Optical orientation of nematic liquid crystal droplets via photoisomerization of an azodendrimer dopant

• Sergey A. Shvetsov,
• Alexander V. Emelyanenko,
• Natalia I. Boiko,
• Alexander S. Zolot'ko,
• Yan-Song Zhang,
• Jui-Hsiang Liu and
• Alexei R. Khokhlov

Beilstein J. Nanotechnol. 2018, 9, 870–879, doi:10.3762/bjnano.9.81

• relaxation. The first term on the right-hand side of Equation 1 describes the increase of the cis isomer fraction due to the light excitation of trans isomers and their possible change (with the probability Φtrans) of the conformational state. The second and third terms describe the decrease of cis isomer

• fraction due to the light excitation (with the probability Φcis = 1 − Φtrans) and thermal cis→trans relaxation. The thermal relaxation can be neglected at . Using this condition, in the stationary case (dXcis/dt = 0), Equation 1 can be rewritten in the following form: Thus the relative concentrations of

Dynamics and fragmentation mechanism of (C₅H₄CH₃)Pt(CH₃)₃ on SiO₂ surfaces

• Kaliappan Muthukumar,
• Harald O. Jeschke and
• Roser Valentí

Beilstein J. Nanotechnol. 2018, 9, 711–720, doi:10.3762/bjnano.9.66

• during geometry relaxation and hence are not discussed further. The calculated adsorption energies (EA) are summarized in Table 1 and the configurations are summarized in Figure 2. The calculated values of EA of (C5H4CH3)Pt(CH3)3 on 11% partially dehydroxylated surfaces indicates that the most stable

• for discussion. In Model-4, where the centroid of the methylcyclopentadienyl ring is oriented on top of a Si atom in the initial configuration, a spontaneous bond formation between one of the carbon atoms of the ring and the surface Si atom is observed during relaxation. There has been no evidence for

• Figure 1. In the most stable configuration for the 22% case (panel d), one of the three methyl groups bonded to Pt dissociates spontaneously during relaxation. Color code: green – Si, red – O, orange – Pt, gray – C and blue – H throughout this manuscript. To better display the changes occurring the

Electron interactions with the heteronuclear carbonyl precursor H₂FeRu₃(CO)₁₃ and comparison with HFeCo₃(CO)₁₂: from fundamental gas phase and surface science studies to focused electron beam induced deposition

• Ragesh Kumar T P,
• Paul Weirich,
• Lukas Hrachowina,
• Marc Hanefeld,
• Ragnar Bjornsson,
• Helgi Rafn Hrodmarsson,
• Sven Barth,
• D. Howard Fairbrother,
• Michael Huth and
• Oddur Ingólfsson

Beilstein J. Nanotechnol. 2018, 9, 555–579, doi:10.3762/bjnano.9.53

• similar on all metal atoms. Relaxation to the ground state anionic geometry (Figure 6b), however, leads to a relative increase in the spin density on the Ru base plane atoms as compared to the Fe-apex. It is clear that the comparison of the iso-surfaces for the respective MOs for H2FeRu3(CO)13 and HFeCo3

• (CO)12, the spin density of their anions and the geometrical changes between the respective neutral and anionic ground states, does not offer a quantitative explanation of their different behavior with regards to DEA. However, the difference is significant, especially with regards to the relaxation of

• the metal–metal bonds between the base plane and the apex as well as within the base plane. While the relaxation of the ground state anion of HFeCo3(CO)12 leads to a spontaneous and significant weakening of the metal bonds from the base plane to the apex, the bond weakening within H2FeRu3(CO)13 is

Green synthesis of fluorescent carbon dots from spices for in vitro imaging and tumour cell growth inhibition

• Nagamalai Vasimalai,
• Vânia Vilas-Boas,
• Juan Gallo,
• María de Fátima Cerqueira,
• Mario Menéndez-Miranda,
• José Manuel Costa-Fernández,
• Lorena Diéguez,
• Begoña Espiña and
• María Teresa Fernández-Argüelles

