Search

OBJECTIVE To investigate if a self-obtained vaginal sample (SOVAS) contains sufficient DNA for a human papillomavirus (HPV) test and if the results are comparable to those obtained via cervical samples (CS) collected by a physician. METHODS One hundred and fifty-one women who had abnormal cervical smears or who were HPV-positive were enrolled. Self-sampling was done after reading instructions and watching a 2-min-long video, whereas CS was obtained with a cervical cytobrush during a gynecologic examination. RESULTS A multiplex real-time polymerase chain reaction-based assay detected the prevalence of any type of HPV to be 67.5% in the SOVAS and 57.4% in the CS, and that of high-risk (HR-) HPV to be 58.7% in the SOVAS and 48.6% in the CS. The sensitivity of detection of HR-HPV in the SOVAS was 100% (95% confidence interval [CI] -0.09 to 0.32) for high-grade squamous intraepithelial lesion, 78% (95% CI -0.09 to 0.13) for atypical squamous cells of undetermined significance or worse, and 95% (95% CI -0.01 to 0.25) for low-grade squamous intraepithelial lesion or worse, which was statistically within the non-inferiority margin compared with that of CS. CONCLUSION Our study shows that the collection of a SOVAS is feasible and it is comparable to a CS for HPV DNA testing. Future studies are required to investigate the feasibility and cost-effectiveness of a mail-delivered SOVAS for cervical cancer screening.

A field test of a 70 ㎾ heat pump system with flue gas heat recovery was performed by an experiment at theKorea Institute of Energy Research. The flue gas is exhausted from a 320 RT absorption chiller-heater in the heating season.Using this flue gas, source water of the heat pump is heated by a condensed-type heat exchanger in the chimney. Theoperating characteristics of the heat recovery heat pump system were analyzed. Based on the results of the experiments, operating maps were obtained, and an optimum operating range is suggested, in which the return and heat source watertemperature are 51 ℃ and 31 ℃ , respectively. Additionally, economic analysis of this system was conducted and about 50%energy cost savings can be expected in the heating season. Key words Condensing heat recovery(응축열회수), Flue gas(배가스), Heat recovery system(열회수 시스템), Latent heat(잠열), Condensation(응축)†Corresponding author, E-mail: yslee@kier.re.kr 기호설명COP H ： 난방성능계수 Q cond ： 응축(난방)열량 [ ㎾ ] Q evap ： 증발열량 [ ㎾ ]

Objectives: This study was conducted in order to examine the relationship between heavy metal concentrations in the soil and the level of heavy metals in the blood or urine of 216 local residents living near abandoned metal mines. Methods: Residents around abandoned metal mines were interviewed about their dietary habits, including seafood consumption, medical history, cigarette smoking, and drug history. Metal concentrations in the soil were determined by atomic absorption spectrophotometer (AA-7000, Shimadzu, Japan). Lead (Pb) and cadmium (Cd) contents in the blood or urine were analyzed by GF-AAS (AA-6800, Shimadzu). Mercury (Hg) contents in the blood were determined by means of a mercury analyzer (SP-3DS, NIC). Arsenic (As) content in the soil and urine were measured by a HG-AAS (hydride vapor generation-atomic absorption spectrophotometer). Results: The heavy metal concentrations in the soil showed a log normal distribution and the geometric means of the four villages were 8.61 mg/kg for Pb, 0.19 mg/kg for Cd, 1.81 mg/kg for As and 0.035 mg/kg for Hg. The heavy metal levels of the 216 local residents showed a regular distribution for Pb, Cd, Hg in the blood and As in the urine. The arithmetic means were3.37 µg/dl for Pb, 3.07 µg/l for Cd and 2.32 µg/l for Hg, 10.41 µg/l for As, respectively. Conclusions: As a result of multi-variate analysis for the affecting factors on the bodily heavy metal concentrations, gender and concentration in the soil (each, p

We fabricated hydrogenated microcrystalline silicon (μc-Si:H) solar cells on SnO 2 coated glass using a seed layer insertion technique. Since rich hydrogen atoms from the μc-Si:H deposition process degrade the SnO 2 layer, we applied p-type hydrogenated amorphous silicon (p-a-Si:H) as a window layer. To grow the μc-Si:H layer on the p-a-Si:H window layer, we developed a seed layer insertion method. We inserted the seed layer between the p-a-Si:H layer and intrinsic bulk μc-Si:H. This seed layer consists of a thin hydrogen diluted silicon buffer layer and a naturally hydrogen profiled layer. We compared the characteristics of solar cells with and without the seed layer. When the seed layer was not applied, the fabricated cell showed the characteristics of a-Si:H solar cell whose spectral response was in a range of 400–800 nm. Using the seed layer, we achieved a μc-Si:H solar cell with performance of V oc =0.535 V, J sc =16.0 mA/cm 2 , FF=0.667, and conversion efficiency=5.7% without any back reflector. The spectral response was in the range of 400–1100 nm. Also, the fabricated device has little substrate dependence, because a-Si:H has weaker substrate selectivity than μc-Si:H.

