Sunday, November 19, 2017

Photopolymerization-triggered molecular motion for flexible liquid crystal display

Photopolymerization-triggered molecular motion for flexible liquid crystal display

A represents the molecular alignment through conventional photoalignment methods. B represents the molecular alignment achieved through the currently reported scanning wave photopolymerization method. Credit: Atsushi Shishido, Tokyo Institute of Technology

With current 2D techniques, one typically irradiates a liquid crystal film that contains added photoresponsive dye molecules, with uniform polarized light. This controls the net liquid crystal alignment via the interaction of the dye dipole and the polarization axis of light. The drawback with these systems is the need for adding strong dyes, which can discolor or degrade optical and stability properties. Thus, a dye-free method is highly desired in the engineering industry.

Currently, only two approaches to dye-free methods have been explored. The first is a two-step alignment method, in which the liquid crystal materials are coated over a very thin dye-containing photoalignment layer and then aligned or fixed by polymerization. While this method has proven very successful in achieving stimuli-responsive 2D aligned liquid crystals and elastomers used in photonics, solar energy harvesting, microfluidics, and soft-robotic devices, it is expensive and time-consuming. The creation of a film with microscopic arrays of microalignment patterns requires precise and dynamic control of the polarized direction of incident light in each pixel, so this method is unsuitable for aligning patterns on the nanoscale over large areas.

The second approach to the development of a dye-free system uses surface topography to overcome the limitations of conventional photoalignment. In this method, the liquid crystals are aligned over a surface topography template through lithography, nanoimprinting, or inkjet techniques among others. While this method allows for 2D micropatterning of molecular alignment, it still requires multi-step processing, making it costly and time-consuming. Due to the surface roughness from the topographic templates, this method proves difficult in the production of thin films.

Photopolymerization-triggered molecular motion for flexible liquid crystal display
A represents a schematic illustration of the desired patterns of alignment. B represents irradiated light patterns of expanding toroid shapes, periodic dots, and the words Tokyo Tech. C represents POM images under crossed polarizers. Credit: Atsushi Shishido, Tokyo Institute of Technology

A research group led by Atsushi Shishido at Tokyo Tech has reported the development of a new method of scanning wave photopolymerization that utilizes spatial and temporal scanning of focused guided light. As the polymerization reaction proceeds, a mass flow in the film is triggered, and this results in alignment of the liquid crystals with the incident light patterns. The desired alignment is achieved through a single step by light triggered mass flow.
This new method generates arbitrary alignment patterns with fine control over larger areas in a wide variety of liquid crystal materials without the need for strong dyes or additional processing steps, something that previous methods were unable to achieve. This method has the additional advantage of unlimited complexity in 2D patterns that would, in principal, only be restricted by the  diffraction limits.
This new concept of scanning wave photopolymerization is currently limited to photopolymerizable  systems with a thickness below tens of micrometers. However, further investigation can expand material systems that could be used such as nanorods, nanocarbons, and proteins. Scanning wave photopolymerization can be readily introduced into existing photoproduction facilities, allowing for great economic advantages. The scientists at Tokyo Institute of Technology see this  as a powerful pathway for the simple creation of highly functional organic materials with arbitrary, fine molecular alignment patterns on the nanoscale over large areas.

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Monday, October 30, 2017

Structural diversity, single-crystal to single-crystal transformation and photocatalytic properties of Cu(II)-metal-organic frameworks based on 1,4-phenylenedipropionic acid


Four Cu(II)-MOFs containing 1,4-phenylenedipropionic acid have been reported.
The effect of N,N′-donor coligand is critical in the arrangement of polymeric structure.
The 3D framework of 3 is transformed to 4 upon heating in a single-crystal-to-single-crystal manner.
All compounds are photo-catalytically active for the decomposition of MB.


