STM热化学烧孔方式的信息存储——写入脉冲幅值和脉宽对信息点尺寸的影响

以扫描探针显微技术（SPM）为基础的超高密度信息存储是近年的研究的热点。前文^[1]利用STM针尖在TEA（TCNQ）2单晶上施加电压脉冲,得到了超高密度信息孔点阵,提出了热化学烧孔方式的STM信息存储技术,在STM扫描成像的过程中,隧道电流会流经样品,产生焦尔热。但通常扫描成像过程中的隧穿电流较小,焦耳热也较小,如能找到一种二元复合材料,一级分沸点较低,且与另一组分的结合能较弱,当足够大的电流流经时,所产生的焦耳热可能使低沸点的组分气化逸出,在样品表面形成纳米尺度的信息点。我们称这种存储模式为热化学烧孔方式的STM存储。基于这一思想,我们选择电荷转移复合物TEA（TCNQ）2作为存储材料,用STM写下了纳米微级的信息孔。本文通过改变写入电压脉冲的脉幅和脉宽,控制孔的大小,并对孔大小与脉冲电压的关系进行了理论推导和分析。     

用STM针尖诱导热致气化模式的纳米级

以扫描探针显微镜(SPM)为基础的超高密度信息存储是近年来信息存储领域的热点研究之一.其基本原理是利用SPM针尖诱导存储介质表面形貌变化、导电性质改变、电荷分离等来记录信息.提出利用STM隧道电流的焦耳热效应诱导材料发生气化分解的热化学烧孔模式的STM存储新原理,并在电荷转移复合物TEA(TCNQ)2上成功地得到大面积信息孔阵列.空洞大小均一,最小直径约8nm.该存储模式有明显的优点:由于STM隧道电流波及范围很小,只要存储材料的导热性不是很好,则气化分解局限于非常小的范围,从原理上保证了存储的超高密度;写入可靠率非常高,达到99%以上;存储材料具有可设计性,易于优化材料的存储性能.     

用STM针尖诱导热致气化模式的纳米级信息存储

以扫描探针显微镜(SPM)为基础的超高密度信息存储是近年来信息存储领域的热点研究之一.其基本原理是利用SPM针尖诱导存储介质表面形貌变化、导电性质改变、电荷分离等来记录信息.提出利用STM隧道电流的焦耳热效应诱导材料发生气化分解的热化学烧孔模式的STM存储新原理,并在电荷转移复合物TEA(TCNQ)₂上成功地得到大面积信息孔阵列.空洞大小均一,最小直径约8 nm.该存储模式有明显的优点:由于STM隧道电流波及范围很小,只要存储材料的导热性不是很好,则气化分解局限于非常小的范围,从原理上保证了存储的超高密度;写入可靠率非常高,达到99%以上;存储材料具有可设计性,易于优化材料的存储性能.     

含碘系列电荷转移复合物的热分解温度对烧孔阈值电压的影响

合成了5种含碘的电荷转移复合物,对其热化学烧孔性能进行了研究,在它们的单晶上成功写入了信息点阵.通过热重分析获得了5种材料的热分解温度,并测量了它们的烧孔阈值电压.结果表明,材料的热分解温度对烧孔阈值电压有明显影响.理论分析表明,阈值电压对热分解温度的依赖关系反映了活化能对热化学烧孔反应速度的影响.     

丝氨酸织组膜电极的研究

利用猪肝组织膜配合氨气敏电极,研制了丝氨酸生物催化传感电极。丝氨酸浓度的测定范围为5.1×10~(-5)～3.2×10~(-3)mol/L,检出限为3.1×10~(-5)mol/L。研究和讨论了电极的最佳工作条件,并测定了实验条件下酶催化反应的米氏常数Km。该电极用于合成样品分析,效果满意。     

一种含二茂铁的有机分子在超高密度信息存储中的应用研究

通过缩合反应合成了含二茂铁的有机给受体分子1-二茂铁基-2-(4-对硝基苯基)亚胺,利用真空沉积的方法制备了其薄膜,观察了该薄膜形貌,测定了其电学特性。结果发现,该薄膜具有良好的电学双稳态。利用STM成功地在该薄膜上写入了纳米尺度信息点。这一结果表明,该分子可望作为一种具有潜力的超高密度信息存储材料。     

DEA(TCNQ)2与TEA(TCNQ)2单晶上的STM热化学烧孔性能比较

利用STM隧道电流焦耳热诱导分解气化的热化学烧孔方法,对两种存储材料DEA(TCNQ)2和TEA(TCNQ)2的存储性能作了比较,DEA(TCNQ)2可以得到更高的存储密度、更大的信息孔深/孔径比,有更大的写入阈值电压.由此说明通过对存储材料的设计可以对存储系统的性能进行优化.     

