using electrochemical approach. The parameters of developed 4-AP sensor were systematically calculated from the calibration curve by using current versus concentration. The sensor probe response was found linear over 0.1 nM to 0.01 mM, which is known as linear dynamic range (LDR). The slope of LDR was used to calculate the sensitivity of the proposed sensor, which was measured by considering the active surface area of GCE (0.0316 cm2). It was found to be 43.0127 µAµM-1cm−2. The limit of detection (LOD; 93.48 ± 4.67 pM) of the 4-AP sensor was evaluated from the slope of the calibration curve. Other sensor parameters, such as reproducibility, repeatability, response time, validity, and stability of the fabricated sensor were found to be outstanding. The 4-AP sensor constituting Co-MoS2 NMs deposited on GCE developed by employing an electrochemical approach was perceived to be an efficient sensor for real-time analysis of environmental and extracted samples.

Label-Free Detection of Saxitoxin with Field-Effect Device-Based Biosensor.

Saxitoxin (STX) is a highly toxic and widely distributed paralytic shellfish toxin (PSP), posing a serious hazard to the environment and human health. Thus, it is highly required to develop new STX detection approaches that are convenient, desirable, and affordable. This study presented a label-free electrolyte-insulator-semiconductor (EIS) sensor covered with a layer-by-layer developed positively charged Poly (amidoamine) (PAMAM) dendrimer. An aptamer (Apt), which is sensitive to STX was electrostatically immobilized onto the PAMAM dendrimer layer. This results in an Apt that is preferably flat inside a Debye length, resulting in less charge-screening effect and a higher sensor signal. Capacitance-voltage and constant-capacitance measurements were utilized to monitor each step of a sensor surface variation, namely, the immobilization of PAMAM dendrimers, Apt, and STX. Additionally, the surface morphology of PAMAM dendrimer layers was studied by using atomic force microscopy and scanning electron microscopy. Fluorescence microscopy was utilized to confirm that Apt was successfully immobilized on a PAMAM dendrimer-modified EIS sensor. The results presented an aptasensor with a detection range of 0.5–100 nM for STX detection and a limit of detection was 0.09 nM. Additionally, the aptasensor demonstrated high selectivity and 9-day stability. The extraction of mussel tissue indicated that an aptasensor may be applied to the detection of STX in real samples. An aptasensor enables marine toxin detection in a rapid and label-free manner.

Protective coating of highly porous alginate aerogel particles in a Wurster fluidized bed

Alginate aerogel particles were successfully coated with a copovidone and hydroxypropyl cellulose based polymer in a Wurster fluidized bed. The results indicate that the pores of aerogels were not damaged during the process. Several sets of experiments were conducted at three different temperatures and atomizing air pressures. Coating time for all the runs ranged from 5 min to 40 min and the coating thickness ranged from 12.4 ± 4.6 μm to 170.6 ± 43.3 μm.Changing bed temperature led to significant changes in coating thickness whereas both bed temperature and atomizing pressure affected coating layer surface morphology. The smoothest coating layer surface and the highest coating efficiency which was 69.2 ± 0.4% were achieved at 50 °C with 1.7 bar atomizing pressure. At this condition, the coating layer thickness increased linearly with coating time.

Effect of growth temperature on nitrogen incorporation into GaAsN during liquid-phase epitaxy

We studied the growth temperature effect on nitrogen incorporation into GaAsN layers grown by liquid-phase epitaxy (LPE). The growth of dilute nitrides at nearly equilibrium conditions during LPE presents several major challenges: low solubility of nitrogen in Ga-melt, small incorporation efficiency in the solid and high volatility of nitrogen. GaAsN layers are grown from three different initial epitaxy temperatures: 580 °C, 680 °C and 780° C using GaN powder in the melt as a source of nitrogen. The N content in GaAsN is estimated from X-ray diffraction curves applying Vegard’s law. The local microstructure and surface morphology of the grown layers are studied by Fourier-transform infrared spectroscopy and atomic force microscopy measurements, respectively. The absorption edge and the composition dependence of the effective band gap are determined by employing optical transmission and surface photovoltage spectroscopies.

