In vitro and in vivo stimulation and recording of neuron action potential is currently achieved with microelectrode arrays, either in planar or 3D geometries, adopting different materials and strategies. IrO2 is a conductive oxide known for its excellent biocompatibility, good adhesion on different substrates, and charge injection capabilities higher than noble metals. Atomic layer deposition (ALD) allows excellent conformal growth, which can be exploited on 3D nanoelectrode arrays. In this work, we disclose the growth of nanocrystalline rutile IrO2 at T = 150 degrees C adopting a new plasma-assisted ALD (PA-ALD) process. The morphological, structural, physical, chemical, and electrochemical properties of the IrO2 thin films are reported. To the best of our knowledge, the electrochemical characterization of the electrode/electrolyte interface in terms of charge injection capacity, charge storage capacity, and double-layer capacitance for IrO2 grown by PA-ALD was not reported yet. IrO2 grown on PtSi reveals a double-layer capacitance (C-dl) above 300 mu F center dot cm(-2), and a charge injection capacity of 0.22 +/- 0.01 mC center dot cm(-2) for an electrode of 1.0 cm(2), confirming IrO2 grown by PA-ALD as an excellent material for neuroelectronic applications.

The sluggish kinetics of the oxygen evolution reaction (OER) is the bottleneck for the practical exploitation of water splitting. Here, the potential of a core-shell structure of hydrous NiMoO microrods conformally covered by CoO nanoparticles via atomic layer depositions is demonstrated. In situ Raman and synchrotron-based photoemission spectroscopy analysis confirms the leaching out of Mo facilitates the catalyst reconstruction, and it is one of the centers of active sites responsible for higher catalytic activity. Post OER characterization indicates that the leaching of Mo from the crystal structure, induces the surface of the catalyst to become porous and rougher, hence facilitating the penetration of the electrolyte. The presence of CoO improves the onset potential of the hydrated catalyst due to its higher conductivity, confirmed by the shift in the Fermi level of the heterostructure. In particular NiMoO@CoO shows a record low overpotential of 120 mV at a current density of 10 mA cm, sustaining a remarkable performance operating at a constant current density of 10, 50, and 100 mA cm with negligible decay. Presented outcomes can significantly contribute to the practical use of the water-splitting process, by offering a clear and in-depth understanding of the preparation of a robust and efficient catalyst for water-splitting.

A quantitative study on inelastic electron scattering with a molecule is of significant importance for understanding the essential mechanisms of electron-induced gas-phase and surface chemical reactions in their excited electronic states. A key issue to be addressed is the quantitatively detailed inelastic electron collision processes with a realistic molecular target, associated with electron excitation that leads to potential ionization and dissociation reactions of the molecule. Using the real-time time-dependent density functional theory (TDDFT) modeling, we present quantitative findings on the energy transfers and internal excitations for the low energy (up to 270 eV) electron wave packet impact with the molecular target cobalt tricarbonyl nitrosyl (CTN, Co(CO)3NO) that is used as a precursor in electron-enhanced atomic layer deposition (EE-ALD) growth of Co films. Our modeling shows the quantitative dependence of the wave packet sizes, target molecule orientations, and impact parameters on the energy transfer in this inelastic electron scattering process. It is found that the wave packet sizes have little effect on the overall profile of the internal multiple excited states, whereas different target orientations can cause significantly different internal excited states. To evaluate the quantitative prediction capability, the inelastic scattering cross-section of a hydrogen atom is calculated and compared with the experimental data, leading to a constant scaling factor over the whole energy range. The present study demonstrates the remarkable potential of TDDFT for simulating the inelastic electron scattering process, which provides critical information for future exploration of electronic excitations in a wide range of electron-induced chemical reactions in current technological applications.

