Layer Deposited Aluminum Oxide Research Articles

Restricting Anion Migrations by Atomic Layer-Deposited Alumina on Perovskite Nanocrystals while Preserving Structural and Optical Properties

Restricting Anion Migrations by Atomic Layer-Deposited Alumina on Perovskite Nanocrystals while Preserving Structural and Optical Properties

Non-linear pH responses of passivated graphene-based field-effect transistors

Graphene-based field-effect transistors (FETs) are suitable for pH sensors due to their outstanding surface chemical properties and its biocompatibility. To improve the devices' stability and pH sensitivity, different sets of dielectric passivation layers composed of monolayer hexagonal boron nitride with and without aluminum oxide layers were evaluated. Non-linearities of the pH response were observed. Heterostructure FETs were derived from subtractive manufacturing of commercially transferred two-dimensional materials on four-inch SiO2/Si wafers via stainless steel and polypropylene masking. Phosphate solutions (10 mM) of varying pH were incubated on bare devices, whereby liquid-gating elucidated linear changes in the Dirac voltage of hBN/graphene (−40 mV/pH) that was smaller than a device consisting only of monolayer graphene (−47 mV/pH). Graphene-based FETs were passivated with aluminum oxide nanofilms via electron beam or atomic layer deposition and were observed to have distinct Raman spectral properties and atomic force microscopy topologies corroborating the hypothesis that morphological differences of the deposited aluminum oxide influence the pH-dependent electrical properties. Atomic layer deposition of aluminum oxide on the 2D sensing areas resulted in non-linear shifting of the Dirac voltage with respect to pH that evolved as a function of deposition thickness and was distinct between graphene with and without hexagonal boron nitride as a capping monolayer. The non-linear response of varying thickness of AlxOy on graphene-based FETs was progressively reduced upon basic wet etching of the AlxOy. Overall, passivated graphene-based transistors exhibit deposition-dependent pH responses.

Photovoltaics literature survey (No. 181)

Photovoltaics literature survey (No. 181)

Tube‐type plasma‐enhanced atomic layer deposition of aluminum oxide: Enabling record lab performance for the industry with demonstrated cell efficiencies >24%

AbstractIn this work, single‐side aluminum oxide (Al2O3) deposition enabled by a new tube‐type industrial plasma‐assisted atomic layer deposition (PEALD) technique is presented to meet the increasingly stringent requirements for high‐efficiency solar cell mass production. Extremely low emitter saturation current densities, J0e, down to 15 fA/cm2 are achieved on an industrial textured boron emitter with a sheet resistance of 104 Ω/sq, passivated by PEALD Al2O3/PECVD SiNx stack after firing. An implied open‐circuit voltage of up to 721 mV is obtained on symmetrical lifetime samples. The underlying passivation mechanisms of this new tube‐type PEALD Al2O3 are investigated by contactless corona‐voltage measurements. The results indicate that the superior passivation is mainly attributed to a low interface defect density down to 1.1 × 1011 cm−2 eV−1 and a high negative fixed charge density up to 4.5 × 1012 cm−2. Simulations show that the obtained J0e is close to its intrinsic limit. Lastly, the developed tube‐type PEALD Al2O3 is applied to industrial TOPCon solar cells achieving an average cell efficiency above 24% and a maximum Voc of 707 mV. This work shows that the record level of surface passivation available from lab‐scale PEALD reactors is now available in a flexible high‐throughput industrial PEALD platform, which opens a new route for mass production of high‐efficiency industrial TOPCon solar cells with a lean process at low costs.