Design of nanocatalyst for electrode structure: Electrophoretic deposition of iron phosphide nanoparticles to produce a highly active hydrogen evolution reaction catalyst

• FeP NP electrocatalytic electrode was fabricated via electrophoretic deposition. • Morphology and porosity of catalyst layer were tuned by altering deposition kinetics. • Optimized porosity/catalyst loading lead to the excellent HER activity. • The HER electrode was successfully applied as cathode GDE of high performance PEMWE. The inherent properties of nanoparticles (NPs) can be engineered into macroscopic structures by capturing the collective characteristics of the nanomaterials via a fabrication process to realize macroscopic functionality. Herein, we report a powerful manufacturing technique for fabricating an electrode composed of highly porous iron phosphide (FeP) NP catalyst layers conformally deposited on macroporous Carbon paper (CP) that shows excellent hydrogen evolution reaction activity. The surface morphology and porosity of the FeP NP catalyst layers on the FeP/CP electrode were tuned by altering the deposition kinetics of the colloidal FeP NPs by controlling the solvent system in the electrophoretic deposition process. The FeP/CP electrode achieved a low overpotential of 38 mV at 10 mA cm −2 in 0.5 M H 2 SO 4 due to the highly exposed catalytic surface with a high catalyst loading amount and fast charge transfer. When the FeP/CP electrode was applied as a cathode gas diffusion electrode in a proton exchange membrane water electrolyzer, the single-cell exhibited excellent operating performance (1.48 A cm −2 @ 2.0 V cell , 90 °C). Our results illustrate a facile route for fabricating nanostructured macroscale devices by maximizing the collective properties of the nanoscale materials.

Enhancement of optical property and crystal structure for GaN films on 2D MoS2 buffer layer by nitridation treatment

The growth of GaN films on layered 2D-MoS2/c-sapphire substrate by plasma-assisted molecular beam epitaxy system was investigated. Pre-nitridation process and deposition time as growth parameters were employed to exploit the heteroepitaxial growth of GaN films at the temperature of 700 °C. The characterizations of surface condition, surface morphology, chemical composition, optical properties, crystal orientation and quality of GaN epitaxial layers were conducted by reflection high energy electron diffraction (RHEED), scanning electron microscope (SEM), atomic force microscope (AFM), X-ray photoelectron Spectroscopy (XPS), Raman spectroscopy, photoluminescence spectroscopy (PL) and high-resolution X-ray diffraction (HR-XRD), respectively. The pre-nitridation process and growth duration can enhance the optical properties and crystal quality of GaN films on 2D-MoS2/c-plane sapphire. The pre-treatment of MoS2 layer by nitrogen plasma before the growth, providing a wetting layer of nitrogen for GaN growth, can eliminate the oxygen contamination and reduce the defects in the films. Band-to-band emission of Wurtzite GaN with the bandgap of 3.5 eV can be improved by pre-nitridation process, and yellow band emission can be suppressed due to the elimination of defect states in the films. Meanwhile, the crystal orientation and quality can be improved by the pre-nitridation process and longer duration of growth time. This study demonstrates a van der Waals epitaxial GaN films on 2D-MoS2 layer with higher crystal quality by pre-nitridation process, and it provides a potential solution for the future applications of GaN-based devices.

