| 1. |
- Buttera, Sydney C., et al.
(author)
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Resolving Impurities in Atomic Layer Deposited Aluminum Nitride through Low Cost, High Efficiency Precursor Design
- 2021
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In: Inorganic Chemistry. - : AMER CHEMICAL SOC. - 0020-1669 .- 1520-510X. ; 60:15, s. 11025-11031
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Journal article (peer-reviewed)abstract
- A heteroleptic amidoalane precursor is presented as a more suitably designed candidate to replace trimethylaluminum (TMA) for atomic layer deposition of aluminum nitride (AlN). The lack of C-Al bonds and the strongly reducing hydride ligands in [AlH2(NMe2)](3) (1) were specifically chosen to limit impurities in target aluminum nitride (AlN) films. Compound 1 is made in a high yield, scalable synthesis involving lithium aluminum hydride and dimethylammonium chloride. It has a vapor pressure of 1 Torr at 40 degrees C and evaporates with negligible residual mass in thermogravimetric experiments. Ammonia (NH3) plasma and 1 in an atomic layer deposition (ALD) process produced crystalline AlN films above 200 degrees C with an Al:N ratio of 1.04. Carbon and oxygen impurities in resultant AlN films were reduced to <1% and <2%, respectively. By using a precursor with a rational and advantageous design, we can improve the material quality of AlN films compared to those deposited using the industrial standard trimethylaluminum and could reduce material cost by up to 2 orders of magnitude.
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| 2. |
- Deminskyi, Petro, 1987-, et al.
(author)
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Atomic layer deposition of InN using trimethylindium and ammonia plasma
- 2019
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In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Institute of Physics (AIP). - 0734-2101 .- 1520-8559. ; 37:2
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Journal article (peer-reviewed)abstract
- Indium nitride (InN) is a low bandgap, high electron mobility semiconductor material of interest to optoelectronics and telecommunication. Such applications require the deposition of uniform crystalline InN thin films on large area substrates, with deposition temperatures compatible with this temperature-sensitive material. As conventional chemical vapor deposition (CVD) struggles with the low temperature tolerated by the InN crystal, the authors hypothesize that a time-resolved, surface-controlled CVD route could offer a way forward for InN thin film deposition. In this work, the authors report atomic layer deposition of crystalline, wurtzite InN thin films using trimethylindium and ammonia plasma on Si(100). They found a narrow atomic layer deposition window of 240-260 degrees C with a deposition rate of 0.36 A/cycle and that the flow of ammonia into the plasma is an important parameter for the crystalline quality of the film. X-ray diffraction measurements further confirmed the polycrystalline nature of InN thin films. X-ray photoelectron spectroscopy measurements show nearly stoichiometric InN with low carbon level (amp;lt;1 at. %) and oxygen level (amp;lt;5 at. %) in the film bulk. The low carbon level is attributed to a favorable surface chemistry enabled by the NH3 plasma. The film bulk oxygen content is attributed to oxidation upon exposure to air via grain boundary diffusion and possibly by formation of oxygen containing species in the plasma discharge. Published by the AVS.
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| 3. |
- Deminskyi, Petro, et al.
(author)
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Surface ligand removal in atomic layer deposition of GaN using triethylgallium
- 2021
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In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Institute of Physics (AIP). - 0734-2101 .- 1520-8559. ; 39:1
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Journal article (peer-reviewed)abstract
- Gallium nitride (GaN) is one of the most important semiconductor materials in modern electronics. While GaN films are routinely deposited by chemical vapor deposition at around 1000 degrees C, low-temperature routes for GaN deposition need to be better understood. Herein, we present an atomic layer deposition (ALD) process for GaN-based on triethyl gallium (TEG) and ammonia plasma and show that the process can be improved by adding a reactive pulse, a "B-pulse" between the TEG and ammonia plasma, making it an ABC-type pulsed process. We show that the material quality of the deposited GaN is not affected by the B-pulse, but that the film growth per ALD cycle increases when a B-pulse is added. We suggest that this can be explained by the removal of ethyl ligands from the surface by the B-pulse, enabling a more efficient nitridation by the ammonia plasma. We show that the B-pulsing can be used to enable GaN deposition with a thermal ammonia pulse, albeit of x-ray amorphous films.
