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We studied the chemisorption of silicon tetrachloride (SiCl4) on the NH2/NH-terminated silicon nitride slab model using density functional theory (DFT) for atomic layer deposition (ALD) of silicon nitride. Initially, two reaction pathways were compared, forming HCl or NH3+Cl− as a byproduct. The NH3+Cl− complex formation was more exothermic than the HCl formation, with an activation energy of 0.26 eV. The –NH2* reaction sites are restored by desorption of HCl from the NH3+Cl− complexes at elevated temperatures of 205 °C or higher. Next, three sequential ligand exchange reactions forming Si–N bonds were modeled and simulated. The reaction energies became progressively less exothermic as the reaction progressed, from −1.31 eV to −0.30 eV to 0.98 eV, due to the stretching of Si–N bonds and the distortion of the N–Si–N bond angles. Also, the activation energies for the second and third reactions were 2.17 eV and 1.55 eV, respectively, significantly higher than the 0.26 eV of the first reaction, mainly due to the additional dissociation of the N–H bond. The third Si–N bond formation is unfavorable due to the endothermic reaction and higher activation energy. Therefore, the chemisorbed species would be –SiCl2* when the surface is exposed to SiCl4. [ABSTRACT FROM AUTHOR]

Tetrakis(dimethylamino)-titanium (TDMAT, Ti(NMe2)4) has been used for the low-temperature atomic layer deposition (ALD) process of titanium oxide (TiO2) films. In this study, the chemisorption of TDMAT on a titanium oxide surface using a slab model was simulated by density functional theory (DFT) calculation. We calculated the activation energy for the chemisorption and predicted the final chemisorbed species. A TiO2 slab model was constructed with the optimized number of –OH surface groups. Three serial ligand exchange reactions between a TDMAT molecule and the TiO2 slab were exothermic with low activation energies of 0.16–0.46 eV, which can explain the low processing temperatures of the ALD TiO2 processes. Our DFT calculation showed that three NMe2 ligands of TDMAT would be released and the surface species of –TiNMe2 would be formed, which is in good agreement with the experimental observation in the literature. [ABSTRACT FROM AUTHOR]

Selective etching of silicon oxide (SiO2) against silicon (Si) using anhydrous hydrogen fluoride (HF) vapor has been used for semiconductor device fabrication. We studied the underlying mechanism of the selective etching by density functional theory (DFT) calculation. We constructed surface slab models of SiO2 or Si with different degrees of fluorination and simulated the four steps of fluorination. The calculations show relatively low activation energies of 0.72–0.79 eV for the four steps of fluorination of SiO2, which are close to ∼0.69 eV observed in the experiment. The four-membered ring structure of –Si–O–H–F– in all transition states stabilized the system, resulting in relatively low activation energies. Thus, continuous etching of SiO2 by HF is plausible at near-room temperature. In contrast, the fluorinations of Si showed relatively high activation energies ranging from 1.22 to 1.56 eV due to the less stable transition state geometries. Thus, negligible etching of silicon by HF is expected by the near-room temperature process. Our calculation results explain well the experimental observation of the selective etching of SiO2 against Si by HF vapor. [ABSTRACT FROM AUTHOR]

We report the atomic layer deposition (ALD) of silicon oxide films using a chlorine-free silylamine precursor and ozone (O3). Bis(dimethylaminomethylsilyl)trimethylsilylamine (DTDN-2H2) containing three Si atoms was used as the precursor, and a high growth rate of 1.34 Å per cycle at 400 °C was obtained, which is significantly higher than ∼0.55 Å per cycle using tris-DMAS at the same temperature. DFT calculations showed that a precursor fragment containing three Si atoms could be attached to the SiO2 substrate, which explains the higher growth rate of DTDN-2H2. The ALD temperature window was 350–400 °C with good step coverages. Stoichiometric SiO2 films were prepared with no carbon or nitrogen impurities detected by XPS. The genuine ALD film prepared at 400 °C showed a leakage current density of 26 nA cm−2 at 2 MV cm−1 and an oxide-trapped charge density of 4.7 × 1011 cm−2. [ABSTRACT FROM AUTHOR]

