摘要:

A novel bilayer resist system consisting of a 3 nm thick titanium (Ti) layer on top of a 65 nm thick poly(methylmethacrylate) (PMMA) layer was developed for mechanical nanolithography with the atomic force microscope. The ultrathin Ti layer allowed 20 nm resolution patterning with conventional silicon cantilevers, provided a proper force-depth calibration was performed before lithography. Techniques of pattern transfer were applied to fabricate chromium nanostructures and silicon nanowires from the patterned Ti/PMMA resist.

ISSN:1071-1023    

DOI:10.1116/1.590277

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Positively and negatively charged defects and dopant atoms inn-doped GaAs(110) surfaces give rise, at room temperature, in occupied-state scanning tunneling microscope images to a bright elevation, which is surrounded by a dark depression ring. This oscillating contrast is not observed in empty-state images. A similar effect is found onn-doped GaP(110) surfaces. A simulation of the contrast induced by localized charges on (110) surfaces of III–V semiconductors suggests that the oscillation in room-temperature scanning tunneling microscope images can be explained as the image of the local potential change (screened Coulomb potential) induced by the presence of the charge.

ISSN:1071-1023    

DOI:10.1116/1.590278

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

The scanning tunneling microscope (STM) was used to modify wires of the high temperature superconductorYBa2Cu3O7−δ(YBCO) which had been fabricated by electron beam lithography in order to simulate realistic conditions of a fabrication process. The linewidth of the structures generated with the STM was well below 50 nm. For a deeper understanding of the mechanism responsible for the STM-induced modifications, the experiments were performed under ambient conditions, in ultrahigh vacuum, carbon dioxide atmosphere, and nitrogen atmosphere. Results indicate that both water and carbon dioxide are essential for the modification process on the YBCO wires. This suggests that the modification mechanism is based on a water-mediated electrochemical decomposition of YBCO in the field of the STM tip.

ISSN:1071-1023    

DOI:10.1116/1.590279

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

We describe an experiment in which a scanning tunneling microscope (STM) is employed to selectively contact a lithographically fabricated structure at 350 mK. The STM enables us to probe the structure, a Josephson-junction array, at various positions. The experiment demonstrates that it is possible to combine the use of a scanning tunneling microscope with transport measurements on lithographically fabricated structures at temperatures below 1 K. We focus on the strategy to position the tip above the structure of interest, the influence of the STM on the electronic noise, and on the effective temperature of the sample.

ISSN:1071-1023    

DOI:10.1116/1.590280

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Manipulation of macromolecules in nanometer scale is becoming an interesting research field. An approach to manipulate supramolecular assemblies is reported in this article. Linear phage viruses were aligned in one direction on atomically flat surfaces by a special method called “molecular combing.” Atomic force microscopy was used to check the results. Most of the phage strands were found to be stretch straight from one end to another. A related mechanism is also discussed.

ISSN:1071-1023    

DOI:10.1116/1.590281

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Anisotropic etching of Si with KOH is a well-known method of forming grooves in the Si surface. We report here on the use of KOH solutions for etching extremely sharp silicon tips on silicon on insulator (SOI) material. Etching of (100) silicon on SOI wafers was carried out over a wide range of reaction temperatures and KOH concentrations. Using statistical methods, we show that the factors important in the silicon etch rate are, in decreasing order of importance, reaction temperature, KOH concentration, and interaction between temperature and KOH concentration. The activation energy of etching at different KOH concentration was calculated from Arrhenius plots to be between 0.43 and 0.59 eV. In addition, in this article we report a qualitative study of the sharpness of Si tips formed by KOH etching. The sharpness increases with temperature to a critical point and then decreases at very high temperature and KOH concentration. Hydrogen bubbles formed during etching are very important in determining both etch rate and sharpness of the tips. The sharpest tip dimension was found to occur at 30% KOH and70 °Creaction temperature.

