Atomic Layer Deposition Deposition Research Articles

Elucidating the Surface Reaction Mechanisms During Atomic Layer Deposition of LixAlySizO by in Situ Fourier Transform Infrared Spectroscopy

Reaction mechanisms in the atomic layer deposition (ALD) of LixAlySizO (LASO) using a LiOC(CH3)3/H2O–Al(CH3)3/H2O–Si(OCH2CH3)4/H2O chemistry were studied via in situ Fourier transform infrared spectroscopy (FTIR) at 225 °C. ALD deposition of Al2O3 using an Al(CH3)3/H2O chemistry and LiOH using a LiOC(CH3)3/H2O chemistry demonstrated ideal ALD growth. ALD deposition of SiO2 alone by Si(OCH2CH3)4/H2O chemistry was unsuccessful; however, incorporation of the same Si(OCH2CH3)4/H2O chemistry in between ALD processes of Al2O3 and LiOH resulted in ALD deposition of LixAlySizO. The as-deposited ALD LASO film with a composition of Li0.40Al0.32Si0.28O on a Si(100) substrate was amorphous but crystallized into β-LiAlSiO4 upon rapid thermal annealing (RTA) at 900 °C under N2. The ionic conductivity of as-deposited, amorphous ALD Li0.40Al0.32Si0.28O was as high as 1.62 × 10–6 S/cm at 361 °C with an activation energy of Ea = 0.70 eV.

Atomic layer deposition of cobalt carbide films and their magnetic properties using propanol as a reducing agent

The investigation of highly conformal thin films using Atomic Layer Deposition (ALD) is driven by a variety of applications in modern technologies. In particular, the emergence of 3D memory device architectures requires conformal materials with tuneable magnetic properties. Here, nanocomposites of carbon, cobalt and cobalt carbide are deposited by ALD using cobalt acetylacetonate with propanol as a reducing agent. Films were grown by varying the ALD deposition parameters including deposition temperature and propanol exposure time. The morphology, the chemical composition and the crystalline structure of the cobalt carbide film were investigated. Vibrating Sample Magnetometer (VSM) measurements revealed magnetic hysteresis loops with a coercivity reaching 500Oe and a maximal saturation magnetization of 0.9T with a grain size less than 15nm. Magnetic properties are shown to be tuneable by adjusting the deposition parameters that significantly affect the microstructure and the composition of the deposited films.

Preparation of ZnO/Al2O3 catalysts by using atomic layer deposition for plasma-assisted non-oxidative methane coupling

We prepared a ZnO/mesoporous Al2O3-shell/core structure by using atomic layer deposition (ALD) of ZnO on commercially-available mesoporous Al2O3. We used various analysis techniques such as scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, inductively coupled plasma-atomic emission spectroscopy, and surface area and pore size analyses based on nitrogen isotherm data. A 200 nm-thick slab of mesoporous Al2O3 particles was decorated by ZnO upon ALD deposition, whereas the inner part of the Al2O3 particle was free of ZnO. We evaluated the catalytic activity of the bare and the ZnO-covered Al2O3 for plasma-assisted nonoxidative coupling of methane. The catalytic behavior was shown to be sensitive to the amount of ZnO deposited. Particularly, 40-cycled ZnO/Al2O3 showed an enhanced selectivity to the olefin product with almost the same CH4 conversion as that of bare Al2O3. Preparation of the shell/core structure by using ALD can be an interesting strategy for finding highly-efficient catalysts in a plasma-assisted catalytic reaction.

Homogeneous transparent conductive ZnO:Ga by ALD for large LED wafers

Highly conductive and uniform Ga doped ZnO (GZO) films were prepared by atomic layer deposition (ALD) as transparent conductive layers for InGaN/GaN LEDs. The optimal Ga doping concentration was found to be 3 at%. Even for 4” wafers, the TCO layer shows excellent homogeneity of film resistivity (0.8 %) according to Eddy current and spectroscopic ellipsometry mapping. This makes ALD a favourable technique over concurrent methods like MBE and PLD where the up-scaling is problematic. In agreement with previous studies, it was found that by an annealing treatment the quality of the GZO/p-GaN interface can be improved, although it causes the degradation of TCO conductivity. Therefore, a two-step ALD deposition technique was proposed and demonstrated: a “buffer layer” deposited and annealed first was followed by a second deposition step to maintain the high conductivity of the top layer.

