Layer Deposition Of Thin Films Research Articles

SERS-active substrates using DVD-R coated in silver thin films: A preliminary study for detection of commercial glyphosate

Glyphosate (GLP) is the herbicide with the highest level of global commercialization and historical use. Even though numerous studies have found this substance to be harmless, current research demonstrates that GLP might affect human health. For this reason, researcher efforts are concentrating on alternatives for analytical quantification, such as Surface Enhanced Raman Spectroscopy (SERS). In this work, a DVD-R@AgNPs SERS substrate was produced by the Cathodic Cage Plasma Deposition (CCPD) technique, which allowed a thin film layer deposition of silver nanoparticles (AgNPs) on the PC grating structure from Digital Video/Versatile Disc Recordable (DVD-R). Scanning Electron Microscopy with energy-dispersive X-ray spectroscopy was used to characterize the substrate and chemical changes on the surface after AgNPs deposition. The DVD-R@AgNPs substrate was used to detect standard crystal violet (CV), GLP, and RoundupTM GLP (GLP-RU) using Raman Spectroscopy. The CV was used as a control sample for SERS measurement, allowing the calculation of the substrate enhancement factor, which was in the order of ∼ 105. To evaluate the efficiency of the SERS substrate, the limit of detection was calculated and showed values of ∼ 10-10 mol/L for CV, 10-7 and 10-8 mol/L for GLP, and 10-6 mol/L for GLP-RU. Thus, the DVD-R@AgNPs SERS sensor is a low-cost substrate that analyzes traces of pesticides such as commercial GLP, demonstrating high SERS sensitivities and many applications.

Mechanical Strength Enhancement of Porous Nanocrystalline-Silicon (pnc-Si) Membrane via Titanium-oxide (Ti-O) Coating

Porous nanocrystalline silicon (pnc-Si) membrane is mainly studied as a blood filtration membrane, mimicking the glomerulus filtration membrane of a human kidney. However, the pnc-Si material itself is not hemocompatible and enormous membrane area to thickness ratio makes the membrane to be easily fractured. Silicon surface modification via titanium-oxide (Ti-O) thin film layer deposition has been proven to be hemocompatible and the presence of Ti-O layer has been numerically studied to give higher membrane flexural strength. In this work, square pnc-Si membranes of 2 mm × 2 mm × 20 nm size have been fabricated with and without Ti-O layer. Point loading-unloading nanoindentation method has been performed and the membranes’ displacement behaviour subjected to point loads is studied. The pnc-Si membranes with Ti-O layer were found to attain higher fracture strength, membrane bending stiffness and average hardness with the increase of ~20, ~11 and ~24%, respectively, compared to bare pnc-Si membranes. The mechanical strength of a free-standing pnc-Si membrane is improved by depositing a Ti-O thin film layer on the membrane structure.

Integrating Feedback Control and Run-to-Run Control in Multi-Wafer Thermal Atomic Layer Deposition of Thin Films

There is currently a lack of understanding of the deposition profile in a batch atomic layer deposition (ALD) process. Also, no on-line control scheme has been proposed to resolve the prevalent disturbances. Motivated by this, we develop a computational fluid dynamics (CFD) model and an integrated online run-to-run and feedback control scheme. Specifically, we analyze a furnace reactor for a SiO2 thin-film ALD with BTBAS and ozone as precursors. Initially, a high-fidelity 2D axisymmetric multiscale CFD model is developed using ANSYS Fluent for the gas-phase characterization and the surface thin-film deposition, based on a kinetic Monte-Carlo (kMC) model database. To deal with the disturbance during reactor operation, a proportional integral (PI) control scheme is adopted, which manipulates the inlet precursor concentration to drive the precursor partial pressure to the set-point, ensuring the complete substrate coverage. Additionally, the CFD model is utilized to investigate a wide range of operating conditions, and a regression model is developed to describe the relationship between the half-cycle time and the feed flow rate. A run-to-run (R2R) control scheme using an exponentially weighted moving average (EWMA) strategy is developed to regulate the half-cycle time for the furnace ALD process between batches.

