Graphene is a very interesting nanomaterial with potential for applications in many different fields including nanoelectronics. However, the properties of graphene can vary broadly and depend sensitively on its integration in device structures and the details of its interaction with other materials, such as underlying substrates or gate dielectrics. Unlike other semiconductor electronic devices, where the active layer is buried below the surface and where microscopic details of transport cannot be directly examined, graphene is exposed at a surface and can be directly examined on the atomic scale using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). New work now provides microscopic details of graphene interaction with a substrate in the most common device structure used so far.
Ranging from electronic gadgets to medical applications, many nanomaterial-based devices have appeared in the market. One of the most important issues for these devices is their reliability and life-time of operation. A vital factor behind these issues is the structural stability of the nano-device - debonding of the nanomaterial from the substrate material being the single largest contribution for device degradation. In order to improve bonding between nanomaterials and their substrate, it is essential to understand and quantify the bonding mechanisms. A new nano-scratch technique developed by researchers in the U.S. could serve as the basis for a reliable quantification technique for interpreting nanomaterial-substrate bond strength.
In atomic force microscopy (AFM), tip quality depends mainly on the dimensions and shape of the probe, the durability of the tip apex, and the nature of the interaction between sample and probe. With this in mind, researchers have experimented with mounting ultra sharp and high aspect ratio carbon nanotube (CNT) bundles onto the apex of an AFM tip to improve spatial and potential resolution. Although AFM tips functionalized with a carbon nanotube have attracted considerable attention, attaching CNTs to scanning probes is not a trivial matter, which limits their practical use. An alternative approach, whereby a CNT is grown onto the AFM tip, also can be very time-consuming and requires a costly set-up. A team at the Friedrich-Schiller-University Jena in Germany has now demonstrated a fast and cheap process for the fabrication of carbon nanotube AFM tips with the help of microwave ovens.
Plastic solar cells are emerging as alternative energy sources for the future because of their potential for cheap roll-to-roll printing, ease of processing, light-weight and flexibility. However, their current performance is still low for practical applications which partially originate from the poor understanding of device physics and nanoscale morphology of the photoactive layer. Photoconductive atomic force microscopy (pcAFM)is a powerful characterization tool to better understand the complex optoelectronic and morphological phenomena of organic solar cells at the nanoscale. This article briefly described the applicability of the pcAFM technique for analyzing solution-processed, polymer and small molecule bulk heterojunction solar cells. Due to the nature of charge generation, transport and collection occurring at the nanometer scale, the useful information on device operation can be lost from macroscopic measurements.
An intriguing novel approach to extract the energy from the photosynthetic conversion process has been demonstrated by researchers at Stanford and Yonsei Universities. They have inserted ultrasharp gold nanoelectrodes into living algae cells and extracted electrons, thereby harnessing an - albeit very tiny - electrical current. This is electricity production that doesn't release carbon into the atmosphere. The results demonstrate the feasibility of collecting high-energy electrons in steps of the photosynthetic electron transport chain and prior to the downstream processes associated with energy loss. In addition, the system allows direct monitoring of specific charge transfer reactions in live cells, leading to broad applications for investigating developmental processes and the responses of cells and organelles to light and chemical stimuli.
Most of the material properties investigated by atomic force microscopy are acquired by processing the deflection signal of the cantilever, which is applied to Electrostatic Force Microscopy (EFM) measurements as well. For EFM, the sample surface properties would be electrical properties and the interaction force will be the electrostatic force between the biased tip and the sample. Electrostatic Force Microscopy maps electric properties on a sample surface by measuring the electrostatic force between the surface and a biased AFM cantilever. EFM applies a voltage between the tip and the sample while the cantilever hovers above the surface, not touching it. The cantilever deflects when it scans over static charges.
Imaging soft biological samples in liquid with Atomic Force Microscope has long stood as a very challenging task. Until recently, most of the works in this field has been carried out in tapping mode AFM, during which the cantilever driven by a piezoelectric actuator vibrates in the vicinity of the cantilever's resonance frequency, and briefly touches the sample surface at the bottom of each vibration cycle, resulting in a decrease of its oscillation amplitude. By keeping such amplitude at a preset value using feedback control, a topographic image of the sample surface is obtained. However, stable, high-resolution imaging of very fragile and sensitive biological samples such as live cells or individual proteins is not trivial in tapping mode due to potential sample distortion or even damage during the brief contact between the AFM tip and sample surface at the end of each oscillation cycle. The XE-series AFM with Crosstalk Elimination and high force Z-scanner has successfully solved these problems.
Solar cells, or photovoltaic cells, are used to convert sunlight into electrical power. As traditional power sources grow scarce, other forms of producing electrical power are gaining firm footing in the power supply mix. Solar cells are already widely used in a variety of applications - from spacecraft, to small portable devices, to farm installations, to roadway signs. As energy prices increase, public demand for solar power has surged. In order to meet the longevity, yield, and price requirements of consumers and industry, public and private sector research has increased dramatically. While traditional tools are helpful to investigate and improve solar cells, AFM/SPM offers metrology, topography and roughness analysis at much higher resolution than with optical techniques.