RESEARCH & GALLERY

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See our discussion on Nanomaterials at the 2021 “Science on Tap” Webinar

Some basic research questions that intrigue us are:

  • What role does the substrate play in 2D synthesis and properties?
  • Can advanced heterostructures be directly synthesized?
  • Are there new 2D layers that we haven’t experimentally seen yet?
  • What new functionalities arise when we combine 2D layers with 3D substrates?

Our work has focused on four basic areas:

Area 1: Graphene

Our research group has a long history in graphene, starting in 2007, when Dr. Robinson re-joined Penn State as a research faculty after his post-doctoral stint at the Naval Research Lab. We synthesize graphene via chemical exfoliation from bulk graphite, chemical vapor deposition, and silicon sublimation. The majority of our work currently focuses on epitaxial graphene (graphene grown via silicon sublimation), which is an excellent substrate for synthesis of van der Waals heterostructures. The general process for epitaxial graphene synthesis is illustrated in the figure below:

EG

Area 2: Chalcogenides

The chalcogenide family (those layered materials based on sulfur (S), selenium (Se), and tellurium (Te)) has been a major focus of the group since Dr. Robinson joined PSU-MatSE in 2012. We synthesize, characterize, and fabricate many different chalcogenides including transition-metal dichalcogenides and group-III monochalcogenides.  Such materials include Molybdenum Disulfide (MoS2), Tantalum Disulfide (TaS2), Tungsten Diselenide (WSe2), Molybdenum Ditelluride (MoTe2), Tungsten Ditelluride (WTe2), Gallium Selenide (GaSe), and Indium Selenide (InSe). The processes we use for synthesis are shown below, with our preferred route being metal-organic chemical vapor deposition.

In addition to synthesis of these novel materials, we also design and fabricate basic device structures to understand the electronic properties.  Devices we focus on include capacitors, field effect transistors, and a variety of process monitoring structures. Below if a false color scanning electron micrograph of a radio-frequency (RF) field effect transistor.

MoS2_RF-FET_Bersch_2016

Area 3: Confinement Heteroepitaxy

Confinement heteroepitaxy… or CHet, as we like to call it, began in 2014 when we accidentally discovered that you can do chemistry at the interface of graphene (epitaxial graphene) and silicon carbide. While we weren’t the first to intercalate elements at the interface, we were able to show that you can form compounds and new structures in the confined space between the graphene and SiC. This ultimately led to our discovery of 2D nitrides “beyond hBN”, the first of which was 2D-GaN.  We then identified that there are all sorts of interesting phenomena with just the metals themselves! Below is a schematic overview of how CHet is accomplished, along with a few pubs on the topic.

  • Z.Y. Al Balushi et al.,  Nature Materials (2016); doi:10.1038/nmat4742
  • Briggs et al. Nanoscale 11 (33), 15440-15447
  • Briggs et al. Nature Materials; doi.org/10.1038/s41563-020-0631-x (2020)

The success of the synthesis technique enabled us to successfully become an integrated research group (IRG) within a newly awarded MRSEC at Penn State, the Center for Nanoscale Science, where we work with an awesome group of faculty to explore all the interesting phenomena these new materials exhibit. The schematic below lays out some of the things we are focused on in the MRSEC.

Area 4: Advanced Heterostructures

Since 2013, we have focused on the synthesis of advanced heterostructures on graphene (primarily epitaxial graphene). This work has taken the form of growing monolayer and heterolayer transition metal dichalcogenides on EG to understand the nucleation and growth, as well as the transport properties. Below are some of the advanced structures we have realized.

Vertical Heterostructures

advanced heterostructures

Lateral Heterostructures

lateral-growth

 

 

 



Gallery


Characterizing our 2D materials can lead to MANY fantastic, and artistic, images. Enjoy some of our recent images below!

MRS_Bulletin_Cover_Mos2  MoS2 Fins  sample_0130_B_11_color_findedges-filter_2 TEM_falseColor2   WSe2_EG_pressrelease cropped-Lion_collage-copy2.jpg Picture3-PS   GaneshRBhimanapati_gvb5099 gase_dfimage_161206