Fig. 1 Schematic illustration of the deposition of ceramic thin film from aqueous solution on SAMs
Nanoscale science and technology relies on control of phenomena occurring at the molecular and meso-structural level. In one manifestation of such control, techniques for the synthesis of ceramic thin films from aqueous solutions at low temperatures (chemical bath deposition, CBD) are emerging as possible alternatives to vapor-phase and chemical-precursor techniques, which usually involve high-temperature processing steps. In addition to being carried out at temperatures below 100 oC and allowing the use of substrates that are unstable at high temperature, the equipment is simple and inexpensive since neither vacuum nor high processing temperature are needed. The simple equipment setup also enables coating of over-sized substrates. Moreover, depositions from aqueous media are environmentally benign and do not rely on line-of-sight deposition, so that powders and complex-shaped substrates can be coated or prepared.
A newer technique in research on low-temperature deposition of ceramic thin films has been developed, which is based on the use of organic self-assembled monolayers (SAMs) to promote film deposition (a bio-inspired process). With different surface functional groups, different type of SAMs are found to promote the deposition of different ceramic thin films. In addition to deposit ceramics on the SAMs, it is also possible to deposit noble metals electrolessly. In other words, SAMs can effectively change the surface properties of various substrates and enable the fabrication of new materials.
Fig. 1 Schematic illustration of the deposition of ceramic thin film from aqueous solution on SAMs
SAMs are also known to anchor on a variety of substrates including metals, oxides, and polymers and can be removed selectively by a direct photo-chemical process. Alternatively, a dip-pen process, nano-grafting, or site-selective ion sputtering of SAMs can also be explored. In short, it is possible to prepare nano-patterned and/or compositionally graded thin-film devices on various rigid or flexible substrates. These developments should enable the SAMs approach to have a broader technological impact on applications on the semiconductor processing.
Fig. 2 Nitrogen map of patterned amino-SAMs on glass.
Fig. 3 Site-selective growth of Au on patterned amino-SAMs on glass.
In order to selectively immobilize molecules on SAMs, the surface properties need to be tailored to match the properties of the materials. Using the concept of mixing functional groups with opposite properties, surfaces with arbitrary iso-electric point (IEP) can be prepared.
Fig. 4 Zeta-potential of SAMs with mixed functional group as a function of environmental pH.
One of the key factors in the field of nano-technology is the microcharacterization of materials and the understanding of interactions at atom/molecular level. These subjects (surface analysis techniques, electron microscopes, etc.) are used extensively to understand and improve the synthesis and processing of materials.
Fig. 5 (A) TEM image of TiO2 nanowire, (B) HREM image, and (C) its diffraction pattern.
Fig. 6 Electron Spectroscopic Image of TiO2 on Al2O3.
In responding to the need of profiling multi-layered organic thin-film electronics with high depth-resolution, high-energy buckminsterfullerene (C60) ion guns were constructed and used in conjunction with a low-energy single-atomic ion gun to sputter the surface layer away. Owing to the high surface-sensitivity of x-ray photoelectron spectrometry (XPS), the in situ mixed-ion-sputtering yield high depth-resolution in the profiling of organic electronics. Using this novel technique, the intrinsic degradation mechanism of OLED is observed directly. In addition, the correlation between fabrication process, microstructure, and device performance is studied.
Fig. 7 Depth profile of organic light-emitting diode device.
Fig. 8 Depth profile of inverted polymeric solar-cell.
By combining the high depth-resolution of C60 ion slicing and high lateral-resolution of SPM, 3D molecule distribution of bulk heterojunction is observed. Since SEPM is used to generate the contrast of the difference in contact potential, the resulting 3D volume image contains 4th physical dimension in work function.
Fig. 9 3D volume image of a bulk heterojunction. (click the image for full resolution, ~50MB each)
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Anton Paar SurPASS Electro-Kinetic Analyzer (EKA) The instrument is used for measuring the zeta-potential of bulk materials. This zeta-potential is important to predict the stability if colloidal suspensions and the tendency to agglomerate. |
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Brookhaven 90Plus/ZetaPALs Dynamic Light Scattering (DLS) Based on the dynamic light scattering (DLS), this instrument can be used to determine the particle size and its zeta-potential. Comparing with the electro-kinetic analyzer (EKA) like the SurPASS, this instrument is mainly for nano materials. Comparing with observing the particle size directly with electron microscopes, DLS is quick and non-destructive. |
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PHI VersaProbe XPS Microprobe X-ray Photoelectron Spectrometry (XPS), a.k.a. Electron Spectroscopy for Chemical Analysis (ESCA) In a ultra-high vacuum (UHV) chamber (1E-10 torr), photoelectrons are excited with X-ray. As the escape depth is shallow, the information came from the top few nm. The is important in studying the out-most chemical composition and chemical structure of materials. Combine the the sputtering gun (Ar and/or C60), one can slowly remove the surface and profile the depth. Training Material of XPS Operation Notes Training Video [part 1] [part 2] [part 3] [part 4] |
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FEI Nova200 NanoSEM Scanning Electron Microscope (SEM) Using a electron beam, surface structures can be observed directly with nm spatial resolution. With the high-resolution low-vacuum mode, non-conducting samples can also be observed with ~nm resolution. Combine with the X-ray Energy Dispersive Spectroscopy (XEDS), the chemical composition can also be determined. Training Material of SEM (part I) Training Material of SEM (part II) Training Material of EPMA Operation Notes |
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Veeco Innova SPM Scanning Probe Microscope (SPM) Using a varity of probes, a wide range of surface chemical, physical, mechanical, and electrical properties can be studied with high spatial resolution ( The system is sitting on a Halcyoncs Micro 40 active vibration isolation platform. The vibration level on the surface is better than 5 dB at <10 Hz and <0 dB for higher frequencies. |
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Q-SENSE E4 Qrartz Crystal Microbalance By measuing the change in freqiency of a quartz crystal resonator, mass change per unit area can be measured down to 1 ng/Hz-cm2. In addition to frequency, energy dissipation can also be measured to study the rigidity of deposited film. By using high-order overtones, the system is more stable in liquid environments and provide viscoelastic properties of the film. |
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JEOL JEM-2100F Transmission Electron Microscope (TEM), managed by the Core Facilities for Nanoscience and Nanotechnology The high-resolution electron microscope (HREM) has a resolution about angstrom. Atomic arrangements can be observed directly with this instrument. |
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High-performance parallel computing cluster This is for high-performance computing. The main system consists with 48 computing nodes. Each node has two dual-core 3GHz Woodcrest CPU and 8-32Gb fully-buffered memory. |