Pre-Patterned CVD Graphene: Insights on ALD deposition parameters and their influence on Al2O3 and graphene layers

ABSTRACTFabrication of graphene nanostructures it is important for both investigating their intrinsic physical properties and applying them into various functional devices. In this work we present a study on atomic layer deposition (ALD) of Al2O3 to produce patterned graphene through area-selective chemical vapor deposition (CVD) growth. A systematic parametric study was conducted to determine how the number of cycles and the purging time affect the morphology and the electrical properties of both graphene and Al2O3 layers.

Atomic Layer Deposition of Pt Nanoparticles within the Cages of MIL-101: A Mild and Recyclable Hydrogenation Catalyst.

We present the in situ synthesis of Pt nanoparticles within MIL-101-Cr (MIL = Materials Institute Lavoisier) by means of atomic layer deposition (ALD). The obtained Pt@MIL-101 materials were characterized by means of N2 adsorption and X-ray powder diffraction (XRPD) measurements, showing that the structure of the metal organic framework was well preserved during the ALD deposition. X-ray fluorescence (XRF) and transmission electron microscopy (TEM) analysis confirmed the deposition of highly dispersed Pt nanoparticles with sizes determined by the MIL-101-Cr pore sizes and with an increased Pt loading for an increasing number of ALD cycles. The Pt@MIL-101 material was examined as catalyst in the hydrogenation of different linear and cyclic olefins at room temperature, showing full conversion for each substrate. Moreover, even under solvent free conditions, full conversion of the substrate was observed. A high concentration test has been performed showing that the Pt@MIL-101 is stable for a long reaction time without loss of activity, crystallinity and with very low Pt leaching.

Tuning the mechanical properties of vertical graphene sheets through atomic layer deposition

We report the fabrication and characterization of graphene nanostructures with mechanical properties that are tuned by conformal deposition of alumina. Vertical graphene (VG) sheets, also called carbon nanowalls (CNWs), were grown on copper foil substrates using a radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique and conformally coated with different thicknesses of alumina (Al2O3) using atomic layer deposition (ALD). Nanoindentation was used to characterize the mechanical properties of pristine and alumina-coated VG sheets. Results show a significant increase in the effective Young’s modulus of the VG sheets with increasing thickness of deposited alumina. Deposition of only a 5 nm thick alumina layer on the VG sheets nearly triples the effective Young’s modulus of the VG structures. Both energy absorption and strain recovery were lower in VG sheets coated with alumina than in pure VG sheets (for the same peak force). This may be attributed to the increase in bending stiffness of the VG sheets and the creation of connections between the sheets after ALD deposition. These results demonstrate that the mechanical properties of VG sheets can be tuned over a wide range through conformal atomic layer deposition, facilitating the use of VG sheets in applications where specific mechanical properties are needed.

Recent progress of atomic layer deposition on polymeric materials

As a very promising surface coating technology, atomic layer deposition (ALD) can be used to modify the surfaces of polymeric materials for improving their functions and expanding their application areas. Polymeric materials vary in surface functional groups (number and type), surface morphology and internal structure, and thus ALD deposition conditions that typically work on a normal solid surface, usually do not work on a polymeric material surface. To date, a large variety of research has been carried out to investigate ALD deposition on various polymeric materials. This paper aims to provide an in-depth review of ALD deposition on polymeric materials and its applications. Through this review, we will provide a better understanding of surface chemistry and reaction mechanism for controlled surface modification of polymeric materials by ALD. The integrated knowledge can aid in devising an improved way in the reaction between reactant precursors and polymer functional groups/polymer backbones, which will in turn open new opportunities in processing ALD materials for better inorganic/organic film integration and potential applications.

