Nanoscale dielectric properties of insulating thin films: From single point measurements to quantitative images

Dielectric relaxation (DR) has shown to be a very useful technique to study dielectric materials like polymers and other glass formers, giving valuable information about the molecular dynamics of the system at different length and time scales. However, the standard DR techniques have a fundamental limitation: they have no spatial resolution. This is of course not a problem when homogeneous and non-structured systems are analyzed but it becomes an important limitation for studying the local properties of heterogeneous and/or nano-structured materials. To overcome this constrain we have developed a novel approach that allows quantitatively measuring the local dielectric permittivity of thin films at the nanoscale by means of Electrostatic Force Microscopy. The proposed experimental method is based on the detection of the local electric force gradient at different values of the tip–sample distance. The value of the dielectric permittivity is then calculated by fitting the experimental points using the Equivalent Charge Method. Even more interesting, we show how this approach can be extended in order to obtain quantitative dielectric images of insulating thin films with an excellent lateral resolution.     

DIFFERENTIAL 3ω METHOD FOR THERMAL MEASUREMENTS

The 3ω technique has been applied to measure thermal properties of thin films and suspended wires. In this article, we report the implementation and technical design of a 3ω system to measure the thermal conductivity in small dimension structures. Alternating current is applied to a line heater that dissipates power and varies its resistance. The 3ω voltage drop across the heater provides information that determines the thermal properties of the heater or of the adjacent material. A differential bridge is used to subtract the first harmonic voltage and systematic noise. We introduce the use of a synchronous detector associated with the differential bridge to obtain the in-phase and out-of-phase components of the third harmonic signal. The combination improves the bridge method for a broad range of frequency analysis that permits either thermal conductivity and/or heat capacity measurements.     

Investigation of CdS thin films by a near-field microwave microprobe

Cadmium sulphide (CdS) thin films with different microstructures and morphologies were measured by using a near-field microwave microprobe (NFMM). The NFMM system was coupled to a dielectric resonator with a distance regulation system at an operating frequency f=4.1GHz. The changes in dielectric permittivity of CdS thin films due to different annealing temperatures were investigated by measuring the reflection coefficient S(11). CdS thin films with different microstructures and morphology were characterized by X-ray diffraction, atomic force microscopy and NFMM.     

Fabrication of ionic liquid thin film by nano-inkjet printing method using atomic force microscope cantilever tip

We demonstrate the fabrication of thin films of ionic liquid (IL), 1-butyl-3-methyl-imidazolium tetrafluoborate, by nano-inkjet printing method using an atomic force microscope (AFM) cantilever. The IL filled in a pyramidal hollow of the AFM cantilever tip was extracted from an aperture at the bottom of the hollow and deposited onto a Pt substrate when the bias voltage was applied between the cantilever and the substrate. We succeeded in fabricating IL thin films with a thickness of 4 nm. The areas and thicknesses of IL thin films were controlled by the fabrication conditions in this method, which is also useful for the investigations of nanometer-scale properties of ionic liquid.     

类金刚石薄膜微观摩擦性能的FFM评价——针尖尺度效应

采用等离子体增强气相沉积制备了类金刚石薄膜，利用原子力显微镜的轻敲模式观察了它们的形貌，并在考虑外加载荷和扫描速度的基础上，用摩擦力显微镜（FFM）对比考察了尖端探针和平头探针对类金刚石薄膜摩擦性能评价的影响。结果表明：类金刚石薄膜的表面粗糙度随基底负偏压的增加而减小；存在于探针和类金刚石薄膜之间的水膜对尖端探针的剪切阻力贡献较大，且尖端探针测得的摩擦力变化趋势受扫描速度影响显著；水膜对平头探针起着不同形式的润滑作用，从而导致平头探针和类金刚石薄膜之间摩擦性能的速度效应存在差异；利用摩擦力显微镜考察类金刚石薄膜的摩擦性能时，存在着明显的针尖尺寸效应。     

Noninvasive beam-wave reflectometric instrumentation for measuring complex permittivity of dielectric materials at microwave frequencies

A noncontact and nondestructive method of measuring at microwave frequencies the complex permittivity of a selected region in a dielectric slab is described. For this purpose the test dielectric sample is irradiated with a focused (gaussian) microwave beam by means of a suitable applicator. From the characteristics of the reflected beam wave measured at a reflectometric bridge arrangement, the complex permittivity of the exposed region is determined. Some theoretical and experimental results analysing the test conditions are presented. Application of this method to biological in vivo (or in vitro) measurements of dielectric properties of bones and tissues, with selective partial-body microwave irradiation, is discussed.     