A series of four new copper(II) based metal-organic frameworks containing 1,4-phenylenedipropionic acid and different N,N′-donor coligands, namely, [Cu(ppa)(bpy)]n(1), {[Cu(ppa)(azp)(H2O)](H2O)}n (2), {[Cu(ppa)(tdp)(H2O)](H2O)2}n (3), and {[Cu(ppa)(tdp)](H2O)}n (4), (H2ppa = 1,4-phenylenedipropionic acid, bpy = 4,4′-bipyridine, azp = 4,4′-azobipyridine, tdp = 4,4′-thiodipyridine) have been successfully synthesized and structurally characterized by elemental analysis, IR, UV–vis, TGA, XRPD and single-crystal X-ray diffraction. Compound 1 containing a short and rigid bpy coligand displays a 2D square lattice (sql) topology while 2 and 3 which contain more flexible and longer azp and tdp coligands possess two-fold interpenetrating diamond-like (dia) 3D framework. Finally, the thermal-induced compound 4 is transformed from compound 3 by heating, through single-crystal-to-single-crystal transformation, adopting a CdSO4-like (cds) 3D framework. Additionally, the solid stated compounds 14 exhibit the energy band gaps of 3.50, 3.16, 3.53 and 3.31 eV, respectively. Thus, the photocatalytic properties of 14have been investigated. Approximately 84.9% for 1, 93.3% for 2, 82.0% for 3 and 85.4% for 4 of methylene blue were decomposed within 105 min.

Graphical abstract
Four new Cu(II)-MOFs have been synthesized in the presence of 1,4-phenylenedipropionic acid (ppa) and different N,N′-donor ancillary ligands. The structural diversity indicates that the effect of N,N′-donor ancillary ligand is critical in construction of polymeric arrangement.

Image for unlabelled figure


Sunday, October 22, 2017

Solar-Tectic LLC Develops Inexpensive Sapphire Glass with MOHS 8

In 2015 Solar-Tectic LLC ("ST") announced plans to develop sapphire glass. And recently ST announced that it has succeeded in developing this sapphire glass using its patent pending technique which was reported on in Materials Letters, a peer reviewed journal

(Solar-Tectic/ LEDinside)

The new sapphire glass technique involves the deposition of a highly transparent crystalline Al2O3 (aluminum oxide) thin-film on ordinary soda-lime glass, via a thin buffer layer, using a simple and common deposition technique (e-beam evaporation), thus achieving a breakthrough material which is much less expensive and much lighter than single crystal sapphire, and easily scalable for manufacturing and commercialization.
The sapphire film is extremely thin which is important for cost reduction in manufacturing. In recent years Apple Inc. and others have tried without success in making cost effective sapphire glass for smartphone covers.
In addition to anti-scratch, ceramic glass products are an important part of ST solar technology since they can be used for the deposition of highly textured (oriented), good quality semiconductor films on inexpensive substrates for efficient photovoltaic, display, and LED electronics. 
ST ceramic glass can also be conducting, as in the case of titanium nitride (TiN) for example. A distinguishing feature of ST's approach is to make films that have "texture" or preferential orientation which means the crystals in the films are aligned -- greatly improving the electronic properties of materials.
Remarkably, the new sapphire glass has a MOHS 8 (verified by a 3rd party independent institution).  Single crystal sapphire has a MOHS 9.  Therefore, the ST sapphire glass is close to single crystal sapphire in hardness. This is the first time this hardness has ever been achieved on ordinary soda-lime glass. Al2O3 is one of the hardest materials known, second only to diamond.
ST is also developing this approach using laser instead of e-beam.  ST will be optimizing the films with the aim of achieving MOHS 9, and all kinds of glass substrates can be used in the process, including quartz.



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Plastic yield criterion and hardening of porous single crystals


This article presents an assessment of the yield criterion for porous plastic single crystal, proposed by Paux et al. (2015), for face-centred cubic and hexagonal close-packed crystalline structures. Comparisons with reference FFT full-field computations on single voided cubic unit cells, presenting different crystal orientations, show an overall agreement for the different plastic anisotropies considered at low and high triaxiality. An extension of the criterion to hardenable crystals, which takes into account the spatial heterogeneity of the approximate plastic strain field, is further proposed and compared with FE results from the literature for body-centred cubic crystals.


