Preparation of ideal molecular junctions: depositing non-invasive gold contacts on molecularly modified silicon

Abstract

Recent advances in creating rectifying gold|monolayer|silicon (Au-M-Si) junctions (namely, molecular silicon diodes) are reviewed. It is known that direct deposition of gold contacts onto molecular monolayers covalently bonded to silicon surfaces causes notable disruption to the junction structure, resulting in deteriorated performance and poor reproducibility that are unsuitable for practical applications. In the past few years, several new experimental approaches have been explored to minimize or eliminate such damage, including the "indirect" evaporation method and the pre-deposition of a protective "non-penetrating" metal. To enhance the interactions at the gold-monolayer interface, head-groups that allow bonding to gold are used to maintain the monolayer integrity. Construction of the device via flip-chip lamination and the modified polymer-assisted lift-off techniques also prohibits monolayer damage. Refining the fabrication and design techniques towards reliable molecular junctions is crucial if they are to be used in nanoelectronics for the purpose of miniaturization.

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

“…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.…”

Surface tension of liquid mercury: a comparison of density-dependent and density-independent force fields

“…Therefore the surface of liquid mercury serves as a model system for the experimental study of universal (free of the underlying crystal substrate) properties of numerous organic films [16][17][18][19][20][21][22][23][24][25][26]. Moreover, the unique properties of liquid mercury, especially its high surface tension, make Hg droplets superior to other metals for producing metal-SAM-metal [13,27] and metal-SAM-semiconductor [28,29] junctions. This property motivates the wide usage of liquid mercury in organic electronics [27][28][29][30][31][32][33][34], and even in the design of mixed organic-metal systems for information processing [35].…”

Single-molecule electrical contacts on silicon electrodes under ambient conditions

“…10 −3  cm 2 ) comprising very large ensembles of molecules13141516. The top contact with a second electrode is usually made via metal deposition on the top of the organic layer either by evaporation or via Hg or alloy-metal contacts1718. This macroscopic approach has provided most of the knowledge we have about charge transport across the molecule-semiconductor junction, however, they do suffer from critical drawbacks as fundamental platforms for charge transport studies.…”