Investigation of the dipole formation and growth behavior at In2O3|TiO2 heterojunctions using photoemission spectroscopy and atomic force microscopy

This paper discusses the investigation of the dipole formation at In2O3|TiO2 heterojunctions depending on preparation conditions, i.e., cleaning methods. In2O3 films were deposited using atomic layer deposition (ALD) onto solvent and in situ cleaned anatase and rutile film substrates. The interface dipole strength and film thickness were evaluated by photoemission spectroscopy. Our results indicate the formation of a large intrinsic and film thickness dependent interface dipole that reaches its maximum strength at monolayer thick ALD films. In addition, it was observed that UV photoelectron spectroscopy measurements introduced UV induced surface hydroxylation, which resulted in dipole potentials of −0.70 eV and −0.50 eV on solvent cleaned anatase and rutile, respectively. The overlayers also introduced small amounts of band bending (∼0.10 eV) at the interfaces. Taking these effects into account, the total dipole strength at monolayer thick In2O3 films was determined to be −0.96 eV for solvent cleaned anatase and rutile and −0.81 eV for in situ cleaned rutile. The deposition of single ALD cycles on differently cleaned rutile substrates resulted in similar work function values, suggesting little influence of the sample preparation method prior to ALD deposition on the dipole formation. This was assigned to the fact that ALD oxides benefit from ambient water related contamination by integrating the molecules into the growing ALD layer. Highest initial growth was observed on solvent cleaned rutile, followed by in-situ cleaned rutile and solvent cleaned anatase. The In2O3 growth converged at 0.3 Å/c past the nucleation regime.

Controlled Phase and Tunable Magnetism in Ordered Iron Oxide Nanotube Arrays Prepared by Atomic Layer Deposition.

Highly-ordered and conformal iron oxide nanotube arrays on an atomic scale are successfully prepared by atomic layer deposition (ALD) with controlled oxidization states and tunable magnetic properties between superparamagnetism and ferrimagnetism. Non-magnetic α-Fe2O3 and superparamagnetic Fe3O4 with a blocking temperature of 120 K are in-situ obtained by finely controlling the oxidation reaction. Both of them exhibit a very small grain size of only several nanometers due to the nature of atom-by-atom growth of the ALD technique. Post-annealing α-Fe2O3 in a reducing atmosphere leads to the formation of the spinel Fe3O4 phase which displays a distinct ferrimagnetic anisotropy and the Verwey metal-insulator transition that usually takes place only in single crystal magnetite or thick epitaxial films at low temperatures. The ALD deposition of iron oxide with well-controlled phase and tunable magnetism demonstrated in this work provides a promising opportunity for the fabrication of 3D nano-devices to be used in catalysis, spintronics, microelectronics, data storages and bio-applications.

Room Temperate Bonding of Al2O3 Layers by Atomic Layer Deposition on Polyimide Substrates

Room temperature bonding of Al2O3 layers deposited by Atomic Layer Deposition (ALD) was studied for gas diffusion barrier structures on polymer films. A modified method of the surface activated bonding (SAB) was applied for the bonding of ALD Al2O3 coated polyimide sheets. ALD deposition was performed at different process temperatures of 80, 150 and 250 ºC. The results of AFM surface profile demonstrate that samples prepared at a higher temperature in ALD process exhibit a rougher surface. Also, polymer films processed at high temperature suffer larger warpage. The size of the bonded area was optimized when the ALD synthesis of Al2O3 was performed at 80ºC, leaving only a small, unbonded area.

(Invited) Seebeck Coefficient Measurement of Pbsete / PbTe Nanolaminate Structures

