Nanomesh
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The nanomesh is an
inorganic An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemistry''. Inor ...
nanostructured two-dimensional material, similar to
graphene Graphene () is a carbon allotrope consisting of a Single-layer materials, single layer of atoms arranged in a hexagonal lattice, honeycomb planar nanostructure. The name "graphene" is derived from "graphite" and the suffix -ene, indicating ...
. It was discovered in 2003 at the
University of Zurich The University of Zurich (UZH, ) is a public university, public research university in Zurich, Switzerland. It is the largest university in Switzerland, with its 28,000 enrolled students. It was founded in 1833 from the existing colleges of the ...
, Switzerland. It consists of a single layer of
boron Boron is a chemical element; it has symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the boron group it has three ...
(B) and
nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...
(N) atoms, which forms by
self-assembly Self-assembly is a process in which a disordered system of pre-existing components forms an organized structure or pattern as a consequence of specific, local interactions among the components themselves, without external direction. When the ...
into a highly regular mesh after high-temperature exposure of a clean
rhodium Rhodium is a chemical element; it has symbol Rh and atomic number 45. It is a very rare, silvery-white, hard, corrosion-resistant transition metal. It is a noble metal and a member of the platinum group. It has only one naturally occurring isot ...
or
ruthenium Ruthenium is a chemical element; it has symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is unreactive to most chem ...
surface to
borazine Borazine, also known as borazole, inorganic benzene, is an inorganic compound with the chemical formula B3H6N3. In this cyclic compound, the three BH units and three NH units alternate. The compound is isoelectronic and isostructural with benz ...
under
ultra-high vacuum Ultra-high vacuum (often spelled ultrahigh in American English, UHV) is the vacuum regime characterised by pressures lower than about . UHV conditions are created by pumping the gas out of a UHV chamber. At these low pressures the mean free path of ...
. The nanomesh looks like an assembly of hexagonal poresIn the literature different words referring to similar concepts can be found. Below is a summary of them: * ''Pores, apertures, holes:'' areas of the nanomesh laying the closest to the underlying substrate due to a strong attraction. They form depressions, which are 0.05 nm deep and have a hexagonal shape. * ''Wires:'' areas of the nanomesh referring to the border of the pores, which lay the farer away to the underlying substrate and therefore represent the upper part of the nanomesh. (see right image) at the
nanometer 330px, Different lengths as in respect to the Molecule">molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm), or nanometer (American spelling Despite the va ...
(nm) scale. The distance between two pore centers is only 3.2 nm, whereas each pore has a diameter of about 2 nm and is 0.05 nm deep. The lowest regions bind strongly to the underlying metal, while the wires (highest regions) are only bound to the surface through strong cohesive forces within the layer itself. The
boron nitride Boron nitride is a thermally and chemically resistant refractory compound of boron and nitrogen with the chemical formula B N. It exists in various crystalline forms that are isoelectronic to a similarly structured carbon lattice. The hexago ...
nanomesh is not only stable under vacuum, air and some liquids, but also up to temperatures of 796 °C (1070 K). In addition it shows the extraordinary ability to trap
molecules A molecule is a group of two or more atoms that are held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemistry ...
and metallic
clusters may refer to: Science and technology Astronomy * Cluster (spacecraft), constellation of four European Space Agency spacecraft * Cluster II (spacecraft), a European Space Agency mission to study the magnetosphere * Asteroid cluster, a small ...
, which have similar sizes to the nanomesh pores, forming a well-ordered array. These characteristics may provide applications of the material in areas like,
surface functionalisation Surface modification is the act of modifying the surface of a material by bringing physical, chemical or biological characteristics different from the ones originally found on the surface of a material. This modification is usually made to solid ma ...
,
spintronics Spintronics (a portmanteau meaning spin transport electronics), also known as spin electronics, is the study of the intrinsic spin of the electron and its associated magnetic moment, in addition to its fundamental electronic charge, in solid-st ...
,
quantum computing A quantum computer is a computer that exploits quantum mechanical phenomena. On small scales, physical matter exhibits properties of wave-particle duality, both particles and waves, and quantum computing takes advantage of this behavior using s ...
and data storage media like
hard drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating hard disk drive platter, pla ...
s.