Beilstein J. Nanotechnol. 2018, 9, 530–544, doi:10.3762/bjnano.9.51

• -dependent emission typically observed in C-dots has been attributed to the presence of multi-emission centres, C-dot size distribution, slow solvent relaxation and the existence of multi-aggregation [8][9]. Also, the optical properties of C-dots are strongly dependent on their local environment, and

Influence of the preparation method on the photocatalytic activity of Nd-modified TiO₂

• Patrycja Parnicka,
• Paweł Mazierski,
• Tomasz Grzyb,
• Wojciech Lisowski,
• Ewa Kowalska,
• Bunsho Ohtani,
• Adriana Zaleska-Medynska and
• Joanna Nadolna

Beilstein J. Nanotechnol. 2018, 9, 447–459, doi:10.3762/bjnano.9.43

• energy of photons to penetrate deeper into the surface of the material [11]. This phenomenon can also be explained by the spectroscopic properties of rare earth ions. In our previous paper [23], it has been proven that Nd3+ ions are prone to cross-relaxation (energy migration between Nd3+ ions

Dynamic behavior of nematic liquid crystal mixtures with quantum dots in electric fields

• Emil Petrescu,
• Cristina Cirtoaje and
• Octavian Danila

Beilstein J. Nanotechnol. 2018, 9, 399–406, doi:10.3762/bjnano.9.39

• on a sample containing 0.89% (mass fraction) of CdSe/ZnS quantum dots revealed a decrease of the relaxation time compared to pure 5CB. Keywords: Fréedericksz transition; nematic liquid crystals; quantum dots; Introduction The expansion of liquid crystal (LC)-based devices in common life domains as

• quantum dot surface. Dynamic experiments performed in alternating electric fields proved that by adding a small amount of CdSe/ZnS quantum dots in thermotropic nematic liquid crystal with positive dielectric anisotropy, we obtain a decrease of the relaxation time. When an external electric field higher

• sample. The time period after which a constant intensity is obtained, which means that an equilibrium state is reached, is characterized by the relaxation time and can be experimentally evaluated from plotting the intensity as a function of the time. A theoretical analysis of the LC + QDs system based on

Periodic structures on liquid-phase smectic A, nematic and isotropic free surfaces

• Anna N. Bagdinova,
• Evgeny I. Demikhov,
• Nataliya G. Borisenko,
• Sergei M. Tolokonnikov,
• Gennadii V. Mishakov and
• Andrei V. Sharkov

Beilstein J. Nanotechnol. 2018, 9, 342–352, doi:10.3762/bjnano.9.34

• by similar equations. This mechanism explains why several minutes are needed to form the stripes. This time corresponds to charge diffusion to the stable position in the striped structure. This mechanism explains the striped appearance in the nematic phase and isotropic liquid. After some relaxation

• from the nematic phase. Topographical (a) and SNOM (b) images of SmA on Si substrate droplet edge, cross sections of both images (c) and (d). Equilibrium surface state of SmA phase after 30 minutes of relaxation at room temperature. SNOM image of SmA on Si substrate droplet edge at room temperature (a

Design of polar self-assembling lactic acid derivatives possessing submicrometre helical pitch

• Alexej Bubnov,
• Cyril Vacek,
• Michał Czerwiński,
• Terezia Vojtylová,
• Wiktor Piecek and
• Věra Hamplová

Beilstein J. Nanotechnol. 2018, 9, 333–341, doi:10.3762/bjnano.9.33

• Goldstone mode (this relaxation mode is related to azimuthal fluctuations of the molecules in the smectic layer) with a typical relaxation frequency of several kHz. This behaviour fully confirms the ferroelectric character of the SmC* phase detected for all studied materials from the KL n/m series. The

• relaxation frequency of the mode slightly decreases with the temperature decrease while the dielectric strength is decreased to a local minimum value and then begins to increase until crystallisation occurs. This is quite typical behaviour for the Goldstone mode at the ferroelectric SmC* phase [39][53][54

Dynamic behavior of a nematic liquid crystal with added carbon nanotubes in an electric field