Role of oligomer structures in the surface chemistry of amidinate metal complexes used for atomic layer deposition of thin films

Abstract

Atomic layer deposition of thin films as model electrodes: A case study of the synergistic effect in Fe2O3-SnO2

Developing higher capacity electrode materials is a key challenge in battery advancement. Metal oxides undergoing conversion and/or alloying reactions offer high capacities, but suffer from volumetric changes and poor conductivities. However, combining several of these oxides can induce a synergistic effect, enhancing electrode characteristics. Using atomic layer deposition (ALD), carefully controlled model thin-film electrodes comprised of SnO2 and Fe2O3, and mixtures thereof are deposited to investigate length scales at which intermixing of the oxides is required to maximize this effect. ALD enables the synthesis of both intermixed structures and oxides where Fe, Sn, and O are mixed at the atomic scale and nanolaminated structures where Fe2O3 layer and SnO2 layers form a structure with well-defined interfaces. These model systems reduce the complexity of electrodes by eliminating the need for binders and additives and ensuring one-dimensional charge carrier diffusion. Using ALD enables us to study the influence of interfaces on electrode characteristics. It was found that intermixing of Fe2O3 and SnO2 at the atomic scale kinetically suppresses the alloying of Sn. In the nanolaminated superstructure, however, Sn alloying does take place, causing the well-defined interfaces to break down due to the volume changes brought about by alloying. As a consequence, the electrode capacity is rapidly fades, and thus, this structure type should be avoided. Here, the authors demonstrate that ALD is a unique tool with great potential for unraveling complex mechanisms in battery materials.

Estimating the Interrelation between the Rate of Atomic Layer Deposition of Thin Platinum-Group Metal Films and the Molecular Mass of Reactant Precursors

The published data on the atomic layer deposition of thin platinum-group metal (Ru, Rh, Pd, Os, Ir, and Pt) films with the use of different reactant precursors and second reactants (O2, O3, H2, etc.) are generalized in the context of microelectronic technologies. A procedure for analyzing the data on the atomic layer deposition kinetics is discussed. The rate of atomic layer deposition of metallic ruthenium is not higher than 0.15 nm/cycle. An inverse dependence of the limiting atomic layer deposition growth rate on the precursor molecular mass is established. The rates of atomic layer deposition of thin films of all the remaining metals in the group range between 0.03–0.07 nm/cycle, which is lower than the values for a monolayer of these metals by several times. The methodology and ways of enhancing the reliability of the kinetic data on the atomic layer deposition are discussed, including the need for taking into account the sample surface types and effects of nucleation delays at the initial growth stages of the thin platinum-group metal film. The possible occurrence of chemical deposition reactions with intermediate products involved at the pulsed injection of the reactants is considered.

Redox Layer Deposition of Thin Films of MnO2 on Nanostructured Substrates from Aqueous Solutions

In this work, we report a new method for depositing thin films of MnO2 on planar and complex nanostructured surfaces, with high precision and conformality. The method is based on repeating cycles of adsorption of an unsaturated alcohol on a surface, followed by its oxidation with aqueous KMnO4 and formation of thin, solid MnO2. The amount of manganese oxide formed in each cycle is limited by the quantity of the adsorbed alcohol; thus, the growth exhibits the self-limiting characteristics of atomic layer deposition (ALD). Contrary to the typical ALD, however, the new redox layer deposition is performed in air, at room temperature, using common chemicals and simple laboratory glassware, which greatly reduces its cost and complexity. We also demonstrate application of the method for the fabrication of a nanostructured MnO2/Ni electrode, which was not possible with thermal ALD because of the rapid decomposition of the gaseous precursor on the high surface-area substrate. Thanks to its simplicity, the conformal deposition of MnO2 can be easily upscaled and thus exploited for its numerous (electro)chemical applications.

