近场扫描式光学显微镜.doc

NCKU Micro-Nano Technology Center/Southern Region MEMS Center Page1近場掃描式光學顯微鏡簡易操作手冊NSOMSOP儀器介紹這是型號為Veeco Aurora-3的近場掃瞄式光學顯微鏡(Near-field Scanning Optical Microscope-NSOM)。NSOM是一種可提供比共軛焦顯微鏡更高解析度的光學式顯微技術。由光學以及探針式顯微技術所構成，樣品表面的化學以及幾何特性可同時的被量測紀錄。此結合樣品表面幾何特性與光學影像的功能，對於材料的特性描述與分析是非常有用。Aurora-3為一款具有大範圍的精密成像功能且非常容易操作特性的儀器。 此系統簡潔的整合於一光學的機台架構，電子控制部分也整合為單一系統，整體控制由SPMLab軟件提供，此軟體也提供多樣的數據處理與顯像選擇。Chapter 1Theory of OperationINTRODUCTION近場掃瞄式光學顯微鏡(Near-field Scanning Optical MicroscopyNSOM)是一種結合探針式掃瞄顯微鏡(Scanning Probe MicroscopySPM)以及光學式顯微鏡的成像技術。主要目的為獲得近場的光學訊號，運用SPM的精確位置控制能力去保持探針與樣品表面的距離在一非常小的距離量，進而得到近場的光學訊號，並可同時得到表面的幾何特性訊號，因此可同時比較與分析樣品表面的幾何與光學特性。SPM THEORY探針式掃瞄顯微鏡(Scanning Probe MicroscopySPM)包含感測探針，壓墊陶瓷，電子控制系統，以及用來設定掃瞄參數與訊號成像用的電腦系統。感應探針掃瞄於樣品表面上可感測到幾何特性或其他作用的改變並利用探針感應到的訊號獲得清晰以及高空間解析度的表面特性圖形。NSOM THEORY傳統的光學顯微鏡，在光學解析度上會受到所謂的繞射極限的限制，此限制是光學上的物理限制，因此理論上最小的解析度只能達到所使用光波長的一半大小。因此發展出使用一具有很小孔徑的光纖(約50nm)來作為光源，並利用SPM的控制技術來使此光源非常接近待測物的表面(約10nm)。NSOM PROBES雷射光源直接的耦合到光纖中，此光纖底端直徑逐漸變小到約50nm，且在此光纖末端塗上一層鋁，厚度約100nm。在一般的操作下令此光纖探針非常接近樣品表面令光源直接的照射到樣品，在依照實驗需求將收光裝置於樣品背面(穿透式)或是探針旁(反射式)收集由樣品所發射出的光源。MODES OF OPERATIONNSOM是結合Topography與Optical兩個mode的儀器。Topography mode可測定樣品表面幾何特性，而Optical mode則可操作於tip illumination or tip collection mode。IMPLEMENTATION ON THE AURORA-3Aurora-3系統操在non-contact AFM mode下取得topography and NSOM data.。 在distance control方面此系統是使用tuning fork的機械裝置，此優點在於直接的獲得位置回饋訊號而不會像是傳統的光學回饋裝置易產生不必要的背景雜訊。將光纖探針黏附於tuning fork的一個臂上，並使用一壓電陶瓷來震動此tuning fork使其產生一擺動的現象，擺動幅度約在13nm。由於tuning fork本身也是一壓電陶瓷，因此在受到擺動時也會產生壓電訊號，藉由量測壓電訊號量既可得到tuning fork擺動震幅大小，將此訊號利用鎖向放大器與輸入訊號作相位的比較，作為distance control的回饋訊號。Aurora-3所提供的探針已將光纖探針與tuning fork合併於一基板上，如右圖所示。在光學架構的部分如圖所示： Chapter 2Instrument Overview & Set-UpAURORA-3 PACKAGESPMLAB SOFTWAREStep 1 Launch the SPMLab software.Step 2 Click (on the toolbar) to enter the Data Acquisition module.Step 3 Click , and then click ,when prompted, to turn on the high voltage.AURORA-3 HEAD粗調Z position是由三個z-height screws所控制，兩個由手動調整，第三個由工具列上的控制按鈕與來調整上下位置。(注意：不要調整太高或太低，否則會損壞Z軸軸承。) 馬達電壓控制由(Command XYZ)叫出控制選單。 INSTALLING THE HEADStep 1 Raise the z-height thumbscrews by turning them one full turn clockwise.Step 2 Slide the overhead light source on the reflection tower all the way to the right to provide maximum clearance.Step 3 Hold the head as shown.Step 4 當放下HEAD時，必須注意是否有足夠的空間，切勿使得光纖探針碰到樣品表面，否則會損壞探針。配合需要可手動調整旋扭來保持需要的空間Step 5 Lower the head carefully onto the kinematic mount as follows: a) Tilt the head slightly to guide the motorized screw into the point constrained mount first, as shown in Figure b) Next, guide the appropriate manual screw into the line-constrained mount. c) Finally, lower the other manual screw into the unconstrained mount.Step 6 If a probe is mounted, tape the free optical fiber to the z motor housing on the head.Step 7 Connect the head cable to the connector on the instrument base.REMOVING THE HEADStep 1 Click the Tip Up button on the Data Acquisition tool bar to raise the tip a safe distance away from the sample.Step 2 Rotate the thumbscrews one full turn clockwise.Step 3 Disconnect the cable from the connector on the instrument base.Step 4 Remove the head by first tilting it slightly to lift it out of the line- and surface-constrained mounts so that it pivots on the point-constrained mount, and then lift it safely off the stage.Step 5 Set the head down on a soft, flat surface, making sure there is no obstruction that would strike the probe.SAMPLE STAGEscanning sample stage架設於兩軸x and y translation stages上，可由(CommandXYZ).