The Electronical Design Of Scanning Tunneling Microscopy And Its Application In The Study Of 2D Atomic And Molecular Crystal Materials

Since the beginning of the last century,natural science and technology has gone through a rapid development,experiencing the transformation from classical theory to quantum theory and from macro to micro world.The development of the nano science and technology is inevitable.In the field of physics,chemistry and biology,research need to be be carried out at molecular level.On the technology side,with the development of the micro electronics,the electronic devices are designed to be smaller and faster.However,the silicon based devices will soon come to its physical limitations.Low-dimensional materials,owing to their natural advantages in size and scalability,are believed to be one of the promising candidates in future technology.Tunneling scanning microscope?STM?has proven to be an important tool in studying the low-dimensional materials,especially the 2D materials.It has brought great improvement to the nano science and technology.Under this background,we carried out our studies,including following three parts.1. We introduce the upgrade of a homebuilt tip etching control circuit.The cut-off time was reduced down to 10 ns.The radius of curvature?Roc?of tungsten tips is less than 1 nm,and the success rate of making tips with Roc less than 3 nm is above 80%.Then we studied the relationship between the Roc and etching current and cut-off speed,and got a conclusion that the etching current could cause the melting of the tip and great influence on the Roc.Second,we introduce the upgrade of a low noise current preamplifier,including the principle,methods and difficulties to design the preamplifier.We built an amplifier with gain 10⁹ V/A,bandwidth 4 KHz,high stabilities and ultralow noise,which can compete with the commercial ones.Then we introduced how to drive Beetle-type scanner of our system to approach and retract the tips with a RHK R9controller,and introduced the upgrade of the sample holder.Through programming in the R9 controller and adjusting of the driving voltage of each scanning tube,we succeed to drive the scanner to approach and retract,and drive sample holder to do transnational movements.2. We introduced the fabrication of naphthalocyanine?H₂Nc?molecular crystals and the tip-induced tautomerization of single H₂Nc molecule.The molecules were deposited onto Ag?111?single crystal substrate to form a multilayer.The STM tip was used to induce and manipulate the tautomerization of the top layer molecules.In the STM images of the molecule,noise dots appear in the center part of molecule,caused by the tautomerization process.We found the asymmetric inducing behaviors under positive bias and negative bias.The smallest bias absolute value to excite the tautomerization is much smaller at positive bias than that at negative bias.And when the absolute value of the bias increases,the tautomerization rate increases much faster at positive bias than that at negative bias,which is quite different with previous cases where the molecules were deposited directly onto the metal substrate.Thus,we think that the excitation mechanism should be different.In our case,the top layer molecules are well decoupled from the substrate by the lower layer molecules,which causes the electrons to stay much longer in the molecule and excite the molecule to vibrate effectively.Then the tautomerization of the molecule can be induced by the molecular vibration.This work is important to study the relationship between electrons and molecules,and to study the STM tip induced molecular chemical reactions.3. We introduced the fabrication of monolayer IrTe₂ and its structural transition.First,we used the direct tellurization method to grow the IrTe₂ monolayer,and use STM to characterize it under room temperature.The 1/5 phase and 1/6 phase structures of the IrTe₂ were observed,which could only appear at low temperatures for the bulk materials,suggesting the reduction of the layer thickness has great influences on transition temperatures.Then we introduce the low temperature characterization of the IrTe₂monolayer.The disodered stripe features were observed.The lower the temperature,the more bended the stripes.Under 80 K,the 1/6 phase is replaced by a disordered phase.We conclude that the distortion of the stripes was caused by the strain between the monolayer IrTe₂ and Irsubstrate induced by the temperature reduction,which was supported by the strong interaction between the IrTe₂ and Irsubstrate from DFT calculation.At last,we annealed the IrTe₂ materal under 900?and formed a new material,which had honeycomb structure with super large lattice constant,0.68 nm.This work is important to the study of growth of 2D materials and related phase transitions.