线性变位极谱法研究 ⅩⅥ.铀(Ⅵ)—5—Br—PADAP—磺基水杨酸的配位吸附波

本文提出了铀(Ⅵ)-5-Br-PADAP-磺基水杨酸三元配合物的极谱配位吸附波。在pH为7.5-8.2的醋酸、三乙醇胺、乙醇底液中,该波的峰电位在-0.6855V(vs.SCE)。在1.00×10~(-7)-1.00×10~(-5)mol·dm~(-3)范围内,铀(Ⅵ)浓度与峰电流呈线性关系。对极谱波的电流、电位性质进行了研究,测定了配合物的组成、表观稳定常数和离解及生成速率常数。     

铜、镍、钴、锌与螯合树脂及弱酸性离子交换树脂的络合物的生成常数

本文改进了前人用于测定低分子量配体及可溶性聚电解质配体络合物的生成常数的电位滴定法,以使适用于作为固体络合剂的螯合离子交换树脂和羧酸型弱酸性离子交换树脂的络合物。测得具有亚胺二乙酸功能基的大孔螫合树脂D751和具有羧酸功能基的大孔丙烯酸系树脂D725与Cu、Ni、Co、Zn的络合物的二级积累生成常数B_2。D751树脂的B_2介于5×10~(-4)至4×10~(-7)之间,D725树脂的B_2介于7×10~(-9)至4×10~(-10)之间。     

双偏振极化干涉技术实时研究三磷酸腺苷与其适配体相互作用

利用双偏振极化干涉(Dual polarization interferometry,DPI)测量技术实时研究了三磷酸腺苷(ATP)与其适配体(ATP-binding aptamer, ABA)间的相互作用.将单链ABA固定在DPI氮化硅芯片上,采用DPI技术实时监测ATP与固定的ABA的相互作用过程中敏感层的质量、厚度、密度的变化.通过详细分析敏感层质量变化,得到ATP与ABA间的结合速率常数 (ka=4.66 × 10.3 L/(mol·s)、解离速率常数(kd =1.70 × 10.-2·s.-1)、结合常数 (KA=2.7 × 10.5 L/mol)和解离常数(KD =3.7 × 10.-6 mol/L).通过测定敏感层质量、厚度和密度随ATP浓度的变化,分别建立了测定ATP的方法,检出限(LOD, 3σ)分别为0.22 μmol/L(质量变化)、0.14 μmol/L(厚度变化)、0.32 μmol/L(密度变化).本研究利用DPI技术揭示了ABA与ATP相互作用中结构变化的实时信息,构建了新型ATP传感器,用于实际血清样品中ATP的检测,结果令人满意.     

Possibility of superconductivity in intercalation compound related to MgB2

We investigated the electronic structure of MgB₂ and intercalation compounds, MgBX (X = Li, Be, C), with fully relaxed crystal structure by using density functional theory. The compounds MgBLi and MgBBe could be similar two‐band superconductors to MgB₂ because the Fermi surface crosses σ and π bands. Our results indicate that changing the lattice constants, hole or electron doping, and stacking of B? X effect the energy levels of the σ and π bands in MgBX compounds. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Statistical lattice model for the bimolecular reaction on the dynamically changing surface of a body-centered metal crystal

A statistical lattice model has been constructed for the surface of a body-centered cubic (bcc) crystal whose morphology varies under the action of external factors (temperature and adsorbate coverage). Monomolecular and dissociative bimolecular adsorption on the bcc crystal surface has been investigated. In this model, adsorption smoothens the originally rough surface owing to adsorbate molecules stabilizing their flat adsorption areas, as distinct from adsorption on the primitive cubic lattice. Our model differs from the models with invariable surface morphology in that the number of its accessible adsorption sites is variable and depends on external conditions. The kinetics of a catalytic reaction proceeding by the Langmuir-Hinshelwood mechanism have been studied for the (100) face of a bcc crystal whose morphology varies under the action of the reaction medium.     

