Showing papers on "Atomic layer deposition published in 2011"

Plasma-Assisted Atomic Layer Deposition: Basics, Opportunities, and Challenges

Abstract: Plasma-assisted atomic layer deposition (ALD) is an energy-enhanced method for the synthesis of ultra-thin films with A-level resolution in which a plasma is employed during one step of the cyclic deposition process. The use of plasma species as reactants allows for more freedom in processing conditions and for a wider range of material properties compared with the conventional thermally-driven ALD method. Due to the continuous miniaturization in the microelectronics industry and the increasing relevance of ultra-thin films in many other applications, the deposition method has rapidly gained popularity in recent years, as is apparent from the increased number of articles published on the topic and plasma-assisted ALD reactors installed. To address the main differences between plasma-assisted ALD and thermal ALD, some basic aspects related to processing plasmas are presented in this review article. The plasma species and their role in the surface chemistry are addressed and different equipment configurations, including radical-enhanced ALD, direct plasma ALD, and remote plasma ALD, are described. The benefits and challenges provided by the use of a plasma step are presented and it is shown that the use of a plasma leads to a wider choice in material properties, substrate temperature, choice of precursors, and processing conditions, but that the processing can also be compromised by reduced film conformality and plasma damage. Finally, several reported emerging applications of plasma-assisted ALD are reviewed. It is expected that the merits offered by plasma-assisted ALD will further increase the interest of equipment manufacturers for developing industrial-scale deposition configurations such that the method will find its use in several manufacturing applications.

Atomic layer-deposited tunnel oxide stabilizes silicon photoanodes for water oxidation

Abstract: A leading approach for large-scale electrochemical energy production with minimal global-warming gas emission is to use a renewable source of electricity, such as solar energy, to oxidize water, providing the abundant source of electrons needed in fuel synthesis. We report corrosion-resistant, nanocomposite anodes for the oxidation of water required to produce renewable fuels. Silicon, an earth-abundant element and an efficient photovoltaic material, is protected by atomic layer deposition (ALD) of a highly uniform, 2 nm thick layer of titanium dioxide (TiO(2)) and then coated with an optically transmitting layer of a known catalyst (3 nm iridium). Photoelectrochemical water oxidation was observed to occur below the reversible potential whereas dark electrochemical water oxidation was found to have low-to-moderate overpotentials at all pH values, resulting in an inferred photovoltage of ~550 mV. Water oxidation is sustained at these anodes for many hours in harsh pH and oxidative environments whereas comparable silicon anodes without the TiO(2) coating quickly fail. The desirable electrochemical efficiency and corrosion resistance of these anodes is made possible by the low electron-tunnelling resistance (<0.006 Ω cm(2) for p(+)-Si) and uniform thickness of atomic-layer deposited TiO(2).

Ferroelectricity in yttrium-doped hafnium oxide

Abstract: Structural and electrical evidence for a ferroelectric phase in yttrium doped hafnium oxide thin films is presented. A doping series ranging from 2.3 to 12.3 mol% YO1.5 in HfO2 was deposited by a thermal atomic layer deposition process. Grazing incidence X-ray diffraction of the 10 nm thick films revealed an orthorhombic phase close to the stability region of the cubic phase. The potential ferroelectricity of this orthorhombic phase was confirmed by polarization hysteresis measurements on titanium nitride based metal-insulator-metal capacitors. For 5.2 mol% YO1.5 admixture the remanent polarization peaked at 24 μC/cm2 with a coercive field of about 1.2 MV/cm. Considering the availability of conformal deposition processes and CMOS-compatibility, ferroelectric Y:HfO2 implies high scaling potential for future, ferroelectric memories.