Single crystal

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Tuesday, September 19, 2017

PVT growth of AlN single crystals with the diameter from nano- to centi-meter level


Physical vapor transport (PVT) is the most successful and widely used approach for bulk aluminum nitride (AlN) single crystals. During the process of PVT growing AlN crystals, crucible materials, the growth setup, and the growth parameters (e.g., temperature distribution, growth pressure) are crucial. This work proposes a detailed study on the PVT growth of single AlN crystals with sizes ranging from nanometers to centimeters. AlN crystals with different sizes are grown by spontaneous nucleation. Furthermore, it discusses and contrasts the growth conditions and mechanisms of AlN crystals with different sizes. The structural and optical properties of the AlN crystals are also involved.
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Wednesday, September 6, 2017

Photodriven single-crystal-to-single-crystal transformation


Focusing on photoinduced crystal-to-crystal transformation system and architecture dependent property changes.
Photodriven isomerization of azobenzene cores.
Photodriven open-ring↔closed-ring transformations of diarylethene cores.
Photodriven [2 + 2] cycloadditions of olefin pair cores.
Other types of photoactive crystals.


Molecular architectures containing photosensitive units respond to light, giving dramatic variations of their structure. In particular, the crystalline packing phases offer the possibility of significant advances in crystal design and the understanding of solid-state photoreactivity. In this review we mainly focus on three different photoreactivity patterns, namely the isomerization of azobenzene, open-ring↔closed-ring transformations of diarylethenes and cycloadditions of olefin pairs, as well as some examples of photoreactive crystals outside these types. Many interesting phototriggered functionalities are documented herein, such as photo-tuning of guest adsorption of azobenzene or diarylethene-based porous frameworks and crystalline organic polymers generated by photo-cycloaddition reactions taking place in the different networks.

Graphical Abstract

Unlabelled figure


Crystal transformation
Cycloaddition reaction

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Thursday, August 10, 2017

Single-Crystal Graphene Films Grown More Than 100 Times as Fast as Previously Possible

Growth of graphene on copper foils assisted by a continuous oxygen supply
Image: Peking University/Nature Nanotechnology

The adaptation of chemical vapor deposition (CVD) production of graphene so that it’s compatible with roll-to-roll processing is transforming graphene manufacturing. That effort is being led by companies like Graphene Frontiers, based in Philadelphia.
However, the production of single-crystal graphene on copper foils in a CVD process remains a fairly time consuming procedure. Fabrication of centimeter-size single crystals of graphene still takes as much as a day.

Now researchers at Hong Kong Polytechnic University and Peking University have developed a technique that accelerates the process so that the growth happens at 60 micrometers per second—far faster than the typical 0.4 µm per second. The key to this 150-fold speed increase was adding a little oxygen directly to the copper foils.
In the research, which is described in the journal Nature Nanotechnology, the China-based researchers placed an oxide substrate 15 micrometers below the copper foil. The result: a continuous supply of oxygen that lowers the energy barrier to the decomposition of the carbon feedstock, thereby increasing the graphene growth rate.

The expectations were that the oxide substrate would release the oxygen at the high temperatures inside the CVD surface (over 800 degrees Celsius). The researchers confirmed this through the use of electron spectroscopy. While the measurements indicated that oxygen was indeed being released, the amount was still fairly minimal. Nevertheless, this minuscule amount of oxygen proved sufficient for their purposes because the very small space between the oxide substrate and the copper foil created a trapping effect that multiplied the effect of the oxygen.
In their experiments, the researchers were able to successfully produce single-crystal graphene materials as large as 0.3 millimeter in just five seconds. That, according to the researchers, is more than two orders of magnitude faster than other methods in which graphene is grown on copper foils.

The researchers believe that this ultrafast synthesis of graphene makes possible a new era of scalable production of high-quality, single-crystal graphene films by combining this process with roll-to-roll methods.

Counterintuitively, speeding up the process of producing single-crystal graphene films may not automatically lead to wider adoption of graphene in various devices. Just a few years ago, graphene production was stuck at around a 25-percent utilization rate, and there is no reason to believe that demand has increased enough to have dramatically changed those figures. (Graphene producers will tell you that if demand for CVD-produced graphene suddenly spiked, volume could be doubled nearly overnight.)

Nonetheless, speed in manufacturing is always an attractive option for any product. It just might not offer a change to the graphene landscape as much as a few “killer apps” might.

