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Trimethylaluminum and Oxygen Atomic Layer Deposition on Hydroxyl-Free Cu(111).

Gharachorlou A, Detwiler MD, Gu XK, Mayr L, Klötzer B, Greeley J, Reifenberger RG, Delgass WN, Ribeiro FH, Zemlyanov DY - ACS Appl Mater Interfaces (2015)

Bottom Line: On the other hand, TMA readily adsorbed on the Cu2O/Cu(111) surface at 473 K resulting in the reduction of some surface Cu(1+) to metallic copper (Cu(0)) and the formation of a copper aluminate, most likely CuAlO2.O2 half-cycles at 623 K were more effective for carbon removal than O2 half-cycles at 473 K or water half-cycles at 623 K.According to STM, Al2O3 grows homogeneously on Cu(111) terraces.

View Article: PubMed Central - PubMed

Affiliation: †School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907, United States.

ABSTRACT
Atomic layer deposition (ALD) of alumina using trimethylaluminum (TMA) has technological importance in microelectronics. This process has demonstrated a high potential in applications of protective coatings on Cu surfaces for control of diffusion of Cu in Cu2S films in photovoltaic devices and sintering of Cu-based nanoparticles in liquid phase hydrogenation reactions. With this motivation in mind, the reaction between TMA and oxygen was investigated on Cu(111) and Cu2O/Cu(111) surfaces. TMA did not adsorb on the Cu(111) surface, a result consistent with density functional theory (DFT) calculations predicting that TMA adsorption and decomposition are thermodynamically unfavorable on pure Cu(111). On the other hand, TMA readily adsorbed on the Cu2O/Cu(111) surface at 473 K resulting in the reduction of some surface Cu(1+) to metallic copper (Cu(0)) and the formation of a copper aluminate, most likely CuAlO2. The reaction is limited by the amount of surface oxygen. After the first TMA half-cycle on Cu2O/Cu(111), two-dimensional (2D) islands of the aluminate were observed on the surface by scanning tunneling microscopy (STM). According to DFT calculations, TMA decomposed completely on Cu2O/Cu(111). High-resolution electron energy loss spectroscopy (HREELS) was used to distinguish between tetrahedrally (Altet) and octahedrally (Aloct) coordinated Al(3+) in surface adlayers. TMA dosing produced an aluminum oxide film, which contained more octahedrally coordinated Al(3+) (Altet/Aloct HREELS peak area ratio ≈ 0.3) than did dosing O2 (Altet/Aloct HREELS peak area ratio ≈ 0.5). After the first ALD cycle, TMA reacted with both Cu2O and aluminum oxide surfaces in the absence of hydroxyl groups until film closure by the fourth ALD cycle. Then, TMA continued to react with surface Al-O, forming stoichiometric Al2O3. O2 half-cycles at 623 K were more effective for carbon removal than O2 half-cycles at 473 K or water half-cycles at 623 K. The growth rate was approximately 3-4 Å/cycle for TMA+O2 ALD (O2 half-cycles at 623 K). No preferential growth of Al2O3 on the steps of Cu(111) was observed. According to STM, Al2O3 grows homogeneously on Cu(111) terraces.

No MeSH data available.


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STM images of (a) clean Cu(111) and (b–e) Cu(111) exposedto 4500 L O2 at 623 K. The seven rings of Cu2O with the “44” structure13 are shown in image e. Bias voltages were −0.5 V for all images,and tunneling currents were 0.5 nA (images a, b) and 1.0 nA (imagesc–e). Image e was processed using a wavelet filter in WSxMSoftware;27 see the Supporting Information for more details.
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fig6: STM images of (a) clean Cu(111) and (b–e) Cu(111) exposedto 4500 L O2 at 623 K. The seven rings of Cu2O with the “44” structure13 are shown in image e. Bias voltages were −0.5 V for all images,and tunneling currents were 0.5 nA (images a, b) and 1.0 nA (imagesc–e). Image e was processed using a wavelet filter in WSxMSoftware;27 see the Supporting Information for more details.

Mentions: Oxygen was adsorbed on Cu(111) by exposure to 4500 L O2 at 623 K. O 1s, Al 2s, and C 1s XPS core-level regions obtainedfrom the Cu2O/Cu(111) surface are shown in Figure 5, and STM images are presentedin Figure 6. The O1s peak was fitted with one component at 529.8 eV, which was assignedto oxygen in the Cu2O layer (assignment made by STM below).Reported Cu2O BEs range from 529.9 to 531.0 eV (see reference (45) and references therein).A high BE shoulder at ca. 936.0 eV was observed in the Cu 2p3/2 core-level region following oxygen exposure indicating that someCu2O was present (data shown in SupportingInformation Figure S1). The Cu 3s/Al 2s region was unaffectedby the first O2 exposure. Neither XPS nor HREELS of thissurface revealed any hydroxyl species (HREELS spectrum shown in Supporting Information Figure S2). It shouldbe noted that Al 2s was used instead of Al 2p for UHV XPS experimentsdue to the overlap of Al 2p with Cu 3p.


