Elsevier

Thin Solid Films

Volume 519, Issue 20, 1 August 2011, Pages 7060-7064
Thin Solid Films

A study on the plasma polymer thin film surface modification for DNA alignment by using high energy electron beam irradiation

https://doi.org/10.1016/j.tsf.2011.01.224Get rights and content

Abstract

The plasma polymer thin films were deposited on Si(100) substrate by PECVD (plasma enhanced chemical vapor deposition) method. Liquid cyclohexene was used as single organic precursor. It was heated up to 60 °C and bubbled up by hydrogen gas, which flow rate was 50 sccm (standard cubic centimeters per min). Deposition temperature was room temperature. Plasma was ignited by a radio frequency (RF; 13.56 MHz) of 10 W.

As-deposited plasma polymer thin films were treated by e-beam of 300 keV with various adsorption radiation doses. The plasma polymer films, which were treated by high energy e-beam (HEEB), were investigated by FT-IR (Fourier Transform Infrared), XPS (X-ray Photoelectron Spectroscopy), AFM (Atomic Force Microscopy), and the water contact angles.

From IR spectra, the intensity of single bondOH functional group is increased by increasing electron dose rate. XPS results also show that the intensity of O1s peak is increased by increasing electron dose rate. C1s peak shows that oxygen bonded at carbon site. The water contact angles are decreased by increasing electron dose rate. From the AFM analysis, we observed the formation of λ-DNA (deoxyribonucleic acid) array on plasma polymer film, which was treated by HEEB with 14 kGy of adsorption radiation dose.

Introduction

The existing semiconductor technology let a silicone material make integrations by a top-down form developed by nano or molecule technology merged with nanotechnology, biotechniques and information technology, and by a bottom-up method to constitute a device and a circuit with self alignment of atoms and molecules. Those are common opinions of majority of experts. In spite of basic consensus by such experts, the progress in the nano and molecule device research field is very slow and it is worse now. There are many causes as possible reasons, but it is recognized that the following are still in question: “the choice of the stable molecule and design technology”, “self alignment technology of atoms and molecules”, and “technology to form molecule and contact between the metal electrode for stability” [1], [2]. The realization of nanoscaled electronics expects the development of bottom-up strategies such as chemical synthesis, self alignment of atoms and molecules, and self-assembled supra molecule. All inorganic nanoparticles (NPs) and DNA molecules are attractive building materials and backbone for formation of upper structures. The formation of metal nanowires (MNWs) via DNA and NPs was investigated largely. MNWs were formed by electrostatically attaching metal nanoparticles such as Au, Pd, Pt, and Cu on DNA surface. DNA was electrostatically attached on the substrate surface [3]. λ-DNA molecules were aligned on the Si substrate by the dipping/pulling and the suction techniques with patterned aminopropyl triethoxysilane (APS) and octadecyltrichlorosilane (OTS) [1], [4]. All techniques for DNA patterning need APS (for attaching DNA) and OTS (for passivation of DNA) coating (or pattern). However, APS/OTS coating was easily affected by humidity. Thus, we tried to use plasma polymer and surface modification (or treatment) by HEEB, which is not affected by humidity, for attachment and passivation of DNA. Also, electron beams are becoming an increasing subject of interest for material processing such as surface treatment, drilling, hardening, cutting, welding, and curing. They provide high-density energy sources that allow energy deposition in short times within narrow depths near the material surface. Electron beams are advantageous due to high instantaneous energy density, short irradiation time, and high surface finishing without any change of the substrate [5].

A contact angle is an important element in the alignment of DNA. If a contact angle is very low, DNA solution does not fall down well, and lump DNA is just fixed on a substrate. On the other hand, if a contact angle becomes too big, DNA solution falls down easily with DNA molecules without attaching DNA. Alignment of DNA was not formed on substrate surface with too high or low contact angle. In this study, water contact angle for DNA alignment was optimized by water contact angle and AFM measurement. And attenuated total reflectance (ATR) FT-IR and XPS results show correlation of surface chemical change with increasing e-beam doses.

Section snippets

Experimental

Fig. 1 shows experimental steps such as plasma polymer deposition, e-beam treatment, and alignment of DNA. The experiment step 1 is carried out in a homemade, stainless steel PECVD system as shown in Fig. 2(a). The plasma polymer thin films were deposited by PECVD method. Cyclohexene was utilized as organic precursor and preheated to 60 °C, and bubbled up by 50 sccm of hydrogen. The plasma polymer film thickness was fixed at 100 nm. The general deposition pressure and deposition RF plasma power

Results and discussion

Fig. 3 shows the IR spectra of each sample. Any differences of spectra were not detected in the finger print region (under range of 1500 cm 1). However, OH functional group around 3500 cm 1 was increased by increasing e-beam dose. This means that the e-beam irradiation induced the formation of the single bondOH functional group on plasma polymer surface without any changes in the bulk plasma polymer thin film. From this result, we could predict the changing contact angle by HEEB irradiation [6]. Also, the single bond

Conclusions

The plasma polymer thin films were deposited by using vapor cyclohexene precursor and PECVD system. And then each plasma polymer thin film was exposed by the HEEB to modified surface functionality such as hydrophilic surface by single bondOH group. Finally, λ-DNAs were attached by the tilting technique.

FT-IR result shows only the surface change of the plasma polymer thin film such as single bondOH group of broad peak (3500 cm 1). The IR spectra did not change under the finger printing region. From these results, we

Acknowledgments

This work was supported by NRF 20072001582, NRF-20100025481 (Basic Science Research Program), NRF-20100029417 (Plasma Bioscience Research Center, SRC Program), and Samsung Research Fund, Sungkyunkwan University.

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    CNF-DNA showed C1s peaks at 287.79, 286.46, 286.11, 285.48, 284.78, and 284.22 eV corresponding to the CO, β-glycosidic, COH/COC, CC, CH/CC, and CN/CN bonds, respectively (Fig. 2(d)) (Camacho et al., 2017). Furthermore, CNF-DNA showed O 1s peaks at 531.85 and 530.94 eV corresponding to the COH/COC and CO/COOH bonds, respectively (Fig. 2(e)) (Cho et al., 2011). The N 1s spectrum of CNF-DNA (Fig. 2(f)) showed three peaks at 401.26, 399.65, and 398.88 eV corresponding to CN, OCN, and CNH2/CNH, respectively (He et al., 2020).

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