Journal of Vacuum Science and Technology B:Nanotechnology and Microelectronics最新文献

The creation of nanostructures on polycrystalline silicon wafer surface to reduce the solar reflection can enhance the solar absorption and thus increase the solar-electricity conversion efficiency of solar cells. The self-masking reactive ion etching (RIE) was studied to directly fabricate nanostructures on silicon surface without using a masking process for antireflection purpose. Reactive gases comprising chlorine (Cl₂), sulfur hexafluoride (SF₆), and oxygen (O₂) were activated by radio-frequency plasma in an RIE system at a typical pressure of 120-130 mTorr to fabricate the nanoscale pyramids. Poly-Si wafers were etched directly without masking for 6-10 min to create surface nanostructures by varying the compositions of SF₆, Cl₂, and O₂ gas mixtures in the etching process. The wafers were then treated with acid (KOH:H₂O = 1:1) for 1 min to remove the damage layer (100 nm) induced by dry etching. The damage layer significantly reduced the solar cell efficiencies by affecting the electrical properties of the surface layer. The light reflectivity from the surface after acid treatment could be significantly reduced to <10% for the wavelengths between 500 and 900 nm. The effects of RIE and surface treatment conditions on the surface nanostructures and the optical performance as well as the efficiencies of solar cells will be presented and discussed. The authors have successfully fabricated large-area (156 × 156 mm²) subwavelength antireflection structure on poly-Si substrates, which could improve the solar cell efficiency reproducibly up to 16.27%, higher than 15.56% using wet etching.

The authors developed a class of novel graphite-based field emitters, known as graphite field emitters inflamed at high temperature (GFEIHTs), which includes numerous edges and juts. The GFEIHT field emission characteristics are investigated in a vacuum tube (10^-7 Pa), and an anode current exceeding 2 mA is obtained. The authors also fabricated tipped-off x-ray tubes using GFEIHTs. No degradation in the anode current is observed under the operating conditions of 16.6 kV anode voltage and 160 μA anode current. The current dispersion, defined as the standard deviation (σ)/mean over 24 h, is 2.8%. The authors successfully demonstrated radiography and x-ray fluorescence spectrometry using an x-ray tube with GFEIHT.

Epithelial cells reside on specialized extracellular matrices that provide instructive cues to regulate and support cell function. The authors have previously demonstrated that substrate topography with dimensions similar to the native extracellular matrix (submicrometer and nanoscale features) significantly impacts corneal epithelial proliferation and migration. In this work, synthetic hydrogels were modified with both topographic and biochemical cues, where specified peptide ligands were immobilized within nanopatterned hydrogels. The efficient, systematic study of multiple instructive cues (peptide, peptide concentration, topographic dimensions), however, is contingent on the development of higher throughput platforms. Toward this goal, the authors developed a hydrogel array platform to systematically and rapidly evaluate combinations of two different peptide motifs and a range of nanoscale topographic dimensions. Specifically, distinct functional pegylated peptide ligands, RGD (GGGRGDSP) and AG73 (GRKRLQVQLSIRT), were synthesized for incorporation into an inert hydrogel network. Elastomeric stencils with arrays of millimeter-scale regions were used to spatially confine hydrogel precursor solutions on elastomeric stamps with nanoscale patterns generated by soft lithography. The resulting topographically and peptide-functionalized hydrogel arrays were used to characterize single cell migration. Epithelial cell migration speed and persistence were governed by both the biochemical and topographical cues of the underlying substrate.

Contrast-enhanced ultrasound (CEUS) enables highly specific time-resolved imaging of vasculature by intravenous injection of ∼2 μm gas filled microbubbles. To develop a quantitative automated diagnosis of breast tumors with CEUS, breast tumors were induced in rats by administration of N-ethyl-N-nitrosourea. A bolus injection of microbubbles was administered and CEUS videos of each tumor were acquired for at least 3 min. The time-intensity curve of each pixel within a region of interest (ROI) was analyzed to measure kinetic parameters associated with the wash-in, peak enhancement, and wash-out phases of microbubble bolus injections since it was expected that the aberrant vascularity of malignant tumors will result in faster and more diverse perfusion kinetics versus those of benign lesions. Parameters were classified using linear discriminant analysis to differentiate between benign and malignant tumors and improve diagnostic accuracy. Preliminary results with a small dataset (10 tumors, 19 videos) show 100% accuracy with fivefold cross-validation testing using as few as two choice variables for training and validation. Several of the parameters which provided the best differentiation between malignant and benign tumors employed comparative analysis of all the pixels in the ROI including enhancement coverage, fractional enhancement coverage times, and the standard deviation of the envelope curve difference normalized to the mean of the peak frame. Analysis of combinations of five variables demonstrated that pixel-by-pixel analysis produced the most robust information for tumor diagnostics and achieved 5 times greater separation of benign and malignant cases than ROI-based analysis.