Performance of nanoimprinted and nanocoated optical label-free biosensor - nanocoating properties perspective

In recent years, nanoimprinted structures have gained attention due to development of lithographic techniques and molds that enable mass fabrication of a large variety of devices, including optical sensors and biosensors. In this work, one-dimensional photonic crystals (PhC) were nanoimprinted in UV-curable polymer. To enhance interactions between light and medium at PhC surface, optically transparent, high-refractive-index titanium oxide nanocoating with well-defined thickness was deposited on the structure using magnetron sputtering. Since spectral response of PhC varies with optical properties and thickness of layers formed at their surface, they can be used for biosensing applications. In this work we focus on the impact of the nanocoating properties on performance of the optical label-free biosensor. First, the effect of the bound biological material thickness has been studied numerically and experimentally using an incremental atomic layer deposition of aluminum oxide with refractive index reaching 1.6 in the visible spectral range as a reference layer to a biological film. It was shown that there is an optimal thickness of the coating for which the sensing properties (including capability to detect biomolecules of various sizes) are the greatest. Next, using biotin as a receptor and peridinin-chlorophyll-protein conjugated with streptavidin as a target, we have proven that when the nanocoating properties are not optimized for the biomaterial at the sensor surface, sensing capabilities are highly limited.

Interface doping of zinc oxide nanorods

The effect of an increase in the electrical conductivity of a system of zinc oxide nanorods by a factor of 105 during atomic layer deposition of a thin dielectric layer of aluminum oxide was found. It is shown that a change in the electrical conductivity of zinc oxide during atomic layer deposition of aluminum oxide on the surface is also observed for thin polycrystalline layers of zinc oxide. A study of polycrystalline layers of zinc oxide coated with aluminum oxide using ultraviolet and X-ray photoelectron spectroscopy is presented. Based on the results of photoelectron spectroscopy, two main factors for changing the electrical conductivity are proposed, which consist in the formation of a two-dimensional electron gas at the ZnO|Al2O3 interface and doping of the near-surface region of zinc oxide with aluminum atoms. Keywords: nanorods, zinc oxide, aluminum oxide, atomic layer deposition, transparent electrodes, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy.

Эффект интерфейсного легирования системы наностержней оксида цинка

The effect of an increase in the electrical conductivity of a system of zinc oxide nanorods by a factor of 10^5 during atomic layer deposition of a thin dielectric layer of aluminum oxide was found. It is shown that a change in the electrical conductivity of zinc oxide during atomic layer deposition of aluminum oxide on the surface is also observed for thin polycrystalline layers of zinc oxide. A study of polycrystalline layers of zinc oxide coated with aluminum oxide using ultraviolet and X-ray photoelectron spectroscopy is presented. Based on the results of photoelectron spectroscopy, two main factors for changing the electrical conductivity are proposed, which consist in the formation of a two-dimensional electron gas at the ZnO/Al2O3 interface and doping of the near-surface region of zinc oxide with aluminum atoms.

Selective dry etching of UV-nanoimprinted resin passivation masks for area selective atomic layer deposition of aluminum oxide

To demonstrate area selective atomic layer deposition (ALD) using UV-nanoimprinted resin patterns as physical passivation masks, we investigated the removal of UV-cured resin films subjected to sequential mutual doses of trimethylaluminum (TMA) and H2O by using dry etching procedures. On the basis of the removal of a residual layer characteristic from imprint resin patterns by anisotropic oxygen reactive ion etching (O2 RIE), oxidatively etched UV-cured films were modified with TMA and H2O in an ALD-like cyclic manner. Atomic force microscopy and time-of-flight secondary ion mass spectrometry [time-of-flight secondary ion mass spectrometry (TOF-SIMS)] analysis suggested that the combination of physical Ar ion milling and subsequent chemical O2 RIE enabled the elimination of oxidized UV-cured resin masks modified with 5-cycle TMA doses. By contrast, Ar ion milling or O2 RIE left organic or inorganic residues on silicon surfaces, respectively. A TMA-modified hybridized resin layer was etched by physical Ar ion milling; subsequently, the organic residual resin layer was removed by chemical O2 RIE in the case of 5-cycle modification with TMA. The mapping image of Al+ visualized by TOF-SIMS suggested that line patterns of aluminum oxide were left selectively on unmasked silicon substrate surfaces by site-selective dry etching of TMA-modified imprint resin passivation masks with 500 nm linewidth.