Bend Me, Stretch Me In the push toward flexible electronics, much research has focused on using organic conducting materials, including light-emitting diodes (LEDs), because they are more readily processed using scalable techniques. Park et al. (p. 977 ) have developed a series of techniques for depositing and assembling inorganic LEDs onto glass, plastic, or rubber. Conventional processing techniques are used to connect the LEDs in order to create flexible, stretchable displays, which, because the active diode material only covers a small part of the substrate, are mostly transparent.

This paper describes experimental and theoretical studies of the mechanics of free-standing nanoribbons and membranes of single-crystalline silicon transfer printed onto patterned dielectric layers. The results show that analytical descriptions of the mechanics agree well with experimental data, and they explicitly reveal how the geometry of dielectric layers (i.e., the width and depth of the features of relief) and the silicon (i.e., the thickness and widths of the ribbons) affect mechanical bowing (i.e., ‘‘sagging’’) in the suspended regions of the silicon. This system is of practical importance in the use of semiconductor nanomaterials for electronic devices, because incomplete sagging near defects in gate dielectrics provides a level of robustness against electrical shorting in those regions which exceeds that associated with conventional deposition techniques for thin films. Fieldeffect transistors formedusingsilicon nanoribbonstransferred onto arangeofultrathingate dielectrics, includingpatterned epoxy, organic self-assembled monolayers, and HfO2, demonstrate these concepts.

A p-a-Si:H layer, deposited by a photo-assisted chemical vapor deposition (photo-CVD) method, was adopted as the window layer of a hydrogenated microcrystalline silicon (μc-Si:H) solar cell instead of the conventional p-μc-Si:H layer. We verified the usefulness of p-a-Si:H for the p-layer of the μc-Si:H solar cell by applying it to SnO 2 -coated glass substrate. It was found that the quantum efficiency (QE) characteristics and solar cell performance strongly depend on the p-a-Si:H layer thicknesses. We applied boron-doped nanocrystalline silion (nc-Si:H) p/i buffer layers to μc-Si:H solar cells and investigated the correlation of the p/i buffer layer B 2 H 6 flow rate and solar cell performance. When the B 2 H 6 flow rate was 0.2 sccm, there was a little improvement in fill factor (FF), but the other parameters became poor as the B 2 H 6 flow rate increased. This is because the conductivity of the buffer layer decreases as the B 2 H 6 flow rate increases above appropriate values. A μc-Si:H single-junction solar cell with ZnO/Ag back reflector with an efficiency of 7.76% has been prepared.

A 10-bit driver IC for laser projection full high-definition TV (HDTV) applications using a spatial optical modulator (SOM) has been developed. For high-speed data transfer between the timing controller and driver IC, the driver IC adopts a mini-LVDS interface that operates up to 400 Mbps. To reduce the chip area, a digital-to-analog converter (DAC) structure including a 7-bit resistor-string DAC and a unity-gain buffer, which has a 3-bit linear DAC, is proposed. The area of the proposed DAC is 40% smaller than that of the typical 8-bit resistor-string DAC. The driver IC, which has 546 channels, is fabricated using a 0.35-mum CMOS process, and its area is 21 700 mum times 3 000 mum. The measured INL and DNL of the output voltages are less than 0.13 LSB, and the settling time is 1.93 mus with 40 pF capacitive loads. The output voltage deviation of the driver IC is achieved as 1.3 mV by compensating the nonuniformity among output channels.

