Atomic Layer Chemical Vapor Deposition Research Articles

Morphological and Electrical Characterization of AlGaN/GaN Heterostructures Modified By Atomic Layer Etching

Modern microelectronic components for high-power and high-frequency applications based on III-V compound semiconductors offer high break down voltage (GaN: 5 MV/cm and AlN: 15 MV/cm) at low specific on-resistance. However, it requires reliability and reproducibility of the production processes. Going to higher frequencies (5 GHz and beyond) and more integration in consumer electronics, smaller structure sizes are needed. This is going along with increasing demands on the manufacturing processes like dry etching. The main goal is to reach smaller and high controllable etching rates, going down to single atomic layers, low damage, and minimized surface roughness. Atomic layer etching (ALE) represents a key technology in order to achieve such requirements.An ALE process consists of two independent steps forming a repeatable cycle with a specific etching amount per cycle (EPC). First a surface modification is done by a chemical precursor i.e., adsorbing or oxidizing the surface. The second step is the removal of the modified layer, either physically by low energy non-reactive ion bombardment (Plasma Enhanced ALE [PEALE]) or chemically by a reactive species (Thermal ALE). The two steps are separated by an inert gas purge. This purging grants the removal of the chemistry after the first step, preventing further chemical reaction and transporting the chemical products out of the chamber after the second step.In this study, a PEALE conducted on different tools is used, for gate and contact recess study in a AlGaN/GaN heterostructure to form high electron mobility transistors (HEMT) with reduced ohmic contact resistance and threshold voltages. The results show a reduction of ohmic contact resistance at reduced forming temperatures and a linear dependence of the threshold voltage on gate recess depth. In order to determine the etching rate and roughness, atomic force microscopy (AFM) measurements were performed.The PEALE module is either integrated into a cluster tool consisting of atomic layer deposition (ALD) and chemical vapor deposition (CVD) or done in a combined ALD/ALE chamber. This opens the possibility of etching and depositing in-situ, reducing contamination and degradation of the substrate material.By this means, metal insulator semiconductor (MIS)-HEMTS with a recessed gate are studied. The monitoring of the individual processes is achieved by test structures like transfer length method structures (TLM) and metal oxide semiconductor (MOS), which showed the improved electric performance of these devices and may indicate unwanted interface issues, respectively. Additional, pre- and post-treatments could improve the interfaces further. The results will be presented and discussed in terms of ALE process development and optimization.This work was financially supported within the ALEStar project by the government of the Free-state of Saxony and the European Regional Development Fund under grant no. SAB 100402929.

Novel Volatile Heteroleptic Barium Complexes Using Tetradentate Ligand and β-Diketonato Ligand.

Novel barium heteroleptic complexes were synthesized through the substitution of the bis(trimethylsilyl)amide of Ba(btsa)2·2DME with aminoalkoxide and β-diketonate ligands. Compounds [Ba(ddemap)(tmhd)]2 (1) and [Ba(ddemmp)(tmhd)]2 (2) were obtained and analyzed through Fourier transform infrared spectroscopy, nuclear magnetic resonance, thermogravimetric analysis, and elemental analysis (ddemapH = 1-(dimethylamino)-5-((2-(dimethylamino)ethyl) (methyl)amino)pentan-3-ol and ddemmpH = 1-(dimethylamino)-5-((2-(dimethylamino)ethyl) (methyl)amino)-3-methylpentan-3-ol). In single-crystal X-ray crystallography, complex 1 exhibited a dimeric structure with μ2-O bonds of the ddemap ligand. All complexes exhibited high volatility and could be sublimed under reduced pressure (0.5 Torr) at 160 °C, indicating that these complexes are promising candidates as atomic layer deposition or chemical vapor deposition precursors for the growth of barium-containing thin films.

Can We Rationally Design and Operate Spatial Atomic Layer Deposition Systems for Steering the Growth Regime of Thin Films?