Development of hafnium based high-k materials—A review

Abstract: The move to implement metal oxide based gate dielectrics in a metal-oxide-semiconductor field effect transistor is considered one of the most dramatic advances in materials science since the invention of silicon based transistors. Metal oxides are superior to SiO 2 in terms of their higher dielectric constants that enable the required continuous down-scaling of the electrical thickness of the dielectric layer while providing a physically thicker layer to suppress the quantum mechanical tunneling through the dielectric layer. Over the last decade, hafnium based materials have emerged as the designated dielectrics for future generation of nano-electronics with a gate length less than 45 nm, though there exists no consensus on the exact composition of these materials, as evolving device architectures dictate different considerations when optimizing a gate dielectric material. In addition, the implementation of a non-silicon based gate dielectric means a paradigm shift from diffusion based thermal processes to atomic layer deposition processes. In this report, we review how HfO 2 emerges from all likely candidates to become the new gold standard in the microelectronics industry, its different phases, reported electrical properties, and materials processing techniques. Then we use specific examples to discuss the evolution in designing hafnium based materials, from binary to complex oxides and to non-oxide forms as gate dielectric, metal gates and diffusion barriers. To address the impact of these hafnium based materials, their interfaces with silicon as well as a variety of semiconductors are discussed. Finally, the integration issues are highlighted, including carrier scattering, interface state passivation, phonon engineering, and nano-scale patterning, which are essential to realize future generations of devices using hafnium-based high- k materials.

Thin film encapsulation for flexible AM-OLED: a review

Abstract: Flexible organic light emitting diode (OLED) will be the ultimate display technology to customers and industries in the near future but the challenges are still being unveiled one by one. Thin-film encapsulation (TFE) technology is the most demanding requirement to prevent water and oxygen permeation into flexible OLED devices. As a polymer substrate does not offer the same barrier performance as glass, the TFE should be developed on both the bottom and top side of the device layers for sufficient lifetimes. This work provides a review of promising thin-film barrier technologies as well as the basic gas diffusion background. Topics include the significance of the device structure, permeation rate measurement, proposed permeation mechanism, and thin-film deposition technologies (Vitex system and atomic layer deposition (ALD)/molecular layer deposition (MLD)) for effective barrier films.

Alumina-coated patterned amorphous silicon as the anode for a lithium-ion battery with high coulombic efficiency.

Abstract: A patterned silicon electrode as the anode of lithium ion batteries is fabricated by microfabrication technology. An ultrathin alumina layer is coated on the patterned electrode by atomic layer deposition (ALD). This results in obviously enhanced coulombic efficiency and cycling performance. [GRAPHICS] .

Atomic Layer Deposition of Tin Monosulfide Thin Films

Abstract: Thin film solar cells made from earth-abundant, non-toxic materials are needed to replace the current technology that uses Cu(In,Ga)(S,Se)2 and CdTe, which contain scarce and toxic elements. One promising candidate absorber material is tin monosulfide (SnS). In this report, pure, stoichiometric, single-phase SnS films were obtained by atomic layer deposition (ALD) using the reaction of bis(N,N′-diisopropylacetamidinato)tin(II) [Sn(MeC(N-iPr)2)2] and hydrogen sulfide (H2S) at low temperatures (100 to 200 °C). The direct optical band gap of SnS is around 1.3 eV and strong optical absorption (α > 104 cm−1) is observed throughout the visible and near-infrared spectral regions. The films are p-type semiconductors with carrier concentration on the order of 1016 cm−3 and hole mobility 0.82–15.3 cm2V−1s−1 in the plane of the films. The electrical properties are anisotropic, with three times higher mobility in the direction through the film, compared to the in-plane direction.

Ultrathin coatings on nano-LiCoO2 for Li-ion vehicular applications

Abstract: To deploy Li-ion batteries in next-generation vehicles, it is essential to develop electrodes with durability, high energy density, and high power. Here we report a breakthrough in controlled full-electrode nanoscale coatings that enables nanosized materials to cycle with durable high energy and remarkable rate performance. The nanoparticle electrodes are coated with Al2O3 using atomic layer deposition (ALD). The coated nano-LiCoO2 electrodes with 2 ALD cycles deliver a discharge capacity of 133 mAh/g with currents of 1400 mA/g (7.8C), corresponding to a 250% improvement in reversible capacity compared to bare nanoparticles (br-nLCO), when cycled at this high rate. The simple ALD process is broadly applicable and provides new opportunities for the battery industry to design other novel nanostructured electrodes that are highly durable even while cycling at high rate.

