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We report on the etching of graphene devices with a helium ion beam, including in situ electrical measurement during lithography. The etching process can be used to nanostructure and electrically isolate different regions in a graphene device, as demonstrated by etching a channel in a suspended graphene device with etched gaps down to about 10 nm. Graphene devices on silicon dioxide (SiO(2)) substrates etch with lower He ion doses and are found to have a residual conductivity after etching, which we attribute to contamination by hydrocarbons.
ACS Nano 2009 Sep 22
PMID:Etching of graphene devices with a helium ion beam. 1976 3

The ion beam deposition (IBD) of rhodamine dye molecules on solid surfaces in high vacuum is explored in order to characterize the possibility of fabricating molecular coatings or nanostructures from nonvolatile molecules. Molecular ion beams with a well-defined composition are deposited on silicon oxide surfaces with a controlled kinetic energy. Photoluminescence spectroscopy and time-of-flight secondary ion mass spectrometry (TOF-SIMS) are employed in order to characterize the sample with respect to coverage, homogeneity, and the fraction of intact landed ions (soft-landing ratio). We find that homogeneous rhodamine films of defined composition can be produced at energies of 2-100 eV. The coverage is found to be proportional to the ion dose. Soft-landing is observed for energies up to 35 eV.
ACS Nano 2009 Oct 27
PMID:Electrospray ion beam deposition: soft-landing and fragmentation of functional molecules at solid surfaces. 1977 85

We report high-performance arsenic (As)-doped indium oxide (In(2)O(3)) nanowires for transparent electronics, including their implementation in transparent thin-film transistors (TTFTs) and transparent active-matrix organic light-emitting diode (AMOLED) displays. The As-doped In(2)O(3) nanowires were synthesized using a laser ablation process and then fabricated into TTFTs with indium-tin oxide (ITO) as the source, drain, and gate electrodes. The nanowire TTFTs on glass substrates exhibit very high device mobilities (approximately 1490 cm(2) V(-1) s(-1)), current on/off ratios (5.7 x 10(6)), steep subthreshold slopes (88 mV/dec), and a saturation current of 60 microA for a single nanowire. By using a self-assembled nanodielectric (SAND) as the gate dielectric, the device mobilities and saturation current can be further improved up to 2560 cm(2) V(-1) s(-1) and 160 microA, respectively. All devices exhibit good optical transparency (approximately 81% on average) in the visible spectral range. In addition, the nanowire TTFTs were utilized to control green OLEDs with varied intensities. Furthermore, a fully integrated seven-segment AMOLED display was fabricated with a good transparency of 40% and with each pixel controlled by two nanowire transistors. This work demonstrates that the performance enhancement possible by combining nanowire doping and self-assembled nanodielectrics enables silicon-free electronic circuitry for low power consumption, optically transparent, high-frequency devices assembled near room temperature.
ACS Nano 2009 Nov 24
PMID:High-performance single-crystalline arsenic-doped indium oxide nanowires for transparent thin-film transistors and active matrix organic light-emitting diode displays. 1984 77

We report a new low-cost top-down silicon nanowire fabrication technology requiring only conventional microfabrication processes including microlithography, oxidation, and wet anisotropic plane-dependent etching; high quality silicon nanowire arrays can be easily made in any conventional microfabrication facility without nanolithography or expensive equipment. Silicon nanowires with scalable lateral dimensions ranging from 200 nm down to 10-20 nm and lengths up to approximately 100 microm can be precisely formed with near-perfect monocrystalline cross sections, atomically smooth surfaces, and wafer-scale yields greater than 90% using a novel size reduction method where silicon nanowires can be controllably scaled to any dimension and doping concentration independent of large contacting regions from a continuous layer of crystalline silicon.
ACS Nano 2009 Nov 24
PMID:Top-down fabrication of sub-30 nm monocrystalline silicon nanowires using conventional microfabrication. 1985 5

Chromium silicide nanostructures are fabricated inside silicon nanopillars grown by the vapor-liquid-solid mechanism. The remarkable field-emission behavior of these nanostructures results from extensive improvement of carrier transport due to the reduced energy barrier between the metal and semiconductor layers. The results warrant consideration of chromium silicide as a potentially important contact material in future nanosystems.
ACS Nano 2009 Nov 24
PMID:Core-shell chromium silicide-silicon nanopillars: a contact material for future nanosystems. 1987 41

Silicon quantum dots (QDs) were prepared with a corona of di-n-octyl phosphine oxides, by performing hydrosilylation chemistry on the surface of hydrogen-terminated Si QDs. These novel Si QDs proved well-suited to serve as "ligands" for other semiconductor QDs, such as CdSe, by interaction of the phosphine oxide corona with the CdSe surface. A pronounced photoluminescence quenching of CdSe quantum dots was observed upon introduction of the phosphine oxide functionalized Si QDs to a CdSe QD solution. Surface functionalization of the Si QDs proved critically important to observing these effects, as conventional (alkane-covered) Si QD samples gave no evidence of electronic interactions with TOPO-covered CdSe. In a comparative system, phosphine oxide terminated oligo(phenylene vinylene) molecules acting as CdSe QD ligands provide a similar fluorescence quenching, with exciton decay kinetics supporting the formation of an electronically interacting hybrid materials system.
ACS Nano 2009 Dec 22
PMID:Functional Si and CdSe quantum dots: synthesis, conjugate formation, and photoluminescence quenching by surface interactions. 1990 57