Defect Control for High‐Efficiency Cu2ZnSn(S,Se)4 Solar Cells by Atomic Layer Deposition of Al2O3 on Precursor Film

Cu2ZnSn(S,Se)4 are emerging as promising photovoltaic materials due to their outstanding photoelectrical performances, benign grain boundaries, and Earth‐abundant constituent elements. However, there are largely distributed cation‐disordering defects and defect clusters, which lead to an increase in recombination and a large open‐circuit voltage deficit and thus deteriorate device performance. Herein, defect control for a high‐efficiency Cu2ZnSn(S,Se)4 solar cell by atomic layer deposition of aluminum oxide (ALD‐Al2O3) on the precursor film is reporter. CuZn defects and Sn‐related deep defects are largely suppressed because of the decrease in Sn2+ and the increase in Sn4+ in the film by ALD‐Al2O3 on the precursor are found, and the crystallinity of absorber layer is improved from a double‐layer structure to a completely single‐layer structure. Furthermore, the carrier lifetime and recombination in the bulk and interface are significantly improved for devices with ultrathin Al2O3. Using this approach, the conversion efficiency increases from 8.8% to 11.0% and the open‐circuit voltage deficit decreases from 0.621 to 0.577 V. Herein, a deep understanding of the relationship between Al2O3 incorporation and high‐efficiency Cu2ZnSn(S,Se)4 devices and a new direction for controlling defects to further improve the performance of kesterite solar cells are provided.

Superhydrophobic Antireflection Coating on Glass Using Grass-like Alumina and Fluoropolymer.

This work presents a superhydrophobic antireflective (AR) coating on glass. The coating consists of a grass-like alumina layer capped with plasma-deposited fluoropolymer. The grass-like alumina is formed by hot water treatment of atomic layer-deposited alumina on glass, and the fluoropolymer is plasma-deposited from CHF3. Excellent broadband AR performance is observed in the visible spectrum with an average transmission of 94.9% for single-sided coated glass, which is close to the maximum 95.3% possible for this glass. Extremely desirable contact angles are obtained with 5–7 min-long fluoropolymer treatments on grass-like alumina with 173° advancing and 160° receding contact angles. This type of multifunctional coating can be beneficial in a multitude of applications like self-cleaning AR coating for solar panels, windows in high-rise buildings, sensors, and aerospace applications as well as just utilizing the excellent water repellent behavior in applications where only superhydrophobicity is required.

Spatial Atomic Layer Deposition of Aluminum Oxide as a Passivating Hole Contact for Silicon Solar Cells

Herein, tunneling aluminum oxide (Al2O3) passivation layers are demonstrated to be a candidate for hole collecting, passivating contacts when coupled with a boron‐doped surface. These very thin Al2O3 films (1.5–3 nm) are deposited using spatial atomic layer deposition (ALD) on boron diffused (110–115 Ω □−1) hydrophilic surfaces operating as metal–insulator–semiconductor (MIS) contacts. The emitter saturation current density values of ≈57 fA cm−2 are achieved for the Al2O3 film thicknesses of 2 nm before metallization. At this same thickness, the contact resistivity values of 33 mΩ cm2 are obtained after metallization. Most importantly, the boron diffusion, wet chemical surface preparation, and spatial ALD of Al2O3 used to create these MIS structures are all performed with industrially relevant equipment on Cz wafers.

Evaluating Mechanical Properties of 100nm-Thick Atomic Layer Deposited Al2o3 as a Free-Standing Film

The mechanical properties of free-standing atomic layer-deposited alumina thin films were evaluated in this study. Stress-strain curves were obtained by measuring alumina films floating on the water surface. The Young's modulus, strength, and elongation of the free-standing films were analyzed at varying deposition temperatures of 80-200°C. The results show that the mechanical properties improve with increasing temperature. The microstructures of the films were examined to explain the change of the mechanical properties depending on the deposition conditions. Finally, the underlying causes of the differences in the mechanical properties were analyzed by evaluating the chemical composition of the thin films.