Fine control over the growth of materials is required to precisely tailor their properties. Spatial atomic layer deposition (SALD) is a thin-film deposition technique that has recently attracted attention because it allows producing thin films with a precise number of deposited layers, while being vacuum-free and much faster than conventional atomic layer deposition. SALD can be used to grow films in the atomic layer deposition or chemical vapor deposition regimes, depending on the extent of precursor intermixing. Precursor intermixing is strongly influenced by the SALD head design and operating conditions, both of which affect film growth in complex ways, making it difficult to predict the growth regime prior to depositions. Here, we used numerical simulation to systematically study how to rationally design and operate SALD systems for growing thin films in different growth regimes. We developed design maps and a predictive equation allowing us to predict the growth regime as a function of the design parameters and operation conditions. The predicted growth regimes match those observed in depositions performed for various conditions. The developed design maps and predictive equation empower researchers in designing, operating, and optimizing SALD systems, while offering a convenient way to screen deposition parameters, prior to experimentation.

Interplay between coordination sphere engineering and properties of nickel diketonate-diamine complexes as vapor phase precursors for the growth of NiO thin films.

NiO-based films and nanostructured materials have received increasing attention for a variety of technological applications. Among the possible strategies for their fabrication, atomic layer deposition (ALD) and chemical vapor deposition (CVD), featuring manifold advantages of technological interest, represent appealing molecule-to-material routes for which a rational precursor design is a critical step. In this context, the present study is focused on the coordination sphere engineering of three heteroleptic Ni(II) β-diketonate-diamine adducts of general formula [NiL2TMEDA] [L = 1,1,1-trifluoro-2,4-pentanedionate (tfa), 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedionate (fod) or 2,2,6,6-tetramethyl-3,5-heptanedionate (thd), and TMEDA = N,N,N',N'-tetramethylethylenediamine]. Controlled variations in the diketonate structure are pursued to investigate the influence of steric hindrance and fluorination degree on the chemico-physical characteristics of the compounds. A multi-technique investigation supported by density functional calculations highlights that all complexes are air-insensitive and monomeric and that their thermal properties and fragmentation patterns are directly dependent on functional groups in the diketonate ligands. Preliminary thermal CVD experiments demonstrate the precursors' suitability for the obtainment of NiO films endowed with flat and homogeneous surfaces, paving the way to future implementation for CVD end-uses.

Cut-and-pasting ligands: The structure/function relationships of a thermally robust Mo(VI) precursor

The bis(tert-butylimido)-molybdenum(VI) framework has previously been used for the successful atomic layer deposition (ALD) and chemical vapor deposition of many molybdenum-containing thin films. Here, we have prepared and fully characterized a new thermally robust bis(tert-butylimido)molybdenum(VI) complex, bis(tert-butylimido)-bis(N-2-(tert-butyliminomethyl)pyrrolato)-molybdenum(VI), (tBuN)2Mo(PyrIm)2 (1), that incorporates two N,N’-κ2-monoanionic ligands. The volatility and thermal stability of 1 were measured using thermogravimetric analysis and differential scanning calorimetry, where it was found to achieve a vapor pressure of 1 Torr at 212 °C and had an onset of thermal decomposition at 273 °C. A comparison of its thermal properties with those of the known ALD precursor (tBuN)2Mo(dpamd)2 (dpamd = N,N’-diisopropyl-acetamidinato) showed that 1 had similar volatility but a 78 °C improvement in thermal stability. Preliminary deposition experiments indicated that 1 should be a good ALD precursor; it exhibited self-limiting adsorption and did not decompose on the surface until at least 500 °C, features that will enable its use in the development of new high-temperature ALD processes.

(Invited) Introduction and Overview of Area-Selective Thin Film Deposition

Low temperature Area-Selective Deposition (ASD) is becoming an important need in semiconductor manufacturing to augment photolithography for improved resolution and alignment of printed features. Area-selective deposition is used routinely at temperature in excess of 800°C to form epitaxial transistor contacts, but for back-end applications, new ASD processes are needed that work at <400°C. This tutorial will introduce the challenges of low temperature ASD, and summarize recent advances in this field, including ASD via Atomic Layer Deposition (ALD) and Chemical Vapor Deposition (CVD), and understanding of feature size dependence and lateral “mushroom” growth. We will review approaches using surface passivation, including self-assembled monolayers and small molecule inhibitors, as well as approaches based on inherent differences in nucleation on different clean surfaces. Further, we will present emerging approaches that achieve patterning by taking advantage of native selectivity in nucleation and etching reactions, for example, where ALD and Atomic Layer Etching (ALE) can be combined, either in sequence or in parallel, to achieve desired outcomes. We will also review current modeling efforts, including methods to quantitatively analyze ASD and compare results for different materials and different processes, highlighting the challenges of understanding reactions for initial nucleation and nucleus removal.