Enhanced thickness uniformity of large-scale α-Ga2O3 epilayers grown by vertical hot-wall mist chemical vapor deposition

Smooth surface morphology and high thickness uniformity heteroepitaxy of corundum-structured ( α- ) gallium oxide (Ga 2 O 3 ) crystalline thin films on 100-mm diameter c -plane sapphire substrates were successfully demonstrated using vertical hot-wall mist chemical vapor deposition (CVD). The growth rate and surface morphology of the epitaxial layers were numerically and experimentally found to be dependent on the diameter of the precursor-diluted microdroplets approaching the substrate surface. Since the microdroplet is gradually evaporated while traveling through the furnace, the growth variables such as temperature, mist-flow velocity, and substrate position were tuned to obtain a suitable diameter of microdroplets approaching the substrate. In this study, the diameter of the approaching microdroplet was ≈2 μm, which was optimal for the smooth surface (root mean square roughness ≈1 nm) of α -Ga 2 O 3 epitaxial layers with a growth rate of ≈230 nm/h. Due to the even flow of mist in the vertical furnace, high thickness uniformity of the α -Ga 2 O 3 epitaxial layer is guaranteed on large-scale substrates, with a standard deviation of thickness as small as 28 nm, paving the way for highly reliable Ga 2 O 3 -based electric and optoelectronic devices.

Single-crystalline silicon nanomembrane thin-film transistors with anodized aluminum oxide as a gate dielectric on rigid and flexible substrates

Flexible integrated circuits have gained a lot of attention in recent years for their emerging applications in wearable electronics. Flexible thin-film transistors (TFTs) with low-costs and high-performance are highly desirable as essential and fundamental elements for most flexible applications. In this paper, we fabricate single-crystalline silicon nanomembrane (SiNM)-based TFTs with anodized aluminum oxide (AAO) as a dielectric material on glass and flexible plastic substrates. Good quality AAO was obtained on plastic substrates at room temperature. Atomic force microscopy (AFM)was used for the surface morphology of the AAO gate dielectric layers on different substrates (i.e. glass, polyethylene terephthalate (PET), and SU-8 coated PET). The electrical characteristics of the AAO gate dielectric layers on different substrates were also analyzed with metal–insulator–metal capacitors. The SiNMs were processed with a complementary metal oxide semiconductor (CMOS) compatible semiconductor process (e.g. photolithography, ion implantation, thermal annealing, reactive ion etching, metal evaporation, etc), and then transferred to the substrates with AAO/aluminum stack layers. The performance of the transistors on glass and plastic substrates was characterized. Compared with the TFT fabricated on a glass substrate, the TFT fabricated directly on a PET substrate had lower performance due to poor surface roughness. For optimization of the surface roughness, the PET was modified with a coating of SU-8 photoresist. In this way, the TFT had properties close to that on a glass substrate. AAO that can be manufactured at room temperature provides a simple and low-cost solution for high-performance flexible single-crystalline SiNM TFTs.

Effect of surface topography on injection joining Ti alloy for improved bonding strength of metal-polymer

Titanium matrix fiber-reinforced plastic composites had attracted increasing interest in marine and other fields because of their excellent mechanical and corrosion resistance. However, the interfacial bonding strength between the titanium matrix and the plastic is an important factor limiting its wide application. In this paper, the surface of titanium alloy TC4 (Ti-6Al-4V) was anodized to form an oxide layer with a 1–2 μm crack structure on the surface of titanium alloy. Then the titanium alloy was combined with plastic polyphenylene sulfide (PPS) by direct injection molding. The results show that different oxide layer structures on the surface of titanium alloy, which can be obtained by different anodizing times and anodizing temperatures, can obtain TC4-PPS composites with different bond strengths. The maximum bond strength of TC4-PPS composites was 16.8 MPa when the anodizing temperature was 90 °C and the oxidation time was 30 min. We also discussed the effect of titanium alloy oxide layer surface morphology, wettability, roughness, composition, failure mode, and glass fiber on the bonding strength, which is important for expanding the application of titanium alloy and plastic composite.

Characterization of Luminescent Down-Shifting Spectral Conversion Effects on Silicon Solar Cells with Various Combinations of Eu-Doped Phosphors.