Keywords: chemical vapor deposition (CVD); Graphene Frontiers; single-crystal graphene; Hong Kong Polytechnic University; Peking University;  graphene;

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Wednesday, August 2, 2017

Influence of Mn doping on CuGaS2 single crystals grown by CVT method and their characterization


1 and 2 mole% of Mn doped CuGaS2 (CGS) single crystals were grown by the chemical vapour transport (CVT) technique using iodine as the transporting agent. The analysis of the single crystal x-ray diffraction data suggests that the doping of 1 and 2 mole% Mn in the CGS single crystal does not affect the tetragonal (chalcopyrite) crystal structure. The optical absorption spectrum shows that the Mn ion induces a very strong absorption band in the UV–visible–near IR regions. The values of the crystal parameter (Dq) and the Racah parameter (B) calculated from the absorption spectra show d electron delocalization in the host crystal CGS. Room temperature photoluminescence spectra of undoped CGS only exhibited a band–band emission. But 1 and 2 mole% Mn doped CGS single crystals show two distinct CGS and Mn2+ related emissions, both of which are excited via the CGS host lattice. Raman spectra of 1 and 2 mole% Mn doped CGS single crystals exhibit a high intensity peak of the A1 mode at 310 cm−1 and 300 cm−1, respectively. EDAX, optical absorption and Raman spectrum studies reveal that Mn2+ ions are substituted in the Ga3+ ions and incorporated into the CGS lattice. The magnetization of Mn doped CGS single crystals was measured as a function of the magnetic field and temperature. Paramagnetic behaviour typical of spin S = 5/2 expected for Mn2+(d5) magnetic centres was observed in the temperature range 2 K < T < 300 K. In Mn doping, the increase in bulk conductivity of the Mn doped CGS single crystals at room temperature indicates an increase in the hole concentration.
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Tuesday, July 25, 2017

Breaking the Rules with Cutting-Edge Lighting for the Home

Buster + Punch take their lighting to unexpected yet stylish levels with their HEAVY METAL Pendant and LED BUSTER Bulb. A London-born home fashion label that works with unusual, solid materials to make extraordinary items for everyday use, Buster + Punch's custom lighting fuses unique design and attitude to light up any room in the home from the kitchen to the bathroom and even the home bar area. Buster + Punch's striking British-infused lighting makes a design statement for all.

Buster + Punch

Buster + Punch's HEAVY METAL Pendant adds a bold and refined look to any room. The eclectic lighting piece features a single light pendant that is made from solid Steel, Brass, Smoked Bronze or Matt Black with signature knurled satin metal and Matt rubber detailing. Buster + Punch also offer a range of light bulbs with original styling, including the LED BUSTER Bulb.

Buster + Punch

The LED BUSTER Bulb is the industry's most innovative eco-friendly LED alternative to traditional filament bulbs and the first to implement novel changes in design. With an E26 base, it can also be used as a direct replacement for standard screw-thread incandescent bulbs. The resin light pipe at the center of the bulb is where all of the magic happens. It allows the bulb to perform two incredible functions: a focused spotlight to illuminate surfaces below and a warm ambient glow to light faces and spaces around it. Defining the next evolution in an industry that is undergoing a change in ideals, the LED BUSTER Bulb raises the bar in lighting technologies.

·         Available in dimmable and non-dimmable options 
·         At 2700K, provides a soft, flattering ambient light 
·         At 5W (dimmable) and 2W (non-dimmable), the bulbs consume just 1/20th of the energy of a conventional incandescent bulb 
·         Lasts over seven times longer than a standard bulb or incandescent 
·         Bulbs exceed all applicable U.S. safety standards 
·         Bulb life is an excellent 30,000 hours 
·         Available in Warm Gold, Smoked Grey and Bright Crystal bulb finishes 
·         Bulbs are finished with a satin metallic sheen
Keywords:LED bulbs,lighting design,home lighting.custom lighting.Buster+Punch,

Source:  LEDinside

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Monday, July 10, 2017

KxFe2−ySe2 single crystals: floating-zone growth, transport and structural properties