Synthesis and electromagnetic transport of large-area 2D WTe2 thin film

Tungsten telluride thin films were successfully prepared on monocrystal sapphire substrates by using atomic layer deposition and chemical vapor deposition technology, and the effects of different tellurization temperatures on the properties of tungsten telluride films were investigated. The growth rate, crystal structure and composition of the film samples were characterized and analyzed by using scanning electron microscope, Raman spectroscopy and X-ray photoelectron spectroscopy. The results showed that tungsten telluride thin films with good crystal orientation in (001) were obtained at telluride temperature of 550 °C. When the telluride temperature reached 570 °C, the tungsten telluride began to decompose and unsaturated magnetoresistance was found.

Chemical Vapor Deposition of Wide-Bandgap p-Type Semiconductor Cuprous Iodide for Optoelectronic Device Applications

Continuous, pinhole-free thin films of transparent conductive materials (TCMs) with p- and n-type conductivity are critical components of optoelectronic devices including photovoltaics (PV), transparent electronics, and LEDs [1]. TCMs with n-type conductivity are widely available in the form of semiconducting oxides [2]; however, p-type TCMs (hole transport materials, HTMs) with suitable conductivity are comparatively rare [1]. Particularly in the rapidly growing field of thin film perovskite PV, device-quality thin films of HTMs with high stability and conductivity are urgently needed to replace the organic HTMs typically employed in perovskite PV research [3]. As such, techniques to deposit inorganic HTM thin films are desired.With a focus on applying HTMs in optoelectronic devices at the commercial scale, these materials must be deposited by a scalable technique yielding thin, continuous, pinhole-free films. Chemical vapor deposition (CVD) is a highly scalable thin film deposition technique widely used in industry, with a proven ability to yield high-quality thin films on large-area substrates [4]. A variety of n-type TCMs are accessible by CVD techniques, but few CVD methods exist for p-type TCMs; examples include atomic layer deposition of NiOx and VOx [5].The cuprous halides (CuX, X = Cl, Br, I), which are optically transparent p-type semiconductors with bandgaps ~3 eV, are promising inorganic HTM candidates. Cuprous iodide is of particular interest due to its low resistivity (~10-2 Ohm·cm), high hole concentration and mobility (~1019 cm-3 and ~1-10 cm2V-1s-1, respectively), and its valence band maximum position (ionization potential: 5.0-5.4 eV), which is well-aligned with common perovskite absorber materials [6]. While CuI crystallite arrays have been obtained by metal-organic CVD [7], CVD of continuous CuI thin films has only been achieved by a two-step vapor conversion process, requiring initial deposition of a copper chalcogen followed by vapor-phase conversion to the halide [6].Our group has recently published a CVD technique enabling direct deposition of continuous CuBr thin films via CVD reaction between hydrogen bromide and vinyltrimethylsilane(hexafluoroacetylacetonato)copper(I) [Cu(hfac)(vtms)] [8], and this technique has been extended to deposition of CuI. X-ray photoelectron spectroscopy indicates pure CuI films with an atomic ratio of approximately 1:1 Cu:I, and x-ray diffraction confirms deposition of γ-CuI. Similar to our observations for CuBr films, substrate identity has significant effects on CuI film continuity. Progress towards CVD of continuous CuI films on substrates of interest for practical application in optoelectronic devices will be discussed, with a particular focus on perovskite PV.[1] A. N. Fioretti and M. Morales-Masis, "Bridging the p-type transparent conductive materials gap: synthesis approaches for disperse valence band materials," J. Photon. Energy, 10, 042002 (2020).[2] M. Morales-Masis, S. De Wolf, R. Woods-Robinson, J. W. Ager, and C. Ballif, "Transparent Electrodes for Efficient Optoelectronics," Adv. Electron. Mater., 3, 1600529 (2017).[3] B. Gil, A. J. Yun, Y. Lee, J. Kim, B. Lee, and B. Park, "Recent Progress in Inorganic Hole Transport Materials for Efficient and Stable Perovskite Solar Cells," Electron. Mater. Lett., 15, 505 (2019).[4] R. Gordon, "Chemical Vapor Deposition of Coatings on Glass," J. Non-Cryst. Solids, 218, 81 (1997).[5] J. A. Raiford, S. T. Oyakhire, and S. F. Bent, "Applications of atomic layer deposition and chemical vapor deposition for perovskite solar cells," Energy Environ. Sci., 13, 1997 (2020).[6] R. Heasley, L. M. Davis, D. Chua, C. M. Chang, and R. G. Gordon, "Vapor Deposition of Transparent, p-Type Cuprous Iodide Via a Two-Step Conversion Process," ACS Appl. Energy Mater., 1, 6953 (2018).[7] V. Gottschalch, S. Blaurock, G. Benndorf, J. Lenzner, M. Grundmann, and H. Krautscheid, "Copper iodide synthesized by iodization of Cu-films and deposited using MOCVD," J. Cryst. Growth, 471, 21 (2017).[8] C. M. Chang, L. M. Davis, E. K. Spear, and R. G. Gordon, "Chemical Vapor Deposition of Transparent, p-Type Cuprous Bromide Thin Films," Chem. Mater., 33, 1426 (2021).