ZnO thin films and nanostructures are applied in various devices due to their interesting optical and electrical properties. Atomic layer deposition (ALD) of ZnO offers unique advantages such as precise thickness control, uniformity, and conformality. Using reactive plasma species as the co-reactant (PE-ALD) allows further enhancement of the material characteristics and tunable properties. The substrate temperature has been reported to be the most influential parameter in this technique, as it affects the growth per cycle (GPC) and material properties. However, an investigation on how the film properties are linked to the GPC is lacking in the literature. Herein, the temperature dependence of several material properties is found closely related to the GPC. The preferential crystal orientation switches from (100) to (002) up to the constant region of the GPC versus temperature, the so-called ALD window. Refractive index and mass density show different slopes in temperature regions outside and within the ALD window. Excitonic absorption is only found for films prepared within the ALD window, and the resistivity drops rapidly above the ALD window. Following these results, more insights can be gained on the ALD growth (especially the role of the ALD window) and ideal temperature ranges for specific applications.

Hexagonal boron nitride (h-BN) has been considered a promising dielectric for two-dimensional (2D) material-based electronics due to its atomically smooth and charge-free interface with an in-plane lattice constant similar to that of graphene. Here, we report atomic layer deposition of boron nitride (ALD-BN) using BCl3 and NH3 precursors directly on thermal SiO2 substrates at a relatively low temperature of 600 °C. The films were characterized by X-ray photoelectron spectroscopy, atomic force microscopy, and transmission electron microscopy wherein the uniform, atomically smooth, and nanocrystalline layered-BN thin film growth is observed. The growth rate is ~0.042 nm/cycle at 600 °C, a temperature significantly lower than that of h-BN grown by chemical vapor deposition. The dielectric properties of the ALD-BN measured from Metal Oxide Semiconductor Capacitors are comparable with that of SiO2. Moreover, the ALD-BN exhibits a 2-fold increase in carrier mobility of graphene field effect transistors (G-FETs/ALD-BN/SiO2) due to the lower surface charge density and inert surface of ALD-BN in comparison to that of G-FETs fabricated on bare SiO2. Therefore, this work suggests that the transfer-free deposition of ALD-BN on SiO2 may be a promising candidate as a substrate for high performance graphene devices.

Due to its excellent physical properties and availability directly on a semiconductor substrate, epitaxial graphene (EG) grown on the (0001) face of hexagonal silicon carbide is a material of choice for advanced applications in electronics, metrology and sensing. The deposition of ultrathin high-k insulators on its surface is a key requirement for the fabrication of EG-based devices, and, in this context, atomic layer deposition (ALD) is the most suitable candidate to achieve uniform coating with nanometric thickness control. This paper presents an overview of the research on ALD of high-k insulators on EG, with a special emphasis on the role played by the peculiar electrical/structural properties of the EG/SiC (0001) interface in the nucleation step of the ALD process. The direct deposition of AlO thin films on the pristine EG surface will be first discussed, demonstrating the critical role of monolayer EG uniformity to achieve a homogeneous AlO coverage. Furthermore, the ALD of several high-k materials on EG coated with different seeding layers (oxidized metal films, directly deposited metal-oxides and self-assembled organic monolayers) or subjected to various prefunctionalization treatments (e.g., ozone or fluorine treatments) will be presented. The impact of the pretreatments and of thermal ALD growth on the defectivity and electrical properties (doping and carrier mobility) of the underlying EG will be discussed.

In this work, hafnium oxide (HfO2) thin films have been grown on (0 0 1)Si substrates by two different Atomic Layer Deposition (ALD) methods, namely thermal and plasma-enhanced modes. Films have been deposited using tetrakis-dimethylamino hafnium as metal precursor, while water vapor was used as an oxygen reactant in the case of the thermal ALD (T-ALD) process, and oxygen plasma was used as oxidant during the plasma enhanced ALD (PE-ALD) process. A systematic study by varying the deposition temperature (200 °C <= Tdep <= 300 °C) and number of cycles (i.e. film thickness in the 10-100 nm range) has been carried out for both ALD methods, and the influence on their physical properties has been evaluated. In particular, the comparison of the growth rates and refractive indexes has been carried out by spectroscopic ellipsometry. All the collected results provided data to identify the best suited deposition process.