Single crystals of superconducting KxFe2−ySe2 have been grown with the optical floating-zone technique under application of 8 bar of argon pressure. We found that large and high quality single crystals with dimensions of  ~ 6 mm ×10 mm could be obtained at the termination of the grown ingot through quenching, while the remaining part of the ingot decomposed. As-grown single crystals commonly represent an intergrowth of two sets of c-axes characterized by slightly different lattice constants. Single-crystal K0.80Fe1.81Se2 shows a superconducting transition at Tc = 31.6 K, leading to a near 100% expulsion of the external magnetic field in magnetization measurements. On the other hand, neutron diffraction data indicate that superconductivity in the sample coexists with a $\sqrt{5}\times \sqrt{5}$ iron-vacancy superstructure and static antiferromagnetic order. The anisotropic ratio of the upper critical field Hc2 for both H ∥ c and H ∥ ab configurations is  ~ 3.46.
Keywords:Single crystal,
Source:  LEDinside

Tuesday, July 4, 2017

New data reduction protocol for Bragg reflections observed by TOF single-crystal neutron diffractometry for protein crystals with large unit cells


In protein crystallography, high backgrounds are caused by incoherent scattering from the hydrogen atoms of protein molecules and hydration water. In addition, the scattering intensity from large unit-cell crystals is very small, which makes it difficult to improve the signal-to-noise ratio. In the case of time-of-flight (TOF) single-crystal neutron diffractometry, the measured spectra cover four-dimensional space including X, Y, and TOF in addition to intensity. When estimating the integrated intensity, 3D background domains in the vicinity of peaks should be clearly classified. In conventional 1D or 2D background evaluation, the evaluation is applied for individual peaks assigned using peak searches; however, it is quite difficult to classify the 3D background domain in TOF protein single-crystal neutron diffraction experiments. We undertook the development of a data reduction protocol for measurements involving large biomacromolecules. At the initial stage of the reduction protocol, appropriate 3D background estimation and eliminations were applied over the entire range of X, Y, and TOF bins. The histograms were then searched for peaks and indexed, and the individually assigned peaks were finally integrated with an effective profile function in the TOF direction. Three-dimensional deconvolution procedures for overlapping peaks associated with large unit cells were implemented as necessary. This data reduction protocol may lead to the improvement of signal-to-noise ratios to enable TOF spectral analysis of large unit-cell protein crystals.
Source:  iopscience

Tuesday, June 27, 2017

Segmentation Effect on Inhomogeneity of [110]-Single Crystal Deformation

This work presents a detailed analysis of segmentation process in FCC single crystals with compression axis [110] and side faces( ̅110) and (001) considering effect of octahedral shear crystal-geometry and basic stress concentrators. Sequence of meso-band systems formation on side faces is determined. Macro-segmentation patterns are specified, that are common to the FCC single crystals under investigation. It is proved that rectangular shape of highly compressed crystals, elongated in direction of operating planes, is conditioned by orientation symmetry of compression axis, single crystal side faces and shears directions, which are characteristic for the given orientation. The specified patterns are characteristic only for the samples with initial height-to-width ratio equal to 2. When varying sample height relative to the initial one, segmentation patterns will also vary due to crystal geometry variations.

Source: iopscience

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Monday, June 5, 2017

In atomic propellers, quantum phenomena can mimic everyday physics

In atomic propellers, quantum phenomena can mimic everyday physics

June 1, 2017

In atomic propellers, quantum phenomena can mimic everyday physics

Dr. Piotr Bernatowicz from the Institute of Physical Chemistry of the Polish Academy 
of Sciences in Warsaw and Prof. Slawomir Szymanski from the Institute of Organic 
Chemistry of the PAS have predicted and observed that quantum phenomena …more

