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Los Alamos National LaboratoryCenter for Integrated Nanotechnologies
Helping you understand, create, and characterize nanomaterials
DOE

Fall 2015

Select science highlights from Fall 2015.

Synthesizing Graphene by Ion Implantation

sythesizing graphene by ion implantation

Scientific Achievement: The precise control of graphene layer thickness by ion implantation has been achieved by taking advantage of the dual metal substrate of the Nickel (Ni)-coated Copper (Cu) foils. We created high quality layers of graphene that strictly correlate with predetermined layer numbers.

Significance: Graphene is a promising material in nanoelectronics and flexible electronic devices due to its unique 2D hexagonal lattice. However, synthesis of layer-tunable graphene by using traditional chemical vapor deposition method still remains a great challenge. Since our technique is compatible with large-scale microelectronics processing, it is expected that this approach will expedite the application of high-quality graphene to graphene-based nanoelectronic devices.

Research Details:

  • The Ni/Cu bilayer is implanted with 60 keV C ions. The samples were then annealed at 950 oC. During this process, the inter-diffusion of Ni and Cu forms a Cu-Ni alloy. Because the carbon (C) solubility is moderate in Ni and extremely low in Cu, the implanted C ions are expelled to the surface and transformed into graphene.
  • Raman, scanning tunneling microscopy (STM) and electrical measurements indicate that both monolayer and bilayer graphene films possess excellent crystalline quality.

Contact:

Publications: G. Wang, M. Zhang, S. Liu, X. M. Xie, G. Q. Ding, Y. Q. Wang, P. K. Chu, G. Heng, W. Ren, Q. H. Yuan, P. H. Zhang, X. Wang and Z. F. Di. “Synthesis of Layer‐Tunable Graphene: A Combined Kinetic Implantation and Thermal Ejection Approach”, Adv. Funct. Mater. DOI: 10.1002 (2015).

 

Size Effects on the Kinetics and Structure of Nickelide Contacts to InGaAs Fin Structures

Scientific Achievement: We found that the reaction kinetics during the formation of compound contacts to Indium gallium arsenide fin-like channels to be strongly dependent on size and orientation.

Significance: InGaAs fin channels are touted as the most serious candidate for replacing Si in sub-10nm technology nodes. Developing a self-aligned contact using nickelide (compound alloy between Ni and InGaAs) can pave the way for understanding and controlling the structural and electrical contact properties that become extremely important for overall device performance in atomic scale devices.

Research Details: nickelide

  • Systematic studies of thermal annealing of Ni contacts on <100> and <110> oriented InGaAs fins with fin widths in the range of 30 – 500 nm have shown strong size-dependent growth mechanism and incubation times.
  • Detailed analysis revealed a surface-dominant diffusion at small fin sizes, which is different from a volume-dominant diffusion for the large fin width.

Contact:

Publications: S.A. Dayeh,  R. Chen, Nano Letters 2015 doi: 10.1021 (2015).

High precision and broadband tuning of nanowire lasers

Scientific Achievement: We created a technique to achieve continuous and dynamic spectral tuning of single nanowire lasers by strain engineering. This work used high hydrostatic pressure to introduce compressive strain. We achieved sub-nanometer resolution with 30 nm tuning range in single GaN nanowire lasers, leading to ~40% larger pressure coefficient for GaN nanowires than bulk GaN.

nanowire lasers(A) SEM image GaN NWs after wet etch showing straight and smooth side-wall.
(B) Schematic of GaN NWs under hydrostatic pressure applied by a diamond anvil cell.
(C) The lasing spectra of a single GaN NW at different pressures showing ~30 nm wavelength tuning with subnanometer resolution.

Significance: Nanowire lasers that could be tuned at precise wavelengths and over a wide wavelength range will enable advances in variable applications such as optical communications, sensing, signal processing, and spectroscopy analysis.


Research Details

  • High hydrostatic pressure was used to introduce compressive strain that increases the bandgap of GaN. We achieved broadband and dynamic lasing tuning with subnanometer resolution.
  •  We first observed ~40% higher pressure coefficients of these nanowires than bulk GaN.
  • The strain can also be applied by other technique such as MEMS, which can be integrated in a ultra-compact platform for on chip applications.

Contact:

Publications: S. Liu, C. Li, J. J. Figiel, S. R. J. Brueck, I. Brener, and G. T. Wang,  “Continuous and dynamic spectral tuning of single nanowire lasers with subnanometer resolution using hydrostatic pressure” Nanoscale 7, 9581 (2015).


Improving Lithium Battery Performance by Characterizing Native Processes

Scientific Achievement: Actual lithium-ion-battery operating conditions now can be replicated inside a transmission electron microscope (TEM). Compared to other liquid cells, this new platform uniquely enables nanoscale observations of lithium cycling at controlled rates.

Significance: High-capacity lithium battery electrodes can be improved by preventing dendritic lithium deposits. By understanding how these deposits form, we can reduce safety concerns and dramatically increase electrode capacity, potentially by 10x.

lithium battery

Research Details:

  • Cycled battery-relevant electrolytes in our chemically compatible, multi-electrode device.
  • Observed lithium deposit nucleation and growth.
  • Manipulated the lithium deposit structures using electrochemical and electron beam control.

Contact:

Publications: A. J. Leenheer, K. L. Jungjohann, K. R. Zavadil, J. P. Sullivan, and C. T. Harris, ACS Nano  9, 4379 (2015).