Thickness determination of porous Pt cathode thin film capped by atomic layer-deposited alumina for low-temperature solid oxide fuel cells

This study investigated the effects of the apparent thickness of porous Pt cathode thin films thermo-mechanically stabilized by an atomic layer-deposited (ALD) alumina capping agent on effective electrical conductivity and electrochemical performance. Four-point probe resistance measurements revealed that a 120 nm-thick porous Pt film exhibits a relatively high electrical conductivity of 9.2 × 103 S/cm. Cathode reaction resistance measurements by means of alternating current impedance spectroscopy (ACIS) analysis show that ALD alumina can act as a thermo-mechanical stabilizer for a 120 nm-thick porous Pt cathode film. The ACIS analysis results for solid oxide fuel cells (SOFCs) with porous Pt cathode thin films of various thicknesses showed that a 120 nm-thick porous Pt cathode film is thermo-mechanically stabilized by the conformal coating of an ALD alumina capping agent. The iR-free polarization curves show that an ALD alumina-capped 120 nm porous Pt cathode film-embedded SOFC delivers ~65% higher power density than an ALD alumina-capped 480 nm-thick porous Pt cathode film-embedded SOFC.

Controlled Atomic Layer Deposition of Aluminum Oxide to Improve the Performance of Lithium–Sulfur Batteries

The high capacity of sulfur makes lithium–sulfur (Li–S) batteries the most promising next‐generation battery systems. With a significantly higher theoretical specific energy than conventional lithium‐ion batteries, this technology is intensely investigated. However, currently used cathodes have some critical drawbacks which affect the performance of Li–S batteries. Atomic layer deposition (ALD) demonstrates its power for solving some emerging issues in energy‐storage systems. The application of alumina (Al2O3) to the cathode surface improves the morphology and/or chemistry, providing a solution for some of the most common issues of Li–S batteries. Herein, the cathode of Li–S batteries is coated with alumina by ALD. In addition, the optimal parameters for ALD application to sulfur‐based electrodes are reported. It is demonstrated that alumina deposition results in an improved capacity of the system. The process temperature plays an important role, in particular for few‐cycle ALD processes, aiding better cell performance. Higher numbers of ALD cycles, especially at elevated process temperatures, result in considerable sulfur loss, which significantly lowers the cell performance. Cathodes coated with alumina at low process temperatures and with low numbers of ALD cycles are promising alternatives for conventional Li–S cathodes as they increase the capacity of the system considerably.

Material-Selective Doping of 2D TMDC through AlxOy Encapsulation.

For the integration of two-dimensional (2D) transition metal dichalcogenides (TMDC) with high-performance electronic systems, one of the greatest challenges is the realization of doping and comprehension of its mechanisms. Low-temperature atomic layer deposition of aluminum oxide is found to n-dope MoS2 and ReS2 but not WS2. Based on electrical, optical, and chemical analyses, we propose and validate a hypothesis to explain the doping mechanism. Doping is ascribed to donor states in the band gap of AlxOy, which donate electrons or not, based on the alignment of the electronic bands of the 2D TMDC. Through systematic experimental characterization, incorporation of impurities (e.g., carbon) is identified as the likely cause of such states. By modulating the carbon concentration in the capping oxide, doping can be controlled. Through systematic and comprehensive experimental analysis, this study correlates, for the first time, 2D TMDC doping to the carbon incorporation on dielectric encapsulation layers. We highlight the possibility to engineer dopant layers to control the material selectivity and doping concentration in 2D TMDC.

Dual nanotransfer printing for complementary plasmonic biosensors

One of the main challenges in the widespread utilization of localized plasmon resonance-based biosensors is the fabrication of large-area and low-cost plasmonic nanostructures. In this work, we fabricated large-area and low-cost complementary plasmonic biosensors such as nanohole and nanodisk arrays using dual nanotransfer printing (NTP) with a single metal deposition and a single reusable mold. The suspended nanohole arrays and the suspended nanodisk arrays were fabricated using the subsequent dry etching process. We confirmed a maximum enhancement in bulk sensitivity in experiments and simulations by controlling the vertical and lateral etching depths of the dielectric layer underneath the gold (Au) nanohole and nanodisk arrays. Furthermore, we show that the surface sensitivity evaluated by atomic layer deposition of aluminum oxide increased because appropriate vertical and lateral etching depths allow the target analyte to access the additional near-field formed at the bottom of the Au nanostructure. The dual NTP method provides a practical solution for the realization of large-area and low-cost label-free plasmonic biosensing systems, with a reduction in complexity and cost of the fabrication process of complementary plasmonic structures and metasurfaces.