呼叫出Primary XYZ dialog box。 MIRROR CONTROLS使用圓形把mirror knobs推出或推入控制光路。FOCUS CONTROLS使用focus screws旋扭來調整焦距(注意：調整時要注意鏡頭與樣品的距離，否則會使鏡頭頂到樣品，使其損壞。)VIDEO MONITORING此系統具備兩組CCD cameras分別可監控穿透與反射面。CCD與光源的控制可由SetupVideo呼叫出，並同時操作兩組CCD cameras。並可由可由(CommandXYZ)呼叫出Primary XYZ dialog box來調整樣品位置。SPLICER利用此裝置將由雷射光源的光纖與探針光纖耦合在一起PMT此系統是由一組光電倍增管(photomultiplier tubePMT)來收集光學訊號。可由SetupPMT呼叫出控制選單，最大電壓可調整到1000V。(注意：在開啟PMT時，要卻定將所有光源關閉，否則會使PMT損壞。)(注意：因此PMT必須保持關閉狀態，確定後才可開啟。)Chapter 3Setting Up to Take an ImageINSTALLING A PROBEStep 1 Open the probe box, and make sure that the probe you will be using is facing up (with the three metal contact pads visible).Step 2 Carefully pull the tape off the optical fiber so the probe can be removed from the box.Step 3 Unroll the fiber, taking care not to touch the tuning fork or put any strain on the fiber.Step 4 Grasp the probe with the probe installation tool by positioning the tool over the probe and fitting the two “teeth” into the corresponding gaps on either side of the probe cartridge, as shown in Figure.Step 5 Press down firmly into the foam lining of the probe box until the probe snaps into place in the teeth of the tool. Close the probe box to protect the other probes from dust.Step 6 Load the probe into the probe mount on the head so that the probe cassette slides under the clips .Step 7 Gently twist the tool to disengage it from the probe, to minimize stress on the contact clips.Step 8 Make sure the three clips make contact with the three metal contact pads on the probe as shown in Figure.If necessary, use one or both thumbs to gently push the probe into place and position it, being careful not to touch the probe tip or tuning fork.Step 9 Turn the thumbscrews on the head one full turn clockwise to keep the tip from hitting the sample or stage when the head is placed on the kinematic mount.Step 10 Carefully place the head on the stage, and plug the cable into the connector on the instrument base, as described in Chapter 2.Step 11 Tape the fiber to the z motor enclosure on the head. This takes strain off the fiber and helps prevent accidental separation from the probe.USING THE OPTICS在此說明如何使用配合video monitor，手動粗調探針接近樣品表面。(注意：此時PMT必須保持關閉狀態。)Step 1 Place a transparent sample on the scanning stage so that it covers the aperture over the transmission objective.Step 2 Make sure the PMT voltage is off.Step 3 Turn on the video monitor.Step 4 Select SetupVideo to open the Video dialog box, and make the following selections:a) Turn the light on.b) Turn the camera on.c) Toggle the view on thevideo monitor, ifnecessary, to select thetransmission mode view. Step 5 Use the transmission focus screw to bring the top surface of the smudged sample into focus (turning the screw clockwise raises the objective). First, the bottom of the sample will come into focus, then the top of the sample.Step 6 Turn the transmission focus screw two more full clockwise turns.Next, you will bring the tip down into the focus plane.Step 7 Monitoring the tip and sample carefully with the naked eye, use the z-height screws to lower the tip, bringing it as close to the