A Dendrite‐Free Lithium‐Metal Anode Enabled by Designed Ultrathin MgF2 Nanosheets Encapsulated Inside Nitrogen‐Doped Graphene‐Like Hollow Nanospheres

Uncontrolled lithium dendrite growth and dramatic volume change during cycling have long been severely impeding the practical applications of Li metal as the ultimate anode. In this work, ultrathin MgF2 nanosheets encapsulated inside nitrogen-doped graphene-like hollow nanospheres (MgF2 NSs@NGHSs) are ingeniously fabricated to address these problems by a perfect combination of atomic layer deposition and chemical vapor deposition. The uniform and continuous Li-Mg solid-solution inner layer formed by the MgF2 nanosheets can reduce the nucleation overpotential and induce selective deposition of Li into the cavities of the NGHSs. Furthermore, the Li deposition behavior and mechanism of the hybrid host are comprehensively explored by in situ optical microscopy at the macroscopic level, in situ transmission electron microscopy at the microscopic level, and theoretical calculations at the atomic level, respectively. Benefiting from a synergistic modulation strategy of nanosheet seed-induced nucleation and Li-confined growth, the designed composite demonstrates an endurance of 590 cycles for asymmetric cells and a lifespan over 1330 h for corresponding symmetric cells. When applied in LiFePO4 full cells, it provides a reversible capacity of 90.6 mAh g-1 after 1000 cycles at 1 C.

Thermal Stability and Decomposition Pathways in Volatile Molybdenum(VI) Bis-imides.

The vapor deposition of many molybdenum-containing films relies on the delivery of volatile compounds with the general bis(tert-butylimido)molybdenum(VI) framework, both in atomic layer deposition and chemical vapor deposition. We have prepared a series of (tBuN)2MoCl2 adducts using neutral N,N'-chelates and investigated their volatility, thermal stability, and decomposition pathways. Volatility has been determined by thermogravimetric analysis, with the 1,4-di-tert-butyl-1,3-diazabutadiene adduct (5) found to be the most volatile (1 Torr of vapor pressure at 135 °C). Thermal stability was measured primarily using differential scanning calorimetry, and the 1,10-phenanthroline adduct (4) was found to be the most stable with an onset of decomposition of 303 °C. We have also investigated molybdenum compounds with other alkyl-substituted imido groups: these compounds all follow a similar decomposition pathway, γ-H activation, with varying reaction barriers. The tert-pentyl, 1-adamantyl, and a cyclic imido (from 2,5-dimethylhexane-2,5-diamine) were systematically studied to probe the kinetics of this pathway. All of these compounds have been fully characterized, including via single-crystal X-ray diffraction, and a total of 19 new structures are reported.