1200-V Normally Off GaN-on-Si Field-Effect Transistors With Low Dynamic on -Resistance

Abstract: This letter reports high-voltage GaN field-effect transistors fabricated on Si substrates. A halide-based plasma treatment was performed to enable normally off operation. Atomic layer deposition of Al2O3 gate insulator was adopted to reduce the gate leakage current. Incorporation of multiple field plates, with one field plate connected to the gate electrode and two field plates connected to the source electrode successfully enabled a high breakdown voltage of 1200 V and low dynamic on-resistance at high-voltage operation.

Tailoring nanoporous materials by atomic layer deposition.

Abstract: Atomic layer deposition (ALD) is a cyclic process which relies on sequential self-terminating reactions between gas phase precursor molecules and a solid surface. The self-limiting nature of the chemical reactions ensures precise film thickness control and excellent step coverage, even on 3D structures with large aspect ratios. At present, ALD is mainly used in the microelectronics industry, e.g. for growing gate oxides. The excellent conformality that can be achieved with ALD also renders it a promising candidate for coating porous structures, e.g. for functionalization of large surface area substrates for catalysis, fuel cells, batteries, supercapacitors, filtration devices, sensors, membranesetc. This tutorial review focuses on the application of ALD for catalyst design. Examples are discussed where ALD of TiO2 is used for tailoring the interior surface of nanoporous films with pore sizes of 4–6 nm, resulting in photocatalytic activity. In still narrower pores, the ability to deposit chemical elements can be exploited to generate catalytic sites. In zeolites, ALD of aluminium species enables the generation of acid catalytic activity.

Water Splitting by Tungsten Oxide Prepared by Atomic Layer Deposition and Decorated with an Oxygen‐Evolving Catalyst

Abstract: When sunlight is used as direct energy input, water can be split into hydrogen and oxygen at conversion efficiencies similar to those of solar cells. This process offers a method for energy storage to address the problem that the sun does not shine continuously, and is a particularly appealing approach to solar-energy harvesting. Notwithstanding the intense research efforts, progress in this area is extremely slow. Efficient and inexpensive water splitting remains elusive. A key reason for the sluggish progress is the lack of suitable materials. The “ideal” material must absorb strongly in the visible range, be efficient in separating charges using the absorbed photons, and be effective in collecting and transporting charges for the chemical processes. Such a material has yet to be found. The difficulties in finding a suitable material stem from the competing nature of intrinsic material properties (e.g., optical depth, charge diffusion distance, and width of the depletion region, among others), which leaves limited opportunity for tunability. We recently demonstrated that heteronanostructures, a type of nanoscale material consisting of multiple components that complement each other, have a combination of properties which are not available in singlecomponent materials. For instance, we can add chargetransport components to oxide semiconductors to solve the issue of low conductivity that oxide semiconductors generally suffer. In a similar fashion, one can add an effective catalyst to address the challenge that oxygen evolution is complex and tends to be the rate-limiting step. These new materials will likely lead to significant improvement in solar watersplitting efficiencies. The success of a heteronanostructure design relies on the ability to produce high-quality components with interfaces of low defect density, and on the availability of various components. Here we show that crystalline WO3 can be synthesized by the atomic layer deposition (ALD) method in the true ALD regime. When coated with a novel Mn-based catalyst, the resulting WO3 survives soaking in H2O at pH 7 and produces oxygen by splitting H2O under illumination. We choose ALD to prepare WO3 because of the following advantages: 1) a high degree of control over the resulting materials; 2) excellent step coverage to yield conformal coatings; and 3) process versatility to tailor the composition of the deposit. WO3 was studied because it is one of the most researched compounds for water splitting. The widely available literature makes it easy to compare our results with existing reports and thus allows us to test the power of the heteronanostructure design. To avoid the production of corrosive byproducts during the ALD process and to ensure the reaction occurs in the true ALD regime, we used (tBuN)2(Me2N)2W as tungsten precursor and H2O as oxygen precursor, as described in the Experimental Section (see Supporting Information for more details). Our first goal was to verify that the growth indeed takes place in the ALD regime. The dependence of the growth rate on the precursor pulse times and on the substrate temperature unambiguously confirms this. In addition, the excellent linear dependence of the deposition thickness on the number of precursor pulses supports the ALD growth mechanism and shows the extent of control we can achieve (see Supporting Information). That a long H2O pulse time is necessary to initiate growth is a key finding of this work. Despite intentional strengthening of the oxidative conditions, as-grown WO3 exhibited a tinted color, indicating the existence of oxygen deficiencies, which was then corrected by an annealing step in O2 at 550 8C. The crystalline nature of the product is manifested in the highresolution (HR) TEM image in Figure 1a. We also synthesized WO3 on two-dimensional TiSi2 nanonets. [18,19] The uniformity and good coverage around the nanonet branches show that this deposition technique is suitable for the creation of heteronanostructures. Ready dissolution of WO3 in aqueous solutions with pH 4 is a significant challenge that impedes its widespread use. We sought to solve this problem by coating WO3 with an Mnbased catalyst. Derived from the Brudvig–Crabtree catalyst, this coating was prepared by thermally decomposing [(H2O)(terpy)Mn(O)2Mn(H2O)(terpy)](NO3)3 (terpy= 2,2’:6’,2’’terpyridine). Similar to the oxo-bridged dimanganese catalyst, the thermal decomposition product exhibits good [*] R. Liu, Y. Lin, S. W. Sheehan, Prof. Dr. D. Wang Department of Chemistry, Merkert Chemistry Center Boston College 2609 Beacon St., Chestnut Hill, MA 02467 (USA) Fax: (+1)617-552-2705 E-mail: dunwei.wang@bc.edu Homepage: http://www2.bc.edu/~dwang