Defects on a reticle are inspected, reviewed, and repaired by different tools. They are located by automated optical inspection (AOI); however, if the characteristic size of defects is similar to that of light and electron beam wavelengths, they are often unclassified or misclassified by AOI. Atomic force microscopes (AFM) along with electron microscopes are used for investigating defects located by AOI to distinguish false defects from real defects and effectively classify them. Both AFM and electron microscopes provide high resolution images. However, electron microscopy is known to be destructive and have less accuracy in 3rd dimension measurement compared to AFM [1]. On the other hand, AFM is known to have low throughput and limited tip life in addition to requiring significant effort to finding the defects. These limitations emanate from having to perform multiple large scans to find the defect locations, to compensate for stage coordinate inaccuracies, and to correct the mismatch between the AFM and the AOI tools. In this work we introduce automatic defect review (ADR) AFM for defect study and classification of EUV mask reticles that overcomes the aforementioned limitations of traditional AFM. This metrology solution is based on an AFM configuration with decoupled Z and XY scanners that makes it possible to collect large survey images with minimum out of plane motion. To minimize the stage errors and mismatch between the AFM and the AOI coordinates, the coordinates of fiducial markers are used for coarse alignment. In addition, fine alignment of the coordinates is performed using enhanced optical vision on marks on the reticle. The ADR AFM is used to study a series of phase defects identified by an AOI tool on a reticle. Locating the defects, imaging, and defect classification are performed using the ADR automation software and with the throughput of several defects per hour. In order to preserve tip life and data consistency, AFM imaging is performed in non-contact mode. The ADR AFM provides high throughput, high resolution, and non-destructive means for obtaining 3D information for defect review and classification. Therefore this technology can be used for in-line defect review and classification for mask repair.

Atomic force microscopes (AFM) have been widely used for precision metrology. However, most conventional AFM revealed their limits in accuracy due to the inferior characteristics of piezoelectric tube scanner. In order to overcome these limits, we introduced the new XE AFM, which has a z-scanner separated from the x–y scanner. With the new XE AFM, we were able to successfully measure dimensions of pole-tip recession (PTR) in magneto-resistance (MR) head, which had been difficult to be measured by conventional AFM. In addition, we found that it is important to use non-contact AFM, not tapping mode AFM for accurate measurement of PTR since the tapping force can depress the pole-tip region and make the PTR value appear larger than it actually is. In order to confirm this phenomenon, we performed force modulation microscopy and contact mode AFM at various force set points.

We have developed a new atomic force microscope (AFM), with a z scanner independent of the xy scanner. Unlike conventional AFM systems, our xy scanner moves only the sample in the xy plane, while the z scanner controls the AFM probe along the z axis. The xy scanner is a single module parallel-kinematics flexure stage that guarantees high orthogonality and minimum out-of-plane motion. The z scanner is a one-dimensional flexure stage with negligible out-of-axis motion. Separating the z scanner from the xy scanner practically eliminates the x–z cross coupling problem inherent in conventional AFMs. Furthermore, the z servo response is no longer limited by the xy scanner characteristics, allowing us to make full use of our high performance z scanner. Our system uses the laser beam bounce detection method, and only the cantilever and the photodetector are mounted on the z scanner to realize a lightweight probing unit. We have devised a unique design such that the photodetector signal measures only the cantileve...

We report a noninvasive high speed voltage sampling technique by using atomic force microscope. This technique is based on the mixing of interaction forces between a conductive probe-tip and a device interconnect line. Mixing phenomena allow measurements of signals with frequencies far above the mechanical resonance frequency of the cantilever. To increase the sensitivity and stability of the signal detection in ambient environment, we employed a delayed pulse sampling and lock-in amplifier detection of the small electrostatic force resulting from a high frequency signal on integrated circuits. The probing pulse is first modulated by a low frequency sinusoidal voltage using a double-balanced diode mixer. The junction between probe-tip and integrated circuit interconnection line works as the second mixer which mixes the probing voltage with the high speed waveform in the interconnection line. This technique can sense voltage signals even through a passivation layer of a 0.5 μm in thickness. We sampled an 8...

As the feature size of the semiconductor device is becoming increasingly smaller and the transistor has become three-dimensional (e.g. Fin-FET structure), a simple Line Edge Roughness (LER) is no longer sufficient for characterizing these devices. Sidewall Roughness (SWR) is now the more proper metric for these metrology applications. However, current metrology technologies, such as SEM and OCD, provide limited information on the sidewall of such small structures. The subject of this study is the sidewall roughness measurement with a three-dimensional Atomic Force Microscopy (AFM) using tilted Z scanner. This 3D AFM is based on a decoupled XY and Z scanning configuration, in which the Z scanner can be intentionally tilted to the side. A sharp conical tip is typically used for imaging, which provides high resolution capability on both the flat surfaces (top and bottom) and the steep sidewalls.