Comparison of mechanical properties and composition of magnetron sputter and plasma enhanced atomic layer deposition aluminum nitride films

A comparative study of mechanical properties and elemental and structural composition was made for aluminum nitride thin films deposited with reactive magnetron sputtering and plasma enhanced atomic layer deposition (PEALD). The sputtered films were deposited on Si (100), Mo (110), and Al (111) oriented substrates to study the effect of substrate texture on film properties. For the PEALD trimethylaluminum–ammonia films, the effects of process parameters, such as temperature, bias voltage, and plasma gas (ammonia versus N2/H2), on the AlN properties were studied. All the AlN films had a nominal thickness of 100 nm. Time-of-flight elastic recoil detection analysis showed the sputtered films to have lower impurity concentration with an Al/N ratio of 0.95, while the Al/N ratio for the PEALD films was 0.81–0.90. The mass densities were ∼3.10 and ∼2.70 g/cm3 for sputtered and PEALD AlN, respectively. The sputtered films were found to have higher degrees of preferential crystallinity, whereas the PEALD films were more polycrystalline as determined by x-ray diffraction. Nanoindentation experiments showed the elastic modulus and hardness to be 250 and 22 GPa, respectively, for sputtered AlN on the (110) substrate, whereas with PEALD AlN, values of 180 and 19 GPa, respectively, were obtained. The sputtered films were under tensile residual stress (61–421 MPa), whereas the PEALD films had a residual stress ranging from tensile to compressive (846 to −47 MPa), and high plasma bias resulted in compressive films. The adhesion of both films was good on Si, although sputtered films showed more inconsistent critical load behavior. Also, the substrate underneath the sputtered AlN did not withstand high wear forces as with the PEALD AlN. The coefficient of friction was determined to be ∼0.2 for both AlN types, and their wear characteristics were almost identical.

Passivation of Plasmonic Colors on Bulk Silver by Atomic Layer Deposition of Aluminum Oxide.

We report the passivation of angle-independent plasmonic colors on bulk silver by atomic layer deposition (ALD) of thin films of aluminum oxide. The colors are rendered by silver nanoparticles produced by laser ablation and redeposition on silver. We then apply a two-step approach to aluminum oxide conformal film formation via ALD. In the first step, a low-density film is deposited at low temperature to preserve and pin the silver nanoparticles. In the second step, a second denser film is deposited at a higher temperature to provide tarnish protection. This approach successfully protects the silver and plasmonic colors against tarnishing, humidity, and temperature, as demonstrated by aggressive exposure trials. The processing time associated with deposition of the conformal passivation layers meets industry requirements, and the approach is compatible with mass manufacturing.

Comparative study of thermal and plasma enhanced atomic layer deposition of aluminum oxide on graphene

Atomic layer deposition of alumina on graphene was studied in thermal and plasma enhanced process. Deposition was controlled by in situ ellipsometry every half cycle, which allows measuring of Al2O3 thickness and graphene equivalent thickness during the process. Properties of graphene were measured by Raman spectroscopy prior and after deposition of dielectric layer. It was shown that plasma enhanced deposition leads to decrease of effective graphene thickness, while thermal deposition does not affect graphene layer. No substantial nucleation lag was observed in both types of deposition.

Energy Storage: High‐Performance High‐Loading Lithium–Sulfur Batteries by Low Temperature Atomic Layer Deposition of Aluminum Oxide on Nanophase S Cathodes (Adv. Mater. Interfaces 17/2017)

Energy Storage: High‐Performance High‐Loading Lithium–Sulfur Batteries by Low Temperature Atomic Layer Deposition of Aluminum Oxide on Nanophase S Cathodes (Adv. Mater. Interfaces 17/2017)