• Emil Petrescu and
• Cristina Cirtoaje

Beilstein J. Nanotechnol. 2018, 9, 233–241, doi:10.3762/bjnano.9.25

• theoretical model based on elastic continuum theory was developed and the relaxation times of nematic liquid crystals with CNTs were evaluated. Experiments made with single-walled carbon nanotubes dispersed in nematic 4-cyano-4’-pentylbiphenyl (5CB) indicated a significant difference of the relaxation time

• when compared to pure liquid crystal. We also noticed that the relaxation time when the field is switched off depends on how long the field was applied. It is shorter when the field is switched off immediately after application and longer when the field was applied for at least one hour. Keywords

• movement is characterized by the relaxation time. Experimentally it can be determined by measuring the intensity of a light beam traversing the sample as a function of the time. A theoretical model based on elastic continuum theory, in which the interaction between carbon nanotubes and LC molecules is

Dielectric properties of a bisimidazolium salt with dodecyl sulfate anion doped with carbon nanotubes

• Doina Manaila Maximean,
• Viorel Cîrcu and
• Constantin Paul Ganea

Beilstein J. Nanotechnol. 2018, 9, 164–174, doi:10.3762/bjnano.9.19

• low frequencies confirm the presence of EP. Keywords: activation energy; carbon nanotubes; dielectric spectroscopy; ionic liquid crystal; relaxation time; Introduction Ionic liquid crystals (ILCs) represent a very appealing class of materials that has found various recent applications in dye

• CNT concentration. The characteristic relaxation times were obtained by fitting the spectra of the dielectric loss with the Havriliak–Negami (HN) function [52]: where ε′(ω) is the permittivity and ε″(ω) is the dielectric loss, εLF is the low-frequency (LF) permittivity and ε∞ is the permittivity in

• the high-frequency (HF) limit and τmax is the characteristic relaxation time of the dielectric relaxation process. The dependency τmax = f(1/T) can be modeled using the Vogel–Fulcher–Tammann (VFT) law, as follows: where A is a material constant, kB is Boltzmann’s constant, T is the temperature, TV is

Electrical properties of a liquid crystal dispersed in an electrospun cellulose acetate network

• Doina Manaila Maximean,
• Octavian Danila,
• Pedro L. Almeida and
• Constantin Paul Ganea

Beilstein J. Nanotechnol. 2018, 9, 155–163, doi:10.3762/bjnano.9.18

• techniques, such as polarized optical microscopy, dielectric spectroscopy and impedance measurements. Dielectric constant and electric energy loss were studied as a function of frequency and temperature. The activation energy was evaluated and the relaxation time was obtained by fitting the spectra of the

• in the high frequency (HF) domain, one notices a relaxation process outside the measurement domain, while in the low frequency (LF) range, two CA-attributable almost overlapping relaxation processes can be observed at 1 Hz and 1000 Hz. The CA/E7 sample exhibits a relaxation process due to the LC in

• the HF measurement range, and two almost overlapping relaxation processes in the LF range. The characteristic relaxation times were obtained by fitting the spectra of the dielectric constant and dielectric loss with the Havriliak–Negami function [37][38][39][40]: where ε′(ω) is the dielectric constant

Dopant-stimulated growth of GaN nanotube-like nanostructures on Si(111) by molecular beam epitaxy

• Alexey D. Bolshakov,
• Alexey M. Mozharov,
• Georgiy A. Sapunov,
• Igor V. Shtrom,
• Nickolay V. Sibirev,
• Vladimir V. Fedorov,
• Evgeniy V. Ubyivovk,
• Maria Tchernycheva,
• George E. Cirlin and
• Ivan S. Mukhin

Beilstein J. Nanotechnol. 2018, 9, 146–154, doi:10.3762/bjnano.9.17

• defect-free structures on highly mismatched substrates, e.g., GaN NWs on Si [7][8]. NWs usually possess high crystal quality due to the effective mechanical stress relaxation at a distance of about one NW base diameter from the substrate. Nanowires synthesized on Si are very promising nanostructures in

