The Langmuir-Blodgett (LB) technique is a way of making supra-molecular assembly in ultrathin films with a controlled layered structure and crystal parameter, which have many envisioned technological applications for optical and molecular electronic devices as well as signal processing and transformation. Probably LB technique is the best method to manipulate materials at molecular level and provides a scope to realize the molecular electronics in reality. In this review article, we have discussed about the general introduction of LB technique and recent development on LB and related system including (i) LB methodology, (ii) characterizations of LB films, (iii) LB films and molecular electronics, (iv) historical review of LB films, (v) research and applications including fundamental research and application towards devices.

Bipolar resistive switching using organic molecule is very promising for memory applications owing to their advantages, such as simple device structure, low manufacturing cost, stability, and flexibility. Herein we report Langmuir–Blodgett (LB) and spin-coated-film-based bipolar resistive switching devices using organic material 1,4-bis­(di­(1H-indol-3-yl)­methyl)­benzene (Indole1). The pressure–area per molecule isotherm (π–A), Brewster angle microscopy (BAM), atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to formulate an idea about the organization and morphology of the organic material onto thin films. On the basis of the device structure and measurement protocol, it is observed that the device made up of Indole1 shows nonvolatile resistive random access memory (RRAM) behavior with a very high memory window (∼106), data sustainability (5400 s), device yield (86.7%), and repeatability. The oxidation–reduction process and electric-field-driven conduction are the keys behind such switching behavior. Because of very good data retention, repeatability, stability, and a high device yield, the switching device designed using compound Indole1 may be a potential candidate for memory applications.

A metal-free three component cyclization reaction with amidation is devised for direct synthesis of DFT-designed amido-phenazine derivative bearing noncovalent gluing interactions to fabricate organic nanomaterials. Composition-dependent organic nanoelectronics for nonvolatile memory devices are discovered using mixed phenazine-stearic acid (SA) nanomaterials. We discovered simultaneous two different types of nonmagnetic and non-moisture sensitive switching resistance properties of fabricated devices utilizing mixed organic nanomaterials: (a) sample-1(8:SA = 1:3) is initially off, turning on at a threshold, but it does not turn off again with the application of any voltage, and (b) sample-2 (8:SA = 3:1) is initially off, turning on at a sharp threshold and off again by reversing the polarity. No negative differential resistance is observed in either type. These samples have different device implementations: sample-1 is attractive for write-once-read-many-times memory devices, such as novel non-editable database, archival memory, electronic voting, radio frequency identification, sample-2 is useful for resistive-switching random access memory application.

Interest in biodegradable and transient electronics is gaining due to their potential use in green electronics, biomedical devices, and sustainable solutions for ewastes. In this paper we employed Protamine Sulfate (PS) as the active layer to demonstrate biodegradable transient resistive memory devices. The Au/PS/ITO device exhibits nonvolatile resistive switching with write-once-read-many (WORM) memory behavior. The observed WORM memory performance was very good with high memory window (4.57× 10 3 ), data retention (experimentally >10 6 s, extrapolated >10 8 s), device yield (∼87.5%), read endurance (>3.6 × 10 4 ), and device stability (>210 days). Bias induced charge trapping followed by conducting filament formation was the key to such switching. The electronic as well as optical behavior completely disappeared after 8 min of dissolution of the device in aqueous solution. As a whole this work suggests that the PS based WORM memory device may be a potential candidate toward designing biodegradable transient memory devices.

Molecular electronics is a new, exciting and interdisciplinary field of research. The main concern of the subject is to exploit the organic materials in electronic and optoelectronic devices. On the other hand, the Langmuir–Blodgett (LB) film deposition technique is one of the best among few methods used to manipulate materials at the molecular level. In this article, the LB film preparation technique is discussed briefly with an emphasis on its application towards molecular electronics.

Langmuir-Blodgett (LB) films of N,N'-dioctadecyl thiacyanine perchlorate (TC18) and octadecyl rhodamine B chloride (RhB18) and their mixtures in the presence and absence of clay mineral layers were investigated by recording surface pressure-area (pi-A) isotherms and by UV-vis and fluorescence spectroscopies. The pi-A isotherms of TC18, RhB18, and their mixtures are characteristic of liquid expanded state behavior with repulsive interactions between the two cationic dyes. In the presence of laponite, the pi-A isotherms show liquid expanded and condensed-state behavior. In laponite dispersions and in monolayers, TC18 has a strong tendency to aggregate with formation of H- and J- aggregates. The absorption and fluorescence maxima of the monomers in the films are at 435 nm and at 480 nm; H-dimers have an absorption maximum around 410 nm and do not fluoresce. J-dimers are present in all the films with absorption maximum at 461 nm and fluorescence at 463 nm. RhB18 is mainly present as monomers in the LB films with an absorption maximum at 576 nm and fluorescence at 595 nm. Fluorescence resonance energy transfer from TC18 to RhB18 has been observed in clay dispersions and in films with and without laponite. The optimum condition for TC18 --> RhB18 fluorescence energy transfer in the films is 90 mol % TC18 + 10 mol % RhB18.

In the present Article, a reversible transition behavior from Jaggregates to excimer of an indocarbocyanine dye 1,1′-dioctadecyl-3,3,3′,3′tetramethylindocarbocyanine perchlorate (DiI) in Langmuir−Blodgett (LB) films was reported. Surface pressure−area (π−A) isotherms, UV−vis, and fluorescence spectroscopies as well as atomic force microscopy (AFM) were used for characterizations of the films. π−A isotherms suggest a balance of interactions between DiI and fatty acids in the mixed monolayer at DiI mole fraction X DiI = 0.4, resulting in a stable and ideally mixed monolayer. It has been observed that pure DiI formed excimer in LB films, whereas both J aggregates and excimer were formed in LB films when DiI was mixed with long chain fatty acids, viz., stearic acid or arachidic acid. In fatty acid matrix at X DiI = 0.4, only J aggregates were formed in the LB films. This has been confirmed using deconvolution of spectroscopic results as well as using excitation spectroscopy. The coherent size of the J aggregate was found to be a maximum for the mixed film at the mole fraction 0.4 of DiI in fatty acid matrix. The J-aggregate domain in the LB film contains approximately (20 ± 5) coherent sizes. However, J aggregates were totally absent when DiI was mixed with cationic surfactant, polymer, or nanoclay.

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