Toward 3D Thin-Film Batteries: Optimal Current-Collector Design and Scalable Fabrication of TiO2 Thin-Film Electrodes

Three-dimensional (3D) thin-film solid-state batteries are an interesting concept for microstorage, promising high footprint capacity, fast charging, safety, and long lifetime. However, to realize their commercialization, several challenges still need to be overcome. In this work, we focus on two issues: the conformal coating and the high throughput deposition of thin-film layers. First, to facilitate conformal deposition, a design based on 3D micropillars is chosen. Although such a design has been suggested in the past, we calculate for the first time what (footprint) capacities can be expected when using fully optimized pillar geometries while taking practical manufacturability into consideration. Next, spatial atomic layer deposition (S-ALD) is investigated as a scalable and conformal deposition technique. As proof-of-concept, 100 nm Cl-doped am-TiO2 thin-film electrodes are deposited by S-ALD on TiN-coated silicon micropillars. The influence of deposition parameters (i.e., exposure time and temperature) on the conformality and uniformity across the micropillar substrate is investigated. The results are discussed in terms of precursor diffusion and depletion, which is supported by an analytical model developed for our micropillar array. Furthermore, the Li-ion insertion properties of 3D electrodes fabricated by S-ALD and conventional ALD are compared. This research highlights the challenges and promises of 3D microbatteries and guides future S-ALD development to enable conformal and high-throughput thin-film deposition.

Atomic Layer Deposition of Thin Films onto 3D Nanostructures: The Effect of Wall Tilt Angle and Aspect Ratio of Trenches

A theoretical model predicting the spatial profile of a film grown on walls by atomic layer deposition (ALD) is developed. The possible initial nonverticality of trench walls and the dynamic variation of the aspect ratio of the structure in the process of film growth in nanosized trenches are considered in this model. The dependence of the resulting film thickness and conformity on ALD process parameters is studied theoretically.

Effect of Working Pressure During ZnO Thin-Film Layer Deposition on Transparent Resistive Random Access Memory Device Characteristics

Effect of Working Pressure During ZnO Thin-Film Layer Deposition on Transparent Resistive Random Access Memory Device Characteristics

Thermal conductivity measurement of amorphous dielectric multilayers for phase-change memory power reduction

In this work, we investigate the temperature-dependent thermal conductivities of few nanometer thick alternating stacks of amorphous dielectrics, specifically SiO2/Al2O3 and SiO2/Si3N4. Experiments using steady-state Joule-heating and electrical thermometry, while using a micro-miniature refrigerator over a wide temperature range (100–500 K), show that amorphous thin-film multilayer SiO2/Si3N4 and SiO2/Al2O3 exhibit through-plane room temperature effective thermal conductivities of about 1.14 and 0.48 W/(m × K), respectively. In the case of SiO2/Al2O3, the reduced conductivity is attributed to lowered film density (7.03 → 5.44 × 1028 m–3 for SiO2 and 10.2 → 8.27 × 1028 m–3 for Al2O3) caused by atomic layer deposition of thin-films as well as a small, finite, and repeating thermal boundary resistance (TBR) of 1.5 m2 K/GW between dielectric layers. Molecular dynamics simulations reveal that vibrational mismatch between amorphous oxide layers is small, and that the TBR between layers is largely due to imperfect interfaces. Finally, the impact of using this multilayer dielectric in a dash-type phase-change memory device is studied using finite-element simulations.

Life‐cycle greenhouse gas emissions and energy payback time of current and prospective silicon heterojunction solar cell designs

AbstractSilicon heterojunction (SHJ) cells offer high efficiencies and several advantages in the production process compared to conventional crystalline silicon solar cells. We performed a life‐cycle assessment to identify the greenhouse gas (GHG) footprint, energy payback time (EPBT) and cumulative energy demand of four different SHJ solar cell designs. We analyse these environmental impacts for cell processing and complete systems for both current and prospective designs. On the basis of in‐plane irradiation of 1700 kWh/m2, results for current designs show that life‐cycle GHG emissions could be 32 gCO2‐eq/kWh for complete SHJ photovoltaic (PV) systems (module efficiencies of 18.4%), compared with 38 gCO2‐eq/kWh for conventional monocrystalline silicon systems (module efficiency of 16.1%). The EPBT of all SHJ designs was found to be 1.5 years, compared with 1.8 years for the monocrystalline PV system. Cell processing contributes little (≤6%) to the overall environmental footprint of SHJ PV systems. Among cell processing steps, vacuum based deposition contributes substantially to the overall results, with 55–80%. Atomic layer deposition of thin films was found to have a significantly lower environmental footprint compared to plasma enhanced chemical vapour deposition and sputtering. Copper‐based compared with silver‐based metallization was shown to reduce the impact of this processing step by 74–84%. Increases in cell efficiency, use of thin silicon wafers and replacement of silver‐based with copper‐based metallization could result in life‐cycle GHG emissions for systems to be reduced to 20 gCO2‐eq/kWh for SHJ systems and 25 gCO2‐eq/kWh for monocrystalline system, while EPBT could drop to 0.9 and 1.2 years, respectively. Copyright © 2014 John Wiley & Sons, Ltd.