• threading dislocations [32][33][34] followed by transition to three-dimensional growth of nanoislands [33][35]. The phenomenon of the Si solubility limit elevation in GaN NWs is usually explained again through effective stress relaxation due to the large surface area of these nanostructures. This work is

Nematic topological defects positionally controlled by geometry and external fields

• Pavlo Kurioz,
• Marko Kralj,
• Bryce S. Murray,
• Charles Rosenblatt and
• Samo Kralj

Beilstein J. Nanotechnol. 2018, 9, 109–118, doi:10.3762/bjnano.9.13

• parameters {q1,q2,q3} are solved using the standard over-relaxation method, the calculation details of which are given in [15]. Geometry of the problem We consider thin plane-parallel cells of thickness h. The top and bottom plates are placed at z = 0 and z = h, respectively. We consider the cells either in

Study of the vertically aligned in-plane switching liquid crystal mode in microscale periodic electric fields

• Artur R. Geivandov,
• Mikhail I. Barnik,
• Irina V. Kasyanova and
• Serguei P. Palto

Beilstein J. Nanotechnol. 2018, 9, 11–19, doi:10.3762/bjnano.9.2

• to sub-micrometer scale) influences the switching speed, especially the LC relaxation to the initial homeotropic state. We have found that there are two types of the relaxation: a fast relaxation caused by the surface LC sub-layer deformed in the vicinity of the electrodes and the slower relaxation

• of the bulk LC. The speed of the fast (surface) mode is defined by half of a period of the electrode grating, while the relaxation time of the bulk depends on the LC layer thickness and the length of the driving electric pulses. Thus, the use of the surface mode and the reduction of the electrode

• grating period can result in significant increase of switching speed compared to the traditional LC modes, where the bulk relaxation dominates in electrooptical response. We have studied thoroughly the conditions defining the surface mode applicability. The numerical simulations are in good agreement with

A robust AFM-based method for locally measuring the elasticity of samples

• Alexandre Bubendorf,
• Stefan Walheim,
• Thomas Schimmel and
• Ernst Meyer

Beilstein J. Nanotechnol. 2018, 9, 1–10, doi:10.3762/bjnano.9.1

• inverse of typical material relaxation time, we can assume that the measured storage modulus is independent on the frequency. The measurements yielded values in the range of the Young’s moduli of bulk LLDPE, PP and PS as seen in Table 3. The investigation also evidenced regions of different elastic moduli

• viscoelastic materials, the elastic modulus Eeff,meas measured in dynamic mode corresponds to the storage modulus. We assumed a frequency independence of the measured storage modulus as the measured contact resonances are quite large compared to the inverse of typical material relaxation times. The

Electro-optical characteristics of a liquid crystal cell with graphene electrodes

• Nune H. Hakobyan,
• Hakob L. Margaryan,
• Valeri K. Abrahamyan,
• Vladimir M. Aroutiounian,
• Arpi S. Dilanchian Gharghani,
• Amalya B. Kostanyan,
• Timothy D. Wilkinson and
• Nelson Tabirian

Beilstein J. Nanotechnol. 2017, 8, 2802–2806, doi:10.3762/bjnano.8.279

• cell, with different conducting electrodes (i.e., graphene–graphene and ITO–ITO), show almost identical characteristics. A similar pattern was observed during the study of the reorientation and relaxation processes under the influence of an external bipolar pulse voltage (Figure 6). As shown, at the

• oscillations). Then the relaxation process takes place only under the influence of the molecular forces of elasticity. The system returns to its original oriented state, similar to relaxation after influence of an electric field. The above-mentioned feature of the reorientation process under the influence of

• (high voltage, V >> Vth) and slow switching (the voltage is close to the threshold, V < 5Vth). In the fast switching mode (Figure 7), under the influence of a strong electric field, the bulk and boundary layers of the LC are involved in the reorientation process. This reduces the relaxation time due to

Thermo- and electro-optical properties of photonic liquid crystal fibers doped with gold nanoparticles

• Agata Siarkowska,
• Miłosz Chychłowski,
• Daniel Budaszewski,
• Bartłomiej Jankiewicz,
• Bartosz Bartosewicz and
• Tomasz R. Woliński

