Jump to Content
View Cart
Top 20 Most Read Articles
May 2007
The 20 articles with the most full-text downloads during the month, in descending order.
 |
Prevention of overload in high‐vacuum systems J. Vac. Sci. Technol. A 10, 2629 (1992); http://dx.doi.org/10.1116/1.577949 (4 pages)
Full Text:
|
Download PDF
|
|||
|
Show Abstract
High‐vacuum pumps, like other compressors, have basic limitations in regard to the maximum pressure difference (and pressure ratio) and maximum mass (and volume) flow rates that they can produce. Because high‐vacuum pumps are usually made to discharge into another pump, their tolerable discharge pressure must be associated with the characteristics of the backing pump. However, it is also necessary to coordinate the performance of the high‐vacuum pump with the performance of the pumping system used for pre‐evacuation of the vacuum chamber. The traditional concept of a single absolute value for the crossover pressure used for the initiation of high‐vacuum pumping is fundamentally incorrect because it is not based on a clear mass flow limitation. To prevent overloading high‐vacuum pumps during and immediately after switching from pre‐evacuation to high‐vacuum pumping, a simple rule must be observed: the crossover must be performed when the gas mass flow from the vacuum chamber is less than the maximum throughput capacity of the high‐vacuum pump. Typically, at the end of the pre‐evacuation period, there are two somewhat distinct gas quantities associated with the vacuum chamber, the gas in the space of the chamber and the quasisteady outgassing rate. There are distinct pressure decays associated with those two gas quantities. The overloading of the high vacuum pump due to the space gas can be prevented by opening the high‐vacuum valve slowly or by using a parallel low‐conductance bypass. However, the overload due to the outgassing rate can only be prevented by following the golden rule of mass flow limitation. An immediate corollary of matching mass flows is that the larger the roughing pump, the lower the crossover pressure must be. In capture pumps, the maximum throughput value for the crossover condition must be correlated with the period of regeneration (for cryopumps) or cathode replacement (for ion pumps). |
||||
|
Show PACS
|
||||
|
|
Application of porcelain enamel as an ultra-high-vacuum-compatible electrical insulator J. Vac. Sci. Technol. A 18, 1751 (2000); http://dx.doi.org/10.1116/1.582418 (4 pages)
Full Text:
|
Download PDF
|
||
|
Show Abstract
Many accelerator vacuum system components require electrical insulation internal to the vacuum system. Some accelerator components at Brookhaven National Laboratory are installed in ultra-high-vacuum systems which require the insulation to have excellent vacuum characteristics, be radiation resistant, and be able to withstand high temperatures when used on baked systems. Porcelain enamel satisfies all these requirements. This article describes the process and application of coating metal parts with porcelain enamel to provide electrical insulation. The mechanical and vacuum testing of Marman flanges coated with porcelain and using metal Helicoflex seals to form a zero-length electrical break are detailed. The use of porcelain enameled parts is attractive since it can be done quickly, is inexpensive and environmentally safe, and most of all satisfies stringent vacuum system requirements. © 2000 American Vacuum Society. |
|||
|
Show PACS
|
|||
|
|
Beyond β-C3N4—Fullerene-like carbon nitride: A promising coating material J. Vac. Sci. Technol. A 25, 633 (2007); http://dx.doi.org/10.1116/1.2738505 (12 pages) Online Publication Date: 11 May 2007
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
Even though the synthesis of super-hard-crystalline β-C3N4 remains elusive, noncrystalline CNx compounds are of increasing importance owing to their competitive properties. Especially the fullerene-like allotrope of CNx exhibits outstanding elasticity in combination with low work of indentation. This new class of thin solid film materials is characterized by a microstructure of bent and intersecting basal planes. Substitutional incorporation of nitrogen into the predominantly sp2 hybridized graphitic layer triggers the formation of curvature-inducing pentagons and interplanar cross-links at a much lower energy cost as compared to carbon-only materials. The term “fullerene-like” was coined to reflect the nanometer scale of curved structural units. Thus, fullerene-like CNx deforms by bond angle deflection and compression of the graphitic interplanar lattice spacing, whereas the superior strength of the sp2 bonds inhibits plastic deformation giving the material an extremely resilient character. The orientation, radius of curvature of basal planes, and density of cross-linking can be adjusted by the synthesis conditions. Here, the existence of significant numbers of precursor molecules is a determining factor. The inherent resiliency of the material in combination with the carbon-based beneficial friction promises to give rise to numerous tribological applications.
