Research & News

Recent Publications!!

     Improved Charge Extraction Beyond Diffusion Length by Layer‐by‐Layer Multistacking Intercalation of Graphene Layers inside Quantum Dots Films
    Wenjun Chen, Wenjun Chen  Joshua Castro  Seungbae Ahn  Xiaochen Li  Oscar Vazquez‐Mena
     Advanced Materials, 2019, 31 , pp  1807894 (Link)            

     Integration of Nanomaterials into Three-Dimensional Vertical Architectures
    Jiaying Wang, Stefan Wagner, Wenjun Chen, Yuesong Shi, Abdoulaye Ndao, Leon Li, Boubacar Kante, Donald Sirbuly , Max C. Lemme , and Oscar Vazquez-Mena
     ACS Appl. Mater. Interfaces, 2018, 10 (34), pp 28262–28268  (Link)    

    Implementation of Metallic Vertical Interconnect Access in Hybrid Intercalated Graphene/Quantum Dot Photodetector for Improved Charge Collection
    Wenjun Chen, Seungbae Ahn, Carlos Rangel, Oscar Vazquez-Mena
     Frontiers in Materials, Accepted     


News

-Wenjun Chen and Jiaying have passed their Senate exams, becoming now Ph.D. candidates
-Prof. Oscar Vazquez received the prestigious DARPA-Young Faculty Award to work on acoustic metamaterials for non-invasive brain interfaces
-Prof. Oscar Vazquez received a seed funding from the UCSD Center for Brain Activity Mapping
-We have been granted an NSF grant to work on hybrid graphene/quantum dot photodetectors
-Congratulations to Jiaying for publishing his paper on 3D assambling of nanostructures and thin films: "Integration of Nanomaterials into Three-Dimensional Vertical Architectures" in ACS Applied materials (Link)


Our research group focuses on the integration and application of 2-D materials like graphene and other nanoscale structures for applications in optoelectronics, biosensing, biology and 3-D architectures. Our expertise covers the fields of two-dimensional (2-D) atomic materials, nanofabrication, photovoltaics and biosensing. Our research aims to develop hybrid metamaterials, 2-D materials and 3-D architectures integrating different nanomaterials with novel functionalities and capabilities for applications in optoelectronics, light harvesting, biosensing, bioengineering and biomedical devices.



Acoustic Metamaterials

Acoustic metamaterials have shown extraordinary capabilities such as artificial negative density and negative modulus, subwavelength imaging resolution with hyperbolic materials, and acoustic cloaks among other applications. One of the challenges in this field is to develop more capabilities for metamaterials above the 1 MHz range. One of the challenges is that the metamaterials operating at this frequency require unit cells arranged in 3-D with dimensions well below the resonance wavelength. This implies length scales in the order of 100 microns for 1 MHz. In our lab we are using the large toolbox of semiconductor technology to push the operation of acoustic metamaterials well above the 1 MHz range.  
  


2D Materials
The discovery of graphene, a single atomic layer of graphite, is one of the most remarkable achievement in material science and physics in the modern world. It is the thinest material being only one-atom thick, it has the strongest tensile modulus of 130 GPa (steel is 0.5 GPa), and it has the highest electron mobility (200000 cm2/Vs). In addition, atomic layered semiconductors like MoS2 ans insulators like h-BN are adding to the library of 2D materials. Integrating 2D materials with other nanostructures would be the key to developing new types of ultrathin materials with unprecedented low power consumption and ultra-fast operation.  



Quantum Dots
QDs have size modulated direct band gaps that enable strong light absorption and photocarrier generation. The band gap modulation is a direct consequence of quantum confinement as the quantum dot size is comparable with hole-electron size binding. They can be used both as light absorbers for photodetection or solar cells, as well as for light emitting diodes with controlled over abosrption and emission spectrum. They are also handled in solution allowing low-temperature processing. Integrating quantum dots with other nanomaterials can maximize their potential and applications in a variety of fields. (Image: Sigma-Aldrich)


3D Nanostructuring
Nanopatterning methods have for long time limited to surface patterning approaches. Therefore, most devices based on nanotechnology are limited to surface and the interaction between components is limited to an interface. This a striking difference with biological systems, in which tissued, cells and proteins have full volume designed components that can achieve a vast range of functionalities. In recent years, semicondutor industry has started looking into 3D nano-architectures aiming to improve performance and storage capacity. The latest generation of flash memories are based on vertical stacking that easily outperforms 2D designs. In our group we aim to build nanoscale material with vertical ordering incorporating nanomaterials and nanostructures.  


Photovoltaics and Optoelectronics
Graphene has a high-mobility for both electrons and holes and its electron Fermi level can be tuned. As opposed to conventional materials with fixed band gap and energy levels, the Fermi level in graphene can be tuned. We have used this property to realize a tunable solar cell that allows us to tune the potential barrier and therefore optimize the photovoltaic output of the device using a gate voltage.



Nanobiosensing by Plasmonic Nanoparticles
Nanostructures have very high surface-to-volume ratio, making them perfect candidates to sensing as their properties and behavior is very susceptible to their environment. One of such properties is the plasmon resonance of metallic nanoparticles. The strong enhanced electric field at metallic nanoparticles is highly dependent on the dielectric surrounding. When biomolecules adsorb on the metallic nano particles, the plasmon resonance shifts indicating a binding event. The metallic nano particles can be functionalized to detect specific species.


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