Beilstein J. Nanotechnol. 2017, 8, 2790–2801, doi:10.3762/bjnano.8.278

• about 8.0 V/µm and higher, the relaxation time could exceed even the times for an undoped LC. This effect could be connected with the electric constant of metallic dopants. High concentrations of Au NPs give good response times (25–30% shorter than for the undoped LC), but the relaxation times reduce

Ab initio study of adsorption and diffusion of lithium on transition metal dichalcogenide monolayers

• Xiaoli Sun and
• Zhiguo Wang

Beilstein J. Nanotechnol. 2017, 8, 2711–2718, doi:10.3762/bjnano.8.270

• phase (Figure 1a), whereas M atoms are located at the octahedral/disordered octahedral centre of six S atoms in the 1T/1T' phase (Figure 1b,c). Some compounds are not stable in the 1T' phase, which will be relaxed to the 1T phase after relaxation. The energy related to the 2H phase per formula unit (f.u

• represented as double zeta basis sets plus polarization, and a cut-off energy of 250 Ry was chosen to calculate the Hamiltonian element. The Monkhorst–Pack scheme with 11 × 11 × 1 k-point meshes were used for integration in the irreducible Brillouin zone for the relaxation of the primitive cell. A 2 × 2 × 1 k

Nanoprofilometry study of focal conic domain structures in a liquid crystalline free surface

• Anna N. Bagdinova,
• Evgeny I. Demikhov,
• Nataliya G. Borisenko and
• Sergei M. Tolokonnikov

Beilstein J. Nanotechnol. 2017, 8, 2544–2551, doi:10.3762/bjnano.8.254

• about 0.1 μm. For the next experiments, the 8CB materials was heated up to 43 °С – the temperature of the isotropic liquid phase, and then cooled down to the smectic-A (SmA) phase temperature. Figure 2 shows the process of formation and relaxation of the craters over the course of 10 min at 30 °С in the

• stabilized at 30.5 °C. Figure 4 illustrates the structure in smectic phase at 30.5 °C. Figure 4a,b demonstrates the appearance of small crater-like structures around larger ones and that the average depth changes from 329 nm (Figure 4a) to 408 nm (Figure 4b) after 15 min of relaxation. Discussion 8CB is a

Dynamic behavior of a nematic liquid crystal mixed with CoFe₂O₄ ferromagnetic nanoparticles in a magnetic field

• Emil Petrescu,
• Cristina Cirtoaje and
• Cristina Stan

Beilstein J. Nanotechnol. 2017, 8, 2467–2473, doi:10.3762/bjnano.8.246

• Fréedericksz threshold. Here τon and τoff are the relaxation times for each case and they contain all the influences of the added ferroparticle and the applied external field as follows: and with where B is the applied magnetic field, Bc is the Fréedericksz transition threshold for the pure liquid crystal and

• relaxation times for this mixture were calculated using experimental results and the theoretical model described above. They are presented in Table 1 where τon is the relaxation time after the field is switched on, and τoff is the relaxation time after the field is switched off. In pure nematic substances

• , the relaxation time τoff does not depend on the applied field as long as it is higher than the Fréedericksz transition threshold. As it can be observed from Table 1, when ferro-particles are added, the relaxation time decreases with increase of the applied field. Conclusion A new alignment was

Laser-assisted fabrication of gold nanoparticle-composed structures embedded in borosilicate glass

• Nikolay Nedyalkov,
• Mihaela Koleva,
• Nadya Stankova,
• Rosen Nikov,
• Mitsuhiro Terakawa,
• Yasutaka Nakajima,
• Lyubomir Aleksandrov and
• Reni Iordanova

Beilstein J. Nanotechnol. 2017, 8, 2454–2463, doi:10.3762/bjnano.8.244

• annealing times, the entire sample became pink colored. At temperatures below 500 °C, the coloration induced by laser irradiation at 266 nm disappeared and the glass became again transparent in the laser-irradiated areas. This effect has to do with the thermally induced relaxation of the color centers [31