|
|||
|
Show PACS
|
|||
|
|
Simple versatile vacuum feedthrough J. Vac. Sci. Technol. A 25, 626 (2007); http://dx.doi.org/10.1116/1.2720847 (2 pages) Online Publication Date: 30 April 2007
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
|
|||
|
Show PACS
|
|||
|
|
Dry etching of polydimethylsiloxane for microfluidic systems J. Vac. Sci. Technol. A 20, 975 (2002); http://dx.doi.org/10.1116/1.1460896 (8 pages) Online Publication Date: 7 May 2002
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
A fluorine-based reactive ion etch (RIE) process has been developed to anisotropically dry etch the silicone elastomer polydimethylsiloxane (PDMS). This technique complements the standard molding procedure that makes use of forms made of thick SU-8 photoresist to produce features in the PDMS. Total gas pressure and the ratio of O2 to CF4 were varied to optimize etch rate. The RIE recipe developed in this study uses a 1:3 mixture of O2 to CF4 gas resulting in a highly directional and stable etch rate of approximately 20 μm per hour. Selective dry etching can be performed through a photolithographically patterned metal etch mask providing greater precision and alignment with preexisting molded features. The dry etch process is presented in this article along with a brief comparison to recently reported wet etch approaches. © 2002 American Vacuum Society. |
|||
|
Show PACS
|
|||
|
|
Ion-assisted physical vapor deposition for enhanced film properties on nonflat surfaces J. Vac. Sci. Technol. A 23, 278 (2005); http://dx.doi.org/10.1116/1.1861049 (3 pages) Online Publication Date: 10 February 2005
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
We have synthesized Ta thin films on Si substrates placed along a wall of a 2-cm-deep and 1-cm-wide trench, using both a mostly neutral Ta flux by conventional dc magnetron sputtering (dcMS) and a mostly ionized Ta flux by high-power pulsed magnetron sputtering (HPPMS). Structure of the grown films was evaluated by scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The Ta thin film grown by HPPMS has a smooth surface and a dense crystalline structure with grains oriented perpendicular to the substrate surface, whereas the film grown by dcMS exhibits a rough surface, pores between the grains, and an inclined columnar structure. The improved homogeneity achieved by HPPMS is a direct consequence of the high ion fraction of sputtered species.
|
|||
|
Show PACS
|
|||
|
|
J. Vac. Sci. Technol. A 25, 411 (2007); http://dx.doi.org/10.1116/1.2712196 (4 pages) Online Publication Date: 7 March 2007
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
A thin passivation layer of aluminum oxide was deposited on polyimide by using the combined plasma immersion ion implantation and deposition (PIII&D) and cathodic vacuum arc technique. X-ray photoelectron spectroscopy C 1s spectra showed that the carbonyl bond (CO) and ether group (C–O–C and C–N–C) presented in pristine polyimide were damaged by implantation of aluminum ions and deposition of an aluminum oxide passivation layer. O 1s and Al 2p spectra confirmed the formation of a thin aluminum oxide passivation layer. This passivation layer can be implemented in aerospace engineering where polyimide may suffer degradation from fast atomic oxygen in the low-earth-orbit environment. To test the protection of this passivation layer to energetic oxygen ions, a plasma-enhanced chemical vapor deposition system was used to simulate the oxygen-ion irradiation, and the results showed that a higher weight occurred for passivated samples compared to pristine ones. X-ray diffraction showed that Al peaks were presented on the surface region, but no aluminum oxide peak was detected. The authors then concluded that Al clusters were formed in polyimide besides aluminum oxide, which was in an x-ray amorphous state. Furthermore, contact-angle measurements showed a reduced contact angle for passivated polyimide from a pristine value of 78° to 20° by using deionized water. Several discussions have been made on the surface chemical and structural property changes by using the combined PIII&D and cathodic vacuum arc technique.
