Amplitude dependence of image quality in atomically-resolved bimodal atomic microscopy

In bimodal FM-AFM, two flexural modes are excited simultaneously. The total vertical oscillation deflection range of the tip is the sum of the peak-to-peak amplitudes of both flexural modes (sum amplitude). We show atomically resolved images of KBr(100) in ambient conditions in bimodal AFM that display a strong correlation between image quality and sum amplitude. When the sum amplitude becomes larger than about 200 pm, the signal-to-noise ratio (SNR) is drastically decreased. We propose this is caused by the temporary presence of one or more water layers in the tip-sample gap. These water layers screen the short range interaction and must be displaced with each oscillation cycle. Further decreasing the sum amplitude, however, causes a decrease in SNR. Therefore, the highest SNR in ambient conditions is achieved when the sum amplitude is slightly less than the thickness of the primary hydration layer.Comment: 3000 words, 3 Figures, 3 supplimentary figure

Electric conductance through chemical bonding states being formed between a Si tip and a Si(111)7x7 surface by bias-voltage noncontact atomic force spectroscopy

金沢大学理工研究域　数物科学系The change in electric conductance through bonding states being formed between a Si tip and a Si surface is examined by bias-voltage noncontact atomic force spectroscopy: current I and force interaction Δf (AFM cantilever resonance frequency shift) are simultaneously measured versus bias voltage V. A peak in I-V curves appears at close tip-sample separation over adatoms at the same V as a sharp peak in the Δf-V does. The peak possibly corresponds to channel formation through bonding states induced by changing V, leading to current saturation on tunnel barrier collapse with decreasing separation

Observation of Electronic States on Si(111)-7x7 through Short-Range Attractive Force with Noncontact Atomic Force Spectroscopy

金沢大学理工研究域　数物科学系The electronic states between Si(111) and a Si(111)-(7×7) surface was observed using the noncontact atomic force spectroscopy (nc-AFS). The nc-AFS provides new analytical prospects for force interaction between solid bodies, including metals. The spectra show prominent peaks and a broad peak, which are attributed to quantum mechanical resonance as the energy levels of sample surface states are tuned to those of the tip states by shifting the Fermi level through changing bias voltage. The energy level tuning by shifting the Fermi level has great potential for atom recognition and manipulation

A Si nano-pillar grown on a Si tip by AFM in UHV for a high-quality scanning probe

金沢大学理工研究域　数物科学系We grow a Si nanopillar on a commercial Si tip on an atomic force microscopy (AFM) cantilever using AFM in ultrahigh vacuum for a high-quality scanning force probe, and observe noncontact-AFM (nc-AFM) images of Si (111) 7×7 and Ge deposited Si(111) with the nanopillar. We observe it ex situ by transmission electron microscopy to confirm its growth and crystallinity. The nc-AFM image clearly showed the high performance of the nanopillar as a probe with respect to the spatial resolution, image stability, and reproducibility. This nanopillar growth technique can elongate the lifetime of the cantilever and be applied to other materials. © 2005 American Institute of Physics