To realize three-dimensional vertical phase-change random-access memory (PCRAM) devices, it is essential to fabricate highly conformal GeSbTe (GST) films inside high-aspect-ratio holes using atomic layer deposition (ALD). Different compositions of GST films are favored for various applications of PCRAM devices. In the present work, the [Ge]/[Sb] ratio of GST thin films prepared by tellurization annealing of ALD Ge–Sb films was controlled through the supercycle process of ALD GeSb and ALD Sb. By adjusting the cycle number ratio of ALD Sb to ALD GeSb between 0 and 0.5, we could change the Ge content of the Ge–Sb film from 0.33 to 0.66 and the Sb content from 0.26 to 0.63. After tellurization annealing at 230 °C, the Ge, Sb, and Te concentrations were 0.11–0.25, 0.19–0.37, and 0.52–0.60, respectively. The phase transition temperature was tunable between 90 and 137 °C depending on the Sb concentration. A crystalline GST film with a uniform composition close to Ge2Sb2Te5 was formed, with a step coverage of higher than 85% on a trench pattern with an aspect ratio of 24. [ABSTRACT FROM AUTHOR]

We studied the atomic layer deposition (ALD) of titanium oxide (TiO2) thin films using a newly developed heteroleptic titanium precursor with a linked ligand. The titanium precursor, [2-(N-methylamino) 1-methyl ethyl cyclopentadienyl] bis(dimethylamino) titanium (CMENT), was designed to enhance the maximum ALD process temperature by linking the Cp ligand of tris(dimethylamino)cyclopentadienyl titanium [CpTi(NMe2)3] to an amine ligand. The maximum temperature for the self-limiting ALD growth using CMENT and O3 was 300 °C, 75 °C higher than tetrakis(dimethylamino)titanium (TDMAT) or CpTi(NMe2)3. At 300 °C, high-density (4.0–4.1 g cm−3) high-purity TiO2 films were prepared with a growth rate of ∼0.7 Å per cycle, good step coverage, and wide bandgap (3.0–3.1 eV). CMENT can grow TiO2 films using H2O, unlike heteroleptic precursors with a cyclopentadienyl ligand. The density functional theory (DFT) simulation on the thermolysis of titanium precursors showed that TDMAT has the best thermal stability as a molecule, which could not explain the highest ALD temperature of CMENT. The simulation of the surface reactions of the precursors expected that the linked ligand is the only surface species for CMENT, whereas N(CH3)2 (NMe2) ligands remain on the surface for TDMAT or CpTi(NMe2)3. The absence of thermally unstable NMe2 in the CMENT case explains the highest ALD temperature of CMENT. [ABSTRACT FROM AUTHOR]

Correction for 'Composition control of conformal crystalline GeSbTe films by atomic layer deposition supercycles and tellurization annealing' by Yewon Kim et al., J. Mater. Chem. C, 2022, 10, 9691–9698, DOI: https://doi.org/10.1039/D2TC00784C. [ABSTRACT FROM AUTHOR]

Biomimetic mineralization of vertical N-doped carbon nanotubes is demonstrated as a straightforward route for carbon-based mineral nanocomposites. The N-doped sites along the carbon nanotube backbone play the role of nucleation sites for mineralization. [ABSTRACT FROM AUTHOR]

Substitutional heteroatom doping is a promising route to modulate the outstanding material properties of carbon nanotubes and graphene for customized applications. Recently, (nitrogen-) N-doping has been introduced to ensure tunable work-function, enhanced n-type carrier concentration, diminished surface energy, and manageable polarization. Along with the promising assessment of N-doping effects, research on the N-doped carbon based composite structures is emerging for the synergistic integration with various functional materials. This invited feature article reviews the current research progress, emerging trends, and opening opportunities in N-doped carbon based composite structures. Underlying basic principles are introduced for the effective modulation of material properties of graphitic carbons by N-doping. Composite structures of N-doped graphitic carbons with various functional materials, including (i) polymers, (ii) transition metals, (iii) metal oxides, nitrides, sulphides, and (iv) semiconducting quantum dots are highlighted. Practical benefits of the synergistic composite structures are investigated in energy and catalytic applications, such as organic photovoltaics, photo/electro-catalysts, lithium ion batteries and supercapacitors, with a particular emphasis on the optimized interfacial structures and properties.

We prepared vertically aligned nitrogen doped carbon nanotubes (CNTs) on a rigid glass substrate or flexible plastic substrate via a 'growth-detachment-transfer' process and the vertically aligned N-doped CNT arrays are employed as counter electrodes for novel dye-sensitized solar cells.

Biomimetic mineralization of vertical N-doped carbon nanotubes is demonstrated as a straightforward route for carbon-based mineral nanocomposites. The N-doped sites along the carbon nanotube backbone play the role of nucleation sites for mineralization.