ISSN:1071-1023    

DOI:10.1116/1.590282

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

An inductively coupled plasma (ICP) source has been used to generate aCl2plasma for the etching of Si field emitters and resonators. An optimized etch condition was used to etch Si field emission devices with controllable sidewall angles as well as good uniformity for large arrays of emitters. A mask erosion technique was used to control the Si emitter profile. The sidewall angle of Si emitters increased from55°to75°as plasma pressure was increased from 0.1 to 5.0 mTorr. Sharp tips with good uniformity and a high packing density of6.25×106 tips/cm2were fabricated using 200 W ICP source power, 100 W stage power at 1 mTorr with 20 sccm ofCl2flowing and an ICP source to sample distance of 8 cm. Released Si mechanical resonators were also fabricated with a vertical etch profile and smooth surfaces. An optimized etch condition of 250 W ICP source power and 70 W stage power at 5 mTorr with 20 sccm ofCl2flow and an ICP source to sample distance of 6 cm provided an etch rate of 219 nm/min and a selectivity to a Ni–Ti mask of 26. Due to the high selectivity and etch rate, resonators and cantilevered beams as thick as 40 μm were fabricated giving improved device performance compared to thinner devices. Submicrometer Si resonators were also fabricated that were 3.1 μm thick with 1.7 μm wide comb drive fingers and 0.2 μm gaps between them.

ISSN:1071-1023    

DOI:10.1116/1.590283

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

We studied the interaction of active molybdenum field emitter arrays with molecular hydrogen and helium. Upon impact with the field emitted electrons,H2gas introduced into the system undergoes dissociation and ionization. The emitter surface is conditioned through the interaction of the hydrogen atoms and ions with molybdenum, resulting in the formation of volatile molybdenum hydrides. The volatile species are removed by the vacuum system. Surface conditioning of the tips is reflected in the reduced work function and increased electron emission. Emission enhancement reaches a maximum for total exposures of 1000–1500 L(1 L=1×10−6 Torr s)ofH2.For small exposures of helium (<1500 L), emission enhancement is also observed. Larger exposures result in significant emission degradation. We propose that the interaction ofH2with active molybdenum field emission arrays can be used as an efficient, ultrahigh vacuum compatible method forin situcleaning of the field emitter arrays.

ISSN:1071-1023    

DOI:10.1116/1.590284

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Electron emission from molybdenum field emission microcathode arrays is sensitive to the contamination of the emitters by the residual gases. We studied the effects ofO2exposures on the emission properties of several Spindt type molybdenum field emitter arrays. The arrays were exposed to 0–10 000 L ofO2and the resulting changes in electron emission characteristics were measured. Exposure of the field emitters toO2resulted in emission degradation ranging from6.2±1.3%for 10 L to99.2±0.4%for a 10 000 L exposure. The emission is recoverable for low exposures, but exposures beyond 1000 L result in permanent loss in emission current. We found that the degradation effects are similar in both the dc and pulsed modes of operation of the device. Therefore, dc mode testing can be used as an effective acceleration method in establishing the device lifetimes under various vacuum conditions.

ISSN:1071-1023    

DOI:10.1116/1.590285

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

The effect ofCO2on the emission characteristics of Spindt-type molybdenum field emission cathode arrays is investigated. Exposure of active field emitters toCO2results in emission degradation. The degradation ranges from (11.8±3.8)% for 10 L to (77.2±12.6)% for 5000 LCO2exposures. The emission loss results from the formation of molybdenum oxide on tip surfaces, resulting in an increased work function. Work function changes of 0%–7.5% have been measured. The emission changes resulting fromCO2exposures are similar to the effects observed withO2exposures. The emission degradation mechanism is the interaction of oxygen with molybdenum forming surface molybdenum oxides, thus resulting in a higher surface work function and lower emission current. The emission degradation resulting fromCO2exposure is compared to the emission enhancement produced by exposure toCH4.

ISSN:1071-1023    

DOI:10.1116/1.590240

出版商:American Vacuum Society    

年代:1998

数据来源: AIP