Amorphous silicon (a-Si:H) solar cell fabricated on zinc oxide (ZnO) has poor fill factor (FF) resulting from a high resistive contact between ZnO and p-type amorphous silicon carbide (p-a-SiC:H) films. This is due to the existence of a wide depletion region in the p-a-SiC:H adjacent to the ZnO/p-a-SiC:H interface. To overcome this contact problem, an amorphous tungsten oxide (WO 3 ) layer was inserted between ZnO and p-a-SiC:H. It was found that the insertion of the WO 3 layer improves the cell performance by reducing series resistance. Since this layer has higher optical band-gap (3.35 eV) than a-SiC:H (2.1 eV), there was no change of current density in short wavelength regions. A radio-frequency magnetron sputtering apparatus was used to deposit ZnO:Al on glass. The structure of the cells was ZnO:Al (800 nm)/n-a-WO 3 (4 nm)/p-a-SiC:H (10 nm)/i-a-Si:H (270 nm)/n-a-Si:H (30 nm)/Al (100 nm). As a result of the WO 3 insertion, the efficiency of the solar cell enhanced from 6.89% to 7.45%.

Flexible and lightweight amorphous silicon (a-Si:H) based thin-film solar cells on surface-textured glass-fabric reinforced inorganic-organic hybrid materials (hybrimer) composite films are developed in a superstrate configuration. The flexible and transparent film for the substrate was fabricated by impregnation and lamination of a woven glass-fabric with an epoxy-oligosiloxane based hybrimer on glass used as a temporary substrate. The epoxy hybrimer film showed high optical transparency of more than ∼90% for wavelengths above 500nm and light scattering property. In order to improve light trapping, the surface texture of the film was replicated from a master texture of Asahi U-type glass by nanoimprint lithography. The fabricated cell was a single junction structure of ZnO:Al/p-μc-Si:H/p-a-SiC:H/i-a-Si:H/n-μc-Si:H/Al on the flexible film, and the thickness of i layer is ∼300 nm. The flexible a-Si:H solar cell on surface-textured expoxy hybrimer film showed an conversion efficiency of 6.4%.

Purpose To compare compliance, toxicity, and outcome of weekly and triweekly cisplatin administration concurrent with radiotherapy in locally advanced cervical cancer. Methods and Materials In this open-label, randomized trial, 104 patients with histologically proven Stage IIB–IVA cervical cancer were randomly assigned by a computer-generated procedure to weekly (weekly cisplatin 40 mg/m 2 , six cycles) and triweekly (cisplatin 75 mg/m 2 every 3 weeks, three cycles) chemotherapy arms during concurrent radiotherapy. The difference of compliance and the toxicity profiles between the two arms were investigated, and the overall survival rate was analyzed after 5 years. Results All patients tolerated both treatments very well, with a high completion rate of scheduled chemotherapy cycles. There was no statistically significant difference in compliance between the two arms (86.3% in the weekly arm, 92.5% in the triweekly arm, p > 0.05). Grade 3–4 neutropenia was more frequent in the weekly arm (39.2%) than in the triweekly arm (22.6%) ( p = 0.03). The overall 5-year survival rate was significantly higher in the triweekly arm (88.7%) than in the weekly arm (66.5%) (hazard ratio 0.375; 95% confidence interval 0.154–0.914; p = 0.03). Conclusions Triweekly cisplatin 75-mg/m 2 chemotherapy concurrent with radiotherapy is more effective and feasible than the conventional weekly cisplatin 40-mg/m 2 regimen and may be a strong candidate for the optimal cisplatin dose and dosing schedule in the treatment of locally advanced cervical cancer.

The first generation AFM based on piezoelectric tube scanners has high spatial resolution and performs well in qualitative measurements. However, it suffers from poor repeatability and accuracy due to the background curvature and crosstalk between the x-y-z axes, making it inadequate for quantitative metrology. We developed a new AFM platform with a x-y flexure scanner, decoupled from the z scanner, which has a highly orthogonal and flat scan. The high speed z scanner with minimized drive mass provides a fast z servo response, making true non-contact AFM practical. The new AFM can also be used in critical angle measurements of microstructures such as reflective LCD display substrates. The design concept of the new AFM was utilized to measure under-cut structures by intentionally changing the angle of the z scanner, enabling the measurement and imaging of undercut structures as well as vertical sidewalls for the first time in AFM history.