Surface Selective Atomic Layer Deposition of Hafnium Oxide for Copper Diffusion Barrier Application Using Tetrakis(diethylamino)Hafnium and Ethanol

Atomic layer deposition (ALD) is a thin film deposition technique, in which substrate surface is exposed to reactants in cyclic manner separated by discrete purging steps. Thus one atomic layer of material is deposited per ALD cycle. This cycle is repeated until desired thickness is achieved. The bottom up nature of this deposition process facilitates excellent conformality, uniformity and thickness and composition tunability.Patterning of ALD films for various device applications is commonly performed by removing the specific part of the film or by selectively depositing films on specific areas of the surface. In the former method, patterning is done with the use of extra processing steps such as etching, lithography etc. The latter method involves the use of masking layers to prevent ALD on specific areas.1, 2 Maskless ALD, i.e., surface selective atomic layer deposition of thin films has recently garnered considerable interest due to its simplicity. This method of patterning ALD films is unique in that no surface mask is required. Materials nucleate on different surfaces to different extents. This difference in nucleation time is used to achieve selective atomic layer deposition (SALD). In our earlier studies on SALD of HfO2 and TiO2, we used water as the oxygen source.3, 4 In this study, ALD of HfO2 was carried out using tetrakis(diethylamino)hafnium and a primary alcohol (ethanol) in a custom built ALD reactor (Fig. 1). Unlike common ALD processes, here we used ethanol as the oxygen source. Ethanol reacts with the hydroxyl (-OH) groups on silicon surface and forms alkoxides that serve as a starting surface for the ALD film growth. Thus the film growth is obtained on the Si surface. Figure 2 shows the thickness tunability of the HfO2 ALD process on Si surface using ethanol as the oxygen source. HfO2 was found to grow at a rate of 0.05 nm/cycle, without any growth inhibition on the silicon surface. Linear dependence indicates self-limited growth of HfO2 thin film, typical to the ALD process. On the other hand, significant growth delay was observed on copper surface. The use of ethanol reduces surface copper oxide into metallic copper and reduces the number of potential ALD nucleation sites. Thus selective deposition of HfO2 was achieved on silicon surface over copper surface. Such selectivity depends on many ALD processing parameters and substrate pretreatment conditions. In this report, the effect of these parameters on the extent of selectivity will be discussed in detail along with copper diffusion barrier characteristics of such selectively deposited ultrathin (1-2 nm-thick) HfO2 layers. The growth rate on silicon side was measured using spectral ellipsometry. X-ray photoelectron spectroscopy was used to probe the presence of HfO2 on copper surface. Results of this study can be used to selectively deposit ultra-thin layers of HfO2 on silicon surface over copper surface for copper diffusion barrier applications. This work was supported in part by the National Science Foundation (CBET 1067424 and EEC 1062943). We also thank Dr. Gregory Jursich for many helpful discussions.

Atomic layer deposition of thin films of titanium dioxide from titanium tetramethoxide and water

The atomic layer deposition of titanium oxide in the precursor systems Ti(OCH3)4-H2O and Ti(OC2H5)4-H2O was compared. The growth rate of titanium oxide formed by the atomic layer deposition in the Ti(OCH3)4-H2O system can be adequately estimated with due to regard for the number and size of ligands of a metal-containing precursor. The study in simulated body fluid solutions showed that polycrystallin TiO2 coatings with anatase structure are prone to accelerated osseointegration and, consequently, promising for the development of new biomedical products.

