Decomposition Of Self-assembled Monolayers Research Articles

The role of atomic oxygen in the decomposition of self-assembled monolayers during area-selective atomic layer deposition

Utilising self-assembled monolayers (SAMs) to achieve area-selective atomic layer deposition (AS-ALD) as an approach to bottom-up nanofabrication has recently gained significant attention from the nanoelectronics industry. With the continued downscaling of feature sizes, top-down processing can no longer reach the challenging demands of the industry which requires conformal coating of high aspect ratio vias and a reduction in misalignment errors in multi-layered devices. In this work we attempt to imitate the effects of the ALD oxidation pulse experienced by the SAMs during the AS-ALD process by exposing two SAMs of different chain lengths and different functional groups, (3-trimethoxysilylpropyl)diethylenetriamine (DETA) and octadecyltrimethoxysilane (OTMS), to numerous controlled in-vacuo atomic oxygen exposures with subsequent characterisation by X-ray photoelectron spectroscopy (XPS). We monitor the sequential removal of the deposited monolayers with each successive atomic oxygen exposure for both SAMs. The etch rate is observed to be distinct for the different SAMs, the amino-terminated short chain DETA SAM reveals a linear etch rate while the longer chain OTMS SAM reveals an exponential etch rate. The results presented provide some insights into what characteristics are important for choosing the correct SAM for AS-ALD applications.

Thermal Stability of Thiolate Self-Assembled Monolayers on Copper Surface

The formation of self-assembled monolayers (SAMs) of organothiol is one of the excellent methods for corrosion protection. This work studies the thermal stability of thiolate SAMs coating on a copper surface. Three types of thiolate SAMs including 1-octanethiol (OTT), 2-ethylhexanethiol (2-EHT), and 2-phenylethanethiol (2-PET) are investigated. These chemicals are similar in terms of the chemical formula but different in chemical structure. Contact angle, AFM, FT-IR, XPS, and potentiodynamic polarization are used to analyze hydrophilic and hydrophobic features, roughness, decomposition of SAMs, and corrosion inhibition efficiency, respectively. The optimum condition of oxygen plasma treatment is determined. The results show that the optimum time for the treatment is 15 s. The oxygen plasma increases roughness of the Cu surface and induces the hydrophilic feature, which is suitable for SAMs to form on the Cu surface. The Cu surfaces coated by each SAMs are annealed at the temperature ranging from 25 to 250°C. The OTT is decomposed at 80°C while the 2-EHT is decomposed at 140°C. The 2-PET is not decomposed at 140°C, because the 2-PET consists of aromatic rings that are more stable than other functional groups in OTT and 2-EHT structures. These results also refer to improvement of thiolate bond stability aided by aromatic ring in the 2-PET molecule. All SAMs are completely decomposed at 250°C. In conclusion, the 2-PET is the most favorable in terms of thermal stability.

Bottom-up fabrication and piezoelectric properties of CaBi4Ti4O15 micro-plateaus

CaBi4Ti4O15 (CBTi144) micro-plateaus were fabricated on Si wafers and Pt foils using a self-assembled monolayer (SAM) and a complex metal alkoxide solution. The micro-plateaus are delineated by metal masks, which are used for shadowing against the ultraviolet (UV) irradiation for decomposition of SAM to make the surface hydrophilic. The micro-plateaus crystallized to a ferroelectric phase with random orientation. The crystallization depended on the SAM-derived ultra thin layers at the surface of the substrates. The primitive PFM measurements without any top electrodes confirmed that the micro-plateaus exhibited the piezoresponse behaviors. The piezoelectric constant, d33, had some distribution, and the maximum d33 was confirmed as about 45 pm/V, which is identical to the d33 of the polar-axis oriented CBTi144 thin films.

A thermal stability study of alkane and aromatic thiolate self-assembled monolayers on copper surfaces

The thermal stability of 1-decanethiol (C10) and benzenethiol (BT) Self-Assembled Monolayers (SAMs) on metallic and oxidized copper surfaces has been investigated by thermal desorption spectrometry. High quality C10 and BT SAMs exhibit low thermal stabilities on clean copper surfaces with a maximum in decomposition occurring between 100 and 150 ∘C. The decomposition of SAMs follows different mechanisms. For the alkanethiol, a direct interaction between the alkyl group of the thiolate and the metallic copper surface is the dominant pathway for the C–S bond scission. The head group desorbs as oxidized sulfur and this is followed by the desorption of the alkyl fragments of the chain adsorbed on the clean copper surface. In the case of benzenethiol, a simultaneous desorption of the head group as oxidized sulfur and the benzene group occurs. SAM formation on the oxidized copper surface results in complete removal and/or reduction of the CuO layer. Higher SAM surface coverages on the resulting Cu/Cu 2O surface result from the enhanced surface roughness of the substrate. The decomposition mechanisms and thermal stabilities of the C10 and BT SAMs are dependent on the oxidation state of the underlying substrate and the chemical nature of the chain.