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Photoemission spectroscopy has detected two different populations of spin-polarized electrons that are “hidden” within a layered, graphene-like material.

The layers inside certain materials can carry spin-polarized electrons, but this polarization is hidden to measurements that aren’t sufficiently localized. A new study using photoemission spectroscopy has detected the hidden spin polarization in a graphene-like material called molybdenum disulfide (MoS22). Unique to this work is the ability to target specific populations of spin-polarized electrons with circularly polarized light.

The majority of quantum dot (QD) blinking studies have used a model of switching between two distinct fluorescence intensity levels, “on” and “off”. However, a distinct intermediate intensity level has been identified in some recent reports – a so-called “grey” or “dim” state, which has brought this binary model into question. While this grey state has been proposed to result from the formation of a trion, it is still unclear under which conditions it is present in a QD. By performing shell-dependent blinking studies on CdSe QDs, we report that the populations of the grey state and the on state are strongly dependent on both the shell material and its thickness. We found that adding a ZnS shell did not result in a significant population of the grey state. Using ZnSe as the shell material resulted in a slightly higher population of the grey state, although it was still poorly resolved. However, adding a CdS shell resulted in the population of a grey state, which depended strongly on its thickness up to 5 ML. Interestingly, while the frequency of transitions to and from the grey state showed a very strong dependence on CdS shell thickness, the brightness of and the dwell time in the grey state did not. Moreover, we found that the grey state acts as an on-pathway intermediate state between on and off states, with the thickness of the shell determining the transition probability between them. We also identified two types of blinking behavior in QDs, one that showed long-lived but lower intensity on states and another that showed short-lived but brighter on states that also depended on the shell thickness. Intensity-resolved single QD fluorescence lifetime analysis was used to identify the relationship between the various exciton decay pathways and the resulting intensity levels. We used this data to propose a model in which multiple on, grey and off states exist whose equilibrium populations vary with time that give rise to the various intensity levels of single QDs, and which depends on shell composition and thickness.

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A NIMS research group led by Masahiro Goto, Distinguished Chief Researcher, Center for Green Research on Energy and Environmental Materials, and Michiko Sasaki, postdoctoral researcher, Center for Materials Research by Information Integration (currently a postdoctoral fellow at the University of Tokyo) discovered that the amount of friction force between organic molecules and a sapphire substrate in a vacuum can be changed repeatedly by starting and stopping laser light irradiation. This discovery could potentially lead to the development of technology enabling the movement of micromachines and other small driving parts to be controlled.

The performance of micromachines—used as moving components in small devices such as acceleration sensors and gyroscopes—is greatly affected by adhesion force (the attractive force between two or more materials that stick to each other). Adhesion force in a micromachine increases the friction force. Since increased friction force seriously impedes the movement of moving components, it is necessary to maintain a low level of adhesion force. In addition, if the level of friction force can be controlled, it may be feasible to control the movement of micromachines, leading to expansion of their use and enhancement of their functions. A great deal of attention was previously drawn to techniques enabling silicon-based materials, a major micromachine material, to be coated with diamond-like carbon, self-assembled monolayers, or fluorine-containing organic films in order to reduce friction force and thereby improve the movement of micromachines.

For the first time, researchers have synthesised a strange and unstable triangle-shaped molecule called triangulene, which physicists have been chasing for nearly 70 years.

Triangulene is similar to the ‘wonder material’ graphene in that it’s only one-atom-thick. But instead of sheet of carbon atoms, triangulene is made up of six hexagonal carbon molecules joined along their edges to form a triangle — an unusual arrangement that leaves two unpaired electrons unable form a stable bond. No one has ever been able to synthesise the molecule until now.

The elusive molecule was created by a team of researchers from IBM, using a needle-like microscope tip to manipulate individual atoms into the desired format.

Continue reading “Scientists Have Created a Long-Fabled Triangle-Shaped Molecule in the Lab” »

Harvard scientists have created the rarest material on earth.

3D printing is profoundly changing not just how we make things, but how we design them as well. As well as saving materials, time, water and waste, it is also opening up possibilities for new products and is set to unleash a wave of innovation in the industrial sector.

Experiments show how electrons in Mott insulators with strong spin-orbit coupling arrange themselves to make the materials magnetic at low temperatures. The work helps bring us closer to a more complete quantum theory of magnetism.

Making small graphene devices more of a reality.

Since its discovery, graphene has held great promise as a two-dimensional (2D) metal with massless carriers and, thus, extremely high-mobility that is due to the character of the band structure that results in the so-called Dirac cone for the ideal, perfectly ordered crystal structure.