The authors report the synthesis, from simple salts, and the physical characterization of superparamagnetic iron platinum nanoparticles (SIPPs) suitable for use as contrast agents in magnetic resonance imaging. The properties of these particles were determined by means of transmission electron microscopy (TEM), thermogravimetric analysis, inductively coupled plasma-optical emission spectroscopy (ICP-OES), superconducting quantum interference device (SQUID) magnetometry, and nuclear magnetic resonance relaxivity at 4.7 T. TEM showed that the diameters of the particles ranged from 9.3 to 10 nm, depending on the mole ratio of iron to platinum precursors, and on the concentration of octadecylamine (ODA) used in their preparation. The iron to platinum stoichiometry determined by ICP-OES varied from 1.4:1 to 3.7:1 and was similarly dependent on the initial mole ratios of iron and platinum salts, as well as on the concentration of ODA in the reaction. SQUID magnetometry showed that the SIPPs were superparamagnetic and had magnetic moments that increased with increasing iron content from 62 to 72 A·m²/kg Fe. The measured relaxivities of the SIPPs at 4.7 T were higher than commercially available superparamagnetic iron oxide nanoparticles, suggesting that these particles may be superior contrast agents in T₂-weighted magnetic resonance imaging.

In this study the binding and assembly of bovine serum albumin (BSA) onto three different calcium phosphate phases (hydroxyapatite, dibasic calcium phosphate dihydrate, and β-tricalcium phosphate) was investigated using a combination of X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). XPS was used to record adsorption isotherms and to quantify the amount of BSA adsorbed onto the different CaP surfaces. On all three surfaces a monolayer of adsorbed BSA was formed. ToF-SIMS was then used to investigate how the structure of BSA changes upon surface binding. ToF-SIMS data from BSA films on the three CaP surfaces showed intensity differences of secondary ions originating from both hydrophobic and hydrophilic amino acids. For a more quantitative examination of structural changes, we developed a ratio comparing the sum of intensities of secondary ions from hydrophobic and hydrophilic residues. A small, but statistically significant, increase in the value of this ratio (7%) was observed between a BSA film on hydroxyapatite versus dibasic calcium phosphate dihydrate. From this ratio we can make some initial hypotheses about what specific changes in BSA structure relate to these differences observed in the ToF-SIMS data.

The authors report a method for rapidly prototyping attonewton-sensitivity cantilevers with custom-fabricated tips and illustrate the method by preparing tips consisting of a magnetic nanorod overhanging the leading edge of the cantilevers. Micron-long nickel nanorods with widths of 120-220 nm were fabricated on silicon chips by electron beam lithography, deposition, and lift-off. Each silicon chip, with its integral nanomagnet, was attached serially to a custom-fabricated attonewton-sensitivity cantilever using focused ion beam manipulation. The magnetic nanorod tips were prepared with and without an alumina capping layer, and the minimum detectable force and tip magnetic moment of the resulting cantilevers was characterized by cantilever magnetometry. The results indicate that this serial but high-yield approach is an effective way to rapidly prepare and characterize magnetic tips for the proposed single-electron-spin and single-proton magnetic resonance imaging experiments. The approach also represents a versatile route for affixing essentially any vacuum-compatible sample to the leading edge of an attonewton-sensitivity cantilever.

Corner cube retroreflectors are objects with three mutually perpendicular reflective surfaces that return light directly to its source and are therefore extremely bright and easy to detect. In this work, we have fabricated suspended corner cube retroreflectors, 5 microns in size, consisting of a transparent epoxy core and three surfaces coated with gold as ultra-bright labels for use in a rapid, low-labor diagnostic platform. The authors have demonstrated that individual cubes are easily imaged using low-cost, low numerical aperture objectives in suspension and that they remain suspended over long periods of time. Moreover, we have demonstrated that the gold outer surfaces can be decorated with proteins, and that individual cubes can be bound to magnetic sample preparation particles bearing antibodies which recognize these proteins. The bound cubes can be imaged and tracked as they move through solution in response to an external magnetic field, and we have, as such, demonstrated the principle of the new biosensing approach.

Soft-polymer based microparticles are currently being applied in many biomedical applications, ranging from bioimaging and bioassays to drug delivery carriers. As one class of soft-polymers, hydrogels are materials, which can be used for delivering drug cargoes and can be fabricated in controlled sizes. Among the various hydrogel-forming polymers, poly(ethylene glycol) (PEG) based hydrogel systems are widely used due to their negligible toxicity and limited immunogenic recognition. Physical and chemical properties of particles (i.e., particle size, shape, surface charge, and hydrophobicity) are known to play an important role in cell-particle recognition and response. To understand the role of physicochemical properties of PEG-based hydrogel structures on cells, it is important to have geometrically precise and uniform hydrogel structures. To fabricate geometrically uniform structures, we have employed electron beam lithography (EBL) and ultra-violet optical lithography (UVL) using PEG or PEG diacrylate polymers. These hydrogel structures have been characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), optical microscopy, and attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) confirming control of chemistry, size, and shape.

A membrane that allows selective transport of molecular species requires precise engineering on the nanoscale. Membrane permeability can be tuned by controlling the physical structure and surface chemistry of the pores. Here, a combination of electron beam and optical lithography, along with cryogenic deep reactive ion etching, has been used to fabricate silicon membranes that are physically robust, have uniform pore sizes, and are directly integrated into a microfluidic network. Additional reductions in pore size were achieved using plasma enhanced chemical vapor deposition and atomic layer deposition of silicon dioxide to coat membrane surfaces. Cross sectioning of the membranes using focused ion beam milling was used to determine the physical shape of the membrane pores before and after coating. Functional characterization of the membranes was performed by using quantitative fluorescence microscopy to document the transport of molecular species across the membrane.