Structure

h-BN nanomesh is a single sheet of
hexagonal boron nitride Boron nitride is a thermally and chemically resistant refractory compound of boron and nitrogen with the chemical formula B N. It exists in various crystalline forms that are isoelectronic to a similarly structured carbon lattice. The hexago ...
, which forms on substrates like
rhodium Rhodium is a chemical element; it has symbol Rh and atomic number 45. It is a very rare, silvery-white, hard, corrosion-resistant transition metal. It is a noble metal and a member of the platinum group. It has only one naturally occurring isot ...
Rh (111) or
ruthenium Ruthenium is a chemical element; it has symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is unreactive to most chem ...
Ru (0001)
crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...
s by a
self-assembly Self-assembly is a process in which a disordered system of pre-existing components forms an organized structure or pattern as a consequence of specific, local interactions among the components themselves, without external direction. When the ...
process. The
unit cell In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector In mathematics, a unit vector i ...
of the h-BN nanomesh consists of 13x13 BN or 12x12 Rh atoms with a
lattice constant A lattice constant or lattice parameter is one of the physical dimensions and angles that determine the geometry of the unit cells in a crystal lattice, and is proportional to the distance between atoms in the crystal. A simple cubic crystal has ...
of 3.2 nm. In a cross-section it means that 13 boron or nitrogen atoms are sitting on 12 rhodium atoms. This implies a modification of the relative positions of each BN towards the substrate atoms within a unit cell, where some bonds are more attractive or repulsive than other (site selective bonding), what induces the corrugation of the nanomesh (see right image with pores and wires). The nanomesh corrugation amplitude of 0.05 nm causes a strong effect on the
electronic structure Quantum chemistry, also called molecular quantum mechanics, is a branch of physical chemistry focused on the application of quantum mechanics to chemical systems, particularly towards the quantum-mechanical calculation of electronic contributions ...
, where two distinct BN regions are observed. They are easily recognized in the lower right image, which is a
scanning tunneling microscopy A scanning tunneling microscope (STM) is a type of scanning probe 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 ...
(STM) measurement, as well as in the lower left image representing a theoretical calculation of the same area. A strongly bounded region assigned to the pores is visible in blue in the left image below (center of bright rings in the right image) and a weakly bound region assigned to the wires appears yellow-red in the left image below (area in-between rings in the right image). See for more details.


Properties

The nanomesh is stable under a wide range of environments like air, water and
electrolyte An electrolyte is a substance that conducts electricity through the movement of ions, but not through the movement of electrons. This includes most soluble Salt (chemistry), salts, acids, and Base (chemistry), bases, dissolved in a polar solven ...
s among others. It is also temperature resistant since it does not decompose in temperatures up to 1275K under a vacuum. In addition to these exceptional stabilities, the nanomesh shows the extraordinary ability to act as a scaffold for metallic nano
clusters may refer to: Science and technology Astronomy * Cluster (spacecraft), constellation of four European Space Agency spacecraft * Cluster II (spacecraft), a European Space Agency mission to study the magnetosphere * Asteroid cluster, a small ...
and to trap
molecule A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...
s forming a well-ordered array. In the case of
gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...
(Au), its evaporation on the nanomesh leads to formation of well-defined round Au nanoparticles, which are centered at the nanomesh pores. The STM figure on the right shows Naphthalocyanine (Nc) molecules, which were vapor-deposited onto the nanomesh. These planar molecules have a diameter of about 2 nm, whose size is comparable to that of the nanomesh pores (see upper inset). It is spectacularly visible how the molecules form a well-ordered array with the periodicity of the nanomesh (3.22 nm). The lower inset shows a region of this substrate with higher resolution, where individual molecules are trapped inside the pores. In addition, the molecules seem to keep their native conformation, what means that their functionality is kept, which is nowadays a challenge in
nanoscience Nanotechnology is the manipulation of matter with at least one dimension sized from 1 to 100 nanometers (nm). At this scale, commonly known as the nanoscale, surface area and quantum mechanical effects become important in describing propertie ...
. Such systems with wide spacing between individual molecules/clusters and negligible
intermolecular interactions An intermolecular force (IMF; also secondary force) is the force that mediates interaction between molecules, including the electromagnetic forces of attraction or repulsion which act between atoms and other types of neighbouring particles (e.g. ...
might be interesting for applications such as
molecular electronics Molecular electronics is the study and application of molecular building blocks for the fabrication of electronic components. It is an interdisciplinary area that spans physics, chemistry, and materials science. It provides a potential means to ...
and memory elements, in
photochemistry Photochemistry is the branch of chemistry concerned with the chemical effects of light. Generally, this term is used to describe a chemical reaction caused by absorption of ultraviolet (wavelength from 100 to 400 Nanometre, nm), visible ligh ...
or in optical devices. See for more detailed information.