sample surface as possible without crashing it.Step 8 Locate the shadow of the tip, and bring it into focus in the middle of the monitor by alternately adjusting the kinematic mount x and y screws and the transmission focus screw.Step 9 Use the transmission focus screw to bring the image into focus. The image on the video monitor should roughly resemble Figure, with the image of the probe tip emerging from a dark region of shadow; there may also be another, less dark, region of shadow in the lower right area of the monitor.Step 10 Switch to reflection view (select SetupVideo and then Toggle View). The focus plane should appear as a clear, vertical band somewhere on the monitor.Step 11 Use the reflection focus screw to bring the focus plane into the center of the monitor.Step 12 Monitoring the tip and sample carefully on the video monitor, use the z-height screws to bring the tip closer to the sample surface without crashing into the surface, i.e., do not let the two images actually meet!The images of the probe tip and its reflection should approach each other and meet at the focus plane, as shown in FigureAPPROACHING THE SAMPLE在調整Tip-Sample approaching時，必須注意不要驅動motorized z screw大大距離(using the and buttons)，否則會損壞。另外必須將光纖探針與樣品表面間保持水平。COUPLING THE LASER INTO THE TIPStep 1 Use the fiber stripper tool to strip away about 25 mm of the polymer buffer off the free end of the tip fiber.Step 2 Use the optical fiber cleaver from the tool kit to cleave the end of the tip fiber (you may also want to refer to the documentation supplied with the fiber cleaver):a) Open the jaws of the cleaver, and seat the fiber into the notch in the lower jaw.b) Insert the fiber until the stripped portion on the end aligns with the 16 mm mark.c) Press the scoring bar down on the fiber.d) Gently flex the tongue of the cleaver down until the fiber cleaves.e) Remove the fiber, being careful not to touch the tip (except to clean).Step 3 To clean the fiber, moisten a clean lens cleaning tissue with isopropyl alcohol, and very carefully wipe the stripped portion of the fiber in the direction of the cleaved tip.Step 4 Push the fiber down into the other foam clamp of the splicer assembly tool.The laser fiber should already be temporarily installed in one side of the splicer.Step 5 Carefully insert the end of the tip fiber into the other end of the splicer.Insert it far enough to touch the laser fiber, gently rolling or twisting it to help it enter. Pushing on one fiber should move the other.Step 6 Slowly rotate both levers all the way down.Step 7 Check to see that laser light is coupled into the tip fiber.The laser light may not be visible at the tip, but if the room lights are turned off, the tip fiber should be glowing. If there is no light visible in the tip fiber, repeat the above steps.Step 8 Remove the splicer from the assembly tool by gently releasing the fibers from the foam clamps and lifting the splicer from the assembly tool (lift up on the right side first).Step 9 Set the assembly tool aside.Step 10 Secure the splicer to a convenient surface with tape.Chapter 4Taking a Topographic ImageSOFTWARE SETUPStep 1 Power up the system components as described in Chapter 2.Step 2 Launch the SPMLab software, and enter the Data Acquisition module.The Non-Contact Control window and