The structural evolution during heteroepitaxial growth of ZnO/sapphire(001) by radio-frequency magnetron sputtering has been studied using real-time synchrotron x-ray scattering. The two-dimensional (2D) ZnO(002) layers grown in the initial stage are highly strained and well aligned to the substrate having a mosaic distribution of 0.01° full width at half maximum (FWHM), in sharp contrast to the reported transition 2D layers grown by molecular-beam epitaxy. With increasing film thickness, the lattice strain is relieved and the poorly aligned (1.25° FWHM) three-dimensional (3D) islands are nucleated on the 2D layers. We attribute the 2D–3D transition to the release of the strain energy stored in the film due to the film/substrate lattice mismatch.

Flexible, stretchable, and spanning microelectrodes that carry signals from one circuit element to another are needed for many emerging forms of electronic and optoelectronic devices. We have patterned silver microelectrodes by omnidirectional printing of concentrated nanoparticle inks in both uniform and high–aspect ratio motifs with minimum widths of approximately 2 micrometers onto semiconductor, plastic, and glass substrates. The patterned microelectrodes can withstand repeated bending and stretching to large levels of strain with minimal degradation of their electrical properties. With this approach, wire bonding to fragile three-dimensional devices and spanning interconnects for solar cell and light-emitting diode arrays are demonstrated.

Charge trapping induced by hot carriers in a metal–oxide–semiconductor capacitor was studied with a scanning capacitance microscope (SCM). The local charge trapping/detrapping and the readout of the trapped charge in SiO2 was performed using a SCM combined with an atomic force microscope. When applying a voltage between the conductive probe tip and the p-type silicon substrate, hot carriers injected from silicon substrate into the SiO2 generated a positive trapped charge in the 10-nm-thick SiO2 layer. The resulting shift in capacitance–voltage (C–V) curves due to the locally trapped charge was measured by the high-frequency C–V measurement. For an application to the ultrahigh density data storage field, we investigated how the charge trapping and detrapping characteristics depend on the writing speed and bias voltage.

Self refresh current in modern DRAMs is becoming more difficult problem to handle because the decreasing cell transistor size has a negative effect on the uniformity of capacitor charge. In order to solve this issue, adaptive self refresh(ASR) scheme has been developed. A dual period based refresh is performed in the ASR scheme to reduce power dissipation using row register information. The row register information is adaptively modified according to the cell data retention characteristics. When DRAM enters self refresh mode, only the rows which were activated for write are tested using internal refresh test circuits. The test results are used to choose the appropriate period for the dual period base self refresh operation. This paper demonstrates 512M mobile SDRAM utilizing this adaptive self refresh(ASR) capability to minimize standby power to 150 uA @85degC while maintaining chip area of the conventional scheme using the same process technology.

A stereo sound generation apparatus and method of reproducing multi-channel sound input signals through two-channel speakers. The stereo sound generation apparatus includes: a preprocessing filter unit to reduce correlation between two-channel audio signals from among multi-channel audio signals and to generate a presence perception, a virtual speaker filter unit to convert the two-channel audio signals output from the preprocessing filter unit into a virtual sound source at a predetermined position, a signal correction filter unit to correct a signal characteristic between remaining multi-channel audio signals excluding the two-channel audio signals, and the two-channel audio signals output from the virtual speaker filter unit, and an addition unit to add signals to be output to a first channel from among the multi-channel audio signals output from the virtual speaker filter unit and the signal correction filter unit, and to add signals to be output to a second channel from among the multi-channel audio signals output from the virtual speaker filter unit and the signal correction filter unit.

A thermally evaporated molybdenum oxide (MoO3) film was used as a window layer of a hydrogenated amorphous silicon (a-Si:H) solar cell instead of the conventional p-type hydrogenated amorphous silicon carbide (p-a-SiC:H) film. The short circuit current density (JSC) and fill factor were increased due to the wide optical band gap and high conductivity of the MoO3 film. As a result, the conversion efficiency of the fabricated MoO3 solar cell was increased to 6.21% compared to the typical a-Si:H solar cell (5.97%).