Preparation and analysis

Well-ordered nanomeshes are grown by
thermal decomposition Thermal decomposition, or thermolysis, is a chemical decomposition of a substance caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic ...
of
borazine Borazine, also known as borazole, inorganic benzene, is an inorganic compound with the chemical formula B3H6N3. In this cyclic compound, the three BH units and three NH units alternate. The compound is isoelectronic and isostructural with benz ...
(HBNH)3, a colorless substance that is liquid at room temperature. The nanomesh results after exposing the atomically clean Rh (111) or Ru (0001) surface to borazine by
chemical vapor deposition Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high-quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films. In typical CVD, the wafer (electro ...
(CVD). The substrate is kept at a temperature of 796 °C (1070 K) when borazine is introduced in the vacuum chamber at a dose of about 40 L (1 Langmuir = 10−6
torr The torr (symbol: Torr) is a Pressure#Units, unit of pressure based on an absolute scale, defined as exactly of a standard atmosphere (unit), atmosphere (101325 Pa). Thus one torr is exactly (≈ ). Historically, one torr was intended to be ...
sec). A typical borazine vapor pressure inside the ultrahigh vacuum chamber during the exposure is 3x10−7
mbar The bar is a metric unit of pressure defined as 100,000  Pa (100 kPa), though not part of the International System of Units (SI). A pressure of 1 bar is slightly less than the current average atmospheric pressure on Earth at sea ...
. After cooling down to room temperature, the regular mesh structure is observed using different experimental techniques.
Scanning tunneling microscopy A scanning tunneling microscope (STM) is a type of scanning probe 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 ...
(STM) gives a direct look on the local real space structure of the nanomesh, while
low energy electron diffraction Low-energy electron diffraction (LEED) is a technique for the determination of the surface structure of single-crystalline materials by bombardment with a collimated beam of low-energy electrons (30–200 eV) and observation of diffracted el ...
(LEED) gives information about the surface structures ordered over the whole sample.
Ultraviolet photoelectron spectroscopy Ultraviolet photoelectron spectroscopy (UPS) refers to the measurement of kinetic energy spectra of photoelectrons emitted by molecules that have absorbed ultraviolet photons, in order to determine molecular orbital energies in the valence regio ...
(UPS) gives information about the electronic states in the outermost atomic layers of a sample, i.e. electronic information of the top substrate layers and the nanomesh.


See also


Other forms

CVD of
borazine Borazine, also known as borazole, inorganic benzene, is an inorganic compound with the chemical formula B3H6N3. In this cyclic compound, the three BH units and three NH units alternate. The compound is isoelectronic and isostructural with benz ...
on other substrates has not led so far to the formation of a corrugated nanomesh. A flat BN layer is observed on
nickel Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...
and
palladium Palladium is a chemical element; it has symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1802 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas (formally 2 Pallas), ...
, whereas stripped structures appear on
molybdenum Molybdenum is a chemical element; it has Symbol (chemistry), symbol Mo (from Neo-Latin ''molybdaenum'') and atomic number 42. The name derived from Ancient Greek ', meaning lead, since its ores were confused with lead ores. Molybdenum minerals hav ...
instead.


References and notes

{{Reflist


Other links

http://www.nanomesh.ch http://www.nanomesh.org Two-dimensional nanomaterials Self-organization Thin films Nitrides Boron compounds III-V compounds Transition metals NASA spin-off technologies