共鳴的相互作用を利用した1分子の力学・電子物性計測

本研究では、我々が独自に開発した「表面局在相互作用分光法」を活用して、固体表面上に形成された電子・光デバイスとして機能をもつ単一分子の構造とその結合状態・電子状態を原子スケールで解析することを目的とした。表面局在相互作用分光法は、非接触原子間力顕微鏡(nc-AFM)を利用するナノ力学的分光法である。原子間力顕微鏡の探針と試料間に印加された電圧がもたらすフェルミ準位の変化を利用したナノ構造と界面の物性評価法を確立する。超高真空走査型相互作用分光顕微鏡の高感度化と共に、超高真空極低温環境で動作する走査型相互作用分光顕微鏡を開発した。また、従来のカンチレバーに変わる高感度力センサーの開発に向けて、市販のチューニングフォーク型と長辺振動型水晶振動子センサーを試験した。さらに、東北大学との共同研究で、水晶Z板を用いて、屈曲振動させるタイプと、伸縮振動させるタイプの水晶振動子力センサーを設計・試作した。清浄Si探針先端にGeを蒸着して特異なファセット構造をもつGeクラスターを成長させ、そのクラスターの頂点を探針として利用する。探針を大気中AFMでGeクラスター探針を用いたところ、未処理のSi探針に比べて像の解像度が改善した。また、Geクラスター探針を摩滅させた後、超高真空中で500口に加熱すると再び先端にクラスターが成長した。Geクラスター探針は安定なファセット面で囲まれているため非常に安定な構造であり、加熱により再生能力があり、何度でも同じ電子状態の探針を作れることが示唆された。清浄なSi(111)-7x7にπ共役系分子である4,4" -diamino-p-terphenyl(DAT)を超高真空中で蒸着し、その吸着状態を調べた。また、現実デバイスとの整合性を取るため、原子レベルで平坦なエピタキシャル成長ITO薄膜を単結晶YSZ基板上に形成し、ITO/YSZ基板上への機能性分子の成膜を試みた。ITO基板をアミノ化し、両端にアルデヒド基を持つπ共役系分子と反応させる。The purpose of this study is to analyze the structures, binding states and electronic states of functional single molecules with potential for opto-electronic devices fabricated on solid surfaces by bias-voltage non-contact atomic force spectroscopy (bias nc-AFS), invented by ourselves. The bias nc-AFS is a nanomechanical spectroscopy based on scanning probe microscopy (SPM). Our aim is also to establish this method to evaluate nano-structures using the energy shift of Fermi level induced by applying and sweeping the bias voltage between a tip and a sample.Here we developed ultra-high vacuum (UHV) bias nc-AFM/S together with improvement of the method, and aimed at developing of force sensors based on a commercial quartz tuning fork. In addition, we experimentally designed and fabricated a bending type and a stretching type of quartz force sensors in cooperation with a group in Tohoku University.Furthermore, we grew Ge clusters on a clean Si tip as a functionalized AFM tip. The clusters have specified facetted structures owing to a strained growth with lattice mismatch. Then the corner surrounded with the facets becomes sharper that is applicable to a well-defined scanning tip. We tried to obtain AFM images with it using a commercial AFM. Consequently, the spatial resolution was improved by using the Ge cluster tip compared with that using an uncovered Si tip. After wearing the tip we heated the worn Ge cluster tip in UHV, resulting in resharpening the tip apex with remolding a Ge cluster. Since the facet structure of a Ge cluster on Si is very stable, we resharpened it many times by heating, implying that we acquire a way to reproduce a tip having the same electronic states on the tip apex.We deposited it -conjugated molecules of 4,4"-diamino-p-terphenyl (DAT) on Si(111)7x7 in UHV, and examined their adsorption states using SPM.研究課題/領域番号:17310069, 研究期間(年度):2005-2007出典：「共鳴的相互作用を利用した1分子の力学・電子物性計測」研究成果報告書　課題番号17310069 (KAKEN：科学研究費助成事業データベース（国立情報学研究所）)　　　本文データは著者版報告書より作

Evidence of temperature dependence of initial adsorption sites of Ge atoms on Si(111)-7x7

金沢大学理工研究域　数物科学系Small amounts of Ge atoms are deposited on Si (111) -7×7 surfaces at room temperature (RT) and at 100 °C to clarify the initial adsorption sites using scanning tunneling microscopy. At RT Ge atoms are adsorbed at high coordination B2 sites around the rest atoms, as predicted by Cho and Kaxiras [Surf. Sci. 396, L261 (1998)]. On one hand, at 100 °C Ge atoms are adsorbed on corner adatom sites. With increasing Ge coverage the corner sites are gradually occupied, followed by Ge adsorption at center adatom sites, resulting in Ge cluster growth with a size of the half unit cell. © 2006 American Institute of Physics

Low-flux elucidation of initial growth of Ge clusters deposited on Si(111)-7x7 observed by scanning tunneling microscopy

金沢大学理工研究域　数物科学系Deposition of Ge on Si (111) -7×7 under very low Ge flux is examined using ultrahigh vacuum scanning tunneling microscopy; Ge atoms are deposited at 150°C under a flux of ∼0.005 or 0.05 ML/min. Initially Ge atoms are substituted for Si atoms on corner adatom sites of faulted half unit cells. At a Ge coverage of 0.08 ML under the lower flux, hollow-centered hexagonal Ge clusters with six protrusions are formed preferentially on faulted half unit cells, which are uniform and separated from other clusters. At the higher flux various types of clusters grow, frequently neighboring with others. This indicates that the low flux is needed to elucidate the stable type of Ge clusters grown on Si (111) -7×7. © 2009 The American Physical Society