Methods Epithelial ovarian cancer (n=69), borderline tumor (n=18), benign tumor (n=10) and normal ovary tissues were obtained after operation. SPARC protein expression was examined using immunohistochemistry. With a retrospective review, patients’ characteristics and slide samples were analyzed. Results Cytoplasmic SPARC immunoreactivity was observed in stromal cells in nearly all cases of normal ovary, benign and borderline tumors (100%, 94.7%, and 100%). In contrast, SPARC was detected in the stroma of 63.8% (44/69) and the score of immunoreactivity was signifi cantly reduced in malignant tumors ( P

Publisher Summary This chapter discusses that in the early years the rate of success in the groups that pioneered the new era, with the scanning tunneling microscopy (STM), was limited by the technical difficulties associated with the new instrument. It discusses that the STM is a viable instrument for studying the conducting surfaces with atomic resolution. Since then, the field has experienced a tremendous increase in popularity. The chapter also discusses STM instrumentation. It describes the fundamental application of the STM: imaging and spectroscopy in both ultra-high vacuum (UHV) and ambient environments. The most convenient STM mode is operation in air— that is, the air-STM is often used for inert samples. The most stringent STM mode is operation in ultrahigh vacuum— that is, the UHV-STM is required for accurate and reliable studies of clean surfaces. The design concepts of the two instruments are quite similar, but the construction and operation of the air-STM is simpler by far. Acoustic coupling through the air is always present in the air-STM; however, the air-STM, with its compact and rigid form, is less sensitive to mechanical vibrations. The chapter also presents theoretical analysis of the systems for feedback control and vibration isolation as applied to STM. It is possible to design the STM without this rigorous calculation of the behavior of the feedback and isolation systems, but the analysis allows improving the performance of the STM when it is constrained to operate under specific conditions. It discusses typical problems and difficulties that are encountered in operating an STM together with possible remedies and improvements.

This letter presents approaches for assembly and electrical interconnection of micro/nanoscale devices into functional systems with useful characteristics. Transfer printing techniques provide deterministic control over an assembly process that occurs prior to or simultaneously with a soft lithographic molding step that defines relief features in a receiving polymer. Filling these features with conducting materials that are processable in the form of liquids or pastes yields integrated interconnects and contacts aligned to the devices. Studies of the underlying aspects and application to representative systems in photovoltaics and solid state lighting indicators provide insights into the process and its practical use.

A scanning capacitance microscope was used to study the photoenhanced minority-carrier contribution to the capacitance of the metal-oxide-semiconductor (MOS) capacitor at high frequencies. When a light is induced over the semiconductor surface, electron-hole pairs are generated and recombined. This steady-state generation-recombination process yields the temporary source of minority carriers, and the inversion layer underneath the oxide layer can respond to very fast-varying ac bias. We measured the differential capacitance (dC/dV) of the MOS capacitor under various light intensities, and observed a peak at the inversion region where the amplitude increased as the irradiation intensity increased. By integrating dC/dV with respect to V, we obtained C–V curves in which the capacitance of the depletion region recovered its value up to that of the accumulation region as the light intensity increased. We also observed that the C–V curves shifted in one direction under irradiation which we believe is due to the...

This article describes the design of a scanning tunneling microscope (STM) which is suitable for surface science work. Various concepts in mechanical structure and electronic circuitry of the STM have been pursued to optimize its performance. This STM has been designed especially to meet the requirement of in situ sample preparation and sample transfer in ultrahigh vacuum. The electronics of this STM are capable of taking simultaneous images with opposite polarities of tunneling voltages.

We present several images of the Si(111)7\ifmmode\times\else\texttimes\fi{}7 reconstruction showing the effects of simultaneous tunneling from more than one atom on the tip. The observed topographies are described as a superposition of two 7\ifmmode\times\else\texttimes\fi{}7 adatom patterns coming from a double tip, with a variety of distances between the two tips. Tips placed as closely as 3 A\r{} can still produce two distinct images, demonstrating that each image originates from a single atom on the tip.

The theories of the feedback and vibration isolation systems have been developed to illuminate the essential points in the design and operation of the scanning tunneling microscope (STM). By analyzing a delay differential equation, we can understand the behavior of feedback and estimate the necessary gain and time constant for the best performance of the STM. Design considerations for a vibration isolation system consisting of spring suspension and magnetic damping are discussed with theoretical optimization.

We present scanning tunneling microscope images that confirm a 1 3 ML adatom model for the Ga induced 3 × 3 reconstruction of Si(111). We have also identified the bonding site of the Ga adatoms in this structure as the threefold site above second layer Si atoms. The images also show the presence of defects that arise from Si adatom replacement.

