摘要:

The effects that the thermal evaporation conditions have on the roughness of aluminum-coated near-field fiber-optic probes were investigated using the high-resolution capabilities of atomic force microscopy. The coating conditions studied include the effects of background gas composition, base vacuum pressure, and aluminum evaporation rate. The effects of aging on the aluminum-coated tips were also evaluated. The results from topography measurements of the resulting aluminum film indicated that the most dramatic improvements in the tip coatings can be achieved using high aluminum evaporation rates at base vacuum pressures below10−5 Torr.These results agree with other studies on thin aluminum films and reflect a decrease in oxide formation. For demanding applications of near-field microscopy requiring maximal resolution, the results presented here indicate that it may also be necessary to reduce oxygen and/or water from the vacuum chamber prior to coating. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148836

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Optical fiber cantilevers with uniform diameters are fabricated using an etching method. Resonant frequencies of the optical fiber cantilevers with different lengths and diameters are calculated with the flexural wave theory of elastic beams. An experimental system is built for measuring the spectrum of the resonant frequencies of the optical fiber cantilever. Two optical fiber cantilevers with diameters of 8.8 and 11 &mgr;m and lengths of 568 and 776 &mgr;m, are examined separately with the system. The measurements agree well with theory. The experiments show that the higher vibrational modes of the optical fiber cantilever can be excited with high amplitude, which is well suited for sensing purposes. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148837

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have investigated the reliability of a variety of metal coated and semiconductor tips for use in conducting atomic force microscopy experiments in an ultrahigh vacuum (UHV) environment. In order to obtain reliable conduction data we find it necessary to first clean the tips using a short argon ion sputter. Scanning transmission electron microscopy is used to image tips after the conductivity experiments and found to be very useful for assessing tip wear and interpreting conductivity data. Tip reliability is found to be strongly dependent on the sample and the experimental conditions. Wear and contamination of the tip are found to be severe problems which are related to the tip-sample adhesion. We illustrate these effects and highlight some of the common reliability problems which we encountered using specific examples. In general, we find that metal coated tips are not reliable enough to obtain repeatable data, especially if lateral forces are exerted on the tip. Homogeneous semiconductor tips, once cleaned, are found to be satisfactory and a particular contrast with experiments performed in air is that Si tips can be used reliably. In addition we find that in UHV, conduction experiments may be reliably performed even at very low applied force, of order nano-Newtons. This is a clear advantage in comparison to experiments performed in air where surface contamination is present and applied forces on the order of micro-Newtons are often required to establish stable electrical contact. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148838

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We present the design of a variable-temperature ultrahigh vacuum (UHV) scanning tunneling microscope which can be operated between 20 and 400 K. The microscope is mounted directly onto the heat exchanger of a He continuous flow cryostat without vibration isolation inside the UHV chamber. The coarse approach is performed with an inertial slider driven by the same piezo tube that is also used for scanning. The performance of the instrument is demonstrated by two different kinds of measurements: First we show topographic images of close packed metal surfaces with atomic resolution. Then, we present results from scanning tunneling spectroscopy measurements onWSe2under illumination at variable temperatures. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148839

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

This article describes the development and test of a digital control loop, to control the tip-to-specimen distance in a scanning tunneling microscope. This digital controller performs a frequency-independent linearization of the gap-to-current relationship, as well as the compensation of the undesirable capacitive coupling between the electrodes of the scan tube and the input of the current-to-voltage converter, two difficulties normally associated with analog controllers. In the described work, the control loop is implemented on an inexpensive fixed-point DSP, processing the signals at a 25 kHz sampling rate. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148840

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We present the design of a scanning force microscope and vacuum chamber for the growth and imaging of ice films in thermodynamic equilibrium and under controlled super or undersaturation. The apparatus allows measurements in the temperature range from−60to+80 °Cin a controlled water vapor atmosphere. First results on the morphology and the frictional properties of thin ice films on mica cleavage faces are presented. The films are found to grow in a two-dimensional manner, often exhibiting dendritic growth shapes. The lateral force measured on ice is higher than that observed on the surrounding substrate. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148841