Remote Plasma Atomic Layer Deposition of Thin Films of Electrochemically Active LiCoO2

One of the remaining challenges in the field of portable electronics is the miniaturization of lithium-ion batteries without decreasing their storage capacity. To tackle this challenge and to effectively integrate battery technology in even a wider variety of applications, it is essential to produce high quality thin films for all-solid-state batteries. A remote plasma ALD process for the positive electrode material LiCoO2 was developed using the combination of CoCp2 as the cobalt precursor, LiOtBu as the lithium precursor and O2 plasma as the oxidant source. The thin films were deposited at a temperature of 325 °C with a virtually linear growth rate of 0.06 nm/cycle. After annealing the samples at 700 °C for 6 minutes the high temperature phase LiCoO2 was obtained, as demonstrated by XRD and Raman spectroscopy measurements. Electrochemical charge/discharge cycling showed good electrochemical activity with a promising storage capacity.

Atomic Layer Deposition of Thin Films for Lithium-Ion Batteries

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Crystal structures and thermal properties of Ba(1,2,4- t-Bu 3C 5H 2) 2 and Sr(1,2,4- t-Bu 3C 5H 2) 2: Precursors for atomic layer deposition

Sterically hindered Lewis base free bis(1,2,4-tri- tert-butylcyclopentadienyl)strontium ( 1) and bis(1,2,4-tri- tert-butylcyclopentadienyl)barium ( 2) were synthesized using the common metathesis route and characterized with NMR, MS, TGA/SDTA and XRD. Compound 1 crystallized as a monomer with typical bent structure. Asymmetric unit contains two independent slightly different Sr( t-Bu 3C 5H 2) 2 molecules with Cp(centroid)–Sr–Cp(centroid) angles of 165.1° and 169.4°. Depending on the way of crystallization two polymorphs ( 2a and 2b) were observed for Ba( t-Bu 3C 5H 2) 2. On sublimation Ba( t-Bu 3C 5H 2) 2 crystallizes as chains in which one methyl group of each Ba( t-Bu 3C 5H 2) 2 unit interacts with neighboring Ba( t-Bu 3C 5H 2) 2 unit’s barium atom. Slow crystallization of waxy evaporation residue of toluene solution results in monoclinic crystals ( 2b) whose asymmetric unit contains four slightly different individual Ba( t-Bu 3C 5H 2) 2 molecules with Cp(centroid)–Ba–Cp(centroid) angles of 161.3–164.9°. Both compounds prepared are volatile, thermally stable and reactive and thus suitable precursors for atomic layer deposition of thin films.

A new patterning method using photocatalytic lithography and selective atomic layer deposition.

We report a new patterning method using photocatalytic lithography of alkylsiloxane self-assembled monolayers and selective atomic layer deposition of thin films. The photocatalytic lithography is based on the fact that the decomposition rate of the alkylsiloxane monolayers in contact with TiO2 is much faster than that with SiO2 under UV irradiation in air. The photocatalytic lithography, using a quartz plate coated with patterned TiO2 thin films, was done to prepare patterned monolayers of the alkylsiloxane on Si substrates. A ZrO2 thin film was selectively deposited onto the monolayer-patterned Si substrate by atomic layer deposition.

Atomic layer deposition of thin films of ZnSe—structural and optical characterization

Thin films of sphalerite-type ZnSe were grown by atomic layer deposition (ALD) from elemental Zn and Se precursors. These films, grown on various substrates, show bright blue ‘edge’ emission accompanied by donor–acceptor pair emissions in the blue, green and red spectral regions. Red, green and blue emissions mixed together give a white color, with a color temperature between 2400 and 4500 K depending on a layer thickness and temperature. ZnSe grown by ALD is in consequence a promising material for the fabrication of semiconductor-based white light emitting thin film electroluminescence displays.

Atomic Layer Deposition of Thin Films Using O2 as Oxygen Source

Atomic layer deposition of TiO2 films was realized by using alternate pulses of TiI4 and O2. The film growth mechanism was studied by quartz crystal microbalance in the temperature range 200−350 °C. The adsorption of TiI4 proceeded via partial decomposition of TiI4, which resulted in an enhanced reactivity by the formation of a TiIx surface layer with x < 3. The reactivity of O2 toward this layer was sufficient to form TiO2 at an O2 pulse duration of 2 s when the substrate temperature was not lower than 235 °C. TiO2 films were also grown on Si(100) substrates at deposition temperatures between 230 and 460 °C. No residual iodine could be detected in the films grown at temperatures higher than 230 °C. Phase-pure anatase was formed in the whole temperature range except at the highest temperature where rutile was also obtained.