signal window should be open by default. If necessary, the Non-Contact Control window can be opened by selecting SetupNon-Contact, and the signal window can be opened by clicking the oscilloscope icon on the Data Acquisition toolbar. Make sure that both traces in the signal window are displayed (Top and Bottom should both be checked).Step 3 Select SetupAcquire to open the Image Acquire Setup dialog box.Step 4 Under Data Channels, confirm that Fwd is checked for the Topography and Internal Sensor signals, and click .Step 5 In the signal window, select , and select Internal Sensor, Feedback and Z Piezo from the drop-down Signal lists for the upper and lower oscilloscopes.FINDING THE RESONANT DRIVE FREQUENCY由於每個tuning fork探針元件，所具有的共振頻率接不相同，因此在操作前，必須先找到其共振頻率，在此利用找尋震幅最大值來得到共振頻率。Step 1 In the Non-Contact Control window, select Amplitude from the Mode group box.Step 2 Enter the following starting parameters:Range = 5-120 kHzAmplitude = 0.1 V(drive amplitude)Input Gain = 8.0 (input gain of the I/OMOD+board)Step 3 Select to run a frequency sweep. A single, sharp peak between 90 and 100 kHz should be displayed.Step 4 Zoom in on the peak so that the frequency window is 2 kHz (or less) wide.Step 5 Adjust the Amplitude and Input Gain, alternating between the two, until you have a clean peak with a height of about 5 V, which corresponds to about -30 nA on the internal sensor signal.可利用增Amplitude或Input Gain值來使peck值達到5V但須注意的是，提高Input Gain值雖然可增加相位偵測的靈敏度但相同的也增大了雜訊；而提高Amplitude可增加tuning fork震幅擺動力量，適合用於黏稠性的樣品。Step 6 Click on the peak to select the drive frequency.The peak will be marked by a red pointer, and the drive frequency will appear in the Frequency field, as shown in Figure.Step 7 Select Phase from the Mode group box, and watch the internal sensor signal.Step 8 Click.The internal sensor signal should go to 0 nA (the center line).Step 9 Click on the button three times (for a total of 270 degrees) to find the phase that shows the most negative value for the internal sensor signal, which should be approximately -30 nA.Step 10 Fine-tune the non-contact controls using the following guidelines: The aim is to have the drive amplitude be as low as possible while keeping the internal sensor signal at approximately the same value and the RMS noise (displayed in blue in the signal window) less than 0.1. Reducing the drive amplitude will cause the internal sensor signal to increase (move closer to 0). Increasing the gain will bring the internal sensor signal down (more negative, i.e., further from 0). However, increasing the gain will proportionally increase the RMS noise.Step 11 Minimize the Non-Contact Control window once the non-contact controls have been fine-tuned. To adjust these settings, the tip must be out of feedback. These settings will be saved when you exit the SPMLab software.BRINGING THE TIP INTO FEEDBACK此系統有兩種方式用來進行feedback approach分別為false feedback與jog approach (or “woodpecker approach”)的模式。一般在樣品表面可反射光源時是使用false feedback模式，而樣品表面不是反射面時，才使用jog approach模式。