Coalescence of ultrathin films by atomic layer deposition or chemical vapor deposition: Models of the minimum thickness based on nucleation and growth rates

Ultrathin, pinhole-free, and atomically smooth films are essential for future development in microelectronic devices. However, film morphology and minimum thickness are compromised when growth begins with the formation of islands on the substrate, which is the case for atomic layer deposition or chemical vapor deposition (CVD) on relatively unreactive substrates. Film morphology at the point of coalescence is a function of several microscopic factors, which lead to measurable, macroscopic rates of island nucleation and growth. To quantify the effect of these rates on the morphology at the point of coalescence, we construct two models: (1) a Monte Carlo simulation generates the film height profile from spatially random nucleation events and a constant island growth rate; simulated films resemble AFM images of the physical films; (2) an analytical model uses Poisson point statistics to determine the film thickness required to cover the last bare site on the substrate as a function of the nucleation rate and growth rate. Both models predict the same maximum thickness required to reach 99% coverage and reveal a power law relationship between the maximum thickness and the ratio of the nucleation rate divided by the growth rate. The Monte Carlo simulation further shows that the roughness scales linearly with thickness at coverages below 100%. The results match well with experimental data for the low-temperature CVD of HfB2 on Al2O3 substrates, but there are significant discrepancies on SiO2 substrates, which indicate that additional surface mechanisms must play a role.

Ultrathin PANI-Decorated, Highly Purified and Well Dispersed Array Cncs for Highly Sensitive HCHO Sensors

The flocculation of small surficial groups on pristine CNCs (carbon nanocoils) bundles limit their application. In this study, we designed and fabricated novel array CNCs with a surficial decoration of polyaniline (PANI) using in situ methods. Atomic layer deposition (ALD) and chemical vapor deposition (CVD) methods were employed to fabricate the highly pure array CNCs. The array CNCs decorated with ultra-thin PANI were confirmed by different characterizations. Furthermore, this material displayed a good performance in its detection of formaldehyde. The detection results showed that the CNCs coated with PANI had a low limit of detection of HCHO, as low as 500 ppb, and the sensor also showed good selectivity for other interfering gases, as well as good repeatability over many tests. Furthermore, after increasing the PANI loading on the surface of the CNCs, their detection performance exhibited a typical volcanic curve, and the value of the enthalpy was extracted by using the temperature-varying micro-gravimetric method during the process of detection of the formaldehyde molecules on the CNCs. The use of array CNCs with surficial decoration offers a novel method for the application of CNCs and could be extended to other applications, such as catalysts and energy conversion.

Structural and electrical characterisation of PtS from H2S-converted Pt

A manufacturing-compatible 300 mm chamber reactor for atomic layer deposition or chemical vapour deposition, and pre-fitted with H2/H2S gases that can be uniformly delivered to the wafer surface, is employed to thermally convert Pt to PtS in a H2/H2S gaseous atmosphere for 7 hours at a chamber temperature of 550 °C. Prior to conversion, platinum layers 5 nm thick are uniformly deposited by electron beam evaporation onto ∼30 nm of amorphous aluminium sesquioxide deposited by atomic layer deposition on, (a) p-type silicon, and (b) c-plane sapphire. Structural characterisation is performed by high-resolution cross-sectional transmission-electron microscopy, scanning-electron microscopy and Raman spectroscopy, confirming the formation of continuous films of polycrystalline platinum monosulfide (PtS) with a ∼15 nm thickness. Electrical characterisation is performed by 4-point resistivity and Hall-effect transport measurements on van der Pauw structures of PtS on aluminium sesquioxide on c-plane sapphire, and by back-gate junctionless MOSFET device measurements for PtS on aluminium sesquioxide on p-type silicon, showing that PtS behaves as a semiconductor with a mobility of ∼16 cm2/V.s and with an n-type carrier concentration of ∼1.2 × 1015 cm−3. Advanced commercial-grade Sentaurus simulations, alongside density-functional theory calculations, agree well with the experimental observations and suggest a large bandgap of ∼1.58 eV may be possible that could lead to a low off-current and a high Ion/Ioff ratio, suggesting that PtS may be an advanced material candidate for future device integration with CMOS and for 3D integration applications in Beyond-CMOS and More-than-Moore technologies.