Inorganic Hollow Nanotube Aerogels by Atomic Layer Deposition onto Native Nanocellulose Templates

Abstract: Hollow nano-objects have raised interest in applications such as sensing, encapsulation, and drug-release. Here we report on a new class of porous materials, namely inorganic nanotube aerogels that, unlike other aerogels, have a framework consisting of inorganic hollow nanotubes. First we show a preparation method for titanium dioxide, zinc oxide, and aluminum oxide nanotube aerogels based on atomic layer deposition (ALD) on biological nanofibrillar aerogel templates, that is, nanofibrillated cellulose (NFC), also called microfibrillated cellulose (MFC) or nanocellulose. The aerogel templates are prepared from nanocellulose hydrogels either by freeze-drying in liquid nitrogen or liquid propane or by supercritical drying, and they consist of a highly porous percolating network of cellulose nanofibrils. They can be prepared as films on substrates or as freestanding objects. We show that, in contrast to freeze-drying, supercritical drying produces nanocellulose aerogels without major interfibrillar aggregation even in thick films. Uniform oxide layers are readily deposited by ALD onto the fibrils leading to organic-inorganic core-shell nanofibers. We further demonstrate that calcination at 450 °C removes the organic core leading to purely inorganic self-supporting aerogels consisting of hollow nanotubular networks. They can also be dispersed by grinding, for example, in ethanol to create a slurry of inorganic hollow nanotubes, which in turn can be deposited to form a porous film. Finally we demonstrate the use of a titanium dioxide nanotube network as a resistive humidity sensor with a fast response.

Plasma enhanced atomic layer deposition of SiNx:H and SiO2

Abstract: As the nanoelectronics industry looks to transition to both three dimensional transistor and interconnect technologies at the <22 nm node, highly conformal dielectric coatings with precise thickness control are increasingly being demanded. Plasma enhanced chemical vapor deposition (PECVD) currently fills this role for most applications requiring low temperature processing but does not always meet step coverage and thickness precision requirements. The authors present results for a hybrid technique, plasma enhanced atomic layer deposition (PEALD), which utilizes typical PECVD process gases and tooling while delivering improved topography coverage and thickness control. Specifically, the authors show that alternating SiH4 gas/N2 plasma exposures applied in an atomic layer deposition sequence can be used to deposit SiNx:H films in a self-limiting fashion with improved conformality and superior performance as a moisture barrier. PEALD of SiO2 using alternating SiH4 and CO2 plasma exposures is further demonstr...

