Doping, the process of adding impurity atoms to semiconductors to provide free carriers for conduction, has been pivotal to microelectronics since its early stages. In particular doping germanium at high concentrations to make it highly conductive is the subject of intense research, because it lies at the heart of novel developments in integrated silicon-compatible lasers and quantum information processing devices. Researchers have now demonstrated a method to densely pack dopant molecules on the germanium surface, which then self-organize to form molecular patterns with one phosphorus dopant atom every two germanium atoms. The key finding is that when you deposit phosphine molecules on a germanium surface, they naturally form molecular patterns with one phosphorus atom every two germanium atoms that densely pack the surface.
Researchers have demonstrated that electrons in nanoscale networks can behave like car drivers in congested cities. Traffic planners are sometimes faced with a rather counter-intuitive observation - adding a new road to a congested road network can lead to a deterioration of the overall traffic situation, i.e. longer trip times for individual road users. Or, in reverse, blocking certain streets in a complex road network can counter-intuitively reduce congestion. This has become known as the Braess paradox. Researchers have now applied the concept of the Braess paradox to the quantum world. By combining quantum simulations of a model system and scanning-probe experiments, they have shown that an analogue of the Braess paradox can occur in mesoscopic semiconductor networks, where electron transport is governed by quantum mechanics. The paradox manifests itself by an increase of the conductance network when one arm in the network is partially blocked in a controlled manner.
In nanomedicine, nanoparticles are used as vehicles for efficiently delivering therapeutic nucleic acids, such as disease-fighting genes and small interfering RNA (siRNA) molecules, into cells. But getting nanomedicines to their target sites inside cells is not the only challenge. It also is necessary to assess the intracellular processing of nanomedicines and the efficacy of their payload delivery - a task that is not exactly trivial given the complexity and dynamics of the mechanisms of endocytosis and intracellular trafficking. Researchers are therefore trying to develop robust and reliable tools to characterize and evaluate the intracellular processing of administered nanomedicines. As part of this effort, scientists have now introduced a quantitative approach to study live-cell endosomal colocalization dynamics of nanomedicines for gene delivery, based on single-particle tracking and trajectory-correlation.
Uncertainty evaluation is an often overlooked factor in many AFM material property measurement work - nevertheless it is critical for obtaining truly quantitative measurements. The atomic force microscope is used extensively for measuring the material properties of nanomaterials with nanometer resolution, unfortunately there is a lack of standards and uncertainty quantification in these measurements. Other fields, such as six sigma standards in industry and beam corrections in scanning electron microscopy, have developed thorough methods for quantifying the uncertainty in a given measurement, model, or system. Broadly speaking these methods can be classified as uncertainty quantification. Without applying the methods of uncertainty quantification to AFM measurements it is impossible to say if the measurements are accurate within 5% or 100%.
Fruit flies (Drosophila melanogaster) are the workhorses in countless biomedical research laboratories around the world. The bioimaging of live specimens, ideally through all the stages of the fruit fly life cycle, is a tricky and often complicated undertaking. Researchers in India have now developed a relatively simple way to introduce fluorescent nanomaterials into fruit flies: They prepared carbon nanoparticles from wood waste and added them to the flies' food supply. The fluorescent fruit flies showed no toxic effects - upon withdrawal of the nanoparticles from their food, they excreted the fluorescing material and continued to proliferate to the next generation, demonstrating a return to their normal lives.
The atomic structures of nanoscale contacts are not available in most experiments on quantum transport. Scanning tunneling microscopy operates at a tip-sample distance of a few angstroms and relies on probing a conductive surface in the evanescent tail of electronic states. By decreasing the tip-sample distance the sensitivity to chemical interactions can be enhanced. This has already been demonstrated in non-contact atomic force microscopy, where the oscillating tip comes for short periods of time within the range of chemical interactions. A team of scientists has now developed Quantum Point Contact Microscopy as a novel imaging mode of low-temperature STM, where instead of measuring a current through a tunneling junction, a transport current through a quantum point contact formed by a single atom between the STM tip and the surface is recorded.
Nanoindentation is derived from the classical hardness test but is carried out on a much smaller scale. It can be used to determine the hardness of thin layers as well as material properties such as elasticity, stiffness, plasticity, and tensile strength, or fracture toughness of small objects and microsystems in fields such as biotechnology. These measurements involve applying a small force to a sample using a sharp probe and measuring the resultant penetration depth. The measured value is used to calculate the contact area and hence the particular property of the sample material. Both the method of force application and the geometry of the indentation tip can be adjusted to suit the particular application.
Life as we know it is dominated by friction, the interaction between moving objects. Friction controls our everyday lives, from letting us walk to work, to holding a cup of tea. Friction forces act wherever two solids touch. Although friction has been investigated for hundreds of years - in the 15th century, Leonardo da Vinci was the first to enunciate two laws of friction - it is surprisingly difficult to examine how friction works at the nanoscale level due to the sheer difficulty of bringing nanoscale objects into contact and imaging them at the same time. Researchers have now demonstrated the ability to bring nanoscale objects together, rub them repeatedly across one another and see how friction changes nanosized materials in real time.