Trimethylaluminum and Oxygen Atomic Layer Deposition on Hydroxyl-Free Cu(111).

Gharachorlou A, Detwiler MD, Gu XK, Mayr L, Klötzer B, Greeley J, Reifenberger RG, Delgass WN, Ribeiro FH, Zemlyanov DY - ACS Appl Mater Interfaces (2015)

STM images of (a) clean Cu(111) and (b–e) Cu(111) exposedto 4500 L O2 at 623 K. The seven rings of Cu2O with the “44” structure13 are shown in image e. Bias voltages were −0.5 V for all images,and tunneling currents were 0.5 nA (images a, b) and 1.0 nA (imagesc–e). Image e was processed using a wavelet filter in WSxMSoftware;27 see the Supporting Information for more details.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4528256&req=5

fig6: STM images of (a) clean Cu(111) and (b–e) Cu(111) exposedto 4500 L O2 at 623 K. The seven rings of Cu2O with the “44” structure13 are shown in image e. Bias voltages were −0.5 V for all images,and tunneling currents were 0.5 nA (images a, b) and 1.0 nA (imagesc–e). Image e was processed using a wavelet filter in WSxMSoftware;27 see the Supporting Information for more details.
Mentions: Oxygen was adsorbed on Cu(111) by exposure to 4500 L O2 at 623 K. O 1s, Al 2s, and C 1s XPS core-level regions obtainedfrom the Cu2O/Cu(111) surface are shown in Figure 5, and STM images are presentedin Figure 6. The O1s peak was fitted with one component at 529.8 eV, which was assignedto oxygen in the Cu2O layer (assignment made by STM below).Reported Cu2O BEs range from 529.9 to 531.0 eV (see reference (45) and references therein).A high BE shoulder at ca. 936.0 eV was observed in the Cu 2p3/2 core-level region following oxygen exposure indicating that someCu2O was present (data shown in SupportingInformation Figure S1). The Cu 3s/Al 2s region was unaffectedby the first O2 exposure. Neither XPS nor HREELS of thissurface revealed any hydroxyl species (HREELS spectrum shown in Supporting Information Figure S2). It shouldbe noted that Al 2s was used instead of Al 2p for UHV XPS experimentsdue to the overlap of Al 2p with Cu 3p.

Bottom Line: On the other hand, TMA readily adsorbed on the Cu2O/Cu(111) surface at 473 K resulting in the reduction of some surface Cu(1+) to metallic copper (Cu(0)) and the formation of a copper aluminate, most likely CuAlO2.O2 half-cycles at 623 K were more effective for carbon removal than O2 half-cycles at 473 K or water half-cycles at 623 K.According to STM, Al2O3 grows homogeneously on Cu(111) terraces.

View Article: PubMed Central - PubMed

Affiliation: †School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907, United States.

ABSTRACT
Atomic layer deposition (ALD) of alumina using trimethylaluminum (TMA) has technological importance in microelectronics. This process has demonstrated a high potential in applications of protective coatings on Cu surfaces for control of diffusion of Cu in Cu2S films in photovoltaic devices and sintering of Cu-based nanoparticles in liquid phase hydrogenation reactions. With this motivation in mind, the reaction between TMA and oxygen was investigated on Cu(111) and Cu2O/Cu(111) surfaces. TMA did not adsorb on the Cu(111) surface, a result consistent with density functional theory (DFT) calculations predicting that TMA adsorption and decomposition are thermodynamically unfavorable on pure Cu(111). On the other hand, TMA readily adsorbed on the Cu2O/Cu(111) surface at 473 K resulting in the reduction of some surface Cu(1+) to metallic copper (Cu(0)) and the formation of a copper aluminate, most likely CuAlO2. The reaction is limited by the amount of surface oxygen. After the first TMA half-cycle on Cu2O/Cu(111), two-dimensional (2D) islands of the aluminate were observed on the surface by scanning tunneling microscopy (STM). According to DFT calculations, TMA decomposed completely on Cu2O/Cu(111). High-resolution electron energy loss spectroscopy (HREELS) was used to distinguish between tetrahedrally (Altet) and octahedrally (Aloct) coordinated Al(3+) in surface adlayers. TMA dosing produced an aluminum oxide film, which contained more octahedrally coordinated Al(3+) (Altet/Aloct HREELS peak area ratio ≈ 0.3) than did dosing O2 (Altet/Aloct HREELS peak area ratio ≈ 0.5). After the first ALD cycle, TMA reacted with both Cu2O and aluminum oxide surfaces in the absence of hydroxyl groups until film closure by the fourth ALD cycle. Then, TMA continued to react with surface Al-O, forming stoichiometric Al2O3. O2 half-cycles at 623 K were more effective for carbon removal than O2 half-cycles at 473 K or water half-cycles at 623 K. The growth rate was approximately 3-4 Å/cycle for TMA+O2 ALD (O2 half-cycles at 623 K). No preferential growth of Al2O3 on the steps of Cu(111) was observed. According to STM, Al2O3 grows homogeneously on Cu(111) terraces.

No MeSH data available.


Related in: MedlinePlus