In Situ Transmission Electron Microscopy Observation of Pulverization of Aluminum Nanowires and Evolution of the Thin Surface Al2O3 Layers during Lithiation–Delithiation Cycles

Abstract: Lithiation-delithiation cycles of individual aluminum nanowires (NWs) with naturally oxidized Al(2)O(3) surface layers (thickness 4-5 nm) were conducted in situ in a transmission electron microscope. Surprisingly, the lithiation was always initiated from the surface Al(2)O(3) layer, forming a stable Li-Al-O glass tube with a thickness of about 6-10 nm wrapping around the NW core. After lithiation of the surface Al(2)O(3) layer, lithiation of the inner Al core took place, which converted the single crystal Al to a polycrystalline LiAl alloy, with a volume expansion of about 100%. The Li-Al-O glass tube survived the 100% volume expansion, by enlarging through elastic and plastic deformation, acting as a solid electrolyte with exceptional mechanical robustness and ion conduction. Voids were formed in the Al NWs during the initial delithiation step and grew continuously with each subsequent delithiation, leading to pulverization of the Al NWs to isolated nanoparticles confined inside the Li-Al-O tube. There was a corresponding loss of capacity with each delithiation step when arrays of NWs were galvonostatically cycled. The results provide important insight into the degradation mechanism of lithium-alloy electrodes and into recent reports about the performance improvement of lithium ion batteries by atomic layer deposition of Al(2)O(3) onto the active materials or electrodes.

Al2O3 and TiO2 atomic layer deposition on copper for water corrosion resistance.

Abstract: Al2O3 and TiO2 atomic layer deposition (ALD) were employed to develop an ultrathin barrier film on copper to prevent water corrosion. The strategy was to utilize Al2O3 ALD as a pinhole-free barrier and to protect the Al2O3 ALD using TiO2 ALD. An initial set of experiments was performed at 177 °C to establish that Al2O3 ALD could nucleate on copper and produce a high-quality Al2O3 film. In situ quartz crystal microbalance (QCM) measurements verified that Al2O3 ALD nucleated and grew efficiently on copper-plated quartz crystals at 177 °C using trimethylaluminum (TMA) and water as the reactants. An electroplating technique also established that the Al2O3 ALD films had a low defect density. A second set of experiments was performed for ALD at 120 °C to study the ability of ALD films to prevent copper corrosion. These experiments revealed that an Al2O3 ALD film alone was insufficient to prevent copper corrosion because of the dissolution of the Al2O3 film in water. Subsequently, TiO2 ALD was explored on copper...

Hafnium tantalum titanium oxide films

Abstract: Embodiments of a dielectric layer containing a hafnium tantalum titanium oxide film structured as one or more monolayers include the dielectric layer disposed in an integrated circuit. Embodiments of methods of fabricating such a dielectric layer provide a dielectric layer for use in a variety of electronic devices. An embodiment may include forming hafnium tantalum titanium oxide film using atomic layer deposition.

Structural and Electrical Properties of Atomic Layer Deposited Al-Doped ZnO Films

Abstract: Structural and electrical properties of Al-doped ZnO (AZO) films deposited by atomic layer deposition (ALD) are investigated to study the extrinsic doping mechanism of a transparent conducting oxide. ALD-AZO films exhibit a unique layer-by-layer structure consisting of a ZnO matrix and Al2O3 dopant layers, as determined by transmission electron microscopy analysis. In these layered AZO films, a single Al2O3 dopant layer deposited during one ALD cycle could provide ≈4.5 × 1013 cm−2 free electrons to the ZnO. The effective field model for doping is suggested to explain the decrease in the carrier concentration of ALD-AZO films when the interval between the Al2O3 layers is reduced to less than ≈2.6 nm (>3.4 at% Al). By correlating the electrical and structural properties, an extrinsic doping mechanism of ALD-AZO films is proposed in which the incorporated Al atoms take oxygen from the ZnO matrix and form doubly charged donors, such as oxygen vacancies or zinc interstitials.