Luminescent down-shifting (LDS) spectral conversion is a feasible approach to enhancing the short-wavelength response of single junction solar cells. This paper presents the optical and electrical characteristics of LDS spectral conversion layers containing a single species or two species of Eu-doped phosphors applied to the front surface of silicon solar cells via spin-on coating. The chemical composition, surface morphology, and fluorescence emission of the LDS layers were respectively characterized using energy-dispersive X-ray analysis, optical imaging, and photoluminescence measurements. We also examined the LDS effects of various phosphors on silicon solar cells in terms of optical reflectance and external quantum efficiency. Finally, we examined the LDS effects of the phosphors on photovoltaic performance by measuring photovoltaic current density–voltage characteristics using an air-mass 1.5 global solar simulator. Compared to the control cell, the application of a single phosphor enhanced efficiency by 17.39% (from 11.14% to 13.07%), whereas the application of two different phosphors enhanced efficiency by 31.63% (from 11.14% to 14.66%).

Simple Fabrication of BiVO4 Thin Films Synthesized by Modified SILAR Method: Effect of Film Thickness

In this study, BiVO4 photoanodes were synthesized using a simple and inexpensive modified successive ionic layer adsorption and reaction (SILAR) method. In particular, the effect of the number of SILAR cycles on the photoelectrochemical (PEC) properties of BiVO4 was evaluated. Scanning electron microscopy analysis revealed the porous surface morphology of the BiVO4 thin layers with irregularly shaped particles formed on the surface of fluorine-doped tin oxide substrates. The crystal structure of BiVO4 was confirmed using X-ray diffraction analysis. The ultraviolet–visible spectrophotometry results indicated that the bandgap energy of the deposited film was approximately 2.4 eV. In addition, the PEC properties of the BiVO4 photoanodes using potentiostat were analyzed. The linear sweep voltammetry curves revealed that the photocurrent density of the BiVO4 samples increased with the increasing number of m-SILAR cycles, and a maximum photocurrent density of approximately 0.83 mA cm−2 was achieved for the BVO-35. These results suggest that an efficient photoelectrode for compact PEC cells can serve as a basis for development.

ПОЛУЧЕНИЕ И ПРИМЕНЕНИЕ ГИДРОФОБНЫХ ПОЛИУРЕТАНОВЫХ КРЕМНИЙСОДЕРЖАЩИХ ПОКРЫТИЙ. ЧАСТЬ 1: ОСНОВЫ ЯВЛЕНИЯ ГИДРОФОБНОСТИ (ОБЗОР)

Highly- and superhydrophobic characteristics of surfaces can dramatically increase protective properties of polymeric coatings and may add it new useful functions. For example, fabricating of hydrophobic coatings with self-cleaning, anti-icing, anti-fouling or fouling release properties, as well as producing filtrating systems, compounds that can selectively wets surfaces, coatings decreasing of liquid streams friction exists described in numerous research articles. Despite of an apparent simplicity of a water droplet behavior on the surface in theoretical basis of the wetting phenomena still exists unsolved questions, which prevent developing many new materials, including hydrophobic coatings. In the first part of review, the modern theoretical concepts, relating to the process of surface wetting are review. Advantages and limitations of existing models of liquid drop behavior on solid surface, hysteresis phenomena are discussed. Basic concepts concerning effect of morphology of surface layer on the wetting and value of contact angle and stability of liquid drop on solid surface are represented

Plasmonic Gold Nanorod Size-Controlled: Optical, Morphological, and Electrical Properties of Efficiency Improved Tin Disulfide Vacuum-Free Hybrid Solar Cells

The different size of plasmonic gold nanorods (NRs) were synthesized by the overgrown seeds method and applied to vacuum-free hybrid solar cells (VFHSCs). Tin disulfide (SnS2) quantum dots were synthesized and used as an n-type material of the device. The synthesized materials were characterized by different techniques such as transmission electron microscopy (TEM), UV-Vis spectroscopy, and atomic force microscopy (AFM). The Au (NRs) had a different of size of NR1 (Width: 4 nm; Length: 12 nm), NR2 (Width: 5 nm; Length: 16 nm), NR3 (Width: 6 nm; Length: 22 nm) which were measured using a TEM technique. The Au NR particles were incorporated into the PEDOT:PSS as a hole transport layer (HTL) of solar cells device. The effects of Au NRs size on the device performance were investigated. A thin film of Zin oxide (ZnO) was used as a buffer layer of the device. The influence of buffer layer thickness on the device’s active layer surface morphology was also studied. At the optimized condition, the highest power conversion efficiency was obtained at about ~3.7%.