超高感度電気容量測定法の開発による単分子デバイスへの展開

金沢大学数物科学系本研究では、走査型プローブ顕微鏡(SPM)探針先端と試料表面の間に挟持されている1分子の静電容量変化をナノ力学的に測定し電子状態変化を解析する手法を開発すること、その結果に基づいて分子の力学・電子的特性を利用したデバイスの開拓をめざした。SPM観察中に探針を振動させつつ試料に接近させると種々の現象が発現する。探針-試料間の電流変化、力変化が代表例である。その一つにAFMカンチレバーの振動を一定に保つために必要な励振エネルギーがある。その解釈は不明な点も多く議論が続いている。しかし、探針-試料間が1nm程度のときは、探針-試料間の静電容量の時間的変化によって変位電流が流れることはわかっている。この電流が探針-試料系閉回路を流れジュール発熱が起きる。そこで、励振エネルギー変化の高感度測定によって探針-試料間の静電容量を精密測定するシステムを開発した。本システムでは、振動の1サイクルあたり0.01eV以下のエネルギー変化を計測可能である。典型例で換算するとaFオーダの静電容量変化に相当する。このシステムを非接触AFMとして動作させsi(111)7x7表面に応用し、探針先端の状態によって励振エネルギーが原子位置によって変化する様子を捉えた。とくにSiレスト原子上(AFMで窪んで領域として描きだされる)で強い変化を示した。同時に観察された7x7単位胞のコーナーホール(Siレスト原子と同様な窪み)ではその変化はなかった。AFMによるアーティファクトではなく、Siレスト原子の電子状態を介した静電容量変化に起因していると考えられる。探針-試料間距離を徐々に変えて、励振エネルギー、電流、力変化を同時計測し、極近接で起こる急激な励振エネルギー変化を捉えた。これは、2物体が近接したことによって誘起される量子状態の出現に対応すると考えら、デバイス応用への足がかりになるものである。研究課題/領域番号:21656011, 研究期間(年度):2009 – 2010出典：研究課題「超高感度電気容量測定法の開発による単分子デバイスへの展開」課題番号21656011（KAKEN：科学研究費助成事業データベース（国立情報学研究所）） （https://kaken.nii.ac.jp/ja/grant/KAKENHI-PROJECT-21656011/）を加工して作

Influence of atomic tip structure on the intensity of inelastic tunneling spectroscopy data analyzed by combined scanning tunneling spectroscopy, force microscopy and density functional theory

Achieving a high intensity in inelastic scanning tunneling spectroscopy (IETS) is important for precise measurements. The intensity of the IETS signal can vary up to a factor three for various tips without an apparent reason accessible by scanning tunneling microscopy (STM) alone. Here, we show that combining STM and IETS with atomic force microscopy enables carbon monoxide front atom identification, revealing that high IETS intensities for CO/Cu(111) are obtained for single atom tips, while the intensity drops sharply for multi-atom tips. Adsorbing the CO molecule on a Cu adatom [CO/Cu/Cu(111)] such that it is elevated over the substrate strongly diminishes the tip dependence of IETS intensity, showing that an elevated position channels most of the tunneling current through the CO molecule even for multi-atom tips, while a large fraction of the tunneling current bypasses the CO molecule in the case of CO/Cu(111)

Pass wear resistance for perpendicular recording media

金沢大学理工研究域数物科学系Pass wear resistance of sputtered CoCr perpendicular flexible disks has been investigated. The disk was composed of CoCr film on a heat-resistant base film, a protection layer, and lubricant. The pass wear durabilities were evaluated for a conventional double-sided 3.5-in drive. It was found that the scratch depth (SD) per load force (LF) depends on preparation conditions, and that the CoCr film hardness is related to pass wear durability. SD/LF values range from 0.2 to 0.3 for CoCr films without a protective layer. With a protective layer and lubricant, the range of SD/LF values varies from 0.2-0.3 to 0.1-0.3. The disk hardness, especially for small SD/LF media, has been improved. A pass wear durability of 30 million passes was attained for a disk having SD/LF = 0.1