Apparatus and methods for deposition of silicon carbide and silicon carbonitride films

Abstract: Methods for deposition of silicon carbide films on a substrate surface are provided. The methods include the use of vapor phase carbosilane precursors and may employ plasma enhanced atomic layer deposition processes. The methods may be carried out at temperatures less than 600° C, for example between about 23° C and about 200° C or at about 100° C. This silicon carbide layer may then be densified to remove hydrogen content. Additionally, the silicon carbide layer may be exposed to a nitrogen source to provide reactive N-H groups, which can then be used to continue film deposition using other methods. Plasma processing conditions can be used to adjust the carbon, hydrogen and/or nitrogen content of the films.

ALD Functionalized Nanoporous Gold: Thermal Stability, Mechanical Properties, and Catalytic Activity

Abstract: Nanoporous metals have many technologically promising applications but their tendency to coarsen limits their long-term stability and excludes high temperature applications. Here, we demonstrate that atomic layer deposition (ALD) can be used to stabilize and functionalize nanoporous metals. Specifically, we studied the effect of nanometer-thick alumina and titania ALD films on thermal stability, mechanical properties, and catalytic activity of nanoporous gold (np-Au). Our results demonstrate that even only one-nm-thick oxide films can stabilize the nanoscale morphology of np-Au up to 1000 C, while simultaneously making the material stronger and stiffer. The catalytic activity of np-Au can be drastically increased by TiO{sub 2} ALD coatings. Our results open the door to high temperature sensor, actuator, and catalysis applications and functionalized electrodes for energy storage and harvesting applications.

Electronic and chemical properties of the c-Si/Al2O3 interface

Abstract: Using aluminum oxide (Al2O3) films deposited by atomic layer deposition (ALD), the dominant passivation mechanisms at the c-Si/Al2O3 interface, as well as the chemical composition of the interface region, are investigated. The excellent surface passivation quality of thin Al2O3 films is predominantly assigned to a high negative fixed charge density of Qf = − (4 ± 1) × 1012 cm−2, which is located within 1nm of the Si/Al2O3 interface and is independent of the layer thickness. A deterioration of the passivation quality for ultrathin Al2O3 layers is explained by a strong increase in the interface state density, presumably due to an incomplete reaction of the trimethyl-aluminum (TMA) molecules during the first ALD cycles. A high oxygen-to-aluminum atomic ratio resulting from the incomplete adsorption of the TMA molecules is suggested as a possible source of the high negative charge density Qf at the Si/Al2O3 interface.

Systems and methods for thin-film deposition of metal oxides using excited nitrogen-oxygen species

Abstract: The present invention relates to a process and system for depositing a thin film onto a substrate. One aspect of the invention is depositing a thin film metal oxide layer using atomic layer deposition (ALD).

Method of forming metal oxide hardmask

Abstract: A method of forming a metal oxide hardmask on a template includes: providing a template constituted by a photoresist or amorphous carbon formed on a substrate; and depositing by atomic layer deposition (ALD) a metal oxide hardmask on the template constituted by a material having a formula Si x M (1-x) O y wherein M represents at least one metal element, x is less than one including zero, and y is approximately two or a stoichiometrically-determined number

Novel method for conformal plasma immersed ion implantation assisted by atomic layer deposition

Abstract: Embodiments of the invention provide a novel apparatus and methods for forming a conformal doped layer on the surface of a substrate. A substrate is provided to a process chamber, and a layer of dopant source material is deposited by plasma deposition, atomic layer deposition, or plasma-assisted atomic layer deposition. The substrate is then subjected to thermal processing to activate and diffuse dopants into the substrate surface.