The development of new and better substrates is a major focus of research aimed at improving the analytical capabilities of surface-enhanced Raman spectroscopy (SERS). Perhaps the most common type of SERS substrate, one consistently exhibiting large enhancements, is simple colloidal gold or silver nanoparticles in the 10-150 nm size range. The colloidal systems that are used most for ultrasensitive detection are generally aggregated clusters that possess "hot spot(s)" within some of the aggregates. A significant limitation of these synthetic substrates is that the "hot" aggregates are extremely difficult to create consistently or predict. Electron beam lithography (EBL) along with combinatorial spectral mapping can be used to overcome this limitation. Our previous work, and that of other researchers, invokes the special capabilities of EBL to design and fabricate periodic, highly ordered nanoparticle arrays for SERS. Building on this work, EBL, in conjunction with ancillary fabrication steps, can be used to create complex patterns that mimic random aggregates. These aggregates, unlike those created by colloidal deposition methods, can be uniquely reproduced within the resolution limits of EBL. In the work reported herein, we use a unique approach to create substrates containing a large number of randomly generated cells with different morphologies that are arrayed on silicon wafers. Instead of isolated metal nanoparticles, these structures resemble the aggregates of colloid. By spectral mapping, we investigate the SERS activity of the combinatorial arrays of cells using probe analytes. Two general categories of shapes are randomly designed in different sizes and densities into several hundred different 5 mum square cells. Following fabrication, it is shown that a SERS performance contrast of more than a factor of 44 is achieved among these cells and that the best performing cells can be cloned into uniformly high performing macropatterns of lithographically defined nanoaggregates (LDNAs). In this manner, extended LDNA surfaces with uniform 5 x 10(8) enhancement factors are created. Furthermore, the LDNAs can be further dissected and studied in an effort to increase the SERS enhancement per unit geometric substrate area.
ACS Nano 2009 Dec 22
PMID:Controllable nanofabrication of aggregate-like nanoparticle substrates and evaluation for surface-enhanced Raman spectroscopy. 1991 35

We utilize a vapor deposition setup and cross-diffusion of functionalized chlorosilanes under dynamic vacuum to generate a nearly linear gradient in surface energy and composition on a silicon substrate. The gradient can be tuned by manipulating chlorosilane reservoir sizes and positions, and the gradient profile is independent of time as long as maximum coverage of the substrate is achieved. Our method is readily amenable to the creation of gradients on other substrate surfaces, due to the use of vapor deposition, and with other functionalities, due to our use of functionalized chlorosilanes. Our gradients were characterized using contact angle measurements and X-ray photoelectron spectroscopy. From these measurements, we were able to correlate composition, contact angle, and surface energy. We generated a nearly linear gradient with a range in mole fraction of one component from 0.15 to 0.85 (34 to 40 mJ/m(2) in surface energy) to demonstrate its utility in a block copolymer thin film morphology study. Examination of the copolymer thin film surface morphology with optical and atomic force microscopy revealed the expected morphological transitions across the gradient.
ACS Nano 2009 Dec 22
PMID:Generation of monolayer gradients in surface energy and surface chemistry for block copolymer thin film studies. 1995 Sep 10

Magnetic resonance imaging of hyperpolarized nuclei provides high image contrast with little or no background signal. To date, in vivo applications of prehyperpolarized materials have been limited by relatively short nuclear spin relaxation times. Here, we investigate silicon nanoparticles as a new type of hyperpolarized magnetic resonance imaging agent. Nuclear spin relaxation times for a variety of Si nanoparticles are found to be remarkably long, ranging from many minutes to hours at room temperature, allowing hyperpolarized nanoparticles to be transported, administered, and imaged on practical time scales. Additionally, we demonstrate that Si nanoparticles can be surface functionalized using techniques common to other biologically targeted nanoparticle systems. These results suggest that Si nanoparticles can be used as a targetable, hyperpolarized magnetic resonance imaging agent with a large range of potential applications.
ACS Nano 2009 Dec 22
PMID:Silicon nanoparticles as hyperpolarized magnetic resonance imaging agents. 1995 Sep 73

Metal-assisted chemical etching (MaCE) of silicon in conjunction with shaped catalysts was used to fabricate 3D nanostructures such as sloping channels, cycloids, and spirals along with traditional vertical channels. The investigation used silver nanorods, nanodonuts along with electron beam lithography (EBL)-patterned gold nanodiscs, nanolines, squares, grids, and star-shaped catalysts to show how catalyst shape and line width directly influence etching direction. Feature sizes ranging from micrometers down to 25 nm were achieved with aspect ratios of at least 10:1 and wall roughness of 10 nm or less. This research demonstrates the potential of MaCE as a new, maskless nanofabrication technology.
ACS Nano 2009 Dec 22
PMID:Effect of catalyst shape and etchant composition on etching direction in metal-assisted chemical etching of silicon to fabricate 3D nanostructures. 1995 71


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