SnSe2薄膜的载流子与声子动力学研究

基于自建的超快抽运探测实验系统,研究了化学气相沉积法生长的SnSe₂薄膜的超快载流子与声子动力学。对SnSe₂薄膜随抽运能量密度变化的载流子弛豫过程的测量结果表明该薄膜具有超快的载流子热化过程和皮秒至纳秒时间尺度的复合过程。伴随着光生载流子的超快激发和能量弛豫,SnSe₂薄膜发生晶格热化,产生了特定频率的相干声学声子。通过分析声学声子振荡信号随抽运能量密度变化的规律,揭示了SnSe₂薄膜产生的相干声学声子的特性。研究结果对SnSe₂薄膜在光电器件领域的应用研究具有一定的参考价值。     

Very low voltage sputter coating

Very low voltage sputter coating, in the range 175–300 V, has been used to produce finely structured thin films of noble and refractory metals for use in high resolution scanning electron microscopy. There is a marked diminution in the particle size with a decrease in cathode voltage. Although the sputtering times are longer than with conventional diode sputter coating, such times are shorter than those required to produce similar films by Penning or ion-beam sputtering. The refractory metals produce films which are fine grained and suitable for high resolution studies. The method has been used to sputter coat thin layers of aluminium. All attempts at sputtering carbon have failed; the reasons for this are discussed in some detail.     

用放大器反馈控制消除电桥非线性误差

采用放大器反馈控制法克服了传感器电桥的非线性误差,通过解析的方法找到了克服非线性误差的放大器反馈控制条件。在忽略放大器输入偏置电流和输入噪声电压的情况下,给出了四种校正电路中放大器失调电压对测量系统影响的输出表达式,并分析比较了每一种校正方法的特点,得到最佳的测量线路,使失调电压及其漂移的影响减小了5倍。本研究为传感器电桥测量系统设计中的放大器选择和测量方案的确定提供了理论指导。     

High value resistance comparison using modified Wheatstone bridge based on current detection

In this paper is presented the method for comparison of high value resistance standards by using the modified Wheatstone bridge and picoammeter as current detector. The advantage of current detection method over voltage detection method in bridge balancing using available laboratory equipment was evaluated. A four-step procedure for accurate and fast balancing of the bridge is explained. Experimental results confirm that resistance ratios in gigaohm range can be determined with relative uncertainties of only a few parts per million (ppm). By measuring the ratio on the level of 10:1, this method is introduced in Primary Electromagnetic Laboratory (PEL) for maintaining traceability chain of reference standards ranging from 10 MΩ to 100 GΩ.     

Confocal and differential phase imaging of thin organic films

This paper discusses the imaging of thin organic films in scanning optical microscopes using both differential phase contrast and confocal modes. The Lang-muir-Blodgett technique is used to deposit thin films of controllable thickness. Step structures in these films are considered and theoretical models of the imaging are compared with experimental data. The model provides a measurement of film parameters such as thickness and permittivity. The differential phase contrast mode is also proposed as a simple method of assessment of film quality.     

表面加工多晶硅薄膜热扩散系数在线测试结构

基于目前已有的真空桥式薄膜热扩散系数测试结构和测试方法，综合考虑辐射、对流以及向衬底的传热等因素的影响，从而使得本文设计的测试结构和提取方法更具有实际价值。文中通过分析两个长度不同，但宽度与厚度相同的梁在相同加热电流下的瞬态电阻变化特性，来提取多晶硅薄膜的热扩散系数。同时利用有限元分析软件ANSYS进行了模拟分析，分析表明模拟提取值与理论值较好地吻合，从而验证了模型建立的正确性，说明该方法能够实现对多晶硅薄膜热扩散系数的在线提取，且具有较高的测试精确度。     

Electrostatic force microscopy study on the domain switching properties of the Pb(Zr0.2Ti0.8)O3 thin films with different crystallographic orientations for the probe-based data storage

The domain switching properties of the ferroelectric Pb(Zr_0.2Ti_0.8)O₃ (PZT) thin films with two types of crystallographic orientations were investigated by electrostatic force microscopy (EFM). The crystallographic orientations of the PZT thin films were random on the (1 1 1)Pt/MgO(1 0 0) and c-axis preferred on the (1 0 0)Pt/MgO(1 0 0), respectively. When dc bias was applied to the films for writing in micro-scale area, electrostatic force images showed that the domain switching was hard in the PZT thin films with random orientation, while the pattern could clearly be written in the PZT films with c-axis orientation. The differences in the domain switching properties of each PZT thin film were investigated in the crystallographic orientations point of view, and the domain switching dynamics were also measured by investigating the nano-sized dot switching behavior with respect to the width of the applied voltage pulse.     