|
|||
|
Show PACS
|
|||
|
|
J. Vac. Sci. Technol. A 25, 557 (2007); http://dx.doi.org/10.1116/1.2730513 (9 pages) Online Publication Date: 20 April 2007
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
AlN films were deposited on microscopy glass slide and silicon (111 orientation) substrates by reactive ac magnetron sputtering using two nitrogen concentrations and three discharge powers of 1.5, 2.5, and 5.0 kW. X-ray diffraction studies showed that films prepared on glass and Si substrates were of hexagonal wurtizite phase. Films on Si substrates also contained small amounts of the cubic phase of AlN besides the predominantly hexagonal wurtizite phase. AlN coatings on glass substrates were textured towards the (00∙2) plane; this preferred orientation of crystals was found to decrease with increase in sputtering power. Scanning electron microscopy studies showed that AlN films prepared at higher nitrogen concentration have a microstructure consisting of pebblelike crystals, some of which were hexagonal in shape. The crystal size in the coatings increased with sputtering power and was in the range of 70–230 nm.
|
|||
|
Show PACS
|
|||
|
|
Nanosphere lithography: A materials general fabrication process for periodic particle array surfaces J. Vac. Sci. Technol. A 13, 1553 (1995); http://dx.doi.org/10.1116/1.579726 (6 pages)
Full Text:
|
Download PDF
|
||
|
Show Abstract
In this article nanosphere lithography (NSL) is demonstrated to be a materials general fabrication process for the production of periodic particle array (PPA) surfaces having nanometer scale features. A variety of PPA surfaces have been prepared using identical single‐layer (SL) and double‐layer (DL) NSL masks made by self‐assembly of polymer nanospheres with diameter, D=264 nm, and varying both the substrate material S and the particle material M. In the examples shown here, S was an insulator, semiconductor, or metal and M was a metal, inorganic ionic insulator, or an organic π‐electron semiconductor. PPA structural characterization and determination of nanoparticle metrics was accomplished with atomic force microscopy. This is the first demonstration of nanometer scale PPA surfaces formed from molecular materials. © 1995 American Vacuum Society |
|||
|
Show PACS
|
|||
|
|
Effects of in situ N2 plasma treatment on etch of HfO2 in inductively coupled Cl2/N2 plasmas J. Vac. Sci. Technol. A 25, 592 (2007); http://dx.doi.org/10.1116/1.2731361 (5 pages) Online Publication Date: 23 April 2007
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
The etch selectivity of HfO2 to Si reported to date is poor. To improve the selectivity, one needs to either increase the etch rate of HfO2 or decrease the etch rate of Si. In this work, the authors investigate the etch selectivity of HfO2 in Cl2/N2 plasmas. In particular, the effects of in situ N2 plasma treatment of HfO2 and Si were investigated. The silicon substrate was exposed to nitrogen plasma and was nitrided, which was confirmed by x-ray photoelectron spectroscopy. The nitrided Si etching was suppressed in Cl2/N2 plasmas. The effectiveness of nitridation was studied with varying the plasma power, bias power, pressure, and N2 plasma exposure time. The results show that the etch resistance increased with increased power and decreased pressure. A minimum exposure time was required to obtain etch resistant property. The applied bias power increased the etch rate of Si substrate, so it should not be used during N2 plasma treatment. Fortunately, the etch rate of HfO2 was increased by the nitridation process. Therefore, HfO2/Si selectivity can be improved by nitridation and became higher than 5 under proper exposure condition.