常见客体分子对笼型水合物晶格常数的影响

Natural gas hydrates are considered as ideal alternative energy resources for the future, and the relevant basic and applied research has become more attractive in recent years. The influence of guest molecules on the hydrate crystal lattice parameters is of great significances to the understanding of hydrate structural characteristics, hydrate formation/decomposition mechanisms, and phase stability behaviors. In this study, we test a series of artificial hydrate samples containing different guest molecules (e.g. methane, ethane, propane, iso-butane, carbon dioxide, tetrahydrofuran, methane + 2, 2-dimethylbutane, and methane + methyl cyclohexane) by a low-temperature powder X-ray diffraction (PXRD). Results show that PXRD effectively elucidates structural characteristics of the natural gas hydrate samples, including crystal lattice parameters and structure types. The relationships between guest molecule sizes and crystal lattice parameters reveal that different guest molecules have different controlling behaviors on the hydrate types and crystal lattice constants. First, a positive correlation between the lattice constants and the van der Waals diameters of homologous hydrocarbon gases was observed in the single-guest-component hydrates. Small hydrocarbon homologous gases, such as methane and ethane, tended to form sI hydrates, whereas relatively larger molecules, such as propane and iso-butane, generated sⅡ hydrates. The hydrate crystal lattice constants increased with increasing guest molecule size. The types of hydrates composed of oxygen-containing guest molecules (such as CO₂ and THF) were also controlled by the van der Waals diameters. However, no positive correlation between the lattice constants and the van der Waals diameters of guest molecules in hydrocarbon hydrates was observed for CO₂ hydrate and THF hydrate, probably due to the special interactions between the guest oxygen atoms and hydrate "cages". Furthermore, the influences of the macromolecules and auxiliary small molecules on the lengths of the different crystal axes of the sH hydrates showed inverse trends. Compared to the methane + 2, 2-dimethylbutane hydrate sample, the length of the a-axis direction of the methane + methyl cyclohexane hydrate sample was slightly smaller, whereas the length of the c-axis direction was slightly longer. The crystal a-axis length of the sH hydrate sample formed with nitrogen molecules was slightly longer, whereas the c-axis was shorter than that of the methane + 2, 2-dimethylbutane hydrate sample at the same temperature.     

A2BC60和A3C60晶体中的短程相互作用

研究了Ａ３Ｃ６０和Ａ２ＢＣ６０晶体的结构和稳定性。计算了它们的Ｍａｄｅｌｕｎｇ常数、结合能、晶格常数和体积弹性模量,并讨论了晶体中的短程相互作用。结果显示,短程相互作用结构和八面体空隙碱金属的稳定性具有极大的影响。ＣｓＫ２Ｃ６０、ＲｂＫ２Ｃ６０和Ｋ３Ｃ６０的晶格常数计算结果与实验测量值非常符合。     

Force constants and many-body electrostatic interactions in two-dimensional colloidal crystal

A model of a two-dimensional colloidal crystal with a hexagonal lattice, the electrostatic interactions in which are described by the nonlinear Poisson-Boltzmann equation, is considered. The calculation procedure for force constants of this crystal is treated in detail. Properties of system symmetry, which make it possible to significantly decrease the volume of calculations and to classify force constants, are analyzed. Numerical data for force constants of a crystal as functions of lattice parameters at different particle sizes are reported. A method that allows us to disclose the presence of many-body interactions in a system by the behavior of force constants at some interval of the values of lattice parameters is proposed. The application of this method to the system under consideration demonstrated that electrostatic interparticle interactions in the system cannot be reduced to simply a pair interaction of any kind; the introduction of many-body potentials is required for the adequate representation of the elastic properties of a crystal.     

C60分子间相互作用的Morse势函数及应用

利用C60晶体的升华焓、晶胞参数等性质,得到C60分子间相互作用的Morse势函数，其解析表达式为 u(r)=30.05 exp[－24.96(r－1.005)]－60.10 exp[－12.48(r－1.005)] 采用该作用势研究了C60及其晶体的一些性质, 如计算得到C60晶体(100)面的表面能为7.46×10－2 J•m－2, 在650～4500 K温度范围内计算了C60分子的第二维里系数, 研究了C60面心立方晶体的晶格振动, 并计算得到了晶格振动的态密度分布,还利用该作用势研究了不同晶型时C60晶体的稳定性.     