Changes of the absorption cross section of Si nanocrystals with temperature and distance

• Michael Greben,
• Petro Khoroshyy,
• Sebastian Gutsch,
• Daniel Hiller,
• Margit Zacharias and
• Jan Valenta

Beilstein J. Nanotechnol. 2017, 8, 2315–2323, doi:10.3762/bjnano.8.231

• presence of one e–h pair does not influence the absorption of the second one (because of the relatively high [1] density of optical states (DOS) in Si NCs). According to the first assumption, and therefore relaxation of biexcitons in Equation 3 for a given fraction of excitons N1 (Equation 2) can be

• usually determined directly as the slope of the function 1/τON(Iex). However, our experiments show that the PL lifetime, τPL(Iex), is also a function of the excitation power [28] (Figure 2b). Assuming the radiative relaxation, τr, to be independent on the power, this can be understood by the saturation of

The interplay between spin densities and magnetic superexchange interactions: case studies of mono- and trinuclear bis(oxamato)-type complexes

• Azar Aliabadi,
• Bernd Büchner,
• Vladislav Kataev and
• Tobias Rüffer

Beilstein J. Nanotechnol. 2017, 8, 2245–2256, doi:10.3762/bjnano.8.224

• material that exhibits a slow relaxation of the magnetization below the blocking temperature. Oxamato-based SCMs, especially when equipped with further redox-switchable functionalities, are regarded as novel materials for the design of molecular spintronic devices [8][17][18]. Into such devices [21][22

• orientations with a substantially better S/N ratio as compared to the pulsed ENDOR spectra of 8@7. This improvement can be explained by the different relaxation paths involved in the two experiments and the smaller number of pulses in the EDNMR protocol. The EDNMR spectra have been modeled with the same

• ]. We aim to obtain with such experiments further insights into an understanding of mononuclear type-II and bis(oxamidato) complexes with respect to their electron spin dynamics, spin coherence and relaxation processes as well as their possible applications in molecular electronic devices. Conclusion Is

Material property analytical relations for the case of an AFM probe tapping a viscoelastic surface containing multiple characteristic times

• Enrique A. López-Guerra and
• Santiago D. Solares

Beilstein J. Nanotechnol. 2017, 8, 2230–2244, doi:10.3762/bjnano.8.223

• input are related through a material transfer function, which contains the viscoelastic parameters. Standard inputs are typically strain and stress step functions (in the case of stress relaxation and creep experiments, respectively) or harmonic excitations (in the case of DMA). Following the spirit of

• ) is physically represented in Figure 1 for the case of a Generalized Maxwell model with an arbitrary number of characteristic times. The load in Equation 1 may also be written in the time domain as a convolution of the relaxation modulus (G(t)) with the time derivative of the displacement: where the

• substitution has been made to express the result in terms of the widely known relaxation modulus, which is the stress response to a unit step strain [8][30] (see Supporting Information File 1 for further details about the relaxation modulus). Harmonic excitations in contact mode Before analyzing the case of

Au₅₅, a stable glassy cluster: results of ab initio calculations

• Dieter Vollath,
• David Holec and
• Franz Dieter Fischer

Beilstein J. Nanotechnol. 2017, 8, 2221–2229, doi:10.3762/bjnano.8.222

• ). In case of the crystalline starting configuration (Figure 1a), the initial coordination numbers (equivalent to the crystalline cluster being only relaxed at 0 K without the annealing procedure) and the coordination numbers after annealing at 900 K and subsequent relaxation at 0 K are displayed. For

• the random starting arrangement, the histogram of the coordination numbers after relaxation at 0 K is shown in Figure 1b. The coordination numbers of the crystalline cluster displayed in Figure 1a show that 13 atoms assume the maximum coordination number of twelve as expected for the fcc structure

• . The most frequent coordination number is seven. However, after annealing at 900 K and relaxation at 0 K, the highest coordination number is reduced from twelve to ten, which is close to 10.9 exhibited by liquid gold [27]. The cluster did not crystallize again after quenching it to 0 K but instead it