|
|||
|
Show PACS
|
|||
|
|
Effects of the deposition parameters on the growth of ultrathin and thin SiO2 films J. Vac. Sci. Technol. A 25, 485 (2007); http://dx.doi.org/10.1116/1.2714958 (7 pages) Online Publication Date: 2 April 2007
Full Text:
Read Online (HTML)
|
Download PDF
|
|||||||||||||
|
Show Abstract
SiO2 ultrathin and thin films have been deposited on single-crystal Si substrates by means of nonreactive radio frequency magnetron sputtering. The temperature of the substrate and the deposition times have been varied in the range of 200–500 °C and 60–14 400 s, respectively. The average deposition rate has a range of 0.5–5 nm/min and tends to decrease with the increase of the substrate temperature. Two different growth regimes may be observed for ultrathin and thin films, the transition taking place in the range of 5–10 nm depending on the substrate temperature. The roughness of the film surface and the grain dimensions do increase with the substrate temperature for short deposition times (t ⩽ 300 s), whereas their behavior is less defined for intermediate ones (300 s<t<1800 s). Finally, for long deposition times (t>1800 s) the roughness increases again with T, and its slope is higher, the higher the substrate temperature is.
|
||||||||||||||
|
Show PACS
|
||||||||||||||
|
|
The microstructure of sputter‐deposited coatings J. Vac. Sci. Technol. A 4, 3059 (1986); http://dx.doi.org/10.1116/1.573628 (7 pages)
Full Text:
|
Download PDF
|
||
|
Show Abstract
Microstructure is a critical consideration when polycrystalline or amorphous thin films are used for applications such as microcircuit metallization layers and diffusion barriers. The trend in device fabrication toward lower processing temperatures means that such coatings must often be deposited at substrate temperatures T that are low relative to the coating material melting point Tm. The structure of vapor deposited coatings grown under these conditions consists typically of a columnar growth structure, defined by voided open boundaries, which is superimposed on a microstructure which may be polycrystalline (defined by metallurgical grain boundaries) or amorphous. The voided growth structure is clearly undesirable for most applications. Its occurrence is a fundamental consequence of atomic shadowing acting in concert with the low adatom mobilities that characterize low T/Tm deposition, and its formation can be enhanced by the surface irregularities which are common to microcircuit fabrication. This paper reviews some of the recent developments in understanding the fundamental aspects of the relationship between the deposition conditions and the microstructure of sputter‐deposited thin films, with particular emphasis on the origin of the growth structure and its suppression through energetic particle bombardment. |
|||
|
Show PACS
|
|||
|
|
Thin film deposition with physical vapor deposition and related technologies J. Vac. Sci. Technol. A 21, S74 (2003); http://dx.doi.org/10.1116/1.1600450 (14 pages) Online Publication Date: 2 September 2003
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
The properties of thin films depend critically on how they are made. For the most part, thin films are assembled in ways very different from the production of bulk materials. Thin films are usually deposited on existing, bulk surfaces using techniques based on atomic or molecular scale physics and chemistry. Physical vapor deposition (PVD) of thin films relies on the removal of atoms from a solid or a liquid by energetic means, and the subsequent deposition of those atoms on a nearby surface. Variations of PVD processes include thermal evaporation, physical sputtering, laser ablation, and arc-based emission. Additional modifications to physical sputter deposition have been made to enhance the chemical and/or structural nature of the deposited films. These modifications include reactive sputter deposition, the unbalanced magnetron, collimated and ionized sputter deposition. Each of these systems and techniques will be described as well as some of the current day applications of the films produced. © 2003 American Vacuum Society. |
|||
|
Show PACS
|
|||
|
|
J. Vac. Sci. Technol. A 25, 607 (2007); http://dx.doi.org/10.1116/1.2731369 (8 pages) Online Publication Date: 27 April 2007
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
The transient temperature profile across a commercial wafer temperature sensor device in an inductively coupled Ar plasma is reported. The measured temperatures are compared to model predictions, based on a coupled plasma-wafer model. The radial temperature profile is the result of the radial profile in the ion energy flux. The ion energy flux profile is obtained by combining the Langmuir probe measurement, the ion wall flux probe measurement, and a plasma model. A methodology to estimate the ion flux profile using the sensor measurements has been validated by combining the plasma measurements, the wafer temperature measurements, and the plasma-wafer model. It is shown that with minimal heat transfer between the wafer and the chuck, the initial transient wafer temperature profile after plasma ignition can be used to estimate the ion energy flux profile across the wafer.