Novel P2-Type Na0.66Fe0.5-2xMn0.5TixVxO2 Cathode for High-Capacity

Necessity of energy storage and battery production is soaring up day by day due to the growth of portable electronic devices and surging evolution of electric vehicles (EVs), plug-in-hybrid electric vehicles (PHEVs) and renewables. Lithium-ion battery (LIB) technology has been the primary choice for such applications due to its high-energy-density, high-stability, and longer cycle life. Albeit with all merits of LIB, the prime concern has been the scarcity of lithium in earth’s crust and depletion of lithium reserve due to its wide usage in batteries, resulting in a higher production cost. This has prompted battery researchers to search for new alternatives to LIB for energy storage applications. Sodium, in this respect, can be a viable solution as it is the sixth most abundant element and shares the same group with lithium in the periodic table. Sodium has similar structural and electrochemical working mechanisms of lithium. The pivotal factors hindering the deployment of the laboratory-based sodium-ion battery (SIB) technologies into the commercial energy storage market are low energy density compared to that of LIB, lower stability, lower ion-transport mechanism, and lower operating voltage. Improvement of overall electrochemical performance of cathode materials can be a game-changer as it affects the energy density, lifespan, and tolerance of batteries. In this research, a cobalt-free novel P2-type transition metal cathode Na0.66Fe0.5-2xMn0.5TixVxO2 was synthesized by doping NaFeMnO2 with vanadium and titanium for SIB battery applications. The cathode was synthesized based on a sol-gel reaction where citric acid was used as a chelating agent. A set of physicochemical analysis, including Field-Effect Scanning Electron Microscopy (FESEM) and Energy Dispersive X-ray Spectroscopy (EDAX) analysis, as well as electrochemical analysis like Cyclic Voltammetry and Galvanometric Charge/ Discharge were performed to understand the correspondence between layered transition metal oxide chemistry, surface morphology and electrochemical competence of the new material. The crystal structures of the pristine material and cathodes containing different percentages of doped vanadium and titanium were examined and lattice parameters were refined through X-ray Diffraction (XRD) and Rietveld analysis. These exhaustive structural and morphological comparisons were performed between the pristine and modified NaFeMnO2 (NFM) cathode structures, which provided insights on the effects of vanadium and titanium doping on stabilizing surface structures, reducing Jahn-Teller distortion, enhancing stability and capacity retention and promoting Na+ carrier transport mechanism.

Properties of carbon-doped GaN using isobutane as a dopant

Carbon doping is an effective method to obtain semi-insulating GaN buffer, which is a necessity to prevent current leakage, in the high-electron-mobility-transistor device structure. The properties of intentionally carbon-doped GaN using isobutane gas as a dopant has been studied in detail. The carbon incorporation efficiency has been measured by secondary ion mass spectrometry. It is found that the carbon concentration could be directly controlled by the flow rate of isobutane precursor. The surface morphology of carbon-doped gallium nitride epitaxial layers has been investigated by optical microscopy and atomic force microscopy. The growth mode of GaN layers changes from step-flow to island growth, when the incorporated carbon concentration is higher than 1×1019 cm-3. In order to evaluate the structural quality of intentionally carbon-doped GaN, the full-width-at-half-maximum values are extracted from the rocking curves in six different reflections measured by high resolution X-ray diffraction. Raman spectroscopy is utilized to evaluate the physical properties of the carbon-doped GaN epitaxial layer.