Carrier generation process on photoconductive polymer films as studied by magnetic field effects on the charge-transfer fluorescence and photocurrent

We have studied the magnetic field effects (MFEs) on the charge-transfer fluorescence and transient photocurrent of a 1,2,4,5-tetracyanobenzene-doped poly(N-vinylcarbazole) film, which reflect the recombination and escape yields of the carriers, respectively. The recombination yield dependence of the external magnetic field (B) clearly shows two types of the MFEs, growth with increasing B due to the hyperfine mechanism (HFM) and a negative dip due to the level-crossing mechanism (LCM). On the other hand, the escape yield indicates complementary MFEs with a sharp decrease in yield with increasing B and then a positive dip. Simultaneous observation of the HFM- and LCM-MFEs proves the stepwise hole-hopping mechanism rather the long-range hole-jumping one. The quantitative analysis of the recombination and escape MFEs is performed using the stochastic Liouville equations (SLE) for a one-dimensional lattice model in which the stepwise hole hops take place between the nearest neighbor carbazole units with spin conservation. The SLE analysis provides the recombination and hole transfer rate constants of 7.0 x 10(7) and 4.5 x 10(8) s(-1), respectively. The boundary site number for the ion pairs in the one-dimensional model is estimated by the best fit to the experimental results. The interionic distance of the boundary ion pair in the one-dimensional model including eight sites agrees with the thermalization distance in the Onsager model. Hence, it is concluded that the elementary processes in the Onsager model applied to molecular amorphous solids are the stepwise hole hops rather than a long-range hole jump.     

Influence of lattice dynamics on charge transport in the dianthra[2,3-b:2',3'-f]-thieno[3,2-b]thiophene organic crystals from a theoretical study

The influence of lattice dynamics on carrier mobility has received much attention in organic crystalline semiconductors, because the molecular components are held together by weak interactions and the transfer integrals between neighboring molecular orbitals are extremely sensitive to small nuclear displacements. Recently, it has been shown that the dynamic disorder has little effect on hole mobility in the ab plane of pentacene, but a reasonable explanation is absent for such a puzzle. To better understand the effect of lattice vibrations on carrier transport, a further study is required for other organic materials. In this work, a mixed molecular dynamic and quantum-chemical methodology is used to assess the effect of nuclear dynamics on hole mobility in the dianthra[2,3-b:2',3'-f]-thieno[3,2-b]thiophene (DATT) crystals which exhibit high air stability with the hole mobility as large as that in rubrene-based devices. It is found that the lattice vibrations lead to an increasing encumbrance for hole transport in the ab plane of the DATT crystals as the temperature increases. By comparing the crystal structures of DATT and pentacene, the reduced hole mobility in DATT is attributed to the unsymmetric arrays of nearest-neighboring molecular dimers in the ab plane, because the electronic coupling exhibits unbalanced thermal fluctuations for the nearest-neighboring dimers which then induces a stronger oscillation for carriers along the directions with asymmetric packing. To further relate the dynamic disorder with hole transport, the variations of anisotropic mobilities are also analyzed. As a result, the negligible effect of lattice dynamics on the hole mobility in pentacene is explained by the centrosymmetric molecular packing of the nearest-neighboring molecular pairs in the ab plane.     

Precise determination of the lattice constant of LiF by means of X-ray divergent beam (pseudo Kossel-) technique via computer graphics and multiple intersections

The X-ray interference patterns obtained by the divergent beam transmission technique (pseudo Kossel technique in transmission mode) permit an evaluation of high precision. Especially the low resolution triple intersections appearing in the pattern can be utilized for precise determination of lattice constants. For cubic crystals the parameters can be calculated directly using analytical methods. The computer graphics method is also applicable for crystal systems with low symmetry. It is shown on patterns from LiF obtained with Fe-K and Cu-K radiation that the computer graphics method provides a fast way for the precise determination of lattice constants.     

Electronic Structure and Catalysis on （001） Polar Surface of Cubic Zirconia

The electronic structure of (001) polar surface of cubic zirconia was studied by GGA(WC) approximation. We found the cubic lattice near (001) surface showed an intensive tendency to transfer to tetragonal lattice. The metallic state appeared on both the terminations. For O-termination, some O2p states were vacated and hole carriers concentrated on surface oxygen-ions. For Zr-ermination, some Zr4d states became partial occupied for the loss of O2p states. We observed the hole states were mainly localized at the corresponding ions on surface for both the terminations, while the charge states on Zr-termination were dispersed on surface.