|
|||
|
Show PACS
|
|||
|
|
J. Vac. Sci. Technol. A 19, 1800 (2001); http://dx.doi.org/10.1116/1.1380721 (6 pages)
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
We have demonstrated large-scale production (10 g/day) of high-purity carbon single-walled nanotubes (SWNTs) using a gas-phase chemical-vapor-deposition process we call the HiPco process. SWNTs grow in high-pressure (30–50 atm), high-temperature (900–1100 °C) flowing CO on catalytic clusters of iron. The clusters are formed in situ: Fe is added to the gas flow in the form of Fe(CO)5. Upon heating, the Fe(CO)5 decomposes and the iron atoms condense into clusters. These clusters serve as catalytic particles upon which SWNT nucleate and grow (in the gas phase) via CO disproportionation: CO+CO⇒CO2+C(SWNT). SWNT material of up to 97 mol % purity has been produced at rates of up to 450 mg/h. The HiPco process has been studied and optimized with respect to a number of process parameters including temperature, pressure, and catalyst concentration. The behavior of the SWNT yield with respect to various parameters sheds light on the processes that currently limit SWNT production, and suggests ways that the production rate can be increased still further. © 2001 American Vacuum Society. |
|||
|
Show PACS
|
|||
|
|
Microstructural evolution during film growth J. Vac. Sci. Technol. A 21, S117 (2003); http://dx.doi.org/10.1116/1.1601610 (12 pages) Online Publication Date: 2 September 2003
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
Atomic-scale control and manipulation of the microstructure of polycrystalline thin films during kinetically limited low-temperature deposition, crucial for a broad range of industrial applications, has been a leading goal of materials science during the past decades. Here, we review the present understanding of film growth processes—nucleation, coalescence, competitive grain growth, and recrystallization—and their role in microstructural evolution as a function of deposition variables including temperature, the presence of reactive species, and the use of low-energy ion irradiation during growth. © 2003 American Vacuum Society. |
|||
|
Show PACS
|
|||
|
|
Reactive and anisotropic etching of magnetic tunnel junction films using pulse-time-modulated plasma J. Vac. Sci. Technol. A 25, 432 (2007); http://dx.doi.org/10.1116/1.2712192 (5 pages) Online Publication Date: 14 March 2007
Full Text:
Read Online (HTML)
|
Download PDF
|
||
|
Show Abstract
Reactive and anisotropic etching of magnetic tunnel junction (MTJ) stacked films has been achieved using pulse-time-modulated (TM) plasma. While corrosion and delamination of MTJs are observed in continuous wave discharge plasma, a chlorine pulse-time-modulated plasma achieved a high MTJ etching rate without corrosion or delamination. The authors think that the negative ions enhance the chemical reactions on the surface of magnetic films. The magnetic characteristics are also significantly improved by using TM plasma because of reduced residues and improved tapered profiles. Accordingly, TM plasma etching is a promising candidate for high-rate and damage-free MTJ etching for magnetoresistive random access memory devices.
