Email
Like
Liked ×
Save
Private Content
Embed
Loading embed code…
We have emailed the verification/download link to "".
Login to your email and click the link to download the file directly.

To request the link at a different email address, update it here. Close
Validation messages. Success message. Fail message.

Check your bulk/spam folders if you can't find our mail.
Loading

+ Follow

JPCL jz300111c Balbuena Presentation

by jpcoffice on Jun 04, 2012

389 views

Accessibility

View text version

Upload Details

Uploaded via SlideShare as Microsoft PowerPoint

Usage Rights

File a copyright complaint

Statistics

Likes: 0
Downloads: 0
Comments: 0
Embed Views: 0
Views on SlideShare: 389
Total Views: 389

Hello, my name is Perla Balbuena and I am a professor at Texas A&M University. Today I want to tell you about our recent publication in the Journal of Physical Chemistry Letters that describes the formation of a p-n junction at the interface between metallic systems.
We recently explored an interesting phenomenon that takes place when thin metal films are separated by a sub-nanometer gap. Our density functional theory calculations showed that at these short surface-surface separations, a strong interaction between the metal surfaces leads to migration of electrons to the gap region due to quantum tunneling. One of the reasons why this phenomenon is interesting is because it can induce unusual chemistry.
Let’s consider a composite metallic system formed by two interacting subsystems. At the left, subsystem 1 has two interacting metal thin films each one having a “skin” layer of a metal over platinum. At the right, subsystem 2 has two interacting metal thin films made of pure platinum. At equilibrium, this composite system displays a potential barrier that resembles a semiconductor p-n junction. This is a consequence of the different electron distribution in each region. p-n junctions play important roles as elementary building blocks of electronic devices. Here we study the formation of a junction at the interface for various composite metal systems.
Density functional theory is used to evaluate the electron density in the gap (left image), and also the work function, and potential barrier arising in these composite systems (shown in the image at the right). These variables are then correlated to the nature of the skin metal and to their location in the periodic table.
We first analyze properties of the individual M/Pt subsystems. The table shows the number of electrons in the gap, and the calculated work function for various skin systems. The results can be compared to those of pure Pt and illustrate that properties may be tuned according to the nature of the metal skin layer.
Here we show the variation of the amount of charge in the gap and the work function of the subsystem as a function of the oxidation of the surface atoms, for elements in three different periods of the periodic table. It is found that the amount of electrons in the gap increases as the atomic number Z decreases in a given period. The results are in agreement with the variation of the average work function, reflecting trends in electronegativity.
Lets look now at the results for a composite system. The table shows the built-in potential created at the interface, the work function, and the charge gained by each Pt atom at the interface. If the two subsystems are made of pure Pt, the built-in potential and the charge are practically zero. But if the two subsystems are different, for example Ti/Pt at the left and pure Pt at the right, there is a built-in potential and the Pt atoms at the interface are reduced, gaining electrons.
Analyzing the properties of the composite systems, we observe correlations of the built-in potential and work functions with the degree of reduction of each Pt atom at the interface. The built-in potential increases and the work function decreases in a given period as the atomic number decreases, following electronegativity trends.
In summary, we show the formation of a built-in potential at the junction between two metallic systems. The built-in potential depends on the chemical nature of the metals in the subsystems.The electron density, work function, and potential barrier follow electronegativity trends in the periodic table.

JPCL jz300111c Balbuena Presentation Webinar Transcript

p−n Junction at the Interface betweenMetallic SystemsGustavo E. Ramírez-Caballero,Julibeth M. Martínez de la Hoz,and Perla B. Balbuena*Department of Chemical Engineering andMaterials Science and Engineering ProgramTexas A&M UniversityCollege Station, Texas, 77843, United States*balbuena@tamu.edu 1J. Phys. Chem. Lett. 2012, Vol. 3, 818 - 825
Motivation• Thin metal films separated by a sub-nanometer gap exhibit a strong interaction, which leads to migration of electrons to the gap region Electron migration to the gap Induces unusual chemistry Proprietary and Confidential 2 American Chemical Society
Composite metallic systems• A potential barrier resembles a p-n junction • p−n junctions play an important role as elementary building blocks of electronic devices Electrostatic potential • We study the formation of p-n junctions for various composite systemsProprietary and Confidential 3American Chemical Society
Methodology• Electron density in the gap, work function, and potential barrier at the interface are correlated to the nature of the metal skin of the subsystems and their location on the periodic table. Properties evaluated with density functional theory.Proprietary and Confidential 4American Chemical Society
Results: M/Pt subsystems Pt Pt Pt Pt Pt Pt Pt PtM M M MM M M M Pt Pt Pt Pt Pt Pt Pt PtProperties can betuned by changingthe nature of themetallic skin layer Proprietary and Confidential 5 American Chemical Society
Properties of the subsystemsProprietary and Confidential 6American Chemical Society
Results:M/Pt-Pt/Pt composite systems built-in potentialProprietary and Confidential 7American Chemical Society
Properties of the composite systems Proprietary and Confidential 8 American Chemical Society
Conclusions • A composite system, formed by connecting two metallic subsystems, exhibits two regions with different electrostatic potentials, thus generating a potential barrier or built-in potential at the junction. • The built-in potential depends on the chemical nature of the metal in the subsystems. • The electron density, work function of the system, and potential barrier follow a trend that can be ordered according to the periodic table and correlated to properties such as electronegativity and the number of unpaired electrons in the most external orbitals. (Optional) Acknowledgments Picture of authors or • Financial support from the Department of Energy, research group Basic Energy Sciences, under grant DE-FG02- 05ER15729 is gratefully acknowledged. We thank TAMU Supercomputer Center, TACC, and NERSC for computational resources.Proprietary and Confidential 9American Chemical Society

JPCL jz300111c Balbuena Presentation

by jpcoffice on Jun 04, 2012

Accessibility

Categories

Upload Details

Usage Rights

Statistics

JPCL jz300111c Balbuena Presentation Webinar Transcript