Interfacing ferromagnetic materials with topological insulators is an intriguing strategy in order to enhance spin-to-charge conversion mechanisms, paving the way toward highly efficient spin-based electronic devices. In particular, the use of large-scale deposition techniques is demanding for a sustainable and cost-effective industrial technology transfer. In this work, we study the magnetic properties of the Co/Sb2Te3 heterostructure, where the ferromagnetic Co layer is deposited by atomic layer deposition on top of the Sb2Te3 topological insulator, which is grown by metal organic chemical vapor deposition. In particular, broadband ferromagnetic resonance is employed to characterize the Co/Sb2Te3 system and the reference Co/Pt heterostructure. For Co/Sb2Te3, we extract an effective magnetic anisotropy constant K = 4.26*10^6 erg / cm^3, which is an order of magnitude higher than in Co/Pt (Keff = 0.43*10^6 erg / cm^3). The large difference in the Keff values observed in Co/Sb2Te3 and Co/Pt is explained in terms of the different Co crystalline structures achieved on top of Sb2Te3 and Pt, respectively. Interestingly, the Co/Sb2Te3 system displays a relatively large Gilbert damping constant (? = 0.095), which we suggest as possibly due to spin pumping from the Co layer into the Sb2Te3 topological insulator.

Taking the full advantage of the conformal growth characterizing atomic layer deposition (ALD), the possibility to grow Co thin films, with thickness from several tens down to few nanometers on top of a granular topological insulator (TI) Sb2Te3 film, exhibiting a quite high surface roughness (2-5 nm), was demonstrated. To study the Co growth on the Sb2Te3 substrate, we performed simultaneous Co depositions also on sputtered Pt substrates for comparison. We conducted a thorough chemical-structural characterization of the Co/Sb2Te3 and Co/Pt heterostructures, confirming for both cases, not only an excellent conformality, but also the structural continuity of the Co layers. X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM) analyses evidenced that Co on Sb2Te3 grows preferentially oriented along the [00? ] direction, following the underlying rhombohedric substrate. Differently, Co crystallizes in a cubic phase oriented along the [111] direction when deposited on Pt. This work shows that, in case of deposition of crystalline materials, the ALD surface selectivity and conformality can be extended to the definition of local epitaxy, where in-plane ordering of the crystal structure and mosaicity of the developed crystallized grains are dictated by the underlying substrate. Moreover, a highly sharp and chemically-pure Co/Sb2Te3 interface was evidenced, which is promising for the application of this growth process for spintronics

Texture has a significant impact on several key properties of transition-metal dichalcogenides (TMDs) films. Films with in-plane oriented grains have been successfully implemented in nano- and opto-electronic devices, whereas, films with out-of-plane oriented material have shown excellent performance in catalytic applications. It will be demonstrated that the texture of nanocrystalline TMD films can be determined with polarized Raman spectroscopy. A model describing the impact of texture on the Raman response of 2D-TMDs will be presented. For the specific case of MoS2, the model was used to quantify the impact of texture on the relative strength of the A(1g) and E-2g(1) modes in both the unpolarized and polarized Raman configuration. Subsequently, the capability to characterize texture by polarized Raman was demonstrated on various MoS2 films grown by atomic-layer deposition (ALD) and validated by complementary transmission electron microscopy (TEM) and synchrotron based 2D grazing-incidence X-ray diffraction (GIXD) measurements. This also revealed how the texture evolved during ALD growth of MoS2 and subsequent annealing of the films. The insights presented in this work allow a deeper understanding of Raman spectra of nanocrystalline TMDs and enable a rapid and non-destructive method to probe texture.