Critical tensile and compressive strains for cracking of Al2O3 films grown by atomic layer deposition

Abstract: Al2O3 atomic layer deposition (ALD) is a model ALD system and Al2O3 ALD films are excellent gas diffusion barrier on polymers. However, little is known about the response of Al2O3 ALD films to strain and the potential film cracking that would restrict the utility of gas diffusion barrier films. To understand the mechanical limitations of Al2O3 ALD films, the critical strains at which the Al2O3 ALD films will crack were determined for both tensile and compressive strains. The tensile strain measurements were obtained using a fluorescent tagging technique to image the cracks. The results showed that the critical tensile strain is higher for thinner thicknesses of the Al2O3 ALD film on heat-stabilized polyethylene naphthalate (HSPEN) substrates. A low critical tensile strain of 0.52% was measured for a film thickness of 80 nm. The critical tensile strain increased to 2.4% at a film thickness of 5 nm. In accordance with fracture mechanics modeling, the critical tensile strains and the saturation crack densiti...

Seeding atomic layer deposition of high-k dielectrics on epitaxial graphene with organic self-assembled monolayers.

Abstract: The development of high-performance graphene-based nanoelectronics requires the integration of ultrathin and pinhole-free high-k dielectric films with graphene at the wafer scale. Here, we demonstrate that self-assembled monolayers of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) act as effective organic seeding layers for atomic layer deposition (ALD) of HfO2 and Al2O3 on epitaxial graphene on SiC(0001). The PTCDA is deposited via sublimation in ultrahigh vacuum and shown to be highly ordered with low defect density by molecular-resolution scanning tunneling microscopy. Whereas identical ALD conditions lead to incomplete and rough dielectric deposition on bare graphene, the chemical functionality provided by the PTCDA seeding layer yields highly uniform and conformal films. The morphology and chemistry of the dielectric films are characterized by atomic force microscopy, ellipsometry, cross-sectional scanning electron microscopy, and X-ray photoelectron spectroscopy, while high-resolution X-ray r...

Photoelectrochemical investigation of ultrathin film iron oxide solar cells prepared by atomic layer deposition.

Abstract: Atomic layer deposition was used to grow conformal thin films of hematite with controlled thickness on transparent conductive oxide substrates. The hematite films were incorporated as photoelectrodes in regenerative photoelectrochemical cells employing an aqueous [Fe(CN)6]3-/4- electrolyte. Steady state current density versus applied potential measurements under monochromatic and simulated solar illumination were used to probe the photoelectrochemical properties of the hematite electrodes as a function of film thickness. Combining the photoelectrochemical results with careful optical measurements allowed us to determine an optimal thickness for a hematite electrode of ∼20 nm. Mott−Schottky analysis of differential capacitance measurements indicated a depletion region of ∼17 nm. Thus, only charge carriers generated in the depletion region were found to contribute to the photocurrent.

Progress and future directions for atomic layer deposition and ALD-based chemistry

Abstract: This article reviews and assesses recent progress in atomic layer deposition (ALD) and highlights how the field of ALD is expanding into new applications and inspiring new vapor-based chemical reaction methods. ALD is a unique chemical process that yields ultra-thin film coatings with exceptional conformality on highly non-uniform and non-planar surfaces, often with subnanometer scale control of the coating thickness. While industry uses ALD for high-κ dielectrics in the manufacturing of electronic devices, there is growing interest in low-temperature ALD and ALD-inspired processes for newer and more wide-ranging applications, including integration with biological and synthetic polymer structures. Moreover, the conformality and nanoscale control of ALD film thickness makes ALD ideal for encapsulation and nano-architectural engineering. Articles in this issue of MRS Bulletin present details of several growing interest areas, including the extension of ALD to new regions of the periodic table, and molecular layer deposition and vapor infiltration for synthesis of organic-based thin films. Articles also discuss ALD for nanostructure engineering and ALD for energy applications. A final article shows how the challenge of scaling ALD for high rate nanomanufacturing will push advances in plasma, roll-to-roll, and atmospheric pressure ALD.