Room temperature PVD TiN to improve the ferroelectric properties of HZO films in the BEoL

Zirconium-doped hafnium oxide (HZO) crystallizes at low temperatures and is thus ideal to implement ferroelectric (FE) functionalities into the back end of line (BEoL). Therefore, metal-ferroelectric-metal (MFM) capacitors are of great interest. Placed in the BEoL, they can be connected either to the drain- or the gate-contact of a standard logic device to realize different emerging FE-embedded non-volatile memory (eNVM) concepts. However, the low crystallization temperature increases also the risk for a premature crystallization of the HZO films during the growth of the top electrode (TE), in particular, if high-temperature processes like atomic layer deposition (ALD) or chemical vapor deposition (CVD) are used. Herein, the TE is deposited at room temperature via physical vapor deposition (PVD). The impact of different process gas flows on the FE properties of the HZO films is studied by X-ray diffraction and polarization versus electric field measurements.Graphic abstract

Single atom catalysts by atomic diffusion strategy

The depletion of energy and increasing environmental pressure have become one of the main challenges in the world today. Synthetic high-efficiency catalysts bring hope for efficient conversion of energy and effective treatment of pollutants, especially, single-atom catalysts (SACs) are promising candidates. Herein, we comprehensively summarizes the atomic diffusion strategy, which is considered as an effective method to prepare a series of SACs. According to the different diffusion forms of the precursors, we review the synthesis pathways of SACs from three aspects: gas diffusion, solid diffusion and liquid diffusion. The gaseous diffusion method mainly discusses atomic layer deposition (ALD) and chemical vapor deposition (CVD), both of which carry out gas phase mass transfer at high temperatures. The solid-state diffusion method can be divided into nanoparticle transformation into single atoms and solid atom migration. Liquid diffusion mainly describes the electrochemical method and the molten salt method. We hope this review can trigger the rational design of SACs.

Atomic layer chemical vapor deposition of SiO2 thin films using a chlorine-free silicon precursor for 3D NAND applications

Atomic layer deposition and atomic layer chemical vapor deposition (ALD, ALCVD) of SiO2 films were investigated over a wide range of high temperatures (from 525 °C to 700 °C) using chlorine-free amino silane as the Si precursor and O3 as the oxygen reactant. The ALD window occurred at 550–600 °C. The growth per cycle (GPC) of the SiO2 films was about 1.14–1.58 Å/cycle for deposition temperatures between 525 and 700 °C. There were no chlorine impurities detected in any of the deposited ALCVD films. Above a deposition temperature of 750 °C, the SiO2 films exhibited conventional chemical vapor deposition (CVD) behavior due to precursor decomposition, as evidenced by high GPC (5.51 Å/cycle) and a significant impurity content (carbon 0.2 at% and nitrogen 0.4 at%). The SiO2 films had high film density (2.3 g/cm3), minimal roughness (rms ~ 0.16 nm). In addition, the wet etch rate (WER) of the SiO2 films decreased from 3.0 to 2.1 nm/min. The ALD SiO2 film at 600 °C exhibited excellent electrical performance, such as a leakage current density of 5.03 × 10−9 A/cm2 (at 3 MV/cm) and a breakdown field of 10.3 MV/cm.