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A micropositioning stage with large travel range has been designed and built. The stage combines a piezoelectric driving element, flexure pivoted multiple Scott–Russell linkage, and a parallel guiding spring. Quality engineering techniques are used to optimize the configuration of the device in order to achieve the maximum displacement gain and the minimum angular deviation. A simple open-loop compensator is applied to reduce the hysteresis of the dynamic response of the stage. The experiment shows that the stage achieved a vacuum-compatible device with a travel of greater than 100 &mgr;m, a resolution of 0.04 &mgr;m, and an angular deviation of less than 31.1 &mgr;rad. The first natural frequency of the stage is 80 Hz and the settling time is approximately 50 ms. Compared with the uncontrolled condition, the controlled hysteresis is reduced significantly. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148842

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The use of a modified scanning tunneling microscope (STM) working in controlled oxygen atmospheres to create structures on the surface of a steel sample covered with 10 nm amorphous hydrogenated carbon (a-C:H) is presented. The STM lithography experiments showed the capability of producing either &mgr;m sized hills or holes depending on the oxygen pressure and the other parameters such as feedback-settings, bias-voltage, and setpoint-current. It will be shown that the hills were hollow and consisted of a locally delaminateda-C:H film induced by a dielectric breakdown between tip and sample. This explains the observed mobility and elasticity of the hills. Assuming total relaxation of thea-C:H film within the hills yielded the ratioh/d=0.07–0.1.The measured geometries of the hills were in good agreement with the estimated ratios. The resistance of a hill formed by the local delamination ofa-C:H was measured, yielding a semiconducting behavior. The gap voltage and the total resistance decreased irreversibly, which was interpreted as a transformation of thea-C:H film within the hill to a more graphitic state. Holes were only created when all of the following conditions were fulfilled: (a)O2pressure greater than 1 bar, (b) low energy density dissipated in thea-C:H surface (no dielectric breakdown), (c) positive bias voltage⩾13 Vbetween the sample and the tip. The Fowler–Nordheim plotslog(I/U2)vs1/Ufor the lithography experiments that led to holes were characteristic for field emission of electrons from the tip. From this it was concluded that the process responsible for hole formation is reactive oxygen etching. Other possible processes have been excluded experimentally and theoretically, respectively. For lithography experiments performed with the feedback system on, it was possible to find lithography parameters leading to a reproducible creation of holes. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148843

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A multichannel spectroscopic ellipsometer based on the rotating-compensator principle was developed and applied to measure the time evolution of spectra (1.5–4.0 eV) in the normalized Stokes vector of the light beam reflected from the surface of a growing film. With this instrument, a time resolution of 32 ms for full spectra is possible. Several advantages of the rotating-compensator multichannel ellipsometer design over the simpler rotating-polarizer design are demonstrated here. These include the ability to: (i) determine the sign of thep-swave phase-shift difference &Dgr;, (ii) obtain accurate &Dgr; values for low ellipticity polarization states, and (iii) deduce spectra in the degree of polarization of the light beam reflected from the sample. We have demonstrated the use of the latter spectra to characterize instrument errors such as stray light inside the spectrograph attached to the multichannel detector. The degree of polarization of the reflected beam has also been applied to characterize the time evolution of light scattering during the nucleation of thin film diamond by plasma-enhanced chemical vapor deposition, as well as the time evolution of thickness nonuniformities over the probed area of the growing diamond film. In this article, a detailed description of calibration and data reduction for the new instrument is provided. Future applications of this instrument are expected for real time characterization of film growth and etching on patterned surfaces for microelectronics and on thick transparent substrates for large area displays and photovoltaics. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148844

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A four-point probe, suitable forin situsurface resistance and magnetoresistance (MR) measurements of ultrathin films, is described. The four-point probe head is mounted and fixed at the center of an electromagnet with the probes perpendicular to the applied magnetic field direction. The ultrathin magnetic film sample can be rotated to face the probe and moved to make contact with the probe using the sample manipulator. The resistance and MR of the magnetic ultrathin film can be measured. At the same sample position, the hysteresis loops can be measured using the surface magneto-optical Kerr effect technique. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148845

出版商:AIP    

年代:1998

数据来源: AIP