FALSE FEEDBACKStep 1 Set the following initial scan and feedback parameter values in the Acquisition Control Panel:Set Point of -64.00 nA will always be an Indication of the z-piezo being fully retracted. Scan Rate should be about 1/2 the Scan Range (these will vary with different samples).Resolution of 200 (200x200 scan lines) is adequate for this tutorial; raising the resolution increases scanning time. Integral gain of 0.05 will enable the system to enter into a slow approach, once false feedback has been engaged and the set-point is adjusted. If the integral value is too high, the tip may jump as it approaches the sample. Proportional and Derivative gains should be kept at these values (they may be adjusted when fine tuning the feedback as described later in this chapter).Step 2 Pull both mirror knobs to their out positions so the tip-sample area can be viewed on the video monitor.Step 3 Select SetupVideo to open the Video Setup window.a) Turn on the light.b) Turn on the cameras.c) Switch to the reflection path camera.Step 4 Locate the probe on the video monitor.Step 5 While watching the video monitor, lower the head enough to bring the tip within a few micrometers of the surface.Step 6 Make sure the z-piezo voltage is at 0 V, as displayed on the lower oscilloscope.If it is not, select SetupAcquire to open the Image Acquire Setup dialog box, and set Z Setpoint to 0.(注意：為了避免探針碰撞到樣品，必需確定讓Integral值為0.05。)Step 7 Click on the Acquisition Control Panel.The z-piezo will fully retract, as indicated by a voltage reading of -220 V in the signal window. The tip is now in “false feedback.”(注意：在feedback啟動後，不要移動到儀器，避免探針損壞。)TRUE FEEDBACKStep 1 利用video monitor監視光纖探針與樣品間的距離避免有碰撞的情況發生。在開啟雷射光源後可關掉照明燈，利用光纖以及反射的點光源來做距離的判斷。Step 2 按下設定初始值，一開始的值為上述中的設定。使用可自動校準訊號值於畫面中間。Step 3 利用調整重直軸區域大小。Step 4 設定Setpoint值，使用按鍵慢慢設定，避免撞針，同時注意Z-iezo電壓值保持在小的震動幅度。Step 5 Make sure the set point is high enough so that the z-piezo voltage begins to move slowly up from its initial value of -220 V.If necessary, click thebutton (next to the Set Point field) to raise the set point in increments of 0.05 nA (5 clicks) until the z-piezo moves.If the z-piezo voltage stops rising or begins to return to -220 V, increase the set point.Step 6 判斷探針是否以達足夠近的距離進入feedback的動作的方式如下，當設定Setpoint大於0.1nA時，但z-piezo voltage並沒有抬起的現象，或是往負的電壓值移動時，就是已達此狀態，此時可停止設定Setpoint。 (理想的狀態是讓z-piezo voltage也正好落在+50V-50V之間。)Step 7 假如成功完成上列步驟，既以成功達到足夠近的距離進入feedback的動作， 不必進行下面步驟。如果z-piezo voltage值達到+220V表示失敗，接著下列步驟。Step 8 If the tip does not go into feedback (see Step 7), retract the scanner with the z-piezo by setting the set point to -64 nA.Step 9 注意觀察z-piezo voltage值，使其回復到-220V。Step 10 回到步驟一，重新開始。OPTIMIZING THE PARAMETERS完美的P-I-D值設定，可得到較好的解析度並避免撞針。此部分必須仰賴操作者的經驗。為了避免撞針或避免儀器損壞，請務必小心的慢慢調整，或詢問較有經驗者。LINE SCAN OPTIMIZATIONStep 1 Clickin the signal window to activate the line scan mode.此時可調整P-I-D值設定。Step 2 In the signal window, select Internal Sensor, Feedback (upper oscilloscope) and Topography (lower oscilloscope) from the drop-down Signal lists.Step 3 Selectscaling in both upper and lower displays.Step 4 Check Level for the topography signal.Step 5 利用線掃瞄的再現性判斷是否達到好的解析度，一般情況不調整D值。Step 6 Keep the Scan Rate at about 1/2 the scan range (e.g., 2.5 m/s for a 5 m scan range).Step 7 Slowly increase the set point and integral gain, alternately, allowing enough time for the result of each adjustment to register in the line traces.TOPOGRAPHY IMAGE OPTIMIZATIONStep 1 Click in the signal window to display the line scan of the internal sensor signal, as it will no longer be displayed when a scan begins.Step 2 In the signal window,