Miroslav Penchev

Synthesis of a Pillared Graphene Nanostructure: A Counterpart of Three-Dimensional Carbon Architectures

Graphene is a single sheet of carbon atoms with outstanding electrical and physical properties and is being exploited for applications in electronics, sensors, photovoltaics, and energy storage. A novel 3D architecture called a pillared graphene nanostructure (PGN) is a combination of two allotropes of carbon, including graphene and carbon nanotubes. A one-step chemical vapor deposition process for large-area PGN fabrication via a combination of surface catalysis and in situ vapor-liquid-solid mechanisms is described. A process by which PGN layers can be transferred onto arbitrary substrates while keeping the 3D architecture intact is also described. Single and multilayer stacked PGNs are envisioned for future ultralarge and tunable surface-area applications in hydrogen storage and supercapacitors.

Heterogeneous Graphene Nanostructures: ZnO Nanostructures Grown on Large‐Area Graphene Layers

In this work, the synthesis and characterization of three-dimensional hetergeneous graphene nanostructures (HGN) comprising continuous large-area graphene layers and ZnO nanostructures, fabricated via chemical vapor deposition, are reported. Characterization of large-area HGN demonstrates that it consists of 1-5 layers of graphene, and exhibits high optical transmittance and enhanced electrical conductivity. Electron microscopy investigation of the three-dimensional heterostructures shows that the morphology of ZnO nanostructures is highly dependent on the growth temperature. It is observed that ordered crystalline ZnO nanostructures are preferably grown along the <0001> direction. Ultraviolet spectroscopy and photoluminescence spectroscopy indicates that the CVD-grown HGN layers has excellent optical properties. A combination of electrical and optical properties of graphene and ZnO building blocks in ZnO-based HGN provides unique characteristics for opportunities in future optoelectronic devices.

Molecular absorption and photodesorption in pristine and functionalized large-area graphene layers

We studied the photodesorption behavior of pristine and nitric acid (HNO(3)) treated graphene layers fabricated by chemical vapor deposition (CVD). The decrease in electrical conductivity and a negative shift of the Dirac point in graphene layers illuminated with ultraviolet light are caused by molecular photodesorption, while the UV illumination does not degrade the carrier mobility of graphene layers. When graphene layers were treated with concentrated HNO(3), the photodesorption-induced current decrease became less significant than for pristine graphene layers. We suggest this is due to the passivation of oxygen-bearing functionalities to CVD grown graphene structural defects by HNO(3) functionalization, which prevents the further absorption of gas molecules. Our results provide a new strategy for stabilizing the electrical performance of CVD grown large-area graphene layers for applications ranging from nanoelectronics to optoelectronics.

Data transmission performance of CVD grown sub-20 nm indium antimonide nanowires

We investigated the data transmission performance of indium antimonide (InSb) nanowires (NWs) synthesized on InSb (100) substrate using chemical vapor deposition (CVD) having diameters below 20 nm. The data transmission measurement was accomplished over the NW field effect transistors (NWFETs) fabricated on Si/SiO2 substrates. Digital data stream is randomly generated and then uploaded to a waveform generator which generates the stream and transmits it repeatedly with the desired frequency. The signal was applied on the sources of the NWFETs and collected from the drains of the same devices. Collected data was first filtered with a low pass filter (LPF), and then the output of the filter was used to create the eye diagrams of the NWs. Bit error rate (BERs), attenuation , quality factor (Q-factor) and maximum data transmission are extracted from eye diagrams. The results indicate that the data transmission performance of NWs suffer from low mobility values on the order of 10-to-15 cm2V-1s-1 because of their small diameters, crystal defects and oxidation occurs during growth and cooling. 20 nm NWs can sustain data rates up to 10 mega bits per second (Mbps) and the data rate is directly proportional to the diameter of the NWs.

InSb nanowire based field effect transistor

InSb nanowire field effect transistors (NWFET) were fabricated using electrochemically synthesized nanowires. To accurately extract transistor parameters, we introduced a model which takes into account the often ignored ungated nanowire segments. A significant improvement in extracted device parameters was observed which demonstrated that conventional models tend to underestimate the gate effect and therefore lead to lower carrier mobilities. Based on the model, we obtained a NWFET ON current of 11.8uA, an ION/IOFF ratio of 63.5 and hole mobility of 292.84 cm2V-1s-1.

Size Dependent Thermal Activation Study of Single InSb Nanowire Devices for High Speed and Low Power Digital Logic Applications

InSb nanowire devices at different diameter range from 30 nm-200 nm using electrochemical deposition technique is demonstrated. Electrical properties of nanowires is investigated at different diameters for beyond CMOS applications with high speed and low power characteristics. In particular, InSb nanowire based FET devices is fabricated on Si substrate and presented.