In molecules, there are certain groups of atoms that are able to rotate. This movement occurs under the influence of random stimuli from the environment, and is not continuous, but occurs in jumps. It is generally believed that such jumps occur in a manner that is typical of classical objects, such as a fan blade prodded by a finger. Chemists from the institutes of the Polish Academy of Sciences in Warsaw have, however, observed rotations that follow the non-intuitive rules of the quantum world. It turns out that under the appropriate conditions, quantum rotations can very well mimic normal, classical rotation.
Professor Slawomir Szymanski from the Institute of Organic Chemistry of the Polish Academy of Sciences (IOC PAS) in Warsaw is certain that much more exotic and non-intuitive phenomena of a  are responsible for some of the effects observed in molecules. For years, he has been developing a quantum model of the jump rotations of whole groups of atoms in molecules. The theoretical work of Prof. Szymanski has just found further confirmation in experiments conducted at the Institute of Physical Chemistry of the PAS (IPC PAS) by a group led by Dr. Piotr Bernatowicz, and described in the Journal of Chemical Physics.
"In chemistry, quantum mechanics is used almost exclusively to describe the motion of tiny electrons. Atomic nuclei, even those as simple as the single-proton nucleus of hydrogen, are considered too large and massive to be subject to . In our work, we prove that this convenient but very simplistic view must finally begin to change, at least in relation to certain situations," says Prof. Szymanski.
Prof. Szymanski's quantum rotation model describes the rotation of atomic groups composed of identical elements, e.g. . The latest publication, completed in cooperation with Dr. Bernatowicz's group, concerns CH3 methyl groups. In their structure, these groups are reminiscent of tiny propellers. There are three hydrogen atoms around the carbon atom spaced at equal intervals. It has been known for a long time that the methyl groups connected by a carbon atom to the molecules can make rotational jumps. All the hydrogen atoms can simultaneously rotate 120 degrees around the carbon. These rotations have always been treated as a classic phenomenon in which hydrogen 'balls' simply jump into the adjacent 'wells' that have just been vacated by their neighbours.
"Using , we carried out difficult but precise measurements on powders of single crystals of triphenylethane, a compound of molecules each containing one . The results leave no room for doubt. The shapes of the curves we recorded, so-called powder resonance spectra, can only be explained by the assumption that quantum phenomena are responsible for the rotations of the methyl groups," says Dr. Bernatowicz.
The measurements of the rotation of the methyl groups by nuclear magnetic resonance required precise control of the temperature of the powdered substances. This is because the quantum nature of the rotation only becomes clearly visible in a narrow temperature range. When the temperature is too low, the rotation stops, and when it is too high, the quantum rotations become indistinguishable from the classical ones. The temperatures of experiments at the IPC PAS, in which the quantum nature of the rotations was clearly visible, ranged from 99 to 111 Kelvin.
A new picture of chemical reality emerges from this research. The CH3 group in the molecule is no longer a simple rotor composed of a carbon core and three rigidly attached hydrogen atoms. Its actual nature is different—no hydrogen atom occupies a separate position in space. What's more, each of them continually mixes in a quantum manner with the other two. Under the right conditions, the methyl group, although constructed of many , turns out to be a single, coherent quantum entity that does not resemble any object known to us from the everyday world.
A description of classical atomic rotator motion can be constructed using one constant measuring the average frequency of its jumps. It turns out that in the quantum model, there must be two such constants and they depend on the temperature. When the temperature rises, both constants take on a similar value and the rotations of the methyl group begin to resemble classical rotations.
"In our measurements, we really observed the gradual transformation of the quantum rotations of the methyl groups into rotations difficult to distinguish from the classical ones. This effect should be appropriately understood. Quantum phenomena did not cease to function, but in a certain way imitated classical jumps," explains Dr. Bernatowicz.
Scientists from the IPC PAS and IOC PAS had already confirmed the correctness of the quantum  model in experiments with methyl groups (among others in molecules of dimethyl triptycene, where these effects were accompanied by dynamic changes in the crystal lattice). However, predictions concerning the rotations of a much more complex atomic structure, the C6H6 benzene ring, await experimental verification.
"Our research is of a basic nature, and it is difficult to talk here immediately about specific applications," notes Prof. Szymanski, adding, "It is worth emphasizing, however, that quantum effects are considered to be extremely sensitive to the environment. Chemists and physicists assume that in very dense environments, they are destroyed by the thermal movements of the surroundings. We observe quantum effects at relatively high temperatures, in addition in condensed environments: liquids and crystals. The results we obtain should therefore be a warning to chemists or physicists who like oversimplified interpretations."
The imitation of classical physics by  phenomena, in addition in a dense and relatively warm environment, is a surprising effect that should draw the attention of, among others, the constructors of nanomachines. By designing smaller molecular devices, they may unwittingly move from the world of classical physics to the world of . Under new conditions, the operation of nanomachines could suddenly stop being predictable.
Journal reference: Journal of Chemical Physics 
Provided by: Polish Academy of Sciences