Growth per cycle of alumina atomic layer deposition on nano- and micro-powders

Abstract

Core–shell powders consisting of a tungsten particle core and thin alumina shell have been synthesized using atomic layer deposition in a rotary reactor. Standard atomic layer deposition of trimethylaluminum/water at 150 °C utilizing a microdosing technique was performed on four different batches of powder with different average particle sizes. The particle size of the powders studied ranges from ∼25 to 1500 nm. The high mass-thickness contrast between alumina and tungsten in transmission electron microscopy images demonstrates that the particle core/shell interface is abrupt. This allows for the uncomplicated measurement of alumina thickness and therefore the accurate determination of growth per cycle. In agreement with prior works, the highest growth per cycle of ∼2 Å/cycle occurred on the batch of powder with the smallest average particle size and the growth per cycle decreased with increasing average particle size of a powder batch. However, the growth per cycle of the alumina film on an individual particle in a batch is shown to be independent of the size of an individual particle, and therefore, a powder batch which consists of particles size spanning orders of magnitude has constant shell thickness on all particles. This uniformity of thickness on different particle sizes in a particular batch is determined to be due to the difficulty of removing residual water molecules from the powder during the purging cycle of the atomic layer deposition (ALD) process. Therefore, rotary ALD on a single batch of powder with wide particle size distribution provides the same shell thickness regardless of individual particle size, which may have positive implications for particle ALD applications where the shell thickness determines critical parameters, such as particle passivation and manipulation of optical properties.

Development of nanofluidst based on nanoencapsulated phase change materials

“…In Figure 7.3 (b), the same dimensions can be observed for the particles coated with Al2O3, with a thickness of 10 nm of Al2O3 in this case. Such SiO2 and Al2O3 film thicknesses translate into GPCs of 0.16 nm and 0.2 nm, respectively, which are in agreement with the values reported in literature 127,130 . Both oxide ceramic coatings of SiO2 and Al2O3 are very conformal, and fully confine the nePCM with a constant layer thickness.…”

“…Processing of transition (Ni [114][115][116][117][118][119] , Fe 116,117,[120][121][122][123] , Cu 116,123 and Co 116 ) and post-transition metal particles (Al 117,[124][125][126] , Zn 117 and W 127 has been reported through ALD. Several oxide (Al2O3 [114][115][116][117][119][120][121]123,127 , TiO2 116,118,122 , SnO2 124,125 , Fe2O3 126 , and ZnO 125 ), nitride (BN 117 ) and composite (Al2O3/ZnS 120 and AlN/TiO2 122 ) ALD coatings have been deposited; for an overview see Miikkulainen et al 128 . Different ALD processes have different values for the growth-per-cycle (GPC).…”

“…Due to the oxidation avoidance prerequisites, relatively mild processing conditions in terms of temperature (up to 350 °C) and co-reactant reactivity (mostly H2O or H2O2) are preferred. Agitated reactor vessels such as fluidised beds 114,129 and rotary reactors 123,127 provide favourable coating conformality and uniformity characteristics as compared to viscous flow 125 or flow-type 118 reactors.…”

Reduction of Surface Residual Lithium Compounds for Single-Crystal LiNi0.6Mn0.2Co0.2O2 via Al2O3 Atomic Layer Deposition and Post-Annealing

“…As the high-resolution TEM (HR-TEM) image shown in Figure 2b, the measured lattice spacing is 0.472 nm, which is assigned to the NCM622 (003) plane. Since the theoretical thickness of 2 ALD cycles of Al 2 O 3 is about 2-3 Å, no obvious Al 2 O 3 coating can be observed [31][32][33][34]. In order to identify the existence of Al 2 O 3 coating, EDS analysis in Figure 2c shows a clear Al signal with an atomic concentration of 5.73% at the edge location (P1) of NCM622 particles.…”

Suppressing the Photocatalytic Activity of TiO2 Nanoparticles by Extremely Thin Al2O3 Films Grown by Gas-Phase Deposition at Ambient Conditions

“…ALD has been developed for a few decades [23,24], and utilized in the deposition of a wealth of materials on virtually every substrate for applications in various fields such as microelectronics, catalysis, and energy conversion and storage [21,25,26]. Particularly for coating on nanoparticles, ALD has emerged as an excellent method for the deposition of ultrathin conformal films of SiO 2 and Al 2 O 3 [14,15,24,27,28,29,30,31,32,33,34,35,36]. In particular, recent developments in ALD reactor types, such as rotary and fluidized bed reactors (FBR), have enabled ALD of thin films on large quantities of micro- and nanoparticles [37,38,39].…”