Structure and polarity of 8CB films
evaporated onto solid substrates

Olenik, I. Drevenšek; Kočevar, K.; Muševič, Igor; Rasing, T.H.M.

doi:10.1140/epje/i2003-10013-y

Cited by 23 publications

(5 citation statements)

References 43 publications

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“…The untreated surface of silica and silicon pores enforces planar anchoring without a preferred lateral direction (within the plane) [18,26], whereas the elongated geometry of cylindrical pores yields, additionally, a preferred orientation of molecules along the pores axes. In accordance to the KKLZ model it is convenient to characterize the relevant ordering by the scaled order parameter q = Q/Q 0 , where Q = 1 2 3 cos 2 θ − 1 stands for the nematic (orientational) order parameter in its classical definition, Q 0 = Q(T I N ), and θ is the angle between the long molecular axis and the director.…”

Section: Resultsmentioning

confidence: 99%

Influence of nanoconfinement on the nematic behavior of liquid crystals

et al. 2012

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We explore the nematic ordering of the rodlike liquid crystals 5CB and 6CB, embedded into parallel-aligned nanochannels in mesoporous silicon and silica membranes as a function of mean channel radius (4.7 ≤ R ≤ .3 nm), and, thus, geometrical confinement strength, by optical birefringence measurements in the infrared region. The orientational order inside the nanochannels results in an excess birefringence, which is proportional to the nematic order parameter. It evolves continuously on cooling with a precursor behavior, typical of a paranematic state at high temperatures. These observations are compared with the bulk behavior and analyzed within a phenomenological model. Such an approach indicates that the strength of the nematic ordering fields σ is beyond a critical threshold σ(c) = 1/2 that separates discontinuous from continuous paranematic-to-nematic behavior. In agreement with the predictions of the phenomenological approach, a linear dependency of σ on the inverse channel radius is found and we can infer therefrom the critical channel radii, R(c) separating continuous from discontinuous paranematic-to-isotropic behavior, for 5CB (12.1 nm) and 6CB (14.0 nm). Our analysis suggests that the tangential anchoring at the channel walls is of similar strength in mesoporous silicon and mesoporous silica membranes. A comparison with the bulk phase behavior reveals that the nematic order in nanoconfinement is significantly affected by channel wall roughness, leading to a reduction of the effective nematic ordering.

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Section: Resultsmentioning

confidence: 99%

Influence of nanoconfinement on the nematic behavior of liquid crystals

et al. 2012

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“…18 Furthermore, there have been reports that it is not possible to form multilayers of nCB by L-B method. 13,19 We find that single layer of nCB (n ¼ 8, 9 and 10) can be transferred by L-B method on to mica as well as on to highly ordered pyrolytic graphite (HOPG) substrate. However, trying to transfer another layer immediately leads to dewetting and formation of droplets.…”

mentioning

confidence: 94%

“…Many studies on the materials of nCB series, particularly 8CB and 9CB at air-solid (A-S) interfaces, have been reported and major part of these studies involves thin films of nCB molecules obtained by evaporation onto a solid substrate or heating a drop of material on substrates. [11][12][13] The studies on such thin films show a planar configuration of molecular alignment at A-S interface. 12,14 The LangmuirBlodgett (L-B) technique is a useful method to obtain well organized films of nanoscale thickness at A-S interface, which are of importance in molecular electronics.…”

mentioning

confidence: 97%

“…This has been attributed to large cohesive energy due to the interaction between strongly polar cyano groups. 13 In this article, we present a detailed study of electrical conductivity of 9CB and 10CB monolayer films perpendicular to the plane of the film deposited onto solid substrates using the L-B technique. We have employed the current sensing mode of the atomic force microscope (AFM) to measure the electrical conductivity across the monolayer L-B films.…”

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confidence: 99%

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Electrical conductivity in Langmuir-Blodgett films of n-alkyl cyanobiphenyls using current sensing atomic force microscope

Gayathri

Suresh

2015

Journal of Applied Physics

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We report our studies on the nanoscale electrical conductivity in monolayers of n-alkyl cyanobiphenyl materials deposited on solid surface. Initially, the 8CB, 9CB, and 10CB monolayer films were prepared by the Langmuir technique at air-water interface and characterized by surface manometry and Brewster angle microscopy. The monolayer films were transferred on to solid substrates by the Langmuir-Blodgett (L-B) technique. The 8CB, 9CB, and 10CB monolayer L-B films were deposited on freshly cleaved mica and studied by atomic force microscope (AFM), thereby measuring the film thickness as ∼1.5 nm. The electrical conductivity measurements were carried out on 9CB and 10CB monolayer L-B films deposited onto highly ordered pyrolytic graphite using current sensing AFM. The nanoscale current-voltage (I-V) measurements show a non-linear variation. The nature of the curve indicates electron tunneling to be the mechanism for electrical conduction. Furthermore, analysis of the I-V curve reveals a transition in the electron conduction mechanism from direct tunneling to injection tunneling. From the transition voltage, we have estimated the values of barrier height for 9CB and 10CB to be 0.71 eV and 0.37 eV, respectively. For both 9CB and 10CB, the effective mass of electron was calculated to be 0.021 me and 0.065 me, respectively. These parameters are important in the design of molecular electronic devices.

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“…The SHG technique was also used to confirm spontaneous organization of 8CB molecules evaporated onto a solid substrate into multilayer stacks (Olenik et al 2003). Thus behavior of 8CB in LB systems is well known and described.…”

Section: Introductionmentioning

confidence: 99%

Formation of net-like patterns of gold nanoparticles in liquid crystal matrix at the air–water interface

et al. 2012

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Controlled patterning and formation of nanostructures on surfaces based on self-assembly is a promising area in the field of “bottom-up” nanomaterial engineering. We report formation of net-like structures of gold nanoparticles (Au NPs) in a matrix of liquid crystalline amphiphile 4′-n-octyl-4-cyanobiphenyl at the air–water interface. After initial compression to at least 18 mN m−1, decompression of a Langmuir film of a mixture containing both components results in formation of net-like structures. The average size of a unit cell of the net is easily adjustable by changing the surface pressure during the decompression of the film. The net-like patterns of different, desired average unit cell areas were transferred onto solid substrates (Langmuir–Blodgett method) and investigated with scanning electron microscopy and X-ray reflectivity (XRR). Uniform coverage over large areas was proved. XRR data revealed lifting of the Au NPs from the surface during the formation of the film. A molecular mechanism of formation of the net-like structures is discussed.Electronic supplementary materialThe online version of this article (doi:10.1007/s11051-012-0826-4) contains supplementary material, which is available to authorized users.

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Structure and polarity of 8CB films evaporated onto solid substrates

Cited by 23 publications

References 43 publications

Influence of nanoconfinement on the nematic behavior of liquid crystals

Influence of nanoconfinement on the nematic behavior of liquid crystals

Electrical conductivity in Langmuir-Blodgett films of n-alkyl cyanobiphenyls using current sensing atomic force microscope

Formation of net-like patterns of gold nanoparticles in liquid crystal matrix at the air–water interface

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