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| 4. |
- Hsu, Chih-Wei, et al.
(author)
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Homogeneous high In content InxGa1-x N films by supercycle atomic layer deposition
- 2022
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In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Institute of Physics (AIP). - 0734-2101 .- 1520-8559. ; 40:6
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Journal article (other academic/artistic)abstract
- InxGa1-x N is a strategically important material for electronic devices given its tunable bandgap, modulated by the In/Ga ratio. However, current applications are hindered by defects caused by strain relaxation and phase separation in the material. Here, we demonstrate growth of homogeneous InxGa1-x N films with 0.3 < x < 0.8 up to similar to 30 nm using atomic layer deposition (ALD) with a supercycle approach, switching between InN and GaN deposition. The composition is uniform along and across the films, without signs of In segregation. The InxGa1-x N films show higher In-content than the value predicted by the supercycle model. A more pronounced reduction of GPC(InN) than GPC(GaN) during the growth processes of InN and GaN bilayers is concluded based on our analysis. The intermixing between InN and GaN bilayers is suggested to explain the enhanced overall In-content. Our results show the advantage of ALD to prepare high-quality InxGa1-x N films, particularly with high In-content, which is difficult to achieve with other growth methods.
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| 5. |
- Lu, Can, et al.
(author)
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Fabrication of semi-transparent SrTaO2N photoanodes with a GaN underlayer grown via atomic layer deposition
- 2022
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In: Green Chemistry Letters and Reviews. - : Informa UK Limited. - 1751-8253 .- 1751-7192. ; 15:3, s. 658-670
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Journal article (peer-reviewed)abstract
- Quaternary metal oxynitride-based photoanodes with a large light transmittance are promising for high solar-to-hydrogen (STH) conversion efficiency in photoelectrochemical (PEC) tandem cells. Transparent substrates to support PEC water-splitting were fabricated using atomic layer deposition (ALD) to synthesize 30 and 60 nm GaN on SiC substrates. A generalized approach was used to grow a quaternary metal oxynitride, i.e. SrTaO2N thin film on the GaN/SiC substrates. The transparency above 60% in the wide solar spectrum highlights its availability of transmitting visible light to the rear side. A photocurrent onset at ca. −0.4 V vs. reversible hydrogen electrode (RHE) was achieved by the SrTaO2N/GaN/SiC photoanodes in a 0.1 M NaOH electrolyte under simulated solar irradiation. This paves the way for the construction of hierarchically nanostructured tandem PEC cells. This work demonstrates the viability of integrating ALD in constructing substrates for semi-transparent quaternary metal oxynitride photoanodes.
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| 6. |
- Mpofu, Pamburayi, et al.
(author)
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Thermal atomic layer deposition of In2O3 thin films using a homoleptic indium triazenide precursor and water
- 2022
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In: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 51:12, s. 4712-4719
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Journal article (peer-reviewed)abstract
- Indium oxide (In2O3) is an important transparent conducting material widely used in optoelectronic applications. Herein, we study the deposition of In2O3 by thermal atomic layer deposition (ALD) using our recently reported indium(iii) triazenide precursor and H2O. A temperature interval with self-limiting growth was found between similar to 270 and 385 degrees C with a growth per cycle of similar to 1.0 angstrom. The deposited films were polycrystalline cubic In2O3 with In : O ratios of 1 : 1.2, and low levels of C and no detectable N impurities. The transmittance of the films was found to be >70% in visible light and the resistivity was found to be 0.2 m omega cm. The high growth rates, low impurities, high optical transmittance, and low resistivity of these films give promise to this process being used for ALD of In2O3 films for future microelectronic displays.
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| 7. |
- Mustafa, Elfatih Mohammed, et al.
