Jenna L. Wardini

High-field terahertz response of graphene

We investigate the response of multi-layer epitaxial graphene and chemical vapor deposition (CVD)-grown single-layer graphene to strong terahertz (THz) fields. Contrary to theoretical predictions of strong nonlinear response, the transmitted fields exhibit no harmonic generation, indicating that the nonlinear response is limited by fast electron thermalization due to carrier-carrier scattering. The fast electron heating gives rise to large THz transmission enhancement (>15%) in single-layer CVD graphene at high THz fields (ETHz > 10kVcm 1 ). The nonlinear effects exhibit non-Drude behavior in the THz conductivity, where THz fields induce extreme non-equilibrium electron distributions.

Scalable graphene field-effect sensors for specific protein detection

We demonstrate that micron-scale graphene field-effect transistor biosensors can be fabricated in a scalable fashion from large-area chemical vapor deposition derived graphene. We electrically detect the real-time binding and unbinding of a protein biomarker, thrombin, to and from aptamer-coated graphene surfaces. Our sensors have low background noise and high transconductance, comparable to exfoliated graphene devices. The devices are reusable and have a shelf-life greater than one week.

Origins of Charge Noise in Carbon Nanotube Field-Effect Transistor Biosensors

Determining the major noise sources in nanoscale field-effect transistor (nanoFET) biosensors is critical for improving bioelectronic interfaces. We use the carbon nanotube (CNT) FET biosensor platform to examine the noise generated by substrate interactions and surface adsorbates, both of which are present in current nanoFET biosensors. The charge noise model is used as a quantitative framework to show that insulating substrates and surface adsorbates are both significant contributors to the noise floor of CNT FET biosensors. Removing substrate interactions and surface adsorbates reduces the power spectral density of background voltage fluctuations by 19-fold.

Terahertz induced transparency in single-layer graphene

We demonstrate THz-induced transparency in two types of single-layer CVD graphene samples utilizing high-field THz pulses. The nonlinear THz transmission depends on the local conductivity of the samples and dynamically varies in the time domain.

A spectrally-tunable photocurrent microscope for characterizing nanoelectronic devices

Scanning photocurrent microscopy is a unique tool that facilitates both device characterization and the study of fundamental properties of optoelectronic nanomaterials. We have built a scanning photocurrent microscope that incorporates a super continuum laser as the light source. The microscope illuminates nanoelectronic devices with a micron-scale light spot and a photon energy that is tunable from 0.67 eV to 2.7 eV. We describe the design of our microscope and present measurements of carbon nanotube transistor devices. These measurements highlight the features of our microscope, particularly the advantages of combining spatial and spectral resolution when characterizing nanoelectronic devices.

Terahertz Induced Transparency in Single-Layer Graphene

We demonstrate THz-induced transparency in two types of single-layer CVD graphene samples utilizing high-field THz pulses. The nonlinear THz transmission depends on the local conductivity of the samples and dynamically varies in the time domain.