The single-molecule electric motor is an electrically operated synthetic molecular motor made from a single butyl methyl sulphide molecule. [1] The molecule is adsorbed onto a copper (111) single-crystal piece by chemisorption. [1] The motor, the world's smallest electric motor, [2] is just a nanometer (billionth of a meter) across [3] (60 000 times smaller than the thickness of a human hair). It was developed by the Sykes group and scientists at the Tufts University School of Arts and Sciences and published online September 4, 2011. [4]
Single-molecule motors have been demonstrated before. These motors were either powered by chemical reactions [5] or by light. [6] This is the first experimental demonstration of electrical energy successfully coupling to directed molecular rotation. [3] [7]
Butyl methyl sulfide is an asymmetrical thioether which is achiral in the gas phase. The molecule can be adsorbed to the surface through either of the sulfur's two lone pair. This gives rise to the surface bound chirality of the molecule. [8] The asymmetry of the molecular surface interface gives rise to an asymmetrical barrier to rotation. [9] The molecule rotates around this sulfur-copper bond. Electrons quantum tunneling from the STM tip electrically excite molecular vibrations, which couple to rotational modes. [7] The rotation of the motor can be controlled by adjusting the electron flux from the scanning tunneling microscope and the background temperature. [1] The tip of the scanning electron microscope acts as an electrode. The chiralities of the tip of the STM and the molecule determine the rate and direction of rotation. [1] Images taken of the molecule at 5 K and under non-perturbative scanning conditions show a crescent-shaped protrusion of the molecule. [10] When the temperature is raised to 8 K, the molecule starts rotating along six orientations determined by the hexagonal structure of the copper it is adsorbed on. In this case, a STM image taken of the molecule appears as a hexagon as the timescale of the imaging is much slower than the rotation rate of the molecule. [10]
The six states of rotation of the molecule can be determined by aligning the tip of the scanning electron microscope asymmetrically on the side of one of the lobes of the molecule during spectroscopy measurements. When the butyl tail is nearest to the tip of the microscope, the tunneling current would be maximum and vice versa. The position of the molecule on the surface can be determined by the tunneling current. By plotting the position versus time the rate and direction of rotation can be determined. [10] At higher temperatures, the single-molecule motor rotates too fast (up to one million rotations per second at 100 K) to monitor. [2]
The single-molecule electric motor can be efficiently used in engineering, [2] nanotechnological applications and medicinal applications, [3] where drugs could be delivered to specified locations more accurately. [3] By altering the chemical structure of the molecule, it could become a component of a nanoelectromechanical system (NEMS). It also has potential to be utilized to generate microwave radiation. [3]
A microscope is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisible to the eye unless aided by a microscope.
A scanning tunneling microscope (STM) is a type of microscope used for imaging surfaces at the atomic level. Its development in 1981 earned its inventors, Gerd Binnig and Heinrich Rohrer, then at IBM Zürich, the Nobel Prize in Physics in 1986. STM senses the surface by using an extremely sharp conducting tip that can distinguish features smaller than 0.1 nm with a 0.01 nm (10 pm) depth resolution. This means that individual atoms can routinely be imaged and manipulated. Most scanning tunneling microscopes are built for use in ultra-high vacuum at temperatures approaching absolute zero, but variants exist for studies in air, water and other environments, and for temperatures over 1000 °C.
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Scanning tunneling spectroscopy (STS), an extension of scanning tunneling microscopy (STM), is used to provide information about the density of electrons in a sample as a function of their energy.
The nanocar is a molecule designed in 2005 at Rice University by a group headed by Professor James Tour. Despite the name, the original nanocar does not contain a molecular motor, hence, it is not really a car. Rather, it was designed to answer the question of how fullerenes move about on metal surfaces; specifically, whether they roll or slide.
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Asymmetric induction describes the preferential formation in a chemical reaction of one enantiomer or diastereoisomer over the other as a result of the influence of a chiral feature present in the substrate, reagent, catalyst or environment. Asymmetric induction is a key element in asymmetric synthesis.
A two-dimensional gas is a collection of objects constrained to move in a planar or other two-dimensional space in a gaseous state. The objects can be: classical ideal gas elements such as rigid disks undergoing elastic collisions; elementary particles, or any ensemble of individual objects in physics which obeys laws of motion without binding interactions. The concept of a two-dimensional gas is used either because:
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Nanometrology is a subfield of metrology, concerned with the science of measurement at the nanoscale level. Nanometrology has a crucial role in order to produce nanomaterials and devices with a high degree of accuracy and reliability in nanomanufacturing.
Inelastic electron tunneling spectroscopy (IETS) is an experimental tool for studying the vibrations of molecular adsorbates on metal oxides. It yields vibrational spectra of the adsorbates with high resolution (< 0.5 meV) and high sensitivity (< 1013 molecules are required to provide a spectrum). An additional advantage is the fact that optically forbidden transitions may be observed as well. Within IETS, an oxide layer with molecules adsorbed on it is put between two metal plates. A bias voltage is applied between the two contacts. An energy diagram of the metal-oxide-metal device under bias is shown in the top figure. The metal contacts are characterized by a constant density of states, filled up to the Fermi energy. The metals are assumed to be equal. The adsorbates are situated on the oxide material. They are represented by a single bridge electronic level, which is the upper dashed line. If the insulator is thin enough, there is a finite probability that the incident electron tunnels through the barrier. Since the energy of the electron is not changed by this process, it is an elastic process. This is shown in the left figure.
Molecular scale electronics, also called single-molecule electronics, is a branch of nanotechnology that uses single molecules, or nanoscale collections of single molecules, as electronic components. Because single molecules constitute the smallest stable structures imaginable, this miniaturization is the ultimate goal for shrinking electrical circuits.
Gopakumar Thiruvancheril is an Indian Assistant Professor of molecular electronics from Indian Institutes of Technology. He is an author of certain peer-reviewed articles two of which, as of 2013, were cited over 60 times and appeared in such journals Journal of Physical Chemistry B and C, including others. He completed his Ph.D. in Physics at TU Chemnitz.
Bernard Lucas Feringa is a Dutch synthetic organic chemist, specializing in molecular nanotechnology and homogeneous catalysis. He is the Jacobus van 't Hoff Distinguished Professor of Molecular Sciences, at the Stratingh Institute for Chemistry, University of Groningen, Netherlands, and an Academy Professor of the Royal Netherlands Academy of Arts and Sciences. He was awarded the 2016 Nobel Prize in Chemistry, together with Sir J. Fraser Stoddart and Jean-Pierre Sauvage, "for the design and synthesis of molecular machines".
Maki Kawai is a Japanese chemist who developed spatially selective single-molecule spectroscopy. In 2018, she became the first woman to become president of the Chemical Society of Japan.