薄膜应力的测定

本文介绍一种利用长焦距显微镜观察玻璃薄片由镀膜淀积引起的形变来测量薄膜应力的方法。对于该实验装置的几个主要结构部份、测量的原理及方法和提高测量精度所采取的主要措施作了较详细的描述。最后给出了在不同真空度和蒸发速率时硫化锌膜、氟化镁膜及硫化锌—氟化镁多层膜的应力分别随薄膜几何厚度而变化的实验结果。     

两步压入法--薄膜力学性能的可靠测量方法

提出了采用力学探针测量薄膜力学性能的两步压入法.该方法通过大载荷压入展示基体变形对薄膜硬度的影响,从而选择不影响基体变形的小载荷测出薄膜的硬度和弹性模量.对高速钢基片上的TiN硬质薄膜,单晶硅片上的金属Ni薄膜和(Ti,Al)N/VN纳米多层膜的测量表明,两步压入法能够测出各种性质薄膜的力学性能,并且具有准确可靠的特点.此外,两步法对(Ti,Al)N/VN纳米多层膜的力学性能的测量表明,该体系的纳米多层膜存在硬度和弹性模量异常升高的超硬、超模量效应.     

Electrostatic force microscopy study on the domain switching properties of the Pb(Zr0.2Ti0.8)O3 thin films with different crystallographic orientations for the probe-based data storage

The domain switching properties of the ferroelectric Pb(Zr(0.2)Ti(0.8))O(3) (PZT) thin films with two types of crystallographic orientations were investigated by electrostatic force microscopy (EFM). The crystallographic orientations of the PZT thin films were random on the (111)Pt/MgO(100) and c-axis preferred on the (100)Pt/MgO(100), respectively. When dc bias was applied to the films for writing in micro-scale area, electrostatic force images showed that the domain switching was hard in the PZT thin films with random orientation, while the pattern could clearly be written in the PZT films with c-axis orientation. The differences in the domain switching properties of each PZT thin film were investigated in the crystallographic orientations point of view, and the domain switching dynamics were also measured by investigating the nano-sized dot switching behavior with respect to the width of the applied voltage pulse.     

A novel method of temperature compensation for piezoresistive microcantilever-based sensors

Microcantilever with integrated piezoresistor has been applied to in situ surface stress measurement in the field of biochemical sensors. It is well known that piezoresistive cantilever-based sensors are sensitive to ambient temperature changing due to highly temperature-dependent piezoresistive effect and mismatch in thermal expansion of composite materials. This paper proposes a novel method of temperature drift compensation for microcantilever-based sensors with a piezoresistive full Wheatstone bridge integrated at the clamped ends by subtracting the amplified output voltage of the reference cantilever from the output voltage of the sensing cantilever through a simple temperature compensating circuit. Experiments show that the temperature drift of microcantilever sensors can be significantly reduced by the method.     

截止波导介质腔介电常数测量理论与方法研究

本文提出了用截止波导介质谐振腔测量微波材料相对介电常数和微波损耗的方法.利用开波导法给出了腔中TE0ml谐振模的电磁场,导出了利用此模测量介电常数和微波损耗的公式;通过测量频率和谐振曲线,就能算出材料的复介电常数,并对谐振模TE0ml进行了讨论;比较了这种测量方法与原有的短路金属板介质谐振腔法的优劣,结果表明采用截止波导介质谐振腔测量材料的微波损耗时更有优越性.     

Investigation of intrinsic crystalline Si(111) and amorphous silicon surfaces in air with STM

Crystalline (111) and amorphous silicon surfaces have been studied by scanning tunnelling microscopy. An orientated, reproducible, corrugated structure has been observed on Si(111) surfaces. The voltage dependence of the corrugation amplitude may be attributable to surface states. The surfaces of amorphous silicon thin films show some reproducible structure in the range of a few tens of ångströms, observable only when the applied voltage between the tip and sample is between ?1·3 and +0·4V.     

Near-field nano-ellipsometer for ultrathin film characterization

We describe a near‐field ellipsometer for accurate characterization of ultrathin dielectric films. Optical tunnelling mimics the absorption in metallic films, enabling accurate measurement of the refractive index of ultrathin dielectric film. A regression model shows that a refractive index resolution of 0.001 for films as thin as 1 nm is possible. A solid‐immersion nano‐ellipsometer that incorporates this near‐field ellipsometric technique with a solid‐immersion lens is constructed to demonstrate the viability of this technique. Such a nano‐ellipsometer can accurately characterize thin films ranging in thickness from subnanometre to micrometres with potential transverse resolution of the order of 100 nm.