Nanofabrication techniques of highly organized monolayers sandwiched between two electrodes for molecular electronics

Abstract

Molecular electronics [1,2] is a promising field of research based on the idea that a single molecule or two dimensional assemblies of molecules (monomolecular films) can work as wires, switches, rectifiers, etc. Molecules are the smallest functional units and therefore it is expected that the use of molecules will permit to catch up with the limits of miniaturization (MM: more Moore), with an increase in device density by a factor of several orders of magnitude compared to today's state of the art. At the same time due to quantum effects novel and remarkable properties of organic and organometallic compounds at the nanoscale devices will result in increased performance (MtM: more than Moore) together with the appearance of new functions not possible with conventional semiconductors, and also cheaper devices due to the non-dependence of expensive materials used today in CMOS (complementary metal-oxide semiconductor) technology such as hafnium oxide. Nowadays, the number of research groups from different disciplines of science contributing to molecular electronics is gradually growing, and this field is becoming of great scientific and technological interest [1,3-8]. Since the seminal work of Aviram and Ratner in 1974 who firstly suggested that a single molecule could function as a rectifier [9], molecules have been experimentally demonstrated to work as switches, molecular wires or rectifiers, and a new field of opportunities is opened due to the understanding of electron transport through single entities or assemblies of molecules and expansion towards work on molecular spintronics, vibronic effects, excitation of the molecular junction with polarized light, quantum interference and decoherence, molecular chirality, molecular stretching and distortion as well as work on thermoelectric response in molecular junctions.Abstract: It is expected that molecular electronics, i.e., the use of molecules as critical functional elements in electronic devices, will lead in the near future to an industrial exploitable novel technology, which will open new routes to high value-added electronic products. However, despite the enormous advances in this field several scientific and technological challenges should be surmounted before molecular electronics can be implemented in the market. Among these challenges are the fabrication of reliable, robust and uniform contacts between molecules and electrodes, the deposition of the second (top) contact electrode, and development of assembly strategies for precise placement of molecular materials within device structures. This review covers advances in nanofabrication techniques used for the assembly of monomolecular films onto conducting or semiconducting substrates as well as recent methods developed for the deposition of the top contact electrode highlighting the advantages and limitations of the several approaches used in the literature. This contribution also aims to define areas of outstanding challenges in the nanofabrication of monomolecular layers sandwiched between two electro...

High surface coverage of a self-assembled monolayer by in situ synthesis of palladium nanodeposits

“…Molecular electronics is a dynamic field of contemporary research with enormous potential to approach not only concerns over 'top-down' scaling of electronic components, but also identify a wide range of technological and scientific challenges that are reliant on electron-transfer between molecular systems and solid-state interfaces including solar-energy harvesting, thermoelectric materials, catalysis, and sensing. 1 Significant progress has been made in the last few years including the synthesis of new functional molecular materials, 2-10 development of sophisticated methods for the assembly of either single molecules or monolayers onto electrodes for the achievement of efficient molecule-electrode junctions, [11][12][13][14][15] as well as experimental methods to determine the electrical properties of molecules at a single level [16][17][18][19][20][21][22] or in monolayers. 23,24 However, several challenges remain to be addressed before molecular electronics turns into a truly viable and reliable technology.…”

“…25 The fabrication of the top contact electrode in two terminal sandwich-based metal| organic monolayer|metal devices is one of the major challenges that, despite intense research over more than 30 years, remains to be fully resolved. 15,[26][27][28][29][30] A wide variety of techniques to deposit the top metal electrode onto a molecular monolayer have been described in the literature including direct and indirect evaporation, 11,[31][32][33][34][35][36][37][38] use of liquid metals, 11,34,39,40 flip chip lamination, 34,41 electrodeposition, [42][43][44] surface-diffusion-mediated deposition, 44 chemisorption of metal nanoparticles onto surface-functionalised monolayers, 45 thermal induced decomposition of an organometallic monolayer, 46 and photoreduction of a metal precursor. 47,48 The most significant problems in the deposition of the top-contact electrode are those related to damage of the functional molecules during the metallization process of the monolayer or penetration of the growing top-contact through the monolayer, which results in short circuits.…”

Towards a metallic top contact electrode in molecular electronic devices exhibiting a large surface coverage by photoreduction of silver cations

“…Some recent reviews have analysed in detail the top-contact electrode problem, and summarised the contemporary strategies aimed at overcoming this issue. [3][4][5][6][7][8] Strategies from our group concerning the fabrication of the topcontact electrode have included the thermal induced decomposition of an organometallic compound (TIDOC) method, 9 chemisorption of gold nanoparticles onto a monolayer surface-functionalised with a terminal alkyne moiety (-CCH) resulting in the formation of a s C-Au bond, 10 and photoreduction of a gold precursor incorporated into the monolayer. 11 In the latter method, a metal precursor ([AuCl 4 ] À ) was incorporated onto a Langmuir-Blodgett (LB) film from the sub-phase during the fabrication process, with subsequent photoreduction leading to the formation of metallic gold nano-islands (GNIs) on top of the intact molecular film.…”

Nanofabrication Techniques in Large-Area Molecular Electronic Devices

“…Because of the remarkable ensemble capabilities of each one of these techniques, monolayers or multilayers made of organic, organometallic, hybrid inorganic-organic building blocks, as well as biomaterials have been deposited onto conducting or semiconducting substrates. In addition, the growing knowledge on the electrode | monolayer interface, together with the mature synthetic expertise in this research field, has boosted the ad hoc synthesis of materials with improved anchoring characteristics onto the bottom-electrodes [35,82,[86][87][88][89][90][91]. Table 1, gathers, with no claim of completeness, some of the families of compounds that have been more widely used for fundamental studies in molecular electronics.…”