(author)
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Solar-Driven Photoelectrochemical Performance of Novel ZnO/Ag2WO4/AgBr Nanorods-Based Photoelectrodes
- 2021
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In: Nanoscale Research Letters. - : Springer. - 1931-7573 .- 1556-276X. ; 16:1
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Journal article (peer-reviewed)abstract
- Highly efficient photoelectrochemical (PEC) water oxidation under solar visible light is crucial for water splitting to produce hydrogen as a source of sustainable energy. Particularly, silver-based nanomaterials are important for PEC performance due to their surface plasmon resonance which can enhance the photoelectrochemical efficiency. However, the PEC of ZnO/Ag2WO4/AgBr with enhanced visible-light water oxidation has not been studied so far. Herein, we present a novel photoelectrodes based on ZnO/Ag2WO4/AgBr nanorods (NRs) for PEC application, which is prepared by the low-temperature chemical growth method and then by successive ionic layer adsorption and reaction (SILAR) method. The synthesized photoelectrodes were investigated by several characterization techniques, emphasizing a successful synthesis of the ZnO/Ag2WO4/AgBr heterostructure NRs with excellent photocatalysis performance compared to pure ZnO NRs photoelectrode. The significantly enhanced PEC was due to improved photogeneration and transportation of electrons in the heterojunction due to the synergistic effect of the heterostructure. This study is significant for basic understanding of the photocatalytic mechanism of the heterojunction which can prompt further development of novel efficient photoelectrochemical-catalytic materials.
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| 8. |
- Nadhom, Hama, et al.
(author)
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Area selective deposition of iron films using temperature sensitive masking materials and plasma electrons as reducing agents
- 2021
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In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : A V S AMER INST PHYSICS. - 0734-2101 .- 1520-8559. ; 39:4
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Journal article (peer-reviewed)abstract
- The potential of area-selective deposition (ASD) with a newly developed chemical vapor deposition (CVD) method, which utilizes plasma electrons as reducing agents for deposition of metal-containing films, is demonstrated using temperature sensitive polymer-based masking materials. The masking materials tested were polydimethylsiloxane, polymethylmethacrylate, polystyrene, parafilm, Kapton tape, Scotch tape, and office paper. The masking materials were all shown to prevent film growth on the masked area of the substrate without being affected by the film deposition process. X-ray photoelectron spectroscopy analysis confirms that the films deposited consist mainly of iron, whereas no film material is found on the masked areas after mask removal. Scanning electron microscopy analysis of films deposited with nonadhesive masking materials show that film growth extended for a small distance underneath the masking material, indicating that the CVD process with plasma electrons as reducing agents is not a line-of-sight deposition technique. The reported methodology introduces an inexpensive and straightforward approach for ASD that opens for exciting new possibilities for robust and less complex area-selective metal-on-metal deposition.
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| 9. |
- Nadhom, Hama, 1986-, et al.
(author)
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Area Selective Deposition of Metals from the Electrical Resistivity of the Substrate
- 2021
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In: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 12:17, s. 4130-4133
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Journal article (peer-reviewed)abstract
- Area selective deposition (ASD) of films only on desired areas of the substrate opens for less complex fabrication of nanoscaled electronics. We show that a newly developed CVD method, where plasma electrons are used as the reducing agent in deposition of metallic thin films, is inherently area selective from the electrical resistivity of the substrate surface. When depositing iron with the new CVD method, no film is deposited on high-resistivity SiO2 surfaces whereas several hundred nanometers thick iron films are deposited on areas with low resistivity, obtained by adding a thin layer of silver on the SiO2 surface. On the basis of such a scheme, we show how to use the electric resistivity of the substrate surface as an extension of the ASD toolbox for metal-on-metal deposition.
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| 10. |
- Nadhom, Hama, et al.
(author)
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Chemical vapor deposition of metallic films using plasma electrons as reducing agents
- 2020
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In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : A V S AMER INST PHYSICS. - 0734-2101 .- 1520-8559. ; 38:3
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Journal article (peer-reviewed)abstract
- Metallic thin films are key components in electronic devices and catalytic applications. Deposition of a conformal metallic thin film requires using volatile precursor molecules in a chemical vapor deposition (CVD) process. The metal centers in such molecules typically have a positive valence, meaning that reduction of the metal centers is required on the film surface. Powerful molecular reducing agents for electropositive metals are scarce and hamper the exploration of CVD of electropositive metals. The authors present a new CVD method for depositing metallic films where free electrons in a plasma discharge are utilized to reduce the metal centers of chemisorbed precursor molecules. They demonstrate this method by depositing Fe, Co, and Ni from their corresponding metallocenes using electrons from an argon plasma as a reducing agent.
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