Effects of duty ratio on properties of Ni–P–(sol)Al2O3 coating prepared by pulse-assisted chemical deposition

With the wide application of nanocomposite protective coatings in various fields, there are higher requirements for their properties. At the same time, the traditional chemical deposition and electrodeposition processes have defects with different degrees. Nanocomposite coating was prepared by pulse current assisted chemical deposition process, which has the advantages of effectively improving the chemical deposition rate and ensuring the uniformity and compactness of the deposition layer surface morphology. In this paper, the effect of different duty ratios on Ni–P-(sol)Al2O3 nanocomposite deposition was studied. The surface morphology, composition, hardness, wear resistance and elastoplastic mechanical properties of the nanocomposite coating were tested through experiments. The experimental results showed that, when the duty ratio of pulse current was 20%, the prepared Ni–P-(sol)Al2O3 nano-composite deposition layer has the best performance, and its deposition rate reached 45.99 μm/h, hardness value was 629 HV, friction coefficient was 0.395, wear-width was 126.33 μm, Young modulus was 135.216 GPa, elastic recovery ratio he/hmax reached the maximum value of 0.3976, H3/E2 reached the maximum value of 0.0505 GPa. Compared with the coatings prepared by the traditional chemical deposition process, it is found that both coatings show good compactness and uniformity. However, the pulse-assisted chemical deposition method is significantly superior to the latter in hardness and wear resistance. The deposition layer prepared by pulse-assisted chemical deposition not only has a uniform and compact surface, but also has high hardness, good toughness and optimal wear resistance.

Effects of V/III ratio of InGaN quantum well at high growth temperature for near ultraviolet light emitting diodes

Purpose The aims of this paper is to study the effects of the V/III ratio of indium gallium nitride (InGaN) quantum wells (QWs) on the structural, optical and electrical properties of near-ultraviolet light-emitting diode (NUV-LED). Design/methodology/approach InGaN-based NUV-LED is successfully grown on the c-plane patterned sapphire substrate at atmospheric pressure using metal organic chemical vapor deposition. Findings The indium composition and thickness of InGaN QWs increased as the V/III ratio increased from 20871 to 11824, according to high-resolution X-ray diffraction. The V/III ratio was also found to have an important effect on the surface morphology of the InGaN QWs and thus the surface morphology of the subsequent layers. Apart from that, the electroluminescence measurement revealed that the V/III ratio had a major impact on the light output power (LOP) and the emission peak wavelength of the NUV-LED. The LOP increased by up to 53% at 100 mA, and the emission peak wavelength of the NUV-LED changed to a longer wavelength as the V/III ratio decreased from 20871 to 11824. Originality/value This study discovered a relation between the V/III ratio and the properties of QWs, which resulted in the LOP enhancement of the NUV-LED. High TMIn flow rates, which produced a low V/III ratio, contribute to the increased LOP of NUV-LED.

Kinetics of HfO2 etching and impurity elimination with atomic hydrogen beams

Modification of the surface composition, stoichiometry, morphology, and structure of HfO2 ultra-thin layers upon exposure to atomic hydrogen beams has been investigated by a combination of time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profile analysis, angle-resolved x-ray photoelectron spectroscopy (ARXPS), atomic force microscopy (AFM) imaging, and transmission electron microscopy (TEM). The etching reaction has been found to be thermally activated (Ea = 96 kJ/mol) and governed by the expression Retch(Å/h) = 3.03 × 108e-1.15x104T within the 350–400 °C temperature range. The rate law determined experimentally, i.e., Retch(Å/h) = 1.07 × 10−1[H2]1/2, is consistent with a reaction mechanism that involves the formation of a volatile hafnium dihydroxide, Hf(OH)2 in two successive elementary steps. Precise control of the etching conditions allows to reach atomically smooth HfO2 surfaces having r.m.s. roughness below 0.2 nm, with no evidence of Hf metal formation derived from the reaction with atomic H. Elimination of C, Cl, F, and S contaminants from the HfO2 surface through the formation of the corresponding volatile hydrides has proved to be generally most effective at high temperatures and H2 flow rates.