|
|||
|
Show PACS
|
|||
|
|
Plasma deposition of optical films and coatings: A review J. Vac. Sci. Technol. A 18, 2619 (2000); http://dx.doi.org/10.1116/1.1314395 (27 pages)
Full Text:
|
Download PDF
|
||
|
Show Abstract
Plasma enhanced chemical vapor deposition (PECVD) is being increasingly used for the fabrication of transparent dielectric optical films and coatings. This involves single-layer, multilayer, graded index, and nanocomposite optical thin film systems for applications such as optical filters, antireflective coatings, optical waveguides, and others. Beside their basic optical properties (refractive index, extinction coefficient, optical loss), these systems very frequently offer other desirable “functional” characteristics. These include hardness, scratch, abrasion, and erosion resistance, improved adhesion to various technologically important substrate materials such as polymers, hydrophobicity or hydrophilicity, long-term chemical, thermal, and environmental stability, gas and vapor impermeability, and others. In the present article, we critically review the advances in the development of plasma processes and plasma systems for the synthesis of thin film high and low index optical materials, and in the control of plasma–surface interactions leading to desired film microstructures. We particularly underline those specificities of PECVD, which distinguish it from other conventional techniques for producing optical films (mainly physical vapor deposition), such as fabrication of graded index (inhomogeneous) layers, control of interfaces, high deposition rate at low temperature, enhanced mechanical and other functional characteristics, and industrial scaleup. Advances in this field are illustrated by selected examples of PECVD of antireflective coatings, rugate filters, integrated optical devices, and others. © 2000 American Vacuum Society. |
|||
|
Show PACS
|
|||
|
|
Entropic trapping and sieving of long DNA molecules in a nanofluidic channel J. Vac. Sci. Technol. A 17, 2142 (1999); http://dx.doi.org/10.1116/1.581740 (6 pages)
Full Text:
|
Download PDF
|
||
|
Show Abstract
Entropic trapping of long DNA was demonstrated in an artificial channel, fabricated by silicon based lithography and etching techniques. This channel consisted of alternating thick and thin regions, where the thickness of the thin region was as small as 90 nm. The electrophoretic mobility of long DNA molecules in this channel was measured as a function of the applied electric field. Because the radius of gyration of DNA used was much larger than the thin gap, DNA molecules were trapped when they moved from the thick to the thin region. This trapping determined the mobility of DNA in the system. Surprisingly, longer DNA molecules moved faster than shorter DNA molecules in the channel. This may be due to the fact that a larger DNA molecule has a better chance of escaping entropic traps because of the larger contact area with the thin slit. This device could enable fast manipulation and separation of long polymers. © 1999 American Vacuum Society. |
|||
|
Show PACS
|
|||
|
|
J. Vac. Sci. Technol. A 24, 1197 (2006); http://dx.doi.org/10.1116/1.2167077 (6 pages) Online Publication Date: 21 June 2006
Full Text:
Read Online (HTML)
|
Download PDF
|
|||||||||||||||
|
Show Abstract
Ultrathin coatings of fluorosilane films for silicon and polydimethylsiloxane (PDMS) nanochannels are desirable to control the hydrophobicity of the surface and reduce or prevent undesired protein adsorption or cell interactions critical for the performance of most biomedical micro/nanodevices. Surface modifications using vapor-phase deposition become increasingly important for some biomedical nanodevices and have advantages over liquid-phase deposition since the vapor phase can permeate more efficiently into silicon nanochannels. In this study, vapor-phase deposition was used to deposit ultrathin films of four fluorosilanes on silicon and PDMS and identify deposition conditions for an optimal process. The films were characterized by means of a contact angle analyzer for hydrophobicity, an ellipsometer for film thickness, and an atomic force microscope for surface roughness of these films. Results of this study and relevant mechanisms are the subject of this article.
|
||||||||||||||||
|
Show PACS
|
||||||||||||||||
This Publication
Scitation
SPIN
Scitopia
Google Scholar
PubMed