【作者】 李扬；

【导师】 朱小鹏；

【作者基本信息】 大连理工大学 ， 材料工程（专业学位）， 2021， 硕士

【摘要】 近年来,强流脉冲离子束(HIPIB)技术在材料工程领域的应用价值得到了广泛的关注。同其他高功率脉冲技术相比,HIPIB有着高能量沉积效率,较大的辐照面积,较深的改性层等优势。提高其输出的稳定性,包括能量分布、焦点位置和能量密度的稳定性、束流密度波动大小是把这项技术在工程应用领域推广的关键。只有满足高重复性的要求才能实现HIPIB技术在工程领域的广泛应用。本文在HIPIB技术的基础上,采用金属栅网二极管新结构,研究了二极管间隙、栅网材料、栅网透过率、网孔尺寸和中心孔大小对聚焦离子束的总能量、能量密度、束流密度及稳定性的影响规律,建立了离子束电子中和程度(中性束占比)与离子束聚焦特性(发散角)的对应关系。实验结果表明,在最佳等离子体引出时间450 ns的条件下,10-9-12 mm的二极管间隙最优,铝栅网阴极和不锈钢栅网阴极对离子束的焦点能量密度都有所提升,由无栅网的4.3 J/cm~2分别增加到6.4 J/cm~2和6.0 J/cm~2,铝栅网比不锈钢栅网能量密度高的原因是不同材料的二次电子产额不同,对离子束产生的聚焦效果也不同。铝栅网阴极的离子束成分由原来的H~+、C~+变成了C~+和Al~+,不锈钢栅网阴极则还是H~+、C~+,并且能量密度和束流密度的波动都较铝栅网阴极低。阴极栅网透过率对离子束输出特性有很大影响,总能量随透过率降低而减小,焦点能量密度和中性束占比都随透过率降低整体呈上升趋势,透过率最低0.38的不锈钢栅网将焦点能量密度提高到了12.4 J/cm~2。相同透过率,网孔大小不同的阴极栅网结构中,总能量大致相同,能量密度和中性束占比都是小孔都比大孔高。栅网阴极结构使离子束的稳定性降低,透过率为0.48时波动最小,焦点位置波动的变异系数(CV值)在10%左右,和无栅网较为接近。不锈钢栅网开中心孔实验中,20 mm方孔对能量密度提高最为显著,并且对离子束的稳定性有所改善,变异系数都有着不同程度的降低,透过率0.48的不锈钢栅网的CV值水平位置为4.6%,竖直位置为7.6%,低于无栅网的5.6%和14.1%。对离子束散度的分析发现,焦点能量密度和中性束占比随透过率变化规律和散度随透过率变化规律趋于一致,散度越小聚焦效果越好,焦点能量密度越高,中性束占比也越高。栅网阴极的聚焦效果使离子束焦点位置前移,距阳极表面13 cm处成为了实际焦点,总能量、焦点能量密度均达到了最大值。13 cm以后,HIPIB在继续向前传输的过程中会逐渐发散,能量也会渐渐损失,所以总能量和能量密度都呈下降的趋势。对不同透过率栅网阴极的HIPIB电子流密度的分析可知,透过率0.38-0.78的电子总电量是一个两边大致相同,中间低的趋势。相同透过率不同网孔大小的实验表明,网孔大小在0.35-1.5之间,总电量是先降低后升高的过程。考虑到栅网透过率对电子流密度的影响,中性束占比、焦点能量密度随透过率变化的规律与产生的电子总电量规律趋于一致,可以说明离子束的中和、聚焦效果的提升主要取决于离子束轰击栅网的二次电子产额。更多还原

【Abstract】 In recent years,the application value of high-current pulsed ion beam(HIPIB)technology in the field of materials engineering has received extensive attention.Compared with other high-power pulse technologies,HIPIB has the advantages of high energy deposition efficiency,larger irradiation area,and deeper modified layer.Improving the stability of its output is the key to popularizing this technology in engineering applications,including energy distribution,stability of focus position and energy density,and beam density fluctuations.Only by meeting the requirements of high repeatability can the HIPIB technology be widely used in the engineering field.Based on the HIPIB technology,this paper uses a new structure of metal grid diodes to study the effects of diode gap,grid material,grid transmittance,mesh size and center hole size on the total energy,energy density,and beam of the focused ion beam.The influence law of current density and stability establishes the corresponding relationship between ion beam electron neutralization degree(neutral beam proportion)and ion beam focusing characteristic(divergence angle).The experimental results show that under the condition of the best plasma extraction time of 450 ns,the diode gap of 10-9-12 mm is the best,and the aluminum grid cathode and the stainless steel grid cathode both increase the focus energy density of the ion beam.From 4.3J/cm~2 without grid to 6.4 J/cm~2 and 6.0 J/cm~2,the energy density of aluminum grid is higher than that of stainless steel grid.The reason is that the secondary electron yield of different materials is different.The focusing effect is also different.The ion beam composition of the aluminum grid cathode has changed from the original H~+,C~+to C~+and Al~+,while the stainless steel grid cathode is still H~+,C~+,and the fluctuation of energy density and beam current density is lower than that of the aluminum grid cathode.The transmittance of the cathode grid has a great influence on the output characteristics of the ion beam.The total energy decreases as the transmittance decreases.Both the focal energy density and the neutral beam ratio show an overall upward trend as the transmittance decreases.The lowest 0.38 stainless steel grid increases the focal energy density to 12.4 J/cm~2.In a cathode grid structure with the same transmittance and different mesh sizes,the total energy is roughly the same,and the energy density and the proportion of neutral beams are both higher for small holes than large holes.The grid cathode structure reduces the stability of the ion beam.When the transmittance is 0.48,the fluctuation is the smallest,and the coefficient of variation(CV value)of the focus position fluctuation is about 10%,which is closer to that of the non-grid.In the experiment of opening the center hole of the stainless steel grid,the 20 mm square hole has the most significant increase in the energy density.The energy density of the 10 mm hole and the non-opening hole are close,but the fluctuation is reduced by 15%.Opening a 20 mm central square hole has improved the stability of the ion beam,and the coefficient of variation has been reduced to varying degrees.The CV value of a stainless steel grid with a transmittance of 0.48is 4.6%in the horizontal position and 7.6%in the vertical position.It is lower than 5.6%and14.1%of gridless,which not only improves the focus energy density,but also improves the stability.The analysis of the ion beam divergence found that the focus energy density and the proportion of neutral beams change with the transmittance and the divergence changes with the transmittance tend to be consistent.The smaller the divergence,the better the focusing effect,and the greater the focus energy density.High,the higher the proportion of neutral beam.The focusing effect of the grid cathode makes the ion beam focus position move forward,and the point 13 cm from the anode surface becomes the actual focus,and the total energy and the focus energy density both reach the maximum.After 13 cm,HIPIB will gradually diverge as it continues to transmit,and energy will gradually be lost,so the total energy and energy density are in a downward trend.The analysis of the HIPIB electron flow density of different transmittance grid cathodes shows that the total amount of electrons with a transmittance of 0.38-0.78 is roughly the same on both sides and low in the middle.Experiments with the same transmittance and different mesh sizes show that the mesh size is between 0.35-1.5,and the total power is a process of first decreasing and then increasing.Taking into account the influence of grid transmittance on the electron current density,the law of the proportion of neutral beam and the change of focal energy density with transmittance and the law of the total amount of electrons generated tend to be consistent,which can explain the neutralization and focusing of the ion beam.The improvement of the effect mainly depends on the secondary electron yield of the ion beam hitting the grid.更多还原