Simultaneous imaging by multiple atomic tips in scanning tunneling microscopy has the effect of superimposing displaced images, which for a two-atom tip may appear as a doubling of atoms. In this paper we present spectroscopic images where the doubling is voltage dependent. We interpret this effect by proposing a tunneling tip with two protruding chemically different atoms. The relative contribution of each atom to the total current is proportional to the atoms' local density of states that can participate in tunneling. If the two protruding tip atoms are chemically different, then the contribution of each tip, and thus the doubling of the image, can be voltage dependent.

SUMMARY We have used scanning tunnelling microscopy (STM) to study changes in the structure of the Si(111) surface induced by deposition of the group III metals In and Ga. For both metals, several different ordered reconstructions are seen as a function of coverage. The STM images provide new structural information on each of these reconstructions. With In metal deposition, we have seen the surface reconstructions √3×, √3, √31× √31, √7×√3 and 4×1 as the coverage increases. In the case of Ga on Si(111), we have studied structures that exist up to 0·7 ML. At 1/3 ML, there is a √3×√3 structure identical to that of In. Above 0·3 ML there is a different phase that may correspond to the (6·3times6·3) RHEED pattern reported in this coverage range. This surface tends to grow as triangular islands at higher coverages.

The images from the scanning tunneling microscope (STM) can be improved with digital filtering using the fast Fourier transform. In this communication we discuss the noise characteristics for images taken in air with the STM. The STM images are significantly enhanced if we assume the noise has an 1/f characteristic and use a Weiner optimal filter to remove this type of noise.

Tilt boundaries have been observed on the (0001) surface of graphite by scanning tunneling microscopy (STM). Rotation angles about the c axis of 6.5°, 8°, and 19° were found, indicating no preferential orientation of grains in the basal plane of graphite. The grain boundary region between crystallites appears disordered with a width varying between 10 and 100 A. Moire patterns are observed near grain boundaries when multiple tips scanning over different grains contribute to the image simultaneously. Such images support the theory that multiple isolated tips, occasionally hundreds of angstroms apart, can contribute to STM images.

Images of graphite have been recorded with a scanning tunneling microscope operating in air at ambient pressure. The results, which are in agreement with theory and previous experiments in vacuum, confirm that with a surface such as graphite the tunneling microscopy in air can be used to examine the geometry of the surface with a resolution that is less than 2 A.

The structure of different reconstructions of Sn on Si(111) has been studied by scanning tunneling microscopy. For less than a monolayer (ML) of Sn, three reconstructions are seen with 7×7, 7/8 × 7/8 , and 2 7/8 ×2 7/8 periodicities. The 7×7 structure is similar to that of the clean surface. The 7/8 × 7/8 phase is a (1)/(3) ML array of adatoms similar to that of Al, Ga, or In on Si(111). The 2 7/8 ×2 7/8 structure is twofold symmetric with three possible orientations on the surface giving the threefold symmetry apparent in the low‐energy electron diffraction pattern. All three surface phases coexist above 0.3 ML.

The behavior of gallium on the Si(100) surface has been studied with scanning tunneling microscopy at low metal coverages. The Ga atoms are more mobile on Si(100) than on Si(111) under the same conditions. At less than 0.1 monolayer, the Ga atoms line up in rows parallel to the Si dimerization direction with a two unit cell periodicity. At higher metal densities, these rows are organized into areas of 3×2 two‐dimensional order. The relevance of these results to studies of the initial stages of growth of GaAs on Si is discussed.

The scanning tunneling microscope(STM) has the capability of mapping the topography of a surface with unprecedented resolution in both vertical and lateral directions. STM has been used to obtain real space images of individual atoms on a surface. In this paper we review the principles and technical aspects of STM, and give some examples of its applications both in air and vacuum. These include images of graphite, silicon, and indium on silicon. Several techniques of digital image processing developed to facilitate the analysis of STM data are also described.

The simple metal indium is known to induce different reconstructions of the silicon (111) surface in the range of metal coverages below one monolayer (1 ML). We have studied both the $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ and the 4\ifmmode\times\else\texttimes\fi{}1 reconstructions with scanning tunneling microscopy. Images of the $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ surface are consistent with $\frac{1}{3}$ ML of In adatoms resting in threefold sites. The higher-coverage 4\ifmmode\times\else\texttimes\fi{}1 surface consists of large reconstructed terraces often bounded by abrupt, stepped edges. Growth of flat metal islands is also seen around 1 ML.