Graphene (Gr) with its distinctive features is the most studied two-dimensional (2D) material for the new generation of high frequency and optoelectronic devices. In this context, the Atomic Layer Deposition (ALD) of ultra-thin high-k insulators on Gr is essential for the implementation of many electronic devices. However, the lack of out-of-plane bonds in the sp(2) lattice of Gr typically hinders the direct ALD growth on its surface. To date, several pre-functionalization and/or seed-layer deposition processes have been explored, to promote the ALD nucleation on Gr. The main challenge of these approaches is achieving ultra-thin insulators with nearly ideal dielectric properties (permittivity, breakdown field), while preserving the structural and electronic properties of Gr. This paper will review recent developments of ALD of high k-dielectrics, in particular Al2O3, on Gr with "in-situ" seed-layer approaches. Furthermore, recent reports on seed-layer-free ALD onto epitaxial Gr on SiC and onto Gr grown by chemical vapor deposition (CVD) on metals will be presented, discussing the role played by Gr interaction with the underlying substrates.

Atomic layer deposition (ALD) is the method of choice to obtain uniform insulating films on graphene for device applications. Owing to the lack of out-of-plane bonds in the sp(2) lattice of graphene, nucleation of ALD layers is typically promoted by functionalization treatments or predeposition of a seed layer, which, in turn, can adversely affect graphene electrical properties. Hence, ALD of dielectrics on graphene without prefunctionalization and seed layers would be highly desirable. In this work, uniform Al2O3 films are obtained by seed-layer-free thermal ALD at 250 degrees C on highly homogeneous monolayer (1L) epitaxial graphene (EG) (>98% 1L coverage) grown on on-axis 4H-SiC(0001). The enhanced nucleation behavior on 1L graphene is not related to the SiC substrate, but it is peculiar of the EG/SiC interface. Ab initio calculations show an enhanced adsorption energy for water molecules on highly n-type doped 1L graphene, indicating the high doping of EG induced by the underlying buffer layer as the origin of the excellent Al2O3 nucleation. Nanoscale current mapping by conductive atomic force microscopy shows excellent insulating properties of the Al2O3 thin films on 1L EG, with a breakdown field > 8 MV cm(-1). These results will have important impact in graphene device technology.

Memory stacks for charge trapping cells have been produced exploiting Al-doped Hfo(2), AL(2)O(3), and SiO2 made by atomic layer deposition. The fabricated stacks show superior stability and electrical characteristics, allowing for the engineering of sub-1 nm equivalent oxide thickness Al doped HfO2 trapping layer with excellent retention characteristics, also at high temperature. The low Al doping content (4.5%) used in this work leads to the HfO2 crystallization, upon thermal annealing, in the cubic/tetragonal phase with a dielectric constant value of 32. The trapping properties of the proposed stacks have been studied by means of physics-based models, highlighting the role of the different layers and the nature of the traps contributing to the charge storage in the memory stack.

In this work, we investigate the effect of thermal treatment on CeO2 films fabricated by using atomic layer deposition (ALD) on titanium nitride (TiN) or on silicon (Si) substrates. In particular, we report on the structural, chemical and morphological properties of 25 nm thick ceria oxide with particular attention to the interface with the substrate. The annealing treatments have been performed in situ during the acquisition of X-Ray diffraction patterns to monitor the structural changes in the film. We find that ceria film is thermally stable up to annealing temperatures of 900 degrees C required for the complete crystallization. When ceria is deposited on TiN, the temperature has to be limited to 600 degrees C due to the thermal instability of the underlying TiN substrate with a broadening of the interface, while there are no changes detected inside the CeO2 films. As-deposited CeO2 films show a cubic fluorite polycrystalline structure with texturing. Further, after annealing at 900 degrees C an increase of grain dimensions and an enhanced preferential (200) orientation are evidenced. These findings are a strong indication that the texturing is an intrinsic property of the system more than a metastable condition due to the ALD deposition process. This result is interpreted in the light of the contributions of different energy components (surface energy and elastic modulus) which act dependently on the substrate properties, such as its nature and structure.