Volatile and thermally stable silver pyrazolate complexes containing N-heterocyclic carbene ligands

Treatment of [Ag((CF3)2pz)]3 or [Ag(tBu,C3F7)pz)]3 (pz = pyrazolate) with various stable N-heterocyclic carbenes (NHC) afforded silver(I) complexes containing pyrazolate and NHC ligands in 10–81% crystalline yields. These complexes were analyzed by spectral and analytical techniques and by X-ray crystal structure determinations. The solid state structures showed monomeric, dimeric, or tetrameric formulations, depending upon the pyrazolate and NHC substituents. To evaluate their potential as thin film growth precursors, [Ag((CF3)2pz)]3, [Ag(tBu,C3F7)pz)]3, and the new complexes were evaluated by thermogravimetric analyses, sublimation studies, thermal decomposition temperatures, and solution reduction experiments with potential reducing agents. The decomposition temperatures were higher for complexes containing (CF3)2pz ligands (203 to 293 °C) than for those containing (tBu,C3F7)pz ligands (160 to 200 °C). The complexes sublimed between 110 and 140 °C at 0.2 Torr. Solution reactions of several complexes with aqueous hydrazine, 1,1-dimethylhydrazine, formic acid, and tBuNH2 led to the formation of silver metal. Several of the new complexes have promising precursor properties for use in thin film growth by the atomic layer deposition and chemical vapor deposition techniques.

(Invited) In-Situ and Combinatorial Techniques for Spatial ALD

Atmospheric-pressure spatial atomic layer deposition (AP-SALD) and chemical vapor deposition (AP-CVD) have been developed in recent years as scalable techniques for the rapid deposition of oxide thin films on different substrates for a variety of applications. The atmospheric nature of these techniques facilitates the integration of characterization tools and the modification of the experimental setup to produce novel materials. Here we report in-situ electrical and optical characterization methods that have been developed for our AP-SALD/CVD system, as well as new techniques to deposit oxide films with nanoscale thickness gradients. The in-situ electrical measurements are enabled by a custom-designed, flexible printed circuit board substrate and the optical measurements are performed via reflectometry techniques. The thickness, resistance, and optical constants of prototypical AP-SALD films (ZnO and Al2O3) were monitored during depositions, providing insight into film nucleation and growth. The nanoscale thickness gradient films facilitate combinatorial high-throughput screening of devices, where a multitude of devices with varying film thicknesses can be fabricated on a single substrate. This combinatorial approach was applied to study the role of Al2O3 film thickness as an insulating layer in quantum-tunneling metal-insulator-metal diodes and as an encapsulation layer in metal halide perovskite solar cells.

Applications of atomic layer deposition and chemical vapor deposition for perovskite solar cells

A review on the versatility of atomic layer deposition and chemical vapor deposition for the fabrication of stable and efficient perovskite solar cells.

Characterization of Hydrophobic Silane Film Deposited on AISI 304 Stainless Steel for Corrosion Protection

This present study was conducted to determine the aptitude of hydrophobic silane coating in corrosion resistance of AISI 304 stainless steel substrate at the nanoscale. Three newly developed hydrophobic silane-based compounds of compositions, namely [tris(trimethylsiloxy)silyethyl]dimethylchlorosilane (alkyl); tridecafloro-1,1,2,2-tetrahydrooctyltrichlorosilane (FOTS); and henicosyl-1,1,2,2-tetrahydrododecyltricholrosilane (FDDTS), were used as precursors to coat AISI 304 stainless steel surfaces. Prior to deposition, the substrate surfaces were pretreated with plasma oxide via a multi-step treatment to serve as adhesion. The plasma oxide and the silane precursors were deposited by using a hybrid atomic layer deposition and chemical vapor deposition process. The structural, chemical and electrochemical stabilities were investigated using SEM, AFM, XRD, ATR-FTIR, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results showed that the microstructures and morphology of the coated samples were similar, due to the chlorosilane functionalization. The FTIR indicated complete hydrolysis at the nanoscale while the polarization results showed that nano-coating can hamper the corrosion propagation mechanisms. Furthermore, the EIS results revealed that all the precursors acted as a barrier to AISI 304 dissolution into the electrolyte. The electrochemical effect was observed in the microstructural transformation of the coatings. Although all the precursors were shown to have been effective at few nanoscales, the stability of the FDDTS showed to have superseded that of alkyl and FOTS.