Thermoelectric (TE) materials can be applied for solid state power generation or heating/cooling systems that convert heat into electricity and vice-versa. The green renewable technology related to thermoelectrics could play an important role to decrease the energy consumption from fossil fuels and decrease greenhouse gas emission. The main challenge for thermoelectric devices produced currently is their low efficiency. Therefore, it is essential to develop high efficiency TE materials and devices with superior performance. The efficiency of TE materials is expressed by the dimensionless thermoelectric figure of merit, ZT = S2σT/ k, where S is the Seebeck coefficient, σ is the electrical conductivity, and kis the thermal conductivity [1]. Previous work has demonstrated two main TE materials have higher ZT values. The first TE material with a complex crystal structure called a phonon glass electron crystal in which the voids, defects, and rattlers could scatter phonons to decrease the lattice thermal conductivity, and thus to increase ZT. Another one is called nanomaterials: including quantum wells, quantum dots, superlattice, quantum wires and nanolaminates, which introduce a large density of interfaces to enhance phonon scattering. The thermal conductivity of these nanomaterials was effectively reduced, and the ZT of TE materials was improved significantly. The IV-VI semiconducting lead chalcogenides, such as PbTe and PbSe, have been investigated due to their high figure of merit, good chemical stability, low vapor pressure and high melting point. Therefore, they are promising thermoelectric materials for intermediate temperature applications ranging from 600 to 800 K. There are different techniques that can be used to synthesis PbTe and PbSe, including pulsed laser deposition (PLD), metal-organic chemical vapor deposition (MO-CVD), magnetron sputtering deposition, molecular beam epitaxy (MBE) and atomic layer deposition (ALD). The ALD is a self-limiting technique that allows atomic layer growth each time. ALD can precisely control the film layer thickness, stoichiometry, composition, uniformity, and sharp interface. ALD also shows perfect conformal coverage when it is deposited on complex surface structures. Therefore, ALD is considered as a novel and competitive method to deposit PbTe/PbSe nanolaminate structures. It is possible to generate the reproducible and well-defined nanolaminate structures. In addition, the ALD deposition can be operated at rather low temperature compared to other techniques. In this work we report on the Seebeck coefficient measurements in PbSeTe / PbSe nanolaminate structures. The multiple PbTe/PbSeTe nanolaminates were deposited on silicon substrates by a thermal ALD system. This new nanolaminate structure was achieved by first depositing a very thin layer of the PbSeTe ternary compound with binary PbTe layers. The PbSeTe ternary compound is formed by nucleation of PbSe quantum dots between binary PbTe layers, and followed by an annealing process step. It is noted that the formation of the PbSe quantum dots is facilitated by the prevailing Volmer-Weber island growth mode. Lead bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (Pb(C11H19O2)2), (trimethylsilyl) telluride ((Me3Si)2Te) and (trimethylsilyl) selenide ((Me3Si)2Se) were employed as the chemical ALD precursors for lead, telluride and selenide, respectively. 20 sccm N2 was used as a carrier gas to transport the chemical precursors into the ALD reaction chamber. The ALD growth temperature was 170 oC. The solid lead precursor was volatilized at a temperature of 140 oC, the liquid Te precursor required heating to 40 oC, and the liquid Se precursor was kept at room temperature. The chamber base pressure was kept at 30 mTorr. Several physical characterization techniques have been employed to determine the ALD nanolaminate formation. The crystal structure was analyzed by X-ray diffraction (XRD). The film morphology and structure of the products were determined by field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HR-TEM).The surface roughness was analyzed by atomic force microscopy (AFM). The analysis of the composition and stoichiometry of the ternary and binary layers were carried out by X-ray photoelectron spectroscopy (XPS) and Energy dispersive X-ray spectroscopy (EDS). The Seebeck coefficient of the sample was also measured in order to calculate ZT value using Seebeck coefficient measurement equipment of MMR SB100. Figure 1 shows an FE-SEM image of surface morphplogy of PbTe/PbSe nanolaminate films on silicon substrate.

Room Temperate Bonding of Al2O3 Layers by Atomic Layer Deposition on Polyimide Substrates

Atomic layer deposition (ALD) gas barrier layer coatings on polymer substrates have been studied to address the problem of short-lifetime of polymer devices. ALD Al2O3 layers deposited with trimethylaluminium (TMA) and H2O vapor precursors are relatively dense and conformal, so ALD Al2O3 layers are good candidates for effective gas barriers against water vapor and oxygen permeation. In order to seal such ALD Al2O3 coated polymer substrates without organic adhesives, the bonding technique of choice has to satisfy low temperature bonding requirements. Utilizing a high temperature bonding process would damage thermally sensitive polymer substrates during thermal compression bonding. Furthermore the gas barrier property of organic adhesives would be too low for effective sealing. The polymer substrates used in this study are polyimide (PI) sheets from XENOMAX® from Toyobo Co., Ltd that are widely used as substrates for flexible electronics. These polyimide sheets have extremely smooth surfaces (RMS ~1 nm), which are conducive for bonding, because good large contact areas can be obtained. These polyimide substrate sheets of 35 μm thickness were coated with Al2O3 films of 250 ALD cycles using different process temperatures ranging from 80 ºC, 150 ºC and 250 ºC, while 100 ALD cycles were used at 250 ºC. The warpage of the polyimide sheets, the surface morphology, and the results of bonding for these ALD Al2O3 coated polyimide samples were investigated as a function of different ALD deposition temperatures. The polyimide sample processed at the higher ALD Al2O3 temperature of 250 ºC exhibited much larger warpage, which is detrimental for bonding. We prepared PI sheets whose size was 10 cm x 10 cm. The ALD Al2O3 on polyimide samples deposited at 80, 150, and 250 ºC display warpage, and these edges lifted up to 1 mm, 3 mm, and 5 mm from a horizontal plane, respectively. This warpage is attributed to the difference of thermal expansion coefficients between the polyimide sheet and the deposited ALD Al2O3 layer. The surface morphology of the ALD layer was studied using atomic force microscopy (AFM) surface profiling. The sample deposited at a lower ALD temperature has smoother surface morphologies. Our ALD Al2O3 films synthesized at 80 ºC exhibited a very smooth surface morphology indicative of amorphous material, while the Al2O3 film synthesized at 250 ºC was observed to possess a granular structure demonstrating recrystallization into a polycrystalline film. The rough grain structure of ALD Al2O3 films deposited at 250 ºC exceeds the critical surface roughness and as a consequence prevents surfaces from bonding. For the bonding experiment, all PI samples coated by ALD Al2O3 were bonded using a modified method of Surface Activated Bonding (SAB) employing a nano-adhesion layer. First, ALD Al2O3 layers of about 25 nm are deposited on the surface of the polyimide substrates using trimethylaluminium (TMA) and water as precursors. Next, the Al2O3-coated surfaces are moved inside a high vacuum bonding machine and cleaned using Ar-ion beam bombardment. After the surface cleaning process step, Si nano-adhesive layers are deposited via ion-beam sputtering. Subsequently, the surface of the nano-adhesion layers are activated using the Ar-ion beam SAB method. Finally, surfaces were brought into close contact and bonded under compression in ultra-high vacuum. The structure of the bond interface was PI/Al2O3/Si/Si/Al2O3/PI. Here the thickness of each ALD Al2O3 layer and Si layer are 25 nm and 10 nm, respectively. We compared the results of the bonding of PI films coated at different ALD process temperatures. All bonding processes were performed at room temperature in ultra high vacuum. While the ALD Al2O3 samples deposited at 150 ºC suffered various non-bonded areas due to warpage and surface roughness, the ALD films deposited at 80 ºC revealed near perfect bonding without any voids, which is desirable for tight sealing of gas barrier layers. Room temperature bonding of ALD Al2O3 films on Si and polyimide substrates was successfully performed. Due to high temperature gradient induced warpage of the polymer substrate and elevated surface roughness of the ALD layer, a lower process temperature of 80 ºC for ALD synthesis of Al2O3 provided optimum gas barrier conditions. The results of our bonding experiments demonstrate that larger bonded areas were achieved when the ALD synthesis of Al2O3 gas barrier layers was performed at 80 ºC. This bonding method is expected to be used for future microelectronics packaging and gas barrier sealing for polymer substrate.

Surface compositions of atomic layer deposited Zn1−xMgxO thin films studied using Auger electron spectroscopy

In this paper, the authors present Auger electron spectroscopy (AES) studies of Zn1−xMgxO (ZMO) films grown via interrupted atomic-layer deposition (ALD) techniques. The ZMO films were fabricated by alternating ALD deposition of ZnO and MgO layers up to 1000 cycles. Zn1−xMgxO films with progressively decreasing Mg/Zn ratios (Mg/Zn = 1/1, 1/2, 1/3, 1/4, 1/5, 1/6, 1/9, and 2/8, 3/12, 4/16, and 5/20) were fabricated for this study. The AES results exhibit an abrupt drop of Mg composition on the ZMO surface when the Mg/Zn < 1/3. Additionally, the surface composition ratios of O to Mg, O to Zn, and Mg to Zn were estimated with known Auger sensitivity factors. The results indicate that Mg ions diffuse into the bulk, forming Zn1−xMgxO alloys.

Effects of substrate conductivity on cell morphogenesis and proliferation using tailored, atomic layer deposition-grown ZnO thin films.

We demonstrate that ZnO films grown by atomic layer deposition (ALD) can be employed as a substrate to explore the effects of electrical conductivity on cell adhesion, proliferation, and morphogenesis. ZnO substrates with precisely tunable electrical conductivity were fabricated on glass substrates using ALD deposition. The electrical conductivity of the film increased linearly with increasing duration of the ZnO deposition cycle (thickness), whereas other physical characteristics, such as surface energy and roughness, tended to saturate at a certain value. Differences in conductivity dramatically affected the behavior of SF295 glioblastoma cells grown on ZnO films, with high conductivity (thick) ZnO films causing growth arrest and producing SF295 cell morphologies distinct from those cultured on insulating substrates. Based on simple electrostatic calculations, we propose that cells grown on highly conductive substrates may strongly adhere to the substrate without focal-adhesion complex formation, owing to the enhanced electrostatic interaction between cells and the substrate. Thus, the inactivation of focal adhesions leads to cell proliferation arrest. Taken together, the work presented here confirms that substrates with high conductivity disturb the cell-substrate interaction, producing cascading effects on cellular morphogenesis and disrupting proliferation, and suggests that ALD-grown ZnO offers a single-variable method for uniquely tailoring conductivity.

Platinum-Enhanced Electron Transfer and Surface Passivation through Ultrathin Film Aluminum Oxide (Al₂O₃) on Si(111)-CH₃ Photoelectrodes.

We report the preparation, stability, and utility of Si(111)-CH3 photoelectrodes protected with thin films of aluminum oxide (Al2O3) prepared by atomic layer deposition (ALD). The photoelectrodes have been characterized by X-ray photoelectron spectroscopy (XPS), photoelectrochemistry (Fc in MeCN, Fc-OH in H2O), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) simulation. XPS analysis of the growing Al2O3 layer affords both the thickness, and information regarding two-dimensional versus three-dimensional mode of growth. Impedance measurements on Si(111)|CH3|Al2O3 devices reveal that the nascent films (5-30 Å) exhibit significant capacitance, which is attenuated upon surpassing the bulk threshold (∼30 Å). The Al2O3 layer provides enhanced photoelectrochemical (PEC) stability evidenced by an increase in the anodic window of operation in MeCN (up to +0.5 V vs Ag) and enhanced stability in aqueous electrolyte (up to +0.2 V vs Ag). XPS analysis before and after PEC confirms the Al2O3 layer is persistent and prevents surface corrosion (SiOx). Sweep-rate dependent CVs in MeCN at varying thicknesses exhibit a trend of increasingly broad features, characteristic of slow electron transport kinetics. Simulations were modeled as slow electron transfer through a partially resistive and electroactive Al2O3 layer. Lastly, we find that the Al2O3 ultrathin film serves as a support for the ALD deposition of Pt nanoparticles (d ≈ 8 nm) that enhance electron transfer through the Al2O3 layer. Surface recombination velocity (SRV) measurements on the assembled Si(111)|CH3|Al2O3-15 device affords an S value of 4170 cm s(-1) (τ = 4.2 μs) comparable to the bare Si(111)-CH3 surface (3950 cm s(-1); τ = 4.4 μs). Overall, the results indicate that high electronic quality and low surface defect densities can be retained throughout a multistep assembly of an integrated and passivated semiconductor|thin-film|metal device.

Nanomechanical properties of platinum thin films synthesized by atomic layer deposition

The nanomechanical properties of Pt thin films grown on Si (100) using atomic layer deposition (ALD) were investigated using nanoindentation. Recently, atomic layer deposition (ALD) has successfully demonstrated the capability to deposit ultra-thin films of platinum (Pt). Using (methylcyclopentadienyl) trimethylplatinum (MeCpPtMe3) as chemical platinum precursor and oxygen (O2) as the oxidizing agent, the ALD synthesis of Pt can be achieved with high conformity and excellent film uniformity. The ALD process window for Pt films was experimentally established in the temperature range between 270°C and 320°C, where the sheet conductance was constant over that temperature range, indicating stable ALD Pt film growth rate. ALD growth of Pt films exhibits very poor nucleation and adhesion characteristics on bare Si surfaces when the native oxide was removed by 2% HF etch. Pt adhesion improves for thermally oxidized Si wafers and for Si wafers covered with native oxide. Three ALD Pt films deposited at 800, 900, and 1000 ALD deposition cycles were tested for the structural and mechanical properties. Additionally, the sample with 900 ALD deposition cycles was further annealed in forming gas (95% N2 and 5% H2) at 450°C for 30min in order to passivate dangling bonds in the grain boundaries of the polycrystalline Pt film. Cross-sectional transmission electron microscopy (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscope (SEM) were employed to characterize the films' surface structure and morphology. Nanoindentation technique was used to evaluate the hardness and modulus of the ALD Pt films of various film thicknesses. The results indicate that the films depict comparable hardness and modulus results; however, the 800 and 1000 ALD deposition cycles films without forming gas annealing experienced significant amount of pileup, whereas the 900 ALD deposition cycles sample annealed in forming gas resulted in a smaller pileup.

Nanomechanical and Morphological Characterization of Tungsten Trioxide (WO3) Thin Films Grown by Atomic Layer Deposition

This study investigates the nanomechanical properties and surface morphology of tungsten oxide (WO3) thin films deposited on p-type Si (100) substrates using atomic layer deposition (ALD) technology with 2000 ALD deposition cycles at a growth temperature of 300°C and annealed at different temperatures. The samples were further furnace annealed at 500, 600 and 700°C for 60 min. The influence of the deposition process on the structure and properties of the WO3 films is discussed, presented and correlated to the characteristic features of the ALD technique. The results depict significant difference in the hardness and modulus measurements between the as deposited sample and the annealed ones. The hardness and modulus drop from 14 and 170 GPa for the as deposited sample to 10 and 140 GPa for the annealed ones respectively. Surface roughness was observed to increase with annealing temperature and the initially amorphous as deposited sample reached complete recrystallization and transformed into polycrystalline films as indicated by XRD.

ALD Zirconium Oxide (ZrO2) Thin Films Mechanical/Structural Properties for High-Tech Applications

The nanomechanical and structural properties of atomic layer deposition (ALD) zirconium oxide (ZrO2) films of varying thickness deposited on p-type Si (100) substrates with 200, 300, and 500, ALD deposition cycles were investigated. The 300 ALD deposition cycles ZrO2 films were further annealed at 600°C. The nanomechanical properties of the films were tested using nanoindentation and the surface morphology was investigated using AFM. The structural and surface properties were explored using field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). We discuss the influence of the deposition technique on the structure and properties of the ZrO2 films resulting from ALD synthesis. The nanoindentation results indicate that the films become consistently softer as the number of ALD deposition cycles increase and the film grows thicker. Further annealing of the films at 600°C slightly enhanced the hardness and fracture toughness of the films. The annealed ALD films depicted shorter radial cracks compared to the films under the same applied stress, which were not annealed in forming gas.

Co3O4-modified TiO2 nanotube arrays via atomic layer deposition for improved visible-light photoelectrochemical performance.

Composite Co3O4/TiO2 nanotube arrays (NTs) were fabricated via atomic layer deposition (ALD) of Co3O4 thin film onto well-aligned anodized TiO2 NTs. The microscopic morphology, composition, and interfacial plane of the composite structure were characterized by scanning electron microscopy, energy dispersion mapping, X-ray photoelectron spectra, and high-resolution transmission electron microscopy. It was shown that the ultrathin Co3O4 film uniformly coat onto the inner wall of the high aspect ratio (>100:1) TiO2 NTs with film thickness precisely controlled by the number of ALD deposition cycles. The composite structure with ∼4 nm Co3O4 coating revealed optimal photoelectrochemical (PEC) performance in the visible-light range (λ > 420 nm). The photocurrent density reaches as high as 90.4 μA/cm(2), which is ∼14 times that of the pristine TiO2 NTs and 3 times that of the impregnation method. The enhanced PEC performance could be attributed to the finely controlled Co3O4 coating layer that enhances the visible-light absorption, maintains large specific surface area to the electrolyte interface, and facilitates the charge transfer.