Atomic layer deposition (ALD), a gas-phase thin film deposition technique based on repeated, self-terminating gas-solid reactions, has become the method of choice in semiconductor manufacturing and many other technological areas for depositing thin conformal inorganic material layers for various applications. ALD has been discovered and developed independently, at least twice, under different names: atomic layer epitaxy (ALE) and molecular layering. ALE, dating back to 1974 in Finland, has been commonly known as the origin of ALD, while work done since the 1960s in the Soviet Union under the name "molecular layering" (and sometimes other names) has remained much less known. The virtual project on the history of ALD (VPHA) is a volunteer-based effort with open participation, set up to make the early days of ALD more transparent. In VPHA, started in July 2013, the target is to list, read and comment on all early ALD academic and patent literature up to 1986. VPHA has resulted in two essays and several presentations at international conferences. This paper, based on a poster presentation at the 16th International Conference on Atomic Layer Deposition in Dublin, Ireland, 2016, presents a recommended reading list of early ALD publications, created collectively by the VPHA participants through voting. The list contains 22 publications from Finland, Japan, Soviet Union, United Kingdom, and United States. Up to now, a balanced overview regarding the early history of ALD has been missing; the current list is an attempt to remedy this deficiency.

Atomic layer deposition is widely acknowledged as a powerful technique for the deposition of high quality layers for several applications including photovoltaics (PV). The capability of ALD to generate dense, conformal, virtually pinhole-free layers becomes attractive also for the emerging organo-metal halide perovskite solar cells (PSCs), which have garnered the interest of the PV community through their remarkable efficiency gains, now over 20%, in just a few years of research. Until now, the application of ALD layers in PSCs has almost exclusively been restricted to the stages of device fabrication prior to perovskite deposition. Researchers have mainly focused on fabricating efficient electron and hole transport layers (TiO, SnO, ZnO, NiO) and ultra-thin AlO or TiO passivation layers for several device configurations. The first section of this contribution reviews the current state-of-the-art ALD for perovskite solar cells. Then, we explore other potential opportunities, such as the fabrication of doped metal oxide selective contacts and transparent electrodes, also for use in tandem solar cell architectures, as well as barrier layers for encapsulation. Finally, we present our own experimental investigation of the challenges involved in depositing directly on perovskite absorbers in view of replacing organic electron and hole transport layers with ALD metal oxides (MOs). Therefore, the effects of temperature, oxidizing agents and metal precursors on perovskite are studied. A number of insights are gained which can lead to the development of ad hoc ALD processes that are compatible with the underlying perovskite, in this case, methylammonium lead iodide, MAPbI. The phase purity and surface chemistry of the perovskite were used as metrics to quantify the feasibility of depositing selected MOs which can be adopted as selective contacts and passivation layers.

High-quality thin insulating films on graphene (Gr) are essential for field-effect transistors (FETs) and other electronics applications of this material. Atomic layer deposition (ALD) is the method of choice to deposit high-kappa dielectrics with excellent thickness uniformity and conformal coverage. However, to start the growth on the sp(2) Gr surface, a chemical prefunctionalization or the physical deposition of a seed layer are required, which can effect, to some extent, the electrical properties of Gr. In this paper, we report a detailed morphological, structural, and electrical investigation of Al2O3 thin films grown by a two-steps ALD process on a large area Gr membrane residing on an Al2O3-Si substrate. This process consists of the H2O-activated deposition of a Al2O3 seed layer a few nanometers in thickness, performed in situ at 100 degrees C, followed by ALD thermal growth of Al2O3 at 250 degrees C. The optimization of the low-temperature seed layer allowed us to obtain a uniform, conformal, and pinhole-free Al2O3 film on Gr by the second ALD step. Nanoscale-resolution mapping of the current through the dielectric by conductive atomic force microscopy (CAFM) demonstrated an excellent laterally uniformity of the film. Raman spectroscopy measurements indicated that the ALD process does not introduce defects in Gr, whereas it produces a partial compensation of Gr unintentional p-type doping, as confirmed by the increase of Gr sheet resistance (from similar to 300 Omega/sq in pristine Gr to similar to 1100 Omega/sq after Al2O3 deposition). Analysis of the transfer characteristics of Gr field-effect transistors (GFETs) allowed us to evaluate the relative dielectric permittivity (E-BD = 7.45) and the breakdown electric field (EBD = 7.4 MV/cm) of the Al2O3 film as well as the transconductance and the holes field-effect mobility (similar to 1200 cm(2) V-1 s(-1)). A special focus has been given to the electrical characterization of the Al2O3-Gr interface by the analysis of high frequency capacitance-voltage measurements, which allowed us to elucidate the charge trapping and detrapping phenomena due to near-interface and interface oxide traps.

Graphene is an ideal candidate for next generation applications as a transparent electrode for electronics on plastic due to its flexibility and the conservation of electrical properties upon deformation. More importantly, its field-effect tunable carrier density, high mobility and saturation velocity make it an appealing choice as a channel material for field-effect transistors (FETs) for several potential applications. As an example, properly designed and scaled graphene FETs (Gr-FETs) can be used for flexible high frequency (RF) electronics or for high sensitivity chemical sensors. Miniaturized and flexible Gr-FET sensors would be highly advantageous for current sensors technology for in vivo and in situ applications. In this paper, we report a wafer-scale processing strategy to fabricate arrays of back-gated Gr-FETs on poly(ethylene naphthalate) (PEN) substrates. These devices present a large-area graphene channel fully exposed to the external environment, in order to be suitable for sensing applications, and the channel conductivity is efficiently modulated by a buried gate contact under a thin Al2O3 insulating film. In order to be compatible with the use of the PEN substrate, optimized deposition conditions of the Al2O3 film by plasma-enhanced atomic layer deposition (PE-ALD) at a low temperature (100 degrees C) have been developed without any relevant degradation of the final dielectric performance.

Al2O3 films were grown by plasma enhanced-atomic layer deposition (PE-ALD) on 4H-SiC substrates, with and without the presence of a thin SiO2 layer. The collected data indicated the formation of amorphous, adherent, and uniform Al2O3 thin films with a thickness of about 30 nm. The electrical characterization has been performed on metal-oxide-semiconductor (MOS) structures by both capacitance-voltage (C-V) and current-voltage (I-V) measurements. All these analyses demonstrated a better dielectric behavior of the Al2O3 film deposited on the SiO2/SiC stack, with respect to that deposited directly on the SiC substrate. In particular, higher dielectric constant value, lower leakage current density, and higher breakdown field have been found in the Al2O3/SiO2/SiC stack. Hence, it has been argued that the presence of the interfacial SiO2 provides a better condition for the growth of high quality Al2O3 films. In this context, the film density has been evaluated, and strong difference has been found in the density values, The correlation between the better electrical properties of the Al2O3 films on SiO2 and their higher density has been demonstrated. These results provide useful insights on the possible application of these Al2O3 films as gate insulator in 4H-SiC metal-oxide-semiconductor field effect transistors. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The investigation of mechanical properties of atomic layer deposition HfO2 films is important for implementing these layers in microdevices. The mechanical properties of films change as a function of composition and structure, which accordingly vary with deposition temperature and post-annealing. This work describes elastic modulus, hardness, and wear resistance of as-grown and annealed HfO2. From nanoindentation measurements, the elastic modulus and hardness remained relatively stable in the range of 163-165 GPa and 8.3-9.7 GPa as a function of deposition temperature. The annealing of HfO2 caused significant increase in hardness up to 14.4 GPa due to film crystallization and densification. The structural change also caused increase in the elastic modulus up to 197 GPa. Wear resistance did not change as a